A11101 31T004

NBS

PUBLICATIONS

MBSIR 82-2615

AlllOb 407^41

Mechanical Relaxation of Liner

Materials in Acetic Acid

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Polymer Science and Standards Division

Washington, DC 20234

January 1 983

?ared for QC source Recovery Program

100

.U56

NO. 82-261

1983 e.i

NBSIR 82-2615

MECHANICAL RELAXATION OF LINER

MATERIALS IN ACETIC ACID

NATIONAL BUREAU OF STANDARDS

LIBRARY

APR 1

1

I'XJtClCXa ~Ct (

C

J (

Joseph C. Phillips

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Polymer Science and Standards Division

Washington, DC 20234

January 1 983

QC Prepared for

]_(JQ Resource Recovery Program

. U5b

82-2615

1985

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Table of Contents

1. Introduction

2. Materials

A. Liquids

B. Liner Materials

3. Experimental

A. Stress Relaxation

B. Environmental Stress Cracking (ESC)

C. Recovery

4. Results and Discussion

A. Stress Relaxation

B. Environmental Stress Cracking (ESC)

C. Recovery

5. Conclusion

6. Acknowledgements

MECHANICAL RELAXATION OF LINER MATERIALS IN ACETIC ACID

Joseph C. Phillips

Polymer Science and Standards Division

National Bureau of Standards

Washington, D. C. 20234

, ABSTRACT

This report describes stress relaxation of three liner materials [high

density polyethylene (HDPE) , chlorinated polyethylene (CPE) , and polyvinyl

chloride (PVC) ] in air and acetic acid (HAc) environments. Additional experiments

of environmental stress cracking (ESC) and recovery were also performed.

Experimental data for stress relaxation were obtained at temperatures

of 30 °C, 50 °C and 72 °C. At the latter temperature (72 °C) stress

relaxation experiments were performed on high density polyethylene (HDPE)

as a function of elongation and concentration (Acetic Acid/H^O mixtures).

Environmental stress cracking experiments at 60 °C and 90 °C were also done for

HDPE using acetic acid and Igepal as ESC agents.

The stress relaxation modulus, E(t), from the stress relaxation data was

O O compared for the three liner materials at different temperatures (30 C, 50 C,

and 72°C) and strain levels. The logarithm of E(t) versus the logarithm of

time and the ratio of the modulus in acetic acid to that in air showed a greater

stability in strength for HDPE over the temperature and time ranges used.

Chlorinated polyethylene exhibited the most deviations from linear log-log behavior

with PVC being intermediate between HDPE and CPE at all temperatures and strains

tested. These results seem to suggest that the stress relaxation modulus

measurements coupled with other data from such measurements as ESC and recovery

may be quite useful in helping to assess the mechanical and transport behavior of

a given liner material.
2

INTRODUCTION

Polymers of varied chemical constitution and design have potential use

as barriers for landfills. The essential purpose of these materials is to

prevent or impede the leakage of liquid waste products from entering the

underlying soil and ultimately polluting the groundwater. In order to better

control such a hazard, one has to seek to better characterize both the

transport properties and mechanical behavior of these polymeric materials.

The initial investigation [1] addressed the former problem using low and high

density polyethylene. This report presents the results of a study of the

latter problem using stress relaxation to test the strain performance of three

liner materials (high density polyethylene, HDPE; chlorinated polyethylene,

CPE; polyvinyl chloride, PVC) in acetic acid.

In assessing the mechanical response of a polymer liner either to a

strain and/or a sorbed liquid, the stress relaxation modulus provides information

concerning the enhanced relaxation process due to sorption of any leachates

[2,3]. If the sorption mechanism is Fickian and the diffusion constant does not

depend on time (but concentration only), then transport behavior may be

ascertained from relaxation modulus data [3]. Hence, by comparing modulus data

of different liner materials under similar conditions of temperature, strain,

and leachate, one may establish a basis for discriminating liners from their

strength /time or service behavior.

