Growing More Ductile Epoxies: An Essential Work of Fracture Study Frederick A. Pfaff Stonhard A Division of the StonCor Group, Inc.

Twofold Goal of This Study Feasibility of Using Difunctional Amines as Chain Extenders in Amine-Cured Epoxy Formulations Feasibility of Using Difunctional Amines as Chain Extenders in Amine-Cured Epoxy Formulations Suitability of the Method of Essential Work to Determine Fracture Toughness of Thermoset Epoxy Compositions Suitability of the Method of Essential Work to Determine Fracture Toughness of Thermoset Epoxy Compositions

OUTLINE Amine-Cured Epoxy Formulation Considerations Amine-Cured Epoxy Formulation Considerations Fracture Toughness Test Methods Fracture Toughness Test Methods Experimental Details Experimental Details Tensile Test Results Tensile Test Results Fracture Toughness Results Fracture Toughness Results Solvent Uptake Solvent Uptake Conclusions Conclusions

Formulation Perspectives Amine – Cured Epoxies

Formulation Trends Lower VOC  Lower MWt. Resins Lower VOC  Lower MWt. Resins Liquid Epoxy Liquid Epoxy Amidoamine, Aliphatic & Cycloaliphatic Amine Hardeners Amidoamine, Aliphatic & Cycloaliphatic Amine Hardeners Diluents & Plasticizers Diluents & Plasticizers High Crosslink Density High Crosslink Density Tend to be Relatively Brittle Tend to be Relatively Brittle

Cure & Glass Transition Temperature (T g ) Two Components – Epoxy & Amine Two Components – Epoxy & Amine Cures to Solid Crosslinked Mass Cures to Solid Crosslinked Mass T g of Reacting Mixture Increases as Cure Proceeds T g of Reacting Mixture Increases as Cure Proceeds T g ≤ Cure Temperature + 30 º C T g ≤ Cure Temperature + 30 º C Vitrification Effect Vitrification Effect Properties of Epoxies Used Within Approx. 30 º C of T g Are Not Completely Glass-like Properties of Epoxies Used Within Approx. 30 º C of T g Are Not Completely Glass-like

Managing Formula T g Most Unmodified Amines Cure Liquid Epoxy To a High T g Most Unmodified Amines Cure Liquid Epoxy To a High T g Ultimate T g ºC or Greater Ultimate T g ºC or Greater Will Not Cure to Completion Under Normal Ambient Conditions Will Not Cure to Completion Under Normal Ambient Conditions T g Reduced by Inclusion of Plasticizing Modifiers T g Reduced by Inclusion of Plasticizing Modifiers Term Includes All Non-Fugitive Diluents & Plasticizers Term Includes All Non-Fugitive Diluents & Plasticizers

Plasticizing Modifiers Reactive Reactive Mono-epoxide Diluents Mono-epoxide Diluents Stoichiometric Excess Stoichiometric Excess Non-Reactive Non-Reactive Benzyl Alcohol, Ester & Hydrocarbon Plasticizers Benzyl Alcohol, Ester & Hydrocarbon Plasticizers Lower Tg Lower Tg Reduce Viscosity Reduce Viscosity Important Impact on Cured Properties Important Impact on Cured Properties Proper Choice Critical to Performance!

Side-Effects in Cured State Stoichiometric Excess & Monofunctional Diluents Stoichiometric Excess & Monofunctional Diluents Dangling Chain Ends Dangling Chain Ends Non-Reactive Plasticizers Non-Reactive Plasticizers Not Chemically Bound − Extractable Not Chemically Bound − Extractable Plasticizer Migration Plasticizer Migration Sometimes Count as VOC Sometimes Count as VOC Can Result in Lower Strength & Poorer Chemical Resistance Can Result in Lower Strength & Poorer Chemical Resistance A Fresh Approach Could Be Helpful

Chain Extension Reactants With Functionality = 2 Reactants With Functionality = 2 Amines with Two Active Hydrogens Would be Chain Extenders Amines with Two Active Hydrogens Would be Chain Extenders Mono-Primary Amines Mono-Primary Amines Di-Secondary Amines Di-Secondary Amines “Grow” Higher MWt. Simultaneous With Crosslinking Reaction “Grow” Higher MWt. Simultaneous With Crosslinking Reaction

Goals Partial Replacement for Traditional Plasticizing Modifiers Partial Replacement for Traditional Plasticizing Modifiers Viscosity & T g Reduction Viscosity & T g Reduction Better Cured Property Balance Better Cured Property Balance Reduced Brittleness Reduced Brittleness Minimal Negative Effect on Other Mechanical Properties & Chemical Resistance Minimal Negative Effect on Other Mechanical Properties & Chemical Resistance

