NBSIR 81-2263

Center for Materials Science

Polymer

Science and

Standards

Division

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31-2263

1981

Annual Report 1980

U.S. DEPARTMENT

OF COMMERCE

National Bureau

of Standards
The cover drawing is a schematic representation of the collapse transition

in polymers. It converts a random coil structure of low density to one of

high density. This change can be brought about by small changes in either

temperature or solvent composition and has been suggested as a biological

amplifier. A theoretical description of this process has been developed

by Sanchez. See page 21.
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POLYMER SCIENCE AND STANDARDS DIVISION

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Annual Report 1980

U. S. Department of Commerce

National Bureau of Standards

Bldg. 224/A305

Washington, D. C. 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. 1. 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 1918 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.
I
Table of Contents

Page

I. PREFACE 1

II. DIELECTRIC PLASTICS DESIGN AND PERFORMANCE 3

M. G. BROADHURST - TASK LEADER

- Polymer Insulation for Superconducting AC Power Transmission Cables;

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

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

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

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

M. G. Broadhurst 5

- Automated Dielectric Measurement; F. I. Mopsik, S. J. Kryder, and S. C. Roth . . 6

- ASTM Activities; W P. Harris 7

- Polymer Sensors for NDE; S. Edelman and S. C. Roth 7

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

S. C. Roth, S. J. Kryder, A. S. DeReggi, and S. Edelman 7

- Ultrasonic Hydrophone; A. S. DeReggi, S. C. Roth, J. M. Kenney, and

S. Edelman 8

- Durability of Piezoelectric and Pyroelectric Activity in PVDF; J. M. Kenney

and M. G. Broadhurst 8

- Space Charge Studies; A. S. DeReggi, F. I. Mopsik, and M. G. Broadhurst 9

- Piezoelectric Polymer Fuzing; S. C. Roth, A. S. DeReggi, and S. Edelman 9

- Development of Piezoelectric Polymer Stress Gauges for Rock Studies;

S. C. Roth and S. Edelman 10

- Thick Electrode Transducers; A. J. Bur and M. G. Broadhurst 10

- Fabrication of Piezoelectric Polymer Film; A. J. Bur and M. G. Broadhurst .... 11

- Diffraction From Nonperiodic Structures: The Molecular Conformation of

Polytetrafluoroethylene (Phase II); E. S. Clark, J. J. Weeks, and R. K. Eby ... 11

- Order-Disorder Transitions in Polytetrafluoroethylene; J. j. Weeks,

I. C. Sanchez, C. I. Poser, and R. K. Eby 12

III. POLYMER STANDARDS FOR CONTROL AND EQUITY 13

I. C. SANCHEZ - TASK LEADER

- Standards for Gas Transmission Rate Measurements; J. D. Barnes 13

- ASTM Activities; J. D. Barnes 14

- Self-Calibrating Gel Permeation Chromatography ; P. H. Verdier 15

- Dynamics of Polymer Chains; P. H. Verdier and D. E. Kranbuehl 15

- Static and Dynamic Scattering From Polymers; C. C. Ban 16

- Interpretation of Scattering Experiments on Polymer Solutions; A. Z. Akcasu,

M. Benmouna, and C. C. Han 17
- Temperature, Molecular Weight, and Concentration Dependence of Chain

Dimensions Around 0-Temperature; S. J. Bai, D. J. Lohse, I. C. Sanchez,

and C. C. Han 17

- Concentration Dependence of Diffusion Coefficient at Various Molecular

Weights and Temperatures; A. Z. Akcasu and C. C. Han 17

- Dynamic Structure Factor, S(q,u)), of Dilute Polymer Solutions; A. Z. Akcasu

and C. C. Han 18

- Domain Structure of Block Copolymers and Characterization of Polyelectrolyte;

I. Noda., T. Hashimoto, S. J. Bai, D. B. Minor, and C. C. Han 18

- Development of a Digital Lock-in Light Scattering Photometer and the

Measurement of Polystyrene 1479 and UHMW Polyethylene; D. B. Minor,

H. L. Vagner, and C. C. Han 18

- Configurations of Polymer Chains; R. J. Rubin 18

- The Characterization of Ultra-High Molecular Weight Polyethylene For Synthetic Implants; H. L. Wagner and J. G. Billon 19

- Cell Model Theory of Polymer Solutions; J. C. Sanchez and D. J. Lohse 20

- Interfacial Tension Theory of Low and High Molecular Weight Liquid Mixtures;

J. C. Sanchez and C. I. Poser 20

- Configurational Properties of Comb-Branched Polymers; F. L. McCrackin and

J. Mazur ... 20

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

and G. B. McKenna 21

- Collapse Transition of the Isolated Polymer Chain; I. C. Sanchez 21

IV. MIGRATION AND THE DURABILITY OF POLYMERS IN USE . . 22

L. E. SMITH - TASK LEADER

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

R, E. Lowry, and L. E. Smith 22

- Thermogravimetry Studies of Polymer Degradation; B. Dickens 23

- Variable Heating Rate Thermogravimetry; J. H. Flynn 24

- Chemiluminescence From Oxidizing Polymers; R. E. Florin and B. Dickens 24

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

W. J. Rummer, J. R. Maurey, and L. E. Smith 25

- A Critical Compilation of Data on the Diffusion of Additives in Polymers;

J. H. Flynn .............. 28

- Measurement of Migration in Polymers by Inverse Gas Chromatography

G. A. Senich 29

- Diffusion Coefficient of Medium Size Molecules in Semicrystalline Polymers;

A., Peterlin and F. L. McCrackin 30

- Measurement of Antioxidant Migration by Fluorimetry; F. W. Wang 30

- Excimer Fluorescence Technique for the Study of Polymer-Segment Mobility;

F. W. Wang and R. E. Lowry 30

- Assessment of Transport Mechanisms for Radon in and Through Building

Materials; R. J. Rubin ........ 31
V. MECHANICAL DURABILITY OF PLASTICS FOR DESIGN AND USE 32

B. M. FANCONI - TASK LEADER

- Mechanical Durability of Polyethylene; J. M. Crissman, L. J. Zapas, and

G. M. Martin 32

- Stress-Cracking Test for ASTM; J. M. Crissman, L. J. Zapas, and G. M. Martin . . 33

- Ductile and Brittle Behavior of Polyethylene; A. Peterlin 33

- Spectroscopic Investigation of Failure Mechanisms in Polyethylene;

B. M. Fanconi, J. P. Colson, and K. L. DeVries 34

- Fracture Mechanics of Polymers; E. Passaglia 35

- Physical Testing of Polymers for Use in Circulatory Assist Devices;

Ft. W. Penn, G. B. McKenna, F. A. Khoury, and G. W. Bullman 36

- Response of Carbon Black Filled Rubber to Cyclic Loading; G. B. McKenna

and L. J. Zapas 36

- Relationship Between Morphology and Mechanical Properties of Ultra High

Molecular Weight Polyethylene; G. B. McKenna, F. A. Khoury, and

J. M. Crissman 38

- The Crystallization, Morphology, Deformation, and Orientation of Polymers;

F. A. Khoury and L. H. Bolz 40

- Polymeric Sealants for Geothermal Energy; E. A. Kearsley 41

- Characterization of Polymeric Solids by 13

C NMR; D. L. VanderHart and

S. J. Kryder . 42

- Acoustic Emission of Crazing Polymers; A. Peterlin, Ft. E. Green,

B. B. Djordjevic, and R. C. Murphy 44

- Non-Linear Elastic Behavior of Polymeric Materials; E. A. Kearsley,

G. B. McKenna, and L. J. Zapas 44

- Non-Linear Viscoelastic Behavior of Poly(methyl methacrylate); G. B. McKenna

and L. J. Zapas 45

- Retractive Forces in Drawn Low Density Polyethylene During Annealing;

A. Peterlin, R. Russo, F. DeCandia, and V. Vittoria . 47

- Permeation Performance of Polyethylene Used in Containers for Hazardous

Materials Transportation; J. C. Phillips ....... 47

- Durability of Paper; J. C. Smith, E. E. Toth, and E. L. Graminski 48

- Disorder in Drawn and Annealed Polyethylene; A. Peterlin, R. G. Snyder, and

J. R. Scherer 49

VI. TESTS, STANDARDS, AND CHARACTERIZATION FOR MANUFACTURING AND DURABILITY OF DENTAL AND MEDICAL MATERIALS . 50

J. M. CASSEL - TASK LEADER

- Dental Composite, Resin, Sealant, and Cement Chemistry and Development;

G. M. Brauer, J. M. Antonucci, J. W. Stansbury, R. E. Dehl, J. M. Cassel,

R. L. Bowen, H. Argentar, D. W. Misra, and T. Chen

- Development of Adhesive Bonding Technique; G. M. Brauer, R. L. Bowen,

J. M. Antonucci, D. W. Misra, J. W. Stansbury, and J. M. Cassel

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

J. E. McKinney, J.. M. Cassel, and E. Cobb 51
- Auger Electron Spectroscopy (AES) Applied to Wear Analysis of Dental

Alloys; J. E. McKinney, R. E. Dehl, and W. H. Grant 52

- Porcelain Fused to Base Metal Alloys; J. A. Tesk, R. W. Hinman, E. E. Parry,

and A. Holmes 52

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

E. E. Parry 53

- Dental Ceramics; C. P. Mabie, D. L. Menis, and R. L. Trout 53

- Irradiation Effects From Neutron Activated Dental Materials; J. A. Tesk 54

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

G. C. Paffenbarger, R. M. Waterstrat, and R. Busby ...... 54

- Dental Enamel Chemistry and Preventive Dental Treatments; w. E. Brown,

L. C. Chow, M. Mathew, G. L. Vogel, M. Tung, S. Takagi, T. Gregory,

H. Heaton, and P. Patel 55

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

R. E. Dehl and W. H. Grant 56

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

W. H. Grant, A. Bur, and J. M. Cassel 56

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

and N. W. Rupp 57

- Investigation of Epitaxy Relationships Between Ca 5 (P 0 4 ) 30 H and Other

Calcium Ortho-Phosphates; B. Dickens and L. W. Schroeder 57

- Development of Improved^ ield Dental Composite Restorative Materials for

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

and J. Cassel ....................... . 58

VII. OTHER DIVISION ACTIVITIES

- Invited Talks ..................... 59

- Publications and Patents ..... . 57

- Seminars for Staff and Guests ............ 73

- Technical and Professional Committee Participation and Leadership 77

- External Recognition ...... ..... 80

VIII. ORGANIZATIONAL CHART ............... 81

i v
POLYMER SCIENCE AND STANDARDS DIVISION'

Ronald K. Eby, Chief

Leslie E. Smith, Deputy Chief

S. M. Thomas, Administrative Assistant

B. M. Weeks, Secretary

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

4 culture and technology untouched. We have moved rapidly into an age in which an overwhelming

number of humanity's needs are served by polymers. The increase in production and use has been

spectacular; the volume of polymers produced last year exceeded that of steel. Recent

summaries show that polymers research already accounts for about forty-seven percent of the

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

materials, polymers also constitute about thirty-nine percent of the value added by manufacture

(a measure of the relative economic importance of manufacturing among industries), forty-five

percent of the number of scientific publications, and thirty-nine 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

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

density, corrosion resistance, and toughness. They are energy efficient, with the largest

volume polymer, polyethylene, using twenty-eight percent of the energy per unit volume required

by steel for the conversion from raw to refined material and yielding further savings in

processing and shipping.

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

encompassing trends for the increased use of polymers in packaging, constraction,

transportation, energy, electronics, information handling, clothing, appliances, dentistry,

and medicine. Since polymer technology is on the steep part of the learning curve, these trends

create new needs for concepts, measurements, standards, and data that can be used to insure

reliable performance in use, processing, and other phases of the material cycle.

To identify the key needs, the managers of the Polymer Science and Standards Division make

structured visits to government and industrial laboratories. Recent visits have included Bell

Labs, Du Pont, Army R&D Command, General Motors, Boeing, and Lawrence Livermore. Surveys have

been conducted in the areas of durability, processing, and composites. These and other

contacts with experts in industry, trade associations, standards associations, government, and

academia insure that the Division's efforts are directed toward fostering the effective use of

polymers in solving national problems cited by our Director as appropriate for NBS. These

include the growth of industrial productivity, prudent utilization of energy sources, a reasonable system for regulation of the effects of technology, and a wise policy of materials

uti 1 ization.

The Division has used its survey activities as a basis for participating in budget

initiatives to secure the resources necessary to meet the emerging needs. For the budget cycles

currently active, programmatic initiatives that include additive migration, composites

(biaxial orientation), blends, ionic conduction, and thin films are under consideration.

Competence building initiatives on the science of collapse transitions, electronic conduction,

high field NMR, and electron microscopy have been prepared.

The present 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 the Food and Drug

Administration, the Department of Defense, the National Institutes of Health, the American

Dental Association, the Department of Energy, the Bureau of Engraving and Printing, and others.

All the efforts lead the scientists in the Division into productive examination of those

1
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.

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

Tasks, each described separately:

DIELECTRIC AND PIEZOELECTRIC PLASTICS PERFORMANCE

POLYMER STANDARDS FOR CONTROL AND EQUITY

MIGRATION AND THE DURABILITY OF POLYMERS

MECHANICAL DURABILITY OF POLYMERS FOR DESIGN AND USE

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

cables results in lifetime limiting voids and inclusions. With a trend toward increased use of

underground transmission of electric power, improved insulation performance is required. 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.

Other trends are new, rapidly growing applications of polarized polymers as pyro- and

piezoelectric transducers. 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 will help 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 anti fouling coatings, mine disaster

warning devices) and in the areas of national security (microphones, hydrophones, intrusion

detectors, ultrasonic and infrared imaging devices, fuzing 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 methods which are becoming

possible with newly developed polymers. For example, this work attempts to show how polymers

interact with electronic and ionic charges and how structure can be modified to optimize

piezoelectric and semi-conducting properties.

Polymer Insulation for Superconducting AC Power Transmission Cables

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

This project, sponsored by and carried out in collaboration with Brookhaven National

Laboratory (BNL) with DOE funds, is part of a program for evaluating the suitability of various

types of polymer films for use (in tape form) as the electrical insulation in high power

superconducting AC transmission cables operated at 6-8 K. Such cables, in which the

superconductor is Nb 3 Sn, are currently under development at BNL. Among the guidelines used for

selecting the insulation for such cables is that the dielectric constant (c) should be 2.5 or less and that the dielectric loss (tan 6) should preferably not exceed 20 x 10 6 at the cable

operating temperature range and 60 Hz

This subtask is primarily concerned with the measurement of the dielectric properties (e,

tan 6) of polymer films at cryogenic temperatures. These measurements, for which NBS has a unique instrumental facility, are coupled with studies of aspects of the fine structure of the

films in an effort to determine the influence of various structural parameters (e.g.,

crystallinity, molecular orientation, voids) on the dielectric properties of the films. In addition to determining whether specific types of commercially available films meet the

established criteria for dielectric properties, these studies are aimed at providing data

relevant to the design and production of films exhibiting optimum dielectric properties for the

intended end use. In a less extensive effort, the compressibility of the polymer films is

measured. This latter feature is relevant to the determination of the optimum conditions

(e.g. , tape tension) necessary for winding the films (sliced into tapes) around the cable core,

so as to yield a cable exhibiting appropriate flexibility for winding onto storage drums

10 feet in diameter.

In FY80, this project was mainly concerned with studying laminates made from two layers of

a new, ^50 pm thick polypropylene bound together by a polyurethane layer. Measurements made

last year indicated that these laminates had substantially lower loss than ones made from

older, Jthinner (25 pm) polypropylenes and could meet the requirement that tan 8 not exceed

20 x 10 6 at 6-8 K, which the older ones could not.

3
Dielectric loss studies were made on two series of laminates. The two series had different

yellow dye concentrations (0.7 percent and one percent) in order to see if the presence of dye

affected the dielectric loss. The dye is added for visual monitoring of tapes made from the

laminates as they are wound to form the cable insulation. In both cases, tan 6 was 12-15 x 10 6 at 6-8 K, indicating that the added dye did not affect the loss and that the loss criterion

could be met.

Another series of measurements was made on laminates of nominal 80, 100, and 120 pm

thickness from polypropylenes of 40 and 60 pm thickness. In addition, the 60 pm polypropylene

film was measured separately. These graded thicknesses for the laminates will be used in a cable made for voltage testing to better distribute the voltage stresses across the insulation.

The results showed that the loss at 6-8 K decreased with increasing thickness showing that the

polyurethane layer, which had a constant thickness in all_the laminates, contributed

significantly to the loss. The values for tan 6 were 18-20 x 10 6 for the 80 pm laminate and

10-12 x 10 6 for the 120 pm laminate. The loss for the polypropylene alone was 6-7 x 10 6

, one

of the lowest values seen for any polypropylene. These data were then combined to show that the

suitably low loss of the present laminate as compared to the older, less satisfactory,

laminates was due both to the intrinsically lower loss of the polypropylene itself and to the

reduction in the amount of polyurethane present, since only one bonding layer was needed.

In other dielectric measurements, an epoxy composite that was intended for use in bushings

was measured for dielectric loss.

All the laminates measured dielectrically were also measured for compressibility when

stacked in layers. These data are necessary for predicting cable bendability. The series of

graded laminates was also examined microscopically. There was a considerable reduction in void

content in the polyurethane layer compared to earlier laminates. This indicates better control over the laminating process and a reduction in possible breakdown problems under voltage

stress.

Successful improvement of these materials is traceable in large part to the measurements

and analysis from this work which is fed back to the manufacturers to guide processing changes.

Polymer Tape Insulation for Oil Impregnated AC Power

Transmission Cables

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

Oil impregnated paper (cellulose) tape has been, for many years, one of the most commonly

used types of electric insulation in high power AC transmission cables. The current and

projected needs for more efficient power transmission systems have elicited considerable

interest in the development of oil impregnated or oil filled cables operated at 700-1000 KV, in

which polymer tape insulation will be used instead of the conventional paper tape which is

unsuitable because of its large dielectric loss.

In a project sponsored by Brookhaven National Laboratory with DOE funds, a program has

been initiated in the Polymer Science and Standards Division for evaluating the suitability of

various types of impregnated AC transmission cables. The goals of this study are: (a) the

measurement of the dielectric constant and dielectric loss of candidate films between 273 K and

423 K; (b) the determination of the dependence of the dielectric loss on the fine structural

characteri si tics of the films; and (c) the specification of the dielectrically most suitable

type of film for the intended end use.

The dielectric measurements carried out this past year have focused on a series of drawn

polyethylene tapes prepared for Brookhaven by Battel le Institute. Three different base

polymers were used under two different rolling conditions. The conditions were a roll

temperature of 298-303 K with a thickness reduction ratio of 5-7, and a roll temperature of

348 K with a thickness reduction ratio of 8.3. All the samples were measured under standard

temperature cycling to check the effects of thermal cycling.

The three different polyethyl enes showed quite different loss characteristics. One of

them exhibited a low level of loss (tan 6 less than 30 x 10 6

) that did not change_ much on thermal cycling. The other two had an initial tan 6 at 303 K of 80 x 10 6 and 50 x 10 6 all at

100 Hz. The latter two showed substantial reductions in loss at 303 K with thermal cycling to

4
353 K, 373 K, and 383 K in three successive sets of measurements. All the specimens showed

substantial changes in dimensions as reflected in the measured capacitance. The reason for

these loss differences as well as the changes in loss with thermal cycling is unknown. One

possibility may be differences in the raw polymer (cleanliness and additive content). There

were some hints that relatively volatile materials did contribute to the loss. No correlation

was found with sample density.

The density, wide angle x-ray diffraction, and small angle x-ray diffraction of the

samples were measured both before and after thermal cycling. The most notable effects were

found in the density. The tapes rolled at 298-303 K had an increase in density corresponding to

an increase in crystallinity from ^66 percent to ^75 percent, while those rolled at 348 K had an increase of crystallinity of ^72 percent to v77 percent. Some samples of one of the tapes

rolled at 298-303 K were thermally cycled as in the dielectric measurements and forwarded to

Brookhaven for measurement of thermal conductivity changes induced by the thermal cycling.

These data are important for predicting the dissipation of heat generated during power

transmi ssi on.

The results summarized above, coupled with earlier measurements on the effect of thermal

cycling on the dielectric properties of the experimental polyethylene tapes made by Battel le

Institute, have emphasized the need for modifying processing conditions in order to produce

tapes which are dimensionally and dielectrically stable to thermal treatments in the range 273-

383 K. It is expected that the normal operating temperature of the cables will be 355-365 K.

Structure and Performance of Piezoelectric Polymers

G. T. Davis and 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. The interest in the use of polymeric transducers continues to increase as evidenced by the requests from other government agencies, by the large number of requests for

information by mail, phone, and personal visits, and by the 20 papers presented at the American

Physical Society meeting in March 1980.

During the past year, considerable effort was expended in the preparation and

characterization of gamma phase PVDF in order to investigate its poling characteristics. A surfactant, si 1 oxane-oxyal kylene block copolymer (L-520) produced by Union Carbide was deposited from ethanol solution onto PVDF powder so as to comprise two weight percent additive.

The alpha phase which forms upon cooling from the melt is transformed to gamma phase when heated

in the presence of the surfactant at l°/min to 176 °C. Films without the additive, subjected to

the same thermal treatment, melt and recrystallize in the alpha form when cooled. X-ray

diffraction is the most convenient means of distinguishing between the two crystal phases. (IR

and DSC are less definitive). Films of alpha and gamma phases were subjected to the same poling

conditions, and the piezoelectric and pyroelectric responses were measured. The much larger

response from gamma phase for all electric fields less than 1.25 MV/cm confirms that this is a polar crystal phase. The value of 1.3 nC/cm2 K for pyroelectric coefficient after poling for

10 3 seconds at 80° and 1 MV/cm is almost the same as that reported for unoriented beta phase

obtained by pressure quenching and poled at the same field for one hour at 23 °C. For values of

electric field 750 kV/cm and greater, the alpha phase undergoes the electric field induced

phase transition to a polar form, so that at 1.25 MV/cm the responses from alpha and gamma phase

films are comparable. It has not been possible to pole at fields greater than 1.25 MV/cm

because of electrical breakdown. In the course of this investigation we discovered that simply

orienting the polymer film reduces electrical conductivity by more than a factor of 100. An

improvement in electrical breakdown strength is indicated but not fully quantified at this

time. Because of the field-induced phase transition of alpha phase, there seems to be no practical advantage for promoting the formation of gamma phase unless one must be confined to

low poling fields. A detailed report on these results is in preparation.

5
We have also poled PVDF as it undergoes the alpha to gamma phase transition in the vicinity

of 176 °C for the purpose of studying the stability of the resultant piezoelectric film.

Unfortunately, the breakdown strength at these temperatures is about 400 kV/cm so that only low

activity is achieved, and the response resulting from these low poling fields decays with time even at room temperature.

We have recently succeeded in increasing the piezoelectric and pyroelectric charge

response (as opposed to voltage response) of PVDF by improving the coupling between the polar

crystals and the external electrodes. A 0.1 H solution of tetrabutyl ammonium bromide in

dichloroethane was diffused into a poled film which greatly increases the conductivity of the

film. The initial pyroelectric activity of 2.4 nC/cm2 K increased to 3.3 nC/cm2

K. (Solvent

without the electrolyte has no effect.) As the volatile solvent is removed, the response

returns to its initial value but can be increased again by the sorption of dichloroethane from

the vapor phase. A more highly poled sample subjected to similar treatment increased from an initial value of 3.3 nC/cm2 K to a maximum value of 4.4 nC/cm2

K. When the exposure time to the

electrolyte solution was increased from 1 day to 3 days at 23 °C, the activity as we measure it was greatly reduced, presumably because the impedance of the polymer film becomes comparable to or less than that of the measuring circuit. Preliminary experiments using the same salt in the

much less volatile 1 ,6-dichlorohexane have shown similar enhancements without loss of the

enchanced activity with subsequent storage time at ambient conditions. These investigations

are continuing.

In the past year we published a summary of a cooperative six-site model for ferroelectric

switching in p-phase PVDF. This model predicts the essential features of polarization and IR transmission hysteresis curves and data on crystal plane reorientation with applied field.

These data all apply to changes that occur well below the order-disorder (or Curie) transition

implicit in the model and occurring in PVDF well above the melting point. This past year, Dr. Furukawa published data on a copolymer of PVDF and tri f 1 uoroethyl ene which showed a Curie

temperature at 70 °C. It was possible then to extend the model calculations to the transition

region. The experimental observation that the critical switching field decreased with

increasing temperature and vanishes at 70 °C is consistent with the model, as is the

anomalously high dielectric constant which has a maximum of about 70 at 70 °C. Using structural

information, this dielectric constant anomaly was calculated for the six-site model. As

expected, the calculated dielectric constant for the crystal phase was considerably larger than

that for the semi crystal 1 i ne sample. This occurs in any composite since the lower dielectric

constant component reduces the electric field in the higher dielectric constant component.

Because the particle shapes and orientations are so important in composite dielectrics, we are not able to calculate exactly what the semi crystal! i ne sample dielectric constant is, even if we know the dielectric constants of the components. Flowever, it looks as if there are some significant trends in the data not predicted by the model. A complete publication of the

calculations to date is in preparation.

Automated Dielectric Measurement

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

The automated dielectric spectrometer is nearing completion. This instrument wi 1 1 record

the transient response of a dielectric sample in real time and using numerical transforms will

automatically determine the dielectric constant and loss of the sample over the frequency range

of 10 kHz to 0.001 Hz or below. The instrument should have a resolution of 10 5

, which is an order of magnitude improvement over most designs. This will allow determination of the

dielectric properties of low loss polymers with much greater speed than previously possible.

Work done in FY80 includes completion of the charge detector. This detector can resolve

0.1 pC with a 10 ps rise time and for time up to 100 s. A major challenge that was overcome was the design of a reset circuit so that the output could be zeroed with negligible charge transfer

or drift. In addition, the final interface boards have been acquired. Currently, the computer

interconnections are being made prior to testing as a complete unit.

In addition, some of the programming for data treatment has been tested by its use with the

thermal pulse experiment. In particular, the idea of data selection and interpolation for

optimal computation has been successfully incorporated in the thermal pulse experiment and will

be used in the spectrometer. This allows the actual data sampling to be done in an experimentally convenient manner with a sufficient excess of points to obtain significant noise

reduction.

6
ASTM Activities

W. P. Harris

Mr. Harris chaired the final meeting of his six year chairmanship of ASTM Committee D-9,

Electrical Insulating Materials, at Dearborn in October 1979. There he received an award of

appreciation for his excellent service. He attended the March 1980 ASTM meeting in Dallas and

continues to serve as a member of the executive committee. Current activity in D-9 consists of

revising D- 150, which is one of the committee's most widely used and cited testing documents.

Polymer Sensors for NDE

S. Edelman and S. C. Roth

The 1980 NDE work of the Electrical Properties Group consisted of the use of polymer

sensors to measure dynamic elastic moduli and to detect wear in airplane control cables.

Making use of the sensitivity, low density, and flexibility of piezoelectric polymer

strain gauges, we have worked out a non-resonant method for measuring both the real and

imaginary parts of both the dynamic Young's modulus and the dynamic shear modulus of structural

materials in the form of long, thin rods. All four quantities can be obtained as continuous

functions of both frequency and static load. The frequency can be varied over a wide range, and

the static load can be varied from a large compressive value through zero to a large tensile

val ue.The method can be used to study the basic dynamic properties of materials. It should be

especially useful in studying composite materials and polymers, materials whose dynamic

properties are likely to vary with static load. In the case of composite materials, variation

of damping characteristics with static load can be expected to be a sensitive test of the

quality of the bonding between components. The method can be used to provide basic engineering

data needed for designing structures which are to be subjected to dynamic stresses or for which

particular levels of internal damping must be obtained.

