NBSIR 88-3705 GRI-87/0326

NBS

PUBLICATIONS

Reference Standard Polyethylene

Resins and Piping Materials

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Final Report

(October 1, 1986 - September 30, 1987)

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Issued March 1988

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U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

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#88-3705

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1988

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Reference Standard

Polyethylene Resins and Piping Materials

Research Information Center

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Gaithersburg, Maryland 20899

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Final Report

October 1, 1986 - September 30, 1987

Prepared by:

J. M. Crissman

For

GAS RESEARCH INSTITUTE

Grant No. 5084-260-1013

GRI Report No. GRI-87/0326

GRI Project Manager

Max Klein

Physical Sciences

March 1988

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, expressed 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.
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 necessarily the best available for the purpose.
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 C. M. Guttman

J. R. Maurey

B. M. Fanconi

D. L. VanderHart

F. W. Wang

Report Period October 1, 1986 - September 30, 1987

Obj ectives

(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.

Technical

Perspective 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. This store

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

.
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.

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.

(3) Warehouse and distribute the resin

and products through the NBS Standard

Reference Materials Program.

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
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 by NBS 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
TABLE OF CONTENTS

Page

1.0 Introduction 1

2.0 Melt Flow Rate of the Butt Fusion and Socket T-Joints 2

2.1 Discussion of Samples 2

2.2 Sampling Procedure- -Cutting of the Joints 2

2.3 Results and Discussion. 3

3.0 Size Exclusion Chromatograph 4

3.1 Experimental Procedures 5

3.2 Data Analysis 6

3.3 Calibration 6

3.4 Results of SEC Done on Samples From the Two

Types of T-Joints 10

3.5 Molecular Weight Distribution of the Pigmented

Resin ( SRM 1497) 10

4.0 Density Variations Within the Two Types of T-Joints 13

5.0 Examination of the T-Joints by IR and NMR 14

6.0 Mechanical Behavior Studies 16

6.1 Environmental Stress-Crack Resistance (ESCR) 17

6.2 Uniaxial Creep Behavior 19

7.0 Intrinsic Viscosity of Unpigmented Resin (SRM 1496) 21

7.1 Sampling of SRM 1496 21

7.2 Batch Uniformity 21

7.3 Solution Density and Partial Specific Volume 23

7.4

Estimation of Concentration 24
7.5 Viscosity Runs on SRM 1496 25

7.6 Measurement Scheme 27

7.7 Results of Viscosity Measurements 28

7.8 Error Analysis 29

8.0 Summary 33

References 38

List of Tables 39

List of Figures 47
1 . Introduction

This final report describes work done under GRI Contract Number 5084-260-

1013 during the year starting October 1, 1986 and ending September 30, 1987.

In our final report for the period October 1, 1985 - September 30, 1986 [1]*,

it was reported that the melt flow rate of the joints and piping materials was

in some instances measurably different from that of the starting pigmented

resin. The most significant difference occurred between the two types of Tjoints. Whereas the "butt fusion" joint exhibited a melt flow rate ranging

from 1.103 to 0.988 g/10 min (condition 190/5.0 in ASTM Method D1238 - 82 [ 2 ] )

the melt flow rate for the "socket" joint was in the range 0.605 to 0.411 g/10

min. The melt flow rate for the starting resin was in the range 0.878 to 0.758

g/10 min, as determined under the same conditions.

Although the results for the joints were based on only one determination

from each position within one joint of each type, the values obtained were well

outside the range of data observed for the starting resin. It was concluded

that the changes which had occurred were a consequence of the processing. A

similar result was also found for the 6.03 and 11.4 cm O.D. pipes, where, in

both cases, the melt flow rate was measurably lower for the pipe material than

for the starting resin. The work done during the current reporting period has

been concerned principally with examining more closely the observed differences

in melt flow rate and to establish whether or not this phenomenon is general to

the entire lot of piping and joint materials, or represents an isolated case.

Work was also done to determine to what extent the observed differences in melt

flow rate may be reflected by differences in mechanical performance.

* Numbers in brackets correspond to references which are found at the end of

this report.

1
2 .

0

Melt Flow Rate of the Butt Fusion and Socket T-Joints

Preliminary data on the melt flow rate of the joints and pipes obtained

during the last reporting period showed that the joints and pipes had

significantly different Melt Flow Rates from one other and from the pigmented

resin from which they were made.

In that report only one melt flow rate was done on each position chosen

and on only one pipe or joint of each type, except for the 11.4 cm OD pipe

where measurements were made on two different pipes. Thus, there is nothing

from that data that can be inferred about pipe to pipe or joint to joint

variation. In this report a more detailed study has been performed on the melt

flow rate of the butt fusion and socket joints. The current work has been done

to determine whether the differences observed previously between the butt

fusion and socket joints are consistent with the kind of joint, or the range of

data seen is a result of random fluctuations in the processing conditions for a

given joint.

2 . 1 Discussion of Samples

The piping and joints were processed from the same batch of PE resin used

for SRM 1497. Melt flow rate data were obtained only for the butt fusion and

socket joints since these showed the greatest variation in the earlier

measurements. The melt flow rate of five joints was determined at several

locations deemed to be significantly affected by the processing conditions.

The sites selected were the injection ports of the joints, seam intersection

lines of the joints, and ends of joints. Positions of cuts used to make

charges from the joints are shown in Figure 1.

2 . 2 Sampling Procedure -- Cutting of the Joints

After an unsuccessful attempt to obtain small samples from the joints by

2
cryogenic fracture at liquid nitrogen temperatures, samples were cut from the

joints with a sharp knife blade at ambient temperature.

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

joints. The slow sawing apparently did not heat the resin significantly above

ambient temperature since the sample felt only warm to touch after cutting. As

a further precaution, the sawed surfaces of these samples were removed by

slicing off a few millimeters with a knife blade. It is presumed that this

procedure removed any resin modified as a result of heating and tearing by the

saw.

Charges to be extruded were obtained by cutting the samples with a knife

blade into pieces which would fit down inside the bore of the plastometer.

2 . 3 Results and Discussion

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

small) that the use of ASTM condition 190.0/2.16 was found to yield data

outside of the acceptable range for that condition as prescribed by the ASTM

Method. The melt flow rate under conditions 190/5.0 of ASTM Method D1238-82

was found to be adequate for these measurements. The technique for the melt

flow rate measurement and the calibration of the equipment has been discussed

in our earlier report [lj. Nothing has changed from that discussion for the

present set of measurements except that the charge weight was varied among the

various samples. This was caused by the wide variation in the melt flow rate

of these samples. The charge weight of each of the samples was precalculated

to achieve conformity with both the uniform 6 minute preheat condition and the

piston start position requirements of the method. Nonetheless, the mass of

each of the initial charges was within 5% of the 3 grams specified in the

earlier discussion. This minor variation in initial charge was considered to

3
have no effect on the measured flow rate.

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

Although there were drifts in the measurements similar to those reported in the

discussion of the melt flow rate measurement on the resins in the previous

report[l], those drifts are not reported here because the differences between

the melt flow rate from charge to charge was much greater than the drifts.

Thus we report the overall average from all three measured timed extrudates.

Average values and their standard deviations are given in Table 1. The

averages are for material taken from five different joints. Two conclusions

are evident from the average values of melt flow rate reported. First, the two

joints are different from each other and both are different from the resin.

The socket joint has a lower melt index indicating a higher melt viscosity than

the resin. The butt fusion joint has a higher melt index indicating a lower

melt viscosity than the resin or the socket joint. The fact that the standard

deviation with any one joint set is small compared to the differences measured

among them suggests that the differences are real, and not just random

fluctuations. Second, the material from the vicinity of the injection ports in

each joint had a higher melt index than did material taken from other locations

in the joint. The data for the two joints differ from the resin data and are

clearly outside the data range for the resin. It would seem that the

processing has had a significant effect on the measured melt flow properties of

the joints and pipes.

3 . 0 Size Exclusion Chromatography

This section of the report deals with the size exclusion chromatography

(SEC) of SRM 1497 (pigmented gas pipe resin), as well as samples taken from the

two types of T-joints manufactured from SRM 1497. The pipe resin is known to

4
contain short butyl branches in an abundance of approximately 4.5 per 1000

carbon atoms. Since it is not expected that the hydrodynamic volume will be

changed significantly by the presence of less than one percent short chain

branches it is assumed that the backbone chain is essentially linear. Thus the

reported values for the molecular weight (MW) and the molecular weight

distribution (MWD) should be viewed as apparent values. Since the reported

values of MW may be in error by twenty percent, the effect of the few short

chain branches on the quantities is expected to be insignificant.

