AlllOE bEDTLb

Reference Standard Polyethylene

Resins and Piping Materials

Final Report

(October 1, 1985 - September 30, 1986)

Issued March 1987

Gas Research Institute

8600 West Bryn Mawr Avenue

Chicago, Illinois 60631

QC

100

.U56

87-3506

1987

c. 2

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

MBS

RESEARCH

IWFORMATION

CENTER

REFERENCE STANDARD POLYETHYLENE

RESINS AND PIPING MATERIALS

FINAL REPORT

(October 1, 1985 - September 30, 1986)

f ‘.‘B7-2£bfc

Prepared by

J. M. Crissman

National Bureau of Standards

Gaithersburg, MD 20899

For

GAS RESEARCH INSTITUTE

Grant No, 5084-260-1013

GRI Project Manager

Max Klein

Physical Sciences

October 1986
GRI Disclaimer

LEGAL NOTICE This report was prepared by the National Bureau of

Standards as an account of work sponsored by the Gas Research

Institute (GRI). Neither GRI, members of GRI, nor any person acting

on behalf of either:

a. Makes any warranty or representation, express or

implied, with respect to the accuracy, completeness,

or usefulness of the information contained in this

report, or that the use of any apparatus, method, or

process disclosed in this report may not infringe

privately owned rights; or

b. Assumes any liability with respect to the use of, or

for damages resulting from the use of, any

information, apparatus, method, or process disclosed

in this report.
RtPOirr DOCUMENTATION

PACE

1. RCKHTT NO.

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Reference Standard Polyethylene Resins and Piping Materials

7. Awthorfm) J. M, Crissman, F. W, Wang, C. M. Guttman,

J. R. ^^rey, H. L. Wagner, B. M. Fanconi, and D .L. Vander

4. Pvrfofminc OfS*ni(*t<on Nam« and Addraaa

Polymers Division

National Bureau of Standards

Gaithersburg, MD 20899

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Issued 1-87

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la RfPtact/Taak/Work UnH No.

12. SponaoNnc Orsanicatlon Nama and Addfpaa

Gas Research Institute

8600 West Bryn Mawr Ave,

Chicago, IL 60631

IS. Supplamantary Notaa

11. ContracMO or GranlfG) No. (O

(G) 5084-260-1013

IS. Typo of Rapoft & Rariod Coworad

Final Report

10/85 - 09/86

14.

IS. Abatract (Llmtt; 200 «mrda>

Polyethylene piping is currently in widespread use in gas distribution in

the United States, and represents approximately 80% of new installation.

Research that is currently being performed on gas pipes often employs many

different polyethylenes selected from the large number of polyethylenes

available for this use. This variation in materials makes it difficult to

compare results from different research laboratories, or to compare

measurements carried out in the same laboratory at different times. To

avoid this difficulty Gas Research Institute and the National Bureau of

Standards (NBS) have undertaken to provide a permanent store of one

particular polyethylene resin as well as piping and fittings made from it

which would provide a source of well characterized materials for research

related to gas distribution systems. This report describes the choice of

this resin and the types and quantities of the materials to be provided by

NBS and the characterizations performed which include the determination of

the branch content, melt flow rate, molecular weight and molecular weight

distribution, density, and specific tensile properties.

17. Ooeumamt Analymis a. Oasertpters

Gas Pipe, Polyethylene, Molecular Weight, Molecular Weight Distribution, Melt Index,

Tensile Test, Branching, Size Exclusion Chromatography, NIIR.

b. Idantlfiart/Opan-Cndod To?mt

Polymer Characterization, Molecular Weight Distribution, Size Exclusion

Chromatography, Melt Index

c. cosATi Fiaid/Gfoup chemis try /Polymer Characterization

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RESEARCH SUMMARY

Title Reference Standard Polyethylene Resins and

Piping Materials

Contractor National Bureau of Standards

GRI Contract Number: 5084-260-1013

Principal

Investigator J. M. Crissman

Co investigators F . W . Wang

C. M. Guttman

J . R . Maurey

H. L. Wagner

B. M. Fanconi

D. L. VanderHart

Report Period

Obj ectives

;

Technical

Perspective

October 1, 1985 - September 30, 1986

(1) The procurement of sufficient piping

resin and piping products to supply the

needs of the gas industry for at least 5

years

.

(2) Conduct characterization of the PE in

various forms to ensure uniformity

throughout the batch of resin and

products to be warehoused.

(3) Establish a storage and distribution

system to ensure that the materials will

be available for at least 5 years.

Polyethylene pipe is currently in

widespread use in gas distribution in

the United States, and represents

approximately 80% of new installation.

It has been found to be a reliable and

cost effective alternative to the more

traditional materials . At the same

time there is a need to deepen our

understanding of the long time behavior

of the poyethylene material used in gas

piping. The research that is currently

being performed often employs many

different polyethylenes selected from

the large number of polyethylenes

available. This variation in materials
makes it difficult to compare results

from different research laboratories

,

or even to compare measurements carried

out in the same laboratory at different

times. This difficulty would, to a

large extent, be alleviated if there

were a permanent store of one

particular polyethylene resin as well

as piping and fittings made from it

which would provide a source of well

characterized materials for research

related to gas distribution systems.

Results Recognizing the need to establish a

supply of reference materials, a

workshop, sponsored by GRI, was held at

Northwestern University, Evanston, IL

on September 7 and 8, 1983. A

consensus was reached at the workshop

as to the need for a sample bank of

reference polyethylene. The attendees

also reached a consensus that the

medium density polyethylene resin TR418

from Phillips Petroleum Co. , be the

recommended polyethylene. The

following inventory of reference

materials was also recommended.

1. Polyethylene resin (natural) 455 kg.

2. Polyethylene resin (pigmented) 4550 kg.

3. PE pipe (6,03 cm OD, 0.55 cm wall) 1.52 km in 0.76 M

sections

4. PE pipe (11.4 cm OD, 1 . 0 cm wall) 0.15 km in 0,76 M

sections

5. PE pipe (1,59 cm OD, 0.23 cm wall) 0.15 km in 0.76 M

sections

6

.

PE 5.1 cm socket T joint 500

7. PE 5.1 cm butt T joint 500

As a result of the workshop, GRI entered

into a contract with the National Bureau of

Standards (NBS) to carry out the

establishment of such a reference sample

bank.

4
Technical Approach NBS will perform the following tasks:

(1) Procure the resin, piping, and

joint materials specified by the

workshop

.

(2) Characterize the resin and

products for certain molecular and

physical properties to ensure their

uniformity, and thus to enhance

calibration and inter- laboratory

comparisons of data.

(3) Warehouse and distribute the resin

and products through the NBS Standard

Reference Materials Program.

Characterization of the materials will

include determination of the melt

index, viscosity number, molecular

weight and molecular weight

distribution, degree of branching,

density, thermal properties, and loadextension data where appropriate.

Project Implications It is common practice for polyethylene

resin manufacturers to make changes

from time to time in their resins.

These changes are generally made for

proprietary reasons and in a

proprietary manner. While these

changes may not affect the behavior of

the pipe in the field, they do modify

the behavior of the material enough

under research conditions to make the

intercomparisons of results among

researchers and even among results

obtained at the same laboratory at

different times difficult. This

results from the fact that these

different experiments can be expected

to have been performed on different

material in a different laboratory

and/or at different times. In order

for different results to be

intercompared, it is necessary that

each researcher be able to calibrate

his apparatus by means of a set of

measurements carried out on a standard,

well characterized polyethylene

material of stable characteristics. It

is the purpose of this project to make

5
such material available over a period

of time of five or more years. This is

being done through the purchase,

characterization and storage of a

particular batch of material which will

be available for sale to the research

community. By making it possible for

measurements at different laboratories

at different times to be referred to

the same basis, the utility of the

limited research resources currently

being applied toward developing a

fundamental understanding of the field

behavior of polyethylene pipe material

is increased. This, in turn, makes it

more likely that it will become

possible to design such material to

satisfy criteria for behavior in the

field in a predictable fashion.

In addition to certified values of

certain properties, NBS will supply

each purchaser of the material with a

copy of this report to ensure that the

procedures used in the characterization

are understood.

GRI Project Manager

Max Klein

Physical Sciences

6
Table of Contents

Page

1. Introduction 9

2. Characterization of Branching

2.1. FT-IR Studies of Gas Pipe

Polyethylene Resins 13

2.2. NMR Study 17

3. Melt Flow Index 17

3.1. Experimental Procedures 18

3.1.1. Instrument Calibration

and Alignment. . 18

3.

1.1.

a. Temperature Indication 18

3.1.1.

b. Metering of Plastometer

Components 19

3.1.1.

C, Alignment of Plastometer 19

3.1.1.

d. Effect of Piston Diameter

on Melt Flow Rate 20

3.2. Melt Flow Rate

3.2.1. Unpigmented Resin (SRM 1496) ................ 22

3.

2.1.

a. Sampling and Randomization

of Charge Sequence of SRM 1496 22

3.2.1.

b. Melt Flow Rate on SRM 1496. .............. . 22

3.2.

1.

c. Data Analysis on the Melt

Flow Rate of SRM 1496 .................... 23

3.2.

1.

d. Error Analysis on the Melt

Index of SRM 1496 23

3.2.2. Pigmented Resin (SRM 1497) ................... 28

3. 2.

2.

a. Sampling and Randomization

of Charge Sequence of

SRM 1497 28

3.2.2.

b. Melt Flow Rate on SRM 1497 29

3.2.2.

C. Drift in Melt Flow Rate From

the First Extrudate to the

Third Extrudate 32

3.2.2.

d. Error Analysis on the Melt

Index of SRM 1497 33

3.2.3. Melt Flow Rate of Material Taken

From The Piping and Joints .................. 37

3. 2.

3.

a. Sampling Procedures -- Cutting of

the Piping and Joints . 38

7
3.2. 3. b. Melt Flow Rate of the Piping

and Joints 39

4. Density. 41

4.1 As -Received Pellets, ............................. 41

4 .

2

Piping Materials 41

4 . 3 Tee Joints ....................................... 42

5. Uniformity of Pipe Dimensions of the 1.27 cm

Diameter Pipe 43

6. Size Exclusion Chromatography of the Pigmented

and Unpigmented Resins 43

6 . 1 Experimental Procedures 43

6 .2 Universal Calibration. 45

6.3 Comparison of Pigmented and Unpigmented Resins... 46

6.4 Molecular Weight Calculations. 47

6 . 5 Preliminary Conclusions ......................... 47

7

.

Mechanical Properties

7.1 Tensile Properties of Uniaxial Extension......... 48

7 .

2

Uniaxial Creep of Material Molded

from the Pigmented Pipe Resin 50

8. Comparison Between the GRI Reference Polyethylene

(Pigmented Resin) and Three Commercial

Gas Pipe Resins in Use in Europe: Short Term

Tensile Properties 52

9 . Summary. 55

References .............................................. 60

List of Tables 61

List of Figures ......................................... 81

8
1 . Introduction

This final report describes work done under GRI Contract Number

5084-260-1013 during the period from October 1, 1985 through

September 30, 1986 [1]^. The project entailed the procurement,

characterization, and warehousing of standard reference polyethylene

gas pipe resins, as well as piping and joint materials made from

them. The contract between the Gas Research Institute (GRI) and the

National Bureau of Standards (NBS) is the result of a workshop held

at Northwestern University, Evanston, IL, on September 7 and 8, 1983.

A final report describing the presentations, deliberations, and

recommendations of the workshop was issued on May 14, 1984 [2]

.

Polyethylene (PE) has rapidly become the material of choice for

gas distribution piping in the United States and currently accounts

for about 80% of total new piping installation and accounts for

essentially all new piping installation which is non-metallic . It

has proven itself to be a reliable and cost effective alternative to

the more traditional materials. At the same time, the gas industry

has evolved a variety of standards governing the materials,

production, and utilization of plastic materials, in general, and

polyethylene, in particular, for gas distribution. In spite of the

high degree of success achieved with polyethylene piping materials,

there remains a need to better understand the long time behavior of

both the PE materials being used and of the final products made from

it in the form in which it is made and placed in actual service. As

^Numbers in square brackets indicate references found at the end

of this report.

9
a result, research is currently being performed in the laboratories

of many of the companies involved in PE resin and pipe manufacture,

much of it proprietary. There is also underway unrestricted

research, primarily in universities and not-for-profit laboratories.

Much of this non-proprietary research is sponsored by GRI

.

In the research currently being done, the materials used must be

selected from the large number of different polyethylenes available.

This can lead to uncertainty in comparing results from different

laboratories which might have selected different material.

Moreover, the manner in which specimens are prepared from a given

material can influence significantly the final properties, and

therefore their performance. This can lead to considerable

additional uncertainty in comparing or correlating data generated in

different laboratories. The situation is made worse by the practice

which the polyethylene resin manufacturers have of occasionally

changing their manufacturing processes so that the same material may

not always be available. This can make it difficult even to compare

measurements carried out in the same laboratory at different times

.

