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Center for Materials Science

Polymer

Science and

Standards

Division

Annual Report 1981

U.S. DEPARTMENT

OF COMMERCE

National Bureau

of Standards

POLYMER SCIENCE AND STANDARDS DIVISION

Annual Report 1981

U. S. Department of Commerce

National Bureau of Standards

Polymers Bldg. (224), A305

Washington, DC 20234

(301) 921-3734

Polymer Science

and Standards

Division

RONALD K. EBY, Chief. Dr

Eby was born in Reading,

Pennsylvania in 1929. He earned

the Sc.B. in physics at Lafayette

College and the Sc.M. and Ph.D.

at Brown University. Before joining NBS in 1963, he conducted

polymers research in the Plastics Department of E. I. du Pont de

Nemours & Co., Inc.

LESLIE E. SMITH, Deputy

Chief. Dr. Smith was born in New

York in 1941. He earned degrees

in chemistry from Case Institute of Technology and Catholic University. Except for a three year

period of graduate study, he has

been with NBS since 1964.

ANTON PETERLIN, Assistant

Chief. Dr. Peterlin was born in Yugoslavia in 1908. He earned the M.S. in mathematics at the University of Ljubljana and Ph.D. in physics at the University of Berlin. From 1939 to 1960 he was

professor of physics in Ljubljana

and from 1949 to 1959 was head

of the Josef Stefan Institute.

Before joining NBS in 1973, he was director of the Camille

Dreyfus Laboratory.

MARTIN G. BROADHURST,

Group Leader, Electrical Properties. Dr. Broadhurst was born in Washington, D.C. in 1932, and

earned degrees in physics at Western Maryland College and

Pennsylvania State University.

After teaching at Penn State, he

joined NBS in 1960.

BRUNO M. FANCONI, Group

Leader, Structure and Properties. Dr. Fanconi was born in Merced,

California in 1939. He earned

degrees in physical chemistry

from the University of California

at Los Angeles and the University

of Washington. He joined the

staff of NBS in 1971.

JAMES M. CASSEL, Group

Leader, Dental and Medical

Materials. Dr. Cassel of New

Kensington, Pennsylvania was

born in 1 9 18 and earned the Ph.D.

in chemistry at Georgetown University. He joined NBS in 1946

and today guides a program of

research for improved dental and

medical restorative materials.

ISAAC C. SANCHEZ, Group

Leader, Characterization and

Standards. Dr. Sanchez was born

in San Antonio, Texas in 1941. He

earned degrees in physical chemistry at St. Marys University

(Texas) and at the University of

Delaware. Prior to joining the NBS staff in 1977, he worked at the Xerox Research Laboratories

and was on the Polymer Science

and Engineering faculty at the University of Massachusetts.

LESLIE E. SMITH, Acting

Group Leader, Chemical Durability.

Table of Contents

Page

I. PREFACE 1

II. DIELECTRIC PLASTICS DESIGN AND PERFORMANCE 3

M. G. BROADHURST - TASK LEADER

- Polymer Tape Insulation for Oil Impregnated AC Power Transmission Cables;

F. A. Khoury, F. I. Mopsik, S. J. Kryder, and L. H. Bolz 3

- Polymer Insulation for Superconducting AC Power Transmission Cables;

F. A. Khoury, F. I. Mopsik, S. J. Kryder, and L. H. Bolz 4

- NBS Workshop on Morphological Studies of Power Cable Insulation Failure;

M. G. Broadhurst, F. A. Khoury, A. J. Bur, and G. T. Davis 5

- Space Charge Studies; A. S. DeReggi and F. I. Mopsik 5

- Structure and Performance of Piezoelectric Polymers; G. T. Davis and

M. G. Broadhurst 6

- Aging of Piezoelectric Polymers and Application to Biomedical Uses;

D. E. DeRossi, S. C. Roth, A. S. DeReggi, and M. G. Broadhurst 7

- Automated Dielectric Measurements; F. I. Mopsik, S. J. Kryder, and

S. C. Roth 7

- Depolarization of Poled PVDF Specimens With Thick Electrodes; A. J. Bur

and A. K. Tsao 7

- Fabrication of Thick Piezoelectric Polymer Film; A. J. Bur, M. G. Broadhurst,

and A. K. Tsao 8

- Acoustic Sensors; A. S. DeReggi, S. C. Roth, and S. Edelman 8

- Polymer Stress Gauge for Intaglio Printing Press; M. G. Broadhurst,

S. C. Roth, S. J. Kryder, A. S. DeReggi, and S. Edelman 9

- Resistivity and Piezoelectric Measurement on Oriented and Unoriented PVDF

Films; A. J. Bur 9

- Nondestructive Evaluation; S. Edelman and S. C. Roth 10

- ASTM Activities; W. P. Harris 10

- The Crystal Structure and Disorders of the Low Temperature Phase (II) of

Polytetrafluoroethylene; J. J. Weeks, E. S. Clark, R. K. Ehy, and

B. L. Farmer 11

III. MIGRATION AND THE DURABILITY OF POLYMERS IT

L. E. SMITH - TASK LEADER

- Hydrolytic Degradation of Polyester Polyurethane Elastomers; D. W. Broun,

R. E. Loury, and L. E. Smith 12

- Long Term Aging Studies With Poly(Ethylene Terephthalate) ; D. W. Broun,

R. E. Loury, and L. E. Smith 13

- Oxidation of Polystyrene; B. Dickens 13

- Variable Heating Rate Thermogravimetry; J. H. Flynn 13

- Analysis of the Kinetics of Thermogravimetry; J. H. Flynn 15

- Thermogravimetric Studies of Polymer Degradation; B. Dickens 16

i
Page

- Measurement of Antioxidant Diffusion by Microfl uorimetry; S. L. Sunder,

F. W. Wang, and R. A. Velapoldi

- Migration of Oligomers and Antioxidants From Polyolefins; S. S. Chang

,

W. J. Pummer, J. R. Maurey, and L. E. Smith 17

- Measurements of Diffusion in Polymers by Inverse Gas Chromatography;

G. A. Senich 19

- Measurement of Translational Diffusion of Polymers by Fluorescence

Photobleaching Recovery Technique; F. W. Wang and W. H. Grant 19

- Assessment of Transport Mechanisms for Radon in and Through Building

Materials; R. J. Rubin 21

IV. MECHANICAL DURABILITY OF POLYMERS FOR DESIGN AND USE 22

B. M. FANCONI - TASK LEADER

- Molecular Processes Associated With Mechanical Deformation and Failure;

B. M. Fanconi, D. L. VanderHart, S. L. Wunder, J. P. Colson, S. J. Kryder,

E. E. Toth, K. L. DeVries, S. Abbate, and G. Zerbi 22

- Relationship Between Morphology and Mechanical Properties of Polyethylene;

G. B. McKenna, F. A. Khoury, J. M. Crissman, L. H. Bolz, G. W. Bullman,

and G. M. Martin 25

- Fracture Processes in Polymers; E. Passaglia 28

- Instability and the Phenomena of Necking; L. J. Zapas, J. M. Crissman

,

B. Bernstein, and B. D. Coleman 30

- Test Method Development; J. M. Crissman, D. L. Hunston, E. A. Kearsley,

R. W. Penn, L. J. Zapas, G. M. Martin, and J. L. Rushford 31

- Non-Linear Behavior of Polymeric Materials; L. J. Zapas, G. B. McKenna,

and B. D. Coleman 33

- Durability of Paper; J. C. Smith 34

- Mechanical and Transport Properties of Polyethylene in Organic Solvents;

J. C. Phillips and A. Peterlin 35

V. POLYMER STANDARDS FOR CONTROL AND EQUITY 36

I. C. SANCHEZ - TASK LEADER

- Standards for Gas Transmission Measurements; J. D. Barnes 36

- ASTM Activities; J. D. Barnes 39

- Self Calibrating Gel Permeation Chroma togrpahy; P. H. Verdier 39

- Dynamics of Polymer Chains; P. H. Verdier and D. E. Kranbuehl 41

- Low Shear Rate-High Temperature Rotational Viscometer; H. L. Wagner and

J. G. Dillon 41

- Rubber and Rubber Compounding Standard Reference Materials; G. W. Bullman

and G. B. McKenna 42

- Static and Dynamic Configurational Properties of Polymer Chains: Theory;

F. L. McCrackin, R. J. Rubin, C. C. Han, J. Mazur, I. C. Sanchez, and

D. J. Lohse 42

- Polymer Blends; J. C. Sanchez, F. W. Wang, and R. E. Lowry 43

- Static and Dynamic Scattering From Polymers; C. C. Han, D. B. Minor,

H. L. Wagner, A. Z. Akcasu, S. J. Bai, D. J. Lohse, and T. P. Lodge 44

i i
Page

VI. TESTS, STANDARDS, AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY OF DENTAL AND MEDICAL MATERIALS 46

J. M. CASSEL - TASK LEADER

- Dental Composite Chemistry and Development; G. M. Brauer, J. M. Antonucoi,

J. W. Stansbury, J. M. Cassel, R. L. Bowen, H. Argentar, D. N. Misra

,

T. Chen, and E. E. Toth 46

- Development of Adhesive Bonding Technique and Dental Cements; G: M. Bvauer

,

R. L. Bowen, J. M. Antonucoi, D. N. Misra, J. W. Stansbury, E. Cobb, and

J. M. Cassel 47

- Wear Resistance and Mechanical Properties of Dental Materials; W. Wu,

J. E. McKinney, J. M. Cassel, E. E. Toth, and E. Cobb 49

- Porcelain Fused to Base Metal Alloys and Dental Ceramics; J. A. Tesk,

R. W. Hinrnan, W. de Rijk, E. E. Parry, D. L. Menis, and G. E. 0. Widera ... 49

- Dental Casting Alloys; J. A. Tesk, R. M. Waterstrat, R. W. Hinrnan, and

E. E. Parry 51

- Clinical and Laboratory Investigation of Dental Amalgams; N. W. Rupp,

G. C. Paffenbarger, and R. M. Waterstrat 52

- Dental Chemistry and Preventive Dental Treatments; W. E. Brown, L. C. Chow,

M. Mathew, M. S. Tung, G. L. Vogel, S. Takagi, and T. M. Gregory 52

- Development of Improved Field Dental Composite Restorative Materials for

Military Personnel; G. M. Brauer, N. W. Rupp, J. W. Stansbury, K. Dermann

,

and J. M. Cassel 53

- Adhesion and Surface Coverage of Synthetic Polymers on Solid Substrates;

R. E. Dehl and W. H. Grant 53

- Characterization of Porosity of Porous Implant Materials; R. E. Dehl,

W. H. Grant, and J. M. Cassel 54

- Dental and Medical Materials Standards; J. M. Cassel, J. A. Tesk,

G. M. Brauer, and N. W. Rupp 54

VII. OTHER DIVISION ACTIVITIES

- Invited Talks 55

- Seminars for Staff and Guests 53

- Technical and Professional Committee Participation and Leadership 68

- Publications 73

- Patents 81

- Workshop 81

- External Recognition 82

POLYMER SCIENCE AND STANDARDS DIVISION

Ronald K. Eby, Chief

Leslie E. Smith, Deputy Chief

S. M. Thomas, Administrative Officer

In the seven decades since Leo H. Baekeland introduced the first commercial synthetic plastic

produced entirely by the reaction of small molecules, polymers have left little of our economy, technology, industry, and culture untouched. We have moved rapidly into an age in which an evergrowing

number of humanity's needs are served by polymers. The volume currently produced exceeds that of

steel and forms the basis of industries which add over 90 billion dollars of value by manufacture (a measure of the relative economic importance of manufacturing among industries) and provide 3.4 million

jobs. Recent summaries show that polymers research already accounts for about 47 percent of the total

industrial R&D expenditure for metals, polymers, and inorganic materials. Among these materials,

polymers also constitute about 39 percent of the value added by manufacture, 49 percent of the jobs,

45 percent of the number of scientific publications, and 39 percent of the ASTM standards.

Polymers have been shaped by intellectually sophisticated research which has been recognized by a number of Nobel Prizes. The resulting materials have contributed to national industrial productivity

through their economy, ease of fabrication, and useful properties such as low density, corrosion

resistance, and toughness. Polymers are energy efficient; the largest volume polymer, polyethylene,

uses 28 percent of the energy per unit volume required by steel for conversion from raw to refined

material and yields further savings in processing and shipping. In fact, studies have shown that for

every barrel of oil used to make plastic products, approximately one barrel is saved in comparison

with the use of the next best alternative material. These useful properties have enabled polymers to contribute to increased productivity both by creating entirely new products and by substituting for

other materials in existing products.

Polymers have entered increasingly sophisticated and demanding applications. Polyvinyl idene

fluoride films are used as electromagnetic transducers in high fidelity systems. Structural parts of

aircraft are constructed from composites with a polymer matrix. Polyurethane elastomers are used to pump blood in circulatory assist devices. The list of such examples is very long, and includes trends

for the increased use of polymers in packaging, construction, transportation, national security,

electronics, information handling, clothing, appliances, energy, dentistry, and medicine. Since

polymer technology is on the steep part of the learning curve, these trends create many new needs for

concepts, measurements, standards, and data that can be used to ensure their reliable performance in the use, processing, and other phases of the material cycle.

To identify the key needs, the managers of the Polymer Science and Standards Division make struc- tured visits to industrial and Government laboratories. Visited sites include Bell Labs, DuPont,

Johnson and Johnson, Army R&D Command, General Motors, Boeing, and Lawrence Livermore Laboratories.

Surveys have been conducted in the areas of durability, composites, and processing. These and other contacts with research associates, experts in industry, trade associations, standards associations,

guest workers, Government, and academia ensure that the Division's efforts are directed toward

fostering the effective use of polymers in solving national problems. These national problems include

the growth of industrial productivity, national security, efficient Government, materials utilization,

conservation of critical materials, and reasonable regulation of the effects of technology.

The Division has used these activities as a basis for participating in budget initiatives to secure the resources necessary to meet emerging needs. For the budget cycles currently active, pro- grammatic initiatives emphasize polymer matrix composites because of their role in increasing industrial productivity and substituting for critical materials. Specific areas encompass toughened hybrid

matrix materials, high strength polymer fibers, methods of predicting durability, and methods of

measuring and controlling matrix cure. Competence building initiatives on the science of forced

Rayleigh scattering, polymer morphology, and time-resolved Fourier transform infrared spectroscopy

have been prepared.

Current activities are associated into areas concerned with mechanical reliability in load-bearing

applications, chemical durability and lifetime prediction including the migration of protective additives, characterization methods and standards for molecular composition and use properties, dielectric

properties and electrical conduction, and reliable dental and medical materials. Substantial cooperative efforts are conducted with research associates from a number of industries, the Department of

Defense, the National Institutes of Health, the American Dental Association, the Food and Drug Administration, and the Bureau of Engraving and Printing. All these efforts lead the scientists of the

Division into productive examination of those properties of polymers which are of concern to people

who use, design, and produce useful polymer objects. This work helps society capture, in safe and

satisfying ways, the benefits of the increasingly widespread application of polymers.

1
In the following pages, the activities of the Division are presented formally in five Tasks, each

described separately:

DIELECTRIC PLASTICS DESIGN AND PERFORMANCE

MIGRATION AND THE DURABILITY OF POLYMERS

MECHANICAL DURABILITY OF POLYMERS FOR DESIGN AND USE

POLYMER STANDARDS FOR CONTROL AND EQUITY

TESTS, STANDARDS, AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY OF DENTAL AND MEDICAL MATERIALS

2
DIELECTRIC PLASTICS DESIGN AND PERFORMANCE

M. G. Broadhurst

Task Leader

Trends in dielectric application of polymers include use of higher working voltages in electrical

apparatus and transmission lines to conserve materials, save space, and reduce weight. This work

provides manufacturers (polymer manufacturers, film fabricators, transducer manufacturers), trade

associations (EPRI), and Government agencies (DOE, DOD) with data, measurement methods, and concepts

which identify limitations in polymer performance traceable to manufacturing practices. For example,

steam curing of extruded polyethylene insulated cable results in lifetime-limiting voids and inclusions. With the trend toward increased use of underground transmission of electric power, improved

insulation performance is required. To meet these needs, NBS develops measurement methods and performs

measurements to obtain required data, holds workshops to improve research efforts in the area of power

cable and capacitor insulation, recommends test methods for new material selection, and carries out related activities. Data and recommendations from this work go directly to cable manufacturers and

funding organizations (i.e., EPRI, DOE) who are able to specify and require manufacturing changes

leading to improved products.

Applications of polarized polymers as pyro- and piezoelectric transducers are rapidly growing.

Transducer manufacturers as well as private and Government transducer users (DOD, EPA, HHS) need

reliable information connecting polymer structure and polymer performance to the design of improved

transducers. This work helps transducer material and device manufacturers design and develop commercial polymer transducers for use in health and safety applications (pulse monitors, therapeutic and

diagnostic sound measurements, auto crash sensors, prosthetic fitting devices, nontoxic antifouling

coatings, mine disaster warning devices), and in the areas of national security (microphones, hydrophones, intrusion detectors, ultrasonic and infrared imaging devices, fusing devices, etc.). Important

scientific opportunities of this work include breakthroughs in understanding the basic factors in electrical failure of polymers and discovery of novel measurement techniques which are becoming possible with newly developed polymers. For example, on-going work will show how polymers interact with

electronic and ionic charges and how structure can be modified to optimize piezoelectric and semiconducting properties.

The study of electrical conduction of organic polymers is a major new frontier in solid state

physics. Most current research involves an empirical search for improved dopant-polymer combinations

from a bewildering array of compounds. Chemical structure-electrical property correlations are not yet evident. The key need is for a better knowledge of the molecular packing, dopant locations,

chemical changes with doping, molecular orientation, and charge carrier pathways to form a basis for

modeling and predicting electrical properties. This work is ideally suited to NBS because it involves

improved measurements, standards, and test methods. Polymer conductors have the advantages of being

lightweight, flexible, made from abundant raw materials, resource and energy conserving, and inexpensive. Thus, success of the project will have a potentially significant impact on national problems of

materials replacement, productivity enhancement, energy conversion and storage (polymer batteries),

electromagnetic shielding, and microcircuitry.

Ionic conduction in polymers provides a basis for a large and growing class of important applications including production of chlorine and caustic from brine, hydrogen production from low-head

hydroelectric or ocean thermal energy sources, solid electrolytes for fuel cells and batteries, gas sensors, materials separation membranes, and electrochemical devices. NBS work on conducting polymers

is aimed at characterizing the polymer structures, measuring their properties, and relating the struc- tures and properties to provide a basis for predicting electrical performance from molecular details.

Polymer Tape Insulation for Oi 1 -Impregnated AC Power Transmission Cables

F. A. Khoury, F. I. Mopsik, S. J. Kryder, L. H. Bolz

Brookhaven National Laboratory has established a program to develop an oil-impregnated or oil

filled high power ac transmission cable using polymer tape insulation. Until now, oil impregnated

paper has been used for large power cables, but the relatively high loss of such cables has generated

interest in lower loss systems, such as oil-polymer cables for use at 700 to 1000 kV.

A project sponsored by Brookhaven with DOE funds has been established in the Polymer Science and

Standards Division to evaluate the suitability of polymer films. The aims of this project are: the

measurement of the dielectric constant and dielectric loss of candidate films between 273 K and 403 K, the study of the fine structural characteristics of the films, and the specification of the most

suitable films for the intended end use.

Measurements this past year have been carried out on polyethylene and polypropylene tapes prepared

for Brookhaven by Battel le Institute. They were prepared by rolling at temperatures from 293 to 398 K for polyethylene with thickness reduction ratios of four to ten and at a temperature of 423 K for

3
polypropylene with thickness reduction ratios of five to six. Two different base polymers were used

for both the polyethylene series and the polypropylene series. The dielectric measurements were carried out under standard temperature cycling, and density measurements were carried out on the tapes

both before and after the dielectric measurements to check on their stability under thermal cycling.

All the polyethylene tapes showed a significant decrease in loss (tan 6) on thermal cycling. The

decrease at 303 K (after heating incrementally to 373 K over a period of 24 hours) was about a factor

of two. Aside from this decrease, the losses in one base polymer were substantially lower than in the

others (less than 24 x 10~ 6 on the third heating cycle). All the tapes increased in density upon

thermal cycling, but the tapes rolled at 398 K showed a much smaller change, which indicates their

higher mechanical stability.

The polypropylene tapes, which were processed at a roll temperature of 423 K (the maximum temperature of the dielectric measurements) showed behavior dependent on which of two base polymers was used.

Tapes made from one base polymer showed little variation with thermal cycling and had a loss maximum

at 350 K of 35 x 10~ 6. Tapes made from the other polymers showed a loss peak which shifted from 320 K to 370 K upon thermal cycling and which had a maximum value of about 800 x 10~ 6

. Tapes from both

polymers showed an increase in density after the thermal cycling, showing that they had not been fully

stabilized at the rolling temperature.

Brookhaven uses the NBS data to select the most suitable film, including specially oriented or bonded films, for new synthetic-tape-insulated power cables. The development of such cables has been

identified by EPRI as an important short-term research objective in meeting increasing U.S. electric

power requirements.

This project was completed during FY81 and a final report was prepared.

Polymer Insulation for Superconducting AC Power Transmission Cables

F. A. Khoury, F. I. Mopsik, S. J. Kryder, and L. H. Bolz

This project is funded through Brookhaven National Laboratory by DOE. The goal has been to evaluate the suitability of polymer films for use as electrical insulation in a superconducting ac power cable that would operate at 6.0 to 8.0 K. Development of a superconducting power cable has been

identified by EPRI has a long-range research goal in order to meet future demands for very high power

transmission (several giga watts). The measurements provided by NBS have enabled Brookhaven to specify

special composite tapes which are now being built into prototype cables.

The primary task in this project has been the measurement of the dielectric constant (e) and

dielectric loss (tan 6). For suitable insulation these should be less than 2.5 and 20 x 10' 6 respectively at 6.0 to 8.0 K and 60 Hz. These measurements have been coupled with studies of the fine structure of the films (crystallinity, molecular orientation, voids) to guide the development of

optimum films. In addition, measurements of the compressibility of stacks of polymer films have been

made to provide data necessary for winding tapes sliced from the films onto the cable core.

In FY81 , measurements were made on a series of laminates made from polypropylene films of 40 to

60 pm thickness bound together by thin polyurethane layers to provide total thicknesses of 80 to 180 pm. These laminates have shown promise of meeting all necessary requirements in work done in previous years. One series of measurements was made on a set of laminates graded in thickness. Three were bilaminates of total thickness 80, 100, and 120 pm. All the films had suitably low loss levels

with tan 6 ranging from 10-15 x 10 -6

. Low loss was achieved by use of a polypropylene film that had

special antioxidants as well as reduced polyurethane content. Previous work had shown that antioxidants can strongly increase the loss of polypropylene at cryogenic temperatures (< 10 K). Also, it was shown that if too much polyurethane is used as a binder, the higher loss levels of the polyurethane

cause the performance of the laminates to be unsatisfactory.

Another series of measurements was made on a 94 pm thick bilaminate and a 140 pm thick trilaminate

in which a slip agent had been added to the polypropylene in order to obtain better mechanical properties of the finished cable. Losses increased to 16 to 23 x 10 -6 at 6.0 to 8.0 K as a result of this

change.

In addition to the dielectric loss measurements, compressibility measurements were made on stacks

of the first set of bilaminates, carbon loaded polytetrafluoroethylene, and carbon loaded Kraft paper. These data are needed to ensure proper bendability of a finished power cable.

This project has been completed and funding for further research on the insulation for the super- conducting cable terminated. A prototype cable is being built.

4
NBS Workshop on Morphological Studies of Power Cable Insulation Failure

M. G. Broadhurst, F. A. Khoury, A. J. Bur, and G. T. Davis

A two-day workshop on the morphology of polyethylene and its relation to the current state of research on the causes of premature failure of polyethylene insulation on high power transmission

cables was held at NBS. The workshop was organized by Martin Broadhurst of the Polymer Science and

Standards Division and was jointly sponsored by NBS and the Electric Power Research Institute, the

research arm of the U.S. electric utilities. Participants were from electric utilities, cable makers,

polymer manufacturers, and universities. In the welcoming address, J. D. Hoffman, Director of NML,

described his research and its relevance to both the electrical properties and morphology of polymers.

NBS scientist Freddy Khoury delivered the keynote address.

The electric utilities requested this workshop because of their continuing concerns for reducing

costs and improving efficiency of electrical transmission systems. A further concern is to minimize

space required for power transmission and the environmental impact of transmission lines; both of

these considerations favor underground cables, for which polymer-insulated cables operating at higher

voltages are attractive solutions provided that improved dielectric performance and durability can be

obtai ned.

Several scientific approaches to eliminating the problem of electric failure in polymers are currently being followed. In one promising approach, morphologists use electron and optical microscopes together with other techniques to examine structural details of the polyethylene cable insulation to deduce reasons for failure and to identify ways to modify processing conditions to achieve

better performance. Recent studies have been at odds as to how failure channels which develop during

cable operation are related to the chemicals and steam used to cross-link or cure the insulation.

There was a consensus that the various etching techniques now being used in cable insulation studies

often produce artifact structures on the surface of polyethylene samples which are not representative

of the original samples. Many structural interpretations are, therefore, in doubt. Improved methods

of carrying out these important measurements to give more reliable results were delineated.

A summary report of the workshop has been prepared by NBS and has been issued as an EPRI publication. This report will be used immediately by EPRI as a guide to planning and funding future research

projects on morphology of polyethylene insulated cables. In the longer term, this work will lead to improved processing conditions and better performance from underground electric power cables.

Space Charge Studies

A. S. DeReggi , F. I. Mopsik

The measurement of charge distributions in solid polymers is basic to understanding polymer-charge

interactions. These interactions are believed to play a key role in a material's insulating or conducting properties, electrical strength, and electrical aging.

During the past year, a thermal pulse method recently developed at NBS has become increasingly

accepted as one of the most powerful, readi ly-avai lable methods for measuring the distribution of

charge or polarization in a dielectric film as a function of depth, where the thickness of the film is of the order of 25 pm (0.001 in). Further development of the technique at NBS has been primarily in the area of data analyses. A recently acquired transient recorder allows digital acquisition of data

which is then transferred to a tape cassette for input to a laboratory minicomputer. A program has

been developed and tested to show that as many as ten Fourier coefficients of the charge or polarization distribution can be extracted from the data. This means tht the resolution of the charge or polarization distribution is on the order of one-tenth of the film thickness. These developments

which enable us to input data from a tape and output a graph of the polarization distribution have

been presented in the Proceedings of the most recent Conference on Electrical Insulation and Dielectric

Properties in Boston (1980), and a more extensive article is in review.

The above progress in data analysis has opened the possibility of obtaining for the first time

quantitative and unambiguous information about polymer charging phenomena. For instance, we have

shown that the piezoelectric polymer, polyvinyl idene fluoride (PVDF), when poled at ambient temperature, poles more or less symmetrically but not uniformly. The regions near the surfaces seem to have

a greater reluctance to responding to applied poling fields than the bulk of the sample. This is manifested by the form of the polarization distribution obtained as progressively stronger fields are applied in the thickness direction and the changes which occur upon applying progressively stronger

fields in the reverse direction. At low forward fields, the polarization in a virgin sample first

forms primarily in the bulk. At medium and high fields, it develops near the surfaces in addition to

in the bulk. Up to the highest attainable fields, it remains somewhat less (~ 15 percent) near the

surfaces than in the bulk. When the applied field is subsequently reversed, the polarization reverses

in the bulk more readily than it does on the surface. A sample which is forward poled at 2.0 MV/cm

and subsequently is reversed poled at -1.0 MV/cm exhibits strong forward polarization near the surfaces

and strong reverse polarization in the bulk, with practically zero mean polarization.

5
These effects are believed to be due to the mechanical constraints imposed during poling by the

deposited aluminum electrodes. Investigations now underway will provide additional information con- cerning the origin of the above effects. These investigations include studies of the dependence on thickness of the A1 , thickness of the polymer, and on the type and thickness of the electrode material.

The effects on charging phenomena associated with work function differences between the polymer

and metal electrode are also of basic interest and could be important in determining poling behavior.

Previous qualitative thermal pulse work at MBS on non-polar polymers strongly indicated differences in charging properties when A1 and Ag were used as electrode materials. During a renewed visit to NBS,

contractor Prof. Sidney Lang of the Ben Gurion University has been studying the effects of electrode

material in the polarization distribution in PVDF poled over a range of applied fields.

We also have begun to apply the thermal pulse method to investigate charging of polymers bombarded

by electron beams. These studies have been motivated by interest at Rome Air Development Center on the electron-beam charging of polyvinyl chloride films. Simple models for the radiation effects on the conductivity which are currently being developed at RADC predict nonuniform distributions. To guide this theoretical work, there is a need for experimental determinations of the charge distribution. Our thermal pulse measurements, so far, for 700 kV electrons and a limited dose range (200 to 2000 seconds at 10-9 A/cm2

) indicate more or less uniform charge distributions at long times after

i rradiation.

Structure and Performance of Piezoelectric Polymers

G. T. Davis, M. G. Broadhurst

The objectives of this task are to study the molecular motions, structural changes, and electrical properties associated with the process whereby polymers are made piezoelectric. Information

gained from these studies will be used to optimize piezoelectric and pyroelectric response with respect

to both initial activity and long-term stability.

While piezoelectric and pyroelectric activity from polymers is comparable to that from good

ceramic materials, other properties of polymers often make them the preferred transducer material.

Some of the polymer properties which make them so useful include toughness, flexibility, low density,

broad band response, close acoustic impedance match to water, and ease of fabrication. Requests for

information from other Government agencies and from industries have remained numerous. Interest in this area of research continues at a high level, as evidenced by the 22 papers on this topic presented

at the American Physical Society meeting in March 1981.

A copolymer of vinylidene fluoride and trifluoroethylene (52.8 mol % VDF) has been studied in terms of structural changes that occur upon poling and subsequent depoling by heating through the

reported ferroelectric Curie temperature of 70 °C. As crystallized from the melt, the polymer is a mixture of two phases. In one phase, the molecular conformation is thought to be (TG) 3 , resulting in

a 3/1 helix as in the trifluoroethylene homopolymer. In the other phase, the molecular conformation

is all trans, in which the molecules are packed hexagonally. The electric fields employed in poling

(0.5 to 1.0 MV/cm) are sufficient to cause a crystal phase conversion to the all trans conformation

with considerable improvement in order, as evidenced by a shift to smaller cell dimensions and sharper

x-ray diffraction maxima. Upon heating, the two coexisting phases initially present undergo large

changes in cell dimension between 60 and 70 °C, and only a single 3/1 helical conformation exists

above 85 °C. Although the change in conformation from all trans to (TG

)

3 which occurs in the vicinity

of 60 to 85 °C, can certainly account for the ferroelectric transition; much of the piezoelectricity

induced by poling at room temperature is lost before the transition to a single 3/1 helical conformation is observed. It therefore seems probable that polarization is lost by randomization of the

dipole direction followed by a change in chain conformation at a somewhat higher temperature.

We have succeeded in varying the small angle x-ray spacing in drawn samples of polyvinylidene

fluoride by adjusting the temperature of extension--a processing characteristic reported years ago for

polyethylene and polypropylene. The linear position-sensitive detector on the Rigaku Denki rotation

anode source was employed to measure long spacings varying from 11.5 nm to 16.5 nm. These films were prepared to study the effect of lamellar spacing on the poling characteristics of PVDF. Over this

range of crystal size, there is no effect on the pyroelectric response for poling fields in excess of

2.0 MV/cm. The ease of switching as determined from hysteresis loops has yet to be measured.

Dielectric and polarization data were compared to calculated results from a ferroelectric theory

developed in our laboratory. The model has six equally spaced rotational energy minima. A first-order

cooperati vi ty assumption is applied, and the dielectric constant and remnant polarization are calculated as a function of temperature. Comparison between the experimental and calculated results gave

good agreement.

