environmental stress crack growth and adhesion of elastomeric copolymers to polypropylene

178 Pages·2009·4.56 MB·English

FAILURE PROCESSES IN POLYMERS:
ENVIRONMENTAL STRESS CRACK GROWTH AND ADHESION OF
ELASTOMERIC COPOLYMERS TO POLYPROPYLENE

by
RAVISHANKAR AYYER

Submitted in partial fulfillment of the requirements
for the degree of Doctor of Philosophy

Dissertation Advisers: Prof. Anne Hiltner and Prof. Eric Baer

Department of Macromolecular Science and Engineering
CASE WESTERN RESERVE UNIVERSITY

August, 2009
CASE WESTERN RESERVE UNIVERSITY
SCHOOL OF GRADUATE STUDIES
We hereby approve the thesis/dissertation of
RAVISHANKAR AYYER
_ ________
______Ph.D.____
candidate for the degree *.
Prof. Anne Hiltner
(signed)________ _______
(chair of the committee)
Prof. Eric Baer
________ ____________
Prof. Alex Jamieson___
________
______Prof. James Anderson
_
________________________________________________
________________________________________________

MAY 05, 2009
(date) ____ ___
*We also certify that written approval has been obtained for any
proprietary material contained therein.
  ii
DEDICATION
To my mother, Rajalaxmi Iyer and my wife Vidhya Chakrapni.
  iii
TABLE OF CONTENTS
LIST OF TABLES iv
LIST OF FIGURES vi
ACKNOWLEDGEMENTS
xi
ABSTRACT
xiii
CHAPTER 1
A FATIGUE-TO-CREEP CORRELATION IN AIR FOR APPLICATION TO 1
ENVIRONMENTAL STRESS CRACKING OF POLYETHYLENE

CHAPTER 2
EFFECT OF AN ENVIRONMENTAL STRESS CRACKING AGENT ON THE 37
MECHANISM OF FATIGUE AND CREEP IN POLYETHYLENE

CHAPTER 3
79
EFFECT OF R-RATIO ON ENVIRONMENTAL FAITUGE AND CREEP IN
POLYETHYLENE

APPENDIX
123
ADHESION OF STATISTICAL AND BLOCKY ETHYLENE-OCTENE
ELASTOMERS TO POLYPROPYLENE
BIBLIOGRAPHY 161

  iv
LIST OF TABLES
CHAPTER 1
1.1 Characteristics of Igepal CO surfactants 21
1.2 Results of fatigue and creep tests in different environments at 50 C and 22
frequency 1.0 Hz
1.3 Results of fatigue and creep tests in air at 50 C 23
CHAPTER 2
2.1 Effect of Igepal-630 concentration on creep lifetime and step length 61
2.2 Effect of Igepal-630 concentration on fatigue lifetime and step length at 62
R=0.1, K = 0.65, 1Hz, 50 C
I,mean
2.3 Effect of 10 vol.% Igepal on lifetime and step length in creep and fatigue at 63
R=0.1, K = 0.65, 1Hz, 50 C
I,mean
CHAPTER 3
3.1 Results of Fatigue and Creep Experiments in Igepal-997 at 50 C and 100
frequency 1.0Hz
3.2 Results of Fatigue and Creep Experiments in 10% Igepal-850 at 50 C and 101
frequency 1.0Hz
3.3 Results of Fatigue and Creep Experiments in 10% Igepal-630 at 50 C and 102
frequency 1.0Hz
3.4 Summary of R-ratio effect on mechanism of crack growth in air and Igepals 103
3.5 Membrane and main craze lengths in Air and Igepal 104
3.6 Membrane and main craze lifetimes in Air and Igepal 105
APPENDIX
A.1. Materials 142
A.2. Selected thermal properties 143
A.3 Comparison of the measured delamination toughness of EO855 tie-layers 144
with the delamination toughness calculated from the yield stress
A.4 Comparison of the measured delamination toughness of EO876 tie-layers 145
with the delamination toughness calculated from the yield stress
A.5 The critical delamination stress and draw ratio for OBC tie-layers 146
A.6 Effect of temperature on the delamination toughness of 4 m EO855 tie- 147
  v
layers
A.7 Effect of temperature on the delamination toughness of 4 m EO876 tie- 148
layers
A.8 Effect of temperature on the critical delamination stress of 4 m OBC tie- 149
layers