In this report stress relaxation data has been presented in terms of the relaxation

modulus. Experiments were performed at 30 °C, 50 °C and 72 °C using actual liners made

of high density polyethylene (HDPE), chlorinated polyethylene (CPE), and polyvinyl

chloride (PVC). The stress realxation modulus data were compared in air and acetic acid

at all three temperatures and acetic acid/H

2 0 mixtures at 72 °C. The environmental

stress cracking (ESC) behavior of HDPE and CPE was also determined at 60 C and 90 C in

acetic acid and Igepal . Recovery measurements were also done for HDPE and PVC at differen

elongations and extension times.
MATERIALS*

3

A. Liquids

Reagent glacial acetic acid (stress relaxation and ESC), Igepal [Nonyl phenoxy

poly(ethyleneoxy ethanol)] (ESC), and distilled water (stress relaxation) were the

liquids used. The acetic acid was used without further purification.

B. Liner Materials

The liner materials used in this work are given in Table I. The particular

high density polyethylene used in this work is a copolymer of ethylene and propylene

(also designated as a polyallomer) . Chlorinated polyethylene is a rubbery material (with

variable chlorine content) . Each liner material listed in Table I has about 3% to 5% added

carbon black (fine to coarse grade). Since these materials are classed as proprietary

products, available information concerning exact composition is quite limited. Other

thicknesses than those listed are also available as well as other polymeric materials.

EXPERIMENTAL

A. Stress Relaxation

Experiments were performed in an apparatus consisting principally of a glass jacketed

tube, stretching frame, and sensor. The upper clamp was attached to the upper part of

the stretching frame via a steel plate. A brass disc at the top of the clamp was

positioned in proximity to the mutual induction coil of the sensor and the induced

voltage due to a vertical displacement of the disc was monitored. The lower clamp was

attachable to an aluminum rod which could be vertically moved through a teflon sleeve

that prevented leakage of any liquid in the tube.

The strain e of the sample (^7 cm long and .5 cm wide) was determined by mechanically

moving the aluminum rod and measuring the change in distance of fiducial marks on the

sample (using a cathetometer) , i.e., e = AL/L

q (L is the initial length; L = L q + AL

is the length after stretching). The stress on the sample was determined from a linear

calibration of mass and mV output (<m> = 200 mV; force = f = <m>g), i.e.,

* Certain commercial equipment, instruments, or materials 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 identified is necessarily the best

available for the purpose.
4

Stress = o = (196 mV/A) x 10

6

(1

)

and the stress relaxation modulus is given as

E = a/e (2)

At each strain e, the stress in Eq. (1) was corrected for changes in the

area A, i.e., A = A(e) = W

Q

2. 0(1+aW/W

q

) (1+aji/£

0

) where W

Q

and i are,

respectively, the width and thickness of the sample at e=0.

At a given temperature the experiment was begun by placing the mounted

sample and stretching frame inside the glass tube. After temperature equilibrium

was attained, the sample was stretched at zero time and the mV response was

monitored as a function of time t (in air). At some chosen time t , after the

sample had relaxed in air, the liquid (HAc or HAc/h^O) was poured into the tube

(at temperature of the experiment) completely submerging the stretched sample

(the values of t

Q

ranged from 40 min to 1270 min). The mV changes were once

again followed as a function of time t or t-t . The stress relaxation results

at 30 °C, 50 °C and 72 °C at the various strains e are shown in Figures 1-7 for

the three liner materials.

B. Environmental Stress Cracking (ESC)

The apparatus for ESC was of a new design [4] to reduce scatter in the data and

to control the geometry of the samples. The sample is folded over a cylindrical

lower clamp and the 'free' ends inserted through an upper clamp. The clamps

are attached to a glass tube that may be placed in a constant temperature bath.