6
Aging of Piezoelectric Polymers and Application to Biomedical Uses

D. E. DeRossi, S. C. Roth, A. S. DeReggi , M. G. Broadhurst

A new research associate in the Polymer Science and Standards Division has begun work on the

aging and durability of piezoelectric polymers for biomedical devices under sponsorship of the Brown University Research Foundation. Dr. Danilo DeRossi, on leave from the University of Pisa where he is on the Faculty of Engineering and a Group Leader in the Institute of Clinical Physiology, sees great

potential for such polymers in biomedical uses and has come to MBS to develop measurements of and

models for the aging of piezoelectric activity in polymers.

The unigue properties of piezoelectric polymers--low density, good mechanical impedance match to human tissue, flexibility, nontoxicity, and ease of fabrication in complex patterns and arrays--are

ideally suited to biomedical transducer applications. The factors which affect the stability of the

piezoelectric activity in polymers are not well understood, however, nor are accelerated tests available to measure the durability of piezoelectricity in these materials. This Research Associate Program

will include the following activities: laboratory research to improve techniques for periodic nondestructive measurements of the performance of piezoelectric polymer samples, experiments to aid in the

development of an accelerated service test to facilitate evaluation of the relative durability of

piezoelectric polymers, design and evaluation of predictive mathematical models relating the molecular

and microstructural characteristics of piezoelectric polymers to aging mechanisms, and evaluation and

recommended improvements of existing methods for calculating the properties of polycrystalline samples

(the commonly available form) from analyses of single crystal results.

Through this program, fundamental polymer transducer science at NBS will be transferred to Brown University and other private sector groups which are inventing and developing devices. NBS will gain

assistance and impetus from their efforts to develop and improve test methods, data, and concepts

regarding durability and aging in the important new class of piezoelectric polymer materials.

This current activity is expected to be followed by other research associate activities related

to the use of polymer transducers in areas such as robotics.

Automated Dielectric Measurements

F. I. Mopsik, S. J. Kryder, and S. C. Roth

This subtask was begun as part of the power cable insulation subtasks (1 and 2) to meet the need

for more rapid dielectric measurements on large numbers of samples. The instrument being developed

will record the transient electric charge response of a dielectric sample to a step change in electric

field in real time. This response will automatically be transformed into dielectric constant and loss over the frequency range of 1 mHz to 10 kHz and plotted by computer. The work directly supports Task

12139 by providing a basic tool for measuring electrical properties.

During FY81 the electronic circuits for an automated dielectric spectrometer were completed. A hardware clock programmer was built to allow for compatiblity between the sampling rates needed at the

beginning of the transient and the time the computer needs to make changes in the operating conditions

during data acquisition. This device provides automatic sequencing through the first of three sampling

rates so that the computer has time to take control of the sampling.

The analog-to-digital converter has been built and tested. The converter has successfully operated at speeds compatible with a 5 ps sampling time so that the beginning of the transient can be well

characterized and extrapolated to the beginning of the charge transient. Its sensitivity and noise

level is such that it will not degrade the performance of the charge detector.

Finally, the first few data acquisition programs have been written, and the interfaces of the

components (generator, detector, converter, clock, clock programmer) to the computer have been successfully tested. The initial results show that the desired loss sensitivity (< 10 prad) can be achieved

and that the design goals will be met. The resolution was sufficient to show that one of a pair of

10 pF standard capacitors was faulty and had an apparent negative loss that was confirmed by transformer bridge to be -70 prad at 100 Hz. For the size of the integrating capacitor used in the detector,

this result was well within the sensitivity limits initially desired.

Depolarization of Poled PVDF Specimens with Thick Electrodes

A. J. Bur and A. K. Tsao

The effect of electrode thickness on the activity of thin film PVDF was investigated by observing

the pyro- and piezoelectric activity of 26 specimens whose electrode thickness varied from 60 to 310 nm. These samples were obtained from Bell Laboratories (Allentown, Pennsylvania) where they were

poled under uniform conditions after the entire electrode was deposited on the sample. This subtask

7
was done partly in cooperation with Bell Laboratories who are interested in the effects of electrode

thickness for telephone switch pad devices and contributes to the MBS task of optimizing transducer

material for appl ications.

The electrodes consisted of two layered metals: first, Ti was deposited to a thickness of 60 nm; Au was then deposited on top of the Ti to a thickness which varied from 15 to 250 nm.

The samples were examined in three experiments: (1) the hydrostatic piezoelectric coefficient

and the pyroelectric coefficient were measured for the original samples; (2) both coefficients were measured after the thick electrodes were removed; and (3) the depolarization charge was measured by

detecting the discharge as the samples were subjected to an abrupt temperature rise through the melting

point. For the second experiment, all samples had Ti electrodes of 60 nm thickness. The results of

these measurements are: (1) the values of the coefficients for the as-received samples were lower the

thicker the electrode; (2) with the thick electrodes removed from the samples, the values were the

same as those for the thick electrodes in place; and (3) the depolarization charge decreased as the

original electrode thickness increased.

We have concluded that the decrease in piezelectric and pyroelectric response as a function of

electrode thickness is essentially due to the decreases in polarization of the thick electroded specimens and that thick electrodes mechanically constrain the sample during poling so that optimum poling

cannot be achieved.

Fabrication of Thick Piezoelectric Polymer Film

A. J. Bur, M. G. Broadhurst, and A. K. Tsao

The subtask results from a direct request from the Navy to explore fabrication of thick piezoelectric polymer film for hydrophone use. Thick film is needed because the voltage response of thin PVDF films is less than typical ceramic hydrophones. The voltage response is inversely proportional to capacitance and hence directly proportional to the thickness of the film. To make the voltage sensitivity of polymers better than that of ceramics the thickness should be at least 750 pm. To stretch

and polarize a film this thick requires special equipment and so far only a couple of European com- panies have been successful at producing it. In this work, NBS is developing techniques whereby

industrial laboratories in the U.S. can produce suitable films.

Ultra-drawn PVDF is material which has been stretched beyond its natural draw ratio of 4:1. Using a PVDF sample which had been previously stretched to its natural draw ratio of 4:1, it is pos- sible to obtain draw ratios of 6.5 or 7.0 to 1.0 by reclamping the sample in the Instron machine and

stretching at 140 °C at a rate of 0.05 in/min. During the ultra-stretch, the load increases while the

sample dimensions decrease, indicating that the modulus increases with increasing draw ratio. The

ultra-drawn material is desired because it contains mostly p phase material which poles at lower

fields and has a larger polarization than other phases, it is highly oriented, and it is able to withstand high poling fields.

Poling these thick samples requires high voltages. For example, to pole a 0.3 mm thick sample at 2.0 MV/cm, 60 kV are needed. Working at these voltages, it is necessary to suppress corona and flash- over conduction by carrying out the poling in oil and to construct the sample electrodes so that high

electric fields are not present at the edges.

Acoustic Sensors

A. S. DeReggi , S. C. Roth, and S. Edelman

Probing hydrophones and biomedical sensors made with the piezoelectric polymer polyvinyl idene

fluoride (PVDF) have been shown to have superior performance characteristics over previously available

piezoelectric ceramic devices in terms of a wide operating band-width and negligible insertion effects.

These favorable characteristics stem from the similarity in acoustic impedance between the PVDF and

the common transmission and test media relevant in ultrasonics, such as water and oils, and in the case of biomedical ultrasonics body tissue. There is currently a growing interest in these polymer

transducers in the ultrasonic community in general and in the biomedical community in particular. The

collaboration between NBS and a guest worker from the Bureau of Radiological Health (BRH) has continued

during the past year. The principal aims of the collaborative work are the development of polymeric

acoustical probes for measuring the radiation pattern of biomedical transducers and the development of

improved methods of characterizing the performance of existing biomedical transducers using the new polymeric probes. The knowledge obtainable with the new polymeric sensors can be used to ensure both

the safety and adequacy of ultrasonic dosage as well as to advance research in ultrasonic treatment.

A variety of ultrasonic probing hydrophones and hydrophone arrays have been constructed, all featuring the spot-poled, tensioned membrane design configuration which was introduced at NBS several

years ago and was publicized extensively during the course of the past year through contributions to the Proceedings of the 25th Annual Meeting of the Institute of Ultrasound in Medicine (September 1980),

8
the 1980 IEEE Ultrasonics Symposium (November 1980), the Sixth International Symposium on Ult, :s Imaging and Tissue Characterization (June 1981), and through the publication of an article LU n, addition, BRH has filed a patent application (November 1980), and NTIS has publicized this patent

application among ultrasonic manufacturers who might be interested in its commercialization.

The typical active electrode diameter of these probes is around 1.0 mm, although useful output

has been obtained from a probe with an active electrode diameter as small as 300 pm. The operating

bandwidth of greatest interest is 0.5 to 5.0 MHz. Over this range, the frequency response of the

polymer sensors is flat, with a sensitivity for a probe with a 1.0 mm diameter active electrode of

-237 dB ± 1.5 dB re 1.0 V/pPa, and an insertion loss not exceeding 2.5 dB. Repeated sensitivity

measurements over a period of 2.5 years have indicated good stability with no credible trend for

reduced sensitivity within the ± 1.0 dB accuracy of the measurements.

Larger diameter (1.0 cm diameter active area) piezoelectric polymer sensors have been used at NBS

for many years to demonstrate the capability of piezoelectric polymers to detect the heart pulse when

held against the skin at the medically common peripheral monitoring sites. In collaboration with NBS,

members of the CNR Institute of Clinical Physiology at the University of Pisa are evaluating piezoelectric sensors for the monitoring of cardiac patients.

Preliminary clinical data on peripheral pulse signals obtained at Pisa with NBS sensors will be

presented at the forthcoming Computers in Cardiology Conference in Florence in September 1981. These

data appear to give information complementary to but not necessarily contained in EKGs.

Reference:

[1] A. S. DeReggi , S. C. Roth, J. M. Kenney, and S. Edelman, J. Acoust. Soc. Am. 69, 853 (1981).

Polymer Stress Gauge for Intaglio Printing Press

M. G. Broadhurst, S. C. Roth, S. J. Kryder, A. S. DeReggi, and S. Edelman

This work is supported by the Bureau of Engraving and Printing, U.S. Department of Treasury. The

purpose is to develop a gauge to measure the dynamic pressure at critical points in the presses used

to print money. The first phase of the work is completed. The accomplishments of the first phase

included measurement of the width of the area of contact between the two cylinders of the press, the

duration of contact of a point on the upper cylinder with the lower cylinder, and a qualitative (uncalibrated) determination of the change of the pressure with time during contact.

The second phase of the work is to provide a calibrated pressure transducer and a complete signal

processing system for transmitting the transducer signals from the operating printing press and providing pressure and temperature vs time data for the nip (region of contact between the printing rollers).

Piezoelectric polymer strips containing a pressure tranducer and thermocouple are placed under the

fiber rigging on the top roller of the press. When the polymer strip moves into position between the

top and bottom rollers, it is subjected to both a pressure increase and a temperature increase due to adiabatic heating of the trapped and compressed air. The thermocouple signal monitors the temperature

change, and the signal processor subtracts from the polymer transducer signal that part which is due

to temperature change. The resulting signal is that due to pressure change only. A calibrator has

been developed to monitor and correct for changes in transducer response due to aging while the trans- ducer is installed on the press. A final check of the system has been performed between metal plates

covered with rigging material and mounted in a hydraulic press. Sudden release of pressure in the

hydraulic press simulates the release of pressure in the printing press as the nip moves past the

transducer. The pressure measurement system will provide the BEP with data on printing pressures and

temperatures which will not only permit better control of printing pressures but also will provide

data needed for improving paper and ink.

Successful demonstration of this measurement technique has received the attention of both the

paper and synthetic polymer film manufacturers who have a long-standing need to measure and control

pressures between the rollers used to make films. Results will be transmitted to these industries.

Resistivity and Piezoelectric Measurement on Oriented and Unoriented PVDF Films

A. J. Bur

This subtask directly supports the optimization of piezoelectric polymers for applications in industry and Government. It concerns that part of the transducer preparation where large electric

fields are applied to the film in order to polarize it. It has been found that the larger the field,

the higher the piezo/pyroelectric activity and this subtask examines the effect of film orientation on the maximum electric field which the material can support.

Thick specimens of PVDF were prepared by molding PVDF powder or pellets in a compression mold

under vacuum. These specimens, in an isotropic unoriented condition, were found to be unsuited for

9
poling because electrical breakdown occurred at fields between 0.3 and 0.6 MV/cm, which are too low to produce significant polarization. When these samples were mechanically oriented, however, poling

fields of 1.0 MV/cm or higher could be attained so that acceptable transducer activity could be

achieved. This much orientation was carried out by means of tensile extension at 55 °C which produced

a natural draw ratio of 4:1.

In order to examine the difference between the electrical properties of mechanically oriented and

unoriented PVDF, we measured resistivity before and after orientation. The resistivity for an oriented

sample at room temperature showed a marked rise by an order of magnitude or more above that of the

unoriented samples. For unoriented samples, resistivities were in the range 1.7 to 2.4 x 10 15 ohm-cm,

whereas for the oriented samples resistivities ranged from 4.2 x 10 16 to > 2.2 x 10 17 ohm-cm.

While we did not establish a correlation between resistivity and electrical breakdown voltage, we

have established that poling fields of 1.0 MV/cm and higher are not possible unless PVF 2 is mechanically oriented. With this knowledge, we have been able to fabricate thick (0.5 mm) PVF 2 transducers.

Nondestructive Evaluation

S. Edelman, and S. C. Roth

A method for nondestructive evaluation and the dynamic elastic properties of some kinds of structural elements was worked out during previous years, and a paper on the subject was presented at the

Spring 1980 meeting of the Acoustical Society of America. The measurement technique made use of the

favorable properties of piezoelectric polymer strain gauges to measure both axial and shear motion on the same specimen. The specimen can be evaluated nondestructi vely while it is in service. This

subtask demonstrates to potential manufacturers this important application of piezoelectric polymers

and is supported by the NDE program at NBS.

During this reporting period, a set of the specialized piezoelectric strain gauges required by

the method was fabricated. The gauges were mounted on a thin-walled PVC cylinder which simulated a structural element under load.

Several measurements were made at different frequencies. The real and the imaginary parts of the

dynamic Young's modulus were calculated. Reasonable agreement with published values of the real part

was found. The results of two sets of measurements at slightly different frequencies are given in the

table below. Each set consists of three nominally identical measurements.

Frequency a P Ei e 2 (m_1

) (nr 1 ) (Pa) (Pa)

6915 3. 19 27.33 3.37 x 10 9 7.97 x 10 8

3. 19 27.32 3.37 x 10 9 7.99 x 10 8

3. 19 27.33 3.37 x 10 9 7.99 x 10 8

6836 2.82 27.36 3.32 x 10 9 6.91 x 10 8 2.82 27.38 3.31 x 10 9 6.92 x 10 8 2.83 27.38 3.29 x 10 9 7.45 x 10 8

a and p are the attenuation and phase constants which make up the propagation constant y where y = a +

P and where y is related to the wave amplitude £ x by the relation 4

x = £ 0 e“^

x

.

E x and E 2 are the real and imaginary parts of the Young's modulus, E = E x + iE 2.

Measurements are presently being made on a section of pipe while the pipe is subjected to a changi ng tensi le stress.

ASTM Activities

W. P. Harris

This involvement in ASTM is one method by which the task output impacts the industry. Mr. Harris

attended the October 1980 and March 1981 meetings of ASTM Committee D-9, Electrical Insulating

Materials. He continues to be active in several subcommittees, especially in the area of electrical measurements. He is also active on the Executive Subcommittee, which is responsible for governing the

main Committee.

10
The Crystal Structure and Disorders of the Low Temperature

Phase (II) of Polytetrafluoroethylene

J. J. Weeks, E. S. Clark 1

, R. K. Eby, B. L. Farmer2

Long-term durability studies of a series of polymers revealed that f 1 uoropolymers have superior

stability of dielectric and mechanical properties. Therefore, they were chosen to make standard

reference materials for calibration of industrial dielectric cells. As noted below, this has indeed

turned out to be the case. To investigate the origin of this superior stability, we have carried out studies of the crystal structure.

An electron diffraction pattern from polytetrafluoroethylene in Phase II was analyzed to determine

a chain conformation of 2.1598 CF 2 units per turn of the helix. A structure was established from a combination of electron and x-ray diffraction data. The structure contains an ordered repeating

pattern of a left- and right-handed pair of chain stems. Although the structure is ordered in three

dimensions, it cannot be described meaningfully in terms of classical space group nomenclature because

very small changes in the structure result in very large changes in the cell parameters. The structure has a volume of 0.03542 nm3 per CF 2 group, corresponding to a density of 2344 kg/m3

.

Energy analysis was used to determine the low energy crystal structure for polytetrafluoroethylene

molecules in the 13/6 and 54/25 conformations. The structure for the 54/25 conformation contains an ordered repeating pattern of a left- and right-handed pair of molecules in a unit cell having projected

O O parameters, a', b ' , and y

1 , of 9.60 A, 5.62 A, and 91.4 degrees, respectively. These results, the

relative orientations of the molecules, and the relative translations of the molecules are in good

agreement with results obtained in a concurrent and independent analysis of diffraction data. Energies

calculated for rotational and translational displacements in various modes suggest that a range of structures and a fairly large amount of disorder may be present, also in agreement with experiment.

X-ray diffraction patterns for oriented and unoriented copolymers of tetrafluoroethylene and

hexafluoropropylene were obtained. They show a transition between 229 and 243 K for a copolymer with

about 3.4 CF 3 per hundred main chain carbon atoms. The lower temperature phase (II) appears to be

similar to that of the tetrafluoroethylene homopolymer. A primary difference is the presence in the

copolymer crystals of small longitudinal displacements of the molecules caused by the randomly located

CF 3 groups. The displacements increase with increasing CF 3 concentration. The higher temperature

phase (I) is similar to that of the homopolymer with a difference again being the longitudinal disorder

of the copolymer. The difference disappears at higher temperatures as longitudinal disorder is introduced thermally in the homopolymer. At 296 K (phase I), the molecular stems in a copolymer with about

3.4 CF 3 per hundred main chain carbon atoms are at an angle of 37.1 degrees with respect to the normal

to the basal plane of the lamellas. In phase II, this number is the same within the limits of error.

MIGRATION AND THE DURABILITY OF POLYMERS IN USE

L. E. Smith

Task Leader

The most promising areas of growth in polymer markets are in construction, transportation, and

electrical systems where long term durability is essential to competitive performance. Increased

awareness of the problems of productivity and heightened competition has intensified this concern with

durability in all polymer materials.

Reliable test methods that reflect long term durability are needed for the selection of appropriate polymers for specific uses or to maximize industrial productivity by reducing overdesign of parts

without inducing premature failure. Reliable methods for the prediction of the lifetime of polymers

in service rely on three separate types of information:

(1) Knowledge of the rates and mechanisms by which the polymers degrade under the appropriate

environmental conditions.

(2) Information concerning the rates of diffusion of protective additives; (Almost all commercial

polymers are too sensitive to environmental attack to be used without protective additives.

These low molecular weight substances such as antioxidants or stabilizers inhibit the degradation

reaction and are dispersed throughoutte polymer to protect it. In use, these additives migrate

through the polymer leaving the polymer markedly more vulnerable to failure.)

(3) Relationships connecting the changes in molecular properties to the commercially useful properties

of the polymers.

Work in this task is concerned with all three of these needs. Item (3) is addressed in both this task

and in task 12135, Mechanical Durability of Polymers.

‘Consultant, University of Tennessee

2 Consultant, Washington State University

11
Technical work this year on degradation mechanisms and rates includes investigations of the

hydrolysis of polyesters, a study of the mechanism of oxidation of polystyrene, the use of thermogravimetry to measure the rates and activation energies of the degradation of several polymers, and

analysis of thermal methods of lifetime prediction.

For most commercial polymers, lifetime prediction methods must explicitly include the rates of

additive diffusion along with the rates of the inhibited and uninhibited degradation reactions. The

number of commercially usable polymer-additive combinations is too large to be considered eficiently

on a case-by-case basis. The emphasis in this task is, therefore, on the development of general

principles or models of diffusion that are applicable to the maximum number of commercially important

systems. In addition, knowledge of the general principles which control diffusion through solid

polymers is important to the design and evaluation of improved additive systems.

Polyolefins, which include psolyethylene and polypropylene, account for approximately half of the

total polymer production. For this reason, the work in this task on models for diffusion is concerned

exclusively with polyolefins which have their amorphous regions above their glass transition temperatures in normal use conditions. We have developed a useful empirical correlation equation which

relates the diffusion constants among a large number of polymer-additive pairs. Current work is now focused on the investigation of rapid and convenient methods for the measurement of diffusion rates by

solvent extraction and inverses chromatography and on the accurate measurement of slow diffusion rates

in solid polymers by microfluorimetry. These accurate measurements will provide improved data with

which refined correlations can be constructed. These refined correlations should lead to theoretical

descriptions of diffusion based on the molecular structure of the additives and the structure and

morphology of the polymers.

Hydrolytic Degradation of Polyester Polyurethane Elastomers

D. W. Brown, R. E. Lowry, L. E. Smith

Polyester polyurethanes are versatile specialty polymers which are used to form tough and durable

cast or molded elastomeric parts such as oil seals, gaskets, and electrical connectors. They are frequently used in critical and demanding service where the lifetime and performance of major systems

depend on their durability. Some examples include aircraft engines, ship propulsion assemblies,

submarine oxygen generators, and nuclear reactor control rod actuators. In order to provide reliable

lifetime prediction methods for such applications, we have measured the rates of chain scission of

unstabilized polyester polyurethanes. Activation energies for the degradation were measured to enable

the use of accelerated test methods. We then devised a rapid and convenient measurement method which

uses the acid contents of the polymers to predict degradation rates in service.

During this year we have measured the rates of the inhibited reaction to evaluate the effect of

stabilizers on the expected lifetime and have produced a test method which gives results that correlate

well with field experience.

We have recently described the hydrolytic breakdown of carbodi imide-stabi 1 ized polyester polyurethanes [1], Polyester degradation ordinarily occurs by an acid catalyzed hydrolysis of the ester

linkages. Carbodiimide stabilizes the polymer by reacting with acid, thus preventing catalysis. We

have shown that uncatalyzed hydrolysis of ester also occurs. This reaction produces acid at a slow

rate which reacts with the carbodiimide, eventually consuming it. Thereafter, acid catalysis again

becomes important. Consequently, there were three rate constants to consider: k0 for uncatalyzed

hydrolysis, k for acid catalyzed hydrolysis, and k' for reaction of acid with carbodiimide. These were evaluated separately from the slow disappearance of carbodiimide, polymer hydrolysis without stabilizers, and reaction of polyester acid and carbodiimide in a dry polyester polyurethane, respectively.

Differential equations for the combined reactions were then numerically integrated to generate curves

that show the time dependence of the acid concentration, [A], the carbodiimide concentration, [M], and

the change in the reciprocal of the number average molecular weight, A(M 1 ). This last is equal to the

number of chain scissions. The figure shows one set of curves and the corresponding experimental data

for stabilized and unstabilized polymers. The increase in service life due to the presence of carbodiimide is approximately equal to ([M0 ]-[A0 ])/k0 , where the subscripts indicate use of concentrations

measured after incorporation of the carbodiimide in the polymer. Values of k0 depend on temperature

but are the same for polycaprol actone and polybutylene adipate based polyurethanes of laboratory and

commercial origin. Consequently, the k0 should be generally useful in estimating lifetimes of stabilized polyurethanes.

Two aspects of the hydrolysis are still being studied. One is the dependence of k0 on the urethane content of the polymer, since k 0 of polyester diols is three- to ten-fold less than k0 of the corres- ponding polyurethanes. The other concerns the position of the ester-acid equilibrium in polyester

diols and polyurethanes. This equilibrium would define an optimum environmental condition where no further hydrolysis would occur. This has important implications for archival uses of polyesters for

information storage and retrieval.

12
Reference:

[1] D. W. Brown, R. E. Lowry, and L. E. Smith, The Hydrolytic Degradation of Polyester

Polyurethanes Containing Carbodi imides , submitted to Macromolecules.

Long Term Aging Studies With Poly(Ethylene Terephthalate)

D. W. Brown, R. E. Lowry, L. E. Smith

Polyesters are the base material of a number of information storage and retrieval systems, such as photographic film, magnetic video and audio recording tape, and electrographic record systems. These

storage media are replacing paper books and records even in archival storage because of their much

higher information densities. In a project sponsored by the National Archives, we are investigating

methods for estimating the useful lifetimes of polyesters and attempting to define optimum storage

conditions for these materials.

Hydrolysis of the ester linkage is the most important cause of degradation. Thus, the general

features of the degradation of the polyester polyurethanes are expected to be followed with complications caused by the higher glass temperature 70 °C), the presence of crystallinity, and the extreme orientation needed to make a strong film.

Experiments that have been set up include agings in air at 0, 25, 50, and 100 percent relative

humidity (RH) at temperatures of 35, 55, and 85 °C. One set of samples at 100 percent relative humidity is in sealed tubes under nitrogen. Amorphous, unoriented samples are also being aged. Samples

include a variety of commercial record-keeping films as well as samples of the NBS SRM 1470, a poly- ester film. Measurements being made on the samples include tensile tests, acid analysis by titration,

molecular weight measurements by gel permeation chromatography, and examination by differenital scanning calorimetry.

To date, we have found that 90 days aging of SRM 1470 at 100 percent RH at 85 °C causes ~ 90 per- cent loss in tensile strength and a reduction in the number average molecular weight from 14500 to

6300. A sample aged at 100 percent RH at 55 °C for 90 days lost negligible tensile strength, and its

molecular weight was 12600. Calorimeter scans showed no significant effects on the main melting peak

255 °C) compared with the original material, but small peaks were introduced near the aging temperature. Very severe degradation resulting in weak, brittle samples occurred at 100 percent RH in 13 days

at 115 °C and in 39 days at 100 °C, molecular weights being ~ 2800 and ~ 3100, respectively. With

these samples, the melting peak was much broadened, with maxima occurring at 243 and 249 °C, respectively. Peak areas were increased about 20 percent.

It is planned to take advantage of the autocatalytic effect by preaging samples at 85 °C, 100 per- cent RH and then aging the samples under milder conditions, where the high acid content will result in more rapid changes.

Oxidation of Polystyrene

B. Dickens

Polystyrene is a high volume commodity polymer subject to oxidation in use. The mechanism of oxidation under normal use conditions is not known with certainty. Studies carried out in collaboration

with Dr. Jean Marchal of the CNRS, Strasbourg, have used y-ray initiated oxidation of polystyrene to simulate the low temperature oxidation process encountered under normal use but with control over the

rate of radical initiation.

Oxidation studies were carried out on polystyrene in chlorinated hydrocarbon solutions to produce

readily radicals which are capable of attacking the polymers. Product analysis coupled with measurements of molecular weight changes have led to a number of conclusions. Under these circumstances, we conclude that: the initial attacking species are Cl radicals, attack is random along the PS chain,

intramolecular propagation of the oxidation chain occurs by hydrogen abstraction by peroxyl radicals,

on the average there is one such propagation step on the PS backbone in CHC

3 and six in CC1 4 , higher

molecular weights are attacked less per monomer unit than lower molecular weights, and alkoxyl radicals

are formed and undergo p-scission to break the polymer backbone and produce small molecules. In the

solid these small molecules would plasticize the material and impair its useful mechanical properties.

An oxidation mechanism to account for these facts has been devised.

Variable Heating Rate Thermogravimetry

J. H. Flynn

The concept of measuring the degradation of a polymeric material under conditions designed to accelerate its rate and extrapolating the rates to milder conditions so as to predict the lifetime of

the material has great appeal. The practical uses and commercial importance of reasonably accurate

13
Figure 1. Hydrolytic degradation of a polybutylene adipate-based polyurethane at 85 °C,

100 percent relative humidity: with carbodi imide, triangles; without carbodiimide, circles, [A] shaded, [M] half-shaded (aM" 1

) unshaded. Lines with

k

0 = 1.2 x 10 -6 equi val ent/g*day , k = 0.26 day -1

, and k' = 3.0 x 10 5 g/eq*day.

14
lifetime prediction methods are obvious. The methods of thermal analysis are often used in lifetime

prediction procedures. They offer practical advantages such as accessibility of apparatus, simplicity

of application, and rapid accumulation of data. Thermogravimetry is the method of thermal analysis

most often used for this purpose because the kinetics of volatilization are often closely coupled to the kinetics of degradation in the condensed phase.

Unfortunately, the application of the Arrhenius equation to polymer degradation processes for the

purpose of predicting aging at service conditions is complicated by the complex kinetics of these

reactions. Such heterogeneous systems are often composed of at least several "elementary processes,"

each with its own set of Arrhenius parameters. A change in activation energy will result from a change in the rate-limiting step of the degradation mechanism. If this occurs in the unmonitored

kinetic gap between the lowest experimental temperature and the service temperature, then the lifetime

prediction is invalid.

In our variable heating rate method, kinetic data are compared over a thousand-fold range of

heating rates--from six degrees/minute to nine degrees/day. As a result, activation energies are obtained from five to 95 percent conversion for over a hundred degree temperature range and down to much lower temperatures than those of the conventional methods of thermal analysis. From isoconversional diagnostic plots of logarithm heating rate vs reciprocal absolute temperature, activation

energies are calculated for each fraction of conversion. The wide range of temperatures which these

measurements cover gives one the precision necessary to determine the activation energies from the

slope between each successive pair of points on each isoconversional . A grid may be set up from these

values in which activation energies (E) are displayed as a function of conversion and temperature.

This new technique has been applied to the degradation kinetics of polystyrene, polymethylmethacrylate), and polyurethanes in inert atmosphere and in air. In the case of poly(methylmethacryl ate) in

nitrogen, for example, activation energy grids demonstrate that E increases with increasing temperature at constant conversion, but E appears to be nearly independent of conversion at constant temperature.

Analysis of the Kinetics of Thermogravimetry

J. H. Flynn

The kinetic analysis of the thermogravimetry of polymers requires the comparison of data from

experiments performed at differing temperature programs. These data reflect divergent physical properties and chemical compositions among the specimens resulting from their diverse thermal histories.

The effect of thermal history on the kinetics of weight-loss processes is a serious problem. However,

it is not usually dealt with during the modeling of the kinetics of these processes. A reason for

this is that often the effect can be exposed only through the comparison of calculated parameters from

two separate series of kinetic measurements on identical specimens of polymers. Otherwise, contra- dictions in values of kinetic parameters from different techniques and investigations may either be

overlooked or falsely ascribed to other causes such as experimental error, differences in initial

chemical or physical properties of the samples, differences in experimental conditions, etc.

The critical test for thermal history dependence is differing rates of weight loss from two experiments at the same temperature and conversion, i.e., at a point of concurrence. The conventional

methods for the determination of Arrhenius parameters involve either the comparison of two or more

isothermal experiments at differing temperatures or the comparison of two or more constant heating

rate experiments at differing heating rates. Neither of these cases realize a point of concurrence

between two experiments.

Two experimental techniques and methods of data analysis have been developed to detect thermal

history dependence of Arrhenius parameters. In the first method, logarithms of the times to reach

various fractions of conversion for several isothermal experiments are plotted against the reciprocal

absolute temperatures at which the same fractions of conversion were reached in a single experiment at constant heating rate. The slopes of the isothermals are given by:

isothermal slope ~ -1.05 ER -1

and the isoconversional distance between two isothermals, T and T, , is

a b isothermal distance = ER

-1 (Tr 1 - T

_1

v ). b a'

If thermal history effects are present, then the activation energy (E) calculated from the slopes will

differ significantly from E calculated from the isothermal distances.