3 . 1 Experimental Procedures

Size Exclusion Chromatography (SEC) was run using a Waters 150C ALC/GPC 1

operated at 140°C with trichlorobenzene (TCB) as the solvent. Two Shodex high

temperature mixed bed columns with quoted exclusion limits of 50,000,000 MW

polystyrene were employed for the separations. The columns were designated

Shodex 80M/S 4704 and Shodex 80M/S 4H729. The detector was the differential

refractive index detector used on the Waters instrument. Before it was put

through the SEC the solvent TCB was first run through a silica gel column and

then filtered using a Mitex 5 micrometer pore size filter.

Solutions with polystyrene were made up in TCB with 0.01% Santinox as an

antioxidant. Solutions of the Polystyrene standards used for the hydrodynamic

volume (universal) calibration were dissolved in Santinox-TCB solutions,

filtered into a high temperature GPC vial at room temperature and put into the

GPC carousel for an hour to allow it to warm up to 140° C. Solutions of PE

material were made up in 0.01% solution raised to 160°C in an air bath to

1 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 necessarily the best available for the purpose.

5
dissolve all gels (see Rudin [3]). It was then transferred in the air bath at

160° C using a syringe with a 5 Mitex filter into the GPC high temperature

vials. Solutions were immediately transferred to the GPC oven and allowed to

equilibrate at 140° C for at least one hour before the GPC was started.

3 . 2 Data Analysis

Data from the chromatograph were collected and stored on the disc of a

personal computer. The raw data were reduced by first subtracting a baseline

determined in the region of 7 mL and 25 mL far away from the high cut off on

the 7 mL side and beyond the solvent and so called "extraneous peak" on the low

MW side. Then the solvent peak or Santinox and solvent peak was subtracted.

This was done because the solvent with Santinox had a large peak just at the

edge of the low MW end in the range of 19 to 20 mL. This subtraction allowed a

slightly longer baseline in this region. Since the GRI gas pipe PE did not

return to baseline before the elution volume, Ve = 19 mL, this procedure allowed

a better determination of the baseline. The chromatogram in this form was used

to estimate MW moments and MWD . The final chromatograms were then compared

with each other to determine possible effects of the processing on MW and MWD

(as in this case where we wished to compare chromatograms between resin and

joint materials). The curves were then normalized to one with the chromatogram

cut at 7.25 and 19.00 mL. The treatment of chromatograms obtained for the

calibration is described in the calibration section.

3.3. Calibration

A . Calibration of the Columns at 140°C

1 . Column cutoff

All SEC columns have high and low molecular weight cutoffs. The

specifications on these columns suggest a polystyrene (PS) cut off of

6
MW=50 , 000 , 000 . For these columns a few high MW polystyrenes were used to

estimate the high MW or high end hydrodynamic volume cutoff which was found to

be near VE =19.5 mL for a PS having an MW of 20,000,000. Biphenyl was used to

estimate the low MW cutoff. With and without Santinox, the peak was 20.13 and

20.11 mL respectively. Thus the low MW cutoff on these columns was at 20.11

mL. Octadecane (C 18 H 38 ) was also run which showed a peak at 19.02 mL,

demonstrating that we could easily distinguish C 18 H 38 from biphenyl.

2 . Calibration

Table 2 lists the materials used for calibration of the columns and their

peak positions and hydrodynamic volumes to be used for column calibration in

the universal calibration. Except for SRM 1482, SRM 1483 and SRM 1484 the

hydrodynamic volumes for the calibrants were estimated using the Mark-Houwink

equations [4,5]

[rj] = 14.6xl0" 3 M

0-689 for PS's

[r/] = 52. 6x10" 3 M

0-70 for PE's and octadecane

where the hydrodynamic volume in mL is given by Mn x[r7], [ r?

] being the intrinsic

viscosity. For SRM 1482, 1483 and 1484 the intrinsic viscosity is provided on

the NBS certification.

MW calibration was done in the following way. For the universal

calibration we found that between the elusion limits of 10 and 20 mL the

hydrodynamic volume, VH , was well represented by the equation

log(VH )=a+bx+cx3 (1)

where X=Ve -14.961, Ve being the elution volume for the particular column set

used. The values found were

a = 6.357, b = .7943, and c = .00678

All the points fit well except the point corresponding to the lowest molecular

7
weight polystyrene. This point may be in error for a variety of reasons, among

them are

:

(1) The weight average molecular weight (MW) as reported by the provider is

in error.

(2) The Mark Houwink single parameter equation for intrinsic viscosity is not

expected to work for low molecular weight polymers in a good solvent.

For another solvent it has been shown that the power law changes as

expected by theory as one goes ( in a good solvent) from high molecular

weight to low molecular weight (see for example Han et al[6], McCrackin

[7], and DeGennes [ 8 ] ) . Therefore, for our purposes we did not use the

one point.

The data and the linear fit to it are given in Figure 2. With this

simple fit we find that all the points fall on the universal calibration curve

very nicely. Since the universal calibration curve fit over a broad MW range,

we assumed that the same functional form could be used to fit the PE data alone

(a much smaller data set)

.

This functional form allows us to extrapolate the

PE data to much higher MW than that for which we had calibrants. The log

molecular weight versus elution volume using a linear fit is shown in Figure 3

for the PE samples alone.

Next, using the four PE calibrants, we fit the data set to the equation

log(M)=A+Bx+Cx3 (2)

By using this equation over the entire range from high molecular weight

exclusion to low molecular weight cutoff, we obtained the following values for

A , B , and C

.

A=4 . 476 , B=0 . 527 , and C=0 . 000932

In general it was found that the cubic coefficient was insignificant. These

8
equations are given in Table 3. The calibrations obtained from a log molecular

weight versus elution volume fit of the data was checked against SRM 1475 for

which the number average molecular weight (Mn ) , weight average molecular weight

(M^, ) , and the integral molecular weight distribution (MWD) are known. SRM 1475

was not used initially in determining the universal calibration since it is not

a narrow molecular weight fraction. By not using the data for SRM 1475, the

calibration gave a too high value of M^ (but correct Mn ) and a poor fit of the

MWD at high molecular weights. The log molecular weight calibration curve was

then modified to include the data for SRM 1475 in the fit. This was done by

finding the elution volume that a given fraction of the mass is equivalent to

from the chromatogram. This elution volume was then related to the MW given in

the integral MWD provided on the SRM certificate. A much better fit for M^ and

Mw then resulted, as can be seen in Table 3. However, the calibration point

for SRM 1484 is now almost 20% in error in the calibration curve shown in

Figure 4.

B . Effect of Keeping PE Material at High Temperature

We were concerned that keeping the PE material at high temperatures for

an extended length of time would result in degradation. To check this

possibility, one solution of the GRI pigmented sample was kept in the SEC

sample oven at 140° C for a variety of times from one hour to 14 hours. The SEC

was then run on them and compared. The last run remained at 140° C 14 hours

longer than the first run. In Figure 5 are the chromatograms for the two runs.

No difference in the chromatograms is apparent which suggests that there was no

significant change in the material due to sitting at 140°C for 14 hours.

Due to interference of the Santinox we also ran one run without Santinox

added to the solution. A comparison of chromatogram for runs both with and

9
without Santinox is shown in Figure 6. Little or no difference can be observed

in this case as well.

3 . 4 Results of SEC Done on Samples From the Two Types of T-Joints

In our previous annual report[l] it was reported that a preliminary

examination of material from the two types of T-joints revealed a significant

difference between them in melt flow rate. Section 2 of this report describes

the results of a more detailed examination of the two types of joints and

confirms the initial findings. Since the melt flow rate is highly sensitive to

changes in molecular weight and molecular weight distribution, it is of

particular interest to look for possible changes in the SEC of these materials

which resulted from the processing. The same samples used for the melt flow

rate determination were used here for the SEC measurements. The two areas

examined were the side seam of the socket joint and the injection port of the

butt fusion joint (see Figure 1). These two areas were chosen because they

showed the greatest difference in melt flow rate (see Table 1). The resulting

chromatograms for these two samples were then compared to the chromatograms for

a sample from the pigmented PE resin (SRM 1497). The results are shown in

Figures 7 and 8. It can be seen that there is little or no difference in

either set of chromatograms. It would appear that any changes in the MW or MWD

which may have taken place as a result of the processing occurred in that

portion of MWD outside the limits of resolution of our SEC instrument.

3 . 5 Molecular Weight Distribution of the Pigmented Resin (SRM 1497)

An estimation of the MWD of the pigmented resin requires the calibration

curve for log hydrodynamic volume versus elution volume. This has been

discussed and the calibration curve given in a previous section. To obtain a

reasonable MWD of the polymer from SEC it is necessary that the chromatogram

10
return to the baseline before reaching each of the cut offs. That is, there is

no polymer above or below the cut off. If there is, it is important to have

some idea of mass balance for the chromatogram. Both of these criteria were

not obtainable for this polymer. As is seen in Figure 5, we have marked the

cutoffs with vertical dashed lines on the chromatogram. It is possible that we

may still be below the cutoff for the high MW end, and that the extraneous peak

enters in before the baseline is reached on the low MW end. The chromatogram

for SRM 1475 in Figure 9 is shown as an example of a chromatogram that returns

to baseline before both cutoffs. Since the columns are advertised to be as

broad based as possible for high temperature work, it is felt that changing

columns will not improve the resolution. Since the main problem appears to be

with the cutoffs, rerunning the chromatograms also will not improve resolution.