Since all measurements are made on a single specimen under identical conditions (except

for the type of excitation) any deductions about the internal structure are free of the

uncertainties introduced where measurements at different frequencies require different

specimens and where measurements of the different moduli require different apparatus. The

method can be used for nondestructive evaluation of structural elements either for compliance

with design specifications or for monitoring a change in properties during service. A paper

describing the method was presented at the April 1980 meeting of the Acoustical Society of

America. Support for a laboratory installation to apply the method is being sought.

The study of airplane control cables is being performed on an apparatus in which the cable,

under tension, is pulled around a small pulley by a cam which converts the rotation of an electric motor to reciprocating motion. A polymer sensor, attached to the cable near the

pulley, detects the noise of the motion of the strands as they deform on the pulley. The sensor

can be removed from the cable and reattached readily so that the same sensor can be used to

compare different cables or different conditions. An elaborate mechanical filter eliminates

motor noise from the signal. A spectrum analyzer operates on the sensor signal, and changes in

the spectrum are monitored to detect the effects of fatigue and wear.

Polymer Stress Gauge for Intaglio Printing Press

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

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

Treasury, involves the development of a gauge to measure the dynamic pressure at critical

points in the presses used to print money. The first phase of the work was completed last year.

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.

7
This year work began on the second phase which is to provide calibrated pressure

measurements. Specifications for telemetry have been written and equipment ordered. Dedicated

data processing equipment has also been ordered. Preliminary design and construction of

polymer gauges is well along. A start has been made on design of a field calibrator for

checking the calibration of pressure gauges after installation.

Ultrasonic Hydrophone

A. S. DeReggi , S. C. Roth, J. M. Kenney, and S. Edelman

This project is partly sponsored by the Bureau of Radiological Health, which is

contributing the services of a guest worker. One objective of the project is to develop a piezoelectric polymer hydrophone for characterizing, point-by-point, the acoustic field beamed

by ultrasonic transducers, such as those used in biomedical equipment. Accurate knowledge of

the details of the acoustic field is not otherwise obtainable. The knowledge can be used to ensure both the safety and adequacy of ultrasonic dosage and for research in ultrasonic

treatment.

During this year, the performance of several prototype hydrophone probes has been

investigated thoroughly, with regard to both frequency response and performance stability at room temperature. The sensitivity, the broadband responsivity , the non-perturbing properties,

and the long-term stability have been judged good enough for the Bureau of Radiological Health

to adopt the probe as a standard probing hydrophone. A paper is currently under review for

publication in the Journal of the Acoustical Society of America. In addition, a patent is being

sought.

Several prototype annular arrays have been constructed and tested. These arrays consist

of concentric ring-detectors formed as common parts of a tensioned polymer membrane. They are being used in ultrasonic research to verify ideas in the theoretical modeling of disc-shaped

ultrasonic projectors. The geometry of the polymeric arrays allows the measurement with

unprecedented precision of the relative contribution of the ring diffraction term and the

piston plane wave term of the projected acoustic beam. This work is the subject of the Ph.D.

dissertation of our guest worker, Gerald Harris of the Bureau of Radiological Health, who is

also a part-time student at Catholic University. A preliminary account of this work has been

submitted for presentation at the 25th Annual Meeting of the Institute of Ultrasound in

Medicine in New Orleans on September 15-19, 1980 and for publication in the Proceedings of that

Conference.

Durability of Piezoelectric and Pyroelectric Activity in PVDF

J. M. Kenney and M. G. Broadhurst

This work was initiated with the Naval Undersea Systems Command because of their interest

in widespread use of polymer hydrophones by the U.S. Navy. Since good durability of activity is

crucial for this application and since long time testing makes it difficult to judge the effects

of structural or processing modifications on durability, we have developed a short time test

procedure which will give a rapid measure of relative durabilities of different samples. The

test consists of continuously recording pyroelectric activity while the temperature is being

increased linearly to the melting point of the sample. Samples show a broad maximum in activity

vs. temperature. We use the temperature at which the activity falls as a measure of

durabi 1 ity--the higher the temperature the more durable the sample.

Dramatic differences were seen between samples of PVDF and a copolymer of PVDF with

tetrafluoroethylene. The temperature at which the activity falls to zero is 100 °C for the

copolymer and 170 °C for the PVDF.

While this short time test will be useful for comparing effects of different structures

and treatments, it must be calibrated with longer time aging studies. This year we made

measurements of 38 PVDF samples which had been stored at room temperature for 15 months. It was found that the activity of the specimens as a fraction of the initial activity was 0.91 ± 0.05.

The magnitude is similar to that measured at two D0D laboratories in previous studies.

The mechanism of loss of activity of PVDF has not yet been established, and these

measurements should provide valuable data for the development of a suitable aging model.

8
Space Charge Studies

A. S. DeReggi , F. I. Mopsik, and M. G. Broadhurst

The static and kinetic effects of space charge in polymers subjected to electric fields

continues to be of interest as different groups in the USA and outside are developing new methods to measure these effects. In the poling of piezo- and pyroelectric polymers where near- breakdown fields are applied temporarily and in the standing-off of high potentials by

polymeric electrical insulation where moderate fields are sustained for extended periods of

time, space charge is either initially present as an ionic impurity, is produced through fieldenhanced degradation, or is injected across the electrode-polymer interface. The space charge

typically distorts the applied electric field and gives rise to regions of field concentration.

In the case of insulation, there is a resultant acceleration of the aging process leading to premature breakdown. In the case of piezoelectric polymers, there is a resultant non-uniform

distribution of polarization which in combination with a small but finite conductivity gives

rise to unusual transduction phenomena.

Until recently, only qualitative information was obtained about the space charge and

polarization distributions because of the preliminary stage of development of the methods used

to measure these distributions. For example, using the thermal pulse method we were able to show that in PVF subjected to a poling voltage, polarization tends to reside near the negative

poling electrode for a wide range of poling voltages and poling times and furthermore, that a threshold mean field of M50 v/pm must be exceeded in order for significant remnant

polarization to be found. Extremely weak remnant polarization was measured for mean fields as low as 24 v/pm. We suppose that positive space charge plays an important role in producing a distribution of electric fields in the sample and hence a distribution of applied poling

fields. These observations are markedly different from those made on PVDF where polarization

tends to reside near the positive poling electrode (presumably due to negative space charge)

and where there is a more gradual increase in remnant polarization as a function of the mean applied field. A paper discussing the role of space charge on the poling behavior of PVF has

been written with a recent guest worker, Professor Sidney Lang of the Ben Gurion University

(Israel), and has been submitted for publication in Ferroelectrics.

We have recently been able to acquire the transient charge response from the thermal pulse

experiment in digital form, and the computer programming for data analysis has been completed

and tested. From the data, one extracts the coefficients of a Fourier series representing the

polarization distribution in the film. When data can be obtained by illuminating first one side

of the film and then the other, the sum and difference of the two signals yield only even or only odd Fourier coefficients. This separation of terms facilitates a good determination of

the thermal time constant x for the sample. An important feature of the program is that data

are not chosen at equal increments of time but are taken at times chosen to yield the most

information about the relaxation time of the nth term which varies as x/n2. When data are available by pulsing alternate sides of the film, as many as ten Fourier coefficients can be

determined. This means, very roughly, that the "resolution" is about one-tenth of the film

thickness. This amount of detail in the charge and/or polarization distribution is expected to be of of great value in directing the development of models for non-uniform field distribution

during the early stages of poling.

Piezoelectric Polymer Fuzing

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

This project is sponsored by the U.S. Army Armament Research and Development Command. It

is developed from previous work by NBS in cooperation with Frankford Arsenal reported in NBSIR

75-724 (R). NBS is to assist ARRADCOM to determine the feasibility of using piezoelectric

polymer film in impact sensors for fuzing applications in several particular geometries.

An equation was developed describing the performance of piezoelectric polymer in fuzing.

When reasonable values, supported by the results of impact studies, were used in the equation,

it was predicted that sufficient energy would be released to detonate a 105 mm high energy

antitank round.

A technique using heat, vacuum, and pressure was developed for shaping piezoelectric

polymer to the inside of an ogive (forward part of a munitions casing). An ogive instrumented

in this way was delivered to ARRADCOM for testing.

9
A draft of the final report has been sent to ARRADCOM for comment and approved by them.

Development of Piezoelectric Polymer Stress Gauges for Rock Studies

S. C. Roth and S. Edelman

This work, funded by the Denver Mining Research Center of the Bureau of Mines, is a continuation of work described in the report for last year to measure noise from grinding

together of rock specimens.

Most of a series of polymer gauges for measuring rock noises were developed at NBS and

delivered last fiscal year. The remaining gauges have been constructed and will be delivered

this fiscal year. The gauges have been effective in detecting and measuring the acoustic

emission from rock samples under stress. Also, they have been found to survive collapse and

crushing of the rock specimens unless a crack develops directly across the active area. Future

work on rock and soil transducers is expected to result from tests on these transducers.

Thick Electrode Transducers

A. J. Bur and M. G. Broadhurst

The fabrication of transducer specimens of PVF 2 with thick, well adhering electrodes was attempted. The objective was to study the influence of the mechanical properties of the

electrodes on the PVF 2 transducer behavior. It is expected that the hydrostatic response will

be enhanced by a factor of two to three if the electrodes maintain their own integrity and exert

a stress on the polymer film during temperature and/or pressure changes. Transducers

previously fabricated in our laboratory have had very thin evaporated electrodes, several

hundred angstroms thickness. Because the electrode is so thin, the mechanical properties of

the polymer substrate dominate.

Metals such as Ni, Au, Ag, and Cu have elastic moduli which are 30 to 40 times larger than

that of PVF 2. A metal electrode of 0.4 pm thickness will have the same rigidity as 12 pm of

PVF 2

. A metal electrode of 4 pm thickness will have 10 times the rigidity of the polymer.

Relative to the polymer, a thick electrode can be considered rigid so that when the polymer

contracts, a stress between electrode and polymer develops. The predicted effect of this

stress is to enhance the change in the thickness of the polymer film by a factor of two or three

relative to the change with thin electrodes.

Previous attempts to detect a significant electrode thickness effect have been

unsuccessful, presumably due to poor adhesion between polymer and metal. This year we have made

measurements on a series of specimens furnished by Bell Telephone Laboratories which showed a systematic dependence of piezoelectric response due to stretching in the plane of the film with

different thicknesses of gold making up the electrodes. As in previous studies, we have yet to find a large difference (more than 10-20 percent) in pyroelectric response or hydrostatic

piezoelectric response before and after the gold electrodes are removed. The differences we

see in the activity of these specimens with electrode thickness seem to be due in part to

differences in sample polarization.

We suspect that stiff electrodes inhibit polarization of these films by restricting the

local strains needed to accommodate changes in crystal phase and orientation which occur as part of the poling process. We are presently conducting experiments to measure this

polarization for specimens with differing electrode stiffness to characterize this effect. We are making sure that the polarization measurements made during poling agree with those made

while the specimens are depoled (melted) and will then depole the Bell Lab specimens to determine their state of polarization.

As a final attempt to measure thick electrode effects, we have arranged to obtain samples

from EMI with well attached electrodes of differing thickness. If these do not show the

expected effects, we will be forced to conclude that the effect does not exist, though no explanation for its absence has yet been found.

10
Fabrication of Piezoelectric Polymer Film

A. J. Bur and M. G. Broadhurst

The Department of the Navy is supporting a project to fabricate piezoelectrical ly active

PVDF specimens with thicknesses of 0.79 mm (31 mil). A thick transducer is desired because it

will have a lower capacitance than the thin film PVDF transducers which we have routinely

prepared and a correspondingly higher voltage response for a given strain.

The problems with making thick polymer transducers are the large stresses needed to

stretch thick samples and the large voltages needed to apply a polarizing field to them. Large

Instron machines were used to stretch our materials while the high voltage group at NBS assisted

in poling them. Initial failures at poling thick samples were due to low breakdown strength

which we suspected was an inherent disadvantage of thicker, more defect prone samples. Further

investigation, however, showed that there was a large difference between oriented and

unoriented material. The oriented material is able to withstand poling fields of 1 MV/cm so that acceptable transducer activity can be achieved. We have not established the quantitative

difference in breakdown strength between unoriented and oriented PVDF, but qualitatively it can

be concluded from these observations that such a difference exists.

To better understand this dependence of breakdown strength on stretching, we measured the

resistivity of stretched and unstretched PVDF from several sources. The data distinctly show

that the resistivities for unoriented PVDF are lower than those for the oriented material by at

least an order of magnitude. While we have not established a relationship between resistivity

and breakdown strenth, we conclude that the state of orientation is an important factor which

affects the electrical properties of PVDF.

Molecular orientation is extremely important to making successful thick polymer

hydrophones. These thick hydrophones are equal to, and may exceed, the performance of present

state-of-the-art ceramic hydrophones. The use of this effect to study the basic nature of

conduction is equally important scientifically.

Diffraction From Nonperiodic Structures: The Molecular Conformation

of Polytetraf 1 uoroethyl ene (Phase II)

E. S. Clark 1

, J. J. Weeks, and R. K. Eby

The crystal structure of polytetraf 1 uoroethyl ene has been a subject of discussion among

spectroscopi sts , crystal lographers , and others. However, the determination of structure in

synthetic polymers is made difficult by the lack of resolution in the diffraction data. The

diffuseness of the reflections observed in most x-ray fiber patterns results from the small

size, mi sori entation , and imperfect lattice nature of the crystallites. This lack of

resolution leads to poor accuracy in measurement of peak position and makes determination of

layer line heights difficult with a corresponding loss of significant figures in evaluation of

the repeat distance for the molecular conformation. In helical conformations, the repeat

distance may be of considerable length or indeterminate and, in effect, nonperiodic.

Remarkable electron diffraction patterns of the low temperature form of polytetraf 1 uoroethyl ene have been obtained which exhibit layer lines sharply resolved to the 26th order. These patterns

permit accurate measurements of the layer line heights. Equations have been developed to

relate these heights to a molecular conformation defined in terms of an incommensurable helix

of ratio, r = u/t, defining a conformation of u motifs regularly spaced along t turns of the

helix. The electron diffraction data yield a molecular conformation of r = u/t = 2.159, with

the molecule slightly untwisted from the previously assigned conformation of r = 13/6 = 2.167.

The newly determined conformation corresponds within the limits of error to r = 948/439.

However, the practice of expressing a helical conformation in terms of some commensurable

ratio, u*/t*, is questionable. If the helical conformation is not expressed accurately in

terms of simple smal

numbers, it is preferable to define the conformation in terms of the

ratio, r, limited to the number of significant figures. This point is made tellingly in the

present case where a change of one standard deviation in r changes u*/t* from 948/439 to 54/25.

Furthermore, the error limits admit 82 other possibilities for t*<500.

University of Tennessee.

11
Order-Disorder Transitions in Polytetrafluoroethylene

J. J. Weeks, I. C. Sanchez, C. I. Poser1

, and R. K. Eby

The phase diagram of polytetrafluoroethylene has been enlarged by differential scanning

calorimetry to include the concentration of hexaf 1 uoropropylene comonomer units. The two

transitions near 292 and 303 K in the homopolymer move to lower temperatures with increasing

concentration and apparently become one at a small concentration. Analysis of the data for this

single transition yields 295 K for the temperature and 13.2 J/g for the heat of transition of an infinitely large homopolymer crystal. The heat of transition associated with the formation of

a crystal defect is 0.021 eV. The qualitative features of the transitions can be accounted for

by a mean-field model which involves two order parameters corresponding to planar units and

helix reversals. This model yields two transitions which move closer together and to lower

temperatures with increasing comonomer concentration. Decreasing lamellar thickness will have

a qualitatively similar effect.

^uest worker. University of Massachusetts.

12
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 billion dollar/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.

Our basic mission is to maintain and extend our expertise in polymer physical

characterization. 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. Some of these activities during the past year include:

o Production of a new, narrow-fraction polystyrene standard, SRM 1479 (M ^ 10 6

).

o Completion of a new computerized gas permeation measuring facility.

o Continued development of a new state-of-the-art, self-calibrating GPC; selfcalibration is achieved by making simultaneous light scattering measurements at nine

angles on the GPC effluent

o Characterization, by intrinsic viscosity and light scattering measurements, of a ultrahigh molecular weight polyethylene used in prosthetic devices.

o Development of the concept that all dilute polymer solutions possess certain

"universal" physical properties characterizable by a single excluded volume

parameter.

Standards For Gas Transmission Rate Measurements

J. D. Barnes

Engineering work on the new NBS automated manometric permeation measuring facility is

substantially complete. Operational trials and calibration measurements are currently under

way. The efforts expended on the design of safety interlocks, control circuitry, interfaces,

and operating software have provided valuable experience for future ventures in measurement

automation. There are some improvements which must be made to the temperature controls and the vacuum manifold before routine experiments can be conducted.

Recent trends in gas transmission measurements have been toward instruments that are simpler to manipulate and more selective than the manometric technique. Our experience with

our automated measuring system indicates that the manometric method is capable of considerable

improvement at a relatively modest cost. The time scale of the measurements is determined

completely by the diffusion coefficient of the gas, the thickness of the film being measured,

and, in some instances, the time scale of concomitant viscoelastic processes. These factors

are independent of the technique used to measure the transport properties. The optimization

that is built into the controlling software we have devised does, however, result in

significant time savings because there is no need for a human decision regarding the recovery of

the system from the previous measurement cycle or the achievement of a steady state. The

experience should prove useful to those who wish to devise simpler instruments for use in

qual i ty control applications.

The new facility was used to investigate the feasibility of adding transmission rates for

He, N 2 , and C0 2 to the certificate for gas transmission SRM 1470, which is currently certified

only for oxygen. These preliminary experiments demonstrated that the apparatus obtains valid

data for these gases. An experimental design has been formulated for carrying out the

measurements of transmission rates of He, N 2 , 0 2 , and C0 2 at a number of pressures and

temperatures as required for an SRM certificate. OSRM is providing support for these

13
measurements, and it is expected that they will be complete by the third quarter of FY81. The

measurements of 0 2 permeance are being redone because it is expected that some aging of the

material has taken place during storage.

Correlations which are possible when four different gases with different molecular sizes

and different thermodynamic properties are measured on the same sample should provide a clearer

picture of the gas transport mechanisms in this polymer.

The preliminary experiments revealed, as expected, that C0 2 exhibits the phenomenon of

partial immobilization in SRM 1470. New models must be devised for fitting the experimental

data, and the ramifications of partial immobilization on the mechanical properties and

morphology of the polymer must be explored before we can specify the best way to use SRM 1470 in

calibrating C0 2 permeance measuring apparatus.

A publication describing the construction and operation of the automated manometric

permeation measuring apparatus will be prepared as time becomes available once the apparatus is

being used for routine measurements.

After completing the recertification of SRM 1470, we expect to evaluate candidate

materials for an SRM with transmission rates approximately 50-100 times that of SRM 1470.

These materials are needed because existing instrumental methods perform poorly at high gas

fluxes. It is likely that minor changes will have to be made in our interfaces in order to

accomodate the higher data collection rates found in this work.

Work is continuing on devising a system of units that is both compatible with SI and

scientifically consistent. The SI base units of moles, meters, pascals, and seconds are the

starting point. While the logic of this scheme is recognized, there is considerable resistance

from users of the wide variety of customary unit systems.

A publication outlining ways in which SRM 1470 can be used to improve the performance of

existing gas transport measurement systems is in preparation.

NBS played an influential role in promulgating a substantially revised edition of ASTM D- 1434, the standard method for measuring gas transmission rates. The new document features more consistent terminology, an improved set of SI units, the use of safer equipment, the use of

SRM 1470 for calibration checking, and a clearer derivation of the equations used to fit the

data.

ASTM Activities

J. D. Barnes

J. D. Barnes serves 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 currently working on test methods relating to materials characterization, barrier

properties, sealing and bonding properties, and additive migration. Subcommittee F-2.93 is

responsible for providing statistical assistance to all task groups operati ng within F-2. The

design and analysis of i nterlaboratory testing programs are the major forms this assistance

takes.

Dr. Barnes and Dr. John Mandel conducted a workshop on Interlaboratory Testing during the

February 1980 ASTM Committee Week in San Diego, California. Over 100 individuals from ASTM

Committees D-20, F-2, and F- 1 7 participated. Interlaboratory testing programs are the

principal technique used to validate ASTM Methods of Test.

Dr. Barnes is also a member of ASTM Committee D-20 (Plastics) and its subcommittees on Plastic Film and Sheeting D-20. 19, Olefin D-20, and F-2. Dr. Barnes led the task group that

recently promulgated a revised version of ASTM D-1434, the standard Method of Test for Gas

Transmission Properties of Plastic Film and Sheeting.

14
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 commercially 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 instrument has been designed, and construction of its mechanical components is

scheduled for completion by the end of the current fiscal year. The dedicated minicomputer

system has been installed, with a video display which will permit real-time plotting of the

angular dependence of the scattering. In the coming fiscal year we expect to assemble and align

the instrument and begin testing.

Dynamics of Polymer Chains

P. H. Verdier and D. E. Kranbuehl

The dynamic behavior of polymer chains is important for two reasons. First, the principal

methods used to estimate molecular weight, and in particular gel permeation chromatography, the

only method available at present for estimating distribution in molecular 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.

Second, 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.

15
We have previously shown that for our simple chain models, self-entanglement effects

lengthen the longest relaxation times of the chains by a factor proportional to about the first

power of chain length. However, our models differ from polymer chains in solution in (at least)

two obvious respects: the chains are constrained to lie upon a lattice, and motion from one configuration to another is accomplished solely by a series of purely local chain motions.

Theoretical work carried out elsewhere appeared to predict a much weaker dependence of the

lengthening of relaxation times upon chain length than we had found, leading to the suggestion

that our results were artifacts arising from special constraints in the local chain motions we

had employed. We subsequently obtained results for chains with modified rules of motion free of

these constraints and showed that the suggestion was incorrect. We have now completed a series

of studies of the effects of local bead motion constraints and of the type of lattice employed

upon relaxation behavior. The results show that although self-entanglement effects are weakened by the removal of local bead motion constraints, they are still much stronger than

current theoretical predictions. Further, the self-entanglement effects are essentially the same on simple cubic, body-centered cubic, and face-centered cubic lattices, suggesting that

similar behavior may be obtained when the chains are removed from the lattice. Therefore, we

are preparing to study the motion of chains free of lattice constraints (though still employing

local bead motions). Testing of the programs is currently under way. We expect that it will be

completed and preliminary results obtained by the end of the current fiscal year; the study

should be completed in the coming fiscal year.

Additional work planned for the comi ng year wi 1

1 proceed along two lines. First, 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. Second, as a step in the direction of

investigating melt properties, we will extend the simulation studies to non-dilute solutions.

Static and Dynamic Scattering From Polymers

C. C. Han

Scattering techniques are most effective in measuring space as well as space-and-time

correlations of polymers in both solutions and bulk states. Our effort has been centered around

the universal approach of temperature, molecular weight, and concentration dependence of static

and dynamic properties of polymers. We investigate and compare theoretical predictions based

on modern scaling concepts as well as conventional theories to our experimental results from

the small angle neutron scattering (SANS), light scattering, and quasielastic light scattering

experiments.

In static scattering, spatial correlations of monomer densities in q-Fourier space are measured directly. With the SANS facility at NBS, it is possible to measure single chain

properties in the range of 0.01 < q

< 0.1 A'1 from dilute solution to the bulk state through

deuterium labeling. Also, with the high concentration labeling technique which we developed

last year, it is possible to study single chain properties over a wide range of concentrations

using a medium flux reactor such as the NBS reactor.

On the other hand, dynamic scattering, such as quasielastic light scattering, uses the

photon correlation technique to measure the time correlation function of scattered light from

polymer solutions. This time correlation function at any momentum transfer, q, is related to

the intermediate scattering function, S(q,t), which is a Fourier transform of the space

correlation function of monomer pairs. Therefore, in principle, measurement of S(q,t) can provide not only a measure of the properties associated with the equilibrium distribution of

polymer segments such as the radius of gyration, R^, or the statistical segment length, but can also measure physical properties associated with the time evolution of polymer segment

distributions, such as the hydrodynamic radius ; R^, or the hydrodynamic interaction strength.

Our most recent efforts have been centered on the development of theories for the

intermediate scattering function, S(q,t), and the characteristic frequency, Q(q), for polymer

16
solutions. Such theories are essential for the interpretation of quasielastic light and

neutron scattering data. Our theory includes both temperature and molecular weight dependence

specifically. We have also successfully applied this theory to a different characterization

technique, intrinsic viscosity.

Interpretation of Scattering Experiments on Polymer Solutions

A. Z. Akcasu 1

, M. Benmouna 1, and C. C. Han

Interpretation of dynamic scattering experiments requires, ideally, a theory that can predict the intermediate scattering function, S(q,t), and a chain model consistent with the

chemical structure of the polymer. Unfortunately, exact expressions of S(q,t) are available,

at present, only for single unperturbed (0-condition) gaussian chains without hydrodynamic

interaction (Rouse model), or, in the infinite chain limit, with hydrodynamic interaction and

preaveraged Oseen tensor (Rouse-Zimm model). In this sense, a complete interpretation of

scattering experiments on polymer solutions is an unsolved problem. By using linear response

theory, we have been able to obtain closed form expressions for S(q,t) of both linear and

circular chains for Rouse and Rouse-Zimm cases in the infinite chain limit. Also, we can express S(q,t) for finite linear chains in the Rouse limit and for circular chains in both Rouse

and Rouse-Zimm limits in closed form. All these can be compared with the method of

eigenfunction expansion and the method of solving diffusion equations directly. Advantages of our current scheme have been demonstrated. In the case where an exact solution of S(q,t) can not be obtained, the characteristic frequency, fi(q), which is the initial slope, and defined by

Q(q) = - 1 i

t-»0

dS(q,t)

dt

can be calculated. The temperature and concentration dependence of fi(q) in terms of "blob

model" chain statistics can be calculated not only for the intermediate scaling region, but

also for the upper and lower transition regions where information about polymer chain

parameters such as radius of gyration, R^, statistical length, a, and hydrodynamic interaction,

B, can be extracted.

Temperature, Molecular Weight, and Concentration Dependence of

Chain Dimensions Around 0-Temperature

S. J. Bai 2

, D. J. Lohse3, I. C. Sanchez, and C. C. Han

Chain dimension and the q-dependence of the single chain scattering function, S(q), are being studied at various temperatures and concentrations with different molecular weights by

SANS. Experimental results will be compared with various theroetical predictions. The

difference between dimensions in dilute solution at the 0-temperature and in the bulk state

wi 1 1 be studi ed.

Concentration Dependence of Diffusion Coefficient at Various

Molecular Weights and Temperatures

A. Z. Akcasu 1 and C. C. Han

Experimental results of the concentration coefficient, kp, of the diffusion coefficient,

D, of polymers in dilute solution have been investigated and compared with various theoretical

predictions. The negative kp for small molecular weight and low temperature and the positive kp

for large molecular weight and high temperature can be understood through model calculations

which include chain swelling and i ntermol ecul ar potential. The molecular weight independent,

but negative, concentration dependence of D at 0-temperature indicates the contributions of

overlapping pairs of molecules. Chain expansion at the 0-temperature due to chain overlap is

impl i ed.

University of Michigan.