Much of this confusion would disappear if there were a permanent

store of a particular polyethylene resin as well as piping and

fittings manufactured from it. Researchers could then purchase

supplies from this store at any time and repeat their measurements on

the materials obtained, knowing that the material is from the same

batch as that used by others, or even used in their own laboratories

at an earlier time. Researchers would, of course, remain completely

unrestricted with regard to design of experiments, and they would.

10
therefore, remain free to choose the scientific questions motivating

their research. They could, in fact, carry out most of their

measurements on any material of their choice. They would, however,

have available a reference polyethylene which could be included in

each experimental design and which would provide a means for internal

calibration of the data that a given research effort is producing.

Future workers could thereby successfully build new knowledge by

combining their results in a meaningful and unambiguous manner with

what has already been published. The benefit would be that the

reference polyethylene would provide a means for placing all such

research on a common basis.

The workshop attendees recognized the need to establish such a

supply of reference materials, and came to the consensus that the

inventory of polyethylene needed to be housed in one repository where

it would be readily accessible to workers throughout the world. The

National Bureau of Standards (NBS) was cited as being especially well

suited to serve as the repository because of its experience with

reference materials and, in particular, "standard reference

materials" for many other substances of commercial importance.

Furthermore, it was considered highly important that the resin and

piping to be placed in the repository receive competent and thorough

characterization of all basic properties. Again, the National Bureau

of Standards was cited for its fine reputation for carrying out such

characterizations

.

11
The workshop stipulated the following types and quantities of

material to be characterized and warehoused for distribution:

Item Quantity

1. Polyethylene resin (natural) 455 kg.

2. Polyethylene resin (pigmented) 4550 kg.

3. Polyethylene pipe 1.52 km in 0.76 m

(6.03 cm OD, 0.55 cm wall) sections

4. Polyethylene pipe 0.15 km in 0.76 m

(11.4 cm OD, 1.0 cm wall) sections

5. Polyethylene pipe 0.15 km in 0.76 m

(1.59 cm OD, 123 cm wall) sections

6. Polyethylene 5.1 cm socket T joint 500

7. Polyethylene 5.1 cm butt T joint 500

In addition, it was decided to include one 0.15 km roll of the 1.59

cm OD, 0.23 cm wall pipe.

It was further agreed upon by the attendees at the workshop that

the reference polyethylene would be the medium density polyethylene

resin, TR418, from the Phillips Petroleum Co.^

The principal activities described in this final report are the

characterization of the melt flow index of the pigmented and

unpigmented resins, determination of the density of the as-received

pellets, piping, and joint materials, and mechanical property studies

to determine the yield behavior of the piping materials under

tension. In addition, the butyl branch content was determined both

by Fourier Transform Infrared Spectroscopy (FT-IR) and Nuclear

Magnetic Resonance (NMR)

,

^Certain commercial materials and equipment are identified in

this paper in order to adequately specify the experimental procedure.

In no case does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor does it imply

that the material or equipment is necessarily the best available for

the purpose

.

12
During part of this period, the project leader was assisted in

carrying out the mechanical properties study by Dr. Peter Stockmayer

from the Polymer Testing and Polymer Science Institute (IKP) at the

University of Stuttgart in West Germany. Dr. Stockmayer was a guest

scientist at NBS from October 7, 1985 through November 22, 1985.

From March 16, 1986 until June 15, 1986 the NBS principal

investigator (J. M. Crissman) was engaged in collaborative research

at IKP, Stuttgart. During this time, the tensile properties of the

pigmented TR 418 resin were compared with those of three different

commercial gas pipe resins currently in use in Europe. The results

of this effort are summarized in this report.

2.1. FT-IR Studies of Gas Pipe Polyethylene Resins

Infrared studies were conducted on pipe resin materials to

determine

:

1) the number of methyl groups per 100 carbon atoms

2) the concentration of terminal vinyl groups

3) crystallinity

4) spectral differences among the various specimens.

The polyethylene resins investigated were:

1) unpigmented resin in the form of molded sheets prepared from

pellets

2) pigmented resin molded in sheets from pellets

3) pigmented resin shaved from the 6.03 cm OD pipe.

Spectral differences between the first two of these (i.e. the

unpigmented and pigmented molded samples) were observed. To

determine the source of these differences the infrared spectrum of

13
the pigment was also obtained to see if these differenes were due to

the pigment.

RESULTS

1) Methyl Group Concentration

A wealth of literature is available on the use of infrared

spectroscopy to determine the number of methyl groups per

unit mass of polyethylene. We used the method of Rueda et

al [3] which relates the peak extinction coefficient at

1378 cm"^ to sample thickness and methyl group

concentration expressed as number of groups per 100 carbon

atoms. The results, summarized in Table 1, indicated that

the unpigmented resin contained approximately 0.5 methyl

groups per 100 carbon atoms and the pigmented resins

contained 0.55 methyl groups per 100 carbon atoms. The

uncertainty in the concentration of these groups obtained

by this method is about 10% owing to the precision of the

absorption coefficient. This systematic error applies

equally to the calculated concentration of methyl groups

for both the pigmented and unpigmented resins so that the

difference between them appears to be real. However, as

discussed under item 4 below, other spectral differences

indicate the presence of additional chemical species in the

pigmented resin which may account for the increased

absorption in the 1375 cm” ^ region,

2. End Vinyl Group Concentration

The infrared spectrum of polyethylene containing vinyl end

14
groups has two well-resolved peaks which are assigned to

vibrations localized in terminal vinyl groups. Extinction

coefficients were obtained from studies on alpha-olefins

[4] and both infrared bands were used in the analysis. The

results, given in Table 2, show little variation in the

concentration of terminal vinyl groups, 5x10"^ per CC bond,

among the various specimens.

3) Crystallinity

A number of infrared bands are assignable to vibrations of

atoms in the crystalline regions. The band at 1896 cm'

was selected for crystallinity determination since it is

well-resolved from other bands. It was analyzed by the

method of Okada and Mandelkern [5]

.

The results are given

in Table 3. The only significant difference between the

infrared spectra of samples taken from the pigmented resin

and those taken from the pipe and from the unpigmented

resin resulted from differences in the crystallinity.

4) Other Spectral Differences

Difference spectra were obtained for the pairs unpigmented

pellets/pigmented pellets and pigmented pellets/pipe

specimen. The difference spectrum for the

unpigmented/pigmented pair, shown in Figure 1, has

significant features in the 1750 cm" ^ region, as well as

bands at 1568, 1532, 1373, and 810 cm" ^

.

Aldehyde,

ketones, and acids contribute to the infrared spectrum in

the 1750 cm' ^ region, and the positive/negative feature in

15
the difference spectrum may be due to a slight higher

degree in oxidation in the unpigmented sample (perhaps due

to molding the sheets from the pellets) and the presence of

an organic acid in the pigmented sample. The presence of

an organic acid is also consistent with the appearance of

bands at 1568 and 1532 cm" ^ . No attempt was made to

further identify the origins of the difference bands in

this pair with the exception that the infrared spectrxom of

the pigment was obtained for comparison. No spectral bands

of the pigment spectrum are present in the difference

spectrum indicating that the pigment concentration is too

low in the pigmented resin to be detected at the sample

thicknesses used.

The difference spectrxjun between the pair pigmented

pellets/pipe specimen is shown in Figure 2. The bands in

this difference spectrum can be assigned to a difference in

crystallinity (and amorphous content) between the two

samples with the molded sheets having higher crystallinity

(see Table 3).

5 ) Branch Content

It was reported under 2) that the concentration of vinyl

groups per carbon-carbon bond was approximately 5x10”^ for

the resin containing no pigment. This result yields a

degree of polymerization of 2000, if it is assumed that

each molecule contains one vinyl group which is located at

a chain end. There are then 0.5 methyl groups per 1000

16
carbon atoms associated with chain ends. Under 1) it was

determined that, in total, there were approximately 5.0

methyl groups per 1000 carbon atoms. Therefore the number

of branch- terminated methyl groups is 4.5 per 1000 carbon

atoms. This number is in very good agreement with the

results for butyl groups from the NMR study reported in the

following section.

2.2. NMR Study

The branch content of both the pigmented and unpigmented PE

resins was analyzed by solution-state NMR. Solutions, 15% by weight

in trichlorobenzene, were run at 120°C using a WM400 Bruker NMR

spectrometer operated at 9.4T. The principal analytical result

sought using NMR spectra was the number of butyl branches per 1000

backbone carbon atoms. The numbers determined were 4.2700.25 for the

unpigmented PE and 4. 5600.25 for the pigmented PE. A determination

of the molecular weight was not attempted because of an insufficient

signal to noise ratio. However, a rough estimate for Mj, of 10,000-

15,000 could be made.

3 . Melt Flow Rate

Melt flow rate is widely used in pol3nDiier technology as a product

specification since this value, including a statement of the load and

temperature under which it is obtained, gives an indication of the

processing properties of the polymer. The melt flow rate is defined

as the mass of polymer melt pushed from the heated cylinder of the

extrusion plastometer through its precision bore orifice by a piston

in a specified period of time, the standard units being grams per ten

17
minutes (g/10 min).

The melt flow rates were determined by Procedure A described in

Section 8 of ASTM Method D-1238-82 [6]. The standard test conditions

190/2.16 were used for the unpigmented PE resin (SRM 1496) while

conditions 190/2.16, 190/5.0 and 190/21.6 were used for the pigmented

resin (SRM 1497). The flow rate was determined at 190.0 +/- 0.1®C at

all three loads. The flow rate of the melt was measured by a

manually operated extrusion plastometer obtained from the Tinius

Olsen Testing Machine Co.

3.1.1. Instrument Calibration and Alignment

3.1.1a Temperature Indication

The temperature was indicated by a mercury column thermometer of

the form described in paragraph 4.7 of ASTM Method D 1238-82 [6].

Calibration of the temperature indication is traceable to the NBS

Temperature and Pressure Division. An iron- cons tantan thermocouple

was calibrated by correlating its emf with the scale readings of an

ASTM 68C thermometer at 22 points from 183® C to 195® C, in a

constant temperature oil bath. The ASTM 68C thermometer had been

calibrated at the ice point and at 190® C in the NBS Temperature and

Pressure Division. The thermometer located in the cylinder of the

extrusion plastometer was calibrated by correlating its scale

readings with the temperature indicated by the emf from the

thermocouple when the hot junction of the latter was replaced in a

column of polyethylene melt in the bore of the plastometer, as

described in paragraph 4.5.2 of the ASTM method. The conduction of

heat between cylinder and thermometer, and between cylinder and the

18
temperature control sensing probe, was enhanced by adding silicone

oil to the wells in the cylinder for the thermometer and sensing

probe

.

The uncertainty in the final temperature indication may be

regarded as equal to the nominal limit of resolution on the scales of

the ASTM 68C thermometer, and of the thermometer in the extrusion

plastometer. This was 0.1°C. A determination of melt flow rate

dependence on temperature, for SRM 1496, resulted in a change of

0.00043 g per 10 min in melt flow rate for a 0.1° C change in

temperature under the 2.16 kg load. This result affords an estimate

of 0.17% change in the melt index per 0.1° C change in temperature.

3.1.1b Metering of Plastometer Components

The geometric dimensions of the cylinder, piston assemblies, and

dies were found to comply with the specifications described in the

ASTM method.

The diameter of the cylinder bore was determined by an inner

diameter (ID) micrometer in the NBS Shops Division. The ID of the

bore was measured at three locations at approximately 1 inch

intervals from each end toward the middle. All six of the ID

measurements between the ends of the bore were either 0.3759 in. or

0,3760 in., in compliance with the tolerance of this specification

described in paragraph 4.2 of ASTM D 1238-82.

The apparent mass of the nominal 2.16 kg load was determined in

the NBS Length and Mass Division. The apparent mass of the nominal

2.16 kg load was found to be 2.1599 kg, well within the +0.5%

tolerance described in paragraph 4.4.4 of the ASTM method.

19
3.1.1c Alignment of Plastometer

The cylindrical axis of the bore was aligned with the gravity

vector by the following plumb-line procedure.

First, a die was selected as the "target" die and stationed on

the structural baseplate of the extrusion plastometer directly below

the cylinder. Its position on the plane of the baseplate was

adjusted to have the axis of its orifice coincide with the projection

from the axis of the cylinder bore onto that plane. This was

accomplished by viewing the target die through the orifices of two

"sighting" dies, one stationed at its operational position in the

bottom end of the bore and the other stationed at the top end of the

bore. The position of the target die on the plane of the baseplate

was adjusted until it appeared centered in the view from above the

cylinder through the sighting dies in the bore.

