1
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration
under contract DE-AC04-94AL85000.
Robert Bernstein
Sandia National LaboratoriesOrganic Materials Department
Albuquerque, [email protected]
505-284-3690
179th Technical Meeting Rubber DivisionApril 18-20, 2011
Akron, Ohio
Polymers/Organic Materials Aging Overview
2
O-rings Shorting Plugs
Textiles
Nuclear Power Plant Cable Insulation
CH2 CHCH3
n
13
CH2 CHCH3
n
13CH2 CH
CH3
n
CH2 CHCH3
n
13
Labeled Polymers
Organic Materials Problems; Organic Materials Aging and Degradation
3
‘Accelerated Aging’Te
mpe
ratu
re
Reaction Coordinate
4General Approach/Goals
Physical property Chemical PropertyMacroscopic level Molecular Level
Tensile StrengthUV-VIS
Spectroscopy
Infra-red Spectroscopy
Mol
ecul
ar W
eigh
t Ana
lysi
s
Density
Differen
tial S
canning C
alorim
etry
X-Ray AnalysisSurfa
ce Analy
sis
Additives
Nuclear Magnetic Resonance
Goals• Prediction of physical properties vs. time
• Predict remaining lifetime of field materials• Develop condition monitoring method
GPC
Permeation Elongation
Dimensional changes
Sealing Force Compression Set
5Deception!
Conclusions derived from initial high temperature, short duration (even out to 1 year) accelerated aging can be misleading.
Chemistry / mechanisms must be understood.
Results must be critically analyzed to identify and understand mechanism changes
6Thermal-oxidative Aging: Nylon
100
90
80
70
60
50
40
30
20
10
0
Ave
rage
% te
nsile
str
engt
h re
mai
ning
1 10 100 1000
Time in days at temperature
138 °C 138 °C 2nd Spool 124 °C 124 °C 2nd Run 124 °C 2nd Spool 109 °C 99 °C 95° C 95 °C 2nd Run 80 °C 64 °C 48 °C 37 °C
2000 days ~ 5.5 yearsBernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Nylon 6.6 accelerating aging studies: II. Long-term thermal-oxidative and hydrolysis results 2010, 95, 1471-1479.
7
k =Ae-Ea/RT
Arrhenius equation:
Arrhenius Equation
Old Chemist expression: increase rate by 10 °C will double the rate
8Time Warp
Back to High School….
…..but only briefly….
9Equation of a Line
y=mx + b
what you want
slopewhat you know
y-intercept
10Function of a Line
y=mx + b
x
y
slope =m
y intercept =b
11
k =Ae-Ea/RT
Empirical equation
Arrhenius Equation
rate
Pre-exponential factorTemperature (Kelvin)
Gas constant
e
Activation Energy
12
k =Ae-Ea/RT ln(k) = ln(A) – Ea/RT
Arrhenius Equation
ln(k) =– Ea/RT + ln(A)
ln(k) =–( Ea/R)(1/T) + ln(A)
13Function of a Line
y=mx + b
x
y
slope =m
y intercept =b
14Function of a Line
1/T
ln(k)
slope = -Ea/R
y intercept =ln(A)ln(k) =–( Ea/R)(1/T) + ln(A)
15
Plot log(aT) vs 1/T linear if Arrhenius
k =Ae-Ea/RT
Arrhenius equation:
Arrhenius Equation
What is Ea?
k = anything
ln(k) =–( Ea/R)(1/T) + ln(A)
16Ea
Reaction coordinate
Energyreactants
products
---Imagine a marble---
17Ea
Reaction coordinate
Energyreactants
products
18Ea
Reaction coordinate
Energyreactants
products
Intermediates/Transition states
Ea
19Are Diamonds forever?
20Kinetics vs. Thermodynamics (really the same thing)
Reaction coordinate
EnergyDiamond
Graphite
21Ea
Reaction coordinate
EnergyDiamond
Graphite
Intermediates/Transition states
Ea
22
k =Ae-Ea/RT
Arrhenius Equation
Critical assumption is that Ea is CONSTANT
Ass-u-meAssume
23
Time-Temperature Superposition
If same mechanism:• same shape (log graph)• should be constant acceleration (multiple)
Plot log(aT) vs 1/T linear if Arrhenius
Does mechanism change as a function of temperature?