2 IAP assignment from University of Michigan.

3 NRC/NAS Postdoctoral Associate.

17
Dynamic Structure Factor, S(q,u)), of Dilute Polymer Solutions

A. Z. Akcasu 1 and C. C. Han

Most of the quasielastic neutron and some of the quasielastic light scattering experiments

are performed in the frequency domain due to the characteristics and availability of

experimental facilities. The extraction of the characteristic frequency Q(q) from S(q,w) data

poses difficulties similar to those in time domain analysis. Although S(q,u)) is just the

Fourier transform of S(q,t), it is not straightforward to obtain an analytical expression for

S(q,w) even in the cases where S(q,t) is available. On the other hand, it is not fruitful to perform numerical inverse Fourier transform on the experimental S(q,w), due to the finite data

set and lack of precision. We have, therefore, investigated the shape of S(q,u>) numerically for

various cases to facilitate the extraction of Q(q) from S(q,u>) directly in both light

scattering and neutron scattering experiments.

Domain Structure of Block Copolymers and Characterization of

Polyelectrolyte

I. Noda2

, T. Hashimoto3

, S. J. Bai 4

, D. B. Minor, and C. C. Han

Preliminary study of the domain interface structure of star shaped polystyrenepolyisoprene block copolymers has been carried out by neutron scattering. Data analysis is in

process, and further experiments are in preparation.

Also, the characterization of polyacrylic acid by combined measurement of SANS and LS under various salt concentrations and charge densities is under way.

Development of a Digital Lock-in Light Scattering Photometer and the

Measurement of Polystyrene 1479 and UHMW Polyethylene

D. B. Minor, H. L. Wagner, and C. C. Han

A state-of-the-art light scattering photometer has been developed for the purpose of

measuring the molecular weight of polymer SRM's and ultra high molecular weight synthetic

implant materials. This photometer, which utilizes photon counting and digital lock in, has

been tested by measuring previously certified SRM's.

A temperature controller has been installed and tested for polyethylene measurements at

elevated temperatures. Measurement of polystyrene 1479 (M^ ^ 10 6

) in toluene has been

completed for SRM certification. Measurements of ultra high molecular weight polyethylene is

currently under way.

Configurations of Polymer Chains

R. J. Rubin

A review of applications of the theory of random walks to polymer chain configurations is

being prepared with G. H. Weiss of the National Institutes of Health. This review also includes

a number of new results: 1) a new connection has been established between random walk

probability distributions and a generating function obtained by Rubin [J. Chem. Phys. , 43, 2392

(1965)] for calculating configurational properties of a polymer chain attached to an adsorbing

(or repelling) solution surface. In particular, Eq. (26) of that paper can be expanded as a

r\ power series in e . The coefficient of e is the probability that a random walk originating in

the solution surface layer will return s-1 times to the surface in an N-step walk. Random walk

probability distributions of this type are considered by E. W. Montroll and G. H. Weiss, [J.

Math. Phys., 6, 167 (1965)]. When Rubin's Eq. (26) is viewed in this way, random walk

configurations are classified according to the number of visits, s, to the surface layer. Then

the total probability is the sum of the weighted probabilities where the weight function is

University of Michigan.

2 Nagoya University, Japan.

3 Kyoto University, Japan.

4 IAP assignment from University of Michigan.

18
q A proportional to e , a Boltzmann weight factor. 2) The treatment of a polymer chain between two

plane solution surfaces given by DiMarzio and Rubin [J. Chem. Phys. , 55, 4318 (1971 )] has been

extended to treat polymer chains of finite length. All the results obtained by DiMarzio and

Rubin pertain to the limit in which the ratio of the extended chain length to the separation

between the bounding planes is large compared to unity. One quantity of particular interest is

the average step density as a function of position between the solution surfaces. For random

walks of N steps, configurations can be classified according to the number of visits, r,s, to

the two solution surfaces. The subclass of N-step random walks in which each surface is visited

at least once is identical to the subclass of N-step random walks whose span is the same as the

distance between the solution surfaces. The calculation of the step density for N-step random

walks with a given span is in progress.

In the absence of the complicating effects of interaction with surfaces, probability

distribution functions of configurations of long chain molecules can be modeled by solutions of

a random flight or diffusion equation. However, it is known from studies of lattice models that

if the energy of attraction between links of the polymer chain and the surface becomes

sufficiently high, then there is a discontinuous collapse of the chain on the surface. The

description of such discontinuous behavior within the framework of a diffusion equation appears

to present technical difficulties.

DeGennes [Reports Prog, in Phys. , 32, 187 (1969)] has proposed that the appropriate

boundary condition in the case of a "weakly adsorbed" chain is the mixed boundary condition,

£ 3G/3x + mG = 0 at the solution surface, where G(x,N) is the solution of the diffusion

equation. DeGennes drew the analogy between his suggestion for the boundary condition of the

diffusion equation and the treatment of the bound state of the deuteron. We have approached the

question of the appropriate boundary condition for the diffusion equation in a complementary

way. Starting with the lattice random walk equations in Rubin [J. Chem. Phys., 43, 2392

Q (1965)], we have assumed that not only the surface layer is modified by a factor e , but each of

the first £ layers are modified by this factor. We then go to the random flight limit in which

the lattice equations are replaced by diffusion equations.

For this special model, we see how to establish a correspondence between the solution of a diffusion equation with a source (sink) term in an adsorbing (repelling) layer with an absorbing boundary condition and the solution of a diffusion equation with the mixed boundary

condition proposed by DeGennes.

The Characterization of Ultra-High Molecular Weight Polyethylene

For Synthetic Implants

H. L. Wagner and J. G. Dillon 1

The development of new or modified methods for characterizing the molecular weight and

molecular weight distribution of ultra high molecular weight polyethylene (UHMWPE) has

continued with major emphasis on work on the low shear viscometer. The light scattering

apparatus has been readied for high temperature operation, and a new fractionation bath is

being assembled.

Because of problems with wobble of the rotor and poor reproducibility, major modifications

were made in the viscometer design. As a result of these changes, it is now possible to

reproduce solvent readings to within one percent, and the wobble of the rotor is no longer

noticeable at those periods of rotation required for viscosity number determinations.

A problem remains with reproducibility for solutions of UHMWPE which appears to be due

primarily to solution preparation. If severe enough means are not employed to dissolve the

polymer, complete solution is not obtained. If too severe a method is used, on the other hand,

degradation occurs. Considerable effort has gone into finding a satisfactory technique, and a promising one is now being evaluated. It consists of heating the solution at 150 °C under

nitrogen for one hour with just enough gentle swirling to keep the polyethylene particles

separated before melting. This avoids the formation of globs which are very difficult to

dissolve.

^uest worker, Food and Drug Administration.

19
Viscosity values in decal in in the low shear viscometer are some twenty percent higher

than in tetralin, a surprising result, since if the Mark-Houwink equations (evaluated for lower

molecular weights) are extrapolated to higher molecular weights, very similar viscosity numbers

would be expected for these solvents. It is also found that these high values in decalin

decrease at the rate of two to three percent per hour for the first few hours, a change which

does not occur with tetralin or with either solvent in the ordinary capillary viscometer, which

operates at much higher shear rates. Whether these differences are due to degradation or some other phenomenon has not been determined.

Once the technique for obtaining low shear viscosity numbers is established, fractionation

will begin in order to obtain fractions for establishing the Mark-Houwink equation for UHMWPE.

Cell Model Theory of Polymer Solutions

I. C. Sanchez and D. J. Lohse 1

An incompressible, statistical thermodynamic theory of a polymer solution is formulated

which takes into account concentration inhomogeneities. 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 (FI ory-Huggi ns)

potentials when concentration homogeneity is assumed. Jn/a good solvent, the calculated second

virial coefficient decreases with molecular weight (M 1 5 dependence) in good agreement with

available experimental data. In dilute solutions, chain dimensions can be analytically

determined; the well-known Flory excluded volume equation is obtained. The most important

parameter in the cell model is the average number of chains/cell, A. For semi-dilute solutions

(A»l), it is shown that several important scaling results are recovered from a simple scaling

hypothesi s for A.

Interfacial Tension Theory of tow and High Molecular Weight

Liquid Mixtures

I. C. Sanchez and C. I. Poser2

A generalized van der Waals or density gradient theory of interfaces has been combined

with a compressible lattice theory of homogeneous fluid mixtures. Binary liquid-vapor and

liquid-liquid systems are treated. For non-polar low molecular weight mixtures, liquid-vapor

tensions are calculated as a function of composition with an error of less than five percent.

These calculations involve no adjustable parameters; all required parameters are determined

from pure component properties. For polymer solutions, it is usually necessary to introduce an adjustable interaction parameter to accurately correlate liquid-vapor tensions. Approximate

equations for the interfacial tension and thickness between two immiscible, high molecular

weight polymer liquids have been obtained. These equations are a function of a single

interaction parameter; when this parameter is chosen to match experimental tensions,

interfacial thicknesses of 1 to 5 nm are obtained. To assess the importance of compressibility

effects, the interaction parameter can be chosen so that the heat of mixing is zero for an incompressible system. This "pure compressibility approximation" works well for polymer pairs

with relatively low interfacial tensions. The most serious deficiency of the theory is that

intramolecular correlational effects present in long polymer chains are only crudely

approximated.

Configurational Properties of Comb-Branched Polymers

F. F. McCrackin and J. Mazur

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 nonbonded

segments of the polymer. The ratios, g, of the radius of gyration of a comb-branched polymer to

that of a linear polymer of the same molecular weight at the theta point were found to be larger

a NRC/NAS Postdoctoral Associate.

2 Guest worker, University of Massachusetts.

20
than the g ratios calculated by the unrestricted random-walk model of the polymer. These

calculated g ratios showed better agreement with experimental measurements than did those

calculated by the random walk model.

The radii of gyration of the backbones and the expansion factors of the comb-branched

polymers were also calculated. The radii of gyration of the backbones at the theta condition were greater than that of linear polymers, in contradiction to the random walk model which

requires that they be equal. The calculated expansion factors were less than that of linear

polymers, also in contradiction to the random walk model.

Rubber and Rubber Compounding Standard Reference Materials

G. W. Bullman and G. B. McKenna

The process of streamlining the NBS Rubber 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 are recertifying N-tertiary-butyl-2-benzothiazole sulfenamide [SRM 381(d), a rubber accelerator] in order to maintain inventories of this material. In addition, where

standards involve certification of basic physical properties, we are assuring the renewal of

the SRM's as necessary, and where the need is indicated, we are issuing new SRM's. Thus, last

year we recertified the butyl rubber SRM 388(k) which is used as a Mooney Viscosity Standard.

During this year, we have completed the work necessary for procurement of a new Mooney Viscosity

Standard, thus extending the range of Mooney Viscosity Standards available to the rubber

i ndustry.

Collapse Transition of the Isolated Polymer Chain

I. C. Sanchez

A mean field theory of chain dimensions has been formulated which is very similar to the van der Waals theory of a simple fluid. In the limit of infinite chain length, the chain

undergoes a second-order phase transition. At low temperatures, the chain is in a condensed or globular state, and the mean square gyration radius <S 2 > varies as m2/3 where m is the molecular

weight. At high temperatures, the chain is in a gaslike or coil state where <S 2 > varies as m

6y^. In the globular state, fluctuations in <S 2 > are very small, whereas they are very large

in the coiled state. A characteristic feature of the theory is that ternary and higher order

intramolecular interactions are approximated. At high temperatures, only binary interactions

are important, but at low temperatures, many of the higher order terms contribute. An important

conclusion of this study is that a polymer chain does not obey ideal chain statistics at 0 temperature. Although the second virial coefficient vanishes at 0, the third virial

coefficient does not; its presence is responsible for the perturbation of the chain statistics.

For an infinite chain, 0 and the second-order phase-transition temperature are identical. When

c\ / 0 generalized to d dimensions, the theory yields at low temperatures <S 2 > ~ m for all d and at

high temperatures <S 2 > ~ m6/(d+2)^

d < 4, and <S 2 > ^ m, d > 4.

21
MIGRATION AND THE DURABILITY OF POLYMERS IN USE

L. E. Smith

Task Leader

Polymeric materials now find their principal markets in construction, appliances,

transportation, and electrical systems where long term durability is critical to their

competitive performance. Reliable short term tests are therefore needed for the selection of

durable polymers and knowledge of polymer degradation mechanisms is needed to guide the

development of protective methods and to improve performance. Technical work this year has

emphasized the determination of the mechanism of degradation and stabilization of

polyurethanes, the use of thermogravimetric measurements for lifetime prediction, and the

development of chemiluminescence methods for the detection of photoi ni tiated oxidation in

polymers.

The most general phenomenon related to the durability of polymers is the effect of

protective additives. Almost all commercial plastics have low molecular weight substances

incorporated in them to develop or maintain desirable properties. In use, these substances

inevitably diffuse through the polymer to some extent and may migrate out of the polymer

entirely. The polymer is then left with poorer properties or increased vulnerability to

degradation and failure. This is a major failure mode of polymers, and programs concerned with

polymer durability must explicitly consider the possiblities of additive migration. A second

conseguence of migration is that the migrating substance becomes a contaminant of the

environment or, in the case of plastic packaging materials, a contaminant of the material being

contained. This raises questions about the toxicological consequences of such migration.

Contamination of food from food packaging materials is regulated by the federal government

through the Food and Drug Admi nstration , and the control of migrating substances presents an enormous challenge to the scientific basis of regulations.

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

considered efficiently on a case by case basis, either for selection of materials of optimum

durability or for regulation of food and environmental contamination. General material models

capable of predicting migration under a variety of service conditions are needed to organize

polymer-additive combinations into classes for consideration. The development of these

material models is the overall objective of work done in this task.

Technical activities on additive migration that contribute to this task include 1) the

experimental measurement of additive migration by several methods, 2) the compilation of

critically evaluated data from this laboratory and the literature, 3) mathematical modeling and

empirical correlation of diffusion data for analysis of data and rapid estimation of migration,

and 4) fundamental theoretical studies of polymer behavior that can provide truly general

predictive models.

Hydrolytic Degradation of Polyester Polyurethane Elastomers

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

Polyester based polyurethanes degrade in moist air because of the acid catalyzed

hydrolysis of the ester linkages [1]. With soluble polymers, acid content, A, and number

average molecular weight, M, vary with time, t, according to [2]:

kt k t A = A 0 e and M

-1 = M0 _1 + A0 (e - 1)

Here the subscripts indicate initial values, and k is the fractional rate of increase in acid

content.

These findings were applied to the study of insoluble urethane foams used in the fuel cells

of military aircraft [3]. Foam samples were aged until soluble. Subsequent agings then enabled

us to calculate k, which permitted prediction of the remaining foam life. A test using swelling

in di methyl formamide was developed that permits one to judge very quickly the condition of foam

in existing installations.

22
Polyester polyurethanes are sometimes stabilized against hydrolysis by the incorporation

of carbodi imides [4]. These compounds destroy acid by the reaction:

We have measured k' for reaction of a mono- and of a polycarbodi imide in polyesterdi ol s , in a polyester polyurethane, and in tetrahydrofuran solutions of a polyester-diol [4]. Except for

the reaction of the polycarbodi imide in the polyurethane, the kinetics of reaction [1] were

second order overall. Values of k

1 cover a relatively small range considering the enormous

range of bulk viscosities.

Attempts were made to predict the behavior of polyesters undergoing wet aging using only k and k' . The predicted stabilization is much greater than observed. Reasonably good prediction

can be made if a third reaction, one for disappearance of carbodi imide by a zero order process,

is introduced into the mechanism. This reaction could be due to uncatalyzed hydrolysis or to

hydrolysis catalyzed by a material not reactive with carbodi imide; present evidence favors the

latter hypothesis. If confirmed, better stabilization might be achieved by destroying this

catalyst. Work in this area is continuing.

Polyester polyurethanes containing carbodi imides have been aged for periods approaching

one year at temperatures of 85, 55, and 35 °C at 100 percent relative humidity. Acid content,

molecular weight, and carbodiimide content are all being followed. At 85 °C, lifetimes of

polyester polyurethanes with three weight percent carbodiimide are about threefold longer than

those of unprotected samples. For unknown reasons, the same carbodiimide content in polyesters

gives tenfold greater lifetimes. This study is also being continued.

References:

(1) C. S. Schollenberger and F. D. Stewart, J. Elastoplastics, 3, 28 (1971).

(2) D. W. Brown, R. E. Lowry, and L. E. Smith, Macromolecules, ]_3, 248 (1980).

(3) D. W. Brown, R. E. Lowry, and L. E. Smith, "Hydrolytic Degradation of Polyester

Polyurethane Foams," communication to be sent to Wright Patterson Air Force Base.

(4) D. W. Brown, R. E. Lowry, and L. E. Smith, "Kinetics of the Reaction Between Polyester

Acid and Carbodiimide in Dry Polyester Diols and in a Polyester Polyurethane," manuscript

in review, to be submitted to Macromolecules.

Thermogravimetry is important because several of the constant heating rate and isothermal

techniques are easy to apply, because excellent commercial apparatus is readily available, and

because it can be used to study any condensed phase, soluble or insoluble.

The scientific literature contains many articles on the determination of the kinetic

parameters of polymer degradation using thermogravimetry, but there is little or no agreement

between the published values of the parameters. Various estimates differ by as much as 100

percent. Therefore, we are currently investigating the nature of the rate-determi ni ng weightloss process and the use of thermogravimetry to provide realistic estimates of meaningful

kinetic parameters involved in the thermal degradation of polymers.

To this end, the technique of factor-jump thermogravimetry was developed in our laboratory

and has been used to study the degradation of several vinyl polymers in vacuum and in nitrogen.

The apparatus is more highly automated and more flexible than commercially available apparatus.

The technique has several distinct advantages:

0=C-

(

1 )

Thermogravimetry Studies of Polymer Degradation

B. Dickens

23
(1) it is able to determine activation energy using only one sample so that problems

arising from differing thermal histories of two or more samples are avoided,

(2) several activation energies are determined in each experimental run so that changes

in sample behavior can be discerned,

(3) because the activation energies are determined from locally extrapolated rates, no knowledge of the initial and final sample weights is necessary, and

(4) automatic feedback adjusts the experimental conditions for changing sample behavior.

Points 3 and 4 allow the method to treat multi-stage degradations successfully.

The results of thermogravimetric experiments conducted on several polymers under vacuum conditions were fairly erratic and difficult to interpret. Although it is generally difficult

to determine whether the instability results from the apparatus or the method, it has now been

shown convincingly that a large part of the variation is in the thermal history of the sample.

Only in the cases of polymers degrading with very long zip lengths to produce mainly monomer could results of chemical rather than physical significance be obtained in vacuum. The most

fiducial results for all polymers studied so far have been in slowly flowing N 2 , but even there

the experimental conditions play a surprisingly large role. For isotactic polypropylene, the

apparent activation energy for thermal degradation in vacuum was determined to be 61.5 ± 0.8

kcal/mole; for linear polyethylene it was 65.4 ± 0.5 kcal/mole. In slowly flowing N 2 , the

apparent activation energy is 54 ± 1 kcal/mole for isotactic polypropylene and

51.5 ± 0.5 kcal/mole for atactic polypropylene. For linear polyethylene, the value is

61 ± 1 kcal/mole. These values are significantly different from the vacuum values and from

most of the published values. In the case of polypropylene, a reasonably careful study carried

out elsewhere assigns 56 ± 5 kcal/mole to atactic polypropylene and 51 ±5 kcal/mole to isotactic polypropylene. Those results are 5-10 times more imprecise than the results from

factor- jump thermogravimetry. We will continue to use the factor- jump thermogravimetry

technique to study the effects of experimental conditions, molecular weight, and branching on the activation energy of thermal degradation of polypropylene, polyethylene, and several other

polymers.

Computer programs have been written to drive the apparatus and to conduct various

statistical tests to provide estimates of the precision of the results and to reduce as much as

is feasible the effect of aberrant values. These programs and procedures have been documented

i n a User' s Gui de.

Variable Heating Rate Thermogravimetry

J. H. Flynn

The prediction of the lifetime of a polymer by extrapolation from weight-loss data

requires a thorough analysis of the degradation kinetics over a wide temperature range.

Techniques have been developed in which entire kinetic spectra are compared among experiments

performed at heating rates from 6 deg/mi n to 9 deg/day. Simple methods of plotting data from

these techniques have been used for diagnosing shifts in reaction mechanism, uncoupling of

competing processes, and testing the validity of kinetic models.

Weight-loss studies are continuing on polystyrene, poly(methyl methacrylate), and

polyurethanes in vacuum and in atmospheres containing nitrogen, air, and water vapor. Subtle

changes in mechanism have been exposed for several of these cases under the milder conditions of

the above techniques. It now appears that rapid conventional thermogravimetric techniques at

high temperatures are inappropriate for the prediction of service lifetime of these polymers.

Chemiluminescence From Oxidizing Polymers

R. E. Florin and B. Dickens

Polymers emit light weakly during oxidation. This effect has aroused recent interest as a means of monitoring oxidative deterioration of polymers. A widely accepted theory of the

effect is that the light is emitted during the termination step of the oxidation chain reaction.

Although the quantum yield of light emission is estimated to be only one photon per 10 9 terminations, this inefficiency can be overcome by the technqiue of counting individual

24
photons, which leads to an extremely sensitive method, potentially capable of detecting

oxidation at temperatures only a little above those of normal service. In contrast, more accelerated aging methods require a long extrapolation from high test temperatures to service

temperatures, and the mechanism of degradation probably changes.

The general objective is to obtain a representati ve data base for correlating

chemiluminescence emission rates with overall oxidation rates for polymers of differing

physical and chemical characteristics. The appropriate kinetic parameters are the rates of

initiation, propagation, and termination. We have devised a method for measuring one of the

individual rate constants of the process, that of termination. A prototype photon counting

apparatus has been constructed. Ultraviolet light activates a photoinitiator solute which then

attacks the solvent which may be polymer, rubber, or liquid. The light can be cut off

suddenly, and decay in the oxidation rate followed to give estimates of the rate constants of

the termination reaction. Oxidations initiated thermally, without irradiation by light, give

estimates of the rate of initiation of polymer oxidation itself, i.e. , the rate of transfer from

the initiator to the polymer. This is because under these conditions the polymer oxidation is a chain reaction operating in the steady state, and the rate of initiation is equal to the rate of

termi nation.

Evaluation of transfer of radicals from the photo-initiator to the polymer provides

essential information on the dispersion of the initiator in the polymer and also allows us to

study the influence of the "cage effect" on the initiation process. Evaluation of the

termination rate constant under various conditions allows us to study the influence of the cage

effect on the termination process. One example of the cage effect is when two radicals, newly

produced adjacent to one another by a bond-breaking process, are held in close proximity to each

other by the matrix and react with one another without attacking their environment. If a radical escapes from the cage, it continues the polymer oxidation process until it reacts with

either another similar radical or an added radical -trappi ng molecule. Effects of cages bring

severe complications in the understanding of oxidation and are poorly characterized.

The chemiluminescence will also be used to study initiation by sensitive groups on the

polymer, such as the ROOH groups produced during oxidation under normal conditions. Other

parameters needed to complete the characterization of the oxidative chain reaction are the

kinetic chain length and the total amount of oxidation. These can, in principle, be determined

with techniques already described in the literature. However, to achieve sensitivity useful at

the low levels of oxidation at which the chemiluminescence photon counting method gives useful

information, these literature techniques will need further development.

The extreme sensitivity and very low levels of light emission bring their own problems.

Extreme care was necessary to produce a sample enclosure with a level of luminescence low enough

for the sample to be "seen". There are problems in dissolving enough photoinitiator in polymers

without precipitating it as a second phase. Also, careful measurements have shown that

oxidation phenomena are not as simple as they are usually thought to be.

The procedure described here is now highly automated, the apparatus being controlled by a laboratory computer. The existence of spikes of high counts (cause unknown) and of zero or very

low counts from occasional non-opening of the shutters required the writing of a trimmed-mean

estimating program. Other programs provide needed processing of data and continuously update

the level of photoinitiator left in the sample.

Currently, the optimum technique is being developed, and calibrating runs are being

carried out on simple organic compounds for which the termination rate constants are known. The

procedure and programs developed up to now are being documented in a User's Guide.

Migration of Oligomers and Antioxidants From Polyolefins

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

During the last two years, a rather thorough experimental investigation of the kinetic

behavior of the migration of oligomers and antioxidants from polyolefins into food and foodsimulating solvents has been carried out. This program is under the sponsorship of the Food

and Drug Administration. Extractions of migrants by actual foods are being carried out by a separate FDA contract at Arthur D. Little, Inc. The only food used in the program here is the corn oil, for the purpose of finding some solvents that simulate the extracting action of food

oils.

25
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A large number of experimental variables have been investigated. These variables are 1)

polymers--! inear polyethylene, branched polyethylene, and isotactic polypropylene; 2)

migrants--n-C 18 H 38 , n-C 32 H66 , and BHT ; 3) sol vents--corn oil, tributyrin, trioctanoin,

ethanol, ethanol -water mixtures, water, n-heptane, and n-octadecane ; 4) temperature--30 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 tudied.

The migrants used are labeled with radioactive 14 C, to yield a detectibi 1 ity of 10 "10

g if

needed. The extraction experiments generally require a few weeks to a few months to complete;

however, some experiments are completed within a few days, while some may last longer than a year.

There are about two hundred extraction experiments scheduled. Most of these experiments

are now completed. The diffusion coefficients observed vary from near 10“6 cm2

s _1 to less than

10“ 15 cm2

s -1. Some of the experiments indicate an ideal Fickian behavior, especially for preswollen polymer in one extreme and for non-swelling solvents in the other extreme. For the

intermediate cases, the diffusion coefficient may increase from an initial value and then level

off at a higher value or may increase drastically, such that the migrant is exhausted before

seeing the leveling off of the diffusion coefficient at a higher value.

From these results, certain generalizations and correlations can be drawn for the

migration of oligomers and antioxidants from polyolefins. These findings may form a basis for

the estimation or prediction of the diffusion coefficients in situations not mentioned above.

If all other parameters are held constant, then it seems that the ranking of importance for

the parameters on the diffusion coefficient of migrants from polyolefin is as follows:

solvent, temperature, additive type, polymer type, additive concentration. The first three

parameters are far more important than the remaining two. There are overlapping cases of the

ranking at the extremes of these parameters.

Effect of Solvent

Solvent is the single most important parameter in the correlation scheme. For moderate

solubilities, e.g., above one percent, one may make correlation of the diffusion coefficients

only to the solvents irrespective of other variables such as polymers, additives, additive

concentrations, and temperatures. Figure 1 shows the correlations of diffusion coefficients in

several solvents versus that in ethanol, while other variables being kept identical. Although

by changing solvents the diffusion coefficients may change by a factor of more than 2000, the

simple correlations indicated in Figure 1 can reduce the variation down to a factor of 3 or

less. The two correlations shown are for n-heptane, and for the combination of corn oil,

tributyrin, and trioctanoin.

The diffusion coefficients in corn oil, tributyrin, and trioctanoin are nearly identical

to that in ethanol within a factor of 3. The ratios of diffusion coefficients among the two

pure triglycerides and the corn oil are in general less than 1.5. Therefore, either ethanol,

tributyrin, or trioctanoin can be used to simulate the extractive action of corn oil in a great

variety of conditions involving different additives, polyolefins, and temperatures.

The accelerated action of n-heptane over that of the corn oil or its equivalents is clearly

demonstrated in Figure 1. The diffusion coefficient is only 10 to 20 times higher in the case

of high diffusion coefficients, such as in the case of highly loaded n-C 18 H 38 in branched

polyethylene at 60 °C. However, the disparity increases as the diffusion coefficient is

decreased, as may be seen in other correlations with temperature, etc. Thus, for the case of

extracting higher molecular weight oligomers, n-C 32 H 66 , from linear polyethylene at 30 °C, the

diffusion coefficient in n-heptane is about 1000 times higher than that in corn oil or its

equi val ents.