By anchoring the bottom clamp in the bath, the load is applied to the upper clamp

by use of a pulley system. The glass tube allows a liquid to be used for ESC

or the experiment may be performed in air. The ESC data for HDPE are presented

in Table II for HAc, air and Igepal.

C. Recovery

The recovery measurements were performed in the same apparatus as described

in section A above for stress relaxation. After the stress realxation

experiment was completed on a given sample, the sample was removed from the
5

apparatus and the strain was measured in air (at room temperature) as a

function of time. The recovery results for HDPE and PVC are shown in

Table III.

RESULTS AND DISCUSSION

A. Stress Relaxation

Stress relaxation, a(t), data for liner materials made of HDPE, CPE and

PVC were obtained in air, acetic acid, and acetic acid/water mixtures.

Experiments using air and HAc were performed at 30 °C, 50 °C and 72 °C and

the HAc/H^O mixtures were done only at 72 °C. These results are presented

in Figs. 1-8. All the data have been plotted as the stress relaxation modulus,

E(t), i.e.,E (t) = a(t)/e where e is the imposed strain. Figure 8 shows

the relaxation modulus of HDPE at 72 °C and e = .31 versus the percentage

HAc in a HAc/H^O solution at t-t

Q equal 100 min. and 1000 min. In Fig. 9

the modulus for HDPE at e = .24 is plotted versus the reciprocal temperature

at t-t

Q equal 100 min and 1000 min (the air result is also shown). In

Fig. 10 the relative modulus (acetic acid/air) is plotted versus t-t

Q

at

50 °C and e = .44 for HDPE, CPE and PVC.

When a sample is uniaxially extended to an elongation e and held

constant, the stress relaxes in a manner dependent on the nature of the

polymer, the strain level, the temperature, and the environment (vacuum,

gas, vapor or liquid). In air at 30 °C, 50 °C and 72 °C, HDPE, PVC and

CPE exhibited a normal relaxation behavior [5] as shown in Figs. 1-3 over

the time and strain range given, i.e.,

log E(t) = log k + a log t (3)

where k is a function of e and a is the slope of the log-log plot. It

can be seen from Figs. 1-3 that the slope a depends on the nature of the liner

material and the temperature. For HDPE the slope shows little if any variation

with temperature while the slope for PVC is slightly more negative and CPE has

an even greater negative slope. Although the results are not shown, at 72 °C
6

for CPE in air the modulus completely relaxes to zero in two minutes. The linear

behavior exhibited by Eq. (3) generally holds for materials over extended

decades of time if the material does not undergo extensive structural changes

or craze formations [5].

As a stretched uncrossl inked polymer undergoes the sorption of a gas,

liquid or vapor, the modulus or stress will relax faster than that of the

dry material [2,3]. The enhanced relaxation may be diffusion-controlled and

accompanied by scission of interchain bonds or by a plasticizing effect. The

former mechanism predominates at an experimental temperature below the glass

transition (T ) while the latter mechanism is controlling at T>>T

g [2], Even

though the two mechanisms always act concurrently and cooperatively, their relative

importance may also depend on the nature of the polymer and the experimental

conditions.

In Figures 4-6, the relaxation modulus of the liner materials in acetic

acid has been plotted versus t-t

Q

. In some cases one could also represent the

data in a log-log fashion, i.e.,

log E(t) = log k + 3 log(t-t

Q

) (4)

where E(t) is the modulus due to the presence of HAc, log k is a constant,

6 is the slope, and t-t is the characteristic time of the sorption process.

At 30 °C (Fig. 4), HDPE show a behavior very similar to that in air, i.e.,

3^a and K is a function of e; at 50 °C 3 for HDPE (Fig. 5) seems to change at low e.