Similar sets of equations have been developed in the second case in which a single isothermal

experiment is compared with several experiments at various constant heating rates. For this case, E's obtained from the isothermal distance between two isothermokinetics are compared with those obtained

from the slopes of the i sothermoki neti c lines. As before, any difference between E calculated from

the slopes and E calculated from the distances will indicate thermal history dependence. Also, in

15
either case, any deviation of E from constant value can be observed visually from a distortion of the

uniform distances or from changes in slope of the grids.

Activation energies have been determined with great precision for the degradation of polystyrene

in vacuum from both the factor jump and constant heating rate techniques. The E values from the two methods show a significant difference of 11.1 kJ/mol . This difference has been interpreted as due to

a bias from a constant increment caused by different thermal histories for each rate of heating.

Thermogravimetric Studies of Polymer Degradation

B. Dickens

Because of its ease of application, thermogravimetry is widely used to study polymers. However,

this ease of application also induces a significant amount of misapplication. The appropriate kinetic treatments for thermogravimetric data have been examined and reviewed in a joint publication with

J. H. Flynn. The parameter most readily determined is the activation energy, which can then be used

to shed some light on the degradation mechanism.

In recent degradation studies, the following activation energies were found: 65.4 ± 0.5 kcal/mol

for both linear and branched polyethylene (LPE and BPE) degrading in vacuum, 64.8 ± 0.3 kcal/mol for

LPE and 64.4 ± 0.2 kcal/mol for BPE in slowly flowing N 2 at 8.0 mm Hg, and 6.26 ± 0.5 kcal/mol for LPE and 61.2 ± 0.6 kcal/mol for BPE in N 2 flowing at 1.0 to 4.0 mm/s at 800 mm Hg. The overall activation

energy in vacuum has been related to a degradation mechanism to show that the slow chain-breaking step

is one of p-scission following hydrogen abstraction. The procedure provides an estimate of 33 kcal/mol

for the activation energy of p-scission for secondary alkyl radicals. For degradation by random

scission of C-C backbone bonds in the initial stage, the overall activation energy is estimated to be

70.6 kcal/mol. The lower activation energies in the presence of an external pressure have been shown

to be due to the evaporation of molecules formed in scissions but not volatilized immediately after

their formation. This adds a latent heat term (10 to 50 kcal/mol) to the apparent activation energy.

Similar quantities have been determined for isotactic polypropylene: 61.5 ± 0.8 kcal/ mol in vacuum, 55.9 ± 0.3 kcal/mol in N 2 at 5.0 mm Hg, and 55.1 ± 0.2 kcal/mol in N 2 flowing at 1.0 to 4.0 mm/

s at 800 mm Hg. The decomposition of the activation energy into its components for degradation in vacuum using a degradation mechanism devised to be consistent with the observed degradation behavior

and degradation products provides an estimate of 29.6 kcal/mol for the p-scission of tertiary alkyl

radicals. As was the case for PE, the lower activation energy for degradation under external pressure

has been shown to be due to the latent heat contributions of molecules which do not evaporate as soon

as they are formed. For the initial stage of degradation in vacuum, an activation energy of 71 kcal/

mol is proposed.

Measurement of Antioxidant Diffusion by Microfluorimetry

S. L. Wunder, F. W. Wang, and R. A. Velapoldi 1

Measurement of the concentration profiles of a diffusion substance is an accurate method for

determining relatively small diffusion constants in the solid state. In addition, the effect of

solvent on the diffusion rate can be measured on the same system which will allow direct comparison

with diffusion rates measured by rapid and convenient solvent extraction methods.

The migration of antioxidants from polymer films is being studied by both extraction experiments

and solid state diffusion experiments. In an extraction experiment, a plan sheet of polymer with

uniform concentration of an antioxidant is immersed in a limited amount of well-stirred solvent.

Then, the amount of the antioxidant extracted by the solvent is determined at various times by fluorimetry. The extraction of N,N' -diphenyl-p-phenylendiamine (DPPD) by heptane at 22.0 °C from low density

polyethylene films has been measured. An analytical working curve relating DPPD concentration to fluorescence intensity was linear in DPPD concentration below 4.0 ppm. A preliminary report of the

results has been prepared.

The diffusion of the antioxidant N ,

1 -p-dinaphthyl-p-phenylene-diamine (DNPD) in branched polyethylene (PE) SRM 1476 is being studied using microfluorimetry. After fusion of two plugs, one neat

PE and the other doped with antioxidant, measurement of the antioxidant fluorescence as a function of

distance from the fused boundary yields the diffusion coefficient of the antioxidant. This solid state diffusion technique eliminates the problem of the swelling effects in extraction experiments.

Preliminary work has been performed to optimize the experimental conditions and techniques for the

diffusion measurements. These will be obtained for DNPD in PE as a function of temperature.

A Center for Analytical Chemistry.

16
Migration of Oligomers and Antioxidants From Polyolefins

S. S. Chang, W. J. Pummer, J. R. Maurey, L. E. Smith

Under the sponsorship of the Food and Drug Administration, this project aims at the development

of general principles and models of diffusion that can be used to simplify the regulations governing

polymers in food contact use and thus ease the burden of Federal regulations necessary for public

health and safety. This work is also directly applicable to the design and interpretation of extraction methods for diffusion measurement and the models developed will be applicable to the problem of

lifetime prediction as well. In this year, copolymers of ethylene and vinyl acetate with vinyl acetate

contents of five and 13 percent have been added to the list of polyolefins studied. Several solvents

have also been added to the list of solvents used.

Thus, the experimental variables include (1) polymers--l inear polyethylene, branched polyethylene,

isotactic polypropylene, and copolymers of ethylene and vinyl acetate; (2) migrants--n-C 18 H 38 , n-C 32 H 66 , and BHT; (3) sol vents--corn oil, tributyrin, trioctanoin, ethanol, ethanol -water mixtures,

water, n-heptane, n-octanol , synthetic triglyceride mixture HB307, and n-octadecane ; and (4) temperature--30, 40, and 60 °C. Furthermore, the initial concentrations of the migrants in the polymers and

the thickness of the sample plaques have also been varied. Besides the kinetic studies, equilibrium

properties such as solubilities and partition coefficients have also been studied. The migrants used

are labeled with radioactive 14 C to yield a detectibi 1 i ty of 10 10 g if needed. The extraction experiments generally require a few weeks to a few months to complete; however, some experiments may reach

completion in less than a day, while some may last longer than a year. The diffusion coefficients

observed vary from 10-6 - 10“ 15 cm2

s _1. Some of the experiments indicate an ideal Fickian behavior,

especially for preswollen polymers or for non-swelling solvents. In most solvents, the diffusion

coefficient may increase from an initial value and then level off at a higher value due mainly to

swel 1 i ng effects.

If all other parameters are held constant, then the ranking of importance of the influence of

parameters on the diffusion coefficient of migrants from polyolefins is as follows: solvent, temperature, additive type, polymer type, additive concentration. The first three parameters are far more important than the remaining two.

The nature of the effect of the first three variables is also rather different from those of the

latter. The effect of the most influential group of variables (solvent, temperature, and migrant) is generally much less pronounced for cases producing high diffusion coefficients, e.g., 1CT 6 cm2

s _1

, than for low diffusion coefficients. For instance, the effect of replacing a lower MW oligomeric

migrant, n-C 18 F! 38 , by a higher MW migrant, n-C 32 H66 , under various conditions is shown in figure 2 as an illustration for this type of behavior. The effect is less than a factor of five at diffusion

coefficients of 10~7 to 10 _6 cm2 s _1

, while the ratio is near 1,000 at diffusion coefficients of 10 -1 ° to 10 _9 cm2

s _1. Similar behavior is observed by changing solvents or temperature.

Flowever, in the case of changing polymers, the effect seems to be more or less a constant shift

in the ratio of the diffusion coefficients covering a wide range of diffusion coefficients. This

behavior is illustrated in figure 3 where the diffusion coefficients of migrants from low crystallinity, branched polyethylene are compared against those from highly crystalline, linear polyethylene (as

well as polypropylene) in various combinations of other parameters. The average ratio of the coefficients for changing the base polymer only is about six through the range of diffusion coefficients

from 10 -14 to 10 -6 cm2

s -1.

In contrast to the great accelerating action of n-heptane over that of corn oil in extracting

small molecules from polymers (NBSIR 81-2263), the diffusion coefficients of these small molecules into

liquidus tributyrin, trioctanoin, and synthetic triglyceride HB307 are nearly identical to that into corn oil within a factor of 1.5. Therefore, either tributyrin, trioctanoin, or HB307 can be used to simulate the extractive action of corn oil in a great variety of conditions involving different

additives, polyolefins, and temperatures. Flowever, normal analytical techniques (other than radiolabeling) are difficult with the triglycerides. Diffusion coefficients into ethanol are equal or slightly greater than that into triglycerides under similar combinations of test conditions and chemical analysis in ethanol is generally much easier than in the triglycerides. The slightly enhanced

extraction behavior makes ethanol a slightly accelerating solvent which yields an upper bound for

migration.

Results for n-octanol and 95 percent ethanol yield supplemental information for using ethanol as

a simulating solvent. Octanol also behaves as an accelerating solvent, although its accelerating

action is far below that of n-octadecane and n-heptane. Diffusion coefficients of these small molecules are about the same into pure ethanol and into 95 percent ethanol. Flowever, the lower solubility

and partition coefficients of some of the migrants in 95 percent ethanol yield a lower limit of migration of these molecules at equilibrium than that in anhydrous ethanol.

17
18

Figure

2.

Effect

of

molecular

weight

of

oligomers.
Measurements of Diffusion in Polymers by Inverse Gas Chromatography

G. A. Senich

Diffusivities of volatile compounds or probes in polymers have been obtained from non-equilibrium

inverse gas chromatography (IGC) experiments conducted at rapid carrier gas flow rates. The experiment

is similar to conventional gas chromatography (GC) except that the polymer under study replaces the

usual low molecular weight stationary phase. The quantity of interest is the measured peak broadening

that occurs during flow through the column. Peak spreading arises from the multiplicity of differing

gas paths through the column, diffusion in the gas phase along the flow direction, and resistance to mass transfer in both the gas and polymer phases, among other factors, and is commonly related to the

probe-polymer diffusion coefficient by the well-known van Deemter equation in GC. However, this

relation neglects variations in the local carrier gas flow velocity and some additional diffusive

processes in the gas phase. These factors have been shown to exert a significant influence on the

magnitude of the diffusivity found by IGC studies.

Another important parameter is the diffusion path length in the polymer phase. Two extremes in polymer geometry are possible within the column, a thin, uniformly distributed covering over the

entire surface of the spherical column packing or annulus-like regions collected at the contact points

between spheres, each with a different diffusion path length. These two extremes in the physical

distribution of the polymer phase can lead to polymer-probe diffusivities differing by factors of up to ten thousand. The variability of the polymer film throughout the column makes an accurate determination of the absolute probe-polymer diffusivity unlikely. Experiments on the rate of diffusion of one probe relative to another in the same polymer column are currently in progress. The resulting relative

diffusivities may then be placed on an absolute scale by calibrating the column with a probe whose

diffusion coefficient in the polymer has been determined by an independent method.

The extent of migration of a sufficiently volatile material from a polymer into a contacting

substance (typically a solvent) can be estimated from data readily obtained by IGC studies. The

specific retnetion volume obtained experimentally at slow carrier gas flow rates, which characterizes

the thermodynamic interactions between the probe and polymer, is used to determine the polymer-migrant

interaction parameter. When combined with a value of the solubility of the migrant in the solvent, a calculation of the equilibrium partition coefficient is possible. The latter is a direct measure of

the fraction of the additive which can be expected to migrate from the polymer to the contacting

medium. If the time over which migration can occur is short, an equilibrium prediction may greatly

exaggerate the degree of migration expected. A value for the diffusion coefficient of the migrant in

the polymer may then be obtained from IGC experiments and employed to estimate the degree of migration

which will occur over the given time period. A recent publication [1] outlines in greater detail a procedure for determining the extent of migration at both equilibrium and short times from data derived

by IGC studies.

Reference:

[1] G. A. Senich, Chem. Tech. 11, 360 (1981).

Measurement of Translational Diffusion of Polymers by Fluorescence

Photobl eachi ng Recovery Technique

F. W. Wang, and W. H. Grant

The diffusion coefficient of chain molecules is a dynamical parameter which should provide a test

of both scaling [1] and reptation [2] concepts proposed by de Gennes. Recently, Hervet and co-workers

[3] used the forced Rayleigh scattering technique to measure the diffusion coefficient (D) of polystyrene chains in benzene. They found that in the semidilute regime where the chains overlap, D decreases

with polymer concentration, c, as c

1 7 0 1

, in agreement with scaling law predictions. However,

they pointed out that more experiments are necessary to check the molecular weight dependence of the

diffusion coefficient.

In collaboration with Prof. En-Shinn Wu of the University of Maryland (Baltimore County), we have

initiated a project to measure by the fluorescence photobleaching recovery (FPR) technique the diffusion of chain molecules in the semidilute regime. In the FPR technique, one uses high intensity

illumination to deplete the observed volume element of chromophore-labeled chain molecules by photobleaching. After the bleaching pulse, the diffusion of unbleached chromophore-labeled chain molecules

into the volume element is observed with low intensity illumination. From the time constant for the

recovery of the original fluorescence intensity, the diffusion coefficient can be obtained. The FPR technique can be used to measure diffusion coefficients in the range 10 11 cm2 /s to 10 6 cm2 /s [4].

We have developed a procedure to synthesize polymers labeled with photobleachable chromophores

and have determined the fluorescence properties of one of these polymers. The diffusion coefficients

of this and other similarly prepared polymers will be measured by using the FPR technique to check the

molecular weight dependence of the diffusion coefficient in the semidilute regime.

19
^gUiD/ dd‘3d1

a

2 0

Figure

3.

Effect

of

different

polyolefins.
References:

[1] P. G. de Gennes, Macromolecules, 9, 594 (1976).

[2] P. G. de Gennes, J. Chem. Phys. 55, 572 (1971).

[3] H. Hervet, L. Leyer, and F. Rondelez, Phys. Rev. Lett. 42, 1681 (1979).

[4] D. E. Koppel , D. Axelrod, J. Schlessi nger , E. L. Elson, and W. W. Webb, Biophys. J. J_6, 1315

(1976).

Assessment of Transport Mechanisms For Radon In and Through Building Materials

R. J. Rubin

Accumulation of radioactive radon gas in buildings poses a health hazard. High levels of radon

are encountered in certain geological areas where the naturally occurring amounts of radium-226 are

high. Certain building materials, such as concrete, building blocks, and gypsum board, may also

produce higher than average amounts of radon if one of the components of the building material contains

high trace concentrations of radium-226. Under an interagency agreement with the EPA, NBS has very

recently undertaken the task of studying radon transport in building materials. The study involves a cooperative effort between three NBS Centers: Radiation Research, Building Technology, and Materials

Science. The initial phase of this project, to critically assess the current state of knowledge of

radon transport through or emanation from building materials, has been completed. Because of our expertise in diffusion and transport models, the Polymer Science and Standards Division was asked to assess current mechanisms and models and apply them to some selected cases.

Models of the movement of radon through and from porous building materials such as concrete are based on the assumption that the transport of radon through the air-filled pore system of a porous

material occurs in response to two driving forces: (1) diffusive transport of radon in response to a difference in radon concentration, where the transport coefficient is the diffusion coefficient of

radon in the air-filled pore system, and (2) convective transport of an air-radon mixture in response

to an air pressure difference, where the transport coefficient is the permeability coefficient of air

in the pore system. Among the questions and transport cases which have been treated are: (1) What

are the relative contributions of concentration differences and pressure differences to the steadystate transport of radon in concrete? From literature values of the diffusion coefficient of radon in concrete, the porosity of concrete, and the permeability coefficient of air in concrete, we have found

that a pressure difference of 25 mm Hg across 10 cm of concrete significantly enhances the flux of

radon through a surface. (2) Estimates are obtained of the times required to establish steady-state

behavior in both the case of diffusive transport and convective transport. In general, the time

required for establishing steady-state convective transport is a few hours when the time required for

establishing steady-state diffusive transport is a few days. Thus, it appears that short term variations in radon concentration (of the order of one day or less) are "averaged out." (3) The factor by

which the steady-state radon flux from bare soil is reduced when a concrete slab is interposed has

been calculated.

These and other examples are incorporated in the report, "Review and Assessment of Radon Transport

Through and From Building Materials," which has been reviewed favorably by a number of experts in the

field and will be published as an NBS Technical Note. Among the recommendations which have been made

on the basis of our study for this report are: (1) The time-dependent transport equations for trans- port of radon in a porous medium which include both diffusive and convective terms should be verified

or validated. (2) Measurements of the diffusion coefficient of radon and the permeability coefficient

of air should be made on the same concrete specimens. It is only through such combined measurements

that the relative magnitude or importance of the two kinds of transport can be determined with cer- tainty. (3) An experiment has been proposed to determine the diffusion coefficient of radon in concrete from measurements of the build-up of radon concentration with time when a specimen of welldefined shape is placed in a radon chamber. The model case of a cylinder with exposed ends and coated

side has been analyzed.

21
MECHANICAL DURABILITY OF PLASTICS FOR DESIGN AND USE

B. M. Fanconi

Task Leader

Polymeric materials increasingly are used in applications where long-term mechanical durability

is critically important. The full exploitation of these materials would result in greater productivity

through improved properties at lower costs. The realization of increased productivity is often limited

by the lack of data and models upon which to design for long-term use. Thus, the lack of adequate

test methods and data for evaluation of long-term mechanical performance not only restricts applications, but also leads to over design which results in more expensive items and limits weight savings.

The substitution of polymer composites for critical materials in the aerospace industry has been

limited for this reason. Evaluation and control of materials parameters that affect long-term perfor- mance should lead to more durable materials and, hence, reliable performance for the intended service

life.

The objective of this task is to provide data, test methods, and standards for evaluation of

long-term mechanical durability of polymeric materials. The approach is to identify and analyze

principal failure mechanisms in these materials under mechanical stress in the use environment, to determine the effects of chemical structure and fine structure morphology on mechanical properties and

failure processes and to develop constitutive relationships and models for mechanical properties as the basis for accelerated test methodology and lifetime prediction.

New activities have been initiated in glassy and composite polymeric materials. Theories have

been developed to predict the rate of craze extension and stress relaxation at crack tips in crazes. The fracture energy of elastomer-modified epoxy resin systems has been investigated to elucidate

mechanisms of crack blunting in these composite materials. The identification of failure modes both

at the fine structure and molecular level not only serves as a basis for models to predict long-term

behavior but also leads to quality control methods during processing. For example, incomplete chemical

reactions during curing of composite materials have been shown to affect long-term mechanical performance. The extent of these chemical reactions during the cure process may be determined using spectroscopic techniques of nuclear magnetic resonance and Fourier transform infrared spectroscopy.

The National Bureau of Standards has established joint programs on mechanical durability with

other Federal agencies which are fostering the application of polymeric materials in areas of national

concern. A joint program with the Department of Energy is concerned with the mechanical performance

of elastomeric seals in geothermal energy wells. The Bureau of Medical Devices of the Food and Drug

Administration supports an investigation of relationships between the fine structure morphology of

ultra high molecular weight polyethylene and the long-term mechanical properties of this material when

used in medical implant devices. Improving the mechanical durability of fibrous network materials is the goal of a joint program with the Bureau of Engraving and Printing. In all of the above applications, there exists the need for test methods and standards to ascertain the physical limits of polymeric materials in various use environments. An outgrowth of a recent project with the Department of

Transportation on mechanical durability of plastic shipping containers has been the development of a new test for environmental stress cracking. Optimal testing conditions are being identified for

submission to the ASTM of an improved standard method for environmental stress-crack resistance.

Molecular Processes Associated with Mechanical Deformation and Failure

B. M. Fanconi, D. L. VanderHart, S. L. Wunder, J. P. Colson, S. J. Kryder,

E. E. Toth, K. L. DeVries 1

, S. Abbate2

, and G. Zerbi 2

The elucidation of molecular processes and structure changes accompanying mechanical deformation

and failure not only provides the basis for development of test methods for long-term performance and

quality control but also provides insight into the selection and design of materials with improved

mechanical performance and durability. The semicrystal 1 ine structures found in most polymeric materials present significant challenges to characterization of molecular structure. New spectroscopic

techniques involving 13 C nuclear magnetic resonance and Raman scattering are developed to elucidate

molecular conformations in disordered material. Reorganization of polymer molecules during deformation

affects mechanical performance. Identification of the molecular processes involved and the physical structures which result are the aim of the NMR studies.

Fourier transform infrared spectroscopy is used to determine the number of chain scissions pro- duced per free radical measured during fracture in order to assess the role of free radical chain

propagation reactions in the fracture process.

University of Utah

2 Instituto di Chimica Industriale di Politechnico

22
Spectroscopic Investigations of Mechanical Degradation of Polyethylene . Molecular processes

associated with mechanical degradation of polymeric materials include chain rupture or scission. It has been postulated that chain rupture sites may be highly localized forming microvoids from which

cracks may initiate leading to macroscopic failure [1]. The process of bond scission produces free

radicals that may initiate many additional chain scissions before recombination to form stable chemical

species. This would suggest that mechanical stability might be improved by the addition of free

radical scavengers. The evidence for multiple chain scissions per free radical comes from comparisons

of the number of free radicals generated during mechanical degradation measured by electron spin resonance and new end groups formed as determined by infrared spectroscopy [1]. Other estimates of

the extent of chain rupture derive from viscosity-averaged molecular weight changes [2]. The number

of chain scissions per free radical determined by viscosity measurements on mechanically damaged polyethylene is several orders of magnitude lower than the ratio evaluated from previous infrared data.

Previous infrared determinations were based on spectral differences between deformed and undeformed specimens [1,3]. Effects of molecular orientation, changes in sample thickness and surface

texture, as well as differing void content could not be readily accounted for in these measurements. Another complication derives from the use of specimens with relatively high initial concentrations of

end groups. For these reasons, we have carried out a detailed investigation of free radicals and

chain scissions during mechanical degradation of polyethylene using electron spin resonance and Fourier

transform infrared spectroscopy.

Measurements were made on tensile-fractured polyethylene fibers, rods ground in liquid nitrogen,

and on an ultra-high molecular weight polyethylene that was also mechanically degraded through grinding

in liquid nitrogen. This last sample was of particular interest in that the undeformed material

contained very few end groups. To circumvent spectral effects due to orientation, surface conditions,

void content, and film thickness caused by the deformation, our approach was to cast a film of the

deformed material from solution or the melt. Films for IR analysis were prepared from the reference

material in an identical manner.

Spectral changes from new end groups were observed in the 900 to 1000 cm

-1 region (arising from

vinyl groups), near 1375 cm

-1 (due to methyl groups), and in the 1700 to 1750 cm

-1 region (attributed

to carbonyl groups). Increases were observed in the concentrations of the terminal vinyl, methyl, and

aldehyde groups. The concentrations of new end groups are given in table 1 and compared to the free

radical concentrations in table 2.

As evident from table 2, we find that the ratio of chain scissions to free radicals is lower by one to two orders of magnitude when compared to previous determinations [1]. Our values are still

approximately an order of magnitude larger than the viscosity-determined values [2]. We attribute the

latter discrepancy to differences in molecular weight and the physical state of the samples used in the two studies. The discrepancy with previous IR studies [1,3] arises from sampling methods and the errors in the previous work associated with taking differences between relatively intense bands. In the case of the ultra high molecular weight polyethylene, no change was observed in the vinyl group

concentration, even though the initial concentration of this species was extremely low.

Examination of Drawn PET Fibers by 13 C NMR . Through a collaborative effort with the Firestone

Tire and Rubber Company, several drawn PET fibers having different annealing histories at various

constraints were investigated. Solid state 13 C NMR measurements were made at NBS on specimens furnished by Firestone and characterized by them with respect to mechanical properties, x-ray scattering,

and density. The motivation behind this research was to determine whether solid-state 13 C NMR could:

(1) clarify the concept and/or measurement of crystallinity in these fibers, (2) determine noncrystalline orientation, and (3) aid in relating molecular properties to mechanical properties.

Limited variable temperature data were obtained on non-spinning oriented samples. The rotation

of a large number of aromatic rings about the 1,4 axis at frequencies near one kilohertz was observed

in the temperature range of 130 to 150 °C. At room temperature, a few mobile aromatic rings were

observed to rotate at similar frequencies. In these experiments, ring rotation is observed preferentially for those chains which have been oriented by drawing and/or annealing. The question of the

morphological origin of these chains remains somewhat ambiguous since there has been no clear definition of crystallinity in the 13 C NMR results to date. Possible definitions of crystallinity in terms

of lineshapes (spinning or non-spinning) or relaxation (T^ or T-j’ ) have all given ambiguous results.

X-ray results suggest that the crystallite block length is rather short (3.1 to 8.0 nm) and that

percent crystallinities are low (20 to 40 percent). On the other hand, NMR results, particularly

spinning lineshape analysis, suggest percent crystallinities in the range of 60 to 70 percent. We are considering using Raman or IR in future work on these samples to measure the gauche/trans ratio and how

this ratio is related to the NMR and x-ray observables.

The methylene resonance in these non-spinning oriented samples is rather distinct from the rest of

the 13 C NMR resonances. From this resonance, overall orientation can be determined. This analysis has

not, as yet, been done in detail, but qualitatively, the following statements can be made based on the

observed NMR lineshapes:

23
Table 1

Concentrations of Chemical Groups Formed During Mechanical Degradation of Polyethylene

Concentrations

(No. /cc)

IR Band Freq. Ground PE Fractured PE Group (cm x ) Commercial UHMW Ref. 1

RCH=CH2 909 1.2 ± 0.4 x 10 17 - 1.3 + 0.4 x 10 17 3.4 X 10 18

RCH=CHR' 965 - - - 1.9 X 10 18

rch 3 1 ,370 2.2 ± 1 x 10 18 5.6 ± 3 x 10 18 CO + 4 x 10 17 11.8 X 10 18

RCHO 1 ,735 3.7 ± 0.5 x 10 17 1.1 ± 0.1 x 10 18 1.9 + 0.6 x 10 17 4.6 X 10 18

Table 2

Chain Scissions Per Free Radical

Ground PE Commercial UHMW Tensile

Fractured PE Ref. 1

No. chain scissions

per gram

5.1 ± 1 x 10 17 1.2 ± 0.1 x 10 18 3.4 ± 1 x 10 17 9.9 x 10 18

No. free radicals

per gram

1.2 x 10 161 x 10 17 3.5 x 10 15 5 x 10 15

Chain scissions 34 - 50 11 - 13 68 - 125 1 ,600

per radical

(1) Annealing at constant length improves the orientation of those chains which were already

quite well aligned by the cold drawing. Flowever, there is no appreciable change in the amount of new orientation of those chains whose direction deviated substantially from the

draw direction.

(2) Annealing with free ends broadens the orientational distribution for the highly-oriented

chains and significantly increases the number of poorly-oriented segments.

Examination by NMR of Morphological Changes in the Wet Beating of Cellulosic Materials . A collaborative effort with the Bureau of Engraving and Printing entails the examination of paper-related cellulosic materials. The background for this work was that in previous studies [1] it was shown that NMR could distinguish 13 C resonances associated with cellulose chains near the surface as opposed to the

interior of an elementary fibril. Elementary fibrils are roughly 3.5 nm in diameter.

In paper making, cellulosic materials are soaked in water and then wet beaten. The latter process

seems to plasticize the materials so that they form a good paper. An important question concerns the

fate of the elementary fibril during wet beating. It is known, for example, that wet beating cotton

increases the amount of non-freezing water, while the fiber saturation point increases in wood pulp as

a result of this process. So, in general, the amount of water intimately associated with the cellulose

increases with wet beating.

For this project, a high speed water-tight rotor had to be designed which could spin stably at frequencies of at least 1.5 KHz . Such a rotor was designed, and data were obtained using dry, wet,

and wet beaten samples of microcrystalline cellulose, Norway Spruce Kraft pulp, and purified cotton. The NMR results showed changes in the surface-carbon resonances on going from dry to wet samples. But

no further changes were observed when going to the wet beaten material. Thus, it appears that wet beating does not break up the elementary fibrils to any significant (> 10 percent) degree. Some questions remain as to whether all of the carbons are being observed, but this problem cannot be

addressed unless we acquire the ability to observe proton resonances directly.

24
Study of Crystal Modification and Surface Area Changes in Mechanically-Deformed

Ultra High Molecular Weight Linear Polyethylene . In FY80, we observed that cold (room temperature)

drawn (\ = 2.7) ultra high molecular weight linear polyethylene contained a significant portion of the

monoclinic crystalline phase along with the usual orthorhombic phase. This year, the amount of this

phase was quantified using magic angle spinning (MAS) 13 C NMR. Furthermore, by taking advantage of

magnetization diffusion of proton magnetization in solids along with the cross-polarization process

between 13 C and X H nuclei, an attempt was made to measure the increase in going from the undrawn to the drawn LPE. The results, simply interpreted, indicated a significant increase (> 2x) in surface

area in the drawn material. However, unambiguous interpretation awaits the ability to observe proton resonances directly.

Spectroscopic Investigation of Disorder in Polyethylene . Characterizastion of order at the

molecular level is fundamental to establishing connections between molecular structure and mechanical

properties. The structure of crystalline material can often be deduced from x-ray scattering data,

however, this is not the case for molecular conformations in disordered material. In concert with

suitable calculations of frequencies and intensities, vibrational spectroscopy can provide useful

information on disordered polymeric materials. A case in point is the C-H stretching region of polymethylenes which is sensitive to both intra- and intermolecular order. In the Raman spectra of these

molecules, there is a Fermi resonance interaction between the C-H bending and stretching vibrations,

which depends on the state of the polymethylene chain. In the approximation that a gauche bond can be

modeled by a decoupled CH2 group, the Fermi resonance scheme for this system can be compared to that

for the all-trans chain. The calculations indicate that a redistribution of intensity in the C-H stretching region occurs upon introduction or disordered structures in the all-trans chain. In particular, a band at 2935 cm

-1 increases relative to a band at 2850 cm' 1 as the population of gauche bonds

increases. This was demonstrated to occur for semi crystal 1 ine polyethylene of varying percent crystallinities and for melt polyethylene as a function of temperature.

References:

[1] S. N. Zhurkov, V. A. Zakrevskii, V. E. Korsukov, and V. S. Kuksenko, Sov. Phys. Solid State, 13,

1680 (1973).

[2] T. M. Stoeckel , J. Blasius, and B. Crist, J. Polym. Sci., Polym. Phys. Ed., 16, 485 (1978).

[3] D. L. Tabb, Ph.D. Thesis, 1974, Case Western Reserve University.

[4] D. L. VanderHart and W. L. Earl, J. Am. Chem. Soc. , 102, 3251 (1980).

Relationship Between Morphology and Mechanical Properties of Polyethylene .

G. B. McKenna, F. A. Khoury, J. M. Crissman, L. H. Bolz, G. W. Bullman,

and G. M. Martin

The mechanical properties of semicrystalline polymers and their durability are related to the

fine structure morphology. The work of this subtask is to determine these relationships for polyethylene, a widely used semicrystalline polymer. The morphology is determined by processing conditions

and, to a lesser extent, by the use environment. An examination of processing conditions on morphology

is an important aspect of the work. To improve our knowledge of the organization of polymer chains in bulk crystallized polyethylenes , studies have been carried out on solution crystallization at high

temperatures. These conditions produce morphological features similar to those found in melt crystallized material with the advantage that detailed morphological examinations using electron microscopy

may be made without subjecting the samples to harsh chemical treatments.

The Bureau of Medical Devices of the FDA supports investigations into the relationships between

morphology and mechanical performance and durability of ultra high molecular weight polyethylene.