However, the general features of the MWD are clear. It is a single peak

showing a quite broad MWD which is relatively symmetric in log VH

. This is

seen in Figures 5 to 8 . The peak is not bimodal.

We propose the following description of the curve. Since the extraneous

peak interferes at Ve =20 mL and since octadecane comes out at Ve =19.02 mL, we

have chosen to do the integration from Ve =19 mL and less. The MWD of the

polymer will then be defined for all masses above octadecane. It is estimated

that the fraction of the mass less than that of octadecane to be 0.3%, with an

error of +0.1%. The MWD for the remainder of the polymer is given in Table 4

along with the total estimated error.

Four important sources of error contribute to the error in the

determination of the MWD and the moments of the MW. They are:

(1) repeatability of the SEC chromatogram

(2) calibration of the SEC

11
(3) baseline corrections

(4) column and other broadening

We shall deal with these in order. The estimated contribution of each type of

error is given in Table 5.

(1) The chromatograms are very reproducible. Chromatograms were run on

different days and in different sequences. The small error arising from the

nonrepeatability is given in Table 5. As one can see it is the smallest error

of the four.

(2) We have discussed the calibration earlier. Two sources of error

arise from the calibration. One error is a result of uncertainty in the choice

of the functional form of the equation used to fit the calibration data. The

difference between the molecular weights obtained by choosing a calibration

equation linear in Ve and molecular weights obtained by choosing a calibration

equation cubic in Ve was used to estimate the errors reported in column 3 of

Table 5. As is seen there are significant errors even though there is little

difference between the goodness of each fit. Another significant error arises

from the choice of calibrants used for the calibration curve. If we use SRM

1482, 1483 and 1484 and octadecane only to obtain the calibration curve, then,

as discussed before, we do not represent the molecular weight of SRM 1475 well.

We can also determine a calibration curve using all the data (SRM 1482, SRM

1483 SRM 1484, octadecane and SRM 1475). These two calibrations give different

MWD and MW moments for the gas pipe resin. The difference in MWD and moments

arising from this change of calibration is given in column 2 of Table 5. This

is by far the largest contribution to the error.

(3) The baseline on the SEC refractive index detector trace is very

stable. However, it is difficult to extract the baseline at low MW due to the

12
extraneous peaks, peaks which appear even when the solvent alone (or with

Santinox) is injected into the columns. However, these peaks are not

consistent in magnitude and are not entirely subtracted off by subtracting off

the solvent chromatogram from the polymer chromatogram. We have gone 10 mL

beyond the low MW cutoff and still have found some interference. We have been

able to get a stable baseline by stopping 4 mL before the high MW cutoff and 5

mL beyond the low MW cutoff. However, since the noise is 1/20 of the peak

value of the refractive index at the peak, the moments and distribution

obtained by going too far into the noise region can cause problems. We have

varied the cutoff for the integration on both the low side and high side in

increments of 5 mL in order to estimate the effects of this on the values of

the MWD and moments of the MWD . This is shown in Table 5. The error again is

in the high MW moments and the high end of the MWD.

(4) Since the MWD is so broad, any effects of column broadening were

considered insignificant compared to MWD broadening.

A best choice for the MWD and the moments of MW and our best estimate of

the errors are given in Table 4.

4 . 0 Density Variations Within the Two Types of T-Joints

We have briefly examined density variations within the T-joints. The

density can vary considerably depending upon the temperature profile and rate

of cooling during the processing. From one of each of the two types of Tjoints, specimens were cut from specific regions within the joint. See, for

example, the numbered areas in Figure 1. The specimen size ranged from about

0.1 grams to as much as 2 grams, and in most cases two or more pieces were used

from each region. The density measurements were done by hydrostatic weighings

in degassed distilled water.

13
The results along with the estimated errors are presented in Table 6. In

each case the lowest density occurred in the region of the injection port and

the highest densities found were in regions remote from the injection port.

Since many of the pieces were large enough to contain material from both the

inner and outer wall areas, differences in density across the wall thickness

are not necessarily reflected in these measurements.

5 . 0 Examination of the T-Joints by IR and NMR

In addition to the SEC study discussed in Section 3, both types of joints

were examined by infrared (IR) and nuclear magnetic resonance (NMR) in a

further attempt to ascertain possible changes in the molecular structure which

may have occurred during the processing. IR spectra of material from the two

joints were compared to that of the starting resin in order to detect the

presence of oxidation products or molecular species not intrinsic to the PE

resin, whereas NMR spectra were used to determine the concentration of branch

points before and after processing.

5 . 1 Infrared Spectroscopy (IR)

The specimens used to determine the IR spectra were thin films molded

from the same material used to determine the melt flow rate. Spectra are

presented in Figure 10 for material from location 9 within the socket joint and

location 1 within the butt fusion joint (see Figure 1). The spectra for the

socket joint sample is also representative of that for the starting resin,

except for the carbonyl peak situated at 1750 wave numbers. This peak is

somewhat more intense in the spectrum for the socket joint than in the spectrum

for the resin. The carbonyl peak intensity for the resin is comparable to that

seen in Figure 10 for the butt fusion joint. The difference spectrum for the

two joints shown in Figure 11 reveals significant differences at about 1620

14
wave numbers and in the region between 1100 and 1400 wave numbers. Because of

these differences, a thin section was cut directly from a similar region in the

butt fusion joint and the IR measurements repeated. This procedure eliminated

any possible effects caused by the melt flow rate measurements of the molding

operation. The resulting spectrum was found to be essentially the same as that

shown in Figure 10 for the molded film. The multitude of peaks in the

difference spectrum indicates that in the material from the butt fusion joint

there are chemical species present other than polyethylene which are not

present in either the socket joint or the starting PE strain.

5 . 2 Nuclear Magnetic Resonance (NMR)

NMR was used to estimate the concentration of butyl branches in samples

from the two types of T-joints. As before, material was used from location 9

in the socket joint and location 1 in the butt fusion joint (Figure 1).

Samples of each were prepared by dissolution of one gram of PE in four cubic

centimeters of 1,2,4 trichlorobenzene. Both components were placed in a ten

millimeter NMR tube and the air space flushed with N2 gas. A one millimeter

diameter glass stirring rod was inserted through a hole in the cap and the tube

was then immersed in a bath at 176°C. With occasional stirring, the

dissolution proceeded quite slowly requiring several hours. The stirring rod

was slowly withdrawn; then the samples were left in the bath at 176°C

overnight. The height of the sample in the tube was at least four times the

length of the sensitive region of the NMR coil. Upon removal of the stirring

rod, it was observed that a small amount of material adhered to the rod. It is

estimated that less than one percent of the mass of the polymer remained on the

rod. It is possible that during the slow withdrawl of the stirring rod the

higher molecular weight components in the MWD adhered preferentially on the

15
glass rod and thence were transported to the upper regions of the solution

outside the sensitive region of the coil.

NMR spectra were obtained at 130°C without spinning. The analysis was

based on the spectral peaks corresponding to the me thine branch carbon, the a

and /3 backbone carbons next to the branch, and the B4 carbon of the branch

(attached to the backbone). Values of 4.94 ± 0.15 and 5.21 ± 0.15 butyl

branches per 1000 backbone carbon atoms were determined for the butt fusion and

socket joint respectively. While there appears to be a difference of about 5%

in the branch concentration between the two, the difference must be considered

marginal in view of the error limits. In earlier work [1] it was determined

that the butyl branch concentration of the starting resin was 4.56 ± 0.25

branches per 1000 carbon atoms. The reason, or reasons, for the material from

the two joints having a somewhat higher concentration of branch points is at

this point unclear. In both sets of experiments, the sample preparation and

special acquisition parameters were nominally the same. One difference in the

experimental procedure was that in the original work done on the PE resin the

sample was spun during the NMR run, whereas in the present case the sample was

static. Spinning caused a vortexing action in the tube, which, in turn may

have favored some kind of MW fractionation. To resolve this issue it will be

necessary to rerun the resin under the same conditions used for the two joints.