1. Pick a reference temperature2. Multiply the time at each temperature by the
constant that gives the best overlap with the reference temperature data
3. Define that multiple as ‘aT’ (aT = 1 for ref. temp.)4. Find aT for each temperature
k =Ae-Ea/RT ln(k) = ln(A) – Ea/RT
Empirical equationArrhenius equation:Gillen, K. T.; Celina, M.; Clough, R. L.; Wise, J. Trends in Polymer Science, Extrapolation of Accelerated Aging Data -Arrhenius or Erroneous? 1997, 5, 250-257.
24
Thermal-oxidative Aging: Nylon
100
90
80
70
60
50
40
30
20
10
0
Ave
rage
% te
nsile
str
engt
h re
mai
ning
1 10 100 1000
Time in days at temperature
138 °C 138 °C 2nd Spool 124 °C 124 °C 2nd Run 124 °C 2nd Spool 109 °C 99 °C 95° C 95 °C 2nd Run 80 °C 64 °C 48 °C 37 °C
2000 days ~ 5.5 yearsBernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Nylon 6.6 accelerating aging studies: II. Long-term thermal-oxidative and hydrolysis results 2010, 95, 1471-1479.
25
Thermal-oxidative Aging: Nylon Shifted Data
100
90
80
70
60
50
40
30
20
10
0
Ave
rage
% te
nsile
str
engt
h re
mai
ning
1 10 100 1000Shifted time to 109 °C, days
Shift Factor 138 °C 8.5 138 °C 2nd Spool 9.0 124 °C 3.25 124 °C 2nd Run 2.75 124 °C 2nd Spool 3.0 109 °C 1.0 99 °C 0.45 95 °C 0.75 95 °C 2nd Run 0.65 80 °C 0.25 64 °C 0.20 48 °C 0.12 37 °C 0.08
Bernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Nylon 6.6 accelerating aging studies: II. Long-term thermal-oxidative and hydrolysis results 2010, 95, 1471-1479.
26
Thermal-oxidative Aging: Nylon Shift Factor Graph
0.0001 0.0001
0.001 0.001
0.01 0.01
0.1 0.1
1 1
10 10
Shift
fact
or, a
T
3.53.43.33.23.13.02.92.82.72.62.52.4
1000/T, 1/K
~23 °C
Bernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Nylon 6.6 accelerating aging studies: II. Long-term thermal-oxidative and hydrolysis results 2010, 95, 1471-1479.
27Thermal Exposure
Polymer O2 Oxidized Polymer+
Thermal-Oxidation
Quantify amount of oxygen consumed• Simple in theory• Difficult in practice• Amazingly sensitive
28
Schematic of Oxuptake
Initial Pressure of O2
O2
O2
O2
O2
O2O2
O2
O2
O2O2
O2
O2
O2D + Time
Polymer Oxidized Polymer
Final Pressure of O2
29
Oxygen Consumption
30
Enhanced Extrapolation ‘Good’
1/Temperature, K-1
Nor
mal
ized
Mea
sure
d Pr
oper
ty
XX
XX
X
X
OO
OO
O
O
O
OSh
ift F
acto
r, a T
High Temp Low Temp
X Measured PropertyO Oxygen Consumption
X
31
Enhanced Extrapolation: ‘Bad’
1/Temperature, K-1
Nor
mal
ized
Mea
sure
d Pr
oper
ty
XX
XX
X
X
OO
OO
O
OO
OSh
ift F
acto
r, a T
High Temp Low Temp
X
X Measured PropertyO Oxygen Consumption
O
32
Diffusion Limited Oxidation (DLO) effects if oxygen dissolved in material used up faster by reaction than it can be replenished by diffusion from surrounding air atmosphere
Race between: the oxygen consumption rate versus the oxygen diffusion rate
Therefore we need estimates of:
1. O2 permeability versus aging temperature2. O2 consumption versus aging temperature
DLO, Need to Know
33
Diffusion-Limited Oxidation (DLO)
O2
O2O2
O2
O2
O2
O2
O2O2
O2
O2
O2
