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1 Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energys National Nuclear Security Administration under contract DE-AC04-94AL85000. Robert Bernstein Sandia National Laboratories Organic Materials Department Albuquerque, NM rbernst@sandia.gov505-284-3690 179 th Technical Meeting Rubber Division April 18-20, 2011 Akron, Ohio Polymers/Organic Materials Aging Overview

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2 O-rings Shorting Plugs Textiles Nuclear Power Plant Cable Insulation Labeled Polymers Organic Materials Problems; Organic Materials Aging and Degradation

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3 Accelerated Aging Temperature Reaction Coordinate

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4 General Approach/Goals Physical property Chemical Property Macroscopic level Molecular Level Tensile Strength UV-VIS Spectroscopy Infra-red Spectroscopy Molecular Weight Analysis Density Differential Scanning Calorimetry X-Ray Analysis Surface Analysis Additives Nuclear Magnetic Resonance Goals Prediction of physical properties vs. time Prediction of physical properties vs. time Predict remaining lifetime of field materials Predict remaining lifetime of field materials Develop condition monitoring method Develop condition monitoring method GPC PermeationElongation Dimensional changes Sealing Force Compression Set

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5 Deception ! 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

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6 Thermal-oxidative Aging: Nylon 2000 days ~ 5.5 years 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.

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7 k =Ae -Ea/RT Arrhenius equation: Arrhenius Equation Old Chemist expression: increase rate by 10 C will double the rate

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8 Time Warp Back to High School. ..but only briefly.

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9 Equation of a Line y=mx + b what you want slope what you know y-intercept

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10 Function of a Line y=mx + b x y slope =m y intercept =b

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11 k =Ae -E a /RT Empirical equation Arrhenius Equation rate Pre-exponential factor Temperature (Kelvin) Gas constant e Activation Energy

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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)

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13 Function of a Line y=mx + b x y slope =m y intercept =b

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14 Function of a Line 1/T ln(k) slope = -Ea/R y intercept =ln(A) ln(k) =( Ea/R)(1/T) + ln(A)

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15 Plot log(a T ) 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)

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16 EaEaEaEa Reaction coordinate Energy reactants products ---Imagine a marble---

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17 EaEaEaEa Reaction coordinate Energy reactants products

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18 EaEaEaEa Reaction coordinate Energy reactants products Intermediates/Transition states EaEaEaEa

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19 Are Diamonds forever?

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20 Kinetics vs. Thermodynamics (really the same thing) Reaction coordinate Energy Diamond Graphite

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21 EaEaEaEa Reaction coordinate Energy Diamond Graphite Intermediates/Transition states EaEaEaEa

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22 k =Ae -Ea/RT Arrhenius Equation Critical assumption is that E a is CONSTANT Ass-u-me Assume

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23 Time-Temperature Superposition If same mechanism: same shape (log graph) same shape (log graph) should be constant acceleration (multiple) should be constant acceleration (multiple) Plot log(a T ) vs 1/T linear if Arrhenius Does mechanism change as a function of temperature? 1.Pick a reference temperature 2.Multiply the time at each temperature by the constant that gives the best overlap with the reference temperature data 3.Define that multiple as a T (a T = 1 for ref. temp.) 4.Find a T for each temperature k =Ae -Ea/RT ln(k) = ln(A) Ea/RT Empirical equation Arrhenius 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.

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24 Thermal-oxidative Aging: Nylon 2000 days ~ 5.5 years 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.

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25 Thermal-oxidative Aging: Nylon Shifted Data 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.

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26 Thermal-oxidative Aging: Nylon Shift Factor Graph 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.

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27 Thermal Exposure Polymer O2O2O2O2 Oxidized Polymer + Thermal-Oxidation Quantify amount of oxygen consumed Simple in theorySimple in theory Difficult in practiceDifficult in practice Amazingly sensitiveAmazingly sensitive

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28 Schematic of Oxuptake Initial Pressure of O 2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 + Time Polymer Oxidized Polymer Final Pressure of O 2

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29 Oxygen Consumption

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30 Enhanced Extrapolation Good 1/Temperature, K -1 Normalized Measured Property X X X X X X O O O O O O O O Shift Factor, a T High Temp Low Temp X Measured Property O Oxygen Consumption X

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31 Enhanced Extrapolation: Bad 1/Temperature, K -1 Normalized Measured Property X X X X X X O O O O O O O O Shift Factor, a T High Temp Low Temp X X Measured Property O Oxygen Consumption O

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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 the oxygen consumption rate versus the oxygen diffusion rate Therefore we need estimates of: 1.O 2 permeability versus aging temperature 2.O 2 consumption versus aging temperature DLO, Need to Know

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33 Diffusion-Limited Oxidation (DLO) O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 HomogeneousHeterogeneous rxn rate > diffusion rate rxn rate < diffusion rate

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34 Modulus Profiling Measure of Inverse tensile compliance Closely related to tensile modulus Indentation technique ca. 50 m resolution Excellent to examine geneity of aging (heteo- or homo-) (DLO issues) Modulus vs. Shore A

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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

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36 Modulus Profiler

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37 Modulus Profiler Sample

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38 Aging of a nitrile rubber at temperatures ranging from 65C to 125C ranging from 65 C to 125 C Modulus profiles of samples aged at 65C indicate the presence of homogeneous aging 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.