  vi
LIST OF FIGURES
CHAPTER 1
1.1 Crosshead displacement during fatigue and creep tests of MDPE at 50 ºC and 24
K = 0.65 MPa m1/2: (a) In air; (b) in Igepal 997; and (c) in Igepal 850.
I,mean
Curves are shifted vertically for clarity
1.2 Lifetime at 50 ºC in air and Igepal as a function of R-ratio: (a) Constant 25
K ; and (b) constant K
I,mean I,max
1.3 Effect of R-ratio on the fracture surface of compact tension specimens tested 26
at 50 ºC in air at constant K and at constant K
I,mean I,max
1.4 Light micrographs of the crack tip damage zone showing the periodical 27
formation and fracture of the craze during stepwise fatigue crack propagation
at 50 ºC: (a) 20,000 cycles; (b) 58,000 cycles; (c) 74,000 cycles; and (d)
97,000 cycles. The compact tension specimens were loaded under
K = 0.65 MPa m1/2 and R = 0.1
I,mean
1.5 Dependence of the first step length on the square of K 28
I,mean
1.6 The crosshead displacement curve for creep at K = 0.65 MPa m1/2. The 29
I
optical micrographs show the crack tip damage zone after the creep test was
stopped at the positions indicated
1.7 Transmission light micrographs comparing the crack tip damage zone in 30
fatigue and creep: (a) The fatigue specimen in Figure 4b loaded at
K = 0.65 MPa m1/2 and R = 0.1; and (b) the creep specimen at Position 1
Imean
in Figure 6 loaded at K = 0.65 MPa m1/2
I
1.8 Paris plots of crack growth rate vs. K for fatigue at various R-ratios 31
I
1.9 Fits of fatigue crack growth rate to: (a) K ; and (b) K 32
I,max I,mean
1.10 Fit of all crack growth rate data to K4 1R6 dependence 33
I,max
1.11 The relationship between R-ratio and strain rate at the crack tip at 50 ºC. The 34
curve is the fit to  0.9511R2.0
1.12 Effect of strain rate on measured crack growth rate normalized to the 35
calculated creep contribution to the crack growth rate at 50 ºC. The filled
symbols are tests at R = 0.1 and frequency 0.1 or 0.03 Hz
1.13 SEM images of different magnification showing the entire crack tip craze 36
zone, the crack tip region, and the craze fibrils for fatigue test at frequency
1.0 Hz and frequency 0.1 Hz