Relationship Between Morphology and Mechanical Properties of Ultra High Molecular Weight

Polyethylene . Ultra high molecular weight polyethylene (UHMWPE) is used in a variety of orthopedic

joint prostheses. One factor which limits the expected lifetime of a prosthesis is the durability of

the UHMWPE component. In clinical use, failure of the polymer component is not a result of wear alone

but may occur through creep, fatigue associated with wear, or even fracture. The length of time

between device implantation and clinical failure depends upon the time dependent mechanical response

of UHMWPE to the clinical loading environment.

It is known that the properties of semicrystalline polymers are highly affected by such structure

or morphology related features as degree of crystallinity, orientation, and spherulite size and texture. These features are determined by processing variables such as temperatures and pressures used

during fabrication of a polymer component. Under contract with the Food and Drug Administration's

Bureau of Medical Devices, we are studying the relationship between morphology and the mechanical

behavior of UHMWPE. An important consideration in this work is the determination of the material

behavior variability which can be introduced by changes in the processing conditions and molecular

weight so long as the molecular weight remains in what is considered to be the UHMWPE range, i.e.,

M > 10 6

. w

25
Protocols have been established for preparing compression molded sheets and solid cylinders of

the UHMWPE. Features of the fine structure of both the raw polymer and the compression molded sheets

and cylinders have been examined. Three aspects of the raw polymer have been studied: its morphological characteristics, its melting behavior, and its crystallinity. The polymer, as received, is in its as-polymerized state and consists of fine particles. Because of its very high melt viscosity,

both molded and machined prosthesis components made from it retain a memory of the particulate nature

of the raw polymer. This was also true for specimens molded in our laboratory at temperatures as high

as 90 K above the melting point. This observation emphasizes the importance of characterizing the structure of UHMWPE products, not only to determine their crystallinity but also to monitor those

aspects of their morphology which are directly related to, and a consequence of, the particulate

nature of the raw polymer. Since the nature of the shapes, sizes, and fine textures of nascent polyethylene particles vary depending upon the polymerization conditions, knowledge of the morphology of

the raw polymer is a necessary aspect of the present study.

Differential scanning calorimetry (DSC) was used to examine the melting behavior and crystallinity

of the raw polymer. The melting point was found to be between 413 and 414 K (140 to 141 °C). The

percent crystallinity, as determined from the area under the melting curve, was 78 percent, which

represents a value significantly higher than can be expected for the same material compression molded

at temperatures above the melting point.

The mechanical behavior of the processed polymer has been examined for a variety of different

deformation histories including single step stress relaxation, uniaxial creep, constant rate of strain,

and cyclic loading. Stress relaxation and creep experiments have been done for material which was quenched from the melt (density = 0.923 g/cm3 ), slowly cooled from the melt (0.935 g/cm3

), and slowly

cooled followed by annealing at a temperature near the melting point (0.942 g/cm3

). Quenching of the

polymer reduced the modulus at small strains by about a factor of two from that of the slowly cooled

material, whereas annealing increased the modulus only by about 20 percent. One interesting feature

of this material is that unlike lower molecular weight polyethylenes, in the quenched or slowly cooled

state it does not exhibit the phenomenon of necking during a creep or constant rate of elongation

experiment. However, upon annealing necking does occur.

The uniaxial creep behavior of the quenched and slowly cooled materials has been mapped for stresses in the range from nine to 27.5 MPa and time of from 10 2 seconds to 10 7 seconds (~ one/year).

Although the quenched material is more compliant than the slowly cooled UHMWPE, the maximum stretch

attainable was essentially the same for both (A ~ 6.0). This is significantly less than is achievable

in lower molecular weight polyethylenes which neck and then cold draw. The creep response of the

annealed material was found to be very nearly the same as that of the slowly cooled polymer.

The cyclic fatigue behavior has been studied for two different UHMWPE samples which, based upon intrinsic viscosity measurements, have molecular weights of Mw ~ 4.5 x 10 6 and 2.5 x 10 6

. Tests were carried out at different levels of stress and frequency, and it was found that the fatigue lifetimes

of both samples decreased with increasing test frequency. This behavior is the opposite of that for

lower molecular weight polyethylenes (Mw

< 3 x 10 5

). Further, it was found that the lifetime of the

material having the lower molecular weight was about 30 percent higher than that having the higher

molecular weight. This behavior is also unlike that of the much lower molecular weight polyethylenes

where the fatigue lifetime generally increases with increasing molecular weight. Sorting out the

respective influences of molecular weight and density (fine structure) will require a comparison of

both high and low molecular weight polymers having similar densities.

We have also begun to characterize the environmental stress crack resistance (ESCR) of the UHMWPE polymer prepared under varied processing conditions. The experimental technique being used to evaluate the ESCR is the same as that recently developed by us for application to other ethylene-based

plastics. Preliminary results indicate that the ESCR is greatest for the slowly cooled material and

least for the annealed UHMWPE.

The Morphology of Compression Molded Ultra High Molecular Weight Polyethylene (UHMWPE) . The work

described below is part of a continuing project sponsored by the FDA and the objectives of which are

to characterize the mechanical properties of UHMWPE and to examine the relationships between these

properties and the morphology of the polymer. These relationships are of particular interest to the FDA because numerous components of artificial orthopedic implants (e.g., hip cups and tibial plateaux)

are made from this polymer.

We have previously reported that sheets of UHMWPE (Mol. Wt. ~ 4 x 10 6

) which were compression

molded at 200 °C and then slowly cooled to room temperature did not exhibit any necking when stretched

uniaxially at a strain rate of 0.02/min up to the breaking strain. The density of the undeformed

sheets prior to deformation was 0.936 g/cm3

. The absence of necking contrasts with the behavior of

lower molecular weight linear polyethylene. More recently, the recovery of samples from uniaxial

deformation to various strains below the breaking strain has been examined. The sheets exhibited

considerable recovery. For example, sheets were stretched at 37 °C and at a strain rate of 0.02/min

to strains of 0.25, 0.5, 1.0, 2.0, and 3.0, respectively. They were then released and allowed to cool

26
to room temperature under ambient conditions. The corresponding residual strains after 24 hours at room temperature were 0.06, 0.12, 0.34, 0.92, and 1.15.

Wide angle and small angle x-ray diffraction patterns were obtained from the samples originally

stretched to strains of 1.0, 2.0, and 3.0 at 37 °C. The x-ray beam was normal to the stretching

direction. In the case of the wide angle patterns, the changes associated with increasing residual

strain in the released samples were characterized by a progressive intensification of the 200 arcs in

the equatorial region. Correspondingly, the 110 arcs, which were split about the equator, tended to

be closer to the equatorial direction with increasing residual strain. In addition to the reflections

associated with the usual orthorhombic unit cell of polyethylene, all three samples exhibited fainter

reflections characteristic of a metastable polymorphic form of polyethylene, which form has been

variously described as being monoclinic or triclinic [1]. The main feature exhibited by the small

angle diffraction patterns from the same three samples was that as the residual strain increased, the

patterns became more clearly "four-pointed" in character. This latter feature indicates the occurrence, between crystalline and disordered regions, of interfaces which are appreciably inclined relative to the stretching direction. In addition, the samples originally stretched to strains of 2.0 and

3.0 exhibited a central horizontal streak indicating the presence of long and comparatively narrow

voids whose long dimension is oriented parallel to the stretching direction.

Examination of the samples mentioned in the previous paragraph in a scanning electron microscope

indicated that although they did not exhibit any macroscopic necking when originally strained, stretching did not occur uniformly throughout each sample. The manifestation of nonuniform deformation was evidenced by the occurrence of regions which exhibit an apparent "fibrillar" appearance. These regions

of higher deformation, in which the "fibrils" were oriented parallel to the stretching direction, were interspersed between regions of lower deformation which exhibited no evident fibrillar character. It remains to be determined whether this nonuniform deformation is associated with the memory, which the

molded samples retain, of the grain-like character of the constituent particles of the raw UHMWPE

polymer. This matter is currently under investigation.

The Habits of Polyethylene Crystals Grown From Solution at High Temperatures . The two main

objectives of this investigation have been the following. Fi rst , to seek appropriately "poor" solvents

from which chain folded polyethylene crystals could be grown which exhibit {110} and {200} lateral

faceting and preferential growth parallel to the b-axis (i.e., axial ratios B/A > 1.33*) at temperatures which approach and overlap the temperature range 118 to 130 °C) in which the polymer crystallizes isothermally in the form of axialites and spherulites upon cooling from the molten state. Second , to characterize the lateral growth habits and conformations (non-planar character, e.g., hollow pyramidal or variously curved) of crystals having B/A > 1.33. Interest in the morphology of

such crystals and its dependence on molecular weight and crystallization temperature stems from their

potential usefulness as models for the experimentally less accessible constituent lamellae in the

various axialitic and spherulitic structures which are formed in bulk (melt) crystallized polymer [2]. It has long been known that the preferred growth direction in the radiating lamellae in polyethylene

spherulites is parallel to their b-axis. Notwithstanding the new insights provided by Olley, Hodge,

and Bassett [3], the origins of the twisting of the lamellae in the spherulites as well as other

aspects of the morphology of these lamellae remain obscure.

Using dodecanol as a solvent and two polyethylene fractions, Fraction I (Mn = 11400) and Fraction

II (Mn = 28900), the highest temperatures at which crystallization has been achieved to date from

0.01 percent solutions have been 115 °C (Fraction I) and 120 °C (Fraction II), at which temperatures

crystals having an axial ratio B/A ^ 6.0 were formed. Examination of crystals of both fractions grown

at 105 °C and above revealed that in addition to the fact that in both cases higher crystallization

temperatures yielded crystals with a higher axial ratio, for given crystallization temperatures in the

range 105 to 115 °C, crystals of the higher molecular weight fraction exhibited a smaller axial ratio. For example, the axial ratios of crystals of Fractions I and II grown at 115 °C were ~ 6.0 and ~ 2.4,

respectively. This effect indicates that the axial ratio and, hence, ratio of the growth rates perpendicular to the {110} and {200} planes are governed primarily by the undercooling AT.

Various "self-seeding" procedures are being explored in an attempt to grow crystals of the two fractions at even higher temperatures. In addition, the effect of crystallization temperature on the

habits of crystals of a third polyethylene fraction (Fraction III, Mn = 100500) is being pursued using

the same solvent. Concurrently, experiments aimed at deducing the nature of the as-grown conformations

of crystals exhibiting axial ratios in the range 1.7 to 6.0 are continuing. Scanning transmission

electron microscopy and small area electron diffraction are the main tools being used in this connection. Among the difficulties encountered in characterizing the conformation of the crystals are the

following features which have been encountered in the few species of crystals which have been explored

so far: (a) variations in the tilt of the chain stems relative to the crystal surfaces both along and across the length of the crystals, and (b) apparent differences in stem tilts between crystals of different sizes grown at the same temperature and of the same polymer fraction. The latter effect, which

has been encountered during the course of a comparison between crystals of Fraction I grown at 115 °C

Where B and A are the dimensions of the crystals parallel to [010] and [100], respectively.

27
from unseeded preparations (large crystals) and "self-seeded" preparations (smaller crystals), is cur- rently under study.

References:

[1] See, for example, A. Turner Jones, J. Polym. Sci. 62, 553 (1962).

[2] F. A. Khoury, Faraday Disc. Chem. Soc. 68, 404 (1979).

[3] J. Polym. Sci., Polym. Phys. Ed. 17, 627 (1979).

Fracture Processes in Polymers

E. Passaglia, D. L. Hunston, and J. L. Rushford

At the macroscopic level, the onset of failure under mechanical stress can be identified with

either inhomogeneous deformation (necking) or crack growth. Two aspects of crack growth that are par- ticular to polymers are craze phenomena and time dependent fracture. Glassy polymers exhibit craze formation in the region preceding the crack tip. The failure of these materials is related to the

growth of the craze region and its dependence on stress relaxation processes of the material. An adequate theoretical description of craze growth and its dependence on material properties is the aim of

a recently initiated effort in the fracture of polymers. A successful model of the craze phenomena

would provide an improved basis for lifetime prediction.

A second activity in a study of the fracture of polymers is concerned with elucidating the mechanisms by which elastomer additives improve the fracture toughness of epoxy matrix composites and the

dependence of these mechanisms on time and temperature. Test methods are being developed that adequately measure the resistance of glass fiber reinforced composites to delamination. The dependence of

the failure time of elastomer modified composites on temperature has been established. An Arrheniustype temperature dependence is found that may be the basis for an accelerated test method.

Theoretical investigations of craze and crack growth . The investigation of the effect of relaxation of stresses within a craze at a crack tip on the rate of craze and crack growth is continuing. A manuscript entitled, "Relaxation of Stresses in Crazes at Crack Tips," has been completed and is undergoing editorial review.

For this investigation, the theory of cohesive stresses of Barenblatt [1] was applied to the craze growth problem, considering the uncrazed material to be elastic. In the Barenblatt theory, the

magnitude a of the cohesive (craze) stresses and the distance a (craze region) over which they act are given (for very small craze regions) by the equation

a

I °1L11 d£

= ^72 K (1)

o V! i

where £ is a coordinate within the craze and K x is the applied stress intensity factor. This is related to the applied stress and the crack length a by the equation

K-j^ = Jna f (a/w) (2)

where w is the specimen width and f(a/w) is a geometric factor determined by the specimen configuration.

The fundamental hypothesis of the Barenblatt theory is that the cohesive (craze) stresses cancel

the stress singularity that would exist at the crack tip in their absence. In the present treatment,

it is assumed that this singularity cancellation exists even for moving crazes. It is then clear from

Eq. (1) that, for constant K x , a must increase if a decreases. A simple equation relating the rate of craze growth to rate of stress relaxation is obtained from differentiation of Eq. (1):

p(a,t) . dK1

a

o

(3)

where o(a,t), is the stress at the trailing edge of the craze (i.e. , the tip of the crack).

This integro-differential equation is the basic equation for this type of craze growth, called

"relaxation controlled growth" by Williams and Marshall [2]. Its solution requires knowledge of the rate of change of craze stress over the whole craze region. This latter problem can be formulated in terms of integral equations, but these are in general intractable. Flowever, it can be said that the

28
rate of relaxation of stress within the craze will in general be lower than the rate of the relaxation

of stress for craze material in a normal (i.e., fixed length) stress relaxation experiment.

With some simplifying assumptions, Eq. (3) may be solved. The assumptions are:

(1)

The craze initiation stress at the craze tip is a constant g

q

. This is equivalent to a stress criterion for craze initiation, which is considered reasonable for the triaxial stress state at the craze tip.

(2)

At t = o, i.e., at the time of initial craze formation, the stress in the craze is independent of position within the craze, as in the Dugdale model [3]. This stress then relaxes with time,

except at the craze tip, where growth occurs. This is called the "generalized Dugdale model."

(3)

The stress intensity factor is a constant. Under these conditions, Eq. (3) may be solved to yield

dt

a(a,t)

(4)

o

Assuming now that cr(a,t) varies exponentially with time as follows

0(0 ' l) =

i * <t/,) m (5)

where t is in the nature of a relaxation time, and m is related to the slope of the compliance on a log-log plot, Eq. (4) may be integrated to give

K

2 _ n 1 a ~

8 a*

o

1 + (t/x)

1 2m + 1 ( 6 )

For times long compared to x, this equation gives satisfactory agreement with experimental results

and gives the proper dependence on K x

. For short times, the relevant experiments are complicated by

the presence of solvents. Clearly, the exact form of the solution will depend upon the time dependence

taken for o(a,t) in Eq. (4).

Present work is concerned with investigating more thoroughly the equations that determine the

time behavior of the stress within the craze.

Experimental investigation of craze growth . Considering the importance to craze growth of the

relaxation of stresses within the craze, a small experimental program to measure the creep function in craze material was begun. For this purpose, a sample of polycarbonate with large crazes grown in it was kindly provided by Dr. Roger Kambour of the G.E. Research Laboratory. This was then mounted on a jig, loaded to a stress of 800 psi (0.56 MN/m2 ), and the thickness of the craze measured microscopically for a period of 24 hours. While the experiment suffered from lack of precision, preliminary

results indicate that the function

J(t) - J(o)

J(o)

where J(o) is the instantaneous creep compliance and J(t) is the creep compliance at time t, is the

same for the craze material as for the uncrazed substrate. This implies that the retardation times

for creep are unchanged by the process of crazing, but this result will have to be confirmed in more

careful experiments.

Influence of Matrix Properties on Delamination in Fiber-Reinforced Composites . The testing of fiberreinforced composite panels in aerospace applications has revealed a problem with delamination.

Composites are designed and utilized to take advantage of their high strength in the plane of the

fibers. Unfortunately, it is not possible to totally eliminate out-of-plane loading. One of the

problems encountered in aerospace tests is impact damage during landing and takeoff. Such out-of-plane

loading can lead to serious delamination because the organic matrix resins used to bind the fibers

together in most composites are very brittle. This delamination can substantially reduce performance

for both in-plane and out-of-plane loads. What makes this damage particularly troublesome is that it

29
is often difficult to detect; once detected, it is difficult to assess how much the performance is affected; and if performance is seriously affected, delamination is often difficult to repair.

A number of studies have shown that when a matrix resin with improved fracture properties is used, the composite has significantly higher resistance to matrix cracking and other types of interlaminar fracture. Unfortunately, it is usually necessary to sacrifice other properties, such as modulus,

to obtain improved fracture properties. Current work is investigating the use of rubber-modified

epoxy resins. In these materials, the rubber is present as tiny particle-inclusions in a matrix of

epoxy, and the two phase nature of these systems makes possible toughening mechanisms that cannot be

achieved in single phase materials. As a result, these systems give very high fracture energies with

a minimum sacrifice in other properties.

Fracture tests were conducted on neat resin specimens of modified and simple epoxies, and these tests show the large increase in fracture energy that can be obtained by rubber-modification. Both

glass and carbon fiber reinforced composites were then fabricated with these resins and examined by

propagating a crack in the matrix resin between the fiber layers. This test gives an interlaminar

fracture energy which is one indication of the resistance of the composite to delamination. Such tests indicate that the interlaminar fracture energy of composites can be significantly increased by

rubber-modification. Current work is aimed at developing a basic understanding of the mechanisms

involved in composite failure and the factors which influence them. Such an understanding wi 1

1 provide

guidelines for both improved composite designs and better materials.

Time-Dependent Fracture of Structural Adhesives . The high fracture energy of the rubber-modified

epoxies has also made them the major constituent in most commercial structural adhesives. The mechanisms responsible for this high fracture energy are presently being studied with both bulk and adhesive

bond specimens. A major result of this work is the demonstration that the toughening mechanisms are viscoelastic/plastic in nature, and thus, the fracture energy depends on the loading and temperature

history of the sample. Experiments have shown that the fracture behavior for bulk samples of this

material subjected to simple types of loading and temperature histories can be described with simple

empirical equations. For example, over a range of conditions, the time to failure, t^, in constant

cross-head speed tests can be related to a parameter, S^, that measures the rate of increase in strain

energy during loading by a simple power law with an Arrhenius temperature dependence

t

f = A(S

E )' n eAH/RT

Although this empirical equation only applies to a limited set of conditions, the parameters A, n, and

AH are quite useful for comparing the relative rate and temperature sensitivity for different formulations. Studies are now underway to examine more general histories and models for failure of these

commercially important materials.

References:

[1] G. I. Barenblatt, Adv. i n Appl ied Mech. , Vol. VII, Academic Press, New York, 1969. [2] J. G. Williams and G. P. Marshall, Proc. Roy. Soc. (London), A342, 55 (1975).

[3] D. S. Dugdale, J. Mech. Phys. Solids, 8, 100 (1960).

Instability and the Phenomena of Necking

L. J. Zapas, J. M. Crissman, B. Bernstein 1

, and B. D. Coleman2

Failure of polymeric materials by neck formation and propagation depends on level of mechanical

stress, temperature, as well as aspects of the molecular and physical structure. These relationships

have been determined for polyethylene, a widely used thermoplastic. Analyses of these relationships

have led to an empirical relation between the time required to reach a certain strain and the time at which a neck forms. For practical purposes, neck formation is identified as mechanical failure.

Current work is aimed at developing models and experimental procedures to predict the instability

point, that is, the time required for the material to reach the strain in question. Successful models

and experimental procedures would provide a powerful method for predicting lifetime under conditions

where neck formation is the mode of failure.

The Mechanical Behavior of Isotactic Polypropylene in Uniaxial Extension: Instability and the

Phenomenon of Necking . A theory of stability for the deformation of viscoelastic bars which obey the

BKZ theory [1] has been developed [2]. This theory is an extension of the one given by Ericksen [3]

for elastic bars. For the appropriate strain potentials under certain loads in uniaxial creep and

constant rate of extension, the bar will deform homogeneously for some time and then become unstable

and neck. Ericksen' s type of analysis has been applied to a viscoelastic situation in an effort to

'111 inois Institute of Technology

2 Carnegie-Mel Ion University

30
explain how time effects may enter into the onset of a discontinuity. While the theory does not predict a priori when the material will neck, it does give an explanation for the formation of the

neck, whfch depends on the stretch history, and also shows how a material may, when fully necked, have

a higher modulus than it had originally.

From constant rate of strain experiments in uniaxial extension, we have found that a slowly

quenched sample of isotactic polypropylene can be described rather well by the BKZ theory. By this, we mean that the stresses in a constant rate of strain experiment calculated using the BKZ theory were

in good agreement with the experimental data. In all cases, the calculated values were lower than the

observed values, but the maximum deviation was seven percent or less. This good agreement encouraged

us to examine more closely the model proposed by Bernstein and Zapas concerned with the stability and

cold drawing of viscoelastic bars.

A critical element in the application of the theory of Bernstein and Zapas is knowledge of the

single step stress relaxation behavior. For semi crystal 1 i ne polymers, such as isotactic polypropylene,

single step stress relaxation data can be obtained only over a small region of strain. At strains

above ten percent, the specimen necks during application of the step. Flowever, the theory requires

knowledge of such data over a much greater range of strain than is experimentally possible. Therefore,

we have carried out a series of experiments involving a variety of different strain histories in uniaxial extension; these include single step stress relaxation, creep, constant rate of strain, and

constant rate of loading. With the knowledge of the various strain histories, we have constructed one possible set of isochrones of stress vs strain by extrapolating our data into the regon of very high

strains. From this set of curves and the instability theory, it is then possible to predict the point

at which necking will occur for other strain histories.

We conclude that the Bernstein and Zapas instability theory may provide a reasonable description

of the phenomenon of necking. This, we believe, may turn out to be a valuable procedure for predicting

the incipient point of necking for even more complicated strain histories. The present work was undertaken as a first step for further investigation into understanding the phenomena of instabilities

that may occur in other polymers.

Theory of the Instability and Failure of Viscoelastic Materials in Tension . In a tensile test of

a bar or fiber formed from a transversely isotropic viscoelastic material, the initial motion in regions away from the clamps is a homogeneous uniaxial extension. If the applied tensile load is "tame" in the sense that it is given by a piecewise smooth function of time, then during the early

stages of loading, the homogeneous extension of the specimen is also tame. It is often the case that

at a time t , previous to the instant of fracture, the motion departs from a tame homogeneous extension. The critical time t is the "failure time" of the specimen, i.e., the time at which the motion

first changes character; t precedes, often by a constant factor, the time at which neck-down is easily visible. The problem of calculating t for a given loading program has been treated within the

framework of the general theory of non-linear simple materials with fading memory. For such materials,

the instantaneous tensile modulus, i.e., the derivative of the immediate change in tensile stress with

respect to a sudden change in tensile strain, depends upon the previous history of the strain. An explanation has been put forward for identifying t

c with the earliest time tQ at which the instantaneous tensile modulus becomes zero. It has been shown that at the time at which the instantaneous

modulus vanishes, one cannot arbitrarily assign the rate of change of tensile stress and have the

motion remain in the class of tame homogeneous extensions.

References:

[1] B. Bernstein, E. A. Kearsley, and L. J. Zapas, J. Res. Nat. Bur. Stand., B68, 103 (1964).

[2] J. L. Ericksen, J. Elasticity, 5, 191 (1975).

[3] B. Bernstein and L. J. Zapas, J. Rheology 25, 83 (1981).

Test Method Development

J. M. Crissman, D. L. Hunston, E. A. Kearsley, R. W. Penn, L. J. Zapas,

G. M. Martin, and J. L. Rushford

Test methods are developed for evaluating mechanical performance and durability of polymeric

materials. A joint program with the Department of Transportation led to the development of an improved

test for environmental stress cracking of plastics. The method has been presented to the ASTM and test conditions are being optimized in current work prior to submission for round robin testing. A cooperative effort with DOE addresses the need for test methods to evaluate the long-term performance

of elastomeric seals used in geothermal energy production. A test protocol has been devised that

circumvents the problem of carrying out measurements in extreme environments similar to those found in the use conditions.

31
A nondestructive measurement technique has been developed that permits dynamic mechanical testing

and stress relaxation experiments as a function of temperature and time. The technique has been

applied to the study of cure of composite materials and to the dependence of mechanical properties on aging time. The technique has application as a quality control method since an improperly prepared

batch of thermosetting material can be easily detected.

Development of a New Test Method for Environmental Stress Crack Resistance . For thirty or more years, it has been recognized that ethylene-based plastics are susceptible to environmental stress cracking (ESC). This knowledge led to the rapid development of many test methods for evaluating

environmental stress-crack resistance (ESCR), including those in most widespread use today. More

recently, the use of ethylene-based plastics in the packaging industry has greatly expanded. One

important area is that of hazardous materials transportation where because of increased energy con- straints there is a demand for lighter weight shipping containers. The use of polyethylene in large

shipping containers has been made possible in part by the development of new, more highly stress crack

resistant polymer resins.

One result of this activity is that over the past several years there has been renewed interest

in ESC and the development of new test methods which can, on a reasonable time scale, more adequately

characterize ESCR. We have examined a number of test methods for ESCR and have developed one test which involves a bent strip geometry but differs from the current ASTM bent strip test in two ways:

(1) all specimens are constrained in such a way as to maintain a constant geometry, and (2) the speci- men is subjected to a constant applied load.

Tests are currently being carried out on three different polyethylenes having widely different

ESCR. Two of the samples are linear polyethylenes having weight average molecular weights (M ) of

approximately 10 s and 4.5 x 10 6

, and the third is an ethylene-hexene copolymer having a Mw

of about

2.1 x 10 5

. The test procedures being employed are intended to optimize the experimental conditions in order that data can be obtained in an acceptable time period for as wide a range of different polyethylenes as possible. Such procedures involve systematically changing the bend geometry, specimen

thickness, magnitude of the applied stress, and temperature.

At the present time, the characterization of the two lower molecular weight samples is nearly

complete. Work is continuing on characterization of the ultra high molecular weight material which

requires very long times to collect data. It is anticipated that the data collection will be completed

in about one year. Upon completion, a description of the test method as well as the appropriate

statistical data will be submitted to ASTM Committee D-20.10 for their consideration.

Polymeric Sealants for Geothermal Energy . In a program to assist the Department of Energy to develop geothermal energy resources in the United States, we have been developing test methods for

polymeric sealant materials to be used in the drilling of and producton of geothermal wells. Since

there are many forms of seals used and down-hold environments vary considerably among the different

well locations, it is not possible to specify reasonable requirements for geothermal sealants in general. The most interesting and energetically important wells are potentially those with ambient

down-hold temperatures greater than 260 °C and with strongly corrosive, reducing (rather than oxidizing) atmospheres. The sealant materials should perform (frequently this means maintaining large

elastic stresses for fixed deformations) under these demanding conditions for time periods ranging

from hours for well-drilling sealants to months or years for production seals. Current technology for

such seals is largely based on developments for the petroleum industry and is, consequently, adapted

to lower temperatures and less corrosive conditions.

At present, various ad hoc lifetime tests are used by designers of geothermal equipment to test specific seals under conditions simulating the intended use. Such tests are very specialized and

inconvenient. Failures of the seals are observed to occur either because the sealant hardens and

eventually cracks or because the sealant softens and flows. The program on geothermal sealants in the

Polymer Science and Standards Division aims at a more fundamental test which gets at the causes of

this behavior so that the results can be used to design seals for whatever configuration or geothermal

environment is needed. This is to be achieved by measuring the rates of formation and of breaking of

bonds (cross-links or equivalent) using the method developed by Tobolsky, et al., to study oxidative

degradation of rubber. In that method, two sets of measurements are required: (1) the stress relaxation of material aging while deformed and (2) the change in elastic modulus of material aging in an undeformed configuration. The latter data can be collected rather routinely, but stress relaxation is an inconvenient experiment, particularly under conditions corresponding to geothermal down-well atmospheres. Consequently, we have worked out the theory of a method to substitute permanent-set data for

the stress relaxation data needed for the Tobolsky method. The theoretical work for this was completed

previ ously.

Currently we have assembled apparatus in which we can age test samples in aqueous or dry atmos- pheres at pressures up to 3000 psi and at temperatures up to 300 °C. The apparatus is constructed of

stainless steel. Pressures and atmospheres are limited to the gases available in commercial cylinders. Test specimens can be held in various constant states of strain during their aging. Apparatus has also been developed to facilitate mechanical testing of the specimens without reclamping them. Our

32
computer controlled hydraulic test system has been programmed to conduct the necessary testing efficiently and to reduce the mechanical properties data.

Determination of Mechanical Properties for Characterization, Quality Control, and NDE of Polymers

Satisfactory performance of a polymeric material in a practical application is often

directly related to the proper matching of the mechanical properties of the polymer to those required

for the application over the range of temperatures and time scales involved. As a result, the measurement of mechanical properties can provide not only useful characterization data but also valuable quality control (QC) and NDE information. To obtain maximum benefit from mechanical property measurements

,

however, it is important that the behavior be determined over the widest possible range of temperatures

and time scales (or frequencies). In this regard, a device has been constructed in cooperation with

the Naval Research Laboratory to combine dynamic mechanical testing and stress relaxation experiments

in a single instrument. This device provides data for low amplitude shear properties over an eight

decade time scale range at temperatures from -200 °C to 400 °C. Samples can range from low viscosity

fluids to highly cross-linked solids. The instrument is extremely versatile and has already been used

to examine fiber reinforced composites, structural adhesives, high temperature plastics, elastomers,

propellants, plastisols, and printing inks. To illustrate the use of this device, three particular

examples will be briefly discussed.

The problem of quality control for elastomeric materials is a difficult one because many ingredients are used and a number of processing steps are involved. As part of the manufacturing procedure,

it is customary to make a number of small samples (ASTM plates) for each batch to serve as material

for QC testing. Our test device has been adapted so that a small portion of an ASTM plate can be

utilized to provide a detailed characterization of shear properties. With this information, an improperly prepared batch can easily be detected, and since the mechanical properties are related to molecular structure and morphology, it is possible in a number of cases to determine what mistakes

were made in the formulation.

The nondestructive nature of this measurement technique is particularly helpful when the device

is used to follow changes that occur in a material during cure. Two examples of this type have been

studied during the past year. The Navy is interested in the properties of certain polyvinyl chloride

plastisols for their studies of the interactions between turbulent flow and compliant surfaces. It was found, however, that the properties of this material change as a function of time. Our studies were able to provide not only a detailed characterization of the basic properties of these materials

but also an analysis of how the properties change as a function of aging time. A second example of

this type involves the printing inks used by the Bureau of Engraving and Printing for making currency.

These inks cure during the printing process, and thus, good performance can only be obtained when the

flow properties change in the required ways and at the proper rates during the cure. Studies are currently underway to characterize the properties of the inks as a function of cure so that better

quality control techniques can be developed.

Nonlinear Behavior of Polymeric Materials

L. J. Zapas, G. B. McKenna, and B. D. Coleman

Constitutive relations are needed that adequately describe the nonlinear relationships found

between stress and strain in most polymeric materials. These constitutive relations give connections

between the macroscopic observables stress, strain, stress relaxation, etc., and are the basis for

accelerated test methodology and lifetime prediction.