Combining the effects of the accelerating action and the greater solubility of n-heptane over that of ethanol for polyolefin oligomers, the extract of the whole polymer by n-heptane

contains a large amount of higher molecular weight oligomers that may be barely present or absent in the ethanol extract under the same conditions.

When the solubility is low, e.g. , in the cases of using ethanol -water mixtures or water as solvents, it is difficult to make simple correlations as a function of solvent without taking

27
other variables, such as polymers, additives, partition coefficients, and temperatures, into

account.

Effect of Temperature

Similarly, diffusion coefficients for additive migration at 30 °C may be correlated to the

diffusion coefficients at 60 °C by a single relationship to a factor within 5, irrespective of

all other variables. Again, the effect is minimized at higher diffusion coefficients and

increased at lower diffusion coefficients. Better correlations can be made by separating other

variables such as additives and polymers. The activation energies observed range from

20 kJmol -1 to 200 kJmol -1. Effect of Additive

Changing of additives while keeping all other variables the same also changes the

diffusion coefficients drastically. It is not possible to construct a simple correlation with

respect only to the additives but irrespective of all other variables. Reasonable correlations

may be made for additive-polymer combinations. Even then, definitive structures in the

correlations due to solvent or temperature are observed.

Effect of Polymer

For all cases studied, the diffusion coefficient changes, at maximum, by a factor of less

than 50 due to the changes from low crystallinity branched polyethylene to high crystallinity

linear polyethylene and isotactic polypropylene. Fine correlation requires other variables

such as additive and temperature to be kept constant.

Effect of Additive Concentration

If the additive, such as BHT, is insoluble in the polymer or does not act as a plasticizer,

no significant effect on diffusion coefficients due to the change in additive concentration has

been observed. Changing the concentration of n-C 18 Fl 3 8 from one percent to 0.01 or ten percent

may produce a change in the diffusion coefficient by a factor of 40 in the cases studied.

Correlations as a function of concentration for a particular additive but irrespective of other

variables are possible.

Conclusion

From the above observations, one can make a reasonable order of magnitude estimate of the

diffusion coefficient if any of the variables such as solvent, temperature, polymer, and

additive concentration is changed, while the estimation of the effect of changing of additives

without specifying other conditions would be rather difficult.

A Critical Compilation of Data on the Diffusion of Additives in Polymers

J. H. Flynn

The compilation of kinetic constants for the diffusion of organic compounds in polymeric

materials will result in a reliable data base which may be utilized both to evolve theoretical

models for diffusion mechanisms and to establish empirical relationships for the prediction of

the migration of chemicals and additives in polymers used in the food packaging, chemical

container, and transportation industries. With support from the Office of Standard Reference

Data, a comprehensive collection of kinetic data on the diffusion of organic compounds in

polyolefins has been completed and prepared for publication.

The tables for low density polyethylene, high density polyethylene, polyisobutylene,

polypropylene, hydrogenated polybutadiene, poly(4-methylpentene-l ) , ethylene-propylene

copolymers, and self-diffusion of polyolefins contain over 250 polymer-migrant entries.

Diffusion constants at temperatures from -30 to 190 °C, activation energies and preexponential

factors for the diffusion process and parameters for the concentration dependence of the

diffusion constant are included.

A special feature of this compilation is an extensive section of annotated references.

These include: 1) as complete a characterization of each polymer and migrant as is possible, 2)

a description of the experimental methods used to determine the diffusion constants, and 3) the

28
assumptions made, equations utilized, and calculations performed to obtain the data in the

tables. The justification for this lengthy section is twofold. The large effects of structure

and conditioning of the polymer substrate on the diffusion process require a detailed

description of the characterization and pretreatment of the polymers if the data are to be

compared and their differences interpreted. Secondly, since diffusion constants are a function

of time, concentration, and distance, a knowledge of the experimental conditions, methods of

measurement, and theoretical models evoked for the calculations is also essential for an understanding of the data.

The tables exhibit remarkable consistencies, considering the great variations in diffusion

constants which can be brought about by thermal, mechanical, and solvent action. These

consistencies lend hope that useful correlations may be developed from these data.

Work has begun on a similar compilation of kinetic data for the diffusion of organic

migrants in polystyrene—a polymer of commercial and theoretical importance--which in

contradistinction to the polyolefins, is in a physical state below its glass transition

temperature at normal service temperatures where most of the diffusion data on it have been

obtai ned.

Measurement of Migration in Polymers by Inverse Gas Chromatography

G. A. Senich

Inverse gas chromatography (IGC) is being evaluated as a method for studying the

thermodynamic and kinetic interactions of volatile compounds or probes with polymers. The

experimental procedure is similar to conventional gas chromatography with the exception that a solid or molten polymer replaces the usual liquid stationary phase. Low carrier gas flow rates

insure that the probe retention time is sufficiently long for a steady-state distribution

between the vapor and polymer phases to be established. The specific retention volume V , a

9 measure of the thermodynamic interaction between the probe and polymer, is then determined from

the total amount of carrier gas necessary to elute the probe from the column. Experiments with

alkanes and well characterized NBS polyethylene samples have been performed both above and

below the polymer melting temperature. The \T values determined above the melting temperature

agree with results in the literature derived for similar systems. An error analysis has been

effected to establish the precision which can be expected for such experiments. Since the

amorphous fraction is the sole contributor to bulk sorption of the probe molecules below the

melting temperature, the accuracy to which the percent crystallinity is known limits the

reliability of determinations in this temperature region. The polymer-probe interaction

parameter has been calculated from V by applying relations derived from the equation of state

9

based polymer solution theories of Flory and of Sanchez and Lacombe, both yielding similar

results. This parameter can be used to predict a limiting value of the partition coefficient,

which describes the distribution of the probe between a polymer and a non-swelling liquid in

contact with it, provided that the solubility of the probe in the liquid is known to be small.

The migration kinetics of a probe in the polymer phase can be related to the degree of

broadening of the eluted probe pulse over its initial injection distribution. At high carrier

gas flow rates, there is insufficient time for the probe to reach a steady-state distribution

between vapor and polymer phases. The degree of peak spreading is related to the rate of mass transfer occurring in the column, provided that contributing instrumental factors, such as dead

volume, are negligible. The magnitudes of various gas phase mass transfer processes have been

estimated and their effects minimized in a series of studies on diffusion of octadecane in

polyethylene. The diffusion coefficient has been determined for this system and found to be

extremely sensitive to the geometry of the polymer film present on the spherical support

particles. Knowledge of the film thickness distribution, in addition to its average value, is

critical to the experimental determination of reliable diffusion coefficients by IGC. Future

work will include studies of diffusion in polymer systems with clearly defined geometry. IGC

experiments on diffusive processes in glassy polymers will also begin.

29
Diffusion Coefficient of Medium Size Molecules in Semicrystall ine Polymers

A. Peterlin and F. L. McCrackin

An empirical correlation of the diffusion coefficient of a number of molecules with sizes

between N 2 and SF 6 in natural rubber and in polyethyl enes of increasing crystallinity can be

given by

D' = KD

m

where K and m depend on the polymer but not on the penetrant. The diffusion coefficients are given by this expression within a relative error of 4.7 percent. This expression may be

interpreted in terms of the fractional free volume, f, concept of the material transport.

According to this model, the diffusion coefficient is given by

D = A exp(-B/f)

where B depends on the size and shape of the penetrant molecule while f and, to some extent A,

depend on the particular polymer. By introducing this expression for D and D‘ , one obtains

m = f/f 1 , which permits the calculation of the ratio of the fractional free volume in the

polymers investigated. For the cases investigated, f of the amorphous component, which is

responsible for practically all the material transport, depends substantially on the

crystallinity. At the highest observed crystallinity of 0.77, the fractional free volume seems

to be only 67 percent of the fractional free volume in polymer with the low crystallinity of

0.29. The situation is still more extreme if one includes natural rubber which does not contain

any crystals. Polyethyl enes with crystallinity 0.77, 0.43, and 0.29 have a fractional free

volume which is 0.58, 0.76, and 0.86, respectively, of the fractional free volume of the purely

amorphous natural rubber.

Measurement of Antioxidant Migration by Fluorimetry

F. W. Wang

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

experiments. In an extraction experiment, a plane 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.

Experiments were performed to measure the extraction on N ,

1 -diphenyl-p-phenylene-diamine

(DPPD) by heptane at 22.0 °C from 0.27 mm thick low-density polyethylene films containing

8.4 x 10

-3 percent DPPD. The results showed that all the DPPD had been extracted out of the

films within four hours and that the plots of the weight of DPPD extracted against the square

root of time were sigmoidal and non-Fickian. These results and others to be collected will be

compared with the predictions of a theory being developed by Dr. F. L. McCrackin.

Excimer Fluorescence Technique for the Study of

Polymer-Segment Mobility

F. W. Wang and R. E. Lowry

The study of polymer-segment mobility is of practical as well as scientific interest.

Such a study will on the one hand contribute to the design of polymeric reagents and on the

other hand, shed some light on "internal viscosity", an idea introduced by Kuhn some 35 years

ago and yet still argued about [1,2]. Therefore, we initiated a program to measure polymersegment mobility by a novel technique based on excimer fluorescence.

An excimer is formed by the association of an excited molecule with another molecule in its

ground state. Such an excimer is characterized by a broad structureless fluorescence which is

shifted to longer wavelengths with respect to the fluorescence spectrum of the isolated

molecule. Similarly, excimer formation may take place by i ntramol ecul ar processes in polymers

carrying excimer-forming groups. Thus, excimer fluorescence has been observed in dilute

solutions of polymers such as polystyrene, polyvi nyl naphthalene , and poly( 1 -naphthyl

methacrylate).

30
We synthesized a random copolymer of methyl methacrylate and 1 -pyrenylmethyl methacrylate

as well as a random copolymer of methyl acrylate and 1 -pyrenylmethyl acrylate, the mole

fractions of pyrene-labeled monomers being 0.05 and 0.03, respectively. We then measured the

fluorescence spectra for dilute degassed solutions of these polymers at 22.0 °C in ethyl

acetate and in mixtures of ethyl acetate and glycerol tripropionate, which have the same chemical nature but different viscosity.

For a given polymer, the value of I^/I^, the ratio of the fluorescence flux emitted by

pyrenyl excimers to that by isolated pyrenyl groups, depends on polymer conformation as well as the rate constant k for the diffusion-controlled association of an excited pyrenyl group and a ground-state pyrenyl group to form a pyrenyl excimer. However, by using mixtures of solvents of

the same chemical nature but different visocisty, we were able to study the effects of solvent

viscosity on I^/I^ without modifying the polymer conformation to any significant extent. Thus,

at the low enough temperature of our investigation, the ratio Ip/I^ photostationary

conditions was proportional to k [3]. Since k in turn dependson the polymer-segment

3 3 mobility, measurements of Ip/I^ as a function of solvent viscosity allowed us to determine the

effects of solvent viscosity on the polymer-segment mobility.

We found that the experimental curves of the reciprocal of Ip/I^ (or equivalently the

reciprocal of k ) against the solvent viscosity were concave downwards. This finding agrees

3

with Cerf's proposal [4] that the highly diversified segmental motions of linear polymer chains

belong mainly to two classes which follow diffusional and non-di ffusional behavior,

respectfully, and which may coexist, the former having the reciprocal of the characteristic

rate constant proportional to the solvent viscosity and the latter having the reciprocal of the

characteristic rate constant a linear function in the solvent viscosity with a non-zero constant attributed to "internal viscosity".

Additional experiments will be performed to study the variation of polymer-segment

mobility with polymer structure, solvation of polymer, and polymer-polymer stereocomplex

association.

References:

(1) H. Ott, R. Cerf, B. Michels, and P. Lemarechal , Chemical Physics Letters, 24, 323 (1974).

(2) W. H. Stockmayer, Pure Appl. Chem. Supplement, 8, 379 (1973).

(3) H.-J. Galla and E. Sachmann, Biochim. Biophys. Acta, 339 , 103 (1974).

(4) R. Cerf, Chemical Physics Letters, 22, 613 (1973).

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 "hot" geological areas where it emanates naturally from the

ground. Certain building materials, such as gypsum board, also contain higher than average

amounts of radon. Under an interagency agreement with the EPA, NBS has very recently undertaken

the task of studying radon transport in building materials. It involves a cooperative effort

between three NBS Centers: Radiation Research, Building Technology, and Materials Science.

The initial phase of this project is to critically assess the current state of knowledge of

radon transport through or emanation from building materials. The Polymer Science & Standards

Division's role is to assess current transport mechanisms and models.

31
MECHANICAL DURABILITY OF PLASTICS FOR DESIGN AND USE

B. M. Fanconi

Task Leader

Current trends are to use polymeric materials in applications where long term mechanical

reliability is critically important. Examples in areas of national concern include the

increasing use of plastics and composites in transportation, in energy production, storage and

distribution, and in medical implant devices. The lack of adequate test methods and data for

evaluating long term mechanical performance not only restricts applications, but also leads to

overdesign which results in more expensive items and limits potential weight savings. 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 National Heart, Lung, and Blood Institute is aimed

at developing accelerated test methodologies for evaluation of candidate biocompatible

elastomers for use as bladders in circulatory assist devices. The Bureau of Medical Devices of

the Food and Drug Administration supports an investigation of the 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. The mechanical

performance of elastomeric seals in geothermal energy wells is of concern to the Department of

Energy, and a joint effort is aimed at developing tests to estimate accurately the long-time

behavior of seals in any condition of interest. In all of the above applications, there exists

a 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 the mechanical durability of plastic shipping containers has been the

development of a new test for environmental stress cracking. This test has been reported to

ASTM for evaluation as an improved standard method for stress-crack resistance.

Evaluation and control of materials parameters which affect long-term performance should

lead to more durable materials and, hence, reliable performance for the intended service life.

Task objectives are to identify and analyze principal failure mechanisms in polyethylene and

elastomers under mechanical stress in the use environment. An integral part of these

objectives is to determine the effects of chemical structure and mechanisms and fine structure

morphology on mechanical properties. Activities in nuclear magnetic resonance, vibrational

spectroscopy, electron and optical microscopy, as well as x-ray diffraction, are directed

towards elucidating these effects.

Mechanical Durability of Polyethylene

J. M. Crissman, L. J. Zapas, and G. M. Martin

In previous work done for the U.S. Department of Transportation, Office of Hazardous

Materials Research, a failure mechanism was identified which is highly sensitive to the

presence of a stress-cracking agent. This mechanism is associated with the region of small

deformations. In an effort to obtain a better understanding of this mechanism, experiments

have been carried out on prestretched specimens. In the case of equal biaxial deformations

under inflation, the interesting result is that this mechanism is highly influenced by the

magnitude of the prestretch history and in such a way that the material becomes more stresscrack resistant. For example, a tenfold increase in lifetime was observed for specimens which

were prestretched in air by twenty-five percent, were then left to relax, and subsequently were reloaded in the presence of stress-cracking agent. The eventual failure occurred at strains of

twelve percent or less. After prestretching, the permanent set in the specimen was of the order

of five percent or less. In all cases where the amount of prestretch was higher than the strain

at failure, a significant increase in lifetime was observed. Further investigation is needed

in order to understand this interesting behavior. In the case of uniaxial strain histories, the

results of similar experiments were inconclusive.

In other work related to mechanical durability studies, we have shown that the phenomenon

of neck formation, which occurs for uniaxial deformation histories, can be described by a mechanism leading to instability. Two different theoretical models (phenomenological) have

been derived which lead to such an instability. To test the validity of either model, we have

chosen for study two types of linear polyethylene having widely different molecular weights.

One sample, having a molecular weight (Mw) of 192,000, exhibits necking at room temperature.

32
The other polymer, an ultra high molecular weight material (Mw > 2 x 10 6

) does not show necking

at room temperature, but extends homogeneously until fracture occurs. In both theories one should be able to predict from single step stress-relaxation experiments, carried out at

different levels of strain in uniaxial extension, whether or not an instability occurs. Measurements made at very small deformations indicate that the behavior of the two

polyethylenes is very similar. However, at deformations above eight percent, deviations in

behavior occur which are consistent with both theories. Data have also been obtained for

specimens of highly cross-linked polyethylene which have a density very close to that of the

ultra high molecular weight linear polyethylene. The cross-linked material does show the

phenomenon of necking. Therefore, experiments other than mechanical will be required in order

to elucidate the differences between the two polymers and may lead to a better understanding of

the phenomenon of neck formation from the molecular point of view. We know from previous

experience that the incipient point of instability for linear polyethylenes occurs about a factor of two in time earlier than the time for which the neck becomes visible. One of the

continuum theories predicts that the incipient point of instability will occur when the

instantaneous jump modulus goes to zero. If the model is valid, then it should be possible to devise tests for nondestructive evaluation.

Stress-Cracking Test for ASTM

J. M. Crissman, L. J. Zapas, and G. M. Martin

This project concerns the development of an improved test method for the determination of

the stress-crack resistance of ethylene plastics. Upon its 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. A preliminary report on the test method was presented to the

ASTM Committee D-20.10 at their February meeting in San Diego, California. The test involves

the use of a bent strip geometry, but differs from the current ASTM bent strip test in two

important ways: the specimen is subjected to a constant applied stress and in the region of the

bend, all specimens are maintained in the same geometry.

The failure time can be controlled to some extent by changing one or more of four

parameters: the specimen thickness, the magnitude of the applied stress, the diameter of a metal cylinder (which determines the severity of the bend), and the temperature. In order to optimize these parameters, we are currently in the process of examining three different types

of polyethylene which have widely different stress-crack behavior. Specimens of each polymer

are being tested at two stress levels, two different cylinder radii, two different thicknesses,

and at two or more temperatures. To determine the repeatability of the measurements, ten or more specimens are being tested for each set of parameters. Preliminary results indicate that

two advantages of this test over the current ASTM bent strip test are improved repeatability and

shortened testing time.

Ductile and Brittle Behavior of Polyethylene

A. Peterlin

Creep experiments on isotropic linear polyethylenes by Crissman and Zapas have shown that

failure occurs by brittle fracture at both very small and very large loads. At intermediate

loads, the materials are ductile and after necking may deform to a very large draw ratio before

they break at a substantially higher tensile stress.

The lifetime, t, , at both very small and very large loads may be described as a sum of the

microcrack nucleation time, t

n

, and the microcrack growth time, t , in the brittle range and the

shear band growth time, ts, after which the sample necks and deforms drastically. It turns out

that the nucleus of the microcrack formed under the tensile load may produce a craze perpendicular to the local stress and a shear band at about 45 °C to this stress. The craze growth time is an exponential function of the negative stress, while the shear band formation

time is proportional to the inverse stress. If the curves representing the lifetimes of the two

deformation modes as a function of the applied stress intersect, then the intersections

separate the brittle from the ductile regime of the sample under tensile load. As a rule, with

increasing temperature the shear band formation curve moves more rapidly to lower lifetimes

than the microcrack growth curve. This expands the ductile region at the expense of the brittle

region. A decreasing temperature acts in the opposite direction so that eventually the two curves do not intersect at all, ant the material becomes brittle in the whole load region.

33
In this consideration, one has completely neglected the highest load range where the

deformation is so rapid that the material becomes substantially heated by the deformation work,

and hence, tends to fail like a liquid.

Spectroscopic Investigation of Failure Mechanisms in Polyethylene

B. M. Fanconi , J. P. Colson, and K. L. DeVries 1

The spectroscopic techniques of electron spin resonance and infrared spectroscopy are used

to elucidate molecular mechanisms in polyethylene associated with exposure to y-i rradiation and

with mechanical deformation and fracture. The irradiation studies, which have now been

completed, not only gave information on the relationships between the number of new chemical

species formed and the level of irradiation, but also provided a means of evaluating our experimental methods on samples in which the polymer molecules were not oriented during the

exposure process.

Knowledge of molecular mechanisms associated with deformation and fracture in polymers is

the main objective of the present work. Such information provides the basis for predicting long

term performance from short time tests as well as insights into how the molecular composition

may be changed to improve performance.

Summary of Result on Irradiated Polyethylene

Measurements of the concentrations of free radicals by electron spin resonance and of new chemical species by Fourier transform infrared (FTIR) were carried out on polyethylene

specimens exposed to y-i rradiation at dosages from three to fifty Mrads, both in the presence

and absence of oxygen. The improved signal -to-noi se capability of the FTIR method permitted a direct comparison of the free radical concentration and the resultant concentration of new chemical groups. It was found that approximately ten carbonyl groups and two carbon-carbon

double bonds were formed per free radical. These results are comparable with previous

estimates and form the basis for an investigation of chemical species formed during mechanical

deformation and fracture.

Chemical Changes Accompanying Mechanical Deformation and Fracture

The molecular mechanisms associated with mechanical deformation and fracture in

polyethylene are elucidated through comparisons between FTIR spectra of undeformed and

fractured specimens. Small variations in the concentrations of carbon-carbon double bonds,

methyl groups, and carbonyl groups result from rupture of carbon-carbon backbone bonds and

subsequent free radical reactions. These concentrations can be detected in difference spectra

obtained through subtraction of the digital FTIR data. The ability to detect small

concentration variations is enhanced by the superior sensitivity of the FTIR method over conventional dispersive infrared spectroscopy. The number and type of chemical groups formed

are correlated with ESR measurements of the number of secondary radicals accompanying

mechanical deformation and fracture.

Our results can be divided into two regimes associated with the rate of mechanical

deformation. In one set of experiments, the polyethylene specimens in the shape of dumbbells were rapidly pulled in a tensile tester until ruptured, while in the other set specimens were allowed to deform under dead load conditions. In both cases, the deformed or fractured

specimens were subsequently heated and pressed into thin sheets suitable for infrared analysis.

In this manner, the difficulties inherent in comparing spectra of unoriented (undrawn) and

oriented polyethylene which had plagued previous infrared studies of deformed and fractured

polymers have been circumvented.

For the rapidly deformed specimens, we observed that the number of ketone groups decreases

when compared to the reference polymer. This result is contrary to previous findings and

suggests that bond rupture occurs preferentially near the ketone group and that subsequent

University of Utah.

34
reactions produce low molecular weight ketones which are volatilized during preparation of the

specimens for infrared studies. Assuming that the ketone groups are preferentially located in

the interlamel lar regions, our findings support the notion that fracture occurs at lamellar

i nterfaces.

When polyethylene specimens are slowly deformed, we observe the number of carbonyl and

vinyl groups to increase, which is consistent with previously published reports. Experiments

are in progress to substantiate these results on drawn polyethyl enes to determine whether a relationship exists between the level of deformation and the concentration of each group.

Fracture Mechanics of Polymers

E. Passaglia

In April of this year, a new project on the fracture mechanics of polymers was begun. A complete review of the literature, concentrating on the effects of plasticity and

viscoelasticity, is well along. A review paper in these areas is contemplated.

Technical work has concerned itself with the viscoelastic nature of the craze material at

the tip of a slowly moving crack. Published results by Ward and his co-workers [1,2,3] and by

Weidmann and Doll [4] show that the shape of the crazed region is quite accurately represented

by the Dugdale model [5], which was developed for plastic yielding in metals. In this model,

the stress in the yielded zone (which corresponds to the crazed region) is a constant and equal

to the yield stress, with the length of the zone increasing as the applied stress intensity

factor is increased. In the polymer case, however, it has been shown [4] that the stress in the

crazed region is proportional to the applied stress intensity, with the length of the crazed

region remaining constant. Moreover, other experiments [6,7] indicate that the craze material

is viscoelastic and not plastic. We, therefore, have the unusual result of a theory developed

for an elastic-plastic material accounting well for observations on a viscoelastic material.

This can, in principle, be explained if the relaxation of stress in the craze in the

growing crack is compensated for by the elongation provided as the crack grows, in just such a manner as to produce a constant stress within the craze. Since the shape of the craze region is

known from these results, it is, in principle, possible to determine the relaxation function

for the craze material. For the linear viscoelastic case (which is probably too simple for this

situation), this determination involves calculating the Laplace transform of the crack

displacement, calculating from this the Laplace transform of the relaxation function, and then

inverting this transform. The last step is known to be a delicate mathematical operation, so that while mathematical difficulties have been encountered, preliminary results show that the

method is feasible.

References:

(1) A. R

(2) G. P

(3) G. L

(4) G. W

(5) D. S

Brown and I. M. Ward, Polymer, ]_4, 469 (1973).

Morgan and I. M. Ward, Polymer, J8, 87 (1977).

Pitman and I. M. Ward, Polymer, 20, 895 (1979).

Weidmann and W. Doll, Non-Crystalline Solids, 606 (1977).

Dugdale, J. Mech. Phys. Solids, 8, 100 (1960).

35
2.00 CD

'5frCD

CO

CD

C/3 LU

3'Nivais

cn

u_

36

Creep

of

carbon

black

filled

butyl

rubber

under

continuous

(static)

loading

(•)

and

square

wave

zero-tension

cyclic

loading

(0,X)

at

2.0

MPa.

(0)

1.6

sec.

into
Physical Testing of Polymers for Use in Circulatory Assist Devices

R. W. Penn, G. B. McKenna, F. A. Khoury, and G. W. Bullman

This project is directed to the development of accelerated physical testing procedures and

to the evaluation of candidate elastomers for use in circulatory assist devices. The project is

supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health

under contract #Y01 -HV-8-0003. Three candidate materials are under study along with a standard

butyl rubber. The three candidate materials are a polyolefin rubber, a urethane-silicone

copolymer, and a segmented polyurethane elastomer. During this year, all of these materials

have become, or are becoming, available in adeguate supply.

We have obtained results from both uniaxial and biaxial testing with both static and

dynamic stress histories. Our results show that in static uniaxial loading the butyl rubber is

superior to the polyolefin at short times (high stresses) but that this behavior reverses at

long times (low stresses). Under dynamic (fatigue) loading, the failure times decrease with

increasing test freguency but not rapidly enough to say that the samples fail after a constant

number of cycles. Statistical analysis of the failure data shows that there is greater

variability in the failure times for the polyolefin rubber than for the butyl rubber in all

tests in which a comparison can be made.

Biaxial fatigue test results show that the urethane-silicone copolymer lasts longer than

the polyolefin rubber, which lasts longer than the butyl rubber when they are compared at the same reduced pressures. For both the polyolefin rubber and the butyl rubber, the dependence of

lifetime on stress is the same in static and fatigue loading. The butyl rubber in both cases

shows a higher stress dependence. In the case of both rubbers, the variability in the failure

times is greater in static testing than in dynamic testing. Data for the butyl rubber and

preliminary results for the urethane silicone copolymer from biaxial fatigue tests at 23° and

37 °C reflect activation energies for the failure process of 22 kcal and 25 kcal , respectively.

Creep data under uniaxial loading have been obtained for all four elastomers. Creep rates

range from 1.7 percent per decade of time for the segmented polyurethane elastomer to four

percent per decade for the polyolefin rubber.

Examination of the urethane-silicone copolymer by optical microscopy shows

heterogeneities on a coarser scale than has been previously reported. These structures consist

of flattened spheroids with their short axes perpendicular to the plane of the sheet. Their

sizes parallel to the plane of the sheet vary from a few micrometers up to about 30 pm.

Response of Carbon Black Filled Rubber to Cyclic Loading

G. B. McKenna and L. J. Zapas

We have been examining the deformation behavior of a carbon black filled butyl rubber in

view of the BKZ constitutive equation. Failure behavior has been studied within the context of

cyclic creep and a cycle shifted failure envelope.

