Self-Healing Polymers:Applicable to Polyurethanes?

ENMA 490 Capstone Design Course

Melissa ConsidineErin DreyerPaul FreesePaul Ledwith

Joanna Meador

• Motivation• Materials Selection• Fabrication• Characterization• Future Work• Conclusions• Acknowledgements

Contents

• Problem: Microcrack formation • Previous self-healing research mainly at

University of Illinois at Urbana-Champaign• Our goals

– Extend lifetime of components that are inaccessible for routine maintenance

– Use different polymer matrix than UIUC to determine if self-healing is a general phenomenon or matrix material specific.

Main Goal: Demonstrate that the self healing mechanism can be extended to other polymer classes

Motivation

Crack initiation

site

Materials Selection

• Polyurethane– Desirable properties– Two-part casting system, condensation reaction

• Di- or polysisocyanates (Part A)• Polyol (Part B)

– Classified according to polyol used• Polybutadiene-based

– Best electrical properties– Expensive, not commonly sold

in small quantities• Polyether-, polyester-based

– Inexpensive, commercially available

– Two Different PU Kits• Low viscosity, quick cure PU• Very hard, clay-filled PU

Choice of Materials: Matrix

Source: http://www.tapplastics.com/shop/product.php?pid=74&

Choice of Materials: Microcapsule Shell

• Encapsulation Shell: Urea Formaldehyde• Commonly used encapsulation material• Previous research provides fabrication “recipe”• Minimizes variables in comparing self-healing phenomenon

Choice of Materials: Monomer

• Core / Catalyst: – Dicyclopentadiene (DCPD) / Grubb’s Catalyst

• Low viscosity – can flow into cracks• Commercially available, inexpensive petroleum

byproduct [3]• Rapid polymerization via living ROMP reaction

Fabrication

Matrix Mold Fabrication• Two separate molds used

– One to produce large surface area mold for dog bone shapes to be cut from for tensile testing

– One to produce shapes appropriate for Izod testing• Molds fabricated from cut sheets of acrylic bound by binder clips

PU Matrix Fabrication

• Mix equal parts of A and B• Stir vigorously• Pour mixture into desired

mold• Allow time for

polymerization and initial casting

• Demold after about 15 minutes

• Allow 36 hours for complete curing Figure of PU mixture in mold during

polymerization

Microcapsule Fabrication

• Interfacial in-situ polymerization: – Form oil in water emulsion

(DCPD in water w/ additives)– Formaldehyde and urea

polymerize around DCPD spheres

• Problems Encountered:– DCPD solid at RT – Hot plate heating rate– Stirring – Separation

Composite Fabrication

• Disperse microcapsules in part A, mix in part B and pour into mold

• 5-wt% microcapsules:One specimen:– 0.71g microcapsules– 6 mL Part A– 6 mL Part B

• Microcapsules embedded in matrix (no catalyst)• Tested one with silane wash and one without

Characterization

Characterization –Optical Microscopy

• Used Olympus BLX polarizing microscope, connected to a CCD camera and video system with magnification 100X, 200X, and 500X

• Characterized:– Microcapsules subjected to

various levels of filtration – Silane washed

microcapsules embedded in polyurethane

First Filtration

100μm

Second Filtration

50μm

Maximum Filtration

20μm

Characterization – Environmental Scanning Electron Microscopy

• Able to characterize microcapsules from first filtration, microcapsules from multiple filtrations, and silane washed microcapsules embedded in polyurethane

ESEM – First Filtration

ESEM – Maximally Filtrated

Microcapsule Shell Wall

Brown’s Group at UIUC

Our results

Brown [1]2 um

Tensile Testing• Tested only virgin, as-cast polyurethane specimens (5 specimens)• Data output from computer software not working• Tensile properties determined by software from the load versus

elongation curves

Tensile Test Results- Virgin Polyurethane

Results Units Average Values Std DevWidth in. 0.125 0Thickness in. 0.16 0Peak Load lb 63 4Peak Stress psi 3154 181%Strn @ Pk Ld % 4 11Break Load lb 63 4Break Stress psi 3154 181%Strn @ Break % 4 11Energy @ Break in-lb 3 0.1Yield Load lb 63.1 4Yield Stress psi 3153.8 181%Strain @ Yield % 4 11Energy @ Yield in-lb 3 0.1Modulus psi 97727 6185