Next a plumb-bob was suspended by a plumb-line from the axis of

a die supported in the top end of the bore, with the bob almost

touching the top surface of the target die. The leveling screws were

adjusted until the pointer of the plumb-bob appeared to be centered

above the orifice of the target die.

3.1. Id Effect of Piston Diameter on Melt Flow Rate

A brief study of the variation of melt index with piston land

diameter was conducted in order to estimate the dependence of the

determined melt index value on clearance between the piston and the

bore of the cylinder. Mr. Fred Reckner of Tinius -Olsen generously

provided two piston feet with land diameters at the opposite extremes

of tolerance described in paragraph 4.4.1 of the ASTM method, namely

20
0.3730 +/- 0.0003 in. Metering with a micrometer confirmed that the

smaller piston had a land diameter = 0.3727 in., and the larger

piston had a land diameter = 0,3733 in. A homogeneous supply of the

polymer was collected by transferring approximately 40 grams of

pellets from each of several sample bags of pigmented resin into a

mixing jar, and then propelling the jar on a roll mill for 1 hour.

The predetermined sequence in which the narrow and broad piston feet

were to be applied was randomized by first assigning ordinal numbers

from 1 to 8 to the piston feet identified in perfectly alternating

sequence, and then randomizing the ordinal numbers.

The melt index determinations were performed on eight charges

from the homogeneous polymer supply, in the manner described in

Section 3. The results from these determinations are listed in Table

4.

Inspection of results in each line of Table 4 reveals that the

standard deviation of each mean is greater than the difference

between corresponding means, and the standard deviation of a single

measurement within each mean is also greater than the difference

between corresponding means. Also observe that, in three of the

lines, the mean melt flow rate determined with the broad piston is

greater than the mean value determined with the narrow piston, while

in the other line, the mean value determined with the narrow piston

is greater than those determined with the broad piston. In

particular, observe in the line for the data overall that the

difference between the mean values of the two groups is trivial, and

that the standard deviations of the two group means are more than ten

21
times as great as the difference between the two group means.

Consequently, it appears that the mean index values resulting from

application of the two pistons at opposite extremes of the diameter

tolerance described by the ASTM method are statistically

indistinguishable within the limits of this study.

3 . 2 Melt Flow Rate

3.2.1. Unpjgmented Resin (SRM 1496')

3.2.1a Sampling and Randomization of Charge Sequence

of SRM 1496

Material of the SRM 1496 came in one 455 kg container. Samples

were collected from ten different sites in the container and put into

screw cap jars. Of these sites eight were near each of the corners

of the container, one was at the cubic center of the container and

one was at the center of the container's top face. In preparation

for the melt flow rate experiments two charges were taken from each

sample. Charges to be extruded were identified by an ordinal number,

each associated with an identified sample. The sequence of charges

to be extruded was randomized according to a procedure described by

Natrella [7]

.

3.2.1b Melt Flow Rate on SRM 1496

The melt flow rates on SRM 1496 were determined by procedure A

described in Section 8 of ASTM Method D-1238-82. Standard test

condition 190/2.16 was used. Thus the flow rate was determined at

190.0 + 0.1 ®C using a load of 2.16 kg. The flow rate of the melt was

measured by a manually operated extrusion plastometer obtained from

the Tinius Olsen Testing Machine Co.

22

I
A 2.7 g charge of pellets was used for extrusions under the 2.16

kg load. With such a charge, the 4 nun start section of the

descending piston would enter the top of the guide collar partially

at the end of the 6 min preheat interval without the necessity of any

manipulative adjustment. The end of the 6 min preheat interval was

marked as the beginning of timed extrusion. This was done by making

the initial extrudate cut and discarding the preheat segment. Three

timed extrudate segments were cut at 6 min intervals thereafter.

After the third timed extrudate segment had been cut, the remaining

melt in the cylinder was purged and discarded. The piston, bore, and

die were cleaned free of the polymer at the end of each extrusion

run.

3.2.1c Data Analysis on the Melt Flow Rate of SRM 1496

Data from 20 charges were analyzed for the 2.16 kg load. The

data from a single charge run generally showed a flow rate decrease

in going from the first timed extrudate to the third timed extrudate.

Such a drift is reflected in the data shown in Table 5.

The 20 charges were made up by taking two from each of the 10

jars sampled. The jar to jar variation was less than the standard

deviation of each point. Thus the sample was viewed as homogeneous

with respect to melt flow rate.

Eight to 10 melt flow rate experiments could be done in a single

day. The plastometer was then used on a different material or shut

down for a few days before the next set of unpigmented resins were

run. With this procedure, we hoped to show the effects of day-to-day

23
variability on the equipment and have that reflected in our standard

deviation. However the day to day variability was small compared to

the charge- to -charge variability.

3.2. Id Error Analysis on the Melt Index of SRM 1496

Obtaining an error analysis of the melt index is difficult since

it is not a fundamental property of the material and no simple

relationship exists which describes its estimation. Nonetheless, in

this section we shall make an effort to estimate the possible causes

of error and their contribution to the overall actual error in the

measurement made

.

One estimate of error comes from the ASTM method on which melt

flow rate is based (ASTM D 1238-82). Table 3 in that document

suggests an expected reproducibility for polyethylene of ± 0.04 for a

melt flow range of 0.25 g/10 min and ± 0.48 in the range of 7.0 g/10

min. (These are 95% confidence limits). Since this error estimate

includes inter- laboratory as well as intra- laboratory error one would

expect our error to fall within the ASTM prescribed range, which it

does

.

The source of uncertainty described in Table 3 of ASTM D 1238-82

is not clear. As we have pointed out, melt flow is not a fundamental

physical property. As we have seen from our own measurements, its

value may depend on where one chooses to make the cuts in the

material (first extrudate or second extrudate) . We may then ascribe

part, if not all, of the ASTM error tolerance as described in Table 3

in D 1238-82 to operator- to-operator variability or to instrument to

instrxament variability which we are unable to estimate in our own

24
work. Their estimate yields a possible systematic error of about 15%

on the flow rate for SRM 1496. This is noted in our Table 6 as

instrument variability.

Estimates of our own repeatability are presented in Table 6.

These reflect the repeatability of our own experiments and do not

contain any instrument -to -instrument or operator- to-operator

variation since we had only one instrument and one operator. We did

make our runs on various days and the day-to-day variability of the

overall average of the first timed extrudate is reported in Table 6.

In Table 6 the sample to sample variability is also reported on the

first timed extrudate. Neither of these was significantly different

from the overall error.

Finally, we shall try to estimate the intrinsic error in the

measurement. We do this by considering the errors in the measured

quantities (mass and time) as well as the errors in the controlled

quantities (temperature and the specifications on the instriiment) .

The melt flow rate, Mfr, is given by

Mfr = Mass/Time

Thus any error in the melt flow rate is then

dMfr/Mfr = dM/M + dt/t + dMfr/dT* dT/T

dM/M is the fractional error in the weight of the samples. This is

taken to include not only the possible error in the weighing due to

balance error and moisture pickup but also to errors in the mass of

the extrudate incurred due to the cutting of the material, dt/t is

the fractional error in the timing of the extrudate and therefore

includes only the timing error. The dT/T term arises from the

25
inaccuracy of the temperature controller as well as temperature

inhomogeneity of the instrument. The cause of the errors are

discussed in the next few paragraphs. These, as well as the other

errors, are given in Table 6 along with an estimate of the overall

error resulting from all sources.

Mass Error

The extrudate segments were weighed on a balance with 0.01 mg

resolution in mass indication. Replicate weighing of the segments

agreed to within ± 0.01 mg. in general and never went beyond ±0.02

mg at the extreme. Paragraph 8.8 of ASTM Method D1238-82 instructs

the experimenter to "weigh the extrudate to the nearest 1 mg when

cool." It should be noted that 1 mg of this polymer occupies very

nearly 1 microliter of volume which is probably a valid estimate of

the uncertainty in the cut considering the technique of cutting the

extrudate. Consequently, the uncertainty in extrudate mass resulting

from the process of cutting the segment is estimated to be dm = ± 1

mg. The overall average apparent mass m = 152 for SRM 1496 was

calculated for all the extrudate segments in the characterization of

this polymer. Consequently, the relative error in weight (dm/m)

entering into the melt index characterization is

dm/m = ± 1 mg/151 mg = 0.7% for SRM 1496

The extrudate segments were routinely weighed within 1/2 - 1

hour after having been cut, which is certainly in compliance with the

instruction in paragraph 8.8 of the ASTM method. Considering the

hydrophobic character of polyethylene it would not be anticipated

26
that the extrudate would accumulate moisture beyond the initial

cooling stage prior to being weighed. On a few occasions extrudate

segments, which had been weighed at the end of a day, were weighed

again on the following day without detecting any statistically valid

change of weight within the groups. All individual changes, either

positive or negative, were much smaller than 1 mg. Consequently, it

may be assumed that there was no detectable error in weight

attributable to moisture adsorption, and that the error in extrudate

weight is dominated overwhelmingly by the volume uncertainty

attending the process of cutting the extrudate.

Time Error

The 6 min. interval (t) between extrudate cuts for SRM 1496 was

measured with a battery powered stopwatch having a 0.01 s resolution

in time indication. The extrudate cut was timed to within 0.1 s.

Consequently, the timing error may be equated with 0.1 s as a

practical estimate. Hence, the relative error in time interval may

be expressed

dt/t = ± 0.1 s/360 s. = 0.03%

Thermal Error

The thermal profile of an undisturbed column of polyethylene

melt was scanned along the cylindrical axis of the cylinder bore.

This experiment was conducted in another extrusion plastometer during

an earlier determination of the melt flow rate of NBS SRM 1475 (whole

pol3rmer polyethylene) and NBS SRM 1476 (linear polyethylene) . The

temperature in the stationary melt column was measured with a

thermocouple hot junction stationed at different heights above the

27
top surface of the die, along the cylindrical axis of the bore.

Throughout the experiment, the indicated cylinder temperature

remained at 190.0° C in all observations of the mercury column

thermometer which was used to indicate cylinder temperature. The

results are listed in Table 7.

Inspection of the tabulated results indicates that the departure

of melt temperature from the indicated cylinder temperature is less

than ± 0.1° C, at any location in the melt column from 12 mm above

the die upward. It may be observed that the 0.7 - 0.8° C drop in

temperature, between the 12 mm and 1 mm levels above the die,

occurred in the undisturbed melt column. This temperature drop is

probably reduced by the downward flow of melt during an extrusion.

It is also possible that the apparent smaller variation of

temperature with height from 12 mm upward may simply be the variation

of the temperature with the time at which the temperature was

determined at the different levels. Because its heat capacity and

voltime displacement are considerably greater than those of a

thermocouple junction, the mercury column thermometer is a very

effective temperature averaging device and is far less responsive to

brief and small changes in temperature than a thermocouple would be.

Regardless of whether the temperature is changing with time or with

height, or with both time and height, the maximum temperature error

(ST) may be estimated as ± 1.0° C.

The greater significance of the temperature error is in its

effect on the melt flow rate of the pol3rmer. The variation of melt

flow rate with temperature in the vicinity of 190° C was determined

28
to be 1.65%/°C, as reported in paragraph 2.1.1. This is equivalent

to a 1.7% per degree Celcius error corresponding to the 1.0® C

maximtan error in the melt temperature.

3.2.2 Pigmented Resin (SRM 1497)

Except where otherwise noted, all apparatus and procedures for

determining the melt flow rate of the pigmented resin were the same

as those described in Section 3.1.1 of this report.

3.2.2a Sampling and Randomization of Charge Sequence of

SRM 1497

Samples of the orange pigmented polyethylene pipe resin were

collected from each of the ten 455 kg containers of pellets. Two

samples, each weighing approximately 1 to 1 1/2 kg, were collected

from opposite sides of each container near the top. Two charges were

taken from each sample bag for determining the average melt flow

rate. Charges to be extruded were identified by an ordinal number,

each associated with an identified sample. The sequence of charges

to be extruded was randomized according to a procedure described by

Natrella [ 7 ]

.

3.2.2b Melt Flow Rate of SRM 1497

The melt flow rates were determined by Procedure A described in

Section 8 of ASTM Method D 1238-82. Standard test conditions

190/2.16, 190/5.0 and 190/21.6 were used. Thus the flow rate was

determined at 190.0 ± 0.1® C using loads of 2.16, 5.0 and 21.6 kg.

The flow rate of the melt was measured by the same manually operated

extrusion plastometer described in Section 3.1.1a.

A 2.60 g charge of pellets was used for extrusions under the

29
2.16 kg load. With such a charge, the 4 nun start section of the

descending piston would enter the top of the guide collar partially

at the end of the 6 min preheat interval without the need for any

adjustment. The end of the 6 min preheat interval was marked as the

beginning of timed extrusion by making the initial extrudate cut and

discarding this preheat segment. Three timed extrudate segments were

cut at 6 min intervals thereafter. After the third timed extrudate

segment had been cut, the remaining melt in the cylinder was purged

and discarded. The piston bore and die were cleaned free of the

polymer at the end of each extrusion run.