Nonlinear Elastic Behavior of Rubber Materials . In work carried out during the past year, we investigated the behavior of the derivatives of the strain energy function with respect to the stretch

invariants, DW/alj and 3W/3I 2 , of peroxide cross-linked natural rubber at deformations lower than

those reported previously. In the course of our work, we examined the effects of the degree of cross- linking and of aging on the derivatives of the strain energy function. Our experiments were carried

out in torsion, where both the torque and normal force were measured, to determine the strain energy

function derivatives at values of the stretch invariants of Ij=I 2

. In addition, we carried out experi- ments in simple extension and simple compression at strains as low as £ = ±1 . 0 x 10-4

. By assuming

the validity of the Valanis-Landel form of the strain energy function, we were able to relate the

behavior in torsion with that in extension and compression.

The salient results of our work in torsion are:

(a) In no instance did we find that 3W/3I 2 became negative with decreasing strain; this is at variance with some results reported in the literature.

(b) The small strain torsional modulus, G = 2(3^31! + 3W/3I 2 ), is relatively unaffected by

aging of the rubber, while the individual strain energy function derivatives, SW/SIj and

3W/3I 2 , change significantly.

(c) 3W/3I 2 is relatively independent of cross-linking, while SW/SIx increases with increasing

cross-1 i nki ng. 33
(d) At low degrees of cross-linking, 3W/3I t -v 3W/3I 2 for unaged samples. This result was unex- pected.

The salient results of our work in extension and compression are:

(a) The apparent moduli in tension and compression at small strains are not equal.

(b) The values of the apparent modulus in tension and compression at very small strains does not become constant. Rather, as the deformation approaches zero, the modulus increases significantly.

Non-Linear Viscoelastic Behavior of Polymeric Materials . A new constitutive law which explains

the differences between experimental results and currently existing theories for the nonlinear viscoelastic behavior of materials has been developed. The relationship between stress and strain for a shearing history can be written as:

a(t) = - / f x [C

t (s),s] ds +

o

00 00 / / f 2 [£ ( s 1 ) » 4 (

2 ) » Si, s 2 ] ds x ds 2 0 0

where g (s) = y(t) - y(t-s) and y(t) is the shearing strain. For all s,Si,s 2 ^ 0:

fi(0,s) - 0

f2 (b,0;si ,s 2 ) = f 2 (0,b;s 1 ,s 2 ) = 0

f2 (b,c;s lt s 2 ) = f 2 (c,b;s 2 ,si)

Experimental work has been commenced to determine the material memory functions f x and f2

. This

work is focusing on the torsional responses of epoxy and poly(methyl methacrylate). Single and double

step stress relaxation histories are required to determine these material functions. Results for

other histories, such as constant rate of strain, will be compared with predictions from the theory.

Durability of Paper

J. C. Smith

Paper used to make currency should have a good balance between durability and cost, as the

replacement of worn out currency is an expensive operation. Because of this, the Bureau of Engraving

and Printing supports work at NBS to identify and characterize those aspects of the morphology of

paper networks which affect durability. The research results are expected to contribute to the development of durable paper made from blended wood pulps instead of the more expensive cotton and linen

pulps presently used.

To achieve these objectives, it is necessary to have an improved understanding of the relationship

between the structure of paper, the morphology of the fibers, the processing conditions, and the

mechanical and physical properties of the paper and its components. Over the past several years,

studies at the National Bureau of Standards on interfiber bondability and its relation to the forceelongation behavior of fiber networks have helped to provide some of this background information.

Tensile tests are performed on specimens cut from open-web handsheets of density ~ 2.0 g/m2. Experiments have shown that the resulting force-elongation curves fit an equation of the form

F = A[exp(x/x

c

) - 1]

where F is the force and x is the elongation. x

c is a scaling parameter having the dimensions of

length, and A is a parameter that serves as a modulus of elasticity. The two parameters, A and x

c

, are sensitive to the number of interfiber bonds per unit area in the specimens tested. Moreover,

during a test A and x

c vary in value as the test proceeds, reflecting damage to the specimen and

changes in the location of the bond breaks that occur. This possibility of characterizing the specimen

at various stages of a test is expected to enable the calculation of a force level parameter representative of the average bond strength between fibers in a given test specimen.

34
The average force at which a specimen fails by progressive bond breaks depends upon the density of

bonds and upon the average bond strength. During a test, the density of bonds diminishes, but it is hoped that the A and x

c parameters can be used to compensate partially for this effect. Experiments to test this idea are in progress.

Mechanical and Transport Properties of Polyethylene in Organic Solvents

J. C. Phillips and A. Peterlin

Polymer films are being used as liners for landfills and chemical waste holding ponds to control

the movement of hazardous materials. In order to develop data that can be used to estimate the useful

lifetime of such polymer liners, we have measured the transport of an organic acid through low density

polyethylene (LDPE) and have measured the mechanical properties of LDPE in the presence of an organic

vapor. The organic solvents simulate the action of the landfill leachates or hazardous waste.

The preliminary phase of this work involved measurements of mass loss of acetic acid (HAc) in low

density (LDPE) and high density bottles and sorption/desorption of acetic acid vapor in LDPE films.

The mass loss measurements were performed at 40 °C, 60 °C, and 78 °C. At the highest temperature (t =

78 °C), mass loss for mixtures of HAc/H2 0 were also done; the concentrations of HAc in volume percent

were 100 percent, 75 percent, 50 percent, and 25 percent. From the mass loss-time data, the loss rate and time lag were determined for each density bottle. The former results, as a function of temperature, yield the activation energy of permeation, while the activation energy of diffusion was calculated from the latter results. The activation energy of permeation, E^, was the same for each density

bottle, and the activation energy of diffusion was uncertain due to errors in the time-lag determination. The loss rate data for the solutions of HAc/H2 0 was found empirically to be a function of the

volume fraction, V, of HAc, i.e. , log Q = K + V

a

, where or is a constant equal to 2.5.

The sorption/desorption data were obtained at 30 °C, 50 °C, and 70 °C at a vapor pressure of

p ~ 17 mm Hg. The polyethylene film had a density of p = 0.906 g/cm3 and a thickness of 10.16 x 10 3 cm. Diffusivity and solubility as a function of temperature indicated, respectively, that the

activation energy of diffusion and the heat of solution were roughly constant for the range investigated. The diffusion process seems to be Fickian with differences in sorption and desorption behavior

which suggest a concentration-dependent diffusion coefficient.

This preliminary study has shown that the density of PE is a very important factor in making a choice of a specific liner material. The temperature effect and the volume fraction of HAc in the

leachate are also essential parameters that influence the mass loss and loss rate.

Mechanical properties of LDPE were analyzed by separating the total strain, e, into elastic, e , and plastic, e components. These components were determined in air at t ^ 23 °C from recovery

measurements for imposed strains of £

q = 9.0 percent, 29 percent, and 54 percent by extrapolating e(t)

data to t = 0. The extension times or the time the sample was held, t^, varied from 10 minutes to

30 days. As a function of t^, the elastic strain decreases while the plastic deformation increases.

If recovery measurements are performed in the presence of an organic vapor (e.g., ethyl acetate), e . becomes greater than its air or vacuum value while tends to become less. p

All recovery data could be roughly represented on a single master curve by plotting a reduced

recovery [e(t) - e

oo ]/(e

o

- em ) vs the logarithm of a reduced time of t/t^. The plastic deformation at infinite time, e^, is the permanent set of the material and also is a function of e and t^. The

recovery data obtained in a vapor environment at pressure p could also be plotted on the master curve

by assuming a reduced time of ( t/t. ) f ( p ) where f(p) was found empirically to be 1/(1 + orp) with or being

a constant. n

The results of changes of and with t^ correlate very well with changes of transport (diffusivity and solubility) with t^ and tend to emphasize the influence of the components of the total

strain on the diffusion process.

35
POLYMER STANDARDS FOR CONTROL AND EQUITY

I. C. Sanchez

Task Leader

This task provides molecular and gas transmission standard reference materials (SRM's) to a $30 B/

year plastics and elastomers industry. Molecular SRM's are used extensively in industry to calibrate

gel permeation chromatographs (GPC's) which are used routinely to measure polymer molecular weights

and molecular weight distributions. The latter are the most important physical properties in determining a polymer's processability and its ultimate performance.'

Improved characterization techniques are essential to providing improved SRM's. A fundamental

knowledge of polymer solution properties such as osmotic pressure, viscosity, diffusional behavior,

and scattering power is essential to this goal. As a consequence, a majority of the activities in this task involve experimental and theoretical studies of polymer solution properties. As a spinoff

of our characterization activities, this task also provides data and concepts which are useful in polymer processing. Some of these activities during the past year include:

o Certification of a new, narrow-molecular weight polystyrene standard, SRM 1479 (M ~ 106

).

o Continued development of a new state-of-the-art, self-calibrating gel permeation chromatograph.

o Approximately 300 gas permeation experiments which have been carried out for the purposes of

upgrading the certificate for SRM 1470 to include He, C02 , and N 2

.

o Analytical and computer simulation studies of chain entanglements.

o Development and construction of a new state-of-the-art light scattering photometer. This

instrument will have the option of static or dynamic light scattering measurements at elevated temperatures.

o Completion of a low shear rate rotational viscometer based on the floating rotor type (ZimmCrothers). Viscosities may be determined at shear rates as low as 3.0 s -1 and up to 8.0 s-1

at temperatures up to 150 °C.

o Completion of a theory of the phase behavior of polymer blends.

Standards for Gas Transmission Measurements

J. D. Barnes

Gas transport properties of polymeric materials are vital in assessing end-use suitability and

durability of polymers in such applications as packaging and coating materials. Facilities similar to- the one developed at NBS should prove useful in quality control of processes for manufacturing film

and sheet materials.

The NBS Automated Manometric Permeation Measuring Facility went into routine operation in February. Since that time, approximately 300 experiments have been performed. Each experiment repre- sents a set of measurements at a given temperature and at a given upstream pressure, using one of four

selected gases on three specimens. One hundred experiments are performed on each specimen of SRM 1470

for purposes of upgrading the SRM certificate to include He, C0 2 , and N 2 in addition to 0 2

. The SRM certificate will also provide temperature and pressure coefficients for the time-lags and permeances.

Figure 1 shows the pressure trace from a typical experiment. Note how, in the early phases of the

experiment, sorbed gases from the previous experiment cause the pressure to rise in the cell even when

no upstream pressure is applied. When this happens, the cells must be pumped out again. Upstream gas pressure is not applied until the pressure rise due to sorbed gases has fallen below an acceptable

level. When the upstream pressure jumps from zero to the preset value (at the arrow in figure 1),

there is no change in the trace until an induction period has passed. After a suitably long time, the

pressure rises at a steady rate. The quantities characterizing the specimen are the induction period

(time-lag) and the steady rate of pressure rise. Figures 2 and 3 give results for the rate of pressure

rise and the time-lag of a typical specimen. The time-lag for He gas is less than one second and cannot be measured with our present setup.

The phenomenon of partial immobilization manifests itself when C02 is used as the permeant species

in SRM 1470. The time-lag decreases by about 20 percent at any temperature as the upstream pressure

increases from 45 kPa to 135 kPa. The shape of the time-lag pressure trace is also different in this

case, but we do not yet have a solution to the transport equations which allow us to explicitly account

for the contribution of partial immobilization when fitting data to the time-lag curve.

36
Carbon

Dioxide

T

=

27.0

°C,

P

=

112.5

kPa

o

CM CM

COO

X

</) 0

E

(jjojiu) ejnssajd

37

Figure

1.

Pressure

as

a

function

of

time

for

a

typical

time-lag

permeation

experiment.
CD

ro

CN

ro

O

o

00 ~ CM CD

L_

Z5

-h-* O

L_

CD

CN E

CD

O

CN

CD

O O O

9Siy j.o spy 6o”j

38

Figure

2.

Normalized

rate

of

pressure

rise

as

a

function

of

temperature

for

a

typical

specimen

of

SRM

1470.

Rate

of

rise

is

normalized

to

that

for

an

upstream

pressure

of

9Q

kPa.

Vertical

shift

factors

(in

parentheses),

have

been

applied

to

make

the

temperature

dependence

more

visible.
We found that data-taking totally occupied our apparatus and that it was necessary to send the

data to the NBS central computer for reduction and analysis. In order to achieve this, we implemented

a TIE into the NBS Net using software we developed ourselves. The data reduction programs have been

copied into the 1108 and are presently being rewritten to take care of language and environment differences between the two machines. It is expected that all of the data for the new SRM 1470 certificate

will have been analyzed by October 1.

During FY82, we expect to finish upgrading the data acquisition hardware in the automated mano- metric permeation measuring facility. This replacement of antiquated MIDAS data acquisition equipment

by more modern equipment using the IEEE-488 bus will allow us to study films with shorter time-lags

and higher transmission rates.

We expect to undertake experiments near the glass transition temperature of SRM 1470 in an effort

to better understand the role of molecular motions in transport processes. It is also believed that

the glass transition plays an important role in regulating partial immobilization.

We expect to begin development of a simpler measurement scheme based on gas chromatography that

will allow us to study interactions between permeant species in multicomponent mixtures.

ASTM Activities

J. D. Barnes

J. D. Barnes continues to serve as chairman of ASTM Subcommittees F-2.30 (Test Methods) and

F-2.93 (Statistical Matters) of ASTM Committee F-2 on Flexible Barrier Materials. Subcommittee F-2.30

is responsible for test methods relating to materials characterization, barrier properties, sealing

and bonding properties, and additive migration. Subcommittee F-2.93 provides statistical assistance

to all groups needing it within Committee F-2.

Dr. Barnes has drafted a Standard Practice for Selecting and Distributing Flexible Barrier

Materials for Interlaboratory Testing Programs. This document is in the Subcommittee balloting stage,

and it is expected that the adoption of this practice will enhance the ability of round-robin participants to obtain meaningful characterizations of the test methods they are studying.

Dr. Barnes is also a member of Subcommittees D-20.19 (Film and Sheeting), D-20.12 (Olefin

Plastics), D-20.70 (Analytical Methods), and D-20.13 (Statistics) of ASTM Committee D-20 on Plastics.

Dr. Barnes has played a very active role in reviving interest in Subcommittee D-20.13, and the group

receives many more requests for statistical assistance than formerly.

Self-Calibrating Gel Permeation Chromatography

P. H. Verdier

Gel permeation chromatography (GPC) is a widely accepted technique for estimating the molecular

weight distribution (MWD) of high polymers. However, the usefulness of the conventional GPC apparatus

is limited by the need to provide calibrants for each polymer measured of known molecular weight over

the entire molecular-weight range in which the MWD is significantly different from zero. The calibration depends, among other things, upon the chemical nature, degree of branching, etc., of the polymeric

material, so that each new material requires a fresh calibration. The so-called "universal calibration" hypothesis, while useful, is limited to comparisons of polymers of similar shape and, in any

event, is inadequate for quantitative determinations. Some instruments, an example of which is commer- cially available, attempt to circumvent the need for calibrants by adding a single-angle light

scattering detector to the usual concentration-sensitive detector. However, this does not allow the

extrapolation to zero scattering angle which is required, in principle, to relate scattering intensity

to molecular weight. In addition, qualitative information on the variation of scattering with angle,

normally required to give assurance that meaningful results are being obtained, is not available.

We are designing and constructing a light-scattering detector for the GPC which measures, in real time, the scattering intensity as a function of scattering angle and which is controlled by a dedicated

minicomputer in a way that allows scattering to be measured as a function of scattering angle and

concentration. The instrument will allow continuous monitoring of the variation of scattering with

angle. This will allow immediate identification of difficulties such as association, microgel formation, etc., which could affect the validity of the molecular weight obtained, an important consideration for work on new and unstudied materials. In addition to molecular weight, the mean-square radius

(radius of gyration) will be obtained as a function of molecular weight, at least in the higher ranges

of molecular weight, providing useful information for the characterization of branched polymers.

The mechanical components of the instrument have been constructed, and alignment is under way. The electronic components (preamplifiers, amplifiers, and switches) have been designed and prototypes

built. In the coming year, we expect to complete alignment, construct the electronics, program the

minicomputer and its associated video display, and begin taking measurements.

39
CD

ro

CM

ro

oo

CM

xlCM

O

CM

CD

oo CD LO

o

o

Q)

L_

Z5

-+~> O

CD

Q.

E

<D

S-

6D-]— auuij_ 6o~]

40

Figure

3.

Time-lags

as

a

function

of

temperature

for

the

specimen

in

Figure

2.

Time-lags

for

gases

other

than

C02

do

not

depend

on

upstream

pressure.

The

C02

line

is

for

a

pressure

of

90

kPa.
Dynamics of Polymer Chains

P. H. Verdier and D. E. Kranbuehl

The dynamic behavior of polymer chains is important to improving both characterization and processibility of polymers. The principal methods used to estimate molecular weight, and in particular gel

permeation chromatography, the only method available at present for estimating distribution in molecu

lar weight, are dynamical, non-equilibrium experiments which depend in part upon the relaxation of

polymer chains in dilute solution. In its present state, the theory of these systems does not allow

the calculation of molecular weight directly from measured quantities; a series of calibrants of known

molecular weight is required. Improvements in the theory could reduce or even remove the need for

calibrants, allowing the determination of molecular weight distribution of polymers for which calibrants are not available.

The processability and the final characteristics of both plastics and elastomers depend in large

part upon the relaxation behavior of the high-polymer chains of which these materials are primarily

composed. More realistic theoretical treatments of polymer melts and elastomers, which must start with more realistic treatment of the dynamical behavior of the individual chains, will lead to more efficient processing and better fabricated end-products. A major shortcoming of the present theory is its inability to treat chain entanglements in a realistic way. Our present work is aimed primarily at the study of entanglement effects, using a combination of analytical and computer simulation techniques.

The simulation results provide data on simple model systems and serve to guide the development of

better theoretical treatments.

Present work in this area is proceeding along three main lines. The first is a study of the

effects upon our results of the necessarily crude models of polymer chains employed in our work. This

study was prompted by the fact that our results show much larger effects of self-entanglement upon

chain motion than are predicted by a currently popular theoretical model, which raises the question of

the extent to which the effects we observe are artifacts of the models. We have extended our earlier

studies of chain motion on several lattices to chains which are not constrained to lie on lattices.

Perhaps surprisingly, the self-entanglement effects obtained for chains on lattices, which are largely

independent of the lattice employed, become even more pronounced for chains free of lattice constraints.

During the coming year, we expect to extend this work further by studying the motion of chains with

move rules modified to provide increased local randomness at each step and to write up the results for

publication. Second, there is at present an unresolved disagreement in the literature regarding the

interpretation of the time-correlation functions obtained for flexible chain molecules in the quasielastic light scattering experiment. It is not clear whether these functions exhibit the entire

spectrum of chain relaxation times or are dominated by the longest relaxation time. It appears that

by direct simulation we may be able to resolve the disagreement, which will increase the value of

measurements made by this relatively new technique. These studies have begun and should be completed

in the coming year. Third, as a step in the direction of investigating melt properties, we have begun

a study of systems of many interacting chains, with chain densities corresponding to concentrated

solutions and melts. This work, which was partly supported this year by a grant from the NRCC, will

be continued during the coming year.

Low Shear Rate-High Temperature Rotational Viscometer

H. L. Wagner and J. G. Dillon 1

Limiting viscosity number (intrinsic viscosity) is the most rapid and convenient method of

measuring the molecular weight of high polymers provided the relationship between viscosity and molecular weight is known. However, for polymers greater than about a million in molecular weight, such as UHMWPE, the viscosity depends on shear rate as well as molecular weight. Hence, measurements should

be made at zero or very low shear rate where this dependence is minimal and where, in addition, degradation due to shear is avoided.

A low shear rate rotational viscometer of the floating rotor type (Zimm-Crothers) , which may be

operated at the high temperatures required for polyethylene, has been designed and put into operation.

Viscosities may be determined at shear rates as low as 3.0 s -1 and up to 8.0 s -1 at temperatures up to 150 °C. To assess the performance of the viscometer, measurements were made on several polystyrenes,

two of which were Standard Reference Materials. The viscosity results were consistent with the

previously published data on these samples, indicating that the instrument is operating satisfactorily.

Low shear rate limiting viscosity numbers for several samples of implant UHMWPE in decalin at

135 °C and a shear rate of 3.0 s _1 are shown in table 1, together with the results for these same polymers in capillary viscometers.

The multibulb capillary viscometer used here operates at shear rates of about 50 s _1 to 150 s -1

; the standard type of capillary viscometer ordinarily employed for routine viscosity measurements

^uest Worker, Food and Drug Administration

41
provides a shear rate of about 2000 s _1

. From the table it is seen that serious errors may occur if capillary viscometers are employed, even if extrapolation to zero shear rate is attempted using the

multibulb viscometer.

A problem encountered in these measurements in the low shear viscometer is an initial rapid loss

in viscosity of 2 to 3 percent during the first ten minutes of residence in the viscometer and as much

as a 7 to 9 percent decrease in the first hour. This does not occur with the polystyrenes available

to us. Work to understand and eliminate this difficulty is underway.

Table 1

Sample No. 99716 99881 99974

Maximum Concentration 0.046% 0.03% 0.02%

Limiting Viscosity No.

Decal in 135 °C

(a) Zero shear rate (low shear

viscometer, initial value)

17.7 dL/g 24.2 dL/g 37.8 dL/g

(b) Zero shear rate, estimated

(multibulb viscometer)

18.9 34.0

(c) High shear rate (routine

Canon-Ubbelohde viscometer)

14.6 17.8 26.0

Rubber and Rubber Compounding Standard Reference Materials

G. W. Bullman and G. B. McKenna

The process of streamlining the NBS Rubber SRM Program is continuing in response to reduced

resources available for this program. As part of this reduction, rubber and rubber compounding

Standard Reference Materials, for which NBS serves primarily as a warehouse facility, are being removed

from the SRM list as inventories are exhausted. In addition, several materials are being removed from

the list due to poor sales. These SRM deletions are being coordinated with ASTM Committee D- 1 1 on Rubber and Rubber-Like Materials and Committee D-24 on Carbon Black to assure an orderly change in the

ASTM standards and within the rubber industry.

In order to serve industry's needs for rubber SRM's with our reduced resource base, we are maintaining inventories of materials which industry (through ASTM) has indicated are important, even though NBS's primary function for these materials is to serve as a warehousing facility. For example,

we recertified SRM 381 (N-tertiary-butyl-2-benzothiazole sulfenamide, a rubber accelerator) in order

to maintain inventories of this material. In addition, proposals were written to OSRM requesting

working capital funds for the procurement of materials and recertification of SRM's 371 (Sulfur) and

372 (Stearic Acid) during FY82.

Where standards involve certification of fundamental physical properties, we are issuing new

SRM's when a need is indicated. Thus, during the past year we issued a new Butyl Rubber, Mooney

Viscosity Standard (SRM 1495) with a lower Mooney Viscosity Number than that available with the Butyl

Rubber SRM 388. This new standard extends the range of Mooney Viscosity Standards available to the

rubber industry.

Static and Dynamic Configurational Properties of Polymer Chains: Theory

F. L. McCrackin, R. J. Rubin, C. C. Flan, J. Mazur, I. C. Sanchez, and D. J. Lohse 2

Comprehension of the configurational statistics of polymer chains is indispensable for a rational

characterization of polymer solution properties. Constitutive properties of a polymer which are dependent upon its configuration include the intrinsic viscosity, mean square dipole moment, the

optical anisotropy, and the spectral dichroism. Mechanical properties are also intimately related to the configurational characteristics of the polymer chain.

The hydrodynamic radii of polymers were computed for polymer chains at the theta point created by

a Monte Carlo simulation in which both volume exclusion and the energetics of nearest-neighbor interactions are taken into account. The dimensionless ratios p of the radius of gyration to the hydrodynamic

radius were also computed. The calculated ratios of p were compared with experimental ratios measured

by elastic and inelastic light scattering. The calculated ratios showed better agreement with the

2 Exxon Chemical Company

42
experiment ratios than did values calculated for the analytcal Gaussian coil model of the polymer.

The Monte Carlo calculations are being continued for different coordination numbers of the lattice of

the polymers and for nearest-neighbor interaction corresponding to good solvents. The results are being compared to the blob model of a polymer and to available experimental data.

A review paper has been completed and is presently in the hands of the Washington Editorial

Review Board of NBS. It is intended that this review be published in the series, Advances in Chemical

Physics, edited by I. Prigogine.

In this review, the theory of discrete step random walks in discrete time and continuous time is outlined. The relation between continuous time random walks and a generalized master equation is developed. In the limit of long walks, the following asymptotic properties are discussed: (1) return

to the origin, (2) number of distinct sites visited, (3) central limit results, and (4) walks with

steps of infinite variance. The effect of boundary conditions and traps on random walk behavior,

maximum displacements and spans, and the application of Wald's identity for first passage time problems

is treated in a chapter devoted to boundary conditions.

A general method is outlined for calculating the statistical properties of the number of visits

to a set of points in a random walk. In illustrative examples, a number of known results and new results are easily derived: (a) the generating function of the probability distribution of a random

walk of N steps with an excluded origin; (b) the generating function of the probability distribution

of a random walk of N steps to go from point A to point B with no intermediate visits to A or B, i.e.,

a random walk with excluded origin and end point; and (c) the generating function of the probability

of an N step random walk to visit a surface layer of points m times without ever crossing through the

surface to the other side (i.e., penetrating the solution surface). This last result recovers a result obtained earlier by R. J. Rubin [J. Chem. Phys. 43, 2392 (1965)] for adsorption at a solution

surface.

Mean-square radii of gyration were computed for comb-branched polymers simulated on a cubic

lattice by chains with both excluded volume and attractive energies between non-bonded segments of

the polymer. The ratios, g, of the radius of gyration of a comb-branched polymer of the same molecular weight were found to be larger than the g ratios calculated by the unrestricted random-wal < model of the polymer. The calculations were completed this year.

A statistical thermodynamic theory of a polymer solution is formulated which takes into account

concentration inhomogeneities on size scales equal to or larger than the average size of a polymer

chain. A generalized cell model is used as the basis for the new polymer solution theory. Closed-form,

parametric equations are obtained for solvent and polymer chemical potentials which only reduce to classical (Flory-Huggins) potentials in concentrated solutions. The second virial coefficient A 2 varies as

A2

,-1/5

T » 0

,- 1/2

T = 6

where c* is the overlap concentration (as defined in scaling theories) and M is the molecular weight.

For finite M, A 2 vanishes slightly below 0. At T = 0, the chains are still repulsive because of the

existence of repulsive ternary monomer interactions. For the chain expansion factor a

2

, we obtain

-c* da 2 /dc°

c_0 = positive constant; T > 0.

This result implies that even in the dilute regime, chain dimensions should decrease with

increasing concentration. The physics behind this result is that large fluctuations of the chain

dimensions are damped because such fluctuations increase the probability of unfavorable interchain

interactions. Neutron scattering experiments are being planned to check these predictions.

Reference:

[1] R. J. Rubin, J. Chem. Phys., 43, 2392 (1965).

Polymer Blends

I. C. Sanchez, F. W. Wang, and R. E. Lowry

Mixtures or blends of two or more different polymers can, under the proper conditions, produce

materials with properties intermediate between those of the constituent polymers. This provides a method of tailoring a material to a specific application as well as optimizing the cost/performance

ratio. Many plastic markets are primarily cost limited. Modern Plastics , a trade magazine says, "New polymer development is at a technological plateau. But new al loys--compounds of two or more structurally different polymers--are far more economical to develop than are generically new classes

43
of plastics." Material costs are an important variable in the economic formula because the polymeric

raw material is about two-thirds of the manufacturing cost of a typical plastic part.

A major generic problem associated with blends is the property that most polymer mixtures are incompatible and, given the opportunity, will phase separate. Although separated phases on a micro

scale are often desirable, if the morphology and scale of the separated phases is not within acceptable

limits, parts made from blends are useless. Since polymers tend to phase separate much more rapidly

at the high temperatures encountered during processing, the phase separation problem is a matter of

widespread concern which limits the rate of introduction of polymer blends.

Phase diagrams of liquid polymer/polymer mixtures (blends) are very unusual when compared to similar low molecular weight mixtures. Neither the familiar adage, "like dissolves like," nor the

familiar observation that solubility increases with temperature are in general applicable to polymer

blends. We have examined the thermodynamic and molecular reasons responsible for this unusual phase

behavior. A general thermodynamic analysis of phase stability has been developed which suggests that

thermally induced phase separation near a lower critical solution temperature is an entropy driven

process. The entropic driving force is related to the compressible nature of a fluid mixture and the

propensity of fluids to contract upon mixing (negative volume changes) at sufficiently high temperatures or, equivalently, sufficiently low fluid densities. By using a molecular equation of state

theory, we have shown that volume contraction is always expected at low fluid densities if attractive

interactions exist between dissimilar molecular species. All of the unusual aspects of polymer blend

phase behavior can be given a rational basis.

There has been much effort to prepare polymer blends for the tailoring of polymers to specific

end uses. A simple quantitative method for determining the point of polymer compatibility is needed. We have, therefore, initiated a project to develop a fluorescence energy transfer technique for the

study of the phase behavior of polymer blends.

If the emission spectrum of a donor chromophore overlaps the absorption spectrum of an acceptor

chromophore, nonradiative energy transfer can take place over distances as large as 5 nm. The theory

of this process is due to Forster who obtained for the efficiency, Eff, of the energy transfer on the

donor-acceptor separation, r, Eff = [l+(r/R ) 6

] -1 where the sixth power of the characteristic distance

R

q is proportional to the overlap integral.

Intermolecular fluorescence energy transfer will occur in a film made of two almost identical

polymers, one labeled with a small amount of a donor chromophore and the other labeled with a small amount of an acceptor chromophore. In a blend made of these chromophore-labeled polymers and a third

polymer, the efficiency of intermolecular energy transfer will be larger when the third polymer is incompatible with the first two and forms a separate phase than when it is compatible and serves as a diluting "solvent" for the first two. Thus, measurements of fluorescence energy transfer will allow

us to determine the cloud point curve for the two practically identical labeled polymers and a third

polymer.

We have synthesized donor- or acceptor-labeled polymers of narrow molecular weight distribution.

We shall use the fluorescence energy transfer technique to determine the cloud point curve of these

polymers and a third polymer.

Static and Dynamic Scattering from Polymers

C. C. Han, D. B. Minor, H. L. Wagner, A. Z. Akcasu3

, S. J. Bai 3

, D. J. Lohse 4, T. P. Lodge

Scattering techniques, such as light and neutron scattering, provide valuable characterization

information on polymers. Static light scattering from a dilute polymer solution is the classical

method of determining the weight average molecular weight of a polymer. It is a method widely used in industry for this purpose. Static scattering measurements also provide two other important pieces of

information: the equilibrium size of the polymer molecule, i.e., its radius of gyration, can be

determined as well as the osmotic pressure second virial coefficient. The latter is a thermodynamic

property that is a useful indicator of the solvent power.

Dynamic or quasi-elastic light scattering can provide information on molecular motions, such as the diffusional and hydrodynamic behavior as well as information on equilibrium properties. In this

respect it is a more versatile experimental tool than static scattering methods.

Much of our effort has been devoted to developing the idea that dilute polymer solutions satisfy

a corresponding states principle. Polymer solution properties, such as intrinsic viscosity, are a function of three variables: molecular weight, temperature, and solvent. Scaling theories suggest

that these three variables can be combined into a single excluded volume parameter and that all dilute

3 University of Michigan

4 Exxon Chemical Company

44
solution properties can be expressed as a function of this single parameter. This corresponding

states idea holds considerable potential for simplifying and unifying the different approaches used in polymer characterization. We have tested these ideas by comparing theory with experimental data

collected from small angle neutron scattering, light scattering, and quasielastic light scattering

measurements. To date, satisfactory agreement has been obtained which suggests that the corresponding

states approach is valid.