•Tensile Strength (avg.) = 3154 psi (22 MPa)

- Mfr reported vaule = 5000 psi (34 MPa)

•Modulus (avg.) = 98,000 psi (676 MPa)

Impact Testing

• Used Izod Impact Tester at Adell Plastics• Tested five PU specimens and one specimen

with microcapsules embedded• Porosity/molding defects

evident in test specimens (especially in specimens with microcapsules embedded)

ASTM D256 “Standard Tensile Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics”

Units Virgin PU average values PU with microcapsulesThickness in. 0.44969 0.46275

Izod Value 1 0.2896 0.149Resultant Izod Average ft-lbs/in. 0.562 0.24

Future Work• Fabricate complete system

– Alter amounts of catalyst and monomer– Alter microcapsule to matrix amount ratio– Use different monomer

• Alter surface chemistry– Additives to increase wetting– Determine effects of silane wash

• Failure analysis– Izod testing of complete system – prestressed and unstressed– Fatigue testing

• Analyze results from FTIR

Conclusions• Utilized experimental techniques in order to better

understand a physical phenomenon that presently does not have theoretical underpinning

• Employed design methodology– Took into account material properties and potential composite

system interactions• Utilized knowledge from chemistry to microencapsulate a

hydrophobic monomer for the purpose of self-healing• Successfully fabricated mechanical test specimens to

specific ASTM standards• Employed microscopy techniques to probe the structure

of our samples at different scales.• Extended the concept of self-healing to a matrix material

subject to applications in which maintenance is not an option

Acknowledgments• For faculty consultations

– Dr. Al-Sheikhly– Dr. Briber– Dr. Kofinas

• For the use of labs and laboratory materials– Dr. Al-Sheikhly– Dr. Kofinas– Dr. Martinez-Miranda– Bani Capriano and Dr. Raghavan– Dr. Lloyd

• For assistance in labs– Jung Chul An– Von Wald Cresce– Alia Weaver

• For assistance with ESEM– Tim Zhang

• For the use of video equipment– Exponent, Inc.

References1. Brown, et al. “In situ poly(urea-formaldehyde)

microencapsulation of dicyclopentadiene.”Journal of Microencapsulation. 20.6: 719-730 (2003).

2. White, et al. “Autonomic healing of polymer composites.” Nature. 409, 794-797 (2001).

3. Humble, R.W., “Dicylclopentadiene: A New Resin System for Making Composite TankStructures,” 36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, 16-19 July 2000, Huntsville, Alabama, AIAA-2000-3676

Week by Week Project Schedule

8 9 10 11 12 13 14 15 16

Activity

Research- Materials UsedResearch- Crack PropagationResearch- OptimizationFabrication- Research

Fabrication- In LabPrelim Testing of Host

Testing/CharacterizationCalculations

Visual- SimulationPresentation/Paper

BudgetMaterials Category Supplier Item Cost Shipping Total Cost MATRIX

TAP Plastics PU and supplies 114.5 114.5 ship?Polytek PU 65 65 ship?Physics store1 acrylic sheets 25.76 0 25.76Physics store2 acrylic sheets 30.6 0 30.6Machine shop 1 Sheet Mold for dogbones 50 0 50 approxMachine shop 2 Izod mold 80 0 80 approxPhysics store3 Screws (still need receipt) 4.99 0 4.99Physics store 4 zip disk and CD-R 11.83 0 11.83

MICROCAPSULES Chem store chemicals and supplies 123.02 0 123.02Fisher Resorcinol, 100g 26 26 approx; ship?Sigma EDA 26.7 2.61 29.31Sigma TDI 25.2 7.46 32.66Sigma Silane 75.9 7.43 83.33Fisher Scandium Triflate 48.6 48.6 ship?Fisher Caprolactone 13.14 13.14 ship?Fisher 1-ocatanol 8.55 8.55 ship?Fisher PVA 18 18 ship?Chem store petri dishes and beakers 11.08 0 11.08Chem store books, towels 37.06 0 37.06Chem store slides 13.22 0 13.22