Essentially the same procedure was used during extrusions under

the 5.0 kg load. However, for the 5.0 kg load an initial charge of

3.0 g was used.

Extrusions under the 21.6 kg load were initiated by a special

procedure described in paragraphs 8 . 5 and 8.5.1 of ASTM method D

1238-82 for flow rates greater than 10 to 50 g/10 min. An initial

charge of 5.40 g was used. After the extrusion was initiated, the

descending piston came to rest, for the remainder of the first 6

min. , on two removable sections of bakelite which supported the

piston with the lower scribe mark of its start section 25 1/2 mm

above the top of the guide collar. During this initial descent onto

the temporary supports, the piston extruded 1.3 g pol3rmer through the

die, in compliance with the minimum 1 g extrudate specified by the

ASTM method. At the end of the sixth minute of the preheat interval,

the temporary piston supports were removed and the loaded piston was

allowed to resume its descent. It was observed that the start

30
section of the piston had always entered the top of the guide collar

partially at the end of the seventh minute of preheat. Consequently,

the preheat interval was recorded as 7 min. in this procedure under

the 21.6 kg load. After discarding the preheat extrudate, the

following extrudate was cut into three timed segments. The first two

of such segments were cut at 30 s. intervals after preheat, and the

third segment was cut after an interval of only 20 s . in order to

obtain a third segment before all the polymer melt had been extruded

from the cylinder. These time intervals are within the recommended

limits listed in Table 5 of the ASTM method.

The certified value using ASTM condition 190/2.16 for assignment

to the SRM was determined by analysis of the data obtained from

extrusions of 56 charges. Condition 190/2.16 is the traditional melt

index condition for polyethylene. [Ref; paragraph 13.1.1, ASTM D

1238-82 [6]] Three extrudates were cut from each charge run.

Already mentioned, under the 2.16 kg load, the data from a single

charge run generally showed a flow rate decrease as one went from the

first timed extrudate to the third timed extrudate. Such a drift is

reflected in the data shown in Table 4. In accordance with ASTM

procedure [Ref : paragraphs 8.6 and 8.7, ASTM D 1238-82] the first

timed extrudate was chosen as the certified value.

The 56 charges were made up by taking from 2 to 3 samples from

different positions within each of the ten original bags of resin.

The position- to-position variation was less than the standard

deviation of the point. Thus the sample was viewed as homogeneous

with respect to melt flow rate. The range of the

31
position- to-position variability is given in Table 8 (see also Table

11 ) .

Eight to ten melt flow rate experiments could be done in a

single day. The plastometer was then used on a different material or

shut down for a few days before the next set of pigmented resins were

run. With this procedure, we hoped to show the effects of day-to-day

variability on the equipment and have that reflected in our standard

deviation. However the day-to-day variability was small compared to

the charge- to -charge variability. The range of the day-to-day

variability is given in Table 11.

Data for condition 190/5.0 is given in Table 9. For these data,

there is little drift in the melt index from the first timed

extrudate to the third.

Ten extrusions were also done using the higher load of 21.6 kg.

In this case, the drift in the flow rate with time was opposite to

that observed at the 2.16 kg load, i.e., the melt flow rate from the

first timed extrudate being smaller than that of the later ones. The

results are shown in Table 10.

3,2.2c Drift in Melt Flow Rate from the First Extrudate

to the Third Extrudate

As mentioned in the earlier sections, we found that under

condition 190/2.16 the first extrudate had a higher melt flow rate

than the third extrudate while, under condition 190/5.0 and under

condition 190/21.6, the third extrudate had a melt flow rate greater

than the first. These results were found consistently and the trends

were beyond the error of the measurement. It is often reported that

32
the later extrudates have higher melt flow rates than the earlier

ones . Such phenomena have been observed and reported in the

literature. Rudin and Schrieber [8] have explained these phenomena

by suggesting that the change in the decreasing melt flow rate as a

function of time is a result of the elastic effect of the polymer.

The increasing melt flow rate arises from a variety of causes one of

which is the non-Newtonian behavior of these materials. We have made

one measurement where we have seen both a decrease and a rise in melt

flow rate in the same data. These data are shown in Figure 3.

Stockmayer [9] has observed similar drifts as a function of time

which even appear after the polymer has been degraded.

3. 2. 2d Error Analysis on the Melt Index of SRM 1497

It was noted in Section 3.2. Id of this report that obtaining an

error analysis of the melt flow rate is a difficult matter since it

is not a fundamental property of the material and there is no simple

relationship describing its estimation. In this section the same

error analysis has been used to make an estimate of the possible

causes of error and their contribution to the overall actual error in

the measurements mode on the pigmented resin.

As in the case of SRM 1496, one estimate of error comes from the

ASTM method on which the melt flow rate is based (ASTM D 1238)

.

We

have seen from our own measurements that its value may depend on

where one chooses to make the cuts in the material, for example first

extrudate or second extrudate. We may here too ascribe part, if not

all, of the ASTM error in Table 3 in D 1238-82 to operator- tooperator variability or to instrument- to- instrument variability which

33
we are unable to estimate in our own case. This estimate yields a

possible systematic error of 16% on the flow rate for Condition

190/2.16 and a possible systematic error of about 7% for the higher

flow rates. In Table 11 this error is represented as instrument- to

instrument variability

Estimates of our own repeatability are also shown in Table 11.

These reflect the repeatability of our own experiments and do not

reflect any instrument- to- ins trviment or operator- to-operator

variation. We did make our runs on various days and the day-to-day

variability of the overall average of the first timed extrudate is

also reported in Table 11. In Table 11, the sample- to-sample

variability is also reported on the first timed extrudate. Neither

of these was significantly different from the overall error. Finally

we tried to estimate the intrinsic error in the measurement. We did

this by considering the errors in the measured quantities (mass and

time) as well as the errors in the controlled quantities (temperature

and the specifications on the instr\ament) . The cause of these errors

are discussed in the next few paragraphs. These, along with the

other errors, are given in Table 11 along with an estimate of the

overall error resulting from all sources.

Mass Error

The extrudate segments were weighed on a balance with a 0.01 mg

resolution in mass Indication. Replicate weighing of the segments

agreed to within ± 0.01 mg. in general and never varied beyond ± 0.02

mg at the extreme. Paragraph 8.8 of ASTM method D 1238-82 instructs

the experimenter to "weigh the extrudate to the nearest 1 mg when

34
cool." It should be noted that 1 mg of this polymer occupies very

nearly 1 microliter of volume which is probably a valid estimate of

the uncertainty in the cut considering the technique of cutting the

extrudate . Consequently, the uncertainty in extrudate mass resulting

from the process of cutting the segment is estimated as dm = ± 1 mg.

The overall average apparent mass m = 107 mg was calculated for all

the extrudate segments in the characterization of this polymer.

Consequently, the relative error in mass (dm/m) entering into the

melt index characterization is

dm/m = ± 1 mg/107 mg = 0.0093458 = 0.9% or 1%

The extrudate segments were routinely weighed within 1/2 to 1

hr after having been cut, in compliance with the instruction in

paragraph 8.8 of the ASTM method. Considering the hydrophobic

character of polyethylene, it would not be anticipated that the

extrudate would accumulate moisture beyond the initial cooling stage

prior to being weighed. On a few occasions, extrudate segments,

which had been weighed at the end of a day, were weighed again on the

following day without detecting any statistically valid change of

weight within the groups. All individual changes, either positive or

negative, were much smaller than 1 mg. Consequently, it may be

assumed that there was no detectable error in weight attributable to

moisture absorption, and that the error in extrudate weight is

overwhelmingly dominated by the volume uncertainty attending the

process of cutting the extrudate.

35
Time Error

The 6 min. interval (t) between extrudate cuts was measured with

a battery powered stopwatch having a 0.01 s resolution in time

indication. The extrudate cut was timed to with in 0.1 s.

Consequently, the time error may be equated with 0.1 s. Hence, the

relative error in time interval may be expressed

dt/t = ± 0.1 s/360 s. = 1/3600 = 0.0002778 = 0.03%

Temperature Error

The thermal profile of an undisturbed column of polyethylene

melt was scanned along the cylindrical axis of the cylinder bore.

This experiment was conducted in another extrusion plastometer during

an earlier determination of the melt flow rate of NBS SRM 1475

(polyethylene whole pol3nner) and NBS SRM 1476 (linear polyethylene).

The temperature in the stationary melt column was measured with a

thermocouple hot junction stationed at different heights above the

top surface of the die, along the cylindrical axis of the bore.

Throughout the experiment the indicated cylinder temperature remained

at 190® C. The results are listed in Table 7.

Inspection of the tabulated results indicates that the departure

of melt temperature from the indicated cylinder temperature is less

than ± 0.1° C, at any location in the melt column from 12 mm above

the die upward. It may be observed that the 0.7 - 0,8° C drop iii

temperature, between the 12 mm and 1 mm levels above the die,

occurred in the undisturbed melt column. This temperature drop is

probably at least partially erased by the downward flow of melt

36
during an extrusion. It is also possible that the apparent smaller

variation of temperature with height from 12 mm upward may be a

variation of temperature with time at which the temperature was

determined at different levels. Because its heat capacity and volume

displacement are considerably greater, the mercury column thermometer

is a very effective temperature averaging device and is far less

responsive to brief and small changes in temperature than is a very

small thermocouple junction. Regardless of whether the temperature

is changing with time or with height, or with both time and height,

the maximum temperature error (ST) may be estimated as ± 0.2“ C.

The greater significance of temperature error is its effect on

the melt index of this polymer. The variation of melt flow rate of

this polymer with temperature in the vicinity of 190“ C was

determined to be 1.65% per “C, as reported in paragraph 2.1.1. This

is equivalent to 0.17% per 0.1“ C corresponding to the 0.1“ C nominal

error in the melt temperature.

Piping and joints were made of the same resin used for

polyethylene SRM 1497. These pipes and joints, and their designation

for future discussions, are

3.2.3. Melt Flow Rate of Material Taken from the

Pining and Joints

1.59 cm OD pipe (P.5)

6.03 cm OD pipe (P2)

11.4 cm OD pipe (P4)

butt joint (BJ)

socket joint (SJ)

37
The melt flow rates of these materials were determined at points

deemed to be significantly affected by the processing conditions.

The samples obtained from various positions were

cross section of P.5

Inside part of P2

outside part of P2

inside part of P4

outside part of P4

Positions of cuts used to make charges from the joints are shown in

Figure 4.

3.2.3a Sampling Procedure and Cutting of the Pining

and Joints

After an unsuccessful attempt to obtain samples of the pipe by

cryogenic fracture at liquid nitrogen temperatures , samples were cut

from the pipes and joints with a sharp knife blade at ambient

temperature

In the initial effort to obtain samples by cryogenic fracture, a

section of 1.59 cm OD pipe was scored with a file in the same manner

that one scores a glass tube in preparation for a controlled break.

The pipe was repeatedly immersed in liquid nitrogen for 1/2 hour.

After each 1/2 hour immersion the pipe was subjected to a bending

stress manually applied while the experimenter was wearing asbestos

gloves. In all attempts the pipe would bend under the stress but did

not fracture.

At ambient temperature, the 1.59cm OD and 6,03 cm OD pipes were

cut with a sharp blade without observable surface deformation. A

38
fine- toothed, low speed, band saw was used to cut rough samples from

the 11.4 cm OD pipe and the joints. This slow sawing apparently did

not heat the resin significantly above ambient temperature since the

sample felt only warm to the touch after cutting. As a further

precaution, the sawed surfaces of these samples were removed by

slicing them off with a knife blade to a depth of a few millimeters.

It was presumed that this procedure removed any resin modified as a

result of the heat and tearing from the saw.

Charges to be extruded were obtained by cutting the samples,

with the knife blade, into pieces which would fit down inside the

bore of the plas tome ter.

3.2.3b Melt Flow Rate of the Piping and Joints

The melt viscosity of some of the samples was so great (melt

flow rate so small) that the use of ASTM Condition 190/2.16 was found

to yield data outside of the acceptable range for that condition as

prescribed by the ASTM method. The melt flow rate under condition

190/5.0 using ASTM Method D 1238-82 was found to be adequate for

these measurements. The technique used for the melt flow rate

measurement and the calibration of the equipment has been discussed

earlier in Section 3.1. The measurements were as described earlier,

except that the charge weight was varied among the different samples.

This was necessary because of the wide variation of melt flow rate

among these samples. The charge weight of each of the samples had to

be calculated in advance to order to achieve a conformity with both

the uniform 6 minute preheat condition and the piston start position

as required by the method. Nonetheless, the mass of all the initial

39
charges remained within 5% of the 3 gm specified in the earlier

discussion. This minor variation in initial charge was considered to

have no effect on the measured flow rate.