HomogeneousHeterogeneous
rxn rate > diffusion rate rxn rate < diffusion rate
34
Modulus Profiling
Measure of Inverse tensile complianceClosely related to tensile modulus
Indentation technique ca. 50mm resolution
Excellent to examine ‘geneity’ of aging (heteo- or homo-) (DLO issues)
20 30 40 50 60 70 80 90 100Shore A hardness
1
10
100
Mod
ulus
, MPa
Modulus vs. Shore A
35
Schematic of Modulus Profile Experiment
Mass is applied in two stepsProbe tip, sample and mass
Gillen, K. T.; Clough, R. L.; Quintana, C. A. Polym. Degrad. Stab., Modulus profiling of polymers 1987, 17, 31-47
36
Modulus Profiler
37
Modulus Profiler Sample
38
Aging of a nitrile rubber at temperatures ranging from 65°C to 125°C
0 20 40 60 80 100P, %
735 days
497 days
350 days
226 days
0 days
65oC
B N M O D 65
Modulus profiles of samples aged at 65°C indicate the presence of homogeneous aging
Homogeneous Aging
Wise, J.; Gillen, K. T.; Clough, R. L. Polymer Degradation and Stability, An ultrasensitive technique for testing the Arrhenius extrapolation assumption for thermally aged elastomers 1995, 49, 403-418.
39
0 20 40 60 80 100P, %
1
10
100
1000
Mod
ulus
, MP
a
176 days
127 days
84 days
36 days
0 days
BN M O D 95
95oC
0 20 40 60 80 100P, %
1
10
100
1000
D-1
, MP
a
18 days
14 days
7 days
4 days
0 days
125oC
BNM O D 125
Modulus profiles for samples aged at 95°C show that diffusion-limited oxidation (DLO) is becoming important; at 125°C, DLO effects are very significant
Heterogeneous Aging
Wise, J.; Gillen, K. T.; Clough, R. L. Polymer Degradation and Stability, An ultrasensitive technique for testing the Arrhenius extrapolation assumption for thermally aged elastomers 1995, 49, 403-418.
40
Nylon: Tensile versus Oxygen Consumption
10-5 10-5
10-4 10-4
10-3 10-3
10-2 10-2
10-1 10-1
100 100
101 101
Shift
fact
or, a
T
3.43.23.02.82.62.41000/T, 1/K
Tensile Strength Shift Factor Oxygen Consumption Shift Factor
~23°C
41Thermal-oxidative tensile:Prediction vs. Experimental
Arrhenius predictions severely off targetsuggest change in mechanism/non-Arrhenius behavior
Oxygen consumption suggests no change in thermal-oxidative mechanism
Possible explanation involving mechanism change?
64 °C Thermal-oxidative
Initial data Predicted: 92% at ca. 3700 days Observe: 92% at ca. 835 days
Arrhenius Predictions
42
Nylon 6.6
HN
NH
O HN
OOn
1,6 -Hexanediamine
H2NNH2
O
OHO
OH
Adipic Acid
+
H2O
Nylon Structure
43
Humidity Aging Schematic
Time,D
O2
O2
O2
O2
O2
O2
O2
O2
O2
H2O
H2O
H2O
H2O H2O
H2O
O2
O2
O2
O2
O2O2H2O
H2O
H2O
H2OH2O
H2OH2O
H2O
44
Humidity Aging Hardware
45
Organic Materials Aging and Degradation
Specifics -o-ringsGeneral path –most organic materials
This talk –details not important (all published)
46
O-ring Published Documentation
Gillen, K. T.; Celina, M.; Bernstein, R. In Polymer Degradation and Stability Validation of Improved Methods for Predicting Long-Term Elastomeric Seal Lifetimes from Compression Stress-Relaxation and Oxygen Consumption
Techniques, 2003; Vol. 82, pp 25-35.