A state-of-the-art light scattering photometer was developed and used in the measurement of

polystyrene SRM 1479 at room temperature. However, because of the thermal instability of the optical

bench used in this system, measurements at the elevated temperature, required for ultra high molecular

weight polyethylene, could not be made. Consequently, the optical bench has been redesigned to be thermally isolated from the heated cell. In addition, a stepping motor driven goniometer has been

installed. The redesigned apparatus will now how the option for simultaneous static and dynamic light

scattering measurements at elevated temperatures that are required for polyethylene.

Polystyrene solutions in the dilute region have been studied by dynamic light scattering experiments. The first cumulant, Q(q), has been extracted consistently by either cumulant analysis or shape

function analysis. It is found that Q(q) approaches q

2 dependence as qR << 1 and q3 dependence as qRg >> 1 with a broad transition region. It is also found that the magnitudes of the first cumulant

at q

3 region change from 0-solvent to good solvent condition. In both cases, experimental results

agree better with theoretical calculations which use a preaveraged Oseen tensor. It seems that either

the analytical Gaussian model of equilibrium polymer chain distribution function or the Oseen tensor

hydrodynamic interaction has to be improved.

45
TESTS, STANDARDS, AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY

OF DENTAL AND MEDICAL MATERIALS

J. M. Cassel

Task Leader

The objective of this research is to contribute to health care through development of better

performing materials and test methodology and standards appropriate thereto. Materials research and

techniques are pursued with the goal of developing dental adhesive composite restorative materials of

greater durability and wear resistance and improved base metal alloy alternatives to the costly gold

alloy dental prostheses. Knowledge of the structure and physical chemistry of biologically important

calcium phosphates is used to develop improved preventive dental techniques. Improved test methodology

is sought for characterization of the surfaces of surgical implant materials for defining the interactions that occur thereon. Means for characterizing the porosity of low modulus, polymeric, medical

implant materials are sought.

Dental research directions in support of the objective are established col laboratively with the

American Dental Association, the National Institute of Dental Research, and the Department of Defense

Medical R&D Command. Medical materials research is guided by close interaction with the Food and Drug

Administration's Bureau of Medical Devices and the ASTM F-4 Committee (Medical and Surgical Materials

and Devices).

Dental Composite Chemistry and Development

G. M. Brauer, J. M. Antonucci, J. W. Stansbury, J. M. Cassel, R. L. Bowen 1

, H. Argentar 1

, D. N. Misra 1

, T. Chen 2, and E. E. Toth

Current efforts are directed toward upgrading the quality of composite restorative materials with

regard to color and storage stability, toxicity effects, adhesiveness, and durability.

Chemical and photo (visible and ultraviolet) polymerizations of experimental resin formulations

in which the monomers, the amine or other type accelerator, and the initiator are varied are being

compared for development of dental resin systems having enhanced storage stability and which yield

dental composite restorative materials with improved color, chemical and mechanical stability, and are minimally toxic to the pulp. A number of mono- and dimethacrylate monomers have been prepared that

are bulkier in structure than BIS-GMA and hence may produce less polymerization shrinkage in composite

restorations derived therefrom. Various combinations of base resin, such as BIS-GMA, and new diluent monomers are being investigated for this purpose. Experimentation has shown that the extent of polymerization (or residual unsaturation) in the highly cross-linked dental composite resin systems can be

investigated successfully by DSC. Correlation of DSC results with oxidative stability and wear resis- tance of composites is planned.

Photochemical polymerization-initiating systems that on the basis of their structure would appear

biocompatible are being investigated. Means are being sought to effectively incorporate into clinically

initiated paste/paste composite formulations non-amine type polymerization accelerators, such as ascorbic acid, which give composites with excellent color stability and biocompatibility when adsorbed

onto the powder in powder/liquid systems. Amine accelerators which are esters of dimethylaminophenethanol and succinic, maleic, and acrylic acids have been synthesized and will be evaluated in composite

resin formulations.

Continuation of the investigation of the effect of amines on the silanization of composite filler

particles has shown that primary aliphatic amines are the most effective catalysts and aromatic and

heterocyclic types the least effective. The solvent from which the coupling agent is deposited has

also been shown to be an important factor. Non-polar solvents, such as cyclohexane, yield a higher

degree of silanization with more resistance to hydrolysis than polar solvents such as acetone.

At least one manufacturer is preparing on a commercial scale the semi-porous glass developed

earlier in this laboratory to achieve better reinforcement of the composite resin matrix by the filler

component. The combination of an etched filler surface with the more effective means for applying the

coupling agent will provide a means for achieving more durable composite restorations.

Research Associate, American Dental Association.

2 Guest Worker, Food and Drug Administration.

46
Development of Adhesive Bonding Technique and Dental Cements

G. M. Brauer, R. L. Bowen3

, J. M. Antonucci , D. N. Misra3

, J. W. Stansbury, E. Cobb 4

, J. M. Cassel

Although effective bonding to enamel is presently achieved by means of acid etch treatments,

similar treatments of dentin are contra-indicated in tooth restoration procedures. A bonding procedure

effective with dentin would promote more conservative tooth restoration procedures.

A series of so-called reactive adhesive formulations prepared by solubilizing selected elastomers

in acrylic, methacrylic acid, or methacrylate ester monomers have been examined for their adhesiveness

to mineralized tissue such as bone. Bond strengths after three months storage in water did not exceed

1.0 MPa, and this approach has been discontinued.

While the stability to water of the bonding to dentin with isobutyl cyanoacrylate is not satisfactory, the initial bond strength attained with this material is the highest achieved to date. Attainment

of this high initial bond strength requires a cleaning of the surface of the dentin by a one percent

citric acid pretreatment but this is too severe for the dental pulp. However, pretreatment of the

dentin surface with dilute sodium citrate solutions gave joints with excellent bond strength. To mitigate the response of the pulp to such materials, we have been examining the use of isotonic surface

cleansing solutions to which we have incorporated mordanting agents as a means of altering or increasing

the mineral surface to adhesion. Currently, we are examining the sequential application of two coupling

agents, each applied from a volatile solvent. The coupling agents apparently penetrate into the

altered dentin layer and provide bound molecules that can copolymerize with the resin of the subsequently

applied composite material. The dentinal tubules do not appear to be enlarged or filled to any significant depth with the adhesive or polymeric material, so the very high bond strengths currently being

achieved are not the result of mechanical attachment via resin tags penetrating the tubules and

insulting the pulp. Other coupling agents that are designed to react with labile hydrogen groups in dentinal collagen have been synthesized and will be evaluated, e.g., monomers with pendant isocyanate

and aldehyde groups.

Zinc oxide-eugenol (ZOE) cements, because of the excellent biocompatibility of the hardened

material, are widely used in dentistry. However, they have serious deficiencies: comparatively low

strength, lack of resistance to wear, early disintegration, and inability to adhere well to acrylic

restorations or to mineralized tissue. Further, their inhibiting effect on the free radical polymerization of acrylic resins and to a lesser extent dental composites with which they may be placed in contact, reduces their usefulness. In the past, substitution for the eugenol component which inhibits

polymerization has usually resulted in cements possessing poor physical properties.

Currently, we are investigating cements in which the liquid ingredients are esters of vanillic

acid or its isomers containing o-al koxyphenol or other groups capable of forming chelates with multivalent salts. Neither vanillic acid nor its common isomers are liquids at room temperature, which is

a prerequisite for conveniently preparing a cement by mixing the chelator with a metal oxide. The

hexyl ester of vanillic acid (HV) was synthesized since it is a liquid at room temperature. The

hardening reaction of this ester with zinc oxide is much too slow for dental application, but by

incorporating a second chelating component such as o-ethoxybenzoic acid (EBA), we have increased the

reaction speed within the useful range. The resulting cement has high strength, does not inhibit

dental resin polymerization, and adheres strongly to acrylic resins and composites even after prolonged

exposures in an aqueous environment. Incorporation of dimethacrylates in the formulations allows a rapid cure of such "composites" in the presence of an initiator-accelerator system and yields cements

with good physical properties. Further improvement in these properties is being sought through the

incorporation of di vani 1 1 ates.

The fact that HV-ZOE cements do not inhibit methacrylate resin polymerization has many advantages:

It allows incorporation of polymerizable monomers into the cement mix. By suitable techniques

such as redox polymerization, these monomers can be cured to strengthen the cement and to yield crosslinked, multiphase, or interpenetrating networks which are less soluble, and more degradation resistant

than the presently available cements.

A portion of the cement when used clinically as a temporary restoration can be retained as a base

for an acrylic resin restoration. This should shorten the time necessary for placing the permanent

restoration. A complete reexposure of deep cavities is also avoided, which should reduce irritation

of the dental tissues during the clinical procedure.

3 Research Associate, American Dental Association.

4 Guest Worker, Georgetown University Dental School.

47
Cycles x 10"

Figure 1. Wear track depth(s) for a dental composite plotted against specimen disc revolutions

at indicated stresses.

48
Wear Resistance and Mechanical Properties of Dental Materials

W. Wu, J. E. McKinney, J. M. Cassel , E. E. Toth, and E. Cobb 5

A silver staining technique developed and applied initially last year in a study of the mechanisms

of wear in dental composite restorations is continuing to yield promising results. By this means, the

creation of microdefected subsurface damaged regions is readily observed in both j_n vivo and i_n vi tro worn specimens. This technique has been used to examine the attack of various solvent media including

aqueous organic systems on dental composite materials and when combined with hardness measurements has

shown that establishing solubility parameter data on dental composite resins is important in investigating the mechanisms of degradation that influence wear resistance.

Small angle x-ray scattering experiments to examine the shape of the microdefects created in subsurface damage regions of worn composites are in progress. The necessary theoretical background

for this application has been completed, and the analyses of in vitro compression-fatigued composite

specimens are being compared with that of i_n vi vo exposed materials. Preliminary results indicate a more isotropic-shaped defect in the clinical specimen with the conclusion that compression fatigue may

not be a dominant factor in the j_n vivo wear process.

With our i_n vi tro pin-on-disc accelerated wear test, we are continuing to advance our state of

knowledge of composite wear. Analysis of composites subjected to wear over a range of normal stress

levels from 2.5 to 20 MPa have revealed that abrupt changes by a factor of roughly two in wear rate occur during the course of wear. This is shown in figure 1 where we plot the depth of the wear track

as a function of the cycles of exposure of the dental composite disc to a stainless steel pin. We attribute this result to an initial wear region dominated by an adhesion process followed by a region

in which subsurface damage increases to a point where breakdown occurs from fatigue. Only specimens

with wear terminated in the second region of wear show subsurface damage by the silver staining

technique. Subsurface damage caused by diffusion of solvents in dental composites is being correlated

with i_n vitro wear performance using the silver staining technique. The extensive deterioration in the i_n vi tro wear resistance of a commercial dental composite previously exposed to ethanol-water

solutions is indicated in figure 2 where we plot the depth of wear track generated by a stainless

steel pin in a dental composite disc after each of the first five revolutions of the disc. This type

of information provides clues to efforts here and in industry to develop more durable plastic composite

restorative materials.

Porcelain Fused to Base Metal Alloys and Dental Ceramics

J. A. Tesk, R. W. Hinman6

, W. deRijk7

, E. E. Parry6, D. L. Menis 7, and G. E. 0. Widera8

A major cause of failure in porcelain fused-to-metal restorations involves cracking or delamination of the porcelain veneer. This is thought to arise primarily from residual stress trapped within

the system during cooling from the firing temperature. These stresses originate in the differences in thermal expansion and stress relief characteristics of porcelains and alloys.

To determine optimum combinations of thermophysical properties for porcelains and alloys, a multifaceted investigation of properties is in progress: (a) coefficients of linear thermal expansion

are being determined for several brands of alloys and porcelains which have been subjected to one through seven laboratory firing cycles, (b) viscous flow characteristics are being measured, and (c)

measurements of mechanical properties as a function of temperature are planned. Stress is being

evaluated via a combined experimental and theoretical determination of the change in gap of porcelain

veneered split metal rings using experimentally determined thermophysical properties. Correlation

between measured and predicted gap changes provide the necessary information to calculate stress at any position within the ring. Ring and porcelain dimensions have been chosen to be somewhat representative of a crown.

Thermal expansion data for a number of porcelains have now been acquired and reported on. In addition to this property, information on the temperature dependence of the shear viscosity for a number of dental porcelains has been developed and reported on. A parametric study on the importance

of parameters such as the temperature dependence of the elastic modulus and Poisson's ratio was conducted and discussed. Results of the latter study show that Poisson's ratio is not a critical

factor in determining stress or strain within a system. The elastic modulus, however, is an important

factor in stress. A 40 percent increase in modulus of porcelain can result in a doubling of stress within porcelains.

One area of particular concern involves the influence of transition bonding zones between alloy

and porcelain on experimental determinations of stress and strain. Theoretical calculations of the

effects of differences in thermal expansion showed that interfaces as thick as 20 pm, with differences

5 Guest Worker, Georgetown University Dental School

6 Research Associate, U.S. Navy

7 Research Associate, American Dental Association

Consultant, University of Illinois

49
Revolutions

Figure 2. Wear track depth(s) for a dental composite measured over the first five

revolutions. The specimens were immersed for two weeks in indicated

concentrations of ethanol in water prior to wear tests.

50
in expansion (from that of porcelain or alloy) as large as 10 x 10 -6 /°C, are not capable of producing

significantly measurable effects at the 2.5 percent level of detection, provide d the porcelain to alloy thickness ratio is one. Experimentally, this is the condition achieved in porcelain fused-tometal split rings. A paper was presented on this at the 1981 IADR/AADR meeting. It should be noted

that the analysis used in this case is useful for predicting strain but is not capable of providing

detailed stress analysis.

The theoretical approaches for calculation of stress in split metal rings has been refined; the

finite element program has been reconstructed to include a finer mesh and definition of elements near edges (for edge effects) and to include viscous relaxation of porcelain. Stepwise numerical calculations, incorporating viscous flow, have been made using analytical models and have shown improved

agreement with experimentally determined gap changes of composite rings.

The development of "Gel-route" technology for application to dental porcelain and investments has

continued. "Gel-route" technology, in which the desired composition of a solid phase is obtained by

mixing aqueous solutions rather than by preparing a glassy frit has several advantages over conventional porcelain frit production; among them are lower capital and labor costs for production and less

supply dependence on scarce raw materials. New compositional and heat treatment variations are being

tested. Porcelain frits suitable for metal-ceramic applications have been made that mature in a 12 minute air fire at temperatures 50 to 175 °C lower than the current lowest-fusing commercial metalceramic porcelain. The strength, thermal expansion coefficient, and insolubility (in four vol percent

acetic acid solution at 80 °C for one week) compare favorably with currently available materials.

A device has been constructed to measure the force of investment setting that uses the nondestructive setting-ring test developed for the measurement of both setting expansion and temperature set. Preliminary results using one phosphate bonded investment indicate that the force of setting is over

four times greater with a wet asbestos liner than with an identical dry liner. It also increases

slightly with increasing silica concentration in the liquid and with decreasing 1 iquid-to-powder

ratio. Most of the force, as well as expansion and heat evolved on setting, occurs after a hard set

is achieved.

A patent on a microporous glassy filler for dental resin composites has been issued. Another

patent on the "Gel-route" preparation of dental porcelain frit has been filed. Several dental

companies have shown interest in our "Gel-route" prepared frit.

Dental Casting Alloys

J. A. Tesk, R. M. Waterstrat9

, R. W. Hinman 10, and E. E. Parry 10

Problems of cost and limited availability have been encountered in recent years for commercial

dental casting alloys based on gold or cobalt, and some concerns continue to surface for the toxicity

of nickel-based alloys, although there appears to be very limited evidence that this is indeed a problem except where a skin sensitivity to nickel has been established.

Earlier in this laboratory, we prepared the first titanium-based dental castings using a titanium/

copper alloy. These castings were made under argon with our conventional casting equipment. During

the past year, we have designed and constructed an electric-arc furnace for melting and casting

titanium alloys using conventional dental investment molds heated in the usual manner. The initial

castings with this equipment demonstrate that this technique is feasible and may be more economical

than the present induction centrifugal methods used in commercial dental laboratories. We have cast

both the relatively low-melting titanium/copper alloys and pure titanium in the form of typical test

castings. Much more information is needed relative to dimensional accuracy, mol d material s , porcelainmetal bonding, mechanical properties, and casting techniques.

A study reported from this laboratory two years ago showed that single crowns of base metal

alloys could be cast to sufficient oversize to produce fits which would be considered as clinically

acceptable. However, the question remains as to whether the same techniques would work for multipleunit castings. A series of experiments were, therefore, conducted to investigate the fit of multipleunit fixed partial dentures on a double die system which consisted essentially of combining two single

dies of the pattern previously used. Results to date have shown that although some distortion of

geometry occurred under all conditions investigated thus far, the use of plastic runner bars should be

avoided and a bench setting technique with an all-wax system produced minimum distortion.

A pilot study attempting to join individual base-metal alloy castings by soldering has been

unsuccessful to date. Alloys that performed best in our castability study often contain constituents

which preclude reliable joining by conventional soldering methods. Some manufacturers who have been

in contact with NBS are aware of the problem and are expending effort in this regard to improve their

products.

9 Research Associate, American Dental Association

10 Research Associate, U.S. Navy

51
A simple, objective castability test which does not require sophisticated measurement devices

would be of benefit to both users and developers of dental alloys. For this purpose, we had previously

developed a technique that employs the use of a pattern of polyester mesh, waxed, sprued, and invested

by standard dental laboratory practices. Following burnout of the pattern and casting of the alloy,

the number of completed cast pattern segments provides a measure of castability. Results reported to the 1981 IADR/AADR meeting indicate that the test is sensitive to a number of processing variables

such as casting temperature, mold burnout temperature, and investment brand. This development is being continued with a view toward evaluation of these parameters for a number of alloys and to make

the test more sensitive to them.

Clinical and Laboratory Investigation of Dental Amalgams

N. W. Rupp 11

, G. C. Paffenbarger 1

, and R. M. Waterstrat 11

The deterioration of amalgam restorations often begins with a slight extrusion from the cavity.

This extrusion appears to be caused by some internal transformation which produces an expansion of the

alloy. Recent experiments indicate the expansion is related to the amount of zinc in the amalgam,

particularly in the higher temperature range (60 °C). Metallographic and x-ray diffraction studies

have thus far been unsuccessful in identifying the cause of the expansion. Detailed metallographic

studies of the reacted alloy powders are now underway, and further studies of the amalgams are to be

initiated in the near future using a transmission electron microscope.

In a cooperative study with the University of Virginia, it was found that increasing the zinc content (1) increased the mercury/alloy ratio needed to obtain a proper consistency of mix, (2)

increased the residual mercury content of the amalgam, (3) decreased dimensional changes that occur during hardening, (4) increased the compressive strength, and (5) decreased the creep.

Long-term clinical observations are continuing, and an attempt is being made to determine the causes of success or deterioration.

Dental Chemistry and Preventive Dental Treatments

W. E. Brown 11

, L. C. Chow 11, M. Mathew 11, M. S. Tung 11, G. L. Vogel 11, S. Takagi 11

, and T. M. Gregory 11

The objective of this project is to develop and apply fundamental information on the solubilities

and crystallographic structures of biologically important calcium-containing phosphate compounds to the development of improved dental caries preventive techniques. Important portions of this effort

are concerned with (1) development of physico-chemical models of the caries process to include insight

into the mechanisms by which impurities and defects are incorporated onto tooth enamel, and (2) application of solubility phase diagram analysis and kinetic data to the development of more effective enamel

acid-etch bonding treatments and improved topical fluoride procedures.

Continued progress has been made in developing a new procedure for studying the mechanism by

which enamel crystals grow and react with fluoride. Advances were made in methodology, using rats as an animal model, as well as in collecting new experimental evidence. Considerable in vitro evidence

has accumulated over the years that an acidic salt, octacalcium phosphate, is formed first in the

developing enamel and then is converted to the final form, a basic salt, hydroxyapatite. Fluoride

ions facilitate this conversion. Through the use of radioactive phosphorus, a promising new method was developed which measures the relative amounts of the acidic and basic calcium phosphates reproducibly

in the rat incisor. The experimental results support the view that an acidic calcium phosphate is a precursor in tooth mineral formation, and they bring us a step closer toward understanding how fluoride

in drinking water during tooth formation acts to reduce dental caries. These experiments were carried

out in the animal facilities of the ADA Research Institute in Chicago.

Carbonate is a major impurity in tooth mineral, and its presence there is generally thought to enhance the solubility and, therefore, the caries susceptibility. Solubi 1 ity measurements were carried

out on synthetic and natural tooth mineral in the presence and absence of carbon dioxide in the atmosphere. Contrary to expectations, carbon dioxide lessened the solubility of tooth mineral. These

results indicate that the effects of carbon dioxide in the atmosphere and of carbonate in the mineral

on enamel solubility need to be examined more carefully in order to determine their roles in tooth

decay.

Studies are being carried out on the chemistry of the tooth decay process by using ultramicro

techniques. Small wells are drilled into quarter-millimeter thick tooth sections. These sections are then placed into cariogenic solutions, and the chemical events taking place within the wells are measured. These wells are only about 0.1 mm in diameter and are barely visible to the unaided eye;

since a complete chemical analysis of the solution within such wells must be obtained, it can be seen that the procedures involved are exceedingly delicate. Our recent work has shown that the solution

“Research Associate, American Dental Association

52
within the wells is saturated with respect to enamel mineral and that the response time is relative

slow compared to the rates of change in the environment of the tooth due to normal dietary fluctuation^.

These results require substantial modification of the caries models used in the past. Work of this

type may reveal steps within the process that can be slowed so as to reduce the rate of formation of

cavities.

Neutral salts such as NaCl and KC1 through their ability to function as acids or bases have been

predicted to strongly affect the caries process when the surface of the tooth holds either a positive

or a negative ionic charge, respectively. This theory was tested in bench scale experiments and was found to be valid. The full implications of these results are not yet known, but the importance of

neutral salts in the caries process warrants careful consideration in the future.

A previously reported topical fluoridation procedure which incorporates more permanently-retained

fluoride into the tooth than the treatments now in use has been moved closer to clinical application.

During the past year, several new modalities of treatment were tested in the laboratory and were found

to be effective. Substantial progress was made in preparing for a clinical study of this procedure.

This trial should go a long way toward confirming or refuting the commonly held hypothesis that

increasing the fluoride content of enamel increases its resistance to decay.

We have determined the structures of several calcium phosphates with emphasis on layer-type and

highly hydrated structures. Two of these compounds, CaBr(H2 P0 4 )-4H2 0 and CaI(H 2 P04 )'4H 2 0, are of a new type in that they contain planar calcium phosphate sheets, a structure that has been found only

once before. They provide a plausible structural model for calcium phosphate complexes in concentrated

solutions. The structure of the compound Ca2 KH 7 (P0 4 ) 4 -2H 2 0, which contains a corrugated sheet

arrangement of calcium and phosphate ions, was determined, and work is in progress on a compound which

apparently contains a calcium-phosphate sheet interlayered with urea molecules.

Development of Improved Field Dental Composite Restorative Materials

for Military Personnel

G. M. Brauer, N. W. Rupp 12

, J. W. Stansbury, K. Dermann 13

, and J. M. Cassel

Field use of dental composites would be significantly aided by development of composite systems

which could be more easily placed and have greater storage stability than current materials. As with

all composite restorations, there is also the need for improved marginal adaptation in the hardened

materials in order to prevent microleakage, which reduces the effective lifetime of restorations.

We have examined the roles in the phenomenon of microleakage of polymerization shrinkage, coefficient of thermal expansion, nature of the filler, and properties of diluent monomers. Based on radio- tracer analysis applied to class V restorations placed in extracted caries-free teeth that are subsequently thermocycled, we find the coefficient of expansion of a particular composite to be less

important in microleakage prevention than is the influence of diluent monomer on the overall polymerization shrinkage. Measurements on specimens in which water sorbing diluent monomers have been incorporated to counterbalance polymerization shrinkage do not support this approach to solving microleakage

problems.

A silver staining technique of investigative wear mechanisms of dental composites is being ex- amined as a more sensitive means of assessing microleakage than the radiotracer technique we have been

employing. The possibility of producing composite systems with low polymerization shrinkage but with

a more hydrophobic character than that of currently available materials is also being investigated.

Adhesion and Surface Coverage of Synthetic Polymers on Solid Substrates

R. E. Dehl and W. H. Grant

Two aspects of the adhesion of polymers to surfaces are of great importance in their many commercial applications as protective coatings, namely, (1) the energy of adsorption of individual polymer

molecules on the surface, which determines the adhesive strength of the film and (2) the extent of

surface coverage by the polymer, which determines the effectiveness of the adherent film in protecting

the underlying substrate from chemical attack. We are using radiolabeled polymers to study the adherence of the film. A measure of the energy of attachment of polymers adsorbed on solid surfaces is the

rate at which they become detached when the polymer-coated substrate is placed in contact with a suitable solvent. The results of previous NBS studies, using radiolabeled polystyrene to detect the amount remaining on the surface, indicate that the rate of desorption decreases with increasing molecular

weight of the polymer and with the amount of polymer initially adsorbed.

l2 Research Associate, American Dental Association

13 Freie Universitat in Berlin
We have recently discovered that the rate of desorption of polystyrene from a chromium oxide

surface into cyclohexane solvent depends not only upon the amount adsorbed but also upon the way in which a given amount of polymer is adsorbed. If the time spent in adsorbing a given amount (A) of

polymer is very long or if the surface is first adsorbed to a higher level B > A, the subsequent rate

of desorption into solvent from level A is much slower than if level A is attained quickly before

desorption is begun. We feel that the most likely explanation for these phenomena is that the surface

has at least two types of adsorption sites which differ in their energy of attraction for polymer

molecules. We know that some adsorbed polymer exchanges with dissolved polymer during the adsorption

so that a very slow adsorption allows the higher energy, less easily desorbed sites to fill with

polymer at the expense of the lower energy sites. Similarly, adsorption to a higher level B > A and

desorption back to A leaves the surface with a higher fraction of high energy sites occupied than if the sites are quickly and randomly filled up to level A. The effects of surface roughness and other

surface properties will be examined for their effect on the desorption rate of adsorbed polymers.

We are conducting studies to determine the utility of ESCA for determining the homogeneity of

polymer coatings applied to solid surfaces.

Characterization of Porosity of Porous Implant Materials

R. E. Dehl , W. H. Grant, and J. M. Cassel

The use of porous synthetic implant materials to serve as scaffolding for the ingrowth of natural

hard or soft tissue is a procedure utilized to stabilize selected medical implants. Characterization

of the porosity of these materials is very important, since the porosity governs their successful

utilization. In cooperation with the Bureau of Medical Devices, Food and Drug Administration, we have

concluded a survey of published information and current commercial material specifications and have

performed mercury porisimeter measurements on polymeric (polyethylene) and a composite (graphite fiber

immersed in polytetraf 1 uoroethylene) implant material. The results clearly demonstrate the usefulness

of the mercury porisimeter technique for providing a "fingerprint" characterization of the materials.

A study of the effect of precompression on the composite material has shown that precompression

by a pressure 20 percent greater than that encountered by the material during a mercury intrusion

experiment did not change the ensuing pore size distribution curve. Deformation of the material at higher pressures sufficient to decrease the sample volume inelastical ly by 17, 33, and 67 percent

changed the shape of the mercury intrusion curves significantly, indicating that the technique can be

used to detect prior deformation of an unknown sample. In combination with a quantitative total void

volume measurement, such as a continuation of Hg intrusion into the high pressure mode, this method

can determine the fraction of total void represented by any pore size range of interest.

The accomplishment of this project's objectives will be of significance to the medical device

industry, medical implant standards development, and, ultimately, the users of porous implant materials.

Dental and Medical Materials Standards

J. M. Cassel, J. A. Tesk, G. M. Brauer, and N. W. Rupp 14

Dental and medical implant standards development is strongly supported by persons in positions of

Committee, Subcommittee, and Task Force Chair roles in ANSI MD 156, Dental Materials, Instruments, and

Equipment, and in ASTM F4, Medical and Surgical Materials and Devices. Additional leadership roles are fulfilled through the Chairpersons role in USA TAG ISO/TC 150, Surgical Implants and through

participation in the Executive Committee of the ANSI Medical Device, Standards Management Board.

14 Research Associate, American Dental Association.

54
Other Activities of the

Polymer Science and Standards Division

Invited Talks

A Computer-Controlled Manometric Permeation Measuring: Hardware and Software Considerations

Washington Area MINC Users Group, Washington, D.C.

J. D. Barnes January 15, 1981

Effect of Matrix Toughness on Interlaminar Fracture of Composites

W. D. Bascom and D. L. Hunston American Chemical Society, New York, New York

August 24, 1981

Developments in Composite Resins

Howmedica Biomaterials Seminar, Groton, Connecticut

R. L. Bowen September 24, 1980

Developments in Composite Resins

Academy of Operative Dentistry Annual Scientific Session, Chicago, Illinois

R. L. Bowen February 12, 1981

Recent Developments in Adhesive Resin Formulations for Dentin

International Congress of Implantology and Biomaterials in Stomatology, Kyoto, Japan

R. L. Bowen June 10, 1980

Basis of Piezoelectricity and Pyroelectricity in Polymers

Symposium on Electroactive Polymers and Special Topics, Washington, D.C.

M. G. Broadhurst

January 9, 1981

Electrical Behavior of PVDF Workshop on High Energy Density Capacitors, Maxwell Laboratories, San Diego, California

M. G. Broadhurst

April 28, 1981

Field Induced Phase Transitions of Polyvinyl idene Fluoride

Gordon Research Conference, Ventura, California

M. G. Broadhurst

January 12, 1981

Dielectric Properties of Polyvinyl idene FI uoride--Low Field and High Field Phenomena and Time

Effects

Conference on Electrical Insulation and Dielectric Phenomena, Boston, Massachusetts

M. G. Broadhurst, G. T. Davis, and A. S. DeReggi

October 28, 1980

Current Concepts in Dental Research

Georgetown University, Washington, D.C.