Fracture Toughness Testing

Need For a New Method Linear Elastic Fracture Method for Brittle Break Materials Linear Elastic Fracture Method for Brittle Break Materials Example: ASTM D5045 Example: ASTM D5045 ASTM E1820 for Ductile Materials ASTM E1820 for Ductile Materials J-Integral Method J-Integral Method Successive Loadings & Unloadings Successive Loadings & Unloadings Careful Measurement of Crack Length After Each Loading Cycle Careful Measurement of Crack Length After Each Loading Cycle Inconvenient For Most Industrial Coatings Labs

Method of Essential Work First Proposed by Cotterell & Reddel First Proposed by Cotterell & Reddel Basically a Tensile Test on Notched Specimens Basically a Tensile Test on Notched Specimens LigamentNotches “DENT” Configuration

Method of Essential Work, cont’d. W f = W e + W i (1) w f = W f / l*t = w e + βw i *l (2)

EWF Constraints Dimensional Requirements Dimensional Requirements Full Yielding Before Failure Full Yielding Before Failure Self-Similarity of Load Curves at All Ligament Lengths Self-Similarity of Load Curves at All Ligament Lengths Plastic Zone Constraint Plastic Zone Constraint l < 2r p

Experimental Details

Primary Materials IPDABzOH Bis A Epoxy

Epoxy Materials n Bisphenol A Epoxy C13 Epoxy Diluent

Amine Chain Extenders N-Dodecyl Amine N-Amyl Amine N, N’-Dimethyl Ethylene Diamine

Chain Extension Scenarios

Experimental Formulations IDDESCRIPTION TgTgTgTgSG MOD 1 Control MOD 2 30% Excess Epoxy MOD 3 Hi BzOH MOD 4 Mono-Epoxide MOD 5 Hi MWt Liquid Epoxy MOD 6 n-Amyl Amine MOD 7 DM-EDA MOD 8 n-Dodecyl Amine

Parallel Glass Plate Casting Arrangement

Solvent Uptake Testing Weight Change After 6 Hour RT Immersion Weight Change After 6 Hour RT Immersion Weight Change After 24 Hour 90ºC Immersion Weight Change After 24 Hour 90ºC Immersion Weight Change After Dry Bake Weight Change After Dry Bake Final Weight Change Final Weight Change %Δm f = 100 * [(m w – min(m i, m d ) ) / m i ]

Tensile Test Results

Tensile Load Curves

Tensile Yield Stress vs. T g

Essential Work of Fracture Test Results

EWF Median Load Curves

MOD 1 EWF Results

MOD 2 EWF Results

MOD 3 EWF Results

MOD 4 EWF Results

MOD 5 EWF Results

MOD 6 EWF Results

MOD 7 EWF Results

MOD 8 EWF Results

EWF vs. Yield Stress

EWF vs. T g

Mechanical Properties Summary Chain Extension Via Difunctional Amines Provides: Chain Extension Via Difunctional Amines Provides: Reduction of Viscosity & T g with Less Plasticizer Reduction of Viscosity & T g with Less Plasticizer Tensile Strength Comparable to Strength Obtained With Higher MWT. Epoxy Tensile Strength Comparable to Strength Obtained With Higher MWT. Epoxy Superior to Mono-Epoxide Modification Superior to Mono-Epoxide Modification Superior Balance of Tensile Strength & Fracture Toughness Combined with T g Reduction Superior Balance of Tensile Strength & Fracture Toughness Combined with T g Reduction

Solvent Uptake Test Results

Solvent Exposure % Weight Changes

Conclusions Method of Essential Work Appears to be Applicable to Ductile Thermoset Epoxy Compositions Method of Essential Work Appears to be Applicable to Ductile Thermoset Epoxy Compositions Plastic Zone Requirement Not Met Plastic Zone Requirement Not Met More Work Needed More Work Needed Chain Extension Via Difunctional Amine Insertion Provides: Chain Extension Via Difunctional Amine Insertion Provides: Superior Balance of Mechanical Properties Superior Balance of Mechanical Properties Little to No Adverse Effect on Solvent Uptake Little to No Adverse Effect on Solvent Uptake

Conclusions Solvent Uptake Excessive With Large Stoichiometric Excess of Epoxy Solvent Uptake Excessive With Large Stoichiometric Excess of Epoxy Best Overall Properties Obtained From Non- Pendant Chain Extender, DM-EDA Best Overall Properties Obtained From Non- Pendant Chain Extender, DM-EDA