For materials which follow BKZ type behavior, the single step stress relaxation response

is a lower bound on the cyclic stress relaxation behavior, and the single step creep response is an upper bound on the deformations obtained in cyclic creep. In the responses observed for the

carbon black filled rubber, we found that upon cycling the material, the creep and stress

relaxation responses were outside these bounds. (See, for example, Figure 1). We also found

that the softening was more emphatic in cyclic creep than in cyclic stress relaxation. Further

work needs to be done in order to understand these results for materials which are nearly

elastic in constant stress or strain histories. We have also found that the material creep

response in constant load experiments is stiffer than that predicted from the BKZ constitutive

equation. It is suggested that an adequate description of the material behavior might be

obtained by developing a theory similar to the BKZ theory which includes competing effects of

stiffening in creep and softening under load-unload cycling.

In studying the cyclic creep behavior of the butyl rubber, we found that the creep rate is

dependent upon the waveform and frequency of the test. Also, unlike the case of static creep,

the creep rate under the cyclic loading is a function of the stress level. An interesting point

which arises in examining the cyclic creep data is that the square waveform load-unload cycle

37
1,000

peioipajd ‘ *M

38

Fig.

2.

Number

of

cycles

to

failure

predicted

using

shifted

failure

envelope

vs.

observed

number

of

cycles

to

failure

for

carbon

black

filled

butyl

rubber.

Zero-tension

fatigue

with

peak

stress

of

5.5

MPa.

Loading:

Sinusoidal

()

0.002

H

;

(0)

0.01 H

;

(O)

0.09 H

.

Square

wave

(a)

52,4

sec.

cycles.
which had a test frequency of 0.02 Hz showed nearly the same behavior as the sinusoidal loadunload cycle at 0.01 Hz. This would indicate that stress softening occurs due to cycling but is

independent of the rate of load application. The amount of stress softening depends upon both

time and cycles. This can be seen from the fact that the amount of stress softening per cycle

increases with decreasing frequency, and the stress softening per unit time increases with

increasing frequency.

The lifetime of carbon black filled rubber in cyclic loading depends upon the test

frequency and the waveform of the loading cycle (e.g. , square wave vs. sine save). We have been

able to use cyclic creep data combined with the notion of a shifted failure envelope to account

for the frequency and wave form dependence of the fatigue lifetime of carbon black filled butyl

rubber.

In simple loading histories, failure of rubbers is readily described by a failure envelope

for which the locus of stress at break vs. strain at break can be represented as a unique curve independent of stress history. In general, however, the failure envelope can be dependent upon

the loading history. In addition, the amount of change may depend upon the stress. Since in our cyclic creep experiments we found that the amount of stress softening was relatively

independent of waveform, and all of our tests were conducted at the same peak stress (5.5 MPa), we can express the change in the failure envelope due to cyclic loading by a shift factor a . Then CT

e, = a £ u be ct bo ( 1 )

where is the strain at break under cyclic loading, a^ is a shift factor, which may depend on the level of stress, and is the failure strain (at the same stress) in a simple deformation

history (i.e., creep, stress relaxation, constant rate of deformation). With this assumption,

the same shift factor should permit prediction of all of our cyclic failure data by

extrapolation of the cyclic creep strain data to the determined from Eq. (1) and one set of

the failure data. The results are shown in Figure 2 in a plot of the predicted number of cycles

to failure vs. the observed number of cycles to failure. The points show the data, and their

distance from the dashed line gives the deviation from the predictions. Given the limited

number of data, the agreement is good. The observed deviations could arise from variability in

the cyclic creep data, a possible history dependence (which we have ignored) of the amount which

the failure envelope shifts, as well as the normal amount of variability in the number of cycles

to failure in fatigue type testing.

Work is continuing in our study of the effects of cyclic loading on creep and failure of

carbon black filled rubbers. An effort is being made to find an appropriate constitutive law to

include the effects of stiffening in creep and softing due to cycling of these materials.

Experiments are being conducted to assist in this development. Experimental work is also

continuing to explore in more detail the applicability of the cycle shifted failure envelope to the description of fatigue lifetime of filled rubbers.

Relationship Between Morphology and Mechanical Properties of Ultra

High Molecular Weight Polyethylene

G. B. McKenna, F. A. Khoury, and J. M. Crissman

The starting material used in the manufacture of the polymeric components of orthopedic

prostheses is ultra high molecular weight polyethylene (UHMWPE) in its nascent state (i.e., as polymerized). The devices made from UHMWPE are fabricated in one of two ways: a) they are machined from rods or blocks prepared from the raw polymer (usually by compression molding) or

b) they are molded directly from the nascent polymer powder into the desired shape. In clinical

use, the long term performance of implants made from UHMWPE is determined by time dependent

phenomena such as creep, fatigue, and wear. The manner in which these phenomena depend upon the

thermal history and resultant morphology is not well understood.

Under contract with the FDA Bureau of Medical Devices, we are studying the relationship

between morphology and the mechanical properties of UHMWPE. Our work has three specific goals:

39
(1) To determine the influence of polymer morphology on the time dependent mechanical

properties of UHMWPE and to identify thereby the fine structural parameters which

significantly affect long term performance.

(2) To generate data in the areas of compressive creep, stress relaxation, and time

dependent failure behavior which will be useful as a basis for evaluating the future

and current devices made from UHMWPE.

(3) To devise measurement techniques which will be relevant to the development of

standard test methods for characterizing the time dependent mechanical properties of

implants fabricated from UHMWPE.

During this first year of the project, we have focused our efforts in three areas: a)

developing the molding capabilities and techniques to fabricate samples of UHMWPE in a reproducible manner; b) characterization of the morphology of the UHMWPE polymer as received

after molding and after deformation and failure; and c) characteri zation of the time dependent

mechanical behavior of UHMWPE.

We have developed a technique for fabricating sheets of UHMWPE using a vacuum mold. These

sheets are used for uniaxial and equibiaxial test specimens. We are currently developing a technique for fabricating cylindrical specimens for compression testing.

Morphological characteri sties of the UHMWPE raw polymer and of the fabricated sheets are being characterized using scanning electron microscopy, wide, and small angle x-ray

diffraction, optical microscopy, and differential scanning calorimetry. Initial work has shown

that the raw polymer has a grain-like structure which is carried over into the molded sheets.

Also, the melting point of the raw polymer is significantly higher than that of the molded

sheets, which indicates a higher degree of crystallinity in the raw polymer. X-ray diffraction

patterns from samples which have been drawn to failure and then released show that there is

considerable permanent orientation. Small angle x-ray diffraction shows changes occurring in

the lamellar texture due to the deformation process.

The uniaxial creep and failure behavior of the UHMWPE is being characterized. Room

temperature testing gives the interesting result that UHMWPE does not neck, but rather deforms

and draws homogeneously to failure. This is unlike the behavior of lower molecular weight

polyethylene. Our test results to date indicate that the time to failure in uniaxial testing is

shorter for continuous loading than it is for zero-tension cyclic (fatigue) loading at 0.002

Hz. Further testing needs to be performed to substantiate this result and to determine effects

of test frequency on lifetime.

The Crystallization, Morphology, Deformation, and Orientation of Polymers

F. A. Khoury and L. H. Bolz

Investigations of the morphology of crystalline polymers during the past year have been

mainly in the two areas outlined below.

The Habits of Polyethylene Crystals Grown From Solution at High Temperatures

The objective of this investigation is to determine the effects of crystallization

temperature, molecular weight, and polymer concentration on the morphology of chain-folded

polyethylene crystals grown from solution at temperatures which approach and overlap the

temperature range 1 1 8- 1 30 °C) in which the polymer crystallizes isothermally in the form of

axial ites or spherulites upon cooling from the molten state.

In an earlier experimental study, polyethylene fractions (molecular weights 11,400-

100,500) and unfractionated ultra high molecular weight polyethylene (molecular weight

~4.5 x 10 6

) were crystallized from 0.01 percent solutions in various solvents in the

temperature range 95-115 °C. Distinct trends in the effects of molecular weight and

undercooling on the lateral growth habits of the crystals were observed. During the past year

we have attempted to grow crystals from solutions of the same polymer concentration (0.01

percent) at even higher temperatures. This has been achieved with a fraction of molecular

weight 28,900, crystals of which were grown at temperatures up to 120 °C using docecanol as a solvent. An
In an attempt to deduce the nature of the conformation (e.g., tent-like or variously

curved) of the various species of polyethylene crystals we have grown between 95° and 120 °C, a study is under way in which scanning transmission electron microscopy and small-area (diameter

%0.4 pm) electron diffraction are being used to determine the details of the inclination of the

chain stems relative to the surface of the lamellae. Of particular interest in this connection

are crystals which, earlier results indicated, have asymmetric (apparently S-like) crosssectional shapes when viewed along the b-axis direction. Our present aim is to determine how

widespread and varied is the manifestation of this feature among the various types of

polyethylene crystals we have grown. We believe that such cyrstals will serve as useful models

for the constituent twisted lamellae in polyethylene spherulites grown from the melt at high

undercoolings. It has recently been reported in the literature that the constituent lamellae

in such spherulites, which lamellae are oriented with their b-axis parallel to the spherulite

radius, exhibit S-shaped cross-sections when viewed along that direction [R. H. Olley, A. M. Hodge, and D. C. Bassett, J. Poly. Sci. , Poly. Phys. Ed. , 1_7, 627 (1979)].

The Morphology of Compression Molded Ultra High Molecular Weight Polyethylene

Aspects of the morphology of compression molded ultra high moelcular weight polyethylene

(UHMWPE, molecular weight ^4.5 x 10 6 ), and the fine structural changes induced in molded sheets

of this material as a result of uniaxial deformation have been examined. This work is part of a new project which is sponsored by the FDA, and whose objectives are to characterize the

mechanical properties of UHMWPE (G. B. McKenna and J. M. Crissman) and to examine the

relationships between these properties and the morphology of the polymer. These relationships,

which bear importantly on the durability of products made from UHMWPE, are of particular

interest to the FDA because numerous components of artificial orthopedic implants (e.g., hip

cups, tibial plateaux) are made from this polymer.

Sheets of UHMWPE which were compression molded at temperatures in the range 190-230 °C and were subsequently cooled slowly to room temperature, all exhibited a memory of the grain-like

character of the as-polymerized raw polymer powder which is the usual starting material from

which the implant components are manufactured. The density of the sheets was 0.936.

Examiniation under the optical microscope, with cross polarizers, of thin cross-sections cut

from the sheets revealed a heterogeneous distribution of birefringent structures of varying

sizes. In some regions the sections had a very fine granular appearance. In others, larger

structures were seen, the largest of which were distinctly spherulitic. Small angle x-ray

diffraction patterns obtained from the sheets did not exhibit any distinguishable diffraction

ring. This is either because the thickness of the lamellae was greater than the largest spacing

(^300A), which can be resolved in the present instrument, or because there is a large

distribution in the thickness of the lamellae due to the fact that the polymer was not

crystallized i sothermal ly.

Dumbbell shaped samples cut from sheets molded at 200 °C were subjected to uniaxial

extension at 1 mm/min at 23 °C, 37 °C, and 70 °C. In contrast with lower molecular weight

linear polyethylene (e.g., molecular weight < 200,000) the samples deformed uniformly and did

not exhibit any necking even up to the breaking point. Current experiments are aimed at

determining the recovery of samples from deformation at 23 °C, 37 °C, and 70 °C to various

strains below the breaking strain. Low angle and wide angle x-ray diffraction and scanning

electron microscopy are being used in an attempt to determine the nature of the permanent and

recoverable changes in orientation and fine structure resulting from deformation to various

strain levels. Structural changes resulting from stress relaxation will also be examined.

Polymeric Sealants for Geothermal Energy

E. A. Kearsley

The Department of Energy envisions that within a matter of decades the exploitation of

geothermal energy resources will be making a substantial contribution to our national energy

needs. However, in order for this to be accomplished, it is necessary to stimulate several

associated technologies. The Division of Geothermal Energy of DOE has accordingly requested

help in developing tests of polymeric materials to screen likely candidates for use as geothermal sealants. Since there are many forms of seals used in the drilling and production of

geothermal wells, and down-hole 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

41
ambient down-hole 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 wel 1 -dri 1 1 i ng 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) affecting

the elastic properties of sealant materials aging under controlled conditions. With

information on how these rates depend on the parameters of the down-hole atmosphere, it should

be possible to estimate accurately the long-time behavior of seals of any geometry (e.g.,

packer seals, o-rings, chevron seals, etc.) in any conditions of interest.

The customary way of measuring rates of cross-link breaking and forming is that 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 is

completed, but there remains the task of establishing the most practical experimental methods

of making the measurements.

Currently, the technique is being evaluated using simulating temperatures but not

simulated geothermal fluids. The test samples are sealed in evacuated glass tubes during aging

(at 260 °C) to avoid oxidation, since geothermal atmospheres are normally reducing rather than

oxidizing. The conditions necessary to simulate complete relaxation prior to the measurement

of permanent-set are still not completely known. Concurrently, an apparatus is being

constructed to age samples in more realistic conditions, that is, in water compressed up to pressure of 5000 psi at temperatures up to 350 °C. Such conditions may induce hydrolysis of the

sealant materials, thus affecting bond stability.

Characterization of Polymeric Solids by 13 C NMR

D. L. VanderHart and S. J. Kryder

High resolution 13 C NMR of solid samples has been greatly aided by the recent development

of magic angle sample spinning (MASS) together with the technique of high-power proton

decoupling. With MASS, 13 C NMR lines in solids appear at their isotropic chemical shift

positions, just as they do in liquids, thereby enabling one to separate resonances corresponding to chemically different carbons. In the absence of MASS, 13 C lineshapes are much

broader, and different 13 C resonances are likely to show a modest to severe overlap.

Nevertheless, these lineshapes in chemically simple materials, e.g., polyethylene (PE), contain

interesting orientational information, and as discussed below, we have made use of such

measurements to follow the orientational behavior of noncrystalline PE chains during annealing.

For the last two years MASS capability has also been available on a spectrometer with a magnetic

field of 1.4T. This past year, however, a 4.7T superconducting-solenoid spectrometer was installed as an NML facility. This spectrometer, although principally equipped for liquidstate NMR, also has MASS capability in conjunction with 13 C NMR in solids, and this facility is

expected to become a more significant instrument for our program because of its higher

sensitivity.

Studies of Orientation in the Non-Crystalline Regions of Drawn Polymers

It has been demonstrated here that it is possible to separate 13 C signals in polyethylene

(PE) arising from chains having preferentially high mobility relative to crystalline chains.

42
Furthermore, it is possible to analyze the distribution of orientations. These studies are being extended to include ultra high molecular weight drawn PE whose macroscopic drawing

characteristics (maximum draw ratio, lack of necking) are quite distinct from the lower

molecular weight samples. Further, if samples can be obtained, it would be of interest to

examine Pennings-type solution-shear-aligned PE fibers because the morphology is established by

crystallization in shear flow rather than by deformation. Thus, one might expect more extended

chain material but perhaps a reduction of entanglement-related connectivity. There is current

effort to extend this method for measuring non-crystalline orientation to polyethylene

terephthalate (PET), which is a commonly used commercial fiber. In PET, preliminary

experiments have shown promise that the CH 2 resonance can be used to determine orientation in

the non-crystalline region. But PET is more complicated than PE in that the ratio of relaxation

times (molecular mobilities) between the crystalline and non-crystalline phases is expected to

be smaller than in PE; furthermore, there is some argument about whether crystallinity means organized molecular packing or merely all-trans chains. Further work on these substances will

also involve correlations with mechanical properties as well as the acquisition of a non- spinning probe for the 4.7T NML spectrometer to take advantage of its higher sensitivity. Use

of non-spinning 13 C NMR as a comparative tool in monitoring orientation in glassy polymers

below Tg should also be investigated.

Resolution in 13 C MASS Spectra in Polymers

This work is aimed at evaluating the capabilities of the 13 C MASS technique for 1) studying

relaxation of individual carbon sites, 2) studying tacticity and/or conformation in the solid

state, 3) using the method as an analytical tool, and 4) using linewidths as a source of

information about molecular motion or molecular packing.

We are currently in the final stages of preparing an extensive manuscript on the subject of

resolution in the 13 C NMR of hydrocarbons using MASS. One result of this study is that

molecular motion in the mid-kilohertz region produces overwhelming broadening for protonated

carbon resonances. Thus, if one wishes to perform analytical measurements on a sample and needs

best-available resolution, the ability to vary temperature and move to a region where motions

do not create inordinate broadening is highly desirable. Another outgrowth of looking into the

resolution question is the recognition that solid polymers often exhibit chemical shift

dispersions and discrete magnetic inequivalencies which are unique to the solid and which are averaged in solution. Chemical shift dispersions can arise from variation in the packing of

chains. This is a difficult problem to address theoretically because of the complex nature of

the chemical shift expressions. This problem was addressed experimentally by looking at

changes in resonance positions of the interior methylene resonances in the alkanes as a function of crystal structure. The n-alkanes are found to have four crystal habits, and

corresponding resonances were found to range over 1.3 ppm. Thus, it was concluded that packing

variations, particularly in glassy polymers, can account for chemical shift dispersions of the

order of 1-2 ppm and that no conformational variations need be invoked to explain such

dispersions. This is an important perspective to have gained.

With respect to discrete magnetic inequivalencies, consider crystalline isotactic

polystyrene which shows six distinct aromatic carbon resonances, whereas only four are observed

in solution. Variable temperature studies of the collapse of such inequivalencies in the solid

would give very specific information about the frequency and nature of molecular motion, e.g.,

initial collapse from six to four resonances in polystyrene would correspond to rotation of the

ring about the aromatic-aliphatic C-C bond direction at a frequency closely related to the

splitting. Therefore, one of the badly needed instrumental modifications required is to design

and build a variabl e- temperature MASS probe. It is not a simple matter to design such a probe

without sacrificing sensitivity. Nevertheless, it is a high priority item to equip both the

high and low field instruments with such a probe in order to:

(1) move away from undesirable temperatures to get improved resolution,

(2) study temperature dependent motions in polymers,

(3) improve quantitation (will be discussed) for analytical applications, and

(4) study conformational equilibria.

43
Quantitation in 13 C NMR Spectra of Solids

If a broad-band pulse is applied to 13 C spins having equilibrium Boltzmann populations,

resulting NMR spectra are quantitative in the sense that each 13 C nucleus appears to make an equal contribution to the total signal. Because 13 C signals are inherently weak and because

many carbons have no directly bonded protons (thereby making their relaxation times long), the

method just described is seldom used to generate 13 C signals. Rather, cross-polarization

techniques are usually used in which 13 C magnetization is transferred from protons to carbons.

While this method generally enhances the 13 C signals over the first experiment by a factor of 3-

4, and further, allows one to repeat scans in a time determined by the proton rather than

slowest carbon relaxation, the quantitativeness of the resulting spectra is no longer assured.

On theoretical grounds, distortions of true intensities can be expected both when molecular

motions are in the mid- kilohertz range and when molecules are isotropically tumbling and

translating. This general area deserves more attention in polymers, particularly in blends,

copolymers, or multiphase polymers. Such distortions are observed in the spectra of PE, as well

as polycarbonate and polyethylene oxide. For exploring the problem of quantitation,

temperature is an essential variable. A particular area where quantitation problems are likely

to be severe is analysis of extent of curing, e.g. , in dental composites.

Impact and Use of the High Field NMR

There is no doubt that sensitivity per scan is higher at high field, but relaxation times

for slowly moving molecules may increase tenfold with respect to the lower field, thereby

making relative sensitivities comparable. A perspective must be developed. Resolution using

MASS at high versus low field is still an open question. It is only a rare case where

resolution dramatically improves; nevertheless, a more complete perspective must be developed

here in order to optimize spectral information.

Acoustic Emission of Crazing Polymers

A. Peterlin, R. E. Green 1

, B. B. Djordjevic 1

, and R. C. Murphy 1

After repeated attempts to observe acoustic emission in strained poly(methyl methacrylate)

(PMMA), we have concluded that the emission occurs in the millisecond range where the noise

background of the stretching machine completely masks the acoustic emission. Therefore, a statically bent PMMA specimen was observed with a reflected laser beam during the wetting of the

bent surface by a droplet of benzene. The formation of crazes and vertical displacements of the

surface of the bent slab of PMMA were observed. Indeed, the duration of the pulse, detected by

the vertical motion of the polymer surfaces reflecting the laser beam, turned out to be in the

millisecond range. Time extension of the pulse has shown a fine structure which is mainly

caused by the interference of the primary signal with the waves reflected at the fixed ends of

the bent slab. The reflections distort the acoustic emission signal to such an extent that its

time dependence cannot be determined.

The optical method has definitively shown that the craze forms relatively slowly in about

1 ms and that it forms in a great many single steps of almost equal amplitude. Concurrently,

the bent slab assumes a more bent position as a consequence of the elongation of the convex bent

surface by the newly formed craze. Since the new position is obtained by damped oscillations

which displace the reflecting surface of the bent slab vertically, the laser signal also

records this movement which has no direct connection to the acoustic emission of the craze.

Non-Linear Elastic Behavior of Polymeric Materials

E. A. Kearsley, G. B. McKenna, and L. J. Zapas

The theory of finite deformations of an elastic medium is often used with the added

restriction of incompressibility of the medium. This restriction makes possible the solution

of several classes of problems in terms of an unspecified strain-energy potential; however, it

excludes the possibility that the elastic material properties depend on pressure. To make

possible the use of these solutions in cases where material properties are pressure dependent,

1 Johns Hopkins University.

44
we have derived a different form of the theory. Through a Legendre transformation, the

equations of finite elasticity of a compressible medium were formulated in terms of an elastic

potential whose independent variables are pressure and shear rather than the usual deformation

invariants. This elastic potential has no explicit dependence on volume change. Rather, the

two derivatives of the potential are equal to the stress deviator and the volume change. The

form of the resulting elasticity equations makes clear the mechanical effects of introducing a large ratio of bulk modulus to shear modulus into elasticity theory and leads to a theory of an (almost) incompressible medium for which the shear modulus depends upon the isotropic part of

the stress. Through the elastic potential, some specific relations among the pressure

coefficients of the mechanical moduli and the change of volume with deformation can be derived.

These relations are accessible to experiment, and they suggest an interesting method of

elucidating the effects of pressure on the mechanical behavior of natural rubber.

Our recent work with the theory of rubber elasticity has shown that the strain-energy

function for elastomers (which determines the non-linear elastic behavior) may be measurable

from experiments simpler than hitherto thought possible. However, the method depends upon the

strain-energy relation having a special form (the Valanis-Landel form). Although some data

already in the literature support this requirement, there are also some published data which

raise questions about its validity. The point needs clarification. Experiments are underway

to test the validity of the Valanis-Landel form through an experiment on simultaneous extension

and torsion of cylinders of elastomers.

Non-Linear Viscoelastic Behavior of Poly(methyl methacrylate)

G. B. McKenna and L. J. Zapas

We have conducted single step stress relaxation experiments on cylinders of poly(methyl

methacrylate) (PMMA) where we measured torque and normal force responses as functions of time

and angle of twist. By assuming that torsion is an isochoric motion and that volume effects are separable, we obtained [1] isochronal values for the derivatives of the strain potential

function, 3W/3I 1 and 3W/3I 2. Our results showed that SW/SIi is negative, while 3W/3I 2 is

positive and greater in magnitude than dVI/dl 1. These findings provided the possibility of

explaining the phenomenon observed by Sternstein and Ho [2] that the single step stress

relaxation responses of PMMA are different in torsion and in simple extension. Specifically,

the time rate of decay of stress is significantly higher in torsion than in extension. This

phenomenon was observed at small strains where the stress responses in torsion and extension were linear in the appropriate strain measures.

Using a form of the viscoelastic strain potential function similar to the Valanis-Landel

[3] form of the strain energy function for elastic materials, we calculated the response in

simple extension from our torsion-normal force determined values of 3W/3I! and 3W/3I 2

. Although we obtained good agreement between our calculated and our observed extensional

behaviors, we could not account fully for the observations of Sternstein and Ho [2].

Table 1 shows some isochronal data for 3W/3I 1 (t) = W x (t) and 3W/3l 2 (t) = W2 (t) for

measurements made on PMMA in the form of both annealed rod and unconditioned tube. We remark on three things about these data. First, W x (t) is negative while W2 (t) is positive and of greater

magnitude than W x (t). This is different from the behavior usually observed in rubbers and

polymer melts, where Wi is usually positive and larger than W2

. Another observation we can make

is that W x (t) and W2 (t) exhibit different time dependences.

Also, the time dependence of the modulus, 2(W X +W2 ), is different from that of either W^t)

or W2 (t). (At the limit of small strains, i.e., in the linear range, the modulus

G(t) = 2[W x (t) + W2 (t)]). Finally, the magnitude of W 1 (t) + W2 (t) is different for the two

different PMMA's. This is not attributable to the geometry difference but may be due to the

differences in both source and thermal histories of the materials.

45
Table 1

Some Isochronal Values of W^t) + W2 (t), W x (t) and W2 (t) for PMMA

Annealed Rod

Wi +W2 Wi W2 Wi+W2 Wi W2 YR GPa GPa GPa GPa GPa GPa

1.64s 0.00252 0.63 -2.19 2.82 1678s 0.488 -1.94 2.43

0.00946 0.59 -1.98 2.57 0.456 -1.39 1.84

0.0126 0.58 -1.82 2.40 0.442 -1.15 1.60

0.0252 0.53 -1.10 1.63 0.379 -0.616 0.995

Unconditioned Tube

1.64s 0.0095 0.48 -1.24 1.72 1678s 0.36 -0.79 1.15

0.012 0.46 -1.24 1.70 0.35 -0.76 1.11

0.016 0.45 -1.14 1.59 0.33 -0.65 0.98

0.0208 0.44 -0.96 1.40 0.31 -0.47 0.78

From these data we determined isochrones for the viscoelastic V-L function w' (A)

for both the rods and tubes. From the w'(A,t) we then calculated a xl (t) - cr 22 (t) for

simple extension. The agreement between the calculations and the experiments was within

the uncertainty for our values of w'(A,t). (This uncertainty in the small strain region

is approximately ±15 percent due to the large uncertainties in the normal stress measurements

in this region). Of greater interest is the comparison of the relaxation rates in extension

and torsion.

Table 2 summarizes our results and those of Sternstein and Flo [2]. The relaxation

rates given in Table 2 are calculated from the slopes of log (stress) vs. log (time)

plots. There are several things about these data which need to be discussed. First,

Sternstein and Ho obtain greatly different rates of relaxation in extension and torsion (-0.0195

vs. -0.0329) at strains of s - 0.005 and y = 0.01, respectively. Our data in torsion show

a slightly higher relaxation rate than theirs for y = 0.01 which increases as y increases.

Also, our data indicate that there is little difference in relaxation rates in extension

and torsion at strains less than e = 0.02 and y = 0.04. But at strains of e - 0.02 and

y = 0.04 and higher, we find that there is a more rapid torsional relaxation rate than

extensional relaxation rate (-0.058 vs. -0.047). We are currently planning experiments to

further elucidate these differences and perhaps account for the differences between our data and those of Sternstein and Ho.

Table 2

Relaxation Rates for PMMA for Different States of Deformation

Strai n Relaxation Rate 1 Tension Simple

Predicted Observed Torsi on 2 Shear3

Data of Sternstein & Ho 1

: £ = 0.005; y = 0.01 -- -0.0195 -0.0329 --

Unconditioned Tubes:

£ = 0.01 ; y = 0.02

£ = 0. 02 ; y = 0.04

-0.0397

-0.051

-0.0384

-0.047

-0.0377

-0.0581

-0.0450

-0.0634

Annealed Rods:

£ = 0.005; y = 0.01

£ = 0.0075; y = 0.015

-0.0370

-0.0371

-0.0319

-0.0335

-0.0345

-0.0360

-0.0395

-0.0420

Calculated from the slope of log (stress) vs. log (strain) plots.

Rate is per decade of time.

2 0bserved experimentally, y is the maximum strain in the tube or rod.