J. M. Cassel

January 7, 1981

Application of Factor Jump Thermogravimetry to Polymer Degradation Studies

Eleventh Annual Summer Institute in Polymer Science and Technology, New Paltz, New York

B. Dickens

June 23, 1981

Pressure as an Important Variable in Thermogravimetric Studies of Polymer Degradations

Second European Symposium on Thermal Analysis, Aberdeen, Scotland

B. Dickens

September 2, 1981

Solution Oxidation Studies With Styrene Polymers

Eleventh Annual Summer Institute in Polymer Science and Technology, New Paltz, New York

B. Dickens

June 23, 1981

55
Thermal Degradation of Polyethylene and Polypropylene, Studied Using Thermogravimetry

International Workshop in Thermal Analysis, Salford, England

B. Dickens

September 8, 1981

Overview of the Polymer Science and Standards Division

Environmental Protection Agency, Cincinnati, Ohio

R. K. Eby

September 26, 1980

Overview of the Structure and Properties Group

Environmental Protection Agency, Cincinnati, Ohio

B. M. Fanconi

September 26, 1980

Analysis of Thermogravimetric Kinetics--Overcoming Complications of Thermal History

Symposium on Thermal Analysis in Polymer Characterization, New York, New York

J. H. Flynn

November 20, 1980

Kinetics of Polymer Degradation

Polytechnic Institute of New York, Brooklyn, New York

J. H. Flynn

May 13, 1981

Mettler Award Address

Tenth North American Thermal Analysis Society, Boston, Massachusetts

J. H. Flynn

October 27, 1980

Mettler Award Address

Royal Society of Chemistry, Salford, England

J. H. Flynn

September 7, 1981

New Techniques for the Thermal Analytical Investigation of Polymer Degradation Kinetics New Polymers and New Applications Symposium, Pittsburgh, Pennsylvania

J. H. Flynn

November 13, 1980

Role of Thermal Analysis in the Lifetime Prediction of Polymers

Second European Symposium on Thermal Analysis, Aberdeen, Scotland

J. H. Flynn

September 3, 1981

Thermogravimetric Analysis Kinetics

Symposium on Instrumental and Physical Characterization of Macromolecules of the Macromolecular

Secretariat, Atlanta, Georgia

J. H. Flynn

April 2, 1981

Dynamic Light Scattering From Dilute Polymer Solutions

University of California, Los Angeles, California

C. C. Han January 14, 1981

Dynamic Light Scattering From Dilute Polymer Solutions in the Non-Asymptotic q-Region

University of Washington, Seattle, Washington

C. C. Han January 19, 1981

Dynamic Light Scattering of Polymer Solutions in Dilute Region

Joint U.S. -France Symposium on Small Angle Neutron and X-Ray Scattering, Strasbourg, France

C. C. Han September 23, 1980

Dynamic Light Scattering of Polymer Solutions in the Non-Asymptotic q-Region

State University of New York, Stony Brook, New York

C. C. Han March 6, 1981

56
Effects of Excluded Volume and Pre-Averaging Oseen Tensor for Dilute Polymer Solutions by Dynamic

Light Scattering

University of Michigan, Ann Arbor, Michigan

C. C. Han April 7, 1981

Small Angle Neutron Scattering on Elastomer Networks

Gordon Research Conference, New London, New Hampshire

C. C. Han July 14, 1981

Current Status of the Ceramometal Restoration

National Naval Medical Center, Bethesda, Maryland

R. W. Hinman

April 1 , 1981

Factors Influencing Selection of Fixed Partial Denture Alloys, Part I Annual Meeting of the American Association of Dental Schools, Chicago, Illinois

R. W. Hinman

March 15, 1981

Current Concepts in Meta-Porcelain Systems

University of Texas, San Antonio, Texas

R. W. Hinman and J. A. Tesk

November 14, 1980

Fracture Behavior of Brittle Materials

Workshop on Applied Rheology for Industrial Chemists, Kent State University, Kent, Ohio

D. L. Hunston

June 19, 1981

General Rheology and Its Applications in Adhesion

Workshop on Adhesion and Adhesives, Kent State University, Kent, Ohio

D. L. Hunston

June 8, 1981

Loading Rate and Temperature Effects in the Failure of Adhesives and Composites

Seventh SAMPE Symposium on Advanced Composites, Palo Alto, California

D. L. Hunston January 16, 1981

Review of NBS and NRL Programs on Adhesion

Navy, Army, Air Force, and NASA Workshop on Adhesion, Dayton, Ohio

D. L. Hunston

April 24, 1981

The Use of "Toughened" Polymers in Structural Adhesives and Composites

Martin Marietta Laboratories, Baltimore, Maryland

D. L. Hunston and J. L. Rushford

May 29, 1981

Fracture Toughness of the Polymers Used in Adhesive Bonding and Composites

D. L. Hunston, J. L. Rushford, J. L. Bitner, W. D. Bascom, and R. J. Moretton American Chemical Society, New York, New York

August 24, 1981

Fluid Flow Problems and the Use of Polymeric Additives

Workshop on Applied Rheology for the Inudstrial Chemist, Kent State University, Kent, Ohio

D. L. Hunston and R. Y. Ting June 18, 1981

Elastic Strain Energy Functions

Illinois Institute of Technology, Chicago, Illinois

E. A. Kearsley

May 14, 1981

Measuring Elastic Strain Energies

Catholic University, Washington, D.C.

E. A. Kearsley

April 9, 1981

57
Strain Energy Functions of the Val ani s-Landel Type

Jet Propulsion Laboratory, Pasadena, California

E. A. Kearsley

November 17, 1980

The Diversity of the Habits of Polyethylene Crystals Grown From Solution

Cornell University, Ithaca, New York

F. A. Khoury

October 23, 1980

The Morphology of Uncrossl inked Polyethylene

Workshop on the Morphology of Polyethylene Power Cable Insulation, Gaithersburg, Maryland

F. A. Khoury

March 3, 1981

Deformation and Failure Behavior of Ultra High Molecular Weight Polyethylene

University of Toronto, Toronto, Canada

G. B. McKenna

March 16, 1981

Failure Behavior of Polymeric Materials

Ecole Polytechnique de Montreal, Montreal, Canada

G. B. McKenna

March 12, 1981

Mechanical Durability of Candidate Elastomers for Blood Pump Applications

Toronto Division of the Canadian Society for Biomaterials, Toronto, Canada

G. B. McKenna

March 16, 1981

Adsorption of Benzoic Acid on Hydroxyapatite: Effect of Solvent and Hydrogen Bonding

International Association for Dental Research, Chicago, Illinois

D. N. Misra

March 19, 1981

Copper-Free Amalgams: Dimensional Changes After 4.5 Years International Association for Dental Research, Chicago, Illinois

G. C. Paffenbarger

March 21 , 1981

Dr. Fusayama's Books on Some New Departures in Operative Dentistry

American College of Dentists, New York, New York

G. C. Paffenbarger

September 9, 1981

Linear Dimensional Change for Zinc and Non-Zinc Containing Amalgams During Storage in Air at 60,

37, and 23 °C International Association for Dental Research, Chicago, Illinois

G. C. Paffenbarger

June 6, 1980

Materials Used in Dental Health Therapy

University of Virginia, Charlottesville, Virginia

G. C. Paffenbarger

April 27, 1981

Fracture Mechanics and Fracture Control Design

American University, Cairo, Egypt

E. Passaglia

April 8, 1981

The National Cost of Corrosion and How its Magnitude is Measured

National Research Center, Cairo, Egypt

E. Passaglia

April 5, 1981

Physical Testing of Polymers for Use in Circulatory Assist Devices

Fourth Annual Contractors Meeting, Bethesda, Maryland

R. W. Penn December 3, 1980

58
Mechanical Properties and Orientation in Polymers

University of Leeds, Leeds, England

A. Peterlin

April 7, 1981

Brownian Motion, Polymer Adsorption, and Steady-State Enzyme Kinetics

California Institute of Technology, Pasadena, California

R. J. Rubin

March 10, 1981

Brownian Motion, Polymer Adsorption, and Steady-State Enzyme Kinetics

Stanford University, Palo Alto, California

R. J. Rubin

March 13, 1981

Effect of Solution Surfaces on Polymer Configurations

University of Groningen, Groningen, Netherlands

R. J. Rubin June 24, 1981

Polymer Configurations and Boundaries

NBS Center for Applied Mathematics Colloquium on Mathematical Modeling in Science and Engineering,

Gai thersburg , Maryland

R. J. Rubin

October 29, 1980

Random Walks on Lattices: The Problem of Visits to a Set of Points Revisited

Twente University of Technology, Enschede, Netherlands

R. J. Rubin

June 17, 1981

Transport of Radon in Porous Materials

Lawrence Berkeley Laboratory, Berkeley, California

R. J. Rubin

February 11, 1 981

Achieving Excellence With Modern Dental Materials

Kootenai Study Club, Libby, Montana

N. W. Rupp June 26, 1980

Composites and Amalgams

Mid-Oregon Study Club, Bend, Oregon

N. W. Rupp

May 1 , 1981

Cutting Tooth Tissues, Pulp Protection, and Microleakage

Georgetown University Dental School, Washington, D.C.

N. W. Rupp

February 26, 1981

Dental Amalgam

U.S. Navy Dental Center, Bethesda, Maryland

N. W. Rupp

March 30, 1981

Indirect Restorative Materials

Veterans Administration Hospital, Washington, D.C.

N. W. Rupp

March 30, 1981

Manipulation of Dental Materials

Veterans Administration Hospital, Washington, D.C.

N. W. Rupp

February 5, 1981

Materials for Indirect Restorative Dentistry

Navy Dental School, Bethesda, Maryland

N. W. Rupp

January 12, 1981

59
Materials for Removable Prosthodonti cs Veterans Administration Hospital, Washington, D.C.

N. W. Rupp

November 6, 1980

Materials for the Laboratory Technician

Veterans Administration Hospital, Washington, D.C.

N. W. Rupp

April 28, 1981

Modifications in Cavity Preparation Using Acid Etch Techniques

American Dental Association Annual Scientific Session, New Orleans, Louisiana

N. W. Rupp

October 14, 1980

New Developments in Amalgam and Composites

Montgomery County Study Club, Gaithersburg, Maryland

N. W. Rupp

November 20, 1980

New Developments in Composites

Dental Study Club, Washington, D.C.

N. W. Rupp

October 27, 1980

New Developments in Restorative Dentistry

Navy Dental School, Bethesda, Maryland

N. W. Rupp

October 23, 1980

Prosthodontic Materials: Selection and Use of Amalgam and Composites

Temple University, Philadelphia, Pennsylvania

N. W. Rupp

January 7, 1981

Porcelain-to-Metal Restoration and Impression and Die Materials

D.C. Progress Study Club, Washington, D.C.

N. W. Rupp

January 26, 1981

Recent Developments in Dental Materials

Dentsply International Inc., York, Pennsylvania

N. W. Rupp

July 23, 1980

Restorations of the Future Academy of Gold Foil Operators, New Orleans, Louisiana

N. W. Rupp

October 10, 1980

Selection and Manipulation of Dental Materials

Wilford Hall Dental Center, San Antonio, Texas

N. W. Rupp

August 7, 1980

Selection and Use of Dental Materials

Eg! in Air Force Base, Florida

N. W. Rupp

September 23, 1980

Selection and Use of Dental Materials

Southern Maryland Dental Society, Silver Spring, Maryland

N. W. Rupp

December 1, 1980

Selection and Use of Dental Materials

Barksdale Air Force Base, Shreveport, Louisiana

N. W. Rupp

February 24, 1981

60
Selection and Use of Dental Materials

Sheppard Air Force Base, Wichita Falls, Texas

N. W. Rupp

March 10, 1981

The Selection and Use of Dental Materials

St. Louis Dental Society, St. Louis, Missouri

N. W. Rupp

April 6, 1981

Selection and Use of Dental Materials

Offutt Air Force Base, Omaha, Nebraska

N. W. Rupp

May 20, 1981

Selection and Use of Dental Materials for the General Dentist

Oregon Study Club, McMinnville, Oregon

N. W. Rupp

May 4, 1981

The Selection of Composite Restorative Materials and Their Proper Use Georgetown University Dental School, Washington, D.C.

N. W. Rupp

April 2, 1981

Selection of Materials and Handling to Prevent Microleakage

Georgetown University Dental School, Washington, D.C.

N. W. Rupp

March 26, 1981

Selection of Prosthodontic Materials

Georgetown University Dental School, Washington, D.C.

N. W. Rupp

March 12, 1981

A Mean Field Theory of Polymer Solutions

International Symposium on Phase Transitions in Polymers, Cleveland, Ohio

I. C. Sanchez

June 11, 1 980

Equation of State Theories of Low and High Molecular Weight Liquid Mixtures

Exxon Corporate Research Laboratories , Linden, New Jersey

I. C. Sanchez

July 7, 1.981

Equation of State Theories of Polymer Blends

Centre de Recherches sur les Macromolecules, Strasbourg, France

I. C. Sanchez

October 23, 1980

Equation of State Theories of Polymer Blends

University of Texas, Austin, Texas

I. C. Sanchez

November 25, 1980

Equation of State Theory of Polymer Blends

Center of Molecular and Macromolecular Studies, Lodz, Poland

I. C. Sanchez

October 28, 1980

Molecular Origins of LCST Behavior in Polymer Solutions

CEN de Saclay, Gif-sur-Yvette, France

I. C. Sanchez

October 21 , 1 980

Polymer Collapse Transitions

Institute of Polymer Chemistry, Zabrze, Poland

I. C. Sanchez

October 27, 1980

61
Polymer Collapse Transitions

Institute of Fundamental Technological Research, Warsaw, Poland

I. C. Sanchez

October 30, 1980

Polymer/Polymer Interactions in the Dilute Regime

American Physical Society, Phoenix, Arizona

I. C. Sanchez

March 16, 1981

Statistical Thermodynamics of Fluid Mixtures

Ecole Nationale Superi'eure des Mines, Paris, France

I. C. Sanchez

October 20, 1980

Surface Thermodynamics of Liquid Polymers: Theory

International Symposium on Physicochemical Aspects of Polymer Surfaces, New York, New York

I. C. Sanchez

August 23, 1981

Theory of Interfacial Tension in Polymer Mixtures

McGill University, Montreal, Canada

I. C. Sanchez

December 4, 1980

Diffusion and Transport in Polymers

University of North Carolina, Raleigh, North Carolina

L. E. Smith

Apri 11,1 981

Models for the Diffusion in Polyolefins

New York Academy of Sciences, New York, New York

L. E. Smith

May 27, 1981

A Planar Ca-P04 Sheet Structure: CaBrH 2 P0 4 *4H 2 0 International Association for Dental Research, Chicago, Illinois

S. Takagi

March 20, 1981

Compatibility of Dental Porcelains and Alloys

Johnson and Johnson Research Laboratories , East Windsor, New Jersey

J. A. Tesk

May 1 1 , 1981

Consideration of Some Factors Influencing Compatibility of Dental Porcelains and Alloys

Fourth Annual Meeting of the International Precious Metals Institute, Toronto, Canada

J. A. Tesk, R. P. Whitlock, G. E. 0. Widera, A. D. Holmes, and E. E. Parry June 8, 1980

Applications of High Resolution 13 C NMR Techniques to Polymers

Akron University, Akron, Ohio

D. L. VanderHart

October 3, 1980

Applications of High Resolution Solid-State 13 C NMR in Polymers

Allied Chemical Corporation, Morristown, New Jersey

D. L. VanderHart

November 20, 1980

13 C NMR in Oriented Polymeric Solids

Twenty-Third Rocky Mountain Conference for Applied Spectroscopy, Denver, Colorado

D. L. VanderHart

August 3, 1981

Expectations for Resolution in Solid-State 13 C NMR of Polymers

Bell Laboratories, Murray Hill, New Jersey

D. L. VanderHart

November 21 , 1 980

62
Inferences About Molecular Motion From Proton-Decoupled 13 C NMR Spectra of Polymers

American Chemical Society, New York, New York

D. L. VanderHart

August 25, 1981

Resolution in Solid-State 13 C NMR of Polymers

Monsanto Chemical Company, St. Louis, Missouri

D. L. VanderHart

December 8, 1980

Wear of Dental Composites

U.S. Public Health Service Hospital Seminar, San Francisco, California

W. L. Wu January 26, 1981

Some Aspects of the BKZ Elastic Fluid Theory

Catholic University, Washington, D.C.

L. J. Zapas

March 26, 1981

Seminars for Staff and Guests

The Chemistry and Structure of Guayule Rubber

Donald McIntyre

University of Akron, Akron, Ohio

June 3, 1980

Consideration of Some Factors Influencing Compatibility of Dental Porcelains and Alloys

John A. Tesk

National Bureau of Standards, Washington, D.C. June 30, 1980

Electron Beam Probing of Charge Distributions in Polymer Films

David W. Tong

General Electric Company, Schenectady, New York

July 10, 1980

Dielectric Behavior of Vinyl idene FI uoride-Tetrafl uoroethyl ene Copolymers

Naokazu Koizumi

Kyoto University, Kyoto, Japan

September 3, 1980

Simulation of Polymer Dynamics

Marshall Fixman

Colorado State University, Fort Collins, Colorado

October 6, 1980

Non-Linear Viscoelasticity of Polymers and the Fracture Behavior by Finite Element Analysis

Shiro Matsuoka

Bell Laboratories , Murray Hill, New Jersey

October 6, 1980

Chemical Kinetics in the Hydrolytic Degradation of Polyester Based Polyurethanes

Daniel W. Brown

National Bureau of Standards, Washington, D.C. October 8, 1980

High Modulus/High Strength Organic Fibers: Spinning and Mechanical Properties

W. Bruce Black

Monsanto Textiles Company, Pensacola, Florida

October 29, 1980

Influence of Internal Structure on Small Deformation Properties of Crystalline Polymers

James Sefaris

University of Washington, Seattle, Washington

October 29, 1980

The Role of Chemical Bonding in the Adhesion of Polymers

Alan N. Gent

University of Akron, Akron, Ohio

October 31 , 1 980

63
Crystallization Kinetics of ci

Polyisoprene at High Pressures

Eddy N. Dalai

University of Utah, Salt Lake City, Utah

November 6, 1980

Healing of the Polymer-Polymer Interface by Reptational Motion

Stephen Prager

University of Minnesota, Minneapolis, Minnesota

November 7, 1980

Frequency Dependence of Remanent Polarization and the Correlation of Piezoelectric Coefficients

With Remanant Polarization in PVDF

J. Charles Hicks

Naval Ocean Systems Center, San Diego, California

November 10, 1980

FTIR Characterization of Conformational Changes in Amorphous Poly(Ethyl ene Terephthalate) During

Volume Recovery

Robert S. Moore

Eastman Kodak Company, Rochester, New York

November 13, 1980

Light and Neutron Scattering Studies of Concentrated Polymer Solutions

Jeffrey T. Koberstein

Princeton University, Princeton, New Jersey

November 14, 1980

New Substituted Polyethers and Polysulfides via Ring Opening Polymerization

David Tirrell

Carnegie-Mel Ion University, Pittsburgh, Pennsylvania

November 17, 1980

Fracture Mechanics of Plastic Products

Michael D. Taylor

Manchester Polytechnic, Manchester, England

November 18, 1980

Polymer Compatibility and Phase Transitions

Ludwik Leibler

Centre de Recherches sur les Macromolecules, Strasbourg, France November 21 , 1 980

Fluid Phase Equilibria

Jean-Louis Guillevic

Ecole Nationale Superieure des Mines de Paris, Paris, France November 24, 1980

Dependence of Crystalline Morphology of Polyethylene Fractions on Molecular Weight and

Crystallization Temperature

Ingrid Voigt-Martin

Johannes-Gutenberg-Uni versitat, Mainz, West Germany

November 25, 1980

Fluorescence Studies of Polymer Conformation and Chain Dynamics

Mitchell A. Winnik

University of Toronto, Toronto, Canada

December 11, 1 980

Applications of Finite Element Modeling in Dentistry

Otto Widera

University of Illinois, Chicago, Illinois

December 15, 1980

Irreversible Deformation Processes in Amorphous Polymers

Eric Baer

Case Western Reserve University, Cleveland, Ohio

December 30, 1980

64
Reversible Crystal! ization and the Thermodynamics of Piezoelectricity in PVDF Philip L. Taylor

Case Western Reserve University, Cleveland, Ohio

January 8, 1981

Some Artifacts and Experimental Constraints in SANS Studies of Polymers

George D. Wignall

Oak Ridge National Laboratory, Oak Ridge, Tennessee January 26, 1981

Structural Aspects of Segmented Polyurethanes and Correlations With Mechanical Behavior

Garth Wilkes

Virginia Polytechnic Institute and State University, Blacksburg, Virginia

January 29, 1981

Miscible Polymer Blends

Donald Paul University of Texas, Austin, Texas February 6, 1981

The Role of Mechanical Stress in Polymer Networks in Equilibrium and in Transport

Alexander Silberberg

Weizmann Institute of Science, Rehovot, Israel

February 26, 1981

Block Copolymers as Surfactants Between Immiscible Solvents

Robert Cantor

College de France, Paris, France March 3, 1981

Global and Local Structure Function in a Self-Repelling Chain Polymer

Thomas Witten

University of Michigan, Ann Arbor, Michigan

March 5, 1981

Composite Restorative Materials

Robert Denyer

Imperial Chemical Industries, Ltd., Macclesfield, England

March 23, 1981

Viscosity of Semi-Dilute Polymer Solutions

Mireille Adam

CEN de Saclay, Gi f-sur-Yvette , France March 25, 1981

New Aspects of the Microhardness of Polyethylene Relating to Texture and Morphology

Francisco BaltS Calleja

Instituto de Estructura de la Materia, Serrano, Spain

March 26, 1981

Phase Transition and Morphology in PVDF

B. Servet

Thomson-CSF, Orsay, France March 26, 1981

Molecular Orientation and Chain Relaxation in Polystyrene Stretched Above Tg

Lucien Monnerie

Ecole Superieure de Physique de Chimie Industrielles de Paris, Paris, France March 27, 1981

High Pressure Phase Equilibria of Polyethylene/Ethylene Mixtures

Dominic Richon

Ecole Nationale Superieure des Mines, Paris, France

March 27, 1981

The Morphology of Polyethylene Crystallized Under the Influence of Flow

David Grubb

Cornell University, Ithaca, New York

March 30, 1981

65
Fundamental Processes in the Photo-Oxidation of Polyolefins

James Gui 1 let

Lash Miller Chemical Laboratories , Toronto, Canada

March 30, 1981

The Structure of Aromatic Polyesters

Ivan H. Hall

Purdue University, West Lafayette, Indiana

March 30, 1981

The Diffusion of Linear, Branched, and Cyclic Polymers in Concentrated Solutions and Melts of a Linear Polymer

Jacob Klein

University of Cambridge, Cambridge, England

April 3, 1981

Orientational Distribution and Molecular Motion in Oriented Deuterated Polyethylene From 2 H-NMR Experiments

Hans Sillescu

University of Mainz, Mainz, West Germany

April 3, 1981

Recent Developments in Vibrational Spectroscopy of Polymethylene Molecules

Guiseppe Zerbi

Institute of Macromolecular Chemistry, Milan, Italy

April 9, 1981

Phase Behavior of Polystyrene (I) Poly(2, 6-Dimethyl -1 ,4-Phenylene Oxide) (II) and Their Brominated

Deri vati ves Roger P. Kambour

General Electric Company, Schenectady, New York

April 17, 1981

Morphological and Mechanical Studies of Oriented Block Copolymers by SAXS, SANS, and EM Georges Hadziioannou

University of Massachusetts, Amherst, Massachusetts

April 22, 1981

NMR Spatial Mapping for Medical Applications and Nondestructive Evaluation

Jerome I. Kaplan

Indiana University, Indianapolis, Indiana

April 23, 1981

Ion Distribution Around a Polyelectrolyte by the Monte Carlo Method

Bruno H. Zimm

University of California, San Diego, California

April 29, 1981

Micromechanics, Microstructure, and Fracture of Crazes

Edward J. Kraemer

Cornell University, Ithaca, New York

May 1 , 1981

Mechanical Properties of Polymer Liquid Crystals Masao Horio

Kyoto University, Kyoto, Japan

May 15, 1981

The Physical Properties of Acrylic Blends

Robert Kusy

University of North Carolina, Chapel Hill, North Carolina

May 27, 1981

On the Optical and Mechanical Behavior of Viscoelastic Fluids in Shear

Bernard D. Coleman

Carnegie-Mel Ion University, Pittsburgh, Pennsylvania

June 3, 1981

66
Rheology of Rod-Like Liquid Crystal Polymers

Kurt Wissbrun

Celanese Research, Summit, New Jersey

June 8, 1981

Crystal Structure of a "Simple" Polymer PVF 2 Jerome B. Lando

Case Western Reserve University, Cleveland, Ohio June 9, 1981

Structure Determination of Crosspolymeri zed Pol y ( 1 ,11 -Dodecadiyne)

Jerome B. Lando

Case Western Reserve University, Cleveland, Ohio

June 9, 1981

Light Scattering and Electro-Optics of Biomembrane

Hyuk Yu University of Wisconsin, Madison, Wisconsin

June 12, 1981

The Feasibility of Screen Film Combinations in Intra-Oral Dental Radiography

Tomohero Okano

National Institute for Dental Research, Bethesda, Maryland

June 16, 1981

Activities of the Australian Dental Standards Laboratory and Research on Bonding to Teeth

Derrick Beech

Australian Dental Standards Laboratory, Victoria, Australia

June 17, 1981

Relaxation of Stresses in Crazes at Cracked Tips and Rate of Craze Extension

El io Passagl ia National Bureau of Standards, Washington, D.C. June 18, 1981

Motion of Spheres in Polymer Solutions

Carlos Tiu

Auburn University, Auburn, Alabama

July 6, 1981

"Absolute" Cross-Link Density Determinations

Emory Menefee

U.S. Dept, of Agriculture, Berkeley, California

July 7, 1981

Applications of Finite Element Modeling in Dentistry

Otto Widera

University of Illinois, Chicago, Illinois

July 7, 1981

Behavior of Ferroelectric Ceramics and PVF a Polymers Under Shock Loading

Francois Bauer

Institut Franco-Al lemand de Recherches de Saint-Louis, Saint-Louis, France July 8, 1981

Molecular Weight Distribution From Stretch Relaxation: A New Algorithm for Relaxation

Di stri bution

Emory Menefee

U.S. Dept, of Agriculture, Berkeley, California

July 8, 1981

NMR Study of Dissolution of Highly Insoluble Polysaccharides, Cellulose and Chitin

Marc Vincendon

Centre D'Etudes Nucleaires de Grenoble, Grenoble, France July 10, 1981

A Visit of Research Institutes and Universities in Four Chinese Cities and Sightseeing to Sites

Less-Frequented by Tourists"

Shu-Sing Chang

National Bureau of Standards, Washington, D.C. July 14, 1981

67
Integral Equation Method for the Evaluation of the Entropy of Polymer Chains Confined to Very

Narrow Cyl inders--Appl ication to the Intermediate Phase of Polyethylene

Richard Priest

Naval Research Laboratory, Washington, D.C. July 24, 1981

The Lowest Excited Electronic State in Trans-Polyacetylene

Eugene A. Imhoff

Cornell University, Ithaca, New York

August 4, 1981

Structure and Morphology of Nascent Polyethylene Obtained by Ziegler-Natta Catalysts

Antonio Munoz-Escal ona Ministerio de Sanidad y Asistencia Social, Caracas, Venezuela

September 14, 1981

Technical and Professional Committee Participation and Leadership

Academy of Operative Dentistry

N. W. Rupp

Councilor

American Academy of Gold Foil Operators

N. W. Rupp

Councilor

American Association of Dental Research/International Association of Dental Research

G. M. Brauer

Session Chairman

American Association of Dental Research/International Association of Dental Research

W. E. Brown

Member: Biological Mineralization Research Award Committee

Mineralized Tissue Group, Chairman

Mineralized Tissue Group, Councilor

American Association of Dental Research/ International Association of Dental Research

J. M. Cassel

Washington Section Delegate

American Association of Dental Research/International Association of Dental Research

J. A. Tesk

Member: Dental Materials Group

Executive Committee

American Chemical Society

J. M. Antonucci

Member: Board of Managers

Calendar Editor for Capital Chemists

American Chemical Society

G. M. Brauer

Member: Meetings and Expositions Committee

Special Events Committee, Chairman

American College of Dentists

N. W. Rupp

Member: Award Committee re Robert J. Nelsen, Chairman

American Dental Association Acceptance Program

J. A. Tesk

Member: Porcelain Metal Systems

American Institute of Mining, Metallurgical, and Petroleum Engineers

R. M. Waterstrat

Member: Committee on Alloy Phases

American Institute of Physics

R. K. Eby

Chapter Editor, 1981 Physics Handbook

68
American Institute of Physics

E. A. Kearsley

Member: Committee for Public Policy

American National Standards Institute/MDl 56, Dental Materials and Devices

R. L. Bowen

Member: Toxicity Tests, Secretary

American National Standards Institute/MDl 56, Dental Materials and Devices

G. M. Brauer

Member: Denture Resins, Chairman

American National Standards Institute/MDl 56, Dental Materials and Devices

J. M. Cassel

Member: C054, Medical Devices Standards Management Board, Executive Committee

American National Standards Institute/MD156, Dental Materials and Devices

N. W. Rupp

Member: Alloy for Dental Amalgams, Chairman

Amalgamators for Dental Amalgams, Chairman

Dispensers for Mercury and Alloys for Dental Amalgams, Chairman

Mercury for Amalgams, Chairman

Pit and Fissure Sealants

Restorative Materials Group, Chairman

American National Standards Institute/MDl 56, Dental Materials and Devices

J. A. Tesk

Member: Base Metal Alloys

Dental Implants, Secretary

Dental Materials, Instruments, and Equipment, Chairman

Porcelain/Alloy Systems

USA TAG for ISO TC106, Chairman

American Physical Society/Division of High Polymer Physics

F. A. Khoury

Member: Executive Committee

Committee on History of DMPP

American Physical Society/Division of High Polymer Physics

I. C. Sanchez

Member: Executive Committee

ASTM/Committee on Research and Technical Planning

E. Passaglia

Member: Subcommittee on Research, Chairman

ASTM D-2 Petroleum Products and Lubricants

L. J. Zapas

Member: SC. 07 Flow Properties

SC.07A Newtonian Viscometry

ASTM D-9 Electrical Insulating Materials

W. P. Harris

Member: SC. 05 Ceramic Products

SC. 12 Electrical Tests

SC. 16 Hookup Wire Insulation

SC. 17 Thermal Capabilities

SC. 90 Executive Committee

SC. 93 Education, Research, and Symposia

SC. 94 Nomenclature, Significance, and Statistics

SC. 95 Liaison

ASTM D-ll Rubber and Rubber-Like Materials

E. A. Kearsley

Member

ASTM D-ll Rubber and Rubber-Like Materials

G. B. McKenna Member

69
ASTM D-20 Plastics

R. K. Eby, Chairman-Elect

Member: SC. 01 Executive Subcommittee

ASTM D-20 Plastics

J. D. Barnes

Member: SC. 12 Olefin Plastics

SC. 13 Statistics

SC. 19 Sheeting

SC. 70 Analytical Methods

WG.07 Gas Permeability

ASTM D-20 Plastics

H. L. Wagner

Member: SC. 70 Analytical Methods

WG.04 Liquid Size Exclusion Chromatography

WG.05 Molecular Weight Parameters, Chairman

ASTM D- 27 Electrical Insulating Liquids and Gases

W. P. Harris

Member

ASTM E-9 Fatigue

G. B. McKenna Member

ASTM E-9 Fatigue

R. W. Penn Member

ASTM E- 37 Thermal Measurements

S. S. Chang

Member: SC. 01 Test Methods and Recommended Practices

SC. 05 Thermophysical Properties

ASTM E- 37 Thermal Measurements

J. H. Flynn

Member: SC. 03 Nomenclature and Definitions, Chairman

SC. 90 Executive Subcommittee

ASTM E-45 Geothermal Energy and Resources

E. A. Kearsley

Member: SC. 02 Materials

ASTM F-2 Flexible Barrier Materials

J. D. Barnes

Member: SC. 30 Test Methods, Chairman

SC. 93 Statistical Matters, Chairman

ASTM F-4 Medical and Surgical Materials and Devices

G. M. Brauer

Member: SC. 20 Resources

WG.01 Polymeric Materials, Chairman

ASTM F-4 Medical and Surgical Materials and Devices

J. M. Cassel

Member: SC. 20 Resources

ASTM F-4 Medical and Surgical Materials and Devices

R. K. Eby

Member

ASTM F-4 Medical and Surgical Materials and Devices

G. B. McKenna Member

Biomaterials (Journal)

G. C. Paffenbarger

Editorial Consultant

70
Biomaterial s Society

J. A. Tesk

Member: Finance Committee

Biomedical Research Support Grant

R. L. Bowen

Member: 1980-81 Review Committee

Case Western Reserve University Materials Research Laboratory Advisory Board

R. K. Eby

Member

Chemical Society of Washington

G. M. Brauer

Chairman, Membership Activities

Eleventh NATAS Conference

J. H. Flynn

Symposium on Kinetics of Chemical and Physical Processes, Chairman

Ferroelectrics Journal

M. G. Broadhurst

Guest Editor of Special Issue on PVDF

Fifth International Meeting on Ferroelectrics

M. G. Broadhurst

Member: U.S. Committee

Polymer Session Chairman

Geis Foundation for the Advancement of Dentistry

G. C. Paffenbarger

President

Member: Award Committee for Dental Editorial

Award Committee for Oral Surgery

Award Committee for Poreodontology

Government Interagency Panel on Adhesive Bonding Research

D. L. Flunston Member

International Confederation for Thermal Analysis

J. H. Flynn

Member: Nomenclature Committee

Working Party on Symbols

International Council on Alloy Phase Diagrams

R. M. Waterstrat

Member

International Electrotechnical Commission/TC046, Cables, Wires and Waveguides for