This would suggest some difference in relaxation rate below some critical strain,

but the data are too sparse to make any further comment; at 72 °C, 3 for HDPE

(Fig. 6) is approximately equal to the a value for relaxation in air. The

change of E(t) for CPE in HAc is dramatically different than that in air as

shown by the rapid drop in modulus in Figs. 4 and 5; at 72 °C, the modulus

for CPE was not measurable due to an extremely rapid drop in modulus to zero

immediately after stretching the sample. The only significant changes of the

modulus in HAc for PVC versus that in air occurred at 72 °C for a high strain

(e = .89).
7

The empirical results represented by Eqs. (3) and (4) expresses the fact

that the modulus relaxation rate may be conveniently represented at a given

temperature and strain-level from the linearized data, i.e..

d E(t)/dt = a E( t ) /

(5)

d E(t-t

0

)/d(t-t

Q

)= 3 E(t-t

0

)/t-t

0 (6)

As shown in Figs. 1-3, the slope a in air seems to be independent of time t

over the range shown for all three materials, but the relative differences

in a also suggest a different relaxation rate (CPE>PVC>HDPE) . In HAc the slope 3

for HDPE is approximately equal to that of a at each temperature, but for CPE

at 50 °C and PVC at 72 °C one observes a time dependence of 3. As long as

the data may be represented as a linear plot, one may assume that there exists

a log normal distribution of relaxation times [5,6], otherwise, any time

dependence of a and 3 means deviations from the normal distribution.

In the actual field use of liner materials, the effects of mixtures such

as HAc/H^O on the stress relaxation modulus must also be taken into account in

evaluating these materials [7]. Figure 7 for HDPE at 72 °C shows that the

modulus changes less than a factor of two for e = .24 to .66 and a concentration

of HAc from 0% to 100%. Figures 8 shows the variation of the modulus for HDPE

decreases at a given value of t-t from the 100% H^O value to that of 0% H^O

in a HAc/H

2

0 mixture. These results in Figs. 7 and 8 suggest that the dilution

of HAc with H

2 0 affects the modulus dramatically only at high H

2 0 concentrations

(^80%-l00%). This behavior roughly parallels that of PVAc/H

2 0 [2] in which

the modulus has its greatest variation at high relative humidity vapor pressures

of H

2

0. In many cases, concentration effects of the modulus may be handled

conveniently through the use of a concentration shift factor [2]. Such data

treatment allows for the construction of a master curve that shows over a wide

time-temperature range the different types of viscoelastic behavior [2,6].
8

The data in Fig. 9 suggest that for HDPE at e = .24 the modulus is roughly

linear with the reciprocal temperature for the times indicated. At very high

strains in which the sample may be highly plastically drawn, such a linear

or parallel relationship may not be found; at temperatures much lower or

higher than the range given in Fig. 9 the behavior may also become non-linear [6].

The behavior of E(t-t

Q

) for CPE versus 1/T would be expected to be highly

non-linear, because at 72 °C the relaxation modulus at t-t„ = 100 and 1000 is

o zero in acetic acid. The PVC liner material behaves somewhat intermediate

to HDPE and CPE. In air HDPE and PVC behave similarly to the results in Fig. 9,

but CPE is expected to once again be highly non-linear due to the fact its

modulus goes to zero immediately after stretching at 72 °C.

