growing more ductile epoxies: an essential work of fracture study

Growing More Growing More Ductile Epoxies:Ductile Epoxies:

An Essential Work of An Essential Work of Fracture StudyFracture Study

Frederick A. PfaffFrederick A. Pfaff

Stonhard Stonhard

A Division of the StonCor A Division of the StonCor Group, Inc.Group, Inc.

Twofold Goal of This Twofold Goal of This StudyStudy

Feasibility of Using Difunctional Feasibility of Using Difunctional Amines as Chain Extenders in Amines as Chain Extenders in Amine-Cured Epoxy FormulationsAmine-Cured Epoxy Formulations

Suitability of the Method of Essential Suitability of the Method of Essential Work to Determine Fracture Work to Determine Fracture Toughness of Thermoset Epoxy Toughness of Thermoset Epoxy CompositionsCompositions

OUTLINEOUTLINE

Amine-Cured Epoxy Formulation Amine-Cured Epoxy Formulation ConsiderationsConsiderations

Fracture Toughness Test MethodsFracture Toughness Test Methods Experimental DetailsExperimental Details Tensile Test ResultsTensile Test Results Fracture Toughness ResultsFracture Toughness Results Solvent UptakeSolvent Uptake ConclusionsConclusions

Formulation Formulation PerspectivesPerspectives

Amine – Cured EpoxiesAmine – Cured Epoxies

Formulation TrendsFormulation Trends

Lower VOC Lower VOC Lower MWt. Resins Lower MWt. Resins Liquid EpoxyLiquid Epoxy Amidoamine, Aliphatic & Cycloaliphatic Amidoamine, Aliphatic & Cycloaliphatic

Amine HardenersAmine Hardeners Diluents & PlasticizersDiluents & Plasticizers

High Crosslink DensityHigh Crosslink Density Tend to be Relatively BrittleTend to be Relatively Brittle

Cure & Glass Transition Cure & Glass Transition Temperature (TTemperature (Tgg))

Two Components – Epoxy & AmineTwo Components – Epoxy & Amine Cures to Solid Crosslinked MassCures to Solid Crosslinked Mass TTgg of Reacting Mixture Increases as of Reacting Mixture Increases as

Cure ProceedsCure Proceeds TTgg ≤ Cure Temperature + 30 ≤ Cure Temperature + 30ººCC

Vitrification EffectVitrification Effect Properties of Epoxies Used Within Properties of Epoxies Used Within

Approx. 30Approx. 30ººC of TC of Tgg Are Not Completely Are Not Completely Glass-likeGlass-like

Managing Formula TManaging Formula Tgg

Most Unmodified Amines Cure Most Unmodified Amines Cure Liquid Epoxy To a High TLiquid Epoxy To a High Tgg Ultimate TUltimate Tgg 80 - 150ºC or Greater 80 - 150ºC or Greater Will Not Cure to Completion Under Will Not Cure to Completion Under

Normal Ambient ConditionsNormal Ambient Conditions TTgg Reduced by Inclusion of Reduced by Inclusion of

Plasticizing ModifiersPlasticizing Modifiers Term Includes All Non-Fugitive Diluents Term Includes All Non-Fugitive Diluents

& Plasticizers& Plasticizers

Plasticizing ModifiersPlasticizing Modifiers ReactiveReactive

Mono-epoxide DiluentsMono-epoxide Diluents Stoichiometric ExcessStoichiometric Excess

Non-ReactiveNon-Reactive Benzyl Alcohol, Ester & Hydrocarbon Benzyl Alcohol, Ester & Hydrocarbon

PlasticizersPlasticizers Lower TgLower Tg Reduce ViscosityReduce Viscosity Important Impact on Cured PropertiesImportant Impact on Cured Properties

Proper Choice Critical to Performance!Proper Choice Critical to Performance!

Side-Effects in Cured Side-Effects in Cured StateState

Stoichiometric Excess & Monofunctional Stoichiometric Excess & Monofunctional DiluentsDiluents Dangling Chain EndsDangling Chain Ends

Non-Reactive PlasticizersNon-Reactive Plasticizers Not Chemically Bound − ExtractableNot Chemically Bound − Extractable Plasticizer MigrationPlasticizer Migration Sometimes Count as VOCSometimes Count as VOC

Can Result in Lower Strength & Poorer Can Result in Lower Strength & Poorer Chemical ResistanceChemical Resistance

A Fresh Approach Could Be HelpfulA Fresh Approach Could Be Helpful

Chain ExtensionChain Extension

Reactants With Functionality = 2 Reactants With Functionality = 2 Amines with Two Active Hydrogens Amines with Two Active Hydrogens