6 . 0 Mechanical Behavior Studies

Since the melt flow rate of the resin can change as a result of the

processing, it is important to determine whether mechanical performance is

affected as well. The occurrence of chain scissions, especially within the

high molecular weight components of the molecular weight distribution, can have

a detrimental effect on the long term mechanical behavior. On the other hand,

16
certain types of crosslinking may have a beneficial effect. One measure of

performance which is sensitive to either degradation or crosslinking is the

environmental stress-crack resistance (ESCR) . Degradation results in decreased

lifetime under standard ESCR test conditions, whereas crosslinking may have the

opposite effect. A second measure of performance which is sensitive to changes

in molecular weight and molecular weight distribution is creep. In linear

polyethylenes having a weight average molecular weight (^ ) of about 1.6x10 s or

greater, the maximum stretch ratio (A) attainable prior to fracture tends to

decrease with increasing 1^. For example, a linear polyethylene with an ^ of

1.6x10 s can be extended in creep at 23°C by as much as a factor of 25 before

fracture occurs, whereas one with an of ~ 4.5 x 10 6 can only be extended by

a factor of 6 or 7. Increasing the degree of crosslinking may also lead to a

decrease in the maximum A attainable under creep.

6 . 1 Environmental Stress-Crack Resistance (ESCR)

The ESCR of material taken from the two types of T-joints is currently

under investigation. The two T-joints were chosen for study on the basis that

they showed the largest variation in melt flow rate. The ESCR measurements are

being done using a test method developed in our own laboratory. The method is

described in detail in reference [9], and a schematic of the apparatus is

provided in Figure 10. A thin strip of polymer is formed around a metal

cylinder having a radius of 0.40 cm and the two ends are clamped from above as

shown. The upper clamp is connected through a pulley system to a weight

hanger. In the present set of tests the specimen is subjected to a constant

applied stress of 5MPa. The entire specimen assembly is then kept submerged in

a bath containing a 10% solution of nonylphenoxypoly (ethyleneoxy) ethanol in

distilled water maintained at 75±1°C. In this test method the specimens are

17
not notched.

The thin strip specimens were prepared as follows from extrudate material

taken from the melt flow rate measurements. In our earlier work, melt flow

rate measurements were made on material cut from several locations within each

of the two types of joints (see Figure 4 of reference [1]). Upon completion of

the melt flow rate measurements, the extrudates from the side seam of the

socket joint and injection port of the butt fusion joint were collected and

then remolded into flat sheets by compression molding. The molding procedures

and equipment used were the same as those described in Section 7.2 of reference

[1]. Thin strips 0.38 cm in wide were then cut from the sheets. The nominal

thickness of the strips was 0.125 cm.

The results of all the ESCR. tests are summarized in Table 7. Initially,

two specimens of materials molded directly from the pigmented resin were tested

under the conditions described above. Both specimens failed on the same day by

crack growth after approximately 1630 hours under test. Four specimens of

material from the side seam of the socket T-joint were then placed under test.

This material exhibited the lowest melt flow rate of any of the materials

examined. The four specimens failed by crack growth at times ranging from 5000

to 8950 hours. Six specimens of material from the region of the injection

part of the butt fusion T-joint were then tested. This material exhibited the

highest melt flow rate of any of processed parts or resin. Two the six

specimens necked after the times indicated in Table 7. In each case, the

specimen extended by drawing down until it slipped out of the upper clamp.

Neither specimen showed any sign of crack initiation, or growth. Four

specimens failed by crack growth after the relatively shorter times indicated

in Table 7. For purposes of comparison, the average failure time for specimens

18
of an ultra high molecular weight polyethylene (UHMWPE) having a molecular

weight of approximately 4.5 x 10 6

, tested under the same conditions, was about

1000 hours. Based on this, albeit limited, data set, it would appear that the

ESCR is sensitive to the observed differences in melt flow rate among the

various components

6 . 2 Uniaxial Creep Behavior

Specimens for creep experiments were cut from the same sheets of remolded

joint materials from which the specimens for the ESCR tests were cut. The

cutting die used was the same as the one from our earlier experiments and the

experiments were done according to the same procedures already described in

reference [ 1

]

Five sets of creep curves are shown in Figure 11 for the remolded

material taken from both types of the joints. Two features have relevance to

the fact that the melt flow rate of the two materials is different. At the

largest strains, where the thinned down, or necked, portion of the specimen has

propagated completely through the straight section of the specimen, the creep

curves reach a plateau and become very nearly flat. In this region the stretch

ratio (A) varies from about 6 to 9 depending upon the level of applied stress.

At the three highest levels of applied stress, the strain is consistently

greater in the specimens derived from butt fusion joint than in those from the

socket joint. While the differences are small, the trend is consistent with

our earlier remark that for polyethylenes , the higher the molecular weight the

less is the maximum A achieved prior to fracture.

By far the most striking difference in behavior occurs for the two

specimens under stresses of 9 and 10 MPa. Up to a time of about 10 3 minutes

the creep curves essentially superpose at each level of applied stress.

19
However, after 10 3 minutes the behavior differs significantly. At 10 MPa we

have included, for comparison purposes, creep data for a specimen molded

directly from the pigmented resin. The creep curves for the material from the

butt fusion joint and from the resin are almost identical over most of the time

scale. On the other hand the material from the socket joint shows

significantly less creep at the longer times. For example, at the time at

which the other two specimens necked the third specimen has attained a value of

strain only about one half as much. The specimens under a load of 9 MPa also

show identical creep behavior up to a time of about 10 3 minutes. However,

beyond this point the two curves are separating, with the material from the

butt fusion joint showing a greater amount of creep. The difference is

becoming greater the longer the time under creep.

Taken together, the observations just discussed, strongly suggest that

differences exist in the materials comprising the two T-joints and that the

differences are sufficient to alter the mechanical behavior. The creep data

are consistent with the melt flow rate measurements to the extent that they

both indicate that the polymer in the socket T-joint has a somewhat higher

molecular weight than either the butt fusion joint or the resin itself.

Although only a very limited number of specimens have been tested for ESCR,

there also appears to be a significant difference in failure times for the

material from the two types of T-joints. Further work is necessary to better

define the differences in creep behavior at the very long times, and to

determine apparent morphological changes taking place which involve very long

relaxation times.

20
7 .

Intrinsic Viscosity of the Unpigmented Resin ( SRM 1496)

Standard Reference Material SRM 1496 is an unpigmented polyethylene resin

of the same material used in a pigmented form for the production of gas

distribution piping. This material has an approximate number average molecular

weight of about 13,000 and a weight average molecular weight of about 140,000.

This section describes the characterization of the limiting viscosity number,

or intrinsic viscosity, in TCB at 140°C. The description of the

characterization of this material for melt flow rate is given in reference [1].

7 .

Sampling of SRM 1496

The unpigmented resin arrived in one 455 kg container. Samples were

collected from ten different locations within the container and were put into

screw cap jars [1]. Of these sites, eight were near each of the corners of the

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

the container's top face. Equal amounts of sample from each location were

placed in a single bottle. The bottle was mixed well by rolling. All samples

for the intrinsic viscosity runs were taken from this bottle.

7 . 2 Batch Uniformity

The homogeneity of SRM 1496 was tested by two procedures. It was

checked, as in the case of SRM 1497, by determining the melt index of samples

from each region of the original container. The standard deviation of the melt

flow rate from position to position was not distinguishable from that of a

series of extrusion samples from any given single position. This result

indicated that the samples were homogeneous since the melt index is very

sensitive to small changes in molecular weight distribution.

Another test for homogeneity of the SRM 1496 supply was conducted by

dilute solution viscometry under experimental conditions which differed from

21
the subsequent viscometry done to certify the limiting viscosity number. A

number 75 Cannon- Ubbelohde viscometer (no. Z167) was used to compare the flow

times of 0.2% solutions of the polymer, prepared from pellets taken from three

different sample jars. This viscometry experiment was conducted at 130. 0°C.

Solutions were formed by dissolving 0.090-0.094 g pellets in amounts of solvent

calculated to achieve a common concentration of 0.2000% (w/v) at 130°C. Flow

times were measured on duplicate samples of each solution collected by the same

filtration process to be described subsequently for the characterization

experiments. The results are tabulated below:

Group Std. Dev.

Solution Solvent t 2 Mean of Mean

Sample 1 avg.

t , sec

.

83.9 125.0 125.1 124.7 — —

Sample 2 avg.

t , sec

.

84.0 124.9 125.1 124.7 —

Avg. flow

time, sec.

84.0 125.0 125.1 124.7 124.9 0.21

Visc'y no. — 2.43 2.44 2.41 2.43 0.02

Here t : , t2 , and t 3 refer to average flow times for samples from solutions 1,

2 , and 3

.

The kinetic energy correction was neglected in computing the relative

viscosity numbers tabulated above. The standard deviations, of the group mean

flow time and the group mean viscosity number, appear to be smaller than the

standard deviation of the corresponding means resulting from the subsequent

characterization viscometry yet to be described on samples of polymer from the

blend at 140°C. Within these limitations, the above results do not appear to

22
indicate any detectable heterogeneity in the population of samples of pellets

taken from different locations of the supply provided by the vendor.