The data presented in Fig. 10 was chosen to show how the stress relaxation

results may be used as a screening test for discriminating various polymers

for liner use under given conditions. The parameter used for comparison is

the ratio of the modulus in the liquid (e.g., acetic acid) to that in air versus

the time t-t

Q

. As seen from Fig. 10 at 50 °C and e = .44, the HDPE material

maintains its strength over a much longer time interval than the other two

polymers. The CPE material has a very short-term, strength-time behavior

with PVC being intermediate. The closer the ratio is to unity over an extended

time period, the more useful the material is in maintaining its air behavior

versus that in the liquid environment. It may be noted that the PVC data (if

curve is drawn through all points) seems to indicate the possible occurrence

of crystallization. Such behavior is known to occur for certain polymers

exposed to a given vapor or liquid [8,9]. Hence, in addition to modulus

changes due to the plasticization process, secondary effects such as

crystallization are also important in determining the overall long-term

behavior [8].
9

B. Environmental Stress Cracking (ESC)

The ESC data for HDPE are presented in Table II for air, HAc, and Igepal

at 60 °C and 90 °C. At a load of 5.01 x 10

6 N/m2 no stress cracking was

fi 7 observed in air, HAc, or Igepal at 60 °C. A load of 'vlO x 10 N/m produced

a drawing in Igepal but no breaking. By increasing the temperature to 90 °C

at the initial load, the sample elongated and broke within 1 day [HAc was

not used at this temperature due to its corrosive action on the apparatus].

The polymer CPE and PVC at a load of 5.01 x 10^ N/m2 only "drew" at 60 °C

(no breaking occurred) in air, HAc, and Igepal.

The results presented in Table II suggest that the HDPE liner material is

somewhat inert to the ESC action of HAc (including Igepal) over the strain

and temperature range of the stress relaxation experiments. This result

must be taken very cautiously, because it is known that the change in stiffness

of HDPE due to Igepal depends on other factors such as the density, processing

histories (cooling rates), and added plasticizer content [9].

C. Recovery

Some recovery data for HDPE and PVC are presented in Table III. The CPE

material behaves similarly to PVC. Each sample was stretched to an initial

strain e and at a time t stress relaxation was performed in HAc. After a

total time t^ (=t +At; At = elapsed time during stress relaxation in HAc),

the sample was allowed to recover in air for a given period of time by suddenly

reducing the stress to zero.

The degree to which a sample recovers depend on the extension time t^,

the sorbed liquid, and the strain e[10,ll]. The effect of each factor is the

enhancement of the plastic strain, , with a concomitant decrease in the

elastic strain, e , i.e..

( 7 )
10

where the total strain e is constant. When the end constraints of the sample

are removed, the sample immediately recovers to the instantaneous elastic

strain, e e (o), and the instantaneous plastic strain, e p/

(o) slowly decreases

to e (-»), i.e., structural changes due to stretching or the presence of a

px, sorbed liquid increases with t^ and the sample never recovers completely to

the original state, but eventually reaches a permanent set condition, e (»).

pic These structural changes with time are manifested in measurements of diffusivity

and solubility [10]. Over a given time interval, the former transport property

may differ in a sorption and desorption process while the latter property may

show little or no differences [10]. Hence, the information obtained from the

recovery experiment is quite useful in supplying information about the effects

of strain and sorbed liquid on a given sample.

CONCLUSION

This investigation has presented stress relaxation data on HOPE, PVC,

and CPE as a function of temperature and strain in acetic acid and mixtures of

HAc/H^O. The temperature and strain behavior of the liner materials show distinct

differences in changes of the stress relaxation modulus. The environmental stress

cracking measurements of HDPE and CPE showed that at the imposed stress loads

used, acetic acid and Igepal were not ESC agents at 60 °C, but Igepal did stresscrack HDPE at 90 °C. Recovery data for HDPE and PVC presented additional

information as to the strain behavior of these materials when the stress is

reduced to zero.

This investigation has attempted to show how the relaxation modulus may

be used as a distinguishing parameter for different liner materials under

the influence of a given strain or stress. This seems to be conveniently

done by using the relative stress relaxation modulus, i.e., the ratio of the

modulus in liquid to that in air versus time. Further defined studies may

show this parameter to be quite useful in character!

- zing the mechanical

relaxation of potential liner materials. Although this study did not address
11

the question of failure as a function of stress load or biaxial deformation,

these experiments are indeed necessary for a more complete mechanical and

transport appraisal of a given liner material.

ACKNOWLEDGEMENTS

Appreciation is expressed to Dr. Henry E. Haxo, Jr. of Matrecon, Inc.

for supplying the liner materials and Dr. John M. Crissman of NBS for the

use of the environmental stress cracking (ESC) apparatus and the measurement

of some of the ESC data.