Calculated from values of Wj and W2 obtained from torsion-normal

force measurements, y is the shear strain.

46
References

(1) G. B. McKenna and L. J. Zapas, "Determination of the Time Dependent Strain Potential

Function in Poly(methyl methacrylate)," paper presented at the 49th Annual Meeting of the

Society of Rheology, Houston, Texas, October 1978.

(2) S. S. Sternstein and T. C. Ho, "Biaxial Stress Relaxation in Glassy Polymers: Poly(methyl

methacrylate)," J. Appl. Phys. , 4-3, 4370 (1972).

(3) K. C. Valanis and R. F. Landel , "The Strain Energy Function of a Hyperelastic Material in

Terms of Extension Ratios," J. Appl. Phys., 38, 2997 (1967).

Retractive Forces in Drawn Low Density Polyethylene During Annealing

A. Peterlin, R. Russo 1

, F. DeCandia 1, and V. Vittoria 1

The retractive forces in drawn low density polyethylene depend on temperature and time.

At room temperature, the material looks fairly stable. Above 70 °C, the drawn sample starts to

shrink. The shrinkage forces can be observed on a material with fixed ends. At a given

temperature, they first increase to a maximum and then drop to a relatively high limiting value.

The maximum force and the asymptotic value have a maximum at about 90 °C.

If the sample is heated at a sufficiently slow rate, the restoring force reaches a maximum

at about 90 °C and subsequently drops almost to zero near the melting point of the material.

The molecular explanation of the observed effects is based on the mobilization of taut tie

molecules and on their relaxation at the high temperature of the annealing which permits a pulling of chain sections from the crystal blocks in which the taut tie molecules are fixed.

During cooling, the restoring forces are substantially lower than during heating as a consequence of the relaxation of the taut tie molecules by the annealing effect of the previous

heating.

Permeation Performance of Polyethylene Used in Containers for

Hazardous Materials Transportation

J. C. Phillips

The initial phase of this work involved the development of test methods for the permeation

performance of polyethylene shipping containers to be used by the Department of Transportation.

These experiments consisted of weight loss determinations for an n-alkane series, n-alcohol

series, and n-carboxylic ester series. The loss rate, Q^, results were correlated with an effective carbon atom number, n g

, for each compound. Due to^limited chain lengths (N^ < 8), the

shorter members of the alcohol and ester series showed deviations from linear behavior of log Q. versus N^.

The final phase of this work was concerned with loss rate measurements at t = 50 °C for

permeants of the n-alcohol and n-carboxylic ester series in which chain lengths were extended

to N^ = 16. For the permeants studied and the polyethylene (PE) bottles used (p ^ 0.92 g/cm3 and p ^ 0.94 g/cm3

), the effective carbon atom number was reasonably correlated with the loss

rate (i.e., log Q

A versus n g was linear and parallel for each density bottle). By using loss

rate measurements from the

e low density bottle for a group of miscellaneous compounds (1,2-

dichl oroethane , acetone, methyl ethyl ketone, acetonitrile), the loss rate for the high density

bottle was adequately predicted for these compounds.

This study has verified, at least for the permeants and PE bottles used, that the effective

carbon atom number is a convenient parameter for transferring the results of permeation

measurements among shipping containers made from various PE resins and, thereby, simplifies the

prediction of transmission performance.

’Laboratory for the Technology of Polymers and Rheology, CNR Naples, Italy.

47
Durability of Paper

J. C. Smith, E. E. Toth, and E. L. Graminski

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 the bondability of the

pulp fibers and on the cellulose-water interaction in rag and wood pulps have helped to provide

some of this background information.

Parameters for characterizing interfiber bond strength can be obtained from tensile tests

on a low density open-web handsheet prepared from the pulp to be evaluated. The forceelongation curve from a specimen of this handsheet contains numerous force drops, each drop

caused by the breakage of a bond between fibers constituting the handsheet network. The

relative number of bonds per unit area can be characterized by the average elongation between

bond breaks. The bond strength can be characterized by an average of the force-drop magnitudes,

or by an average of the energy losses resulting from the force drops. The average of the force

levels obtained in a series of tests can also be used to characterize bond strength. The above

parameters, however, are not very precise because of fluctuations in the uniformity of the test

specimens.

Recent work has shown that the force elongation curve of a low density open-web test

specimen has the form

F = A[exp(x/x

c

) - 1],

where F is the force, and x is the elongation. The two parameters, A and x , are sensitive to the number of fibers per unit area in the specimen tested. Moreover, during a test, A and x vary in value as the test proceeds, reflecting damage to the specimen and changes in the

location of bond breaks. This possibility of characterizing the state of a specimen at various

stages of a test may enable the measurement of bonding parameters with improved precision.

Knowledge of the force-elongation curve parameters will also make possible the comparison of

bonding parameters obtained from tests on samples of different densities.

Morphologies of the handsheets and constituent pulp fibers are being examined by scanning

electron microscopy. Results of these investigations suggest that bonding in currency pulps

may be due to the presence of a large fraction of fines which act as a "glue". These fines are not present in the wood pulps, and bonding between wood fibers depends on the ability of their

surfaces to conform and establish intimate contacts at the junctions.

During the preparation process, pulp is subjected to mechanical action such as beating or refining. This treatment causes fibers to imbibe water and become more flexible, thereby

facilitating interfiber conformation. Elowever, the microstructure of the prepared pulp is

influenced by the way in which water is bound to the fibers, and this varies with the kind of

pulp material. This is being studied by measuring the proportions of bound and free water in

different pulp samples.

The water imbibed by a pulp specimen is measured by solute exclusion. A dextran pulp

specimen is added to a solution of dextran in water, and the excess water in the specimen

dilutes the solution. The amount of the dilution is measured by polarimetry, and the imbibed

water, or fiber saturation point, of the specimen is calculated. Part of the imbibed water is

tightly bound to the cellulose and does not freeze at temperatures down to 223 K. This bound

water fraction is measured by differential scanning calorimetry.

It is found that beating causes increasing amounts of water to be imbibed by both cotton

and wood pulp fibers. Elowever, beating causes an increasing fraction of the water imbibed to be

48
bound in cotton. This does not happen to as great an extent in wood pulp. It is believed that

free water promotes flexibility and that bound water is attributed to breakdown of the

crystalline structure. Thus, beating of wood pulp produces flexible conformable wood pulp

fibers, but causes fibrillation and fines formation in cotton fibers.

Disorder in Drawn and Annealed Polyethylene

A. Peterlin, R. G. Snyder 1

, and J. R. Scherer 1

In drawn high density polyethylene, the accordion type Raman scattering indicates the

existence of extremely short chain stems. A possible interpretation is that they are not chain

stems going through the whole crystal blocks from one fold surface to the next one, but straight

chain stems between two gauche defects which interrupt the longitudinal accordion mode

oscillation. If one may assume the existence of one such randomly located gauche defect per two

chain stems in the crystal blocks of the drawn polyethylene, one can well represent the

experimental data.

University of California, Berkeley.

49
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 dental 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 adhesive composite

restorative materials of greater durability and wear resistance, and improved base metal

alloy alternatives to the costly gold alloy 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 and for defining the interactions that occur

thereon.

Dental research directions in support of the objective are established col 1 aborati vely

with the American Dental Association, the National Institute of Dental Research, and the

Department of Defense 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, Resin, Sealant, and Cement Chemistry and Development

G. M. Brauer, J. M. Antonucci, J. W. Stansbury, R. E. Dehl , J. M. Cassel,

R. L. Bowen 1

, H. Argentar 1, D. W. Misra 1, and T. Chen 2

Current efforts are directed toward upgrading the quality of composite restorative

materials with regard to color and storage stability, toxicity effects, adhesiveness, and

durability. Structure-property relationships are developed and used as guides to the

synthesis of new polymerization accelerators for dental resins. Laboratory synthesis and

evaluation efforts have developed an amine accelerator with a reactivity that permits a threefold reduction in the concentration of accelerator required. The generic biocompatible

nature of the amine, combined with the reduced concentration required, indicates that

dimethylaminophenylacetic acid will prove a valuable dental resin component. Strong

interest has been expressed by the dental manufacturers in a second amine developed to

accelerate the curing of denture base materials without imparting any color. Efforts have

continued to make a potentially very useful peroxide ascorbic acid copper initiator accelerator

system more practicable. Invited papers covering initiator accelerator systems for acrylic

resins and composites and new monomers for use in dentistry were presented at the Symposium

on Biomedical and Dental Applications sponsored by the ACS in Houston.

The mechanism of reinforcement of dental composite restorative materials through

silane inorganic fillers is being examined as a means of improving the durability of such

materials when used in stress bearing applications. Bond formation between the silane

coupling agent and the filler is monitored by infrared analysis and indicates that addition

of selected amines to the carrier solvent improves the coupling effectiveness of the

si 1 ane.

A major problem encountered in the investigation of the properties of dental composite

restorative materials is the absence of quantitative analytical methods for determining

chemical composition in the solid state. Infrared (IR) spectroscopy, which is widely used

to analyze chemical composition, is useful for studying dental composites, but Fourier

Transform capability is required because of light scattering and absorption by the glass

filler. Measurements are currently being made with the new IR equipment of the Center for

Materials Science. Recently we have performed some Raman spectroscopic analyses of dental

composites and the various components of the composites, using the spectrometer in the

Center. Preliminary results indicate that the Raman techni que wi 1 1 ci rcumvent many of the

Research Associate, American Dental Association.

2 Guest worker, Food and Drug Administration.

50
problems encountered with infrared analysis and will allow at least semiquantitative

estimates to be made of chemical groups such as unreacted carbon/carbon double bonds in the

polymerized composite matrix. Further work is in progress, as we use the Raman technique

to analyze dental composite materials prepared by different experimental procedures. We

are also investigating NMR as a means of studying the state of molecular motion in these

presumably highly cross-linked resin systems. It is expected that the information thus

obtained will be useful in evaluating the performance of dental materials.

At the request of the Council on Dental Materials, Instruments and Equipment of the

American Dental Association, a status report for publication in the Association's Journal was prepared on the desirability of using radiopaque plastics in dentistry.

Development of Adhesive Bonding Technique

G. M. Brauer, R. L. Bowen 1

, J. M. Antonucci, D. W. Misra 1

, J. W. Stansbury, and J. M. Cassel

Strong mechanical bonding of acrylic resins to enamel surfaces can be obtained through

acid etching of such surfaces, followed by resins or composite formulations capable of

wetting and penetrating the newly created surfaces. Such treatment has not been applicable

to surfaces of dentin and has not been entirely successful in the caries preventive application

of pit and fissure sealants to the occlusal enamel surfaces of children's teeth.

One approach to adhesive bonding that is being pursued is the development of multifunctional molecules designed to interact with calcium on the tooth surface and with the i

si tu polymerizing dental resin. Using the diametral tensile strength of hydroxyapatite filled

composites as a measure of the adhesiveness where the filler is coated with the coupling

agent of interest, several surface active polymerization activators appear to offer promise.

One new direction taken recently has been the development of physiological buffer

solutions capable of dissolving the smeared surface layers on cut dentin and of isotonic

mordant solutions to improve bonding sites. Isotonic methacrylate monomer formulations

containing adhesion promoting coupling agents have been developed that should not induce

osmotic insult to odontoblasts and pulp tissues.

Wear Resistance and Mechanical Properties of Dental Materials

W. Wu, J. E. McKinney, J. M. Cassel, and E. Cobb2

In a study of the mechanisms governing both clinical and laboratory wear of dental

restorative materials, a silver staining technique has been developed to examine structural

changes in the damage zone immediately beneath the worn surface. Worn specimens are cross sectioned and examined by microscopy for quantification of the micro defects. Initially,

clinically worn specimens are being provided through a guest worker from Georgetown University

Dental School. The results to date suggest that greater efforts to introduce erosion

effects into accelerated wear testing are required. Equipment to accomplish this has been

designed and assembled.

With pin-on-disc wear instrumentation we have demonstrated that wear is very irregular,

varying by a factor of two over different positions on the same specimen. The data support

the use of durapatite, a form of sintered hydroxyapatite, as an appropriate substitute for

human tooth enamel for i_n vi tro measurements. However, microdefect analysis of ijn vivo and

i n vi tro worn specimens brings into question the relevancy of j_n vi tro data generated with

enamel pins. The effect of loading on the accelerated wear results generated on dental

composite specimens with hard (durapatite) and softer (steel) pins is under study. Initial

transient wear regions indicate the presence of surface layers that inhibit wear of certain

metals and alloys. These surface layers reform during periods of inactivity. Since this

phenomenon may play a very important role in enhancing i_n vi vo durability of amalgams and

other dental alloys, efforts are in progress to determine surface compositions by means of

Auger Electron Spectroscopy.

Research Associate, American Dental Association.

2 Guest worker, Georgetown University Dental School.

51
Auger Electron Spectroscopy (AES) Applied to Wear Analysis of

Dental Alloys

J. E. McKinney, R. E. Dehl , and W. H. Grant

In vi tro accelerated wear measurements on several dental alloys have been characterized

by low initial wear rates followed by higher steady state rates of wear. We have attributed

this behavior to the formation of a passive oxide surface layer, with higher wear resistance

than the bulk material, that is reformed during periods of mechanical inactivity.

We have initiated examination of these surface layers by AES. Following a period to develop familiarity with the instrumentation (Surface Science Division, Center for Thermodynamics and Molecular Science) and confidence in the technique, measurements have been

made on an amalgam, on three crown and bridge alloys, and on nickel as a standard.

Preliminary measurements by argon ion sputtering of the surfaces to a depth of 10 nm has indicated distinct changes in composition as a function of depth into the surface

layer. It is planned to generate AES depth profiles on a number of dental alloys with

a goal of correlating surface layer analysis to the i_n vi tro wear and finally to

i n vi vo durability. Analysis of wearing surface layers may prove important for long

term biocompatibility consideration including toxicity, chemical irritation,

sensitization, and ginginal inflammation from plaque.

Porcelain Fused to Base Metal Alloys

J. A. Tesk, R. W. Hinman 1 ,E. E. Parry 1

, and A. Holmes

This investigation is designed to develop knowledge of the physical, mechanical, and

chemical properties of porcelain veneering alloys and their associated bonding porcelains

relative to their use in cast crown and fixed partial dentures; to determine the effects of

fabrication techniques on clinical serviceability of the restoration; to investigate

factors affecting the bonding of porcelain to new dental alloys; and to determine potential

methods for modification of fabrication techniques which may lead to improved clinical

service. The chemical, physical, and mechanical properties of new, non-precious alloys are

so different from those of the gold alloys that the application of the same fabrication

techniques for porcelain bonding could be expected to be unsuccessful. This has proven to

be the case, and not enough is yet known to render non-precious metal porcelain restorations

as trouble free as gold porcelain restorations.

It is suspected that a major cause of porcelain metal failure resides in the residual

stress which develops upon cooling of fired porcelain restorations. To address this

problem, a multi -tiered approach has been taken: a) development of precise knowledge of

the thermal expansion behavior and other mechanical and physical properties of porcelain

and alloys after being subjected to dental laboratory firing conditions; b) the fabrication,

according to dental laboratory fabrication procedures, of split ring composites of porcelain

(opaque plus body) veneered to alloys and determination of the accompanying change in gap;

c) the development of finite element model and elasticity analysis to examine the residual

stress states and accompanying gap changes; and d) examination of porcelain and alloy for

microstructural characteristics as well as examination of the microstructure of the porcelain

alloy composite for stress induced (or other) flaws. Ultimately, the data developed in a)

and b) will be used in the theoretical program in c) to determine the "macroscopic" residual

stress states developed in the split ring. The analyses may further be developed with the

knowledge developed in d), which may involve the superposition of microscopic stresses on the macroscopic stresses.

Results obtained thus far have shown that significant differences exist in expansion

of porcelains which have received comparable levels of firing according to manufacturers'

instructions. Differences exist between manufacturers' porcelains, and some develop

significantly different expansions with repeated firing. Large differences in the amount

of residual stress are fired into different porcelains, as indicated by the amount of

stress relief which occurs.

Research Associate, U. S. Navy.

52
As compatibility depends not only on the stresses set up by differences in thermal

contraction, but on geometrical shape and the thermal (or other) relief of stress, a split

ring was conceived as presenting a reasonably close approximation to a clinical crown while

providing a technique to assess the development of residual stress. Experimental and

theoretical results of studies of gap and shape changes indicate that a previously derived

mathematical expression is not sufficient to describe the complex interactions which exist

and that discrepancies between theoretical and experimental results indicate stress relief

at temperatures lower than T . These effects will be evaluated with refinements to finite

element model and in view (?f the differences in crystallinity which have been shown to

exist by Raman laser spectroscopic observations of the procelains.

Dental Casting Alloys

J. A. Tesk, R. M. Waterstrat 1

, R. W. Hinman 2

, and E. E. Parry2

The commercial alloys now available for dental castings contain significant amounts of

gold, silver, palladium, cobalt, nickel, and chromium. These metals formerly were abundantly

available, but in recent years there have been sharp fluctuations in the price of these

materials. It appears that the market for these metals will continue to be increasingly

unstable, since there are no viable domestic sources of the ores, and the United States

must import these metals from foreign countries which are susceptible to political or economic upheavals. The cost of these alloys is an important factor in dentistry; and in

order to avoid future problems, it is prudent to plan some strategies to meet unexpected

shortages or sharp increases in price. This can be accomplished by developing alternate

alloys, and particularly those whose ores are available domestically. Titanium is an example of one such alternate. We have demonstrated that it is possible to produce precision

dental castings based on titanium, but it is necessary to define the basic properties of

these alloys before any laboratory castings can be produced for clinical use. During the

past year, biocompatibility studies were completed on a titanium- 13 percent copper alloy in

cooperation with Dr. Frank Young at the Medical College of South Carolina. The results

indicate that the alloy is very well tolerated in soft tissues. This is an important step

toward eventual clinical trials in humans.

The ease with which a molten alloy fills the refractory mold cavity during the casting

process is another problem that has been associated with the use of non-precious alloys.

In an effort to ascertain the magnitude of this problem, an objective procedure for measuring

the "castabi 1 i ty" of dental alloys was developed as an early phase of this project and

identified in a previous report. Early data resulting from this test method were plagued

by unacceptably high variability. More recently, a modification of the pattern sprue has

been tested, which results in much improved data. Using this procedural modification,

extensive study has been undertaken to illustrate the differences in castabi lity for

various alloys when following the manufacturer's casting instructions. This work suggests

that some non-precious alloys are relatively easy to manage in the laboratory. Early

subjective clinical laboratory results appear to correlate quite well with measured values

gathered in this project. The development of an objective technique to assess the correlation

with margins on clinical crowns is desirable and will be pursued.

Dental Ceramics

C. P. Mabie 1

, D. L. Menis 1

, and R. L. Trout 1

Work continues on the formulation of lower fusing dental porcelain frits prepared by

the gel route. Frits have been made by the gel route which mature in a 12 minute air fire

at 822 °C. These appear suitable for metal ceramic applications and have a thermal expansion

greater than 12 x 10 6 /°C between 23 and 400 °C. A high expansion rate is desirable to

match those of some metals. The fusion or maturation temperature is 125 °C lower than the

current lowest fusing commercial metal ceramic porcelain. Solubility of the low fusing

porcelain is in the range of current commercial products. Deformation temperature under

applied load is about 650 °C, the same as many other metal ceramic body porcelains.

Research Associate, American Dental Association.

2 Research Associate, U. S. Navy.

53
Other porcelain frits have been formulated which fuse at lower than 900 °C. Some of

these have thermal expansions greater than 14 x 10 _6 /°C when measured between 23 and

400 °C. Solubilities tend to be high, but they are still within the commercial range.

Many of these have very low deformation temperatures, i.e., the lowest temperature where

stress between metal and ceramic may be relieved. Work continues on lowering the solubilities

of these porcelains.

At least two dental companies have decided to experiment with gel route prepared

frits. The gel route has potential for facilitating the introduction of nonradioactive

phosphors to replace uranium in teeth.

Irradiation Effects From Neutron Activated Dental Materials

J. A. Tesk

A potential source of radiation exposure which has not received direct attention

involves secondary radiation from dental restorations activated by primary exposure to neutrons. This could present an additional hazard for the civilian and military personnel

surviving exposure to a neutron bomb, for reactor operators and experimentalists suffering

accidental exposure, for cancer patients receiving intense localized neutron radiation

therapy, and others occupationally exposed to neutron radiation. Accordingly, calculations were made to estimate the additional dose of radiation (p + y) delivered to local oral

tissues by neutron activated gold crowns. A primary 50 REM exposure was used as the

baseline neutron exposure, as this clearly appears to be a complete survival dose for

whole body exposure. For calculation purposes, a single gold crown of 2 grams was simulated

by a disc 0.5 cm in radius and 0.14 cm thick located entirely on the buccal or lingual

sides of a tooth to provide close approximation to soft tissue. We have concluded that

secondary radiation doses from gold crowns activated by sublethal neutron fluences are comparable to the original dose from the neutrons. Results indicate that a 50 REM neutron

dose would subsequently be accompanied by ^30 REM. Higher primary neutron doses are followed by higher secondary doses (a high survival, whole body neutron dose of 200 REM is

followed by ^120 REM).

Dental or implant materials with major constituents behaving similarly to gold nuclei

and irradiated by neutrons during cancer therapy will generate secondary doses comparable

to the primary and must be duly considered. Long range effects of partial irradiation of

an organ are not well known. For the levels presented, concern appears warranted for

minimizing exposure. This research has been summarized in an article to be submitted to Medical Physics.

Clinical and Laboratory Investigation of Dental Amalgams

N. W. Rupp 1

, G. C. Paf fenbarger 1, R. M. Waterstrat 1, and R. Busby 1

The reason for the progressive deterioration of amalgam restorations is a subject of

intense interest although the theoretical understanding of this behavior is not well

developed. Creep and corrosion are generally recognized as being important factors, but

there is considerable controversy about the relative importance of these two factors, and

it is possible that other significant factors have been overlooked.

Amalgam is a composite mixture of about six major constituents or "phases". The

chemical and physical properties of such a mixture will depend on the properties of the

individual phases, the percentage of each phase in the mixture, the size and shape of the

crystals, and the properties of the interfaces between each phase. Thus, it is important

to study the microstructures of each phase and to identify the tendencies for a chemical

element to occur preferentially in certain regions of the microstructure. Elements such

as tin, copper, manganese, and zinc are known to exhibit such behavior, and they produce

important effects on the properties of the amalgam. These effects are being identified in

a variety of experimental and commercial amalgams. An effort is then made to determine

the relationships between the observed microstructure and the clinical behavior of the

amal gams.

Research Associate, American Dental Association.

54
Currently, we are concentrating on the laboratory phase of the project. Dimensional

changes are being observed for unrestricted specimens which have been stored in air at

various temperatures for over three years. Seven pairs of alloys (zinc-containing paired

with non-zinc-containing alloys of the same brand) have been under observation. All of

the zinc-containing alloys made amalgams that continued to expand for the three years.

The zinc-free amalgams all contracted. When one percent of powdered zinc was added to one

of the non-zinc alloys, the change in dimension increased from -5 pm/cm for the non-zinc

to +273 pm/cm. Thus, it would seem that zinc plays a role in the diffusion of mercury in

hardened amalgam. This new knowledge of the role of zinc in the alloy may contribute to

formula changes which could further improve the durability of amalgam restorations.

Dental Enamel Chemistry and Preventive Dental Treatments

W. E. Brown 1

, L. C. Chow 1

, M. Mathew 1, G. L. Vogel 1

, M. Tung 1

, S. Takagi 1

, T. Gregory 1

, H. Heaton 1, and P. Patel 1

The objective of this project is to develop and apply fundamental information on the

solubility and crystallographic structure 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 physicochemical

models of the caries process to include insight into the mechanisms by which impurities

and defects are incorporated into 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.

The structure of the following highly hydrated compounds has been determined:

MgNaP04 -9H 2 0 and Ca 4 Al Si (S0 4 )F 13 • 12H 2 0. These studies on some of the first known examples

in which the phosphate ions are completely surrounded with water molecules provide a new structural basis for understanding chemical properties of the physiologically important

phosphate ion in aqueous solutions.

For clinical application of fluoride in the past we have used a two-step process in

which the tooth was first treated with CaHP0 4 *2H 2 0-formi ng solution, and then the CaHP0 4

- 2H 2 0 was converted to fluorapatite by a conventional fluoride solution. This procedure was shown to greatly increase the i ncorporation of permanently bound fluoride into enamel. We now have promising data for a new single step procedure which involves formation of

CaHP04 -2H 2 0 in the enamel. Jji vitro results showed that this procedure should be much

more acceptable for clinical practice than a two-step procedure.

The use of relatively frequent mouth rinses with solutions containing low amounts of

fluoride appears to be coming into favor over the use of infrequent treatments with

concentrated solutions. We have made two j_n vitro studies in which a CaHP0 4

- 2H 2 0-formi ng

step is incorporated into the fluoride rinse procedure. The results from these studies

showed that the permanent fluoride uptake by the enamel was significantly increased over a method currently used.

A new dental cement system comprising primarily calcium phosphate has been developed.

At present, the cement has a compressive strength only about one-half that of ZnO cement

and requires a setting time of about 15 minutes. Both the strength and setting time are expected to improve as the materials and procedures are modified. This cement has many

potential applications in dentistry.

Progress in utilizing ultra-micro techniques to simulate and study the decay process

has been made in several areas. This technique has produced, for the first time, information

on calcium, phosphate, chloride concentration changes and the change in pH within enamel

when the tooth specimen is undergoing a carious- like demineralization. This information

provides important new insights into the mechanism of caries formation and has application

to enamel remineralization processes as well.

Research Associate, American Dental Association.

55
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 presently investigating both aspects of this important problem by the use of radiol abel 1 ed

polymers to study the adherence of the film and by Auger Electron Spectroscopy to study

the uniformity of surface coverage by the polymer.

One measure of the energy of attachment or adhesive strength 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 desorption rate is affected both by the

free energy of attachment of each segment of the polymer molecule with the surface and by

the number of attached segments per molecule. The results of previous NBS studies, using

radiol abel 1 ed 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. Further experiments are in progress to guantitate

these observations by systematically varying the amount of polymer initially adsorbed,

followed by a careful study of the amount remaining after selected intervals of desorption.

In this way, we expect to learn whether the polymer molecules which first arrive at the

surface have a higher adsorption energy than the later arrivals, and whether such variables

as the solvent used to deposit the film and the time spent in depositing a given amount of

polymer on the surface significantly affect the adhesive strength of the film.

Auger Electron Spectroscopy (AES) is a technique for determining the elemental

composition of the topmost 5-10 nm of a solid surface. The AES probe samples an area of

about 20-80 pm2 and can be used to determine variations in the surface chemical composition,

given this lateral resolution. Preliminary AES experiments indicate that we can detect

changes in the average thickness of a polymer film on a metal substrate as we scan across

the sample. We expect to use the AES technique to study the uniformity of polymer film

thickness as it is affected by the molecular weight of the polymer, the mass of polymer

adsorbed per unit area, the time required to adsorb a given mass of polymer, and the

molecular volume of the polymer molecules in solution prior to their adsorption. By

studying the effect of each of these variables, we expect to gain insight into the optimum

parameters for applying uniform polymer coatings to solid surfaces.

Characterization of Porosity of Porous Implant Materials

R. E. Dehl, W. H. Grant, A. Bur, and J. M. Cassel

The use of porous synthetic implant materials to serve as a 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, a project has been initiated to survey

published information and current commercial material specifications, perform void volume

measurements on selected polymeric and composite materials by several alternative methods,

and measure pore size distribution by optical intercept and mercury porosimeter techniques.

In addition, the applicability of an experimental microparticle sieving technique, heretofore

not applied to such systems, will be explored.