Telecommunication Equipment

L. J. Zapas

Member: WG.03 Measuring Methods of Polyethylene

International Standards 0rganization/TC106, Dental Materials and Devices

G. M. Brauer

Member: Task Force on Color Stability

International Standards 0rganization/TC106, Dental Materials and Devices

N. W. Rupp

Member: Restorative Materials

WG.01 U.S. Delegation, Chairman

TG7 Alloys for Dental Amalgams, Chairman

WG.06 Amalgamation Devices and Accessories, Chairman

International Standards Organization/TCI 06, Dental Materials and Devices

J. A. Tesk

USA TAG, Chairman

71
International Standards 0rganizations/TC150, USTAG for Implants for Surgery

J. M. Cassel

Chairman

International Standards Organization/TCI 50, USTAG for Cardiovascular Implants

J. M. Cassel

NBS Representative

National Bureau of Standards Advisory Panel for Tariffs on Electron Microscopes Under

Florence Agreement

F. A. Khoury

Member

National Center for Small Angle Scattering

C. C. Han Member: Users Committee

National Institute of Dental Research

R. L. Bowen

Member: Long Range Research Planning and State-of-the-Science on Composites, Consultant

Panel on Restorative Materials Program

Review Committee for ADA

National Research Council Panel on Polymer Science and Engineering

R. K. Eby

Member

North American Thermal Analysis Society

J. H. Flynn

Editor: NATAS Notes

Member: Awards Committee

Executive Committee

Publications Committee, Chairman

Ohio Dental Association

G. C. Paffenbarger

Member: Callahan Memorial Committee

Polymer Degradation and Stability (Journal)

J. H. Flynn

Editorial Board Member

Society of Plastics Engineers

R. K. Eby

Member: Selection Committee for SPE International Award for Research, Chairman

Society of Plastics Engineers

G. B. McKenna

Member: Technical Publications Committee

Society of Rheology

D. L. Hunston

Member: Committee on Education, Chairman

Society of Rheology

E. A. Kearsley

Member: Executive Committee

Society of Rheology

G. B. McKenna

Member: Committee on Education

Local Arrangements 1981 Spring Meeting, Chairman

U.S. Air Force

N. W. Rupp

National Civilian Consultant to the Surgeon General

University of Massachusetts Advisory Board of Polymer Research Institute

R. K. Eby

Member

72
University of Virginia, Department of Materials Science

G. C. Paffenbarger

Consultant

Washington Area MINC Users Group

J. D. Barnes

Chai rman

Publ ications

Interpretation of Dynamic Scattering From Polymer Solutions

A. Z. Akcasu, M. Benmouna, and C. C. Han Polymer, 21_, 866 (1980)

The Accelerative and Adhesive Bonding Capabilities of Surface-Active Accelerators

J. M. Antonucci, D. N. Misra, and R. J. Peckoo

J. Dent. Res. (in press)

New Monomers for Use in Dentistry

J. M. Antonucci

Biomedical and Dental Applications of Polymers, C. G. Gebelein and F. F. Koblitz, Eds., p. 357

(1981)

Slow-Acting Amine Polymerization Accelerators. Para-Dimethylaminobenzoic Acid and Its Ethyl Ester

J. M. Antonucci, R. J. Peckoo, C. Schruhl , and E. E. Toth

J. Dent. Res., 60, 1325 (1981)

An Amine Accelerator for Colorfree Curing of Cold-Curing Methyl Methacrylate Denture Systems

H. Argentar, J. A. Tesk, and E. E. Parry

J. Amer. Dent. Assoc., 1 02 , 664 (1981)

A Theory of the Effects of Pressure on Finite Elastic Shear

B. Bernstein and E. A. Kearsley

Rheology , G. Arkarita, G. Marrucci, and L. Nicholais, Eds., p. 305 (1980)

Stability and Cold Drawing of Viscoelastic Bars

B. Bernstein and L. J. Zapas

J. Rheology, 2!5, 83 (1981 )

Viscoelastic Fracture of Structural Adhesives

J. L. Bitner, J. L. Rushford, W. S. Rose, D. L. Hunston, and C. K. Riew

J. Adhesion (in press)

Adhesive Bonding of Various Materials to Hard Tooth Tissues. XXIII. Isotonic Monomer

Formulations

R. L. Bowen

J. Dent. Res. , 6CU 901 (1981 )

Adhesive Bonding of Various Materials to Hard Tooth Tissues. XXIV. Recent Developments in Adhesive Resin Formulations for Dentin

R. L. Bowen Proceedings of International Congress of Implantology and Biomaterials in Stomatology, p. 66

(1980)

Initiator-Accelerator Systems for Acrylic Resins and Composites

G. M. Brauer

Biomedical and Dental Applications of Polymers, C. G. Gebelein and F. F. Koblitz, Eds., p. 395

(1981)

Marginal Adaptation of BIS-GMA Based Composites Containing Various Diluents

G. M. Brauer, D. M. Dulik, H. N. Hughes, K. Dermann, and N. W. Rupp

J. Dent. Res. (in press)

4-N,N-Dialkylaminophenylethanols, Alkanoic Acids, and Esters: New Accelerators for Dental

Composites

G. M. Brauer, J. W. Stansbury, and J. M. Antonucci

J. Dent. Res. (in press)

73
High Polymer Physics

M. G. Broadhurst, S. S. Chang, G. T. Davis, E. A. DiMarzio, R. K. Eby, B. M. Fanconi

,

J. H. Flynn, C. C. Han, F. A. Khoury, H. Markovitz, J. E. McKinney, F. I. Mopsik, E. Passaglia,

I. C. Sanchez, L. E. Smith, D. L. VanderHart, and L. J. Zapas AIP 50th Anniversary Handbook (in press)

Ferroelectric Polarization in Polymers

M. G. Broadhurst and G. T. Davis

Ferroelectrics, 3Z_, 177 (1981 )

Dielectric Properties of PVDF--Low Field and High Field Phenomena and Time Effects

M. G. Broadhurst, G. T. Davis, and A. S. DeReggi

Proceedings of the Symposium on High Energy Density Capacitors and Materials (in press)

Pyroelectricity and Charge Transport in a Copolymer of Vinyl idene Fluoride and

Tetrafl uoroethylene

M. G. Broadhurst, G. T. Davis, A. S. DeReggi, S. C. Roth, and R. E. Collins

Polymer (in press)

Summary of Workshop on Morphology of Polyethylene Power Cable Insulation

M. G. Broadhurst, F. A. Khoury, A. J. Bur, G. T. Davis, and W. P. Harris

Electric Power Research Institute Report (in press)

Guest Editorial on Piezoelectric Polymers

M. G. Broadhurst, F. Micheron, and Y. Wada

Ferroelectrics (in press)

Hydrolytic Degradation of Polyester Polyurethane Foams

D. W. Brown, R. E. Lowry, and L. E. Smith

ACS Polymer Preprints, 22, 223 (1981)

Kinetics of Reaction Between Polyester Acid and Carbodi imides in Dry Polyester Diols and in a Polyester Polyurethane

D. W. Brown, R. E. Lowry, and L. E. Smith

Macromolecules, ]_4, 659 (1981 )

Thermodynamics of Apatite Crystal Growth and Dissolution

W. E. Brown and L. C. Chow

J. Crystal Growth, 53^ 31 (1981)

Crystal Chemistry of Octacalcium Phosphate

W. E. Brown, M. Mathew, and M. S. Tung

Prog. Crystal Growth, Charact. , 4, 59 (1981 )

Role of Octacalcium Phosphate in the Incorporation of Impurities Into Apatites

W. E. Brown, M. S. Tung, and L. C. Chow

Proceedings of the Second International Congress on Phosphorus Compounds, p. 59 (1981)

Resistivity and Piezoelectric Measurements on Oriented and Unoriented Thick P V

2 Films

A. J. Bur Polymer (in press)

Depolarization of Poled Polyvinyl idene Fluoride Samples With "Thick" Electrodes

A. J. Bur and A. K. Tsao Ferroelectrics (in press)

Properties and Interactions of Oral Structures and Restorative Materials

J. M. Cassel , J. A. Tesk, G. M. Brauer, J. M. Antonucci, W. Wu, J. E. McKinney, R. P. Whitlock,

and R. Hinman

NBSIR 80-2168 (1980)

A Mechanism for Incorporation of Carbonate Into Apatite

N. S. Chickerur, M. S. Tung, and W. E. Brown

Calcif. Tissue Int. , 32, 55 (1980)

Reactions of Powdered Human Enamel and Fluoride Solutions With and Without Intermediate

CaHP04 * 2 H ^0 Formation

L. C. Chow, M. K. Guo, C. C. Hsieh, and Y. C. Hong

J. Dent. Res. , 59, 1447 (1980)

74
Diffraction From Nonperiodic Structures: The Molecular Conformation of Polytetrafl uoroethyl ene (Phase II)

E. S. Clark, J. J. Weeks, and R. K. Eby

ACS Symposium Series 141, "Diffraction Methods for Structural Determination of Fibrous Polymers,"

p. 183 (1980)

Transport Properties of Annealed Drawn Low Density Polyethylene (LDPE)

F. DeCandia, R. Russo, V. Vittoria, and A. Peterlin

J. Polym. Sci., Polym. Phys. Ed., J8_, 2083 (1980)

Evaluation of Methods of Characterizing the Porosity of Porous Polymeric Implant Materials: A Review of the Current Status of Porosity Measurements

R. E. Dehl , W. H. Grant, and J. M. Cassel

NBSIR 81-2212 (February 1981)

Forward Depolarized Scattering of Semi-Dilute Solutions of Poly (a-Methyl Styrene)

M. Delsanti, C. C. Han, and H. Yu ACS Polymer Preprints, 22 , 76 (1981 )

Piezoelectric Polymer Probe for Ultrasonic Applications

A. S. DeReggi, S. C. Roth, J. M. Kenney, and S. Edelman

J. Acoust. Soc. Am., M, 853 (1981 )

Free Radicals and New End Groups Resulting From Chain Scission. I. y-Irradiation of

Polyethylene

K. L. DeVries, R. H. Smith, and B. M. Fanconi

Polymer, 2J_, 949 (1980)

Factor-Jump Thermogravimetry Applied to Polymer Degradations

B. Dickens

ACS Organic Coatings & Plastics Chemistry, 44, 670 (1981)

Factor-Jump Thermogravimetry Applied to Polymer Degradations

B. Dickens

ACS Polymer Preprints, 22^, 316 (1981)

Thermal Degradation and Oxidation of Polystyrene Studied by Factor-Jump Thermogravimetry

B. Dickens

Polym. Deg. & Stab., 2, 249 (1980)

Investigation of Epitaxy Relationships Between Ca 5 (P 04 ) 3 0H and Other Calcium Ortho-Phosphates

B. Dickens and L. W. Schroeder

J. Res. Nat. Bur. Stand., 85, 347 (1980)

Effect of Diluent Monomer on the Physical Properties of BIS-GMA-Based Composites

D. Dulik, R. Bernier, and G. M. Brauer

J. Dent. Res., 60, 983 (1981)

Observations by High Resolution 13 C NMR of Cellulose I Related to Morphology and Crystal Structure

W. L. Earl and D. L. VanderHart

Macromolecules (in press)

1980 Annual Report of the Polymer Science and Standards Division

R. K. Eby, L. E. Smith, M. G. Broadhurst, B. M. Fanconi, I. C. Sanchez, and J. M. Cassel

NBSIR 81-2263 (April 1981

)

Crystalline Polymers

R. K. Eby, A. Peterlin, F. A. Khoury, M. G. Broadhurst, and B. M. Fanconi

State of Polymer Science in the U.S. , National Academy of Sciences (in press)

Free Radicals and New End Groups Resulting From Chain Scission. II. Mechanical Degradation of

Polyethylene

B. M. Fanconi, J. P. Colson, K. L. DeVries, and R. H. Smith

Polymer (in press)

Energy Calculations of the Crystal Structure of the Low Temperature Phase (II) of Polytetrafluoroethylene

B. L. Farmer and R. K. Eby

Polymer (in press)

75
A Collection of Kinetic Data for the Diffusion of Organic Compounds in Polyolefins

J. H. Flynn

Polymer (in press)

Analysis of Thermogravimetric Kinetics--Overcoming Complications of Thermal History

J. H. Flynn

Thermal Analysis in Polymer Characterization (in press)

Role of Thermal Analysis in the Lifetime Prediction of Polymers

J. H. Flynn

Proceedings of the Second European Symposium on Thermal Analysis (in press)

Thermogravimetric Analysis Kinetics

J. H. Flynn

ACS Organic Coatings & Plastics Chemistry, 44, 657 (1981)

Thermogravimetric Analysis Kinetics

J. H. Flynn

ACS Polymer Preprints, 22_, 310 (1981)

13 C NMR in Organic Solids: Limits to Spectral Resolution and to Determination of Molecular

Motion

A. N. Garroway, D. L. VanderHart, and W. L. Earl Philos. Trans. R. Soc. London, A299 , 609 (1981 )

Adhesive Bonding of Various Materials to Hard Tooth Tissues: Tracer Study of Mordant Adsorption

on Enamel

T. E. Gills and R. L. Bowen Orthodontics : The State of the Art , H. G. Barrer, Ed., p. 163 (1981)

The Adsorption of Human Albumin and y-Globulin on Hydrophobic and Hydrophilic Surfaces

W. H. Grant and R. E. Dehl Adhesion and Absorption of Polymers , Part B, L. H. Lee, Ed., p. 827 (1980)

A Monte-Carlo Calculation of the Hydrodynamic Radius at the Theta Point-Deviations From Analytical Gaussian Behavior

C. M. Guttman, F. L. McCrackin, and C. C. Han Macromolecules (in press)

Concentration Dependence of Diffusion Coefficient of Various Molecular Weights and Temperatures

C. C. Han and A. Z. Akcasu

Polymer (in press)

Dynamic Light Scattering of Dilute Polymer Solutions in the Non-Asymptotic q-Region

C. C. Han and A. Z. Akcasu

Macromolecules (in press)

Dynamic Light Scattering of Polymer Solutions in the Intermediate Momentum Transfer Region

C. C. Han and A. Z. Akcasu

ACS Polymer Preprints, 22, 68 (1981)

On the Dynamic Structure Factor, S(q,w) of Polymers in Dilute Solution

C. C. Han and A. Z. Akcasu

Polymer (in press)

An Experimental Study of Flow-Generated Waves on an Elastic Surface

R. J. Hansen, D. L. Hunston, C. C. Ni , and M. M. Reischman

J. Sound Vibration, 6.B, 317 (1980)

Hydrodynamic Drag and Surface Deformations Generated by Liquid Flows Over Flexible Surfaces

R. J. Hansen, D. L. Hunston, C. C. Ni , M. M. Reischman, and J. W. Hoyt

Viscous Flow Drag Reduction , H. Hough, Ed., p. 439 (1980)

Viscoelastic Characterization of Structural Adhesives Via Forced Oscillation Experiments

D. L. Hunston, W. D. Bascom, E. E. Wells, J. D. Fahey, and J. L. Bitner

Proceedings of the International Conference on Adhesion and Adsorption of Polymers (1980)

Fracture of Rubber-Toughened Adhesives: Loading Rate and Temperature

D. L. Hunston, J. L. Bitner, J. L. Rushford, J. Oroshnik, and W. S. Rose Proceedings of the California Conference on Rubber-Toughened Plastics, 1_, 1 (1980)

76
Mechanical Properties of Solid Polymers as Modeled by a Simple Epoxy

D. L. Hunston, W. Carter, and J. L. Rushford

Developments in Adhesives , A. J. Kinlock, Ed. (1981)

Failure in Elastomer-Toughened Epoxies: Viscoelastic Effects

D. L. Hunston, J. L. Rushford, J. L. Bitner, J. Oroshnik, and R. S. Rose

J. Elastomers and Plastics, 12 , 133 (1980)

Effect of Molecular Parameters on the Flow Rate Dependence of Drag Reduction and Similar Phenomena

D. L. Hunston and J. L. Zakin

Viscous Flow Drag Reduction , H. Hough, Ed., p. 337 (1980)

Mechanical Degradation in Dilute Polystyrene Solutions

D. L. Hunston and J. L. Zakin

Polym. Eng. Sci., 20, 517 (1980)

The Role of Zinc in Dental Amalgams

L. B. Johnson and G. C. Paffenbarger

J. Dent. Res., 59, 1412 (1980)

Crystal Structure of Tritin (II) Hydroxide Oxide Phosphate, Sn 3 0(0H)P04 T. H. Jordan, B. Dickens, L. W. Schroeder, and W. E. Brown

Inorg. Chem. , 1_9, 2551 (1980)

A Basis for Predicting Long-Time Behavior From Short-Time Tests of Geothermal Sealants

E. A. Kearsley

Geothermal Seals , ASTM (in press)

Determining an Elastic Strain-Energy Function From Torsion and Simple Extension

E. A. Kearsley

J. Appl . Phys., 51, 4541 (1980)

Some Methods of Measurement of an Elastic Strain-Energy Function of the Valanis-Landel Type

E. A. Kearsley and L. J. Zapas

J. Rheology, 24, 483 (1980)

Deformation and Failure of Ultra High Molecular Weight Polyethylene

F. A. Khoury

Soc. Plastics Eng., 27_, 82 (1981 )

Relationship Between Morphology and Mechanical Properties of Ultra High Molecular Weight

Polyethylene

F. A. Khoury

NBSIR 81-2209 (April 1981)

Monte Carlo Studies of Polymer Chain Dynamics: Lattice Dependence

D. E. Kranbuehl and P. H. Verdier

ACS Polymer Preprints, 21_, 195 (1980)

Effects of Poling Field and Time on Pyroelectric Coefficient and Polarization Uniformity in Polyvinyl Fluoride

S. B. Lang, A. S. DeReggi, and M. G. Broadhurst

Ferroelectr ics (in press)

Lead Alkali Apatites Without Hexad Anion: The Crystal Structure of Pb 8 K2 (P0 4 ) 6 M. Mathew, W. E. Brown, M. Austin, and T. Negas

J. Solid State Chem., .35, 69 (1980)

New Struvite Analogue, MgNaP04 »7H 2 0

M. Mathew, P. Kingsbury, S. Takagi, and W. E. Brown Acta Cryst. (in press)

The Crystal Structure of Synthetic Chukhrovite, Ca 4 AlSi (S0 4 )F 13 -12H 2 0

M. Mathew, S. Takagi, K. R. Waerstad, and A. W. Frazier

Amer. Mineral., 66, 392 (1981)

Configurational Properties of Comb-Branched Polymers

F. L. McCrackin and J. Mazur Macromolecules (in press)

77
Mechanical Properties of Some Composite Biomaterials After Implantation as Bone Plates

G. B. McKenna, G. W. Bradley, H. K. Dunn, and W. 0. Statton

Biomaterials, 189 (1980)

Deformation and Failure of Ultra High Molecular Weight Polyethylene

G. B. McKenna, J. M. Crissman, and F. A. Khoury

Soc. Plastic Eng., 2]_, 84 (1981 )

Time-Dependent Failure of a Polyolefin Rubber Candidate Material for Blood Pump Applications

G. B. McKenna and R. W. Penn

J. Biomed. Matls. Res., ([4, 689 (1980)

Cyclic Loading of Carbon Black Filled Butyl Rubber

G. B. McKenna and L. J. Zapas

Rubber Chem. Technol. (in press)

The Normal Stress Response in Non-Linear Viscoelastic Material s--Some Experimental Findings

G. B. McKenna and L. J. Zapas

J. Rheology, 24, 367 (1980)

Viscoelastic Behavior of Poly(Methyl Methacrylate). Prediction of Extensional Response From Torsional Data

G. B. McKenna and L. J. Zapas

Rheology , G. Astarita, G. Marrucci, and L. Nicolais, Eds., p. 299 (1980)

Relationship Between Subsurface Damange and Wear of Dental Restorative Composites

J. E. McKinney and W. Wu

J. Dent. Res., 60, 583 (1981)

Monomol ecul ar Adsorption Isotherms

D. N. Misra

J. Coll. Inter. Sci., 77, 543 (1980)

Adsorption of N- (2-Hydroxy-3-Methacryloxypropyl )-N-Phenylglycine (NPG-GMA) on Cupric Ion-Enriched

Hydroxyapatite Surface to Improve Chemical Bonding Between Dental Resins and Teeth

D. N. Misra and R. L. Bowen Biomaterials, 2, 78 (1981)

Adsorptive Bonding to Hydroxyapatite. I. Adsorption of Anthranilic Acid--The Effect of Solvents.

Search for Surface Bonding Groups for Coupling Agents to Teeth

D. N. Misra and R. L. Bowen Biomaterials, 2, 28 (1981)

Adsorption of a Polyfunctional Surface-Active Amine Accelerator on Hydroxyapatite

D. N. Misra, R. L. Bowen, J. M. Antonucci, and W. F. Cuthrell

J. Coll Inter. Sci., 77, 143 (1980)

The Numerical Analysis of the Thermal Pulse Experiment

F. I. Mopsik and A. S. DeReggi

Proceedings of the Conference on Electrical Insulation and Dielectric Phenomenon, p. 251 (1980)

Chain Folding in Lamellar Crystals

A. Peterlin

Macromolecules, 1_3, 111 (1980)

Molecular Interpretation of the Load-Elongation Curve of Crystalline Polymers

A. Peterlin

Intern. J. Polym. Mater., 8, 285 (1980)

Empirical Relation for Diffusion of Gases in Hydrocarbon Polymers: Interpretation in Terms of

Fractional Free Volume

A. Peterlin and F. L. McCrackin

J. Polym. Sci., Polym. Phys. Ed., 19, 1003 (1981)

Apparatus for Infrared Measurement of Sorption/Desorption in Strained Polymeric Films

J. C. Phillips, A. Peterlin, and P. F. Waters

J. Polym. Sci., Polym. Phys. Ed., 19, 789 (1981)

Interfacial Tension Theory of Low and High Molecualr Weight Liquid Mixtures

C. I. Poser and I. C. Sanchez

Macromolecules, 14, 361 (1981)

78
Energy Flow and Thermal Conductivity in One-Dimensional, Harmonic, Isotopically Disordered Crystals

R. J. Rubin

Perspectives in Statistical Physics , H. J. Ravache, Ed., p. 113 (1981)

Radon Transport Through and Exhalation From Building Materials, a Review and Assessment

R. J. Rubin, R. Colle, L. I. Knab, and J. M. R. Hutchinson

NBS Technical Note 1139 (October 1980)

Random Walks on Lattices. The Problem of Visits to a Set of Points Revisited

R. J. Rubin and G. H. Weiss

J. Math. Phys. (in press)

Statistical Thermodynamics of Bulk and Surface Properties of Polymer Mixtures

I. C. Sanchez

J. Macromol . Sci.-Phys., B1

, 565 (1980)

Migration Models for Polymer Additives

I. C. Sanchez, S. S. Chang, and L. E. Smith

Polymer News, 6^, 249 (1980)

Cell Model Theory of Polymer Solutions

I. C. Sanchez and D. J. Lohse

Macromolecules, ([4, 131 (1981)

Application of Photon Correlation Spectroscopy

D. Schaefer and C. C. Han Polymer Solutions (in press)

Polymer Dynamics: When Do Scaling Laws Apply?

D. W. Schaefer and C. C. Han ACS Polymer Preprints, 22, 66 (1981 )

Raman Spectrum From a Single Crystal of SnHP 04

L. W. Schroeder, T. H. Jordan, and W. E. Brown Spectrochimica Acta, 37A , 21 (1981)

Characterizing the Interfiber Bonding of Currency Paper Pulps

J. C. Smith and E. E. Toth

NBSIR 80-2190 (1980)

Models for the Migration of Low Molecular Weight Additives in Polyolefins

L. E. Smith, S. S. Chang, G. A. Senich, F. L. McCrackin, and F. W. Wang

NBSIR 81-2264 (April 1981)

Low-Frequency Raman Study of Drawn Polyethylene

R. G. Snyder, J. R. Scherer, and A. Peterlin

Macromolecules, 14, 77 (1981)

Water Rich Hydrates. The Crystal Structure of Mg 2 KH(As04) 2 '15H 2 0 and Mg 2 KH(P0 4 ) 2 *15H 2 0

S. Takagi, W. E. Brown, and M. Mathew

Acta Cryst. (in press)

The Structure of Diammonium Tricalcium Bis(Pyrophosphate) Hexahydrate

S. Takagi, M. Mathew, and W. E. Brown

Acta Cryst., B3^, 2526 (1980)

Physical Metallurgy of Dental Casting Alloys

J. A. Tesk and R. M. Waterstrat

Encyclopedia of Materials , Science , and Engineering (in press)

Consideration of Some Factors Influencing Compatibility of Dental Porcelains and Alloys, Part II: Porcelain/Alloy Stress

J. A. Tesk, R. P. Whitlock, G. E. 0. Widera, A. Holmes, and E. E. Parry

Proceedings of the Fourth International Precious Metals Conference (1981)

Characterization of Ligand Binding Systems by Continuous Distributions of Arbitrary Shape

A. K. Thakur, P. J. Munson, D. L. Hunston, and D. Rodbark

Anal. Biochem., 1 03 , 240 (1980)

79
Influence of Molecular Packing on Solid-State 13 C Chemical Shifts: The n-Alkanes

D. L. VanderHart

J. Magn. Reson. (in press)

Resolution in 13 C NMR of Organic Solids Using High Power Proton Decoupling and Magic Angle

Sample Spinning

D. L. VanderHart, W. L. Earl, and A. N. Garroway

J. Magn. Reson. (in press)

A Low Shear, High Temperature Rotational Viscometer: The Viscosity of Ultra High Molecular

Weight Polyethylene

H. L. Wagner and J. G. Dillon

ACS Polymer Preprints, 22, 260 (1981)

Novel Cell for Light Scattering From Solutions

F. W. Wang and B. H. Zimm

Biopolymers, 20, 1333 (1981)

Analysis of Selected Alloys in the Systems Cr-Pd, Cr-Ru, V-Pd, and Ta-Pt

R. M. Waterstrat

J. Less-Common Metals (in press)

Binary Phase Diagrams of Transition Elements

R. M. Waterstrat

NBS Special Publication 564 (May 1980)

Structure Relationships Affecting the Stability of A15- and Ti 3 P-Type Compounds

R. M. Waterstrat

J. Solid State Chem. , 37, 370 (1981 )

The Crystal Structure of the Low Temperature Phase (II) of Polytetrafluoroethylene

J. J. Weeks, E. S. Clark, and R. K. Eby

Polymer (in press)

Disorder in the Crystal Structures of Phases I and II of Copolymers of Tetrafl uoroethylene

and Hexafluoropropylene

J. J. Weeks, R. K. Eby, and E. S. Clark

Polymer (in press)

Consideration of Some Factors Influencing Compatibility of Dental Porcelains and Alloys,

Part I: Thermo-Physical Properties

R. P. Whitlock, J. A. Tesk, G. E. 0. Widera, A. Holmes, and E. E. Parry

Proceedings of the Fourth International Precious Metals Conference (1981)

Molecular Interpretations of Modulus and Swelling Relations in Natural Rubber Cross-Linked

by Dicumyl Peroxide

L. A. Wood

Rubber Chem. Technol . , )53, 116 (1980)

Representation of Long-Time Creep in a Pure-Gum Rubber Vulcanizate

L. A. Wood

J. Res. Nat. Bur. Stand., 85, 283 (1980)

Representation of Long-Time Creep in a Pure-Gum Rubber Vulcanizate

L. A. Wood

Rubber Chem. Technol. (in press)

Application of Porod's Law to Fixed Particles With Preferred Orientation

W. Wu

J. Polym. Sci., Polym. Phys. Ed., Ijl, 1659 (1980)

The Correlation Function of Agglomerated Particles and Its Applications in Electromagnetic

Scattering

W. Wu

J. Polym. Sci., Polym. Phys. Ed., ([8, 1993 (1980)

Stretching of Nylon 66 Yarns Saturated With Dry HC1

W. Wu and W. B. Black

ACS Polymer Preprints, 22, 248 (1981 )

80
Deformation of Doubly Oriented Polyethylene, Nylon 66, and Polyethylene Terephthalate)

W. Wu, W. B. Black, and P. G. Simpson

Polymer, 21_, 992 (1980)

A Silver Staining Technique for Investigating Wear of Restorative Dental Composites

W. Wu and E. N. Cobb

J. Biomed. Matls. Res., 1_5, 343 (1981 )

Influence of Chemicals on In Vitro Wear of Dental Restorative Composites

W. Wu and J. E. McKinney

J. Dent. Res., 60, 371 (1981)

Morphology and Tensile Property Relations in High-Strength/High-Modulus Polyethylene Fiber

W. Wu, P. J. Simpson, and W. B. Black

J. Polym. Sci., Polym. Phys. Ed., 18_, 751 (1980)

Alkane Chain Conformation as a Function of Pressure

S. L. Wunder

High Pressure Science and Technology , B. Vodar and P. Marteau, Eds., p. 676 (1980)

Effect of Polymer Molecular Variables on Drag Reduction

J. L. Zakin and D. L. Hunston

J. Macromol . Sci. (in press)

Patents

Composite Dental Material

R. L. Bowen July 29, 1980

U.S. Patent 4,215,933

Tertiary Aromatic Amine Accelerators in Acrylic Resin

H. Argentar

January 6, 1981

U.S. Patent 4,243,763

Non-Polymerization Inhibiting, High Strength Dental Cements, Restoratives and Adhesive Based on Vanillic Acid Esters, Carboxylic Acids and Zinc Oxide

G. M. Brauer, J. W. Stansbury, and H. Argentar

Filed January 1981

Use of Polyfunctional Surface-Active Comonomers and Other Agents to Improve Adhesion Between a Resin or Composite Material and a Substrate

R. L. Bowen February 17, 1981

U.S. Patent 4,251,565

Arc-Furnace for the Production of Small Investment Castings

R. M. Waterstrat

Filed April 1981

Isotonic Monomer Formulation

R. L. Bowen

Filed May 1981

Polymeric Solid State Battery

C. K. Chiang

Filed May 1981

Workshop

Morphological Studies of Power Cable Insulation Failure

Electric Power Research Institute, Gaithersburg, Maryland

M. G. Broadhurst

May 1981

81
External Recognition

1981 Hollenback Memorial Prize

Academy of Operative Dentistry

February 1981

R. L. Bowen

1980 Mettler Award in Thermal Analysis

North American Thermal Analysis Society

October 1980

J. H. Flynn

Fellow

North American Thermal Analysis Society

October 1980

J. H. Flynn
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NBS-1 H4A (REV. 2-8C) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC BATA

| SHEET (See instructions)

REPORT NO.

NBSIR 82-2452 March 1982

4. TITLE AND SUBTITLE

Polymer Science and Standards Division Annual Report 1981

5. AUTHOR(S)

R. K. Eby, M. G. Broadhurst, J. M. Cassel , B. M. Fanconi, I. C. Sanchez, L. E. Smith

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DX. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

10. supplementary notes

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. I f document includes a significant

bi bl iography or literature survey, mention it here)

This publication outlines the organization and programs of the Polymer Science and

Standards Division of the National Bureau of Standards. It contains summaries of

all technical projects in the Division for the 1981 fiscal year.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons,)

polymers, plastics, macromolecules,

13. AVAILABILITY

standards

14. NO. OF

PRINTED PAGES

Q31 Unlimited

(J(J For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

83

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[_ ] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

U S COMM- DC 6043-P80

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