  vii
CHAPTER 2
2.1 Crosshead displacement curves for slow crack growth in creep (R = 1.0) at 64
50 ºC for K = 0.65 MPa(m)1/2
I
2.2 Fracture surfaces from the tests in Figure 2.1 65
2.3 SEM images of the first craze zone from the fracture surfaces in air and water 66
in Figure 2.2
2.4 SEM images of the first craze zone from the fracture surfaces in Figure 2.2 67
showing the effect of Igepal-630 concentration
2.5 Development of the damage zone in creep for 0.1% Igepal-630 at 50 ºC for 68
K = 0.65 MPa(m)1/2. The optical micrographs were taken after terminating
I
the test at: (a) 9,000 cycles; (b) 65,000 cycles; (c) 190,000 cycles; and (d)
240,000 cycles
2.6 Crosshead displacement curves for slow crack growth in fatigue at 50 ºC for 69
R = 0.1 and K = 0.65 MPa(m)1/2
I,mean
2.7 Fracture surfaces from the tests in Figure 2.6 70
2.8 SEM images of the first craze zone from the fracture surfaces in Figure 2.7 71
showing the effect of Igepal-630 concentration
2.9 Development of the damage zone in fatigue for 0.001% Igepal-630 at 50 ºC 72
for R = 0.1 and K = 0.65 MPa(m)1/2. The optical micrographs were taken
I,mean
after terminating the test at: (a) 30,000 cycles; and (b) 56,000 cycles
2.10 Development of the damage zone in fatigue for 0.002% Igepal-630 at 50 ºC 73
for R = 0.1 and K = 0.65 MPa(m)1/2. The optical micrographs were taken
I,mean
after terminating the test at: (a) 11,000 cycles; (b) 70,000 cycles and (c)
135,000 cycles
2.11 Development of the damage zone in fatigue for 10% Igepal-630 at 50 ºC for 74
R = 0.1 and K = 0.65 MPa(m)1/2. The optical micrographs were taken
I,mean
after terminating the test at: (a) 18,000 cycles; (b) 32,000 cycles, (c) 242,000
cycles; and (d) 394,000 cycles
2.12 Development of the damage zone in fatigue for 0.002% Igepal-630 at 50 ºC 75
for R = 0.1 and K = 0.65 MPa(m)1/2. The optical micrographs were taken
I,mean
after terminating the test at: (a) 54,000 cycles; (b) 170,000 cycles; (c)
273,000 cycles; and (c) 287,000 cycles
2.13 Crosshead displacement curves for slow crack growth at 50 C: (a) in creep 76
(R = 1.0) for K = 0.65 MPa(m)1/2; and (b) in fatigue at R = 0.1 and
I
K = 0.65 MPa(m)1/2
I,mean
2.14 Development of the damage zone in fatigue for 10% Igepal-850 at 50 ºC for 77
R = 0.1 and K = 0.65 MPa(m)1/2. The optical micrographs were taken
I,mean
after terminating the test at: (a) 33,000 cycles; (b) 115,000 cycles; (c)
182,000 cycles; and (c) 203,000 cycles.
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2.15 Effect of Igepal-630 concentration on the overall life time at 50 ºC for creep 78
at K = 0.65 MPa(m)1/2 and fatigue at R = 0.1 and K = 0.65 MPa(m)1/2
I I,mean