The accomplishments 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.

56
Dental and Medical Materials Standards

J. M. Cassel , G. M. Brauer, J. A. Tesk, N. W. Rupp 1

Active participation, from Task Force level to the role of Subcommittee Chairman, occurs in development of dental standards through ANSI MD 156, Dental Materials, Instruments,

and Equipment, and ISO TC 106, Dental Materials and Services. Development of medical

implant standards is assisted by serving in roles of Polymeric Materials Chairman and Task

Force leadership in the efforts of ASTM F-4, Medical and Surgical Materials and Devices,

and as Chairman, USA TAG ISO TC 150, Surgical Implants.

Investigation of Epitaxy Relationships Between Ca F,(P0 4 ) 3 0H and

Other Calcium Ortho-Phosphates

B. Dickens, L. W. Schroeder 2

The purpose of this investigation was to examine possible epitaxies between Ca 5 (P0 4 ) 3 0H

(hydroxyapatite) and other calcium ortho-phosphates. These epitactical relationships are of interest for the following reasons: (i) Ca 5 (P0 4 ) 3

0FI may be considered as an idealization

of the major inorganic phase in the human body, and its crystal chemistry obviously

influences the properties of hard tissues, and (ii) epitactical relationships have been

suggested to be important in explaining the apparent nonstoichiometry of Ca 5 (P0 4 ) 3 0H and

in the growth of biomineral i_n vivo .

Similarity in chemical content and periodicity of the chemical pattern between two

planes in the component structures is an important requirement for epitaxy to occur under

mildly forcing conditions. From the purely metric point of view, periodicity may be

treated in terms of matching nets, one in each of the two components. In general, the

metric fit of such nets will not be perfect, and the resultant misfit will be accomodated

by lattice strain near the epitactical layer and/or by dislocations.

For the chemical aspects of epitaxy, structural features such as layers and corrugated

sheets are prime candidates for the interfaces. Many structures contain layers in which

the intra-layer bonds are strong and the interlayer bonds are weak. Especially in the case of inorganic salts, the atomic configurations in such layers will be relatively

stable and, hence, can be expected to be found in more than one structure. The chemical

pattern itself should not have a large motif, because this would have many structural

details, and the probability of finding a similar motif in another compound would necessarily

be low. From the above considerations, it follows that the most likely candidates for

epitaxy-forming layers will be planes of low Miller indices of the form (100), (110), or (210), etc.

A filtering procedure for generating and quantitatively comparing possible cases of

epitaxy and twinning in ionic compounds has been devised to provide quantitative criteria

to evaluate the probability of epitaxy between compounds for which the crystal structures

are known.

The two cornerstones of this procedure are:

(i) Generate and examine in a systematic , quick manner all possible cases of epitaxy

and twinning that may occur.

(ii) Establish a relative probability of occurrence among the possible cases to

delineate those requiring further study.

Research Associate, American Dental Association.

2 Guest worker, Food and Drug Administration.

57
Our approach is completely general in that it can be applied to any substance that forms

a crystalline phase. Generation of possible cases of epitaxy or twinning which are specified

in terms of contact planes requires only unit cell dimensions. Further evaluation of these

cases in terms of atomic correspondences requires atomic positions. The procedure was used

to evaluate the possibility of epitaxy between Ca 5 (P0 4 ) 3 0H and other calcium orthophosphates.

For any two given lattices, pairs of nets which match dimensionally within prescribed limits

are found and sorted in order of increasing mismatch. The crystal structural parameters are used to generate and match atomic patterns correspond!

- ng to each pair of nets. Pattern

matching is done by comparing magnitudes of vectors describing the immediate environment of

representative atoms in the two patterns. Atomic charges related by each vector are also

considered. Use of the vector sets introduces the limitation that twinning involving re- orientation in a contact plane cannot be distinguished from no reorientation. The procedure

is general in nature and has been applied to the study of possible epitaxies between

Ca 5 (P0 4 ) 3 0H and Ca 8

FI 2 (P0 4 ) 6 -5H 2 0 , Ca 4 0(P0 4 ) 2 , CaHPCL, CaHP04 -2H 2 0,

Ca(H 2 P0 4 ) 2

* H 2 0 , p-Ca3 (P0 4 ) 2 , and Ca 5 (P0 4 ) 2 Si04

.

The highest probabilities for epitaxy are between Ca 5 (P0 4 ) 3 0H and Ca 8 (P0 4 ) 6

-5FI 2 0,

Ca 5 (P0 4 ) 3 0H and Ca 4 0(P0 4 ) 2 , and Ca 5 (P0 4 ) 3 0H and Ca 5 (P0 4 ) 2 Si0 4

. Of these, the first is the

most likely and is probably unavoidable under conditions where Ca 8 H 2 (P0 4 ) 6 *5H 2 0 is stable,

and the last is the least likely. Possible epitaxies between Ca 5 (P0 4 ) 3 0H and CaHP04 or p-Ca3 (P0 4 ) 2 are less likely than epitaxy between Ca 5 (P0 4 ) 3 0H and Ca4 0(P0 4 ) 2 .

Although CaHP0 4 *2H 2 0 and Ca(H2 P0 4 ) 2-

2 0 had been suggested to be important in tooth

mineralization, evaluation of the probability of epitaxy in these cases suggests that any

deposition of these phases on one another forms incoherent films which then mechanically

block access of the surrounding solution to the interior and that epitactical growth is not

important. Therefore, among those cases considered, only the epitaxies

Ca 5 (P0 4 ) 3 0H/Ca8 H 2 (P0 4 ) 6 -5H 2 0 and Ca 5 (P0 4 )0H/Ca4 0(P04 ) 2 appear likely to occur in

practice.

Development of Improved Field Dental Composite Restorative Materials

for Military Dentistry

G. M. Brauer, N. Rupp 1

, K. Dermann2, J. Stansbury, J. Cassel

Current thrust of this continuing project is to provide guidelines to the Army regarding

materials and techniques for addressing the problem of poor marginal adaptation that frequently occurs with composite restorative materials. Resultant marginal staining and leakage

compromises the aesthetic advantages of these restorations and can reduce their service life.

The role of polymerization shrinkage, coefficient of thermal expansion, nature of

filler, and properties of diluent monomers are being investigated. Efforts are being made to

establish optimum minimum levels of viscosity-modifying diluent monomers that will produce

adequate working characteristics and physical properties, while at the same time reducing the

polymerization shrinkage that occurs on hardening. Radiotracer techniques are employed to

ascertain leakage around class V restorations placed in extracted caries-free teeth.

Research Associate, American Dental Association.

2 Guest worker, Free University of Berlin.
Other Division Activities

Inv ited Tal ks

The Accelerative and Adhesive Bonding Capabilities of Surface Active Accelerators

International Association for Dental Research, Osaka, Japan

J. M. Antonucci

June 6, 1980

Ferroelectric Polarization in Polymers

International Symposium on the Statistical Mechanics of Phase Transitions in

Polymers, Case Western Reserve University, Cleveland, Ohio

M. G. Broadhurst

June 13, 1980

Piezoelectric and Pyroelectric Applications of Plastics

American Chemical Society, Houston, Texas

M. G. Broadhurst

March 24, 1980

Piezoelectric and Pyroelectric Properties of Polymers With Applications

International Business Machines, Binghamton, New York

M. G. Broadhurst

January 28, 1980

Piezoelectric Polymers

Office of Naval Research Meeting on Electroactive Polymers, Washington, D.C.

M. G. Broadhurst

September 29, 1980

Polarization and Molecular Hysteresis in Polyvinyl idene Fluoride

Gordon Conference on Dielectric Phenomena, New London, New Hampshire

M. G. Broadhurst

July 19, 1980

Polymers as Piezoelectric Elements

Plastics Institute of America, Hoboken, New Jersey

M. G. Broadhurst

November 1, 1979

Recent Developments With Piezoelectric Polymers

Polymer Chapter of the 3M Company Technical Forum, St. Paul, Minnesota

M. G. Broadhurst

June 16, 1980

Ferroelectric Polarization in Polymers

Conference on Electrical Insulation and Dielectric Phenomena, White Haven,

Pennsylvania

M. G. Broadhurst and G. T, Davis

October 24, 1979

Ferroelectric Polarization in Polymers

American Physical Society, New York, New York

M. G. Broadhurst and G. T. Davis

March 27, 1980

Poling Behavior of PVDF

American Physical Society, New York, New York

M. G. Broadhurst and G. T. Davis

March 24, 1980

59
Derivatives of p-N,N-Di ai kyl aminophenyl al kanoic Acid: New Accelerators for Dental

Compos i tes

International Association for Dental Research, Osaka, Japan

G. M. Brauer

June 6, 1980

Enhancing Fluoride Incorporati on into Enamel

School of Dentistry, National Taiwan University, Taipei, Taiwan

W. E. Brown

June 16, 1980

Impregnation and Void Filling of Porous Polymer Tape With Dielectric Oil

Conference on Electrical Insulationand Dielectric Phenomena, White Haven,

Pennsyl vania

A. J. Bur

October 23, 1979

The Development of Test Methods for the Environmental Stress-Crack

Resistance of Ethylene Plastics

ASTM Subcommittee D- 20 . 10. 14, San Diego, California

J. M, Crissman

February 19, 1980

Piezoelectric and Pyroelectric Polymers: Mechanisms and Applications

University of Virginia, Charlottsvil le, Virginia

G. T. Davis

January 28, 1980

Piezoelectric and Pyroelectric Polymers: Mechanisms and Applications

Mechanics and Materials Colloquia, Rutgers University, New Brunswick, New Jersey

G, T. Davis

April 24, 1980

Piezoelectric Polymer Research at NBS

Piezoelectric Polymer Workshop, Naval Research Laboratory, Orlando, Florida

G, T. Davis

June 13, 1980

Piezo- and Pyroelectric Response From PVDF in Form III (y)

American Physical Society, New York, New York

G, T. Davis and M. G. Broadhurst

March 24, 1980

Non-Uniform Polarization and Space Charge in Ferroel ectric Polymers

American Physical Society, New York, New York

A. S, DeReggi and M, G. Broadhurst

March 24, 1980

Temperature Dependence of the Pyroelectric Response and Thermal Depoling

of Vinyl idene Fluoride Polymer

American Physical Society, New York, New York

A, S. DeReggi, G, T. Davis, and M. G. Broadhurst

March 24, 1980

Crystal Disorders in Copolymers of Tetrafl uoroethyl ene and Hexafluoropropylene

Institute of Polymer Chemistry, Zabrze, Poland

R. K, Eby

October 26, 1979

Order-Di sorder Transitions in Polytetrafl uoroethyl ene : Experiment and Theory

Institute of Basic Technical Problems, Warsaw, Poland

R. K, Ebv

October 22, 1979

60
Overview of NBS and the Polymers Division

E. I. du Pont de Nemours & Co., Inc., Wilmington, Delaware

R. K. Eby

April 2, 1980

Polymers in the Future

American Society for Mechanical Engineers Emerging Technology Conference,

San Francisco, California

R. K. Eby

August 15, 1980

The Structure and Transitions in Copolymers of Tetrafluoroethylene

and Flexafluoropropylene

Polish Academy of Sciences, Lodz, Poland

R. K. Eby

October 24, 1979

Crystal Disorders in Copolymers of Tetrafluoroethylene and Flexafluoropropylene

American Chemical Society, Washington, D.C.

R. K. Eby, E. S. Clark, and J. J. Weeks

September 12, 1979

Measurement of Dynamic Elastic Moduli

99th Acoustical Society, Atlanta, Georgia

S, Edelman

April 22, 1980

Raman Frequencies and Intensities of Longitudinal Acoustic Modes of Polymers

University of Massachusetts, Amherst, Massachusetts

B. M. Fanconi

September 21 , 1 979

Application of Varied Heating Rate Methods to Polymer Degradation Reactions

Ninth North American Thermal Analysis Society Conference, Chicago, Illinois

J. H. Flynn

September 25, 1979

Lifetime Prediction of Polymer Stabilization

Institute of Polymer Science and Technology, University of New York,

New Paltz, New York

J. H. Flynn

June 27, 1980

Methods for Testing the Validity of Kinetic Models Using Data From Varied

Heating Rate and Jump Techniques

American Chemical Society, Seton Hall Univ., South Orange, New Jersey

J. H. Flynn

February 25, 1980

Methods for Testing the Validity of Kinetic Models Using Data From Varied

Heating Rate and Jump Techniques

Sixth International Conference on Thermal Analysis, Bayreuth, West Germany

J. H. Flynn

July 8, 1980

Concentration Effect on Polymer Chain Dimensions

Joint U.S. -France Conference on Small Angle Scattering, Strasbourg, France

C. C-, Han

September 17, 1980

61
Dynamic Scattering From Polymer Solutions

University of Michigan, Ann Arbor, Michigan

C. C. Han

October 5, 1979

Molecular Weight and Temperature Dependence of Polymer Dimensions and Intrinsic

Viscosity

University of Massachusetts, Amherst, Massachusetts

C. C. Han

February 15, 1980

Experiments on Non-Linear Elasticity

Short Course on Continuum Mechanics, NBS, Gaithersburg, Maryland

E. A. Kearsley

July, 1979

Non-Equilibrium Thermodynamics of Perfect Elastic Fluids

Seminar on Thermodynamic Inequalities, NBS, Gaithersburg, Maryland

E. A. Kearsley

July 17, 1980

The Diversity in the Habits Exhibited by Polymer Crystals Grown From Solution

Leeds University, Leeds, England

F. A. Khoury

October 2, 1979

Diversity in the Lateral Growth Habits and Non^Planar Character of Polyethylene

Crystals

Bell Telephone Laboratories, Murray Hill, New Jersey

F, A, Khoury

February 21, 1980

Overview of Investigations in the Polymers Division on "The Structure and

Dielectric Properties of Polymer Tape Insulation for High Power Transmission

Cables"

Battelle Laboratories, Columbus, Ohio

F. A. Khoury

December 6, 1979

Scanning Transmission Electron Microscopy of Polyethylene Crystals

Electron Microscopy Society of America, Reno, Nevada

F. A, Khoury

August 4, 1980

A Mean Field Theory of Polymer Solutions

Polytechnic Institute of New York, Brooklyn, New York

D. J. Lohse

April 15, 1980

Concentration Dependence of Polymer Chain Dimensions

Johns Hopkins University, Baltimore, Maryland

D. J, Lohse

January 30, 1980

Dependence of Polymer Chain Dimensions on Concentration

E. I, du Pont de Nemours & Co., Inc., Wilmington, Delaware

D. J, Lohse

February 18, 1980

Dependence of Polymer Chain Dimensions on Concentration

Hercules Corporation, Wilmington, Delaware

D. J. Lohse

February 21, 1980

62
Dependence of Polymer Chain Dimensions on Concentration

Kansas State University, Manhattan, Kansas

D. J. Lohse

April 4, 1980

Statistical Mechanics of Polymer Solutions

Exxon Chemical Co., Linden, New Jersey

D. J. Lohse

April 8, 1980

A Jli story of the Society of Rheology

Fiftieth Anniversary Meeting of the Society of Rheology, Boston, Massachusetts

R. S. Marvin

October 29, 1979

Cyclic Creep and Failure of Carbon Black Filled Rubber

IBM Research Laboratories, San Jose, California

G. B. McKenna

May 9, 1980

Mechanical Durability and Failure of Polymeric Materials

Free University, Amsterdam, Netherlands

G. B. McKenna

April 14, 1980

Non-Linear Viscoelastic Behavior of PMMA in Torsion

Bell Telephone Laboratories, Murray Hill, New Jersey

G. B. McKenna

October 26, 1979

Response of Carbon Black Filled Rubber to Cyclic Loading

Malaysian Rubber Products Research Association, Brickendonberry , England

G. B. McKenna

April 18, 1980

Time Dependent Deformation and Failure Behavior of Poly(Methyl Methacrylate) and

Polyethyl ene University of Leeds, Leeds, England

G. B. McKenna

April 17, 1980

Time Dependent Failure in PMMA and Polyethylene

University of Manchester Institute of Science and Technology, Manchester, England

G. B. McKenna

April 16, 1980

Research and the Saving of Teeth

Tokyo Medical and Dental University, Tokyo, Japan

G. C. Paffenbarger

May 30, 1980

Research and the Saving of Teeth

Taiwan University of Dentistry, Taipei, Taiwan

G. C. Paffenbarger

June 13, 1980

Acoustic Emission of Polymers During Crazing

American Physical Society, New York, New York

A. Peterlin

March 27, 1980

63
Elastic Modulus and Strength of Highly Drawn Polymers

Dutch Staatsmi jnen, Geelen, Holland

A. Peterlin

October 26, 1979

Molecular Interpretati on of the Load-Elongation Curve of Crystalline Polymers

ACS Symposium on Stress-Cracki ng of Plastics, Washington, D.C.

A. Peterlin

September 14, 1979

Polymer Coil Instability in Laminar Flow

American Chemical Society, Carnegie-Mellon University, Pittsburgh, Pennsylvania

A, Peterlin

February 28, 1980

Tensile Failure of Semicrystall ine Polymers

U.S. -Japan Meeting on Crazing, Flow, and Forming of Polymers, Rutgers University,

New Brunswick, New Jersey

A. Peterlin

May 21, 1980

Transport Phenomena and Polymer Morphology

IUPAC Symposium on Polymers, Mainz, West Germany

A. Peterlin

September 18, 1979

Transport Phenomena and Polymer Morphology

Laboratory Technology of Polymers and Rheology, Naples, Italy

A. Peterlin

October 23, 1979

Transport Phenomena in Drawn Semicrystalline Polymers I Laboratory Technology of Polymers and Rheology, Naples, Italy

A. Peterlin

May 7, 1980

Transport Phenomena in Drawn Semicrystal 1 ine Polymers II Laboratory Technology of Polymers and Rheology, Naples, Italy

A. Peterlin

May 12, 1980

Type II Diffusion in Glassy Polymers

Laboratory Technology of Polymers and Rheology, Naples, Italy

A. Peterlin

October 19, 1979

Polymer Morphology and Chain Transport Mechanisms

Boris Kidric Institute of Nuclear Sciences VINCA, Beograd, Yugoslavia

D. H. Reneker

September 25, 1979

Properties of Polymers Including Chain Transport and Piezoelectric Effects

Josef Stefan Institute, Ljubljana, Yugoslavia

D. H. Reneker

September 28, 1979

Dental Materials--Their Selection and Handling Techniques in 1979-80

Travis Air Force Base, Solano, California

N. W. Rupp

September 5, 1979

64
Dental Material s--Thei r Selection and Handling Techniques in 1979-80

Scott Air Force Base, Saint Clair, Illinois

N. W. Rupp

September 12, 1979

Operating Techniques With Recently Introduced Dental Materials

University of West Virginia, Morgantown, West Virginia

N. W. Rupp

September 21, 1979

Recent Developments in Dental Materials and Their Handling Techniques

Lackland Air Force Base, San Antonio, Texas

N. W. Rupp

September 27, 1979

Seminar on Clinical Research

University of Minnesota, Minneapolis, Minnesota

N. W, Rupp

September 18, 1979

Equation of State Theories of Polymer Blends

International Symposium on Polymer Compatibility and Incompatibility, Michigan

Molecular Institute, Midland, Michigan

I. C. Sanchez

August 18, 1980

Interfacial Tension Theory of Polymer Solutions

University of Washington, Seattle, Washington

I. C. Sanchez

March 18, 1980

Phase Diagrams of Polymer Alloys

Washington State University, Pullman, Washington

I. C. Sanchez

March 19, 1980

Phase Diagrams of Polymer Blends

Great Lakes Polymer Conference, Wayne State University, Detroit, Michigan

I. C. Sanchez

February 14, 1980

Phase Equilibrium Behavior of Polymer Blends

University of Akron, Akron, Ohio

I. C. Sanchez

December 6, 1979

Statistical Mechanical Models of Interacting Polymer Chains

NBS Colloquium on Mathematical Modeling in Science and Engineering, Gaithersburg,

Maryland

I, C. Sanchez

February 20, 1980

Statistical Mechanical Models of Polymers and Their Solutions

Massachusetts Institute of Technology, Cambridge, Massachusetts

I. C. Sanchez

November 7, 1979

Statistical Mechanical Models of Polymers and Their Solutions

Michigan Molecular Institute, Midland, Michigan

I. C. Sanchez

February 15, 1980

65
Statistical Mechanics of Dilute and Semi-Dilute Polymer Solutions

Carnegie-Mellon University, Pittsburgh, Pennsylvania

I. C. Sanchez

May 2, 1980

Statistical Thermodynamics of Polymer Solutions

Johns Hopkins University, Baltimore, Maryland

I. C. Sanchez

March 5, 1980

Theory of Polymer Interfacial Tension

E. I. du Pont de Nemours & Co., Inc,, Wilmington, Delaware

I. C. Sanchez

February 14, 1980

Diffusion and Determination of Chain Structure in Polymers

Georgetown University, Washington, D.C.

L„ E. Smith

November 7, 1979

Re-Evaluation of the Safety of Plastics

North Carolina State University, Raleigh, North Carolina

L. E, Smith

April 9, 1980

Dental Alloy and Ceramic Compatibility

International Precious Metals Institute, Toronto, Canada

J. A, Tesk

June 2, 1980

Application of Solid State 13

C NMR in Semicrystal 1 ine Polymers

Firestone Tire & Rubber Co., Akron, Ohio

D. L. VanderHart

December 20, 1979

l3 C Linewidths in Solid Polymers Using High-Power Proton Decoupling and

Magic Angle Sample Spinning

21st Experimental NMR Conference, Tallahassee, Florida

D. L. VanderHart

March 17, 1980

High Resolution Solid State 13

C NMR of Semicrystalline Polymers

Gordon Conference on Fiber Science, New London, New Hampshire

D. l„ VanderHart

June 30, 1980

High Resolution Solid State 13C NMR Techniques for Studying Orientation

and Molecular Motion in Polymers

Gordon Conference on Polymers, New London, New Hampshire

D. L. VanderHart

July 8, 1980

Perspectives on Resolution for 13C NMR in Solid Hydrocarbons Using Magic

Angle Spinning

University of Delaware, Newark, Delaware

D. L. VanderHart

May 22, 1980

Spectral Resolution in Solid Hydrocarbons Using Magic Angle Sample Spinning

13 C NMR

NATO Advanced Study Institute, Cagliari, Italy

D. L. VanderHart

September 3, 1980

66
Solid State 1

C NMR in Polymers

NATO Advanced Study Institute, Cagliari, Italy

D. L. VanderHart

September 4, 1980

An Equilibrium Thermodynamic Approach is Taken to Describe the Morphology and Stress Change

During Crystallization or Melting

Gordon Research Conference on Polymer Physics, New London, New Hampshire

W.-L. Wu June 25, 1980

Non-Linear Behavior of Viscoelastic Rubbers

Firestone Research Laboratories, Akron, Ohio

L. J. Zapas

October 12, 1979

The Strain-Energy Function for Rubber-Like Materials

IUTAM Symposium on Finite Elasticity, Lehigh University, Bethlehem, Pennsylvania

L. J. Zapas

August 11, 1 980

Publications and Patents

Measurement of Single Chain Neutron Scattering in Concentrated Polymer Solutions

A. Z. Akcasu, G. C. Summerfield, S. N. Jahshan, Charles C. Han, C. Y. Kim, and H. Yu

J. Poly. Sci., Poly. Phys. Ed., ljl, 863 (1980)

Isocyanato Urethane Methacrylates Derived From Hydroxyethyl Methacrylate

J. M. Antonucci, G. M. Brauer, and D. J. Termini

J. Dent. Res., 59^ 35 (1980)

New Initiator Systems for Dental Resins Based on Ascorbic Acid

J. M. Antonucci, C. L. Grams, and D. J. Termini

J. Dent. Res., 58, 1887 (1979)

A Theory of the Effects of Pressure on Finite Elastic Shear

B. Bernstein and E. A. Kearsley

Proceedings of the VIII International Congress on Rheology, In Press (1980)

Adhesive Bonding of Various Materials to Hard Tooth Tissues. XXII. The Effects of a Cleanser,

Mordant, and PolySAC on Adhesion Between a Composite Resin and Dentin

R. L. Bowen

J. Dent. Res., 59, 809 (1980)

Compatibility of Various Materials With Oral Tissues. I: The Components in Composite

Restorations

R. L. Bowen

J. Dent. Res. Special Issue, 58, 1493 (1979)

New Amine Accelerators for Composite Restorative Resins

G. M. Brauer, D. M. Dulik, J. M. Antonucci, D. J. Termini, and H. Argentar

J. Dent. Res., 58, 1994 (1979)

Bonding of Acrylic Resins to Dentin With 2-Cyanoacrylate Esters

G. M. Brauer, J. A. Jackson, and D. J. Termini

J. Dent. Res. , 58, 1900 (1979)

Durability of the Bond Between Bone and Various 2-Cyanoacrylates in an Aqueous Environment

G. M. Brauer, J. W. Kumpula, D. J. Termini, and K. M. Davidson

J. Biomed. Mater. Res., 1_3, 593 (1979)

Storage Stability of Dental Composites

G. M. Brauer, N. Petrianyk, and D. J. Termini

J. Dent. Res., 58, 1791 (1979)

Polyvinyl idene Fluoride Viewed as a Polycrystall ine Ferroelectric Material

M. G. Broadhurst

Charge Storage, Charge Transport and Electrostatics With Their Applications , Y. Wada,

M, M. Perlman, and H. Kokado, Eds., p. 143 (1979)

67
Piezoelectric and Pyroelectric Properties

M. G. Broadhurst and G. T. Davis

Topics in Applied Physics, Vol . 33, Electrets (1980)

Piezoelectricity and Pyroelectricity in Poly(Vinyl idene Fluoride)

M. G. Broadhurst and G. T. Davis NML 1979 Technical Highlights, p. 89 (1980)

Piezoelectric and Pyroelectric Applications of Plastics

M. G. Broadhurst, S. Edelman, and G. T. Davis

Organic Coatings and Plastics Chemistry, 42, 241 (1980)

Kinetics of Hydrolytic Aging of Polyester Urethane Elastomers

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

Macromolecules, 1_3, 248 (1980)

General Comments, Session V, Third International Symposium on Tooth Enamel

W. E. Brown

J. Dent. Res. Special Issue B, p. 857 (1979)

Diffraction From Nonperiodic Structures: The Molecular Conformation of

Polytetrafluoroethylene (Phase II)

E. S. Clark, J. J. Weeks, and R. K. Eby

ACS Symposium Series on Diffraction Methods for Structural Determination of Fibrous

Polymers, In Press (1980)

Two Types of Pyroel ectrici ty in a Copolymer of Vinyl idene Fluoride as Tetrafl uoroethyl ene

R. E. Collins, M. G. Broadhurst, G. T. Davis, and A. S. DeReggi

Charge Storage , Charge Transport , and Electrostatics With Their Applications , Y. Wada,

M. M. Perlman, and H. Kokado, Eds., p. 170 (1979)

Performance of Plastic Packaging for Hazardous Materials Transportation, Part V, Mechanical Properties

J. M. Crissrnan, L. J. Zapas, and G. M. Martin

NBSIR 79-1938 (1979)

Acoustically Transparent Hydrophone Probe

A. S. DeReggi and G. R. Harris

Patent Filed April 1980

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, In Press (1980)

Investigation of Epitaxy Relationships Between Ca 5 (P 04 ) 30 H and Other Calcium Ortho-Phosphates

B. Dickens

J. Res. Nat. Bur. Stds., 54, 000 (1980)

User's Manual for Factor-Jump Thermogravimetry Apparatus and Associated Computer

Programs, Including a General Plotting Program

B. Dickens

NBSIR 80-2102 (1980)