As before, three timed extrudates were measured for each charge.

Although there were the same drifts in these measurements with

extrudate ntimber, as reported in the discussion of the melt flow rate

measurement on the resins, the drifts are not reported here because

the differences between the melt flow rate from charge to charge was

much greater than the differences among extrudates for a given

charge. Thus we report the overall average from all three measured

timed extrudates.

Data for the melt flow rates obtained for samples from the

various pipes and joints are given in Table 12. For this preliminary

report, only one melt flow rate for each position chosen and for only

one pipe and joint of a particular type were measured except for the

4 inch pipe where measurements were made on two different pipes.

Thus, except for this last measurement, which shows little pipe-topipe variation there is nothing that can be inferred from the data

about pipe-to-pipe or joint- to- joint variation. This will need to be

studied more in the future.

It is clear from Table 12 that there are significant differences

among the various measurements of melt flow rate. What is clear from

the data in Table 12 is that the joints show variations in the melt

flow rate, it being both greater and smaller than the melt flow rate

of the resin. These values are well outside the range of data

observed for the resin data. Thus, the processing of the resin to

40
make the pipe has changed the melt flow rate. Even the pipes show a

significant effect of their processing, well beyond what is expected

from just measurement variation.

At this point, we shall not speculate on the cause of the large

variations in the melt flow rate. More experiments need be done to

determine the pipe-to-pipe or joint- to- joint variation, as well as

variations within the pipe or joint in order to establish bounds on

the magnitude of the effect.

4 . Density

4 . 1 As-Received Pellets

Density measurements were carried out on the as -received pellets

of both the natural, or unpigmented, resin and the pigmented resin.

In the case of the unpigmented resin one pellet was chosen from ten

different locations within the 455 kg container, whereas for the

pigmented resin one pellet was taken from each of the ten 455 kg

containers. The measurements were done using a density gradient

column which consisted of a mixture of ethyl alcohol and distilled

water. For the particular column arrangement used, the error in each

individual measurement is estimated to be ±0.0003 g/cm^ . Initially,

the pellets were degassed by placing them under vacutom overnight in

an alcohol-distilled water mixture.

The results are presented in Table 13. It can be seen that, on

average, the density of each lot of resin was very nearly the same.

By inspection, it would appear that the majority of the pigmented

pellets have a higher density than the majority of the unpigmented

pellets. However, the average values differ by only 0.0006 g/cm^ , a

41
value which is only about twice the estimated error in each

measurement

4.2 Piping Materials

Density measurements were also carried out on the three piping

materials. From the 1.59 cm OD pipe ten specimens were prepared by

cutting rings, ranging in width from 0.5 to 0.75 cm, from five

different locations along one 25 cm long section. Each ring was then

cut in half to give two crescents . The same procedure was used to

obtain ten specimens from the 6.03 cm OD pipe, except that all ten

pieces were cut from only two rings taken from opposite ends of a 25

cm long section. In the case of the 11.4 cm OD pipe, five specimens

were cut from one ring section. In all cases each specimen contained

material from both the inner and outer surface (complete thickness of

the wall)

The density was determined using the displacement method in

distilled water. The water was degassed by boiling it for twenty

minutes. It was then cooled to 22® C prior to use. A value of

0.99777 g/cm^ was used as the density of water at 22® C and no other

corrections were applied. Based on an analysis of the measurement

technique the experimental error is estimated to be no greater than

±0.001 g/cm^

The results for all twenty five specimens are presented in Table

14. A comparison of the average values indicates that there is very

little difference in density among the three pipe sizes.

^ • 3 Tee Joints

One butt tee joint and one socket joint were also examined for

42
uniformity in density. Six specimens were taken at different

locations from one butt tee joint, and six from one socket tee joint.

For the six piece from the butt tee joint, the density ranged from

0.928 to 0.939g/cm^, whereas for the socket tee joint, the range was

from 0.921 to 0.940 g/cm^ . In both cases, the lowest densities

recorded were for the pieces taken nearest the point of injection and

the highest values were obtained for the pieces taken from a point on

the inside wall well away from the point of injection.

5 . Uniformity of Pine Dimensions of the 1.27 cm Diameter Pine

One 50 cm long section of the 1,27 cm diameter pipe was examined

for uniformity of dimensions over its length. The pipe was marked at

one centimeter intervals and the maximum and minimum values of the

outside diameter was determined using a micrometer at each of the 50

locations along the length of the pipe. The pipe was then cut into

short sections and the maximum and minimum values of the wall

thickness were determined at 13 different locations using a tubing

micrometer

.

The average values for the various dimensions measured, along

with their standard deviations, are shown in Table 15. The maximum

out -of" roundness found among the 50 measurements was 0.024 cm (0.009

in) and the minimum wall thickness among the 13 measurements was

0.232 cm (0.913 in). The average outside diameter as a function of

position along the length of the pipe is shown graphically in Figure

6 , Size Exclusion Chromatoeranhv of the Pigmented

and Unnigmented Resins

Both samples of resin (SRM 1496 and SRM 1497) were studied by

43
size exclusion chromatography in order to examine their molecular

weight and molecular weight distribution.

6 . 1 Experimental Procedures

A set of two Shodex mixed bed (AT-80M/S) columns were used in a

Waters GPC150 Size Exclusion Chromatograph. These columns have 10

micrometer particles. Column #5J704 had 8500 theoretical plates per

25 cm, Column #4H729 had 9200 plates per 25 cm. The columns were

operated at 145° C, at a flow rate of 1.0 ml/min. , except where

noted. The carrier solvent was 1,2,4 trichlorobenzene, 99% pure,

(Aldrich Chemical Co.), which had been passed through a 5 /xm Teflon

(Millipore's Mitex) filter. No antioxidant was added to the eluent,

but sample solutions were made up from trichlorobenzene, taken

directly from the instrument, to which was added 0.2% of the

antioxidant Santonox.

The columns were calibrated with three t3rpes of standards:

narrow molecular weight distribution polystyrenes and polyethylenes

,

and SRM 1475, the NBS whole polymer polyethylene standard with known

molecular weight distribution. The polystyrenes were obtained from

several sources (Table 16)

,

whereas the polyethylene fractions were

SRM's from NBS.

The polystyrene calibrating solutions were made up at the

concentrations shown in Table 16. Although the lower molecular

weight standards were filtered at 60 C through a 10 /xm Teflon filter,

the standards above 1 million were not, in order to reduce the

possibility of shear degradation. The high molecular weight

standards were dissolved without using a shaker but were occasionally

44
tumbled over a period of from several hours to as much as 5 days.

Nevertheless, as shown below, there is still evidence of degradation

in the case of the highest molecular weight standards.

To obtain representative samples of each of the GRI reference

polyethylene resins, solutions were made up by cutting a small piece

from 10 different pellets. In the case of the unpigmented material,

each of the 10 pellets was taken from 10 different positions in the

original container. The 10 pigmented pellets were taken from the

bottle which had been previously mixed by rolling. The total weight

of each sample was of the order of 30 mg, to which sufficient solvent

was added to give a concentration of 0.125% by weight.

All the polyethylenes , standards as well as the reference pipe

resin samples, were dissolved by heating in a 165 C oven for 1 hour

with brief, gentle shaking about every 15 minutes. When dissolved,

the pigmented samples as well as some of the unpigmented samples were

filtered through a 10 fim Teflon filter.

Samples were run one at a time rather than in batches to

minimize exposure of the poljnners to the 145° C temperature for a

long period of time. The polystyrene samples which were made up at

room temperature or at 60° C were kept in the heated injector

compartment for 30 minutes before injection. The polyethylene

samples were transferred directly from the 165° C oven and were

injected after being kept for 10-15 minutes in this compartment.

The injection volume for the narrow molecular weight standards

were 300 , whereas for the whole polymer standard, SRM 1475, it was

200 fi2

.

The reference PE samples were run at 200 /ii at a

45
refractometer sensitivity of 256 and a scale of 99, the maximum

possible

,

The computer was set to acquire data rapidly after the first 5

minutes and to continue doing so for the next 25 minutes.

6 . 2 Universal Calibration

Calibration of the columns was obtained by measuring the peak

elution volume of 18 narrow molecular weight distribution standards

and the whole polymer, SRM 1475. The data are shown in Table 16.

The higher molecular weight polystyrenes, with molecular weights

above 13 million, eluted later than the 13 million standard,

suggesting that degradation of the former had taken place. This

might have occurred either in the solution process or during passage

through the column at 145® C.

It was necessary to use the Mark-Houwink relations that had been

determined at 135® C [10,11] in order to use the universal

calibration method since no data are available at 145® C., the

temperature of the experiment. These relations are:

For polystyrene - [rj] = 14.6 x 10-^ mi/g

polyethylene - [?;] = 52.6 x 10"® mi/g,

where [??] is the intrinsic viscosity.

The calibration curve of hydrodynamic volume vs elution volume

(EV) consisted of 3 straight line segments:

Elution Volume Range Calibration

10-10.5 22.7-1.23 (EV)

10.45-17.43 18.03-0.782 (EV)

17.43-18.94 55.11-2.91 (EV)

46
6 . 3 Comparison of Pigmented and Unpigmented Resins

To determine whether or not there was a difference between the

pigmented and unpigmented resins, a series of runs was made in which

two pigmented resins and two unpigmented resins were run alternately

under the same conditions. The chromatograms, after being normalized,

are superimposable as shown in Figure 6. Hence size exclusion

chromatography does not show any significant difference between the

two resins.

6 . 4 Molecular Weight Calculations

The calculation of molecular weight for these materials presents

some problems because of the presence of both very high molecular

weight species and very low molecular weight species.

The exclusion limit of the chromatographic columns occurs at

about 10 ml which corresponds to a polystyrene molecular weight of

over 20 million or a polyethylene molecular weight of over 5.6

million. The chromatogram indicates that there is material present

at this molecular weight, and perhaps at higher molecular weights,

which cannot be separated but passes through the column at the

exclusion limit. As a result, these higher molecular weight species

cannot be counted in the calculation of molecular weight. If

differences exist in this higher molecular weight region between the

pigmented and unpigmented samples, they will not be observed by this

procedure

.

At the lower molecular weights, a sharp drop occurs at the end

of the polymer peak because of adjacent "peaks" due to other

components in the solvent such as antioxidant or impurities. It was

47
necessary to cut off the polymer peak arbitrarily at the elution

volume at which this peak intersects the base line. The elution

volume limits chosen for the molecular weight calculation were in the

range 10.03 to 10.06 ml at the high molecular weight end and 18.77 or

18.78ml at the low molecular weight end.

6 . 5 Conclusions

No significant difference in the molecular weight or molecular

weight distribution of the pigmented and unpigmented resins was

observed by size exclusion chromatography, although the melt flow

rate indicated the two resins were somewhat different (see Section

3). The weight average molecular weight is 170,400 with a

standard deviation of 4.5%, and the number average molecular weight

Mn is 5500, with a standard deviation of 10.3%.

7 . Mechanical Properties

7 . 1 Tensile Properties in Uniaxial Extension

Two tensile properties, the yield stress and the strain at

yield, were examined as a function of strain rate for two of the

three sizes of pipe. The largest diameter pipe was not included due

to the inadequte load capacity of our test machines. Six pieces of

the 1.27 cm (0.5 in) diameter pipe and four pieces of the 5.08 cm

diameter pipe were selected at random from the two lots of pipe.

From these pieces, 16 specimens were cut from the 1.27 cm pipe and 12

specimens from the 5.08 cm pipe. Each specimen was 25.4 cm (10 in)

long. The specimens were mounted in grips such that the exposed

length, or gage section, was 20.32 cm (8 in). The grips consisted of

three parts, (1) a knurled central post which fitted tightly inside

48
the end of the pipe, (2) a four section tapered split ring, and (3)

an outer tapered compression ring which could be tightened down over

the split ring by means of four Allen head bolts. The experiments

were done in a servo-controlled hydraulic test machine operated in

stroke control, and all of the tests were conducted using a constant

rate of clamp separation. The experiment was stopped once a strain

greater than the strain at yield was achieved. In the present work,

the yield point was taken to be the point at which the stress -strain

curve reached its initial maximum.

In order to obtain a measure of the specimen- to- specimen

variability within the two lots of pipe, 10 specimens of the 1.27 cm

diameter pipe and 6 specimens of the 5.08 cm diameter pipe were

tested at one strain rate (81% per min). The results are presented

in Table 17. The average yield stress for specimens 1 through 10 was

16.4 MPa with a standard deviation of 0.15 MPa. The strain at yield

was found to be very nearly the same for all ten specimens (a=0.125).