7 . 3 Solution Density and Partial Specific Volume

Computation of the solution concentration and density at the temperature

of the experiment required values of the density of the polymer and the solvent

at ambient temperature, as well as the partial specific volume of the polymer

and the density of the solvent at the temperature of the experiment. The

density of the SRM 1496 pellets was determined by an ethanol -water density

gradient column at 23°C [1]. Density measurements on ten pellets resulted in

an average value of 0.9322 g cm" 3

, in a range from 0.9320 to 0.9330 g cm" 3

, and

with a standard deviation of 0.0040 g cm" 3

.

A value of 1.30 cm3 g" 1 was used for the partial specific volume of SRM

1496 in the solvent at 140°C. This value had been determined by pycnometry for

the partial specific volume of another standard reference polyethylene (SRM

1475) in TCB at 130°C. Since the partial specific volume of SRM 1475 had been

reported to only a third significant figure, the difference between the partial

specific volumes of the two polyethylenes in TCB at the two different

temperatures is probably not significant with respect to the objectives of the

viscometric characterization of SRM 1496.

The values of the density of the TCB at ambient temperature and at 140°C

were obtained by interpolation and extrapolation with a line between

experimentally determined densities at 20°C and 130°C. The vendor reports an

average value of 1.454 g cm" 3 at 20°C for the density of several lots of their

product, with a range of a few parts in the third decimal place. For example,

1.452 g cm" 3 is the lowest density they reported having observed at this

temperature. Another supplier also lists a value of 1.454 g cm” 3 for their

23
TCB . A value of 1.323 g cm" 3 at 130°C was determined by pycnometry during the

characterization of SRM 1475. A density value of 1.451 g cm" 3 at ambient

temperature (22-23°C) was estimated by linear interpolation between the two

experimentally determined densities at 20°C and 120°C. For the TCB at 140°C

density of 1.311 g cm3 was obtained by extrapolation of a line through these

two experimentally determined densities at their respective temperatures.

Computations indicated that the presence of antioxidant in the TCB, in the

concentration 0.0100% (w/v) at 140°C, was not adequate to change the TCB

density in the third decimal place. Computation of solution densities at 140°C

from the solvent density and the partial specific volume of polyethylene in

TCB, resulted in values from 1.312 g cm" 3 at the lowest concentration (0.04%),

to 1.310 g cm" 3 at the highest concentration (0.12%). The computed solution

density differences are therefore within the range of uncertainty for the

experimentally determined density of the solvent.

7 . 4 Estimation of Concentration

In obtaining the intrinsic viscosity, it is important to estimate the

range in which the relative viscosity is linear. (The relative viscosity is (rj

' )/r?o c ) )

• -*- n earlier work on unbranched PE polymers of similar molecular

weight, it was found that the relative viscosity was linear up to and beyond

concentrations of 0.12 weight percent polymer per unit weight of solvent in TCB

at 130. °C. Although SRM 1496 is branched, the concentration of branches is

small and the branch size short. Thus the change in molecular dimensions of

the polymer in solution due to branching is considered insignificant. The

choice of 0.12% as the maximum concentration appears realistic for this

particular polymer.

24
Thus for the certification of the intrinsic viscosity no concentration

greater than 0.12% wt/wt was used.

7 . 5 Viscosity Runs on SRM 1496

Viscosity measurements were made on solutions of the polymer in TCB

containing antioxidant, at 140°C. The viscometry experiments were conducted

with a number 50 Cannon -Ubbelodhe semi-micro viscometer (no. K927) . The

viscometer was thermos tatted in a silicone oil bath controlled at 140. 0°C to

within 0.1°C. The temperature was maintained by a Fisher model 22 proportional

temperature controller which provided a nominal resolution of 0.01°C in

temperature selection, and a stability in temperature control expressed by a

nominal variation limit of 0.01°C from the set point. The bath temperature was

indicated by an ASTM 67C mercury column thermometer with a nominal resolution

of 0.1 °C in temperature indication. The thermometer was calibrated at the ice

point and at 130°C by the NBS Temperature and Pressure Division. The flow

times were measured by a Cronus 3-S battery energized stopwatch with a nominal

resolution of 0.01 seconds.

The kinetic energy correction was determined using standard viscosity

oils S3 and N4 from the Cannon Instrument Co., and was found to be essentially

zero. The kinetic energy correction was also estimated from the viscometer

constant and the nominal geometric dimensions of the viscometer as described by

Cannon, Manning and Bell [10]. The viscometer constant was determined from the

standard oil S3 from Cannon Instrument Co. The kinetic energy correction

estimated by this procedure was also found to be zero within the limit of

resolution of the measured experimental flow times.

The TCB was 1 , 2 , 4- trichlorobenzene from Aldrich Chemical Co. A general

supply of solvent was prepared for all viscometry experiments by adding

25
antioxidant in the concentration 0.0100% (wt./vol.) in order to protect the

polymer from degradation at the temperature of the experiment. The antioxidant

was Monsanto Santonox R (4 , 4 ' - thiobis - (6 - tert butyl meta cresol) . All solvents

and solutions were filtered through 25 mm diameter, 5.0 micrometer pore size

membranes

.

A stock blend of pellets was formed for the characterization viscometry

by taking 4.9 g of pellets from each of the ten sample jars. A j ar containing

the resulting blend of pellets was rolled for 1 hr on a roll mill.

A group of 5 pellets, each group weighing 0.099-0.101 g, was taken from

the resulting blend to form each solution. The desired concentration of each

solution was achieved by adding the required amount of solvent. The

concentrations are for the solutions at 140°C, calculated from the absolute

weights of polymer and solvent at ambient temperature, from the thermal

expansion of TCB, and from a value for the partial specific volume of another

standard reference polyethylene (SRM 1475) in TCB at 130°C. Each solution was

formed by placing the bottle in an oven at approximately 160°C, and then

vigorously swirling the contents a few times during the interval between the

initially observed completed melting of the polymer and the beginning of the

filtration process. The filtration was also conducted inside the oven at

160°C, with the solution in the syringe and the filtrate in the receptacle

shielded against losses of solvent by evaporation. In general, the flow time

measurements were completed on samples from one solution within a time interval,

not exceeding 3 hr after the bottle containing the components had been

initially placed in the oven.

However, extended experiments were conducted on a few solutions to test

for an increase in flow time which might result from possible significant

26
increase in solution concentration due to solvent loss during the filtration

process. In such an experiment with one solution, five samples were collected

in series by filtration through the same filtering assembly. In a different

experiment with another solution, a few extra samples were subjected to

replicate filtration. In each of these experiments, the flow times of the

samples did not indicate any detectable increase in concentration with an

extended series of filtrates through the same filtering assembly, or with

replicate filtration of the same sample through different filtering assemblies.

In these experiments, however, the flow times of the final samples were

completed at the end of a time interval probably considerably greater than 3 hr

following the time at which the bottle containing the components had been

initially placed in the oven.

7 . 6 Measurement Scheme

Solutions were run which alternated with measurements of the solvent both

before and after the solution measurements. The sequence of measurements on

solutions was randomized with regard to concentration, within each set of

solutions. All three vertical tube members of the viscometer were rinsed with

hot TCB containing no antioxidant, after the conclusion of the flow time

determination for each solution and solvent. TCB was propelled from a syringe

through a Mitex membrane and an 18 gauge needle which was provided with a

Teflon tube section on the tip to function as a gasket between the needle tip

and the top end of the capillary tube member of the viscometer. The sample

injection tube and vent tube were rinsed 4 times with about 2 cm3 of TCB

propelled onto the glass surface inside the top end of the tube. The capillary

tube was rinsed twice with about 5 cm3 TCB injected into the top end by

application of strong manual force on the syringe.

27
At the conclusion of the flow time measurements on a solution, the

viscometer was rinsed with hot TCB, and solvent samples were added immediately

for flow time determination. The flow times of antioxidant- free TCB were found

to be indistinguishable from the flow times of solvent which contained the

antioxidant. At the conclusion of the flow time measurements on solvents, the

viscometer was rinsed with hot TCB, and the residual TCB vapor was purged from

the viscometer with a slow stream of filtered dry N2 before commencing flow

time measurements on the subsequent solution samples. At the conclusion of the

last solvent flow time determination of each day, the viscometer was filled to

the top with antioxidant- free TCB in order to conserve the solvophilic state of

the inside of the viscometer until the measurements were resumed.

7 . 7 Results of Viscosity Measurements

A total of 12 solutions and 21 solvent measurements were made at 140°C

before the results were considered precise enough for this SRM. During any

given run on a given day, the measurements were started with a measurement of

solvent followed by alternate measurement of solution and then solvent. The

day always ended on a solvent measurement. Data analysis was done in which the

solvent is treated as a zero concentration solution and all the data including

the solvent were fit to one quadratic polynomial.