Would be Chain ExtendersWould be Chain Extenders Mono-Primary AminesMono-Primary Amines Di-Secondary AminesDi-Secondary Amines

““Grow” Higher MWt. Simultaneous Grow” Higher MWt. Simultaneous With Crosslinking ReactionWith Crosslinking Reaction

GoalsGoals

Partial Replacement for Traditional Partial Replacement for Traditional Plasticizing ModifiersPlasticizing Modifiers Viscosity & TViscosity & Tgg Reduction Reduction

Better Cured Property BalanceBetter Cured Property Balance Reduced BrittlenessReduced Brittleness Minimal Negative Effect on Other Minimal Negative Effect on Other

Mechanical Properties & Chemical Mechanical Properties & Chemical ResistanceResistance

Fracture Fracture Toughness Toughness

TestingTesting

Need For a New MethodNeed For a New Method

Linear Elastic Fracture Method for Linear Elastic Fracture Method for Brittle Break MaterialsBrittle Break Materials Example: ASTM D5045Example: ASTM D5045

ASTM E1820 for Ductile MaterialsASTM E1820 for Ductile Materials J-Integral MethodJ-Integral Method Successive Loadings & UnloadingsSuccessive Loadings & Unloadings Careful Measurement of Crack Length Careful Measurement of Crack Length

After Each Loading CycleAfter Each Loading Cycle

Inconvenient For Most Industrial Inconvenient For Most Industrial Coatings LabsCoatings Labs

Method of Essential Method of Essential WorkWork

First Proposed by Cotterell & ReddelFirst Proposed by Cotterell & Reddel Basically a Tensile Test on Notched Basically a Tensile Test on Notched

SpecimensSpecimens

Ligament

Notches

“DENT” Configuration

Method of Essential Work, Method of Essential Work, cont’d.cont’d.

Wf = We + Wi (1)

wf = Wf / l*t = we + βwi*l (2)

y = 0.5052x + 10.366

0

5

10

15

20

25

0 5 10 15 20 25

Ligament (mm)

wf

EWF ConstraintsEWF Constraints

Dimensional RequirementsDimensional Requirements Full Yielding Before FailureFull Yielding Before Failure Self-Similarity of Load Curves at All Self-Similarity of Load Curves at All

Ligament LengthsLigament Lengths Plastic Zone ConstraintPlastic Zone Constraint

ll < 2r < 2rpp

Experimental Experimental DetailsDetails

Primary MaterialsPrimary Materials

IPDA BzOH

Bis A Epoxy

Epoxy MaterialsEpoxy Materials

nBisphenol A Epoxy

C13 Epoxy Diluent

Amine Chain ExtendersAmine Chain Extenders

N-Dodecyl Amine

N-Amyl Amine

N, N’-Dimethyl Ethylene Diamine

Chain Extension Chain Extension ScenariosScenarios

Experimental Experimental FormulationsFormulations

IDID DESCRIPTIONDESCRIPTION TTgg SGSG

MOD 1MOD 1 ControlControl 6565 1.1371.137

MOD 2MOD 2 30% Excess Epoxy30% Excess Epoxy 3939 1.1921.192

MOD 3MOD 3 Hi BzOHHi BzOH 2828 1.1161.116

MOD 4MOD 4 Mono-EpoxideMono-Epoxide 4747 1.1351.135

MOD 5MOD 5 Hi MWt Liquid EpoxyHi MWt Liquid Epoxy 6464 1.141.14

MOD 6MOD 6 n-Amyl Aminen-Amyl Amine 5656 1.1331.133

MOD 7MOD 7 DM-EDADM-EDA 4848 1.1951.195

MOD 8MOD 8 n-Dodecyl Aminen-Dodecyl Amine 5353 1.1391.139

Parallel Glass Plate Casting Parallel Glass Plate Casting ArrangementArrangement

Solvent Uptake TestingSolvent Uptake Testing

Weight Change After 6 Hour RT Weight Change After 6 Hour RT ImmersionImmersion

Weight Change After 24 Hour 90ºC Weight Change After 24 Hour 90ºC ImmersionImmersion

Weight Change After Dry BakeWeight Change After Dry Bake Final Weight ChangeFinal Weight Change

%Δm%Δmff = 100 * [(m = 100 * [(mww – min(m – min(mii, m, mdd) ) / m) ) / mii]]