For the larger diameter pipe, specimens 17 through 22, the average

yield stress was 17,4 MPa, while the strain at yield was the same for

all the samples tested (e=0.127) and was only slightly higher than

for the smaller diameter pipe.

Also shown in Table 17 are values of yield stress and strain at

yield obtained at three other strain rates ranging from 0.82 to 810

percent per minute. At each of the three different strain rates,

only two specimens were tested. The data presented in Table 17 is

summarized in graphical form in Figures 7 and 8, where the points

shown represent the average values obtained from Table 17. On the

49
semilog plot it can be seen that both properties vary linearly with

changing strain rate, at least over the three decade range examined.

In both cases, the larger diameter pipe exhibits somewhat large

values over the entire range of strain rates. Since both sizes of

pipe were found to have very nearly the same density, it would not

appear that differences in crystallinity would account for the

differences in tensile behavior. Differences in the extent of

crystal orientation between the two sizes of pipe could, however,

result in the observed behavior.

For a strain rate corresponding to the condition designated as

speed B in ASTM D 638 [6] and the geometry specified as T3rpe I, II,

or III (100% per minute), the yield stress is 16,8 MPa for the 1.27

cm diameter pipe and 17.4 MPa for the 5.08 cm diameter pipe.

7 . 2 Uniaxial Creep of Material Molded from the

Pigmented Pine Resin

The unaxial creep behavior of specimens prepared from the

pigmented pipe resin has been studied. Tensile specimens were

compression molded according to the following procedure. A mold

consisting of a frame having an opening of 15 cm by 5 cm was placed

between two 1.27 cm thick Teflon coated platens. The frame was

filled with sufficient polymer to produce a sheet approximately 0.1

cm thick. The frame was placed in a press preheated to 150° C and was

held at that temperature under only light contact pressure for a

period of ten minutes. At that time the heat was turned off and the

pressure increased to 15 MPa (2175 psi)The press was then cooled

under ambient conditions (~1°C per minute) to a temperature below

50
80° C before the mold was removed from the press. From each sheet

three specimens were cut using a dumbbell shaped die which had a

width in its narrow straight portion of 0.30 cm.

In order to determine the creep strain, fiducial marks were

placed approximately 3 cm a part on the narrow straight portion of

the specimen. The separation between marks was monitored as a

function of time under load. Loading of the specimen was

accomplished by hanging a bucket containing lead shot from the lower

clamp

.

Results for six specimens subjected to applied stresses ranging

from 10 to 20 MPa are shown in Figure 9. At the two highest

stresses, the creep was sufficiently rapid to cause significant

heating of the specimens and as a consequence failure during the cold

drawing stage after neck formation. The specimen under an applied

stress of 10 MPa required approximately 70 days to form a neck. In

the range of intermediate stresses the specimens exhibit neck

formation followed by a stage of rapid cold drawing until the neck

has propagated through the entire gage section of the specimen. The

one feature which distinguishes this particular polyethylene from

other polyethylenes is the almost complete cessation of creep once

the neck has propagated the length of the gage section. Most

polyethylenes, continue to exhibit creep even in the highly extended

state. The creep rate at high extensions is greatly reduced from

that at the earliest stages, however creep continues until fracture

occurs. In the present case, it would appear that the ethylenehexene copolymer will remain at essentially a constant length out to

51
very long times before fracture will occur. The maximum extension

attained does depend upon the level of applied stress. For example,

the specimen subjected to a stress of 16.25 MPa reached an extension

of 8 times its original gage length, whereas at 10 MPa a specimen

extended only about 5 times its original length. In order to

determine the maximum tensile stress that the pigmented resin can

sustain under creep, the specimen which initially was under a stress

of 15 MPa was subjected to higher and higher stresses until failure

occurred. The stress was increased in steps from 15 MPa to 35 MPa.

In each case, the extension was measured after 2 minutes at the new

stress, and then again after one hour. At each stress level up to 30

MPa there was little, if any, increase in the extension between 2

minutes and one hour. At 35 MPa the specimen failed after 5 minutes.

The maximum extension is shown plotted versus the log of the applied

stress in Figure 10. For the specimens prepared according to the

procedure described above, the maximum extension attainable under

creep was approximately 9.5 times its original length at a stress of

35 MPa.

Two specimens prepared from the unpigmented resin were also

tested at stress levels of 12.5 and 15 MPa. The maximxim extension

for these two specimens was essentially the same as that found for

the pigmented pol}nner at the same two levels of stress.

8 . Comparison Between the Reference Polyethylene

CPigraented Resin) and Three Commercial Gas Pipe Resins

in use in Europe: Short Term Tensile Properties

During the collaborative research carried out at IKP, University

52
of Stuttgart, a comparison was made between the GRI reference

polyethylene (pigmented resin) and three different gas pipe resins

currently in use in Europe, one from Germany, one from Sweden, and

one from Belgium. Each of the European resins was initially in the

form of pellets, and all three contained yellow pigment.

Sheets were prepared from all four materials using the following

procedures. A predetermined weight of pellets was placed in a mold

which consisted of a 25 cm x 25 cm frame held between two ferrotype

plates. The mold was placed in a press and heated under only light

contact pressure to 175 C. The press was maintained at 175® C for 15

minutes at which time a pressure of 5 MPa was applied and the heat

turned off. The mold was then cooled overnight to room temperature.

The nominal thickness of the molded sheets was between 0.14 and 0.15

cm.

From each sheet, a 1 cm x 2 cm piece of material was cut and its

density determined using the displacement technique in isopropyl

alcohol at 23° C. The results are tabulated at the bottom of Table

18, where the error in each individual measurement is estimated to be

no greater than ±0.001 g/cm^

.

Tensile specimens were then cut from each sheet using a die

which conformed to the geometry specified in DIN 53504, Specimen 53A

[12]. Three tensile properties were determined at 23° C for each

specimen, the yield stress, the stress at break (tensile strength),

and the strain at break. For the initial set of tests, six specimens

from each of the four sheets were elongated to failure at one

constant rate of clamp separation which corresponded to a strain rate

53
(initial strain rate) of approximately 73% per minute. The strain at

failure was determined by measuring the elongation of an initially

1.5 cm long gage section within the straight portion of the specimen.

The results from the set of tests are presented in Table 18, where

each value shown represents an average for six specimens. Also given

in Table 18 are the drawing stress and ratio of the yield stress to

drawing stress. The drawing stress is defined here to be simply the

stress in that portion of the stress -strain curve beyond the yield

point where the stress remains essentially constant while the "neck"

propagates through the straight portion of the specimen.

In addition to the tests just described, tests were also done at

three other rates of strain (initial strain rates) 873, 7. 3, and 1.04%

per minute. In this case, only two specimens of each material were

tested at each strain rate. The dependence of all three tensile

properties on strain rate is presented in Figures 11, 12, and 13.

The yield stress increases linearly with the logarithm of the strain

rate (Figure 11), except for the one set of tests at the highest

strain rate for the material from Belgium. All four materials exhibit

a maximum in the stress at break (Figure 12) at a strain rate of 73%

per minute. The material from Belgium shows a much greater decrease

in tensile strength at the highest strain rate than do the other

three. The strain at break decreases monotonically with the

logarithm of the strain rate (Figure 13) for all four materials.

Viewed overall, it is evident that all four materials show the

same general trends in behavior and that there is not a great deal of

difference among them. The material from Sweden shows consistently

54
the highest values of yield stress and strain at break. These two

observations along with the observation that it has the highest

density suggest that, under the same molding conditions, it will have

the highest crystallinity of the four materials. It is also evident

that, at high strain rates, the tensile properties deteriorate most

rapidly for the material from Belgixom.

9 . Summary

This report describes work done under GRI Contract Number 5084-

260-1013 during the period from October 1, 1985 through September 30,

1986. The project entails the procurement, characterization, and

warehousing of standard reference polyethylene gas pipe resins, as

well as piping and joint materials made from them. The contract

between the Gas Research Institute (GRI) and the National Bureau of

Standards (NBS) was recommended at a workshop held at Northwestern

University, Evanston, IL on September 7 and 8, 1983. A final report

describing the presentations, deliberations, and recommendations of

the workshop was issued by GRI (Report No. 84/0107) on May 14, 1984.

The workshop stipulated the following types and quantities of

material to be characterized and warehoused for distribution:

Item Quantity

1. Polyethylene resin (natural)

2. Polyethylene resin (pigmented)

3. Polyethylene pipe

(6.03 cm OD, 0.55 cm wall)

4. Polyethylene pipe

(11.4 cm OD, 1.0 cm wall)

5. Polyethylene pipe

(1.59 cm OD, 123 cm wall)

6. Polyethylene 5.1 cm socket T joint

7. Polyethylene 5.1 cm butt T joint

455 kg.

4550 kg.

1.59 km in 0.76 m

sections

0.15 km in 0.76 m

sections

0.25 km in 0.76 m

sections

500

500

55
In addition, it was decided to include one 0.15 km roll of the 1.59

cm OD, 0.23 cm wall pipe. It was further agreed upon by the

attendees at the workshop that the reference polyethylene would be

the medium density polyethylene resin, TR418, from the Phillips

Petroleum Co.

All of the materials were on site at NBS by October, 1985, when

the characterization work commenced. A detailed description of the

equipment and procedures used in each phase of the characterization

work is contained in this report. The principal areas of

investigation were as follows;

(1) The number of methyl groups, butyl branches, and terminal

vinyl groups was determined for the two polyethylene resins

using FT-IR and NMR. One piece of the 6.03 cm (OD) pipe

was also examined,

(2) The melt flow rate was determined for the two polyethylene

resins. At least ten random samples were tested from each

lot of material. In addition, the melt flow rate of

material cut from various locations within the piping and

joint materials was examined,

(3) The density was determined for all of the reference

materials

,

(4) Both lots of resin were examined by size exclusion

chromatography in order to determine their molecular weight

and molecular weight distribution.

56
(5) The yield stress and strain at yield were determined for

two of the three sizes of pipe. In addition, the creep

behavior of material molded from the pigmented resin was

studied.

Several of the principal findings of this work are summarized

below.

57
(1) Branching Characteristics

Sample

FT-IR

Methyl Groups Vinyl Groups

ner 100 Carbon Atoms ner C-C Bond

NMR

butyl groups

per 1000

carbon atoms

unpigmented

resin

0.50 5X10“^ 4.27

pigmented

resin

0.56 5X10''’ 4.56

pigmented

pipe

0.55 5X10“

(2) Melt Flow Rate^®^

Resin^ ^ ^

Sample Mean

Standard

Deviation

95% Confidence

Interval of Mean

Unpigmented 0.253<'=> 0.007 0.241 to 0.272

Pigmented 0.179^'^^

0.796«®^

0.010

0.025

0.177 to 0.180

0.789 to 0.802

Pining and Joint Materials ^ ® ^

1.59 cm OD 0.851

6.03 cm OD

Inside 0.577

Outside 0.618

11.4 cm OD

Inside 0.625

Outside 0.674

butt joint 0.996

socket joint 0.508

gm/lOmin.

Condition 190®C/2.16 kg.

^ ® ^ mean value for 20 charges

^ ^

mean value for 56 charges

Condition 190°C/5.0 kg

58
(3) Density

Mean Standard Deviation

Sample (gm/cm^

)

(gm/cm^

)

Unpigmented resin 0.9322^®’ 0.0040

Pigmented resin 0.9328^*^ 0.0009

1.59 cm OD pipe 0.938«®> 0.001

6.03 cm OD pipe 0.937«“^ 0.001

11.4 cm OD pipe 0.938<‘’5 0.001

^ ® ^ mean value for 10 samples

mean value for 5 samples

(4) Size Exclusion Chromatography

Standard Standard

Sample Mw Deviation K Deviation

Unpigmented

(a)

Pigmented

17040 7670 5500 565

(a) No difference, was observed between the two resins

(5) Tensile Properties

Standard Standard

Pipe Size Yield Stress Deviation Strain at Yield Deviation

1.59 cm OD 16.40 0.15 0.125 0.001

6,03 cm OD 17.35 0.19 0.127 0.000

< ® ^ MPa

Strain rate = 81% per minute

Finally, it should be noted that the values of melt flow rate for the

two joints differ by a factor of about two (0.996 for the butt joint versus

0.508 for the socket joint), and that both values are different from that of

the base resin (0.796) by an amount well outside the standard deviation for

the twenty charges of the base resin examined. We conclude that these

59
differences are a consequence of changes in molecular parameters which occur

during the processing. It is recommended, therefore, that additional work

be done to determine which molecular parameters are affected and to what

extent these changes may influence long term performance.

60
References

[1] GRI Research Grant No. 5084-260-1013, "Establishment and

Characterization of a Polyethylene Reference Sample Bank"

.

[2] Final Report, "Workshop on Selection of a Reference Standard

Polyethylene Piping Material," GRI Report No. 84/0107, May 1984.