Gillen, K. T.; Bernstein, R.; Wilson, M. H. Polymer Degradation and Stability, Predicting and Confirming the Lifetime of O-rings 2005, 87, 257-270.
Chavez, S. L.; Domeier, L. A. "Laboratory Component Test Program (LCTP), Stockpile O-Rings," BB1A3964, 2004.
Bernstein, R.; Gillen, K. T. "Fluorosilicone and Silicone O-Ring Aging Study," SAND2007-6781, Sandia National Laboratories, 2007.
Bernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Predicting the Lifetime of Fluorosilicone O-rings 2009, 94, 2107-2133.
47
O-rings Background
Used as environmental seals or other seals
O-RING CROSS-SECTIONS
UNAGED 15 yr in field
Most systems filled with inert gas to protect interior componentsfrom oxidation & hydrolysis
Previously:No technique to measure equilibrium sealing forceNo technique to rapidly achieve equilibrium compression setNo correlation
48
CSR Jigs
Gap of jig can be adjusted to any desired size
O-ring pieces cut to allow air circulation
Measurement of force involves very slow and slight compression until electrical contact is broken between the top and bottom plates
Jigs can be placed in ovens, thus providing isothermal measurements
49
Compression Stress Relaxation (CSR)
Shawbury-Wallace Compression Stress Relaxometer (CSR) MK II
(Wallace Test Equipment, Cryodon, England)
Commercial InstrumentMeasure of Force
-O-ring sealing forceCan Adjust Gap Size to Approximate Actual Compression in System
50
Accelerated aging
1) Physical force decay-Equilibrium values achieved –starting point-Ability to get field returned o-ring force –ending point
2) Chemical force decayPrediction of force changes as a function of aging
51
Why we do isothermal measurements…
10 -4 10 -3 10 -2 10 -1 100 101 102
Tim e after rem oval from 110oC oven, days
0
1
2
3
4
5
6
7
8
9
F/L,
N/c
m
Sealing force per unit length versus time out of a 110 °C oven for two CSR jigs containing Butyl-A o-ring segments that had aged under 25% compression until the force degraded by ~42% (top curve) and ~72% (bottom curve), respectively.
~2 hrs
Gillen, K. T.; Celina, M.; Bernstein, R. In Polymer Degradation and Stability Validation of Improved Methods for Predicting Long-Term Elastomeric Seal Lifetimes from Compression Stress-Relaxation and Oxygen Consumption Techniques, 2003; Vol. 82, pp 25-35.
52
All Jigs at Temperatures -Fluorosilicone100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.1 1 10 100 1000Time, Days
Jig #3 138 °C Jig #4 138 °C Jig #5 138 °C Jig #1 138 °C Jig #5 124 °C Jig #6 124 °C Jig #8 124 °C Jig #14 109 °C Jig #15 109 °C Jig #4 80 °C Jig #7 80 °C
Bernstein, R.; Gillen, K. T. "Fluorosilicone and Silicone O-Ring Aging Study," SAND2007-6781, Sandia National Laboratories, 2007.Bernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Predicting the Lifetime of Fluorosilicone O-rings 2009, 94, 2107-2133.
53
Time-Temperature Superposition
If same mechanism:• same shape (log graph)• should be constant acceleration (multiple)
Plot log(aT) vs 1/T linear if Arrhenius
Does mechanism change as a function of temperature?
1. Pick a reference temperature2. Multiply the time at each temperature by the
constant that gives the best overlap with the reference temperature data
3. Define that multiple as ‘aT’ (aT = 1 for ref. temp.)4. Find aT for each temperature
k =Ae-Ea/RT ln(k) = ln(A) – Ea/RT
Empirical equationArrhenius equation:Gillen, K. T.; Celina, M.; Clough, R. L.; Wise, J. Trends in Polymer Science, Extrapolation of Accelerated Aging Data -Arrhenius or Erroneous? 1997, 5, 250-257.