Tensile Test Tensile Test ResultsResults

Tensile Load CurvesTensile Load Curves

% Strain

0 2 4 6 8 10 12 14 16 18

Str

ess

, M

Pa

0

10

20

30

40

50

60

MOD 2MOD 3MOD 4

MOD 7

MOD 1

MOD 5

MOD 6

MOD 8

Tensile Yield Stress vs. TTensile Yield Stress vs. Tgg

Tg, C

20 30 40 50 60 70

Te

ns

ile

Yie

ld S

tre

ss

, M

Pa

20

25

30

35

40

45

50

55

1

2

3

4

5 6

7

8

Essential Work of Essential Work of Fracture Test Fracture Test

ResultsResults

EWF Median Load CurvesEWF Median Load Curves

X Data

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Y D

ata

0

1

2

3

4

5

MOD 1 EWF ResultsMOD 1 EWF Resultsy = 0.3251x + 8.0289

0

2

4

6

8

10

12

14

16

0 5 10 15 20 25

Ligament (mm)

wf

MOD 2 EWF ResultsMOD 2 EWF Results

y = 1.2642x + 8.7536

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25

Ligament (mm)

wf

MOD 3 EWF ResultsMOD 3 EWF Results

y = 0.1145x + 5.8593

0

2

4

6

8

10

12

14

16

18

20

0 5 10 15 20 25

Ligament (mm)

wf

MOD 4 EWF ResultsMOD 4 EWF Resultsy = 0.5945x + 10.708

0

5

10

15

20

25

0 5 10 15 20 25

Ligament (mm)

wf

MOD 5 EWF ResultsMOD 5 EWF Results

y = 0.4353x + 11.025

0

5

10

15

20

25

0 5 10 15 20 25

Ligament (mm)

wf

MOD 6 EWF ResultsMOD 6 EWF Results

y = 0.2766x + 13.049

0

5

10

15

20

25

0 5 10 15 20 25

Ligament (mm)

wf

MOD 7 EWF ResultsMOD 7 EWF Results

y = 0.1162x + 18.236

0

5

10

15

20

25

0 5 10 15 20 25

Ligament (mm)

wf

MOD 8 EWF ResultsMOD 8 EWF Results

y = 0.5052x + 10.366

0

5

10

15

20

25

0 5 10 15 20 25

Ligament (mm)

wf

EWF vs. Yield StressEWF vs. Yield Stress

Yield Stress, MPa

20 25 30 35 40 45 50 55

Es

se

nti

al W

ork

of

Fra

ctu

re, k

J / m

2

4

6

8

10

12

14

16

18

20

1 2

3

4 5

6

7

8

EWF vs. TEWF vs. Tgg

Tg, C

20 30 40 50 60 70

Esse

ntia

l W

ork

of F

ractu

re, kJ / m

2

4

6

8

10

12

14

16

18

20

1 2

3

4 5

6

7

8

Mechanical Properties Mechanical Properties SummarySummary

Chain Extension Via Difunctional Chain Extension Via Difunctional Amines Provides:Amines Provides: Reduction of Viscosity & TReduction of Viscosity & Tgg with Less with Less

PlasticizerPlasticizer Tensile Strength Comparable to Strength Tensile Strength Comparable to Strength

Obtained With Higher MWT. EpoxyObtained With Higher MWT. Epoxy Superior to Mono-Epoxide ModificationSuperior to Mono-Epoxide Modification

Superior Balance of Tensile Strength & Superior Balance of Tensile Strength & Fracture Toughness Combined with TFracture Toughness Combined with Tgg ReductionReduction

Solvent Uptake Solvent Uptake Test ResultsTest Results

Solvent Exposure % Weight Solvent Exposure % Weight ChangesChanges

MOD 1 MOD 2 MOD 3 MOD 4 MOD 5 MOD 6 MOD 7 MOD 8

% W

eig

ht C

ha

ng

e

0

10

20

30

40

ConclusionsConclusions

Method of Essential Work Appears to Method of Essential Work Appears to be Applicable to Ductile Thermoset be Applicable to Ductile Thermoset Epoxy CompositionsEpoxy Compositions Plastic Zone Requirement Not MetPlastic Zone Requirement Not Met More Work NeededMore Work Needed

Chain Extension Via Difunctional Chain Extension Via Difunctional Amine Insertion Provides:Amine Insertion Provides: Superior Balance of Mechanical PropertiesSuperior Balance of Mechanical Properties Little to No Adverse Effect on Solvent Little to No Adverse Effect on Solvent

UptakeUptake

ConclusionsConclusions

Solvent Uptake Excessive With Solvent Uptake Excessive With Large Stoichiometric Excess of Large Stoichiometric Excess of EpoxyEpoxy

Best Overall Properties Obtained Best Overall Properties Obtained From Non-Pendant Chain Extender, From Non-Pendant Chain Extender, DM-EDADM-EDA