[3] Rueda, D. R. , Balta Calleja, F. J. and Hidalgo, A. Spectrochim, Acta,

35A, 847 (1979).

[4] Wexler, A. S., Spectrochim, Acta 21A, 1725, (1965).

[5] Okada, T. and Mandelkern, L.O., J. Pol3nn. Sci. Part A-2, 5, 239 (1967).

[6] ASTM Method D 1238-82, 1986 Annual Book of ASTM Standards, Vol. 08.01,

American Society for Testing and Materials, 1916 Race Street,

Philadelphia, PA 19103.

[7] Natrella, M. G., "Experimental Statistics, NBS Handbook 91," Chapter 1,

U.S. Government Printing Office, Washington, DC (1966).

[8] Rudin, A. and Schreiber, H. P. , SPE Journal, 20, 533 (1964).

[9] Stockmayer, P. , Einfluss der thermischen Behandlung auf Struktur und

Festigkeit von Polyathylen-Halbzeug, insbesondere PE-Rohren, Doctoral

Thesis, Institut fur Kunststoffprufung und Kunststoffkunde , Universitat

Stuttgart (1979).

[10] Wagner, H. L. , J. Physical and Chemical Reference Data, 14, 611

(1985) .

[11] Wagner, H, L. , J. Physical and Chemical Reference Data, 14, 1101

(1985)

.

[12] DIN 53504, DIN Deutsches Institut fur Normung e.V., Deutsches

Informationzentrum fur Technische Regeln (DITR) und Beuth Velag GmbH,

Burggrafenstrasse 6, D-1000 Berlin 30.

61
List of Tables

Table 1

Table 2

Table 3

Table 4

Table 5

Table 6

Table 7

Table 8

Table 9

Table 10

Table 11

Table 12

Table 13

Table 14

Methyl Group Concentration: No/100 carbon atoms

Terminal Vinyl Group Concentration: No. per carbon- carbon

bond

Degree of Crystallinity: weight fraction x density

Variation of Melt Flow Rate with Piston Diameter: Pigmented

Resin

Melt Flow Rate of SRM 1496 at a Load of 2.16 kg

Estimate of Errors in Melt Flow Rate of SRM 1496 Polyethylene

under Condition 190/2.16

Variation of Temperature with Height in Undisturbed Melt in

Cylinder Bore

Melt Flow Rate of the Pigmented Gas Pipe Resin, SRM 2497, at

a Load of 2.16 kg

Melt Flow Rate of the Pigmented Gas Pipe Resin, SRM 1497, at

a Load of 5.0 kg

Melt Flow Rate of the Pigmented Gas Pipe Resin, SRM 1497, at

a Load of 21.6 kg

Estimates of Errors in Melt Flow Rate of the Pigmented PE

Resin (SRM 1497) under Condition 190/2.16

Melt Flow Rate of Parts Cut from Pipes and Joints using ASTM

D 1238-82, Condition 190/5.0

Density of the As-Received Pellets Determined Using a Density

Gradient Column

Density of the Piping Materials at 22° C Determined Using the

Displacement Method

62
Table 15

Table 16

Table 17

Table 18

Average Value of the Outside Diameter and Wall Thickness of

One Section of the 1.27 cm Diameter Pipe

Calibration Data for Size Exclusion

Chromatography

Yield Stress and Strain at Yield as a Function of Strain Rate

for Gas Pipe Tested in Uniaxial Extension

Comparison of Tensile Properties of Four Commercial Gas Pipe

Resins

63
Table 1

Methyl Group Concentration

No./lOO Carbon Atoms

Sample

unpigmented resin

pigmented resin

pigmented (pipe)

Methyl Group Concentration

0.50 + .05

0.56 + .05

0.55 + .05

64
Table 2

Terminal Vinyl Group Concentration

No. per Carbon- Carbon Bond

Sample

unpigmented resin

pigmented resin

pigmented (pipe)

Vinyl Group Concentration

5 ± 0.2 X lO"'*

5 ± 0.2 X 10'^

5 ± 0.2 X lO-'*

65
Table 3

Degree of Crystallinity

Weight Fraction x Density

Sample

unpigmented resin

pigmented resin

pigmented (pipe)

variation among several molded sheets

Crystallinity

0.66 - 0.71^

0.74 ± .03

0.67 ± .03

66
Table 4

Variation of Melt Flow Rate with Piston Diameter: Pigmented Resin

NARROW PISTON FOOT BROAD PISTON FOOT

Std. Dev. Std. Dev.

Mean

Std. Dev.

of Mean

of Sing.

Meas

.

Mean

Std. Dev.

of Mean

of Sing.

Meas

.

1st Time

Extrudate

0.191 0.012 0.014 0.189 0.006 0.007

2nd Time

Extrudate

0.179 0.008 0.009 0.182 0.003 0.004

3rd Time

Extrudate

0.176 0.010 0.012 0.177 0.004 0.004

Data

Overall

0.182 0.012 0.013 0.183 0.007 0.007

All data in g/10 minutes

67
Table 5

Melt Flow Rate of

SRM 1496 at a Load of 2,16 kg

Standard

Deviation of

95% Confidence a Single

Mean (a) (b) Internal of Mean Measurement

1st Timed

Extrudate 0,259 0,256 to 0.262 0.007

2nd Timed

Extrudate 0,252 0,250 to 0.254 0.005

3rd Timed

Extrudate 0,248 0.246 to 0,250 0.004

Overall Mean 0,253 0.251 to 0.255 0.007

Overall Data

Range 0.241 to 0.272

(a) g/10 min

(b) mean value for 20 charges

68
Table 6

Estimates of Errors in Melt Flow Rate

of SRM 1496 Polyethylene

under Condition 190/2.16

1. Overall Estimated Repeatability

of Experiment (see Table 1 of ASTM

D 1238-82) 2.6%

2. dM/M*100 0.7%

3. dt/t*100 0.03%

4. dMfr/dT*dT/T*100

5. Instrument Variability (estimated

from ASTM D 1238-82 Table 3)

6. Range of day-to-day variation

overall mean

7. Range of position- to-position

variability

8. Overall estimated error in melt

flow rate (contributions are from

1-5. 6-7 are included in 1 .

)

1.7%

15

0.250 to 0.253

0.241 to 0.272

15.2%

69
Table 7

Variation of Temperature with Height in

Undisturbed Melt in Cylinder Bore

Height Above

Die , mm

Melt Temp.

Degrees C

48 190.09

36 189.93

24 189.97

12 189.94

1 189.23

70
Table 8

Melt Flow Rate of the Pigmented

Gas Pipe Resin, SRM 1497,

at a Load of 2,16 kg

Standard

Mean (a)(b)

95% Confidence

Interval of Mean

Deviation of

a Single

Measurement

1st Timed

Extrudate 0.186 0.182 to 0.189 0.011

2nd Timed

Extrudate 0.177 0.175 to 0.180 0.009

3rd Timed

Extrudate 0.173 0.170 to 0.175 0.008

Overall Mean 0.179 0.177 to 0.180 0.010

Overall Data

Range 0.160 to 0.209

(a) g/10 min

(b) mean value for 56 charges

71
- Table 9

1st Timed

Extrudate

2nd Timed

Extrudate

3rd Timed

Extrudate

Overall mean

Overall Data

Range

Melt Flow Rate of the Pigmented

Gas Pipe Resin, SRM 1497,

at a Load of 5.0 kg

Mean (a)(b)

95% Confidence

Interval of Mean

Standard

Deviation of

a Single

Measurement

0.788 0.778 to 0.798 0.023

0.797 0.785 to O 00 o 0.025

0.805 0.790 to 0.815 0.026

0.796 0.789 to 0.802 0.025

0.758 to 0.878

(a) gm/10 min

(b) mean value for 20 charges

72
Table 10

Melt Flow Rate of the Pigmented

Gas Pipe Resin, SRM 1497,

at a Load of 21.6 kg

Standard

Mean (a)(b)

95% Confidence

Interval of Mean

Deviation of

a Single

Measurement

1st Timed

Extrudate 15.1 14.8 to 15.4 0.4

2nd Timed

Extrudate 16.4 16.0 to 16.8 0.5

3rd Timed

Extrudate 17.9 17.4 to 18.4 0.6

Overall Mean 16.5 16.0 to 16.9

Overall Data

Range

(a) g/10 min

(b) mean value for 10 charges

14.6 to 19.5

73
Table 11

Estimates of Errors in Melt Flow Rate

of the Pigmented PE Resin (SRM 1497)

under Condition 190/2.16

1. Overall estimated repeatablility

of experiment (see Table 2 of ASTM

D 1238-82)

2. dM/M*100

3. dt/t*100

4. dMfr/dT * dT/T*100

5 . Instrument Variability

(estimated from ASTM

D 1238-82 Table 3)

6. Range of day-to-day variation

of overall mean

7. Range of sample- to -sample

variation of overall mean

Overall estimated error from 1-4

Overall estimated error from 1-5

%

5.9

1.0

.03

.2

16 for Mfr =0.25

7 for Mfr = 7.0

0.176 to 0.186 g/10 min

0.171 to 0,188 g/10 min

6

17

74
Table 12

Melt Flow Rate of Parts Cut from Pipes and Joints

Using ASTM Method D1238-82 Condition 190/5.0

Flow Rate Standard

(g/10 min) Deviation

1.59 cm O.D. pipe cross section 0 .851 0 .020

6.03 cm O.D. pipe inside 0 .577 0 .008

outside 0 .618 0 .014

11.4 cm O.D. pipe inside (pipe 1) 0 .633 0 .004

inside (pipe 2) 0 .617 0 .020

outside (pipe 1) 0 .683 0 .020

outside (pipe 2) 0 .665 0 .014

butt joint injection port 1. 103 0 .023

end 0 .988 0 .053

socket joint injection port 0 .605 0 .026

end 0 .411 0 .026

For comparison from our Table 9

Resin 0 .796

Overall Range of Resin Data 0 .758 to 0.878

75
12

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

Table 13

Density of the As -Received

Pellets at 23° C Determined Using

A Density Gradient Column

Average Standard

Density Density Deviation

Pigment

None

(g/cm^

)

0.9330

0.9322

0.9320

0.9320

0.9320

(g/cm^

)

(g/cm^

)

Orange

0.9320

0.9320

0.9320

0.9330

0.9320

0.9320

0.9330

0.9330

0.9320

0.9335

0.9322 0.004

0.9335

0.9310

0.9335

0.9330

0.9335

0.9328 0.0009

76
Table 14

Pipe

Outside Diameter

cm (in)

1.59 (0.5)

6.03 (2.0)

11.4 (4.0)

Density of the Piping Materials

at 22“ C Determined Using the

Displacement Method

Average Density

and Standard

ipecimen Density Deviation

Number (g/cm^

)

(g/cm^

)

1 0.936

2 0.937

3 0.938

4 0.939

5 0.939 0.938

6 0.938 0.001

7 0.939

8 0.940

9 0.939

10 0.939

11 0.938

12 0.937

13 0.936

14 0.937 0.937

15 0.937 0.0005

16 0.937

17 0.937

18 0.937

19 0.937

20 0.937

21 0.937

22 0.939 0.938

23 0.937 0.001

24 0.938

25 0.937

77
Table 15

Average Value of the Outside

Diameter and Wall Thickness

of One Section of the 1.27 cm

Diameter Pipe

Standard

Dimension

Average Minimum

Outside Diameter (a)

Value (cm)

1.586

Deviation (cm)

0.027

Average Maximum

Outside Diameter (b) 1.601 0.013

Average Outside

Diameter (a) 1.594 0.016

Average Minimum

Wall Thickness (b) 0.233 0.0005

Average Maximum

Wall Thickness (b) 0.242 0.001

Average Wall Thickness (b) 0.237 0.0005

(a) Average for

(b) Average for

50 measurements

13 measurements

78
Table 16

Calibration Data

Con. Peak Elution Log Hydro

Standard Run M.W. Type(a) mg/ml Volume dynamic Volume

SPP 541 388 519 P.S. 1 18.63 1.084

SPP 577 389 1811 P.S. 1 17.99 2.564

TSK A2500 387 2800 P.S. 1.1 17.85 3.987

P.C. 61110 383 4000 P.S. 1 17.42 4.248

P . C . 8b 382 10000 P.S. 1 16.69 4.920

SRM 1478 366 36590 P.S. 1 15.50 5.072

SRM 1482 372 12500 P.E. 1 15.82 5.686

SRM 1483 373 30500 P.E. 1 14.96 6.344

TSK F20 363 1.86e5 P.S. 1 14.11 7.065

SRM 1484 374 1.09e5 P.E. 0.5 13.89 7.285

P.C. 5a 364 4.98e5 P.S. 0.5 13.13 7.787

SRM 1479 365 1.05e6 P.S. 0.5 12.27 8.334

TSK F288 367 2.87e6 P.S. 0.1 11.19 9.072

TSK F720 368 7.5e6 P.S. 0.23 10.55 9.776

TSK F1300 369 1.34e7 P.S. 0.21 10.20 10.202

TSK F1300 384 1.34e7 P.S. 0.19 10.11 10.202

BK2500 399 1.8e7 P.S. 0.33 10.54 10.419

TSK F2000 370 2.06e7 P.S. 0.28 10.55 10.517

TSK F2000 386 2.06e7 P.S. 0.28 10.33 10.517

BK3000 398 2.8e7 P.S. 0.3 10.44 10.743

SRM 1475 375 P.E . (broad) 0.5

SRM1475 376 P.E . (broad) 0.5

Polymer Standard Sources: SPP - Scientific Polymer Products; TSK - Toyo

Soda; P.C. - Pressure Chemical Co.; BK - Japanese Synthetic Rubber Co.; SRM

- Standard Reference Materials, NBS

(a) P.S.