54
Time-Temperature Superposition
100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.1 1 10 100 1000 Shifted time to 109 °C, Days
Shift Factor S Jig #3 138 °C 7 S Jig #4 138 °C 5 S Jig #5 138 °C 3.5 S Jig #1 138 °C 6 S Jig #5 124 °C 2 S Jig #6 124 °C 3 S Jig #8 124 °C 2.5 S Jig #14 109 °C 1 S Jig #15 109 °C 0.9 S Jig #4 80 °C 0.5 S Jig #7 80 °C 0.4
55
Shift Factor Plot
0.0001 0.0001
0.001 0.001
0.01 0.01
0.1 0.1
1 1
10 10
Shift
fact
or, a
T
3.53.43.33.23.13.02.92.82.72.62.52.4
1000/T, 1/K
~23 °C
~80 °C
56
‘Accelerated Aging’Te
mpe
ratu
re
Reaction Coordinate
57
Shift Factor Plot
0.0001 0.0001
0.001 0.001
0.01 0.01
0.1 0.1
1 1
10 10
Shift
fact
or, a
T
3.53.43.33.23.13.02.92.82.72.62.52.4
1000/T, 1/K
~23 °C
~80 °C 23 °C aT = 0.011
23 °C aT = 0.000926
23 °C aT =0.065
58
Shifted Data with RT ‘Prediction’ w/o 80 C data
100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.1 1 10 100 1000 Shifted time to 109 °C, Days
1 10 100 1000
Predicted Time at 23 °C, Years
59
Shift Factor Plot
0.0001 0.0001
0.001 0.001
0.01 0.01
0.1 0.1
1 1
10 10
Shift
fact
or, a
T
3.53.43.33.23.13.02.92.82.72.62.52.4
1000/T, 1/K
~23 °C
~80 °C 23 °C aT = 0.011
23 °C aT = 0.000926
23 °C aT =0.065
60Shifted Data with RT ‘Prediction’ All data
100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.1 1 10 100 1000 Shifted time to 109 °C, Days
0.1 1 10 100
Predicted Time at 23 °C, Years
61
Shift Factor Plot
0.0001 0.0001
0.001 0.001
0.01 0.01
0.1 0.1
1 1
10 10
Shift
fact
or, a
T
3.53.43.33.23.13.02.92.82.72.62.52.4
1000/T, 1/K
~23 °C
~80 °C 23 °C aT = 0.011
23 °C aT = 0.000926
23 °C aT =0.065
62
Shifted Data with RT ‘Prediction’ 109 and 80 only
100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.1 1 10 100 1000 Shifted time to 109 °C, Days
0.01 0.1 1 10 100
Predicted Time at 23 °C, Years
63
Shift Factor Plot
0.0001 0.0001
0.001 0.001
0.01 0.01
0.1 0.1
1 1
10 10
Shift
fact
or, a
T
3.53.43.33.23.13.02.92.82.72.62.52.4
1000/T, 1/K
~23 °C
~80 °C 23 °C aT = 0.011
23 °C aT = 0.000926
23 °C aT =0.065
~50% in ~ 1000 years
~50% in ~ 100 years
~50% in ~ 20 years
64
O-ringSealing force arguably most important parameter
compression setEasy to measurequick and simple
Difficult to measureslow and laborious
sealing forceCorrelation between equilibrium values
O-RING CROSS-SECTIONS
UNAGED 15 yr in field
65
Force versus Compression Set Data -Fluorosilicone100
90
80
70
60
50
40
30
20
10
0
% F
orce
Rem
aini
ng a
t Tem
pera
ture
100806040200% Equilibrium Compression set -Corrected for Temperature
66Field Data** not quite the whole story, but good enough for this conversation!
Compression set measurements of three fluorosilicone o-rings taken on surveillance units approximately 1 day after removal from the unit. The solid curve and the dashed curve assume a linear relationship between set and force decay.