Physical and Chemical Properties and Wear

G. R. Dickson

J. Dent. Res. Special Issue, 58, 1535 (1979)

High Resolution, Magic Angle Sample Spinning 13 C NMR of Solid Cellulose I W. L. Earl and D. L. VanderHart

J. Am. Chem. Soc., 1 02 , 3251 (1980)

Polymer Science and Standards

R. K. Eby

Dimensions, 64, No. 4 (1980)

Fit of Porcelain Fused-to-Metal Crown and Bridge Castings

G. T. Eden, 0. M. Franklin, J. M. Powell, Y. Ohta, and G. Dickson

J. Dent. Res., 58, 2360 (1979)

Molecular Vibrations of Polymers

B. Fanconi

Ann. Rev. Phys. Chem., 3J_, 265 (1980)

68
Electron Spin Resonance Spectra of Polymers During Fluorination

R. E. Florin

J. Fluorine Chemistry, V4, 253 (1979)

Degradation Kinetics Applied to Lifetime Prediction of Polymers

J. H. Flynn

Poly. Eng. Sci., 20, 675 (1980)

The Effect of Heating Rate Upon the Coupling of Complex Reactions. I. Independent and

Competitive Reactions

J. H. Flynn

Thermochim. Acta., 21_, 225 (1980)

Methods for Testing the Validity of Kinetic Models Using Data From Varied Heating Rate and Jump Techniques

J. H. Flynn

Proceedings of the Sixth International Conference on Thermal Analysis, In Press (1980)

The Niobium (Col umbium)-Pall adium Constitution Diagram

B. C. Giessen, N. J. Grant, D. P. Parker, R. C. Manuszewski, and R. M. Waterstrat

Metal. Trans. A, VIA, 709 (1980)

The Effect of pH History on the Stability of Paper

E. L. Graminski and E. J. Parks

J. Res. Nat. Bur. Stds., In Press (1980)

Molecular Weight and Temperature Dependence of Intrinsic Viscosity of Polymer Solutions

C. C. Han Polymer, 20, 1083 (1979)

Use of Solid-State 1

C NMR in Structural Studies of Humic Acids and Humin From Holocene

Sediments

P. G. Hatcher, D. L. VanderHart, and W. L. Earl Organic Geochemistry, 2, 87 (1980)

Determining an Elastic Strain-Energy Function From Torsion and Simple Extension

E. A. Kearsley

J. Appl . Phys., In Press (1980)

Some Non-Linear Effects in Polymer Testing

E. A. Kearsley

Proceedings of ASTM Meeting on Geothermal Seals (1979)

Some Methods of Measurement of an Elastic Strain Energy of the Valanis-Landel Type

E. A. Kearsley and L. J. Zapas

J. Rheology, In Press (1980)

Room Temperature Poling of Poly(Vinyl idene Fluoride) With Deposited Metal Electrodes

J. M. Kenney and S. C. Roth

J. Res. Nat. Bur. Stds., 84, 447 (1979)

Scanning Transmission Electron Microscopy of Polyethylene Crystals

F. Khoury and L. H. Bolz

38th Annual Proceedings Electron Microscopy Society of America, p. 242 (1980)

Simulation of the Relaxation of Random-Coil Polymer Chains by Lattice Models With Excluded

Volume: The Effect of Bead Movement Rules

D. E. Kranbuehl and P. H. Verdier

J. Chem. Phys., 71_, 2622 (1979)

Chain Distribution Functions and Segment Density Function of Polymer Chains Confined by

Absorbing or Reflecting Barriers

D. J. Lohse, R. J. Gaylord, and M. J. Paisner

J. Macromolecular Sci. Phys., B20 , 000 (1980)

Raman Spectra of n-Alkanes: I. Raman Intensities of Longitudinal Acoustic Modes

J. Mazur and B. Fanconi

J. Chem. Phys., 7V 5069 (1979)

69
Measurement of Polydispersity of Narrow Fractions and Column Spreading Parameters by

Recycle Liquid Size Exclusion Chromatography

F. McCrackin and H. Wagner

Macromolecules, 1_3» 685 (1980)

Mechanical Properties of Some Fiber Reinforced Polymer Composites as Fracture Fixation Plates

G. B. McKenna, G. W. Bradley, H. K. Dunn, and W. 0. Statton

Biomaterials, In Press (1980)

Isoprene Isobutyl Butyl Rubber Mooney Viscosity Standards 388(k)

G. B. McKenna and G. W. Bullman

November 1979

Mechanical Durability of Candidate Elastomers for Blood Pump Applications

G. B. McKenna and R. W. Penn Proceedings of the First World Biomaterials Congress, In Press (1980)

Time Dependent Failure in Poly(Methyl Methacryl ate) and Polyethylene

G. B. McKenna and R. W. Penn Polymer, 21_, 213 (1980)

Time Dependent Failure of a Polyolefin Rubber Candidate Material for Blood Pump Applications

G. B. McKenna and R. W. Penn

J. Bio. Mater. Res., In Press (1980)

The Normal Stress Response in Non-Linear Viscoelastic Materials: Some Experimental Findings

G. B. McKenna and L. J. Zapas

J. Rheology, In Press (1980)

Viscoelastic Behavior of Poly(Methyl Methacrylate): Prediction of Extensional

Response From Torsional Data

G. B. McKenna and L. J. Zapas

Proceedings of the VIII International Congress on Rheology, In Press (1980)

Plasma Poling of Poly( Vi nyl idene Fluoride): Piezo- and Pyroelectric Response

J. E. McKinney, G. T. Davis, and M. G. Broadhurst

J. Appl . Phys., 51_, 1676 (1980)

Isoionic Isotope Exchange With Hydroxyl apati te and the Dilution Effect

D. N. Misra

J. Res. Nat. Bur. Stds. , 84, 395 (1979)

Reaction of Anthranilic Acid With Cupric Ion-Containing Hydroxyapati te Surface

D. N. Misra and R. L. Bowen Surface Con taminatio n, Vol. 2, K. L. Mittal, Ed., Plenum Pub. Corp., p. 983 (1979)

Fifty Years of Cooperative Research Between the American Dental Association and the

National Bureau of Standards, A Historical Perspective 1928-1978

G. C. Paffenbarger

J. Dent. Res. Special Issue, 58, 1486 (1979)

Important Accomplishments in Dentistry, 1930-1980: A Personal Appraisal

G. C. Paffenbarger

New York Journal of Dentistry, 50, 190 (1980)

Dental Materials

G. C, Paffenbarger and N. W. Rupp

Kirk-Othmer: Encyclopedia of Chemical Technology, Vol. 7, 3rd Edition, John Wiley & Sons, Inc {T9791

Organizations Engaged in Preparing Standards for Dental Materials and Therapeutic Agents With

List of Standards

G. C. Paffenbarger , N. W. Rupp, and M. M. Malmstedt

NBS Special Publication 571 (1980)

Linear Dimensional Change of Copper-Rich Dental Amalgam

G. C. Paffenbarger, N. W. Rupp, and P. R. Patel

J. Amer. Dent. Assoc., 99, 468 (1979)

Physical Testing of Polymers for Use in Circulatory Assist Devices

R. W. Penn, G. B. McKenna, and F. A. Khoury

NBSIR 80-2008 (1980)

70
Diffusion With Discontinuous Swelling. IV. Type II Diffusion Into Spherical Particles

A. Peterlin

Poly. Eng. Sci., 20, 238 (1980)

Diffusion With Discontinuous Swelling. V. Type II Diffusion Into Sheets and Spheres

A. Peterlin

J. Poly. Sci., Poly. Phys. Ed., 1_7, 1741 (1979)

The Lowest LASER-Raman Active Accordion (ALR) Type Oscillations in Crystalline Polymers

A. Peterlin

J. Mater. Sci., 1_4, 2994 (1979)

The Transient of the Intrinsic Birefringence and Light Scattering of a Suspension of

Rigid Spheroids in the Linear Laminar Jet Flow

A. Peterlin

J. Phys. Chem., 84, 1650 (1980)

Transport Phenomena and Polymer Morphology

A. Peterlin

Makromol . Chem. Suppl . , 3, 215 (1979)

An Empirical Relationship Between Hydrocarbon Polymers and its Interpretation by

Fraction Free Volume

A. Peterlin and F. McCrackin

J. Poly. Phys., In Press (1980)

Performance of Plastic Packaging for Hazardous Materials Transportation, Part VI: Mass Loss and

Effective Carbon Atom Number Measurement

J. C. Phillips

NBSIR, In Press (1980)

An Apparatus for the Infrared Measurement of Sorption/Desorption in Strained Polymeric Films

J. C. Phillips and A. Peterlin

J. Poly. Sci., Poly. Phys. Ed., In Press (1980)

Non-Linear Behavior of Polyesobutyl ene Solutions as a Function of Concentration

J. C. Phillips and L. J. Zapas

Trans. Rheology, In Press (1980)

Analysis of Mathematical Models of Integrating Monitoring Devices

R. J. Rubin

NBSIR 80-1975 (1980)

Energy Flow and Thermal Conductivity in One-Dimensional, Harmonic, Isotopically Disordered

Crystals

R. J. Rubin

M. S. Green Memorial Volume, Perspectives in Statistical Mechanics, In Press (1980)

Clinical Placement and Performance of Composite Resin Restorations

N. W. Rupp

J. Dent. Res. Special Issue, 58, 1551 (1979)

Effect of Residual Mercury Content on Creep in Dental Amalgams

N. W. Rupp, G. C. Paffenbarger , and P. R. Patel

J. Amer. Dent.. Assoc., 100, 52 (1980)

Phase Transition Behavior of the Isolated Polymer Chain

I. C. Sanchez

Macromolecules, 1_2, 980 (1979)

Adhesive Bonding of Various Materials to Hard Tooth Tissues. XX. Calcium-to-Calcium Distances

in Hydroxyapatite

L. W. Schroeder, R. L. Bowen, and J. S. Ferris

J. Bio. Mater. Res., 14, 83 (1980)

A Dynamic Mechanical Study of Phase Segregation in Toluene Diisocyanate Block Polyurethanes

G. A. Senich and W. J. MacKnight

Multiphas e Polymers , S. L. Cooper and G. M. Estes, Eds., ACS Symposium Series 176, p. 97 (1979)

Fourier Transform Infrared Thermal Analysis of a Segmented Polyurethane

G. A. Senich and W. J. MacKnight

Macromolecules, ]_3, 106 (1980)

71
A Dynamic Mechanical Study of the Curing Reaction of Two Epoxy Resins

G. A. Senich, W. J. MacKnight, and N. S. Schneider

Poly. Eng. Sci., 19_, 313 (1979)

Models for the Migration of Additives in Polyolefins

L. E. Smith, S. S. Chang, F. L. McCrackin, I. C. Sanchez, and G. A. Senich

NBSIR 80-1999 (1980)

Models for the Migration of Additives in Polyolefins

L. E. Smith, I. C. Sanchez, S. S. Chang, F. L. McCrackin, and G. A. Senich

NBSIR 79-1779 (1979)

Compatibility of Various Materials With Oral Tissues. II: Pulp Responses to Composite

Ingredients

H. R. Stanley, R. L. Bowen, and J. Folio

J. Dent. Res. Special Issue, 58, 1507 (1979)

Phosphate Ion With Three "Symmetric" Hydrogen Bonds: The Structure of Ca 2 (NH 4 H 7 (P 04 ) 4

‘ 2 H 2 0

S. Takagi, N. Mathew, and W. E. Brown

Acta Cryst. , B36 , 766 (1980)

Annealing Induced Changes in Orientation and Mobility in the Noncrystalline Region of Drawn Linear Polyethylene: A

13 C NMR Study

D. L. VanderHart

Macromolecules, 1_2, 1 232 (1979)

13

C NMR Rotating Frame Relaxation in a Solid With Strongly Coupled Protons: Polyethylene

D. L. VanderHart and A. N. Garroway

J. Chem. Phys., 71_, 2773 (1979)

Mircoanalytical Techniques With Inverted Solid State Ion-Selective Electrodes. II. Microliter Volumes

G. L. Vogel and W. E. Brown

Anal. Chem., 52, 377 (1980)

Microanalytical Techniques With Inverted Solid State Ion-Selective Electrodes. I. Nanoliter

Volumes

G. L. Vogel , L. C. Chow, and W. E. Brown

Anal. Chem., 52, 375 (1980)

A Specification Method for Ultra High Molecular Weight Polyethylene for Implant Use

H. L. Wagner and J. G. Dillon, Jr.

J. Bio. Mater. Res., 13, 821 (1979)

Novel Cell for Light Scatterin From Solutions

F. W. Wang and B. H. Zimm

Biopolymers, In Press (1980)

ARC Furnace Modification for the Production of Small Investment Castings

R. M. Waterstrat

Patent Filed August 1980

Optimizing Creep and Corrosion Properties in a Dispersant Amalgam Using Manganese

R. M. Waterstrat

J. Dent. Res., 57, 873 (1978)

Nb-Si A1 5 Compounds Produced by Liquid Quenching

R. M. Waterstrat, F. Haenssler, and J. Muller

J. Appl . Phys., 50, 4763 (1979)

Order-Di sorder Transitions in Polytetrafluoroethylene

J. J. Weeks, I. C. Sanchez, R. K. Eby, and C. I. Poser Polymer, 21_, 325 (1980)

Internal Configurations of Span-Constrained Random Walks

G, H. Weiss and R. J. Rubin

J. Stat. Physics, 22, 97 (1980)

Theory of the Instability and Failure of Viscoelastic Materials in Tension

L. J. Zapas and B. D. Coleman

J. Poly. Sci., Poly. Phys. Ed., 17, 2215 (1979)

72
Seminars for Staff and Guests

Morphological Studies of Power Cable Insulation

Paul Phillips

University of Utah, Salt Lake City, Utah

September 10, 1979

Structure of Nafion Polymers

Michel Pineri

Centre D' Etudes Nucleaires, Grenoble, France September 12, 1979

Polymeric Structures in Fibers of Polyterephthalate Esters

I. H. Hall University of Manchester, Manchester, England

September 13, 1979

Surface and Bulk Properties of Polymers by Inverse Gas Chromatography

Derek G. Gray

McGill University, Montreal, Canada

September 14, 1979

Current Aspects of the Technology of Large Plastic Shipping Containers

Packaging Institute, National Bureau of Standards, Gaithersburg, Maryland

J. M. Crissman

September 24, 1979

Dielectric Relaxations in Polymer Blends

William J. MacKnight

University of Massachusetts, Amherst, Massachusetts

September 28, 1979

Thermodynamics of Polymer Blend Compatibility

Frank Karasz University of Massachusetts, Amherst, Massachusetts

October 5, 1979

Practical Application of the Thermal Pulsing Technique for Measuring Charge Polarization

Distributions in Insulators

R. E. Collins

New South Wales Institute of Technology, Sydney, Australia

October 18, 1979

Determination of DNA Molecular Weight by Viscoelasticity

Brian C. Bowen Princeton University, Princeton, New Jersey

October 29, 1979

Electropolymerization on Graphite Fibers

T. S. Subramanian

Washington State University, Pullman, Washington

October 29, 1979

Charge Transport in Lossy Dielectrics

Andrew K. Jonscher

Chelsea College, University of London, London, England

November 6, 1979

Modeling Mechanical Behavior of Materials

Douglas MacDonald

National Bureau of Standards, Washington, D.C. November 27, 1979

High Pressure Raman Spectroscopy of Ordered Liquid Phase of n-Alkanes and Polyethylene

Stephanie L. Wunder

Naval Research Laboratory, Washington, D.C. November 30, 1979

73
The Development and Uses of Hydroxyapatite as Scientific Substrates and Potential Hard Tissue

Implant Materials

Michael Jarcho

Carbomedics, Inc., San Diego, California

December 7, 1979

Ferroelectric Behaviors in the Copolymers of Vinylidene Fluoride and Trif 1 uoroethyl ene Takeo Furukawa

Bell Telephone Laboratories, Murray Hill, New Jersey

December 10, 1979

Alkai Ion and Proton Conductivity in (3 11 Alumina

Gregory C. Farrington

University of Pennsylvania, Philadelphia, Pennsylvania

December 12, 1979

Applications of Porous Metals to Skeletal Reconstruction

William Rostoker

University of Illinois, Chicago, Illinois

December 14, 1979

Weathering of Plastics

Field H. Winslow

Bell Telephone Laboratories, Murray Hill, New Jersey

December 14, 1979

The Crystal Structure of Polytetrafl uoroethyl ene ("Teflon") (1) Low Temperature; (2) High Pressure

Edward S. Clark

University of Tennessee, Knoxville, Tennessee

December 19, 1979

Laser Beam Detection of Ultrasonic and Acoustic Emission Signals

B. B. Djordjevic

Johns Hopkins University, Baltimore, Maryland

December 19, 1979

Spacecraft

FI uxes Carolyn K. NASA- Lewis

January 2,

Charging Investigation Studies of Polymer Response to Kilovolt Charge Particles

Purvis

Research Center, Cleveland, Ohio

1980

Biomedical Applications of Ion Thruster Technology

Bruce Banks

NASA-Lewis Research Center, Cleveland, Ohio

January 10, 1980

Structural Rearrangements in Constrained Macromolecules: Histones and DNA in the Nucleosome

Henryk Eisenberg

Weizmann Institute of Science, Rehovoth, Israel

January 17, 1980

Photo-Oxidation of Polymers

Charles Rogers

Case Western Reserve University, Cleveland, Ohio

January 29, 1980

Current Status of Oral Implants, Emphasis on the Subperiosteal Implant

Paul Mentag

Practicing Dentist, Southland, Michigan

February 1 , 1 980

Small Angle Neutron Scattering of Crystalline Polyethylene

Shih-Jung Bai

University of Michigan, Ann Arbor, Michigan

February 7, 1980

74
Concepts in Polymer Processing

Costel Denson University of Delaware, Newark, Delaware

February 7, 1980

Computer Studies of Model Polymers

Marvin Bishop

Fordham University, Manhattan, New York

February 19, 1980

Oscillatory Flow Birefringence of Dilute Polymer Solutions

Timothy P. Lodge

University of Wisconsin, Madison, Wisconsin

February 19, 1980

Interlaboratory Evaluations Workshop

American Standards for Testing and Materials, San Diego, California

J. D. Barnes February 20, 1980

The Structure and Properties of Ultra High Modulus Polyolefins

Ian M. Ward

University of Leeds, Leeds, England

March 3, 1980

Polyoxymethyl ene Whiskers, Their Growth, Structure, and Properties

Masatoshi Iguchi

Research Institute for Polymers and Textiles, Tsukuba, Japan

March 5, 1980

Equilibrium and Non-Equilibrium Properties of Poly(01efinsulfone)s in Solution

Keizo Matsuo

Dartmouth College, Hanover, New Hampshire

March 5, 1980

Mechanical Properties and Fracture Behavior of Epoxies and Rubber Toughened Epoxies

D. L. Hunston

Naval Research Laboratory, Washington, D.C. March 19, 1980

Deuteron NMR in Solids and Solid Polymers

Hans W. Spiess

Johannes-Gutenberg University, Mainz, West Germany

March 26, 1980

Charge Transport in Plasma Polymerized Polysiloxane Films Yvan Segui

University of Toulouse, Toulouse, France March 28, 1980

Photo-Oxidation of Poly(Vinyl Chloride) and Acrylic Coatings

Christian Decker

Ecole Nationale Sup£rieure de Chimie de Mulhouse, Mulhouse, France March 31 , 1 980

Recent Results in Spectroscopy of Disordered Polymers

G. Zerbi

Institute of Macromol ecul ar Chemistry, Milan, Italy

April 4, 1980

The Status of Chain Folding: Report on the Cambridge Meeting

J. D. Hoffman, C. M. Guttman, and E. A. DiMarzio

National Bureau of Standards, Washington, D.C. April 15, 1980

Raman Studies of Thin Polymer Films and Organic Monolayers by Integrated Optical Technique

J. D. Swalen

IBM Research Laboratories, San Jose, California

May 8, 1980

75
Improvements in an Underwater Acoustic Camera Using Polyvinyl idene Fluoride Sensors

Lynn Holt and John McGrath

EMI, London, England

June 6, 1980

High Strength Polyethylene Filaments

Pieter J. Lemstra

Central Laboratory DSM, Geleen, Netherlands

June 11, 1 980

Investigation of Orientation and Crystallization Processes in Polyethyleneterephthalate by Means

of Different Methods Including Synchrotron Radiation

Gerhard Zachmann

Institut fur Anorganische und Angewandte Chemie, Hamburg, West Germany

June 17, 1980

NMR Magic Angle Spinning as a New Method for Investigation of Permanent and Temporary Netpoints

in Polymers

Gerhard Zachmann

Institut fur Anorganische und Angewandte Chemie, Hamburg, West Germany

June 18, 1980

The Study of Textile Fibers With the Help of Paramagnetic Probes

Bernard Catoire

Institut Textile de France, Paris, France

June 20, 1980

Polymer Dynamics in Semidilute Regions

Michel Delsanti

Laboratoire Leon Billouin, Yvette, France

June 30, 1980

Flow-Rate Dependent Degradation of High Molecular Weight Polymers in GPC

Klaus Lederer

Institute for Chemistry and Physics, Leoben, Austria

July 3, 1980

Neutron Scattering Studies of Polyethylene

D. M. Sadler

University of Bristol, Bristol, England

July 9, 1980

China--A Nation Struggling to Recover From War

Charles Proffer Saylor

National Bureau of Standards, Washington, D.C. July 9, 1980

Flow in Porous Membranes

F. W. Wiegel

Twente University, Enschede, Netherlands

July 17, 1980

Effects of Molecular Orientation in the Crystallization of Polymers

Andrzej Ziabicki

Polish Academy of Science, Warsaw, Poland

July 21, 1980

Results of Fundamental Research on Interfacial Phenomena in Polymer Blends

Werner Berger

Technische Universitat Dresden, Dresden, East Germany

July 21, 1980

Cationic Degradation of Hetero-Polymers

Eric Goethals

University of Ghent, Ghent, Belgium

July 22, 1980

Studies of Polymer Conformations in Solid Polymers by Small and Wide Angle Neutron Scattering

Jakob Schelten

Institut fur Festkorperforschung , J Li 1 i c h , West Germany

August 13, 1980

76
Technical and Professional Committee Participation and Leadership

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: Mineralized Tissue Group, Chairman

Biological Mineralization Award Committee

American Association of Dental Research/International Association of Dental Research

J. M. Cassel

Washington Section Delegate

American Chemical Society

G. M. Brauer

Member: Meetings and Expositions Committee

Special Events Committee, Chairman

American Dental Association Acceptance Program

J. A. Tesk

Member: Porcelain Metal Alloys

American Institute of Physics

R. K. Eby

Editor of High Polymer Physics Section, 1 981 Physics Handbook

American Institute of Physics

E. A. Kearsley

Member: Committee for Public Policy

American National Standards Institute/MDl 56, Dental Materials and Devices

J. A. Tesk, Chairman

Member: Base Metal Alloys

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

C092: US TAG for I SO/TCI 50 , Implants for Surgery, Chairman

American National Standards Institute/MDl 56, Dental Materials and Devices

N. W. Rupp

Member: Restorative Materials, Chairman

Alloy for Dental Amalgams, Chairman

Mercury for Amalgams, Chairman

Amalgamators for Dental Amalgams, Chairman

Dispensers for Mercury and Alloys for Dental Amalgams, Chairman

American Physical Society/Division of High Polymer Physics

R. K. Eby

Member: Selection Committee for APS High Polymer Physics Prize

American Physical Society/Division of High Polymer Physics

F. A. Khoury

Member: Executive Committee

Committee on History of DMPP Committee on Short Courses

ASTM D-2 Petroleum Products and Lubricants

L. J. Zapas

Member: SC. 07 Flow Properties

SC.07A Newtonian Viscometry

77
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

ASTM D-20 Plastics

J. D. Barnes

Member: SC. 12

SC. 19

SC. 70

WG.07

Olefin Plastics

Sheeting

Analytical Methods

Gas Permeability

ASTM D-20 Plastics

R. K. Eby, Chairman

Member: SC. 01 Executive Subcommittee

ASTM D-20 Plastics

D. H. Reneker

Member

ASTM D-20 Plastics

J. C. Smith

Member

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

78
ASTM F-2 Flexible Barrier Materials

J. D. Barnes

Member: SC. 30 Test Methods, Chairman

SC. 93 Statistical Matters, Chairman

ASTM F-2 Flexible Barrier Materials

D. H. Reneker

Member

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

Case Western Reserve University Materials Research Laboratory Advisory Board

R. K. Eby

Member

Chemical Society of Washington

G. M. Brauer

Chairman, Membership Activities

International Confederation for Thermal Analysis

J. H. Flynn

Member: Nomenclature Committee

Working Party on Symbols

International Electrotechnical Commission

TC046, Cables, Wires and Waveguides for Telecommunication Equipment

L. J. Zapas

Member: WG.03 Measuring Methods of Polyethylene

International Standards Organization

TC106, Dental Materials and Devices

G. M. Brauer

Member: Task Force on Color Stability

International Standards Organization

TC106, Dental Materials and Devices

N. W. Rupp

Member: Restorative Materials

National Bureau of Standards Advisory Panel for Tariffs on Electron Microscopes Under Florence

Agreement

F. A. Khoury

Member

National Center for Small Angle Scattering

Users Committee

C. C. Han Member

National Research Council Panel on Polymer Science and Engineering

R. K. Eby

Member

North American Thermal Analysis Society

J. H. Flynn

Member: Executive Committee

Publications Committee, Chairman

79
Polymer Degradation and Stability (Journal)

J. H. Flynn

Editorial Board Member

Polymer (Journal)

R. K. Eby

U. S. Associate Editor

Sixth International Conference on Thermal Analysis

J. H. Flynn

Session Chairman

Society of Plastics Engineers

G. B. McKenna

Member: Technical Publications Committee

Society of Plastics Engineers

R. K. Eby

Member: Selection Committee for SPE International Award for Research

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

University of Massachusetts Advisory Board on Polymer Research

R. K. Eby

Member

External Recognition

Charles Gordon Service Award

Washington Section

American Chemical Society

December 1979

G. M. Brauer

1980 Biological Mineralization Research Award

International Association of Dental Research

June 1980

W. E. Brown

Award of Appreciation

American Standards for Testing and Materials

June 1980

R. K. Eby

1980 Mettler Award in Thermal Analysis

North American Thermal Analysis Society

July 1980

J. H. Flynn

,, r Award of Appreciation

American Standards for Testing and Materials

October 1979

W. P. Harris

Honorary Member

Japanese Division

International Association of Dental Research

June 1980

G. C. Paffenbarger

Silver Certificate

American Society for Metals

April 1980

J. A. Tesk

80
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81

NBS-114A irev. 2-bc) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

4. TITLE AND SUBTITLE

PUBLICATION OR

REPORT NO.

NBSIR 81-2263

2. Performing Organ. Report No. 3. Publication Date

April 1981

Polymer Science & Standards Division Annual Report 1980

5. AUTHOR(S)

R. K. Eby, M. G. Broadhurst, J. M. Cassel, B. M.

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s)

Fanconi, I. C. Sanchez, L.

7. Contract/Grant No.

E. Smit h

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

8

.

Type of Report & Period Covered

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, Stole, ZIP)

10.

SUPPLEMENTARY NOTES

J 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. If 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 1980 fiscal year.

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) polymers, plastics, macromolecules, standards

13. AVAILABILITY 14. NO. OF

Jjg^ Uni imited PRINTED PAGES

|

' J For Official Distribution. Do Not Release to NTIS

J Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

81

15. Price

^^Order From National Technical Information Service (NTIS), Springfield, VA. 22161

USCOMM-DC 6043-P80


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