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39 Modulus profiles for samples aged at 95C show that diffusion-limited oxidation (DLO) is becoming important; at 125C, 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.

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40 Nylon: Tensile versus Oxygen Consumption

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41 Thermal-oxidative tensile: Prediction vs. Experimental Arrhenius predictions severely off target suggest change in mechanism/non- Arrhenius behavior Oxygen consumption suggests no change in thermal-oxidative mechanism 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 Observe: 92% at ca. 835 days Arrhenius Predictions

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42 Nylon 6.6 n 1,6 -Hexanediamine Adipic Acid + H2OH2OH2OH2O Nylon Structure

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43 Humidity Aging Schematic Time, O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 O2O2O2O2 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O

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44 Humidity Aging Hardware

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45 Organic Materials Aging and Degradation Specifics -o-rings General path most organic materials This talk details not important (all published)

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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.

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47 O-rings Background Used as environmental seals or other seals O-RING CROSS-SECTIONS UNAGED15 yr in field Most systems filled with inert gas to protect interior components from oxidation & hydrolysis Previously: No technique to measure equilibrium sealing force No technique to rapidly achieve equilibrium compression set No correlation

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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

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49 Compression Stress Relaxation (CSR) Shawbury-Wallace Compression Stress Relaxometer (CSR) MK II (Wallace Test Equipment, Cryodon, England) Commercial Instrument Measure of Force -O-ring sealing force Can Adjust Gap Size to Approximate Actual Compression in System

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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 decay Prediction of force changes as a function of aging

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51 Why we do isothermal measurements 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.

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52 All Jigs at Temperatures -Fluorosilicone 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.

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53 Time-Temperature Superposition If same mechanism: same shape (log graph) same shape (log graph) should be constant acceleration (multiple) should be constant acceleration (multiple) Plot log(a T ) vs 1/T linear if Arrhenius Does mechanism change as a function of temperature? 1.Pick a reference temperature 2.Multiply the time at each temperature by the constant that gives the best overlap with the reference temperature data 3.Define that multiple as a T (a T = 1 for ref. temp.) 4.Find a T for each temperature k =Ae -Ea/RT ln(k) = ln(A) Ea/RT Empirical equation Arrhenius 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.

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54 Time-Temperature Superposition

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55 Shift Factor Plot

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56 Accelerated Aging Temperature Reaction Coordinate

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57 Shift Factor Plot

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58 Shifted Data with RT Prediction w/o 80 C data

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59 Shift Factor Plot

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60 Shifted Data with RT Prediction All data

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61 Shift Factor Plot

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62 Shifted Data with RT Prediction 109 and 80 only

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63 Shift Factor Plot ~50% in ~ 1000 years ~50% in ~ 100 years ~50% in ~ 20 years

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64 O-ring Sealing force arguably most important parameter compression set Easy to measure quick and simple Difficult to measure slow and laborious sealing force Correlation between equilibrium values O-RING CROSS-SECTIONS UNAGED15 yr in field

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65 Force versus Compression Set Data -Fluorosilicone

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66 Field 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 Aging time, years

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67 Other Compression Set Data Different Silicone Different Program Different PI Gillen, K. T. "Silicone seal analysis," Internal Memo, SNL, 2001.

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68 Compression Set Data Analyzed by Gillen Added in 40 year RT data from another source Gillen, K. T. "Silicone seal analysis," Internal Memo, SNL, 2001.

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69 Arrhenius Plot for Compression Set 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.

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70 Force versus Compression Set Data

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71 Force versus Compression Set Data 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*

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72 Butyl Force vs. Compression set; lab and field aged Equilibrium values of compression set plotted versus F/F 0 for laboratory- aged o-rings for three butyl materials plus field results for Butyl-B plotted assuming that F 0 = 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.

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73 Heavily Filled Silicone Conducting o-rings compression set versus force remaining

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74 SIGYY -191 psi=133 N/cm 2 -89 psi= 61 N/cm 2 13 psi= 9 N/cm 2 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

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75 Take home messages 1)Be aware of mechanism changes 2)Understand chemistry/be careful with the details DLO, O 2 vs. H 2 O etc 1)Find something to measure 2)Do things at many temp (as far apart as possible) 3)Do things for very very long time 4)Validate against real world 5)It would be nice to know your performance requirements

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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

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77 Questions