Chapter Outline: Failure Ductile vs. brittle fracture Impact fracture ...
Growing More Ductile Epoxies: An Essential Work of Fracture Study
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Transcript of 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
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12
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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