Two data sets were used in the final fit for the certified value of

intrinsic viscosity. The resulting flow times are given below. The polynomial

fit gave an intrinsic viscosity [ 77 ] of 209.6 ml/g with a standard deviation of

1.4 ml/g (0.67%). Flow times on 12 independently made up solutions and 21

solvent runs were used in the fit to obtain the average.

28
Solution

xlO 3 CONC t/ml Flowtimef

0.400 121 . 13

b2 0.400 121.20

b3 0.400 121.29

b4 0.800 131.74

B5 0.800 131.67

B 6 1.200 143.16

Cl .400 121 . 34

C2 .400 121 . 33

C3 .400 121.26

C4 .800 131.69

C5 .800 131 . 76

C6 1.200 142.70

f The flow times shown represent averages of at least five flow times on each

of at least two samples from the same solution.

7 . 8 Error Analysis

1 . Solvent Density

The solvent density was obtained by extrapolation from 130°C. The

extrapolation from 130°C to 140°C is from 1.323 g/ml to 1.311 g/ml . We

estimate the error to be no grater than .006 g/ml or 0.5% in the density. This

leads to an error of 0.5% in the limiting viscosity number [77].

2. Partial Specific Volume

Partial specific volume, v, of polyethylene in trichlorobenzene was taken

to be 1.30 cm3 g“ 1

, the same as that for SRM 1475 at 130°C. The effect of the

small amount of branching and the 10°C temperature change for the solvents was

assumed to have little affect. We estimate an error of no more than .13 cm3 /g

(this is 3 times expected by Wagner and Verdier [11]). For an [77] of 209.6 ml

g" 1

, the error in v leads to an error in [77] of .05%. Even if v were in error

by 1.0 ml g" 1

, the expected error in the [77] would be no greater than .5%.

29
3. Solute Weights

Assuming a weighing error of 0.1 mg or 0.0001 g at each concentration, we

estimate an error in the relative viscosity of 0 . 1 % due to an error of 0.1 gm

in the solute weight.

4. Timer Errors

A scaling error in the timer should have no effect upon the resulting

[r?]. Comparison calculations were carried by adding 0.05 second, which would

be a rather large error for the time, to the flow time of solvent and to the

flow time for the solvent and lowest concentration. For the solvent and 0.04%

concentration, the errors in [ 77 ] were .06 and .05% respectively.

5. Kinetic Energy Correction Factor

The computed kinetic energy correction is essentially zero. The

systematic error attributed to this factor was estimated to be 1 . 0 % using the

procedures of Wagner and Verdier [11].

6 . Measurement Temperature

The temperature was held to within 0.1°C. Since the variation of

viscosity with temperature is about 1 % per degree, we obtain a maximum error of

0 . 1 %.

7. Evaporation of Solvent

The solvent TCB at 140°C is relatively close to its boiling point. We

were therefore concerned that the solvent evaporated during high temperature

filtration would cause a concentration change and thus an error in the flow

time measured. The error resulting from this was estimated in two ways.

It was found that the measured flow times for consecutive runs of the

same solution in the viscometer did not drift. Once a solution was put into

the viscometer and thermal equilibrium obtained one could make as many as 6

30
more runs and have the times reproducible to better than 0.1s. At the lowest

concentration, the flow time of solution minus that for the solvent was 10s.

Thus the maximum error in finding no drift within 0.1s was .1/10 = 1%.

Another series of experiments was run to see if evaporation during

solution preparation and/or filtration changed the solution viscosity measured.

It was noticed when a small filter was used (so as to cause a slow filtration)

the intrinsic viscosity increased. For the SRM study we used a much larger

filtration assembly. To see the effect of filtration, the viscosity was run

with a solution which had been filtered once and another which had been

filtered twice. The two solutions had the same time to within expected

experimental error.

8 . Shear Rate Dependence

A significant shear rate dependence was found by Wagner and Dillon [11]

for polymers in the molecular weight range of SRM 1496 and for the shear rate

found for the viscometer used in this set of measurements. We estimated the

maximum shear rate for the viscometer used to be 1761 sec

-1 for TCB at 140°C

with an estimated error of 12%. The maximum shear rate for our viscometer, am ,

is given by [ 12

= 4 Q/OR3

)

where Q

= AV/At = flow rate of solvent

AV = volume of viscometer = 0.30 ml ± 5%

At = time for solvent to flow = 111 seconds ± .1%

R = radius of capillary = .125 mm ± 2%

cjm = 1761 ± 12%

For a Newtonian fluid, the average shear rate in the capillary, aA , is given by

aA = 2/3 am

31
The values of AV and R given above are from ASTM Method D 446.

From the data of Wagner and Dillon an error in the estimate of the shear

rate of 12% will result in an error of 6.7% in the measured intrinsic viscosity

at that maximum shear rate. Wagner and Dillon found that the approximate

dependence of [rj] on shear rate is

[ 77 ] = 50 log10 a for a between 10 and 3000

or [ V ] = U5 loge a

The error in [ 77 ] is

8 [rj] - 115 So/a

which is for a material having an apparent molecular weight higher than we have

estimated for SRM 1496.

For a material having a lower [ 77 ] than that used in their study the

constant in the above equation may be less than 115. Therefore we regard our

estimate to be an upper bound to this contribution to the systematic error.

Thus the estimate of 60/0 is 0.12 from which 8 [rj] = 14 mL/s and 5 [ 77 ]/

[

77 ] =

6.7%. A summary of the various contributions to the total error in determining

the limiting viscosity number of SRM 1496 is given below.

Percent Error in [ 77 ] of SRM 1496

Introduced by Assumed Errors in Measured Quantities

1 . Solvent Density 0.5

2 . Partial Specific Volume 0.5

3. Solute Weights 0.1

4. Time Errors 0.6

5. Kinetic Energy Correction 1.0

6 . Measurement Temperature 0.1

7. Solvent Evaporation 1.0

8 . Shear Rate Correction 6.7

Sum of the absolute errors 10.5

Expected limit including

all sources not specifically

identified

.

12 %
8 . 0 Summary

This final report describes worked done under GRI Contract Number 5084-

260-1013 during the period from October 1, 1986 through September 30, 1987.

Much of the work undertaken was a result of preliminary findings reported in

our previous GRI report [1] where it was observed that the melt flow rate of

samples taken from the various piping and joint materials, in some cases,

differed significantly from that of the starting resin from which they were

manufactured. It was further observed that material from a butt fusion Tjoint exhibited a melt flow rate that was different from that for a socket Tjoint by as much as a factor of two. In the preliminary work only one joint of

each type as examined so that it was not established whether this phenomenon

was general to the entire lot of joints or represented an isolated case. The

present work was undertaken to resolve this question and also to determine if

differences in melt flow rate of this magnitude were sufficient to be reflected

in the molecular weight distribution and mechanical behavior.

The current work has centered on a detailed examination of the two types

of T-joints because they exhibited the greatest apparent difference in melt

flow rate of any of the manufactured materials. Five joints of each type were

chosen at random from the two lots of joints and samples were cut from several

regions within each joint where it was deemed that the processing might produce

differences in material properties. Melt flow rate tests were done in

accordance with ASTM D 1238-82, condition 190/5[2]. The results from more than

fifty tests were that the overall mean of the melt flow rate was 0.900 g/10 min

(Std. Dev. 0.080 g/10 min) for the butt fusion T-joints and 0.464 g/10 min

(Std. Dev. 0.057 g/10 min) for the material from the socket T-joints. By way

of comparison, the mean value of the melt flow rate for the starting resin done

33
under the same conditions was 0.796 g/10 min (Std. Dev. 0.025 g/10 min). Since

the data ranges for both types of joints are outside that for the starting

resin, we conclude that the differences are general to the lots of joint

materials and are a result of the processing.

Having determined that the melt flow rates were significantly different

for the two types of joints, they next were examined by size exclusion

chromatography (SEC) in an attempt to detect possible differences in molecular

weight and molecular weight distribution. For this purpose material was taken

from an area along the side seam opposite the injection part of the socket Tjoint and from an area at one of the injection ports in the butt fusion Tjoint. These two regions were found to exhibit the greatest difference in melt

flow rate of any of the positions in the joints examined. A comparison between

the chromatograms of material from these two locations and that of the starting

resin revealed little or no difference in either the molecular weight or

molecular weight distribution. It appears that any changes which may have

occurred as a result of the processing are outside the limits of resolution of

our SEC instrumentation.

Several aspects of the mechanical behavior were also investigated for

material from the two types of T-joints. The occurrence of chain scissions

and/or cross linking , which can occur during the injection molding process, can

be either detrimental or beneficial in terms of long time behavior. Two

measures of mechanical performance which are sensitive to molecular weight and

molecular weight distribution are the environmental stress-crack resistance

(ESCR) and creep.

