Polymers/Organic Materials Aging Overview

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, NMrbernst@sandia.gov

505-284-3690

179th Technical Meeting Rubber DivisionApril 18-20, 2011

Akron, Ohio

Polymers/Organic Materials Aging Overview

O-rings Shorting Plugs

Textiles

Nuclear Power Plant Cable Insulation

CH2 CHCH3

13CH2 CH

CH2 CHCH3

Labeled Polymers

Organic Materials Problems; Organic Materials Aging and Degradation

‘Accelerated Aging’Te

Reaction Coordinate

4General Approach/Goals

Physical property Chemical PropertyMacroscopic level Molecular Level

Tensile StrengthUV-VIS

Spectroscopy

Infra-red Spectroscopy

Density

Differen

tial S

canning C

alorim

X-Ray AnalysisSurfa

ce Analy

Additives

Nuclear Magnetic Resonance

Goals• Prediction of physical properties vs. time

• Predict remaining lifetime of field materials• Develop condition monitoring method

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

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.

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

slope =m

y intercept =b

k =Ae-Ea/RT

Empirical equation

Arrhenius Equation

Pre-exponential factorTemperature (Kelvin)

Gas constant

Activation Energy

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)

y=mx + b

slope =m

y intercept =b

slope = -Ea/R

y intercept =ln(A)ln(k) =–( Ea/R)(1/T) + ln(A)

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)

Reaction coordinate

Energyreactants

products

---Imagine a marble---

Reaction coordinate

Energyreactants

products

Reaction coordinate

Energyreactants

products

Intermediates/Transition states

19Are Diamonds forever?

20Kinetics vs. Thermodynamics (really the same thing)

Reaction coordinate

EnergyDiamond

Graphite

Reaction coordinate

EnergyDiamond

Graphite

Intermediates/Transition states

k =Ae-Ea/RT

Arrhenius Equation

Critical assumption is that Ea is CONSTANT

Ass-u-meAssume

Time-Temperature Superposition

If same mechanism:• same shape (log graph)• should be constant acceleration (multiple)

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

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.

Thermal-oxidative Aging: Nylon

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.

Thermal-oxidative Aging: Nylon Shifted Data

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.

Thermal-oxidative Aging: Nylon Shift Factor Graph

0.0001 0.0001

0.001 0.001

0.01 0.01

0.1 0.1

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

Schematic of Oxuptake

Initial Pressure of O2

O2D + Time

Polymer Oxidized Polymer

Final Pressure of O2

Oxygen Consumption

Enhanced Extrapolation ‘Good’

1/Temperature, K-1

r, a T

High Temp Low Temp

X Measured PropertyO Oxygen Consumption

Enhanced Extrapolation: ‘Bad’

1/Temperature, K-1

r, a T

High Temp Low Temp

X Measured PropertyO Oxygen Consumption

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

Diffusion-Limited Oxidation (DLO)

HomogeneousHeterogeneous

rxn rate > diffusion rate rxn rate < diffusion rate

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

Modulus vs. Shore A

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

Modulus Profiler

Modulus Profiler Sample

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

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.

0 20 40 60 80 100P, %

176 days

127 days

84 days

36 days

0 days

BN M O D 95

0 20 40 60 80 100P, %

18 days

14 days

7 days

4 days

0 days

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.

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

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

Nylon 6.6

1,6 -Hexanediamine

H2NNH2

Adipic Acid

Nylon Structure

Humidity Aging Schematic

Time,D

H2O H2O

O2O2H2O

H2OH2O

Humidity Aging Hardware

Organic Materials Aging and Degradation

Specifics -o-ringsGeneral path –most organic materials

This talk –details not important (all published)

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.

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

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

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

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

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

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.

All Jigs at Temperatures -Fluorosilicone100

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.

If same mechanism:• same shape (log graph)• should be constant acceleration (multiple)

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

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.

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

Shift Factor Plot

0.0001 0.0001

0.001 0.001

0.01 0.01

0.1 0.1

3.53.43.33.23.13.02.92.82.72.62.52.4

1000/T, 1/K

~23 °C

~80 °C

‘Accelerated Aging’Te

Reaction Coordinate

Shift Factor Plot

0.0001 0.0001

0.001 0.001

0.01 0.01

0.1 0.1

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

Shifted Data with RT ‘Prediction’ w/o 80 C data

1 10 100 1000

Predicted Time at 23 °C, Years

Shift Factor Plot

0.0001 0.0001

0.001 0.001

0.01 0.01

0.1 0.1

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

0.1 1 10 100

Shift Factor Plot

0.0001 0.0001

0.001 0.001

0.01 0.01

0.1 0.1

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

Shifted Data with RT ‘Prediction’ 109 and 80 only

0.01 0.1 1 10 100

Shift Factor Plot

0.0001 0.0001

0.001 0.001

0.01 0.01

0.1 0.1

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

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

Force versus Compression Set Data -Fluorosilicone100

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

W 69set2

best pred ic tion

h i-T prediction

Aging time, years

Other Compression Set Data

1 10 100 1000 10000Aging tim e, hrs

S il-set2

40% initia l stra in a t

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

Silsh2

T , oC, aT

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

Arrhenius Plot for Compression Set

2.2 2.4 2.6 2.8 3 .0 3.2 3 .4

1000/T , K -1

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

Force versus Compression Set Data

0.01 0.1 1 10 100

Predicted Time at Room Temperature, Years

Force Compression Set

Force versus Compression Set Data

0.01 0.1 1 10 100

Predicted Time at Room Temperature, Years

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*

Butyl Force vs. Compression set; lab and field aged

0 20 40 60 80 100Com pression set, %

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.

Heavily Filled Silicone 100

100806040200% Equilibrium Compression set -Corrected for Temperature

Conducting o-rings compression set versus force remaining

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

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

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

Questions…

Polymers/Organic Materials Aging Overview

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