CHAPTER 3
3.1 Crosshead displacement during fatigue and creep tests of MDPE at 50C and 106
K = 0.65 MPa m1/2: (a) In 0.1% Igepal-997; (b) in 10% Igepal 997; and
I,mean
(c) in 10% Igepal-630. Curves are shifted vertically for clarity.
3.2 Master plot – Comparison of R-ratio effect and concentration effect on 107
overall lifetime in Igepals with air/water. The concentration effect of Igepal-
630 at 50 C is re-plotted from reference 17. Creep is at K = 0.65 MPa m1/2
I
and fatigue is at K = 0.65 MPa m1/2.
I,mean
3.3 Overall lifetime at 50 C in air and Igepals as a function of R-ratio for 108
constant K = 0.65 MPa m1/2. Arrow positions indicate ‘Igepal transition
I,mean
time’
3.4 Optical micrographs of fracture surfaces showing effect of R-ratio in 10% 109
Igepal-997 for tests under K = 0.65 MPa m1/2 and K = 1.00 MPa m1/2
I,mean I,max
3.5 Optical micrographs of fracture surfaces showing effect of R-ratio in 10% 110
Igepal-630 for tests under K = 0.65 MPa m1/2 and K = 1.00 MPa m1/2
I,mean I,max
3.6 SEM images of the first craze zone for the fracture surfaces under K = 111
I,mean
0.65 MPa m1/2 showing effect of R-ratio in air
3.7 SEM images of the first craze zone for the fracture surfaces under K = 112
I,mean
0.65 MPa m1/2 showing effect of R-ratio in 10% Igepal-997
3.8 Side views of the first craze damage zones in interrupted fatigue and creep 113
tests in 10% Igepal-997 at 50 C. The optical micrographs were taken for
specimens at indicated arrow positions
3.9 Side views of the first craze damage zones in interrupted fatigue and creep 114
tests in 10% Igepal-850 at 50 C showing stepwise main craze and shear
craze growth modes. The optical micrographs were taken for specimens at
indicated arrow positions
3.10 Comparison of Paris plots of crack growth rate vs. K for fatigue in air at 115
I
various R-ratios with (a) 0.1% Igepal-997, (b) 10% Igepal-997 and (c) 10%
Igepal-630
3.11 Comparison of Paris plots of crack growth rate vs. K for creep in air and 116
I
Igepals
3.12 Light micrographs of damage zones in air at R=0.1 and K = 0.65 MPa 117
I,mean
m1/2 showing (a) craze zone near the end of crack arrest period, 57000 cycles
(b) membrane at the crack tip, 63000 cycles, and (c) membrane fracture,
65000 cycles
  ix
3.13 Light micrographs of damage zones in 0.1 % Igepal-997 at R=0.1 and K 118
I,mean
= 0.65 MPa m1/2 showing (a) craze zone near the end of crack arrest period,
38000 cycles (b) membrane at the crack tip, 42000 cycles, and (c) membrane
fracture, 56000 cycles
3.14 Light micrographs of damage zones in 10 % Igepal-997 at R=0.1 and K 119
I,mean
= 0.65 MPa m1/2 showing (a) craze zone near the end of crack arrest period,
36000 cycles (b) membrane at the crack tip, 38000 cycles, and (c) membrane
fracture, 48000 cycles
3.15 Light micrographs of damage zones in air at R=0.7 and K = 1.00 MPa 120
I,max
m1/2 showing (a) craze zone near the end of crack arrest period, 720000
cycles (b) membrane at the crack tip, 920000 cycles, and (c) membrane
fracture, 955000 cycles
3.16 Light micrographs of damage zones in 10% Igepal-997 at R=0.7 and K = 121
I,max
1.00 MPa m1/2 showing craze fracture through the shear craze
3.17 Light micrographs of damage zones in 10% Igepal-630 at R=0.7 and K = 122
I,max
1.00 MPa m1/2 showing (a) craze zone near the end of crack arrest period,
60000 cycles (b) membrane at the crack tip, 80000 cycles, and (c) membrane
fracture, 98000 cycles

APPENDIX
Scheme 1: Schematic representations of the ethylene-octene copolymer tie-layers 150
A.1 AFM phase images of the microlayer tape cross-sections showing the 152
layered structure of tapes with different EO855 tie-layer thicknesses: (a)
0.2 m; (b) 0.4 m; (c) 0.8 m; (d) 1.3 m; (e) 4 m; (f) 10 m
A.2 Identification of matching peel fracture surfaces using ATR-FTIR: (a) and (b) 153
The matching peel surfaces A and B from a tape with 0.4 m EO855 tie-
layers; and (c) and (d) the matching peel surfaces A and B from a tape with
0.4 m OBC tie-layers. The spectra of the tape constituents are included for
comparison
A.3 Effect of tie-layer thickness on the delamination toughness: (a) The entire 154
range of tie-layer thicknesses studied; and (b) a magnified plot of the results
for thinner tie-layers. The crosshead speed was 10 mm min-1 and the
temperature was 21 °C
A.4 SEM images from an in-situ peel test showing the crack tip damage zone for 155
EO855 tie-layers of different thicknesses: (a) 10 m; (b) 4 m; (c) 0.8 m;
(d) 0.2 m (1000x); (e) 0.8 m; and (f) 0.2 m (1000x)
A.5 SEM images from an in-situ peel test showing the crack tip damage zone for 156
EO876 tie-layers of different thicknesses: (a) 10 m; (b) 4 m; (c) 0.8 m;
  x