ESCR tests were done on samples from both types of T-joints, as well as

the starting resin itself. In the case of the joints, the materials used were

34
from the same areas chosen for the SEC measurements. In all three cases flat

sheets were remolded from the starting materials in order to insure that the

test specimens were unoriented. The tests were conducted using an ESCR test

method developed in our own laboratory [ 2 ] . The results are as follows. Four

specimens from the socket T-joint failed by cracking after a time between 5000

and 9000 hours. Two specimens of the remolded starting resin failed by

cracking after about 1630 hours. Four of six specimens of the material from

the injection port of the butt fusion T-joint failed by cracking at times

between 800 and 1580 hours. Two of the specimens necked and drew after several

days under test. The two specimens that necked were the only two specimens

which we have observed to exhibit that behavior in over 500 tests carried out

on a variety of polyethylenes tested under the identical conditions. By way of

comparison, ten specimens of an ultra high molecular weight polyethylene

(MW=4.5 x 10 6 ), on average, were found to fail by cracking after about 1000

hours

Uniaxial creep experiments were also done on material from the two types

of T-joints. Tensile bars were cut from the same sheets of material from which

the ESCR specimens were cut. For both joint materials, a series of creep

experiment was done in which the applied stress was varied from 20 MPa down to

9 MPa (under static load conditions) . Two features of the creep curves are

relevant to the present investigation. First, at high levels of stress where

the specimen exhibits necking and cold drawing, the necked down region

eventually propogates the full length of the straight section of the specimen.

When this condition is reached the rate of creep decreases significantly. In

the case of the pipe resin the creep curves reach a plateau and become

essentially flat. The maximum stretch ratio (A) was found to be from between 6

35
to 9 depending upon the level of applied stress. At a given stress level, the

maximum A attainable depends upon parameters such as the molecular weight and

molecular weight distribution. Generally the higher the molecular weight the

smaller the maximum will be prior to fracture. In the present set of

experiments it was found that at the highest levels of applied stress the

plateau value of A was consistently slightly higher in the specimens derived

from the butt fusion T-joint than in those from the socket T-joint.

The second feature of interest occurred for the specimens under stresses

of 10 and 9 MPa. At the early times, up to about 10 3 minutes, the creep curves

for the materials from the two types of joints essentially superposed. However

at longer times significant differences in behavior ' appeared between the two

materials. At 10 MPa the material from the butt fusion joint was observed to

neck and cold draw at a time of about 8 x 10 4 minutes and a strain of about

0.60. On the other hand the material from the socket joint, for the same time

under creep, had not exhibited necking and had attained a stain of only 0.30.

This specimen has since reached a creep time of 4 x 10 5 minutes and a strain of

0.40 without neck formation. The two specimens under an applied stress of 9

MPa show what it appears it will be a similar behavior at very long times. At

2 x 10 s minutes they have reached strains of 0.30 and 0.24 respectively and the

difference is becoming greater with time.

Taken together, the three sets of observations from the mechanical

behavior study strongly suggest that the differences observed in the melt flow

rate between the two joint materials are sufficient to alter the mechanical

behavior. The differences in behavior found at long times under the smallest

applied stresses may have implications with regard to the phenomenon of slow

crack growth. One can only speculate that under identical conditions the

36
material from the socket joint will exhibit the greater resistance to slow

crack growth of the two. However, the differences in mechanical behavior

observed in this study between the two joints should in no way be interpreted

as implying that either type of T-joint might not meet current or future

industry requirements for long term performance.

We have also carried out a further characterization of the SEC of the

pigmented resin (SRM 1497) . After further analysis of the calibration

procedures and the high and low molecular weight cutoff points, we have revised

our best estimates of the number average molecular weight (MN ) and weight

average molecular weight (M^, ) . The new values along with their estimated

errors are

M„ = 13,000 ± 3,000

M„ = 140,000 ± 30,000

The present values replace those given in our previous GRI report [1].

Finally, work was completed to certify the limiting viscosity number [rj]

for the unpigmented polymer (SRM 1496) . Flow time measurements were done on 12

independently made up solutions at three concentrations. These results along

with 21 solvent runs were used to obtain a quadratic polynomial fit to obtain

an average [ rj

] of 209.6 ml/g.

37
References

[1] Final Report, Gas Research Institute Research Grant No. 5084-260-

1013, "Reference Standard Polyethylene Resins and Piping

Materials", GRI-87/0040, NBSIR 87-3506 [GRI], March 1987.

[2] 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.

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

[4] Wagner, H.L., J. Physical and Chemical Reference Data, .14, 611 (1985).

[5] Wagner, H.L., J. Physical and Chemical Reference Data, V±, 1101 (1985).

[6] Han, C.C., Polymer, 20, 1083 (1979).

[7] McCrackin, F.L., Polymer, In Press, (1987).

[8] DeGennes , P.G., Scaling Concepts in Polymer Physics . Cornell University

Press (1979) .

[9] Crissman, J.M., Journal of Testing and Evaluation, JTEVA, Vol. 11,

No. 4, July 1983, pp . 273-278.

[10] Cannon, M.R., R.E. Manning, and J.D. Bell, Anal. Chem. 32., 355 (1960).

[11] Wagner, H.L., and J.G. Dillon, Polymer Characterization . Advances in

Chemistry Series, 203 . American Chemical Society, Washington, DC, page

165 (1983).

[12] "Viscosity of Flow Measurements, A Laboratory Handbook of Rheology,"

Wiley Interscience, page 194 (1963).

38
List of Tables

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6

Table 7.

Melt Flow Rate of Parts Cut From Joints.

Materials Used for Calibration of the SEC Columns.

Calculated Values of Mn and Mw for SRM 1475 Both With and Without

the Calibration Data for SRM 1475.

Average Values of Mn and Mw and Overall Error Estimates for SRM

1497.

Contributions to the Overall Error in Determining the Molecular

Weight of SRM 1497.

Density Variations Within the Butt Fusion and Socket T-Joints.

Environmental Stress-Crack Resistance (ESCR) of Material From the

Two Types of T-Joints and the Pigmented Pipe Resin.

39
Table 1

Melt Flow Rate of Parts Cut From Joints—

Flow Rate2 Std Dev

(g/ 10 min)

Butt Joint

overall mean of butt joint 0.900 .080

top injection port (l) 3 0.974 .080

side injection port (4) 0.876 .058

side seam (5) 0.880 .041

end (2,3) 0.887 .075

Socket Joint

overall mean of socket joint 0.464 .057

injection port (6) 0.592 .023

side seam (10) 0.420 .023

top seam (11) 0.445 .021

end (7,8,9) 0.445 .024

For comparison from previous report

Resin .796

Overall range of resin data .758 to .878

1 Measurements were done using ASTM D1238-82, Condition 190/5.0.

2 The average values are for material taken from five different joints.

3 Numbers in parentheses indicate positions in each joint which are identified

in Figure 1

.

40
Table 2

Materials Used for Calibration of the Size Exclusion Chromatography Columns

Peak

Position log hyd vol

Run # Polymer ID MW (in mL) (vol in mL)

1337 PS FI 300* 1 . 34xl0 7 10.70 10.202

1338 PS F2000 2 . 06xl0 7 10.59 10.517

1339 PS SRM 1479 1 .05xl0 6 12.54 8.334

1340 PS F40 422,000 13.30 7.665

1341 PS Pressure Chem 2 . 00xl0 6 11.68 8.81

1343 PS A2500* 2,800 17.77 3.987

1345 PS F20 186,000 14.161 7.085

1345 PS SRM 1478 36,590 15.56 5.872

1353 PE SRM 1484 109,000 13.93 7.285

1352 PE SRM 1483 30,500 14.867 6.344

1351 PE SRM 1482 12,500 15.717 5.684

1382 PS A- 300 402 18 . 657 2.56

1383 PS A- 1000 942 18.45 3.19

1384 PS A- 5000 6,700 17.18 4.63

1333 Oc tadecane 254 19.01 2.81

1379 PE SRM 1475 52,000

* Samples prefixed with an A or an F were obtained from TOYO SODA Manufacturing

Inc .

41
Table 3

Calculated Values of and Mr for SRM 1475

Both With and Without the Calibration Data for SRM 1475

Linear Calibration equation

log (M) = A+BVe

Calculated without using the calibration point for SRM 1475

A = 12 ..15 ± 0 ..01 1 475 == 17,000

B = - 0 .,5132 + 0.008 1 4 7 5

== 64,000

Calculated using the calibration point for SRM 1475

A = 11.77 ± 0.01 1475 = 16,000

B = -0.4915 ± 0.10 Mw1475 = 54,000

Certificate values for SRM 1475

M„ = 18,000

M„ = 52,000

42
Table 4

Average Values of and M.. and Overall Error

Estimates for SRM 1497

13,000 3,000*

Mw 140,000 30,000*

tfr X Mw Error in MW*

x= . 95 650,000 150,000

x= . 9 360,000 80,000

x= . 8 180,000 30,000

x= . 7 110,000 15,000

x= . 6 72,000 3,000

x= . 5 49,000 1,000

x= . 4 34,000 1,000

x=. 3 22,000 1,000

x= . 2 12,500 1,000

x=. 1 6,000 600

x=fraction of mass less than MW

$ The overall error estimates represent the square root of the sum of the

squares of the errors given in Table 5.