Composite Chem store bottles, weighing paper 8.22 0 8.22

Characterization Equip ESEM 2 hours?FTIR 1 hr?IzodTensile

834.87

Fabrication

Izod Mold Drawing

Tensile Specimen Mold

Interfacial Polymerization

From p. 270, Controlled Particle, Droplet, and Bubble Formation

Summary of Procedure as Adapted from UIUC Group

1.1. Add 50 ml of 2.5 wt% EMA copolymer solution to 200 ml DI water Add 50 ml of 2.5 wt% EMA copolymer solution to 200 ml DI water in 1000 ml beaker @ RT while agitating.in 1000 ml beaker @ RT while agitating.

2.2. Dissolve 5.00 g urea, 0.50 g ammonium chloride and 0.50 g Dissolve 5.00 g urea, 0.50 g ammonium chloride and 0.50 g resorcinol in the EMA solution.resorcinol in the EMA solution.

3.3. Raise pH to 3.5 by dropRaise pH to 3.5 by drop--wise addition of 10% NaOH solutionwise addition of 10% NaOH solution4.4. Add 1Add 1--2 drops of 12 drops of 1--octanol to eliminate surface bubblesoctanol to eliminate surface bubbles5.5. Add slow stream of 60 ml DCPD to form emulsion Add slow stream of 60 ml DCPD to form emulsion 6.6. Stabilize for 10 minutesStabilize for 10 minutes7.7. Add 12.67 g (11.7mL) of 37 wt% formaldehyde solution to beaker.Add 12.67 g (11.7mL) of 37 wt% formaldehyde solution to beaker.8.8. Cover and heat emulsion to 55 CCover and heat emulsion to 55 C ((target T). Agitate for 4 h while target T). Agitate for 4 h while

maintaining temperature. Switch off mixer and hotplate, and coolmaintaining temperature. Switch off mixer and hotplate, and coolto ambient temperature.to ambient temperature.

9.9. After cooling, wash, filter, and separate microcapsules.After cooling, wash, filter, and separate microcapsules.

Tensile Test Results- Virgin Polyurethane

Results Units Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average Values Std DevWidth in. 0.125 0.125 0.125 0.125 0.125 0.125 0Thickness in. 0.160 0.160 0.160 0.160 0.160 0.160 0Peak Load lb 59.7 60.4 64.6 67.7 59.6 62.4 4Peak Stress psi 2987 3020 3230 3387 2977 3120 181%Strn @ Pk Ld % 27.9 4 4 3.9 4.1 8.8 11Break Load lb 59.7 60.4 64.6 67.7 59.6 62.4 4Break Stress psi 2987 3020.2 3230.2 3387.3 2977.5 3120 181%Strn @ Break % 27.9 4 4 3.9 4.1 8.8 11Energy @ Break in-lb 3.05 2.95 3.07 3.06 2.92 3.0 0.1Yield Load lb 59.7 60.4 64.6 67.7 59.6 62.4 4Yield Stress psi 2987 3020.2 3230.2 3387.3 2977.5 3120 181%Strain @ Yield % 27.9 4 4 3.9 4.1 8.8 11Energy @ Yield in-lb 3.1 2.9 3.1 3.1 2.9 3.0 0.1Modulus psi 13224 93635 101705 104195 91373 80826 38169

Izod Impact Testing

Virgin PUUnits Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average Values Std Dev

Thickness in. 0.45660 0.44385 0.45680 0.44790 0.44330 0.44969 0.00664Izod Value 1 0.280 0.299 0.335 0.258 0.276 0.290 0.029Resultant Izod Average ft-lbs/in. 0.53 0.59 0.66 0.49 0.54 0.56 0.07

PU w/ microcapsules Sample 6

Thickness in. 0.46275Izod Value 1 0.149Resultant Izod Average ft-lbs/in. 0.24