P.E.

polystyrene

polyethylene

79
Table 17

Yield Stress and Strain at Yield

as a Function of Strain Rate for

Gas Pipe Tested in Uniaxial Extension

Pipe

Size

cm (in)

1.27 (0.5)

5.08 (2.0)

Strain Yield Strain . Specimen Rate Stress Yield

Number (% Per Min) (MPa) (%)

1 81 16.4 CM

2 81 16.3 12.5

3 81 16.3 12.5

4 81 16.3 12.5

5 81 16.7 12.5

6 81 16.6 12.5

7 81 16.4 12.5

8 81 16.4 12.5

9 81 16.2 12.5

10 81 16.4 12,5

11 810 19.0 11.7

12 810 19.0 11.7

13 8.3 14.1 13.5

14 8.3 14.2 13.5

15 0.82 11.9 14.3

16 0.82 11.9 14.3

17 81 17.6 12.7

18 81 17.5 12.7

19 81 17.1 12.7

20 81 17.2 12.7

21 81 17.3 12.7

22 81 17.4 12.7

23 810 19.6 11.9

24 810 19.6 11.9

25 8.1 14.5 13.9

26 8.1 14.6 13.9

27 0.80 12.1 14.9

28 0.80 12.8 14.8

80
Table 18

Comparison of Tensile Properties

of Four Commercial Gas Pipe Resins< ^ >

Material

Property< ^

)

U.S.A. Germany Belgium Sweden

Yield Stress (MPa) 20.6 21,8 21.6 22.1

(Std. Dev.) (0.2) (0,5) (0.6) (0.5)

Stress at Break (MPa) 33,8 35,5 31.1 33.9

(Std. Dev.) (1.45) (0.8) (3.5) (2.3)

Strain at Break (%) 850 900 840 990

(Std. Dev.) (30) (23) (50) (50)

Drawing Stress (MPa) 14.1 15.5 14.6 1.45

Ratio of Yield Stress

to Drawing Stress

1.45 1.41 1.48 2.52

Density (g/cm3)<2> 0.944 0.945 0.945 0.949

Initial Strain Rate - 73%/min

< 2 ) 23®C in Isopropyl Alcohol, Estimated Error ±0.001 g/cm^

<3) The values shown for the tensile properties represent the averages for

6 specimens

81
Captions for Figures

Figure 1

Figure 2 ,

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7

Figure 8.

Figure 9

,

Figure 10.

Figure 11.

Figure 12.

Difference spectrum for the unpigmented/pigmented pair.

Difference spectrum for the pigmented pellets/pipe specimen

pair.

Drift of the Melt Flow Rate as a function of time.

Measurements were taken at about every 2 min waiting for the

6 minute preheat.

Location of samples taken from the "T" joints for the

determination of the melt flow rate.

Average value of the outside diameter as a function of

position along the length of one 50 cm long section of the

1.27

cm diameter pipe.

Size exclusion chromatography of pigmented and unpigmented

resins. Pigmented shown with (+) . Unpigmented shown with

(). Notice there is no measurable difference in the SEC of

the two resins although their Melt Flow Rates show a 30%

difference

Yield stress versus log (strain rate) for specimens of the

1.27

cm and 5.08 cm diameter pipe tested in uniaxial

extension at four different strain rates.

Strain at yield versus log (strain rate) for specimens of the

1.27

cm and 5.08 cm diameter pipe tested in uniaxial

extension at four different strain rates.

Log (creep strain) versus log time for specimens prepared

from the pigmented polyethylene resin. The numbers present

the applied stress (MPa) and the arrows indicate fracture.

Maximum extension in creep versus log applied stress

for one specimen prepared from the pigmented resin.

Yield stress versus strain rate (initial) in uniaxial

extension for specimens prepared from four different

commercial pipe resins. O - TR418, U.S.A.; A - Germany; ^ - Sweden; Q - Belgium.

Stress at failure versus strain rate (initial) in uniaxial

extension for specimens prepared from four different

commercial pipe resins. O - TR418, U.S.A.; A- Germany; ^ - Sweden; - Belgium.

82
Figure 13. Strain at failure versus strain rate (initial) in uniaxial

extension for specimens prepared from four different

commercial pipe resins. O - TR418, U.S.A., A- Germany; ^ - Sweden; Q - Belgium.

83
'''® if-

-Ai"'

I,. %, .a«iU::/{-»^l.J'»4-: TuSjrf

:^l •I,"’- ' (.

^

'

' ‘x

'•

'">' j(-

I'fef %1‘ sjj'ft,,. «( .vi'

' r','A->A

f;'^.A'.i,yAA-;'\ . -.V-.A

'

''

.

' A'' <: .{^ ' j

"

A' 4’A"' hr .:;;A'4^'' AfiA .W''li jA-il? A

>1. _^-

'fj y •.yvV>>

•"S f V

.,: '.. .. -' y. .IV • '.I^ ,. ',;( ' VV,\«

;J> >

' ' •' „’^4 («vAsA' 6' " A

" A , A, .

^ AA ; ';, ^ S^r:XM-'

' .Ai'^iV •' t->M 'iN^*

jA *^4^XAA y;

.

-

•

.

, ,

.

•'. .. .'A ••

• A

'

' -V ,,•.'

V'jH ^ I;, . *i>'*f' '’•

f fi./i.V A'i.' A^.' ?• f'fti! ', '^V'" A,,:,:'“A^4 ,^^y \

'-•," .' 'I

• ','A'A ' A' 'p.AA. ;.' y ;:,:V'.A^^

'. .' :; y;rv-»'^'sv^

,)’' '

' ’"i-y '' . '•.v:; ,~, :<''''’*''‘^.«v;, ,; y^SxSm^k n

;' *^-'v y

«.. A/'y-;):# y

^

j'A

.^ V.

' .'*;

i' ‘Ay -A:Ai>AV

..:.,A

. .V . 'f>- •'>'

' -^'. • V-'A* . 'vu' *

.. y y ' r

.

•n?i
PIGMENTED

3DNygyDS0u

Figure

1,

Difference

spectrum

for

the

unpigmented/plgmented

pair.
DIFFERENCE

SPECTRUM

PIGMENTED

PELLETS

-

PIPE

SHAVINGS

3aNygyoggy

Figure

2.

Difference

spectrum

for

the

pigmented

pellets/pipe

specimen

pair»
CV2 O CO CO CV2

CO CO CO z>

(6 (D d d d d d

NM OT/D 3J.VH miA

CO

w

Eiz;

t—

H

s

z

I—

I

H

sHH

EFigure

3.

Drift

of

the

Melt

Flow

Rate

as

a

function

of

time.

Measurements

were

taken

at

about

every

2

min

waiting

f<

the

6

minute

preheat.
1 INJECTION PORT

(a) BUTT FUSION "T" JOINT

(b) SOCKET "T" JOINT

Figure 4.. Location of samples taken from the '*T" joints for the

determination of the melt flow rate.
oooo

-|Z6Q*t

oo

oo

o

&o

o

o

o

IDO

ooe - — o _ _ oo o ^oOo

e- . — . . - - — . Q _Q O _ o_ . ooo ' o j I I I f \ 2

(D in CO CM

O

a> G>

— oyo Gy ov O)m« (LUD) d3i3i^via Baisino 39 vyiAv

om

u

ql

Q_

Llo

o 0) O i=

4^

co

O

o

c

c

o 3

(>_ 4-> o

0) to in

CO

w

<TJ

co

£.

(V

E 4-> Oi O E

(T3 fH

om

•D

01c

0)

o

X3

01

o

4-> 3 c. O

0> x:

c

d)

o 0)

4-> a.

01

a

£

o 4JI £_0)

0)3

bOc

*j

01

oE

(0>

(-H CO CO •o c

QJoE

Cl

CO

td> 01 CM > o • «s Q. fl— m

(U3

U)

•<-1 Cii
o

xn

D5

d

D-,

D

!

40

lO o lO o lO o

02 02 q q

d d d d d d

o

>

:zi

o

D

imom

Figure

6«

Size

exclusion

chromatography

of

pigmented

and

unpigmtnted

resins.

Pigmented

shown

with

(

+)

.

Unpigmented

shown

with

(O).

Notice

there

is

no

measurable

difference

in

the

SEC

the

two

resins

although

their

Melt

Flow

Rates

show

a

30%

difference.
I

Figure

7.

Yield

stress

versus

log

(strain

rate)

for

specimens

of

the

1.27

cm

and

5.08

cm

diameter

pipe

tested

in

uniaxial

extension

at

four

different

strain

rates.
Figure

8,

Strain

at

yield

versus

log

(strain

rate)

for

specimens

of

the

1.27

cm

and

5.08

cm

diameter

pipe

tested

in

uniaxial

extension

at

four

different

strain

rates.
Nivais d33ao

o

o

Figure

9.

Log

(creep

strain)

versus

log

time

for

specimens

prepared

from

the

pigmented

polyethylene

resin.

The

numbers

present

the

applied

stress

(MPa)

and

the

arrows

indicate

fracture.
max

11

Maxirnun extension in creep versus log ( applied stress

(engineering stress) for one specimen prepared from the

pigmentec resin.

igure lO.
Figure

IK

Yield

stress

versus

strain

rate

(initial)

in

uniaxial

extension

for

specimens

prepared

from

four

different

commercial

pipe

resins.

O

-

TR*^l8,

U.S.A.;

Germany;

S7

"

Sweden;

-

Belgium.
1 1 'O

(D

CM CM

(5dH) 3dmiVd IV SSddiS

o

cn

GO Figure

12.

Stress

at

failure

versus

strain

rate

(initial)

in

uniaxial

extension

for

specimens

prepared

from

four

different

commercial

pipe

resins.

O

”

TR*<18,

U.S.A.;

A

”

Germany!

S7

”

Sweden

i

O

”

Belgium.
O 00 CD

3dnn'^ IV Nivyis

Figure

13

.

Strain

at

failure

versus

strain

rate

(initial)

in

uniaxial

extension

for

specimens

prepared

from

four

different

commercial

pipe

resins.

O

"

TR418,

U.S.A.;

{S

"

Germany;

^

"

Sweden;

''

Belgium.
NBS-114A (REV. 2 -ec) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date

BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions) NBSIR 87-3506 MARCH 1987

4. TITLE AND SUBTITLE

Reference Standard Polyethylene Resins and Piping Materials

5. AUTHOR(S) J. M. Crissman* F, W, Wang, C.M, Guttman, J. R. Maurey, H, L. Wagner,

Bo M. Fanconi, and D. L. VanderHart

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contrac?/ Grant No.

5084-260-1013

S^Jype^of Report & Period Covered

Oct. 1, 1985-Sept. 30, 1981

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Gas Research Institute, 8600 Bryn Mawr Ave.

Chicago, IL 60631

10.

SUPPLEMENTARY NOTES

I I Document describes a computer program; SF=I85, FlPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibiiography or literature survey, mention it here)

Polyethylene piping is currently in widespread use in gas distribution in the

United States, and represents approximately 80% of new installation.

Research that is currently being performed on gas pipes often employs many

different polyethylenes selected from the large number of polyethylenes

available for this use. This variation in materials makes it difficult to

compare results from different research laboratories, or to compare measurements

carried out in the same laboratory at different times. To avoid this

difficulty Gas Research Institute and the National Bureau of Standards (NBS)

have undertaken to provide a permanent store of one particular polyethylene

resin as well as piping and fittings made from it which would provde a source

of well characterized materials for research related to gas distribution

systems. This report describes the choice of this resin and the types and

quantities of the materials to be provided by NBS and the characterizations

performed which include the determination of the branch content, melt flow

rate, molecular weight and molecular weight distribution, density, and

specific tensile properties.

12.

KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Branching; FT-IR; gas pipe; melt index; molecular weight distribution; NMR;

polyethylene size exclusion chromatography; tensile tests.

13- AVAILABILITY

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20402.

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USC0MM"0C 3043-P80

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