REFERENCES

1. Phillips, J. C. , NBSIR Report: Transport of Acetic Acid in Polyethylene , to be published.

2. Fujita, H. and Kishimoto, A., J. Polym. Sci . 28, 547 (1958).

3. Kishimoto, A. and Fujita, H., J. Polym. Sci. 28, 569 (1958).

4. Crissman, J., (NBS), unpublished data.

5. Litt, M. H. and Torp, S., unpublished data.

6. Ferry, J. D. , "Viscoelastic Properties of Polymers", 2nd ed. , John Wiley

and Sons, Inc., New York, 1970.

7. Bondi, A., "Physical Properties of Molecular Crystals, Liquids and Glasses",

John Wiley and Sons, New York, NY, 1968.

8. Kambour, R. P., Karasz, F. E. and Daane, J. H., J. Polym. Sci. 4, Part A-2,

327 (1966).

9. Frayer, P. D. , Long, P. P. and Dreher, W. W. , Polym. Eng. Sci. 1_7, 27 (1977).

10. Phillips, J. C., Polym. Eng. Sci., to be published.

11. Djiauw, L. K. and Gent, A. N., Polym. Preps. 1_4, 62 (1973).
LIST OF TABLES

I. Density and Thickness of Liner Materials.

II. Environmental Stress Cracking of HDPE.

III. Recovery of HDPE and PVC.

LIST OF FIGURES

1. Relaxation Modulus Versus Time (t), HDPE, CPE in air (30 °C).

2. Relaxation Modulus Versus Time (t), HDPE, CPE, PVC in air (50 °C).

3. Relaxation Modulus Versus time (t), HDPE, PVC in air (72 °C).

4. Relaxation Modulus Versus Time (t-t

Q

), HDPE, CPE in HAc (30 °C).

5. Relaxation Modulus Versus Time (t-t

Q

), HDPE, CPE in HAc (50 °C).

6. Relaxation Modulus Versus Time (t-t

Q

), HDPE, PVC in HAc (72 °C).

7. Relaxation Modulus Versus Time (t-t

Q

), HDPEAHAc/H^O) [72 °C].

8. Relaxation Modulus Versus Volume % HAc, e = .31 (72 °C).

9. Relaxation Modulus Versus Reciprocal Temperature (1/T), e = .24.

10. Relative Relaxation Modulus Versus Time (t-t ), e = .44 (50 °C).
13

Table I. DENSITY AND THICKNESS OF LINER MATERIALS (ACTUAL "FIELD" MATERIALS).

Material 3 Thickness, cm density, g/cm3 (25 °C )

HDPE

CPE

PVC

.102

.0762

.0762

.95

1.22

1.15

designations : HDPE = high density polyethylene; CPE = chlorinated polyethylene

PVC = polyvinyl chloride.

Table II. ENVIRONMENTAL STRESS CRACKING (ESC) OF HDPE LINER MATERIAL

(THICKNESS = .102 cm).

Material Temperature

rcy

ESC Agent Time (days) Load (N/m

2

) Resul ts

HDPE 60 Acetic Acid 24 5.01 x 10

6 no effect

HDPE 60 Ai r 24 5.01 x 10® no effect

HDPE 60 Igepal 44 5.01 x 10® no effect

HDPE 90 Igepal 1 5.01 x 10

6 sample

elongates

& breaks

TABLE III. RECOVERY DATA FOR LINER MATERIALS

Material Initial Elonqation 3 Elongation^ at time t Time, t (days)

~ur (%)

HDPE 35 16 3

HDPE 24 13 7

PVC 42 16 3

PVC 89 69 30

a Sample was initially stretched in air at 72 °C and stress relaxation was subsequently performed in acetic acid.