43
Table 5

Contributions to the Overall Error in Determining

the Molecular Weight of SRM 1497

error due to

calib w/o

and with

SRM 1475

error due to

calib with

linear or

cubic fit

estimated

error due to

integration

limit change

estimated

error due

to repeatability

of the chromatogram

1600 1300 2000 500

15,000 20,000 20,000 5000

x

(1) Errors in MW( 2)

x= . 95 100,000 50,000 100,000 34,000

x=. 9 30,000 25,000 60,000 17,000

x= . 8 8,000 10,000 30,000 5,000

x=. 7 4,000 2,000 15,000 2,000

x= . 6 3,000 1,000 ’3,000 1,300

x= . 5 3,000 1,000 1,000 1,000

x= . 4 1,500 1,000 1,000 800

x— . 3 1,000 1,000 1,000 60

x= . 2 500 700 1,000 400

x=.l 300 300 600 300

(1) x = fraction of mass less than MW.

(2) The four right hand columns represent the estimated errors in MW

resulting from the four categories of errors listed at the top of

the table.

44
Table 6

Density Variations Within the Butt

Fusion and Socket T-Joints

Type of Joint Density (g/cm3

)

Butt Fusion

Injection Port (4)*

Wall Opposite Injection Port

Fusion Area (2,3)

0.928 ± 0.001

0.937

0.934

Socket

Area Near Injection Port (6)

Wall Opposite Injection Port

Socket Area (8,9)

0.921 ± 0.001

0.931

0.939

Numbered locations are identified in Figure 1.

45
Table 7

Environmental Stress-Crack Resistance

of Material from the Two Types of

T-Joints and Pigmented PE Resin

Material and Specimen Time to Failure (Hours)

Pigmented Resin 1 1630

2 1630

Socket T-Joint 1 4750

2 4800

3 8400

4 8950

Butt Fusion T-Joint 1 Necked after 48 hours

2 800

3 800

4 Necked after 430 hours

5 1050

6 1580

UHMWPE (MW-4.5xl0 6

) 1000

46
Figure Captions

Figure 1

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

Figure 11.

Figure 12.

Figure 13.

Location of samples taken from the two types of joints

for the determination of the melt flow rate.

Universal calibration curve for all PE and PS data except SRM 1475.

Points are experimental data (assuming an intrinsic viscosity as described in text). The solid line is a linear fit.

Calibration curve of log(M) versus elution volume without SRM 1475

data. Points are the experimental data, the solid line represents

a linear fit to the data.

Calibration curve of log(m) versus elution volume including SRM

1475 data. The solid line represents a linear fit to the data.

Comparison of chromatograms of two samples of the pigmented resin.

One was run after being kept at 140°C for 14 hours (dotted line).

Comparison of chromatograms from SEC runs done both with (solid

line) and without (dashed line) Santinox.

Comparison of chromatograms for material from a socket T-joint and

the pigmented pipe resin. Resin - solid line, socket joint - dashed line.

Comparison of chromatograms for material from a butt fusion T-joint

and the pigmented pipe resin. Resin - solid line, butt fusion

joint - dashed line.

Chromatogram for SRM 1475.

Schematic of apparatus used to determine environmental stress -crack

resistance. The specimen is subjected to a constant applied stress

of 5MPa at 75°C.

Uniaxial creep curves for specimen molded from material taken from

a butt fusion (filled symbols) and a socket (open symbols) T-joint.

The X's represent data obtained at a stress of 10 MPa for material

molded directly from the pigmented resin. All data were obtained

at 23° C

Schematic of apparatus used to determine environmental stress -crack

resistance. The specimen is subjected to a constant applied stress

of 5MPa at 75°C.

Uniaxial creep curves for specimens molded from material taken from

a butt fusion (filled symbols) and a socket (open symbols) T-joint.

The x's represent data obtained at a stress of 10 MPa for material

molded directed from the pigmented resin. All data were obtained

at 23 ° C

47

1 INJECTION PORT

(b) SOCKET "T" JOINT

Location of samples taken from the two types of joints

for the determination of the melt flow rate.

por t

Figure 1
aremoA onwnagohgah dog

Figure

2.

Universal

calibration

curve

for

all

PE

and

PS

data

except

SRM

1675.

Points

are

experimental

data

(assuming

an

intrinsic

viscosity

as

described

in

text).

The

solid

line

is

a

linear

fit.
lLHOI&m. HvinoaioK ooi

Figure

3.

Calibration

curve

of

log(H)

versus

elution

volume

without

SRM

1475

data.

Points

are

the

experimental

data,

the

solid

line

represents
r

k

1 T T T

th

r*

|

1

i

)r

r

*

J

i

iL

CD m ^

co w

LHOI3A1 NYin0310JT 001

V3

CO u

<a bO no c

QJ "o x: a 4-> 0 o

C 4-> •H

4-1 0) i-l 1

4-1 —I >-l

iH CO

4-1 4-> <S CO U T3 -O

•i-4 lO

•-h rcc <r O 1-1

<r0) 3

bO

•rH

Cfc.

ELUTION

VOLUME
7 T T

!

|

i-

<

CV2

’ CV2

I

j

-I

i

i

J

J<

f

i J1

\

\

1

CO

CV2 CD CO o CO

CO CV2 rH o o o

d o d o o o

3as moaj ibuSis

Figure

5.

Comparison

of

chromatograms

of

two

samples

of

the

pigmented

resin.

One

was

run

after

being

kept

at

1A0°C

for

1A

hours

(dotted

line).
oas tuo-t; ibu§is

i

Figure

6.

Comparison

of

chromatograms

from

SEC

runs

done

both

with

(solid

line)

and

without

(dashed

line)

Santinox.
Figure

7.

Comparison

of

chromatograms

for

material

from

a

socket

T-joint

and

the

pigmented

pipe

resin.

Resin

-

solid

line,

socket

joint

-

dashed

line.
s

!

I

|

t

I

r- -i

L l . L_ ! L_ i cv? CO CD o 00

CO CV? o o o

d d d o o o

u

C

o

• c H O

•fH C w

O 3

•*-1 <4-1 w

3 4-) 4-1 4J3 X XI

4-1 3 - X 0>C

CD i-l s

IX M

C *i-t co O 0.3

M

i-l i »* X CD 4-> 4-) a c

E "O i-l o c o

CJ CD i—

)

oo

ai

!-i 3X

*tH

Cjh

33S ui OJJ I^uSiS

Elution

Volume
oas uiojj pauSig

Figure

9.

Chromatogram

for

SRM

1475.
z

l—l in H

h~

111 H ¥

1— u

D _

CD in 9

Figure

10.

Infrared

spectra

for

samples

taken

from

the

butt

fusion

and

socket
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04u

3

tio

•rH u*c

o

XLW

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04CL

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04

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WAVENUMBERS
Schematic of apparatus used

resistance. The specimen is

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NBS-I l»A (REV. 2>«0> U.S. OEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

4. TITLE AND SUBTITLE

Reference Standard Polyethylene Resins & Piping Materials

5. author(S) J.M. Crissman, C.M. Guttman, J.R. Maurey, B.M. Fanconi, D.L. VanderHart,

and F.W. Wang

S. PERFORMING ORGANIZATION (If joint or other than N 8S. see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Con tract/ Grant No.

5084-260-1013

I. Type of Report & Period Covered

Final GRI-87/0326

10/1/86 - 9/30/87

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

Gas Research Institute

8600 Bryn Mawr Ave

Chicago, IL 60631

10. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gn i fi cant in formation. If document includes a si gn i fi cant

bi bliography 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. To avoid this difficulty, the 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 characterizations performed on the two

types of T-joints and the starting resin from which they were manufactured. In

preliminary work it was found that the melt flow rate of material taken from the two

types of joints differed from that of the starting resin and differed from each other

by as much as a factor of two. The current work demonstrates that the observed

differences are general to the two lots of joints and do not represent an isolated

case. As a result, additional characterizations have been performed to determine

whether the molecular weight and molecular weight distribution of the joints have

been altered as a result of the processing. Differences in mechanical behavior from

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Branching, Environmental stress-crack resistance; FT-IR; gas pipe; intrinsic viscosity;

melt index; molecular weight distribution, nmr; polyethylene size exclusion

chromatography; uniaxial creep

13. AVAILABILITY

[XU. Unl imited

| | For Official Distribution. Do Not Release to NTIS

Order From Suoerintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

| | Order From National Technical Information Service (NTIS), Springfield. VA. 22161

14. NO. OF

PRINTED PAGES

15. Price

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