Bernstein, R.; Gillen, K. T. Polymer Degradation and Stability, Predicting the Lifetime of Fluorosilicone O-rings 2009, 94, 2107-2133
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28Aging tim e, years
0
10
20
30
40
50
60
70
80
90
100
Com
pres
sion
set
(~1
day)
, %
W 69set2
J1
J2
J8
best pred ic tion
h i-T prediction
Aging time, years
67
Other Compression Set Data
1 10 100 1000 10000Aging tim e, hrs
0
20
40
60
80
100
10,0
00-h
our C
ompr
essi
on S
et, %
S il-set2
40% initia l stra in a t
25C
66C
100C
121C
149C
XE-5601 S ILIC O N E (E . A . Salazar data)
Different SiliconeDifferent ProgramDifferent PI
Gillen, K. T. "Silicone seal analysis," Internal Memo, SNL, 2001.
68Compression Set
10 -3 10 -2 10 -1 100 101 102
Aging tim e, years at 25C
0
20
40
60
80
100
10,0
00-h
our C
ompr
essi
on S
et, %
Silsh2
T , oC, aT
25 1
66 3.1
100 21
121 55
149 320
Filled circ les show40 yr B ritish data for-"tem perate conditions" Data Analyzed by Gillen
Added in 40 year RT data from another source
Gillen, K. T. "Silicone seal analysis," Internal Memo, SNL, 2001.
69
Arrhenius Plot for Compression Set
2.2 2.4 2.6 2.8 3 .0 3.2 3 .4
1000/T , K -1
100
101
102
103
Shift
fact
or a
T
Sil-A rr2
10,000 hour recovery data
Arrhenius plot of the shift factors for silicone compression set which leads to an aging room temperature prediction for compression set
Gillen, K. T. "Silicone seal analysis," Internal Memo, SNL, 2001.
70
Force versus Compression Set Data
100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.01 0.1 1 10 100
Predicted Time at Room Temperature, Years
100
80
60
40
20
0
Com
pres
sion
set
, %
Force Compression Set
71
Force versus Compression Set Data
100
90
80
70
60
50
40
30
20
10
0
% F
/Fo
0.01 0.1 1 10 100
Predicted Time at Room Temperature, Years
100
80
60
40
20
0
Com
pres
sion
set
, %
Force Compression Set
Correlation between current Silicone Force data and Compression set data obtained from three different sources (and different sizes!)
Fluorosilicone versus Silicone!!
Displays confidence in generalized predictions about silicone o-rings state of health (CS easy to measure) under oxidative environments*
72
Butyl Force vs. Compression set; lab and field aged
0 20 40 60 80 100Com pression set, %
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
F/F 0
0
1
2
3
4
5
6
7
8
9
10
F, N
/cm
lab-aged Buty l-A
lab-aged Buty l-B
lab-aged Buty l-C
fie ld-aged Butyl-B
Equilibrium values of compression set plotted versus F/F0 for laboratory-aged o-rings for three butyl materials plus field results for Butyl-B plotted assuming that F0 = 10 N/cm.
Gillen, K. T.; Bernstein, R.; Wilson, M. H. Polymer Degradation and Stability, Predicting and Confirming the Lifetime of O-Rings 2005, 87, 257-270.
73
Heavily Filled Silicone 100
90
80
70
60
50
40
30
20
10
0
% F
orce
Rem
aini
ng a
t Tem
pera
ture
100806040200% Equilibrium Compression set -Corrected for Temperature
Conducting o-rings compression set versus force remaining
74
SIGYY-191 psi=133 N/cm2
-89 psi= 61 N/cm2
13 psi= 9 N/cm2
Time = 0 Time = .5sec Time =.8sec Time = 1sec
Time = 30 years Time = 56 year Time 90 years
Slide Courtesy of David Lo
Progression of Stress Relaxation due to Chemical Aging
75
Take home messages…
1) Be aware of mechanism changes2) Understand chemistry/be careful with the details
–DLO, O2 vs. H2O etc3) Find something to measure4) Do things at many temp (as far apart as possible)5) Do things for very very long time6) Validate against real world
7) It would be nice to know your performance requirements
76
Lots of help…
Dora Derzon, Brad Hance, Don Bradley, Roger Assink, James Hochrein, Steven Thornberg, David Lo, Kathy Alam, Laura Martin,
John Schroeder, Patti Sawyer, Mark Stavig, and Ken Gillen
77
Questions…