^Sample was removed from acetic acid and clamps; sample recovery was performed

at time t in air at room temperature.
Relaxation

Modulus

[Polyethylene/Air] t(min)
Relaxation

Modulus

[In

Air]

ziuo/seuAQ g-Oi- x 4)3

t

(min)
Relaxation

Modulus

[In

Air] t

(min)
Relaxation

Modulus

[Polyethylene/Acetic

Acid]

t-t0

(min)
E(t-t

0 )x

10

b

Dynes/cm

Relaxation Modulus

[Polyethylene/Acetic Acid]

10 , 000 - Temp. = 50°C

1000 -

CPE ©,£ = .46

O', £ = .96

fa, £ = .028

HDPE <ET,£ = .16 |b , £ = .41

| 100 -

Fig. 5
Relaxation

Modulus

[In

Acetic

Acid]

i

oo<N

hII Q.

E

<D

O

o

o

o

o

-LUO/seuAQ 9-01 x(°H)3

t-tG

(min)
Relaxation

Modulus

[HDPE/(HAc/H

2

0)]

x x

_ _ _ o o o ^5 <5

O)

CT) 22 22 LO o o

o o o o o T— T“ T“ LO T"

CD CO CO LO 1— <T un CO CO CO CM

II II II II II II CO CO co co CO co

fcl <3 *] b ®

oo

CM

hII CL

E

Cl)

1 O

O o

o

OT" o

e ujo/seuAa 9

_ 01- x(°H)3

O

o

o

t

0

(min)
E(t-t

0

)x

10

-6

Dynes/cm

100 r

Relaxation Modulus

[HDPE/(HAc/H20)]

Temp. = 72°C

£~.31

X, t-tQ = 100 min

• , t-t0 = 1000 min

-X

10

0 50

% HAc

100

Fig.S
Relaxation Modulus

[HDPE/HAc]

1/T (°K)" 1

Fig. 9
Relative

Relaxation

Modulus

[Acetic

Acid/Air]

(“HPa/OWa

Fig.

10

NBS-114A (REV. 2-80

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBSIR 32-2615

2. Performing Organ. Report No. 3. Publ ication Date

January 1983

4. TITLE AND SUBTITLE

MECHANICAL RELAXATION OF LINER MATERIALS IN ACETIC ACID

5. AUTHOR(S)

Joseph C. Phillips

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

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

10.

SUPPLEMENTARY NOTES

Document describes a computer program; SF-I8S, FIPS Software Summary, is attached.

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

bibliography or literature survey, mention it here) This report describes stress relaxation of three liner materials [high density

polyethylene (HDPE) , chlorinated polyethylene (CPE), and polyvinyl chloride (PVC)] in

air and acetic acid (HAc) environments. Additional experiments of environmental stress

cracking (ESC) and recovery were also performed.

Experimental data for stress relaxation were obtained at temperatures of 30°C,

50°C and 72°C. At the latter temperature (72°C) stress relaxation experiments were

performed on high density polyethylene (HDPE) as a function of elongation and concentration (Acetic Acid/^O mixtures) . Environmental stress cracking experiments at 60°C

and 90°C were also done for HDPE using acetic acid and Igepal as ESC agents.

The stress relaxation modulus, E(t), from the stress relaxation data was compared

for the three liner materials at different temperatures (30°C, 50°C, and 72°C) and

strain levels. The logarithm of E(t) versus the logarithm of time and the ratio of

the modulus in acetic acid to that in air showed a greater stability in strength for

HDPE over the temperature and time ranges used. Chlorinated polyethylene exhibited

the most deviations from linear log-log behavior with PVC being intermediate between

HDPE and CPE at all temperatures and strains tested. These results seem to suggest

that the stress relaxation modulus measurements coupled with other data from such

measurements as ESC and recovery may be quite useful in helping to assess the mechanical and transport behavior of a given liner material.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s)

Acetic Acid, mechanical relaxation, liner materials.

13.

AVAILABILITY

recovery, stress cracking.

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