Self-Healing Polymers: Applicable to Polyurethanes?

Transcription

1 Self-Healing Polymers: Applicable to Polyurethanes? ENMA 490 Capstone Design Course Melissa Considine Erin Dreyer Paul Freese Paul Ledwith Joanna Meador

2 Contents Motivation Materials Selection Fabrication Characterization Future Work Conclusions Acknowledgements

3 Motivation 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

4 Crack initiation site

5 Materials Selection

6 Choice of Materials: Matrix 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 Source: shop/product.php?pid=74&

7 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

8 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

9 Fabrication

10 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

11 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

12 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

13 Composite Fabrication Microcapsules embedded in matrix (no catalyst) Tested one with silane wash and one without Disperse microcapsules in part A, mix in part B and pour into mold 5-wt% microcapsules: One specimen: 0.71g microcapsules 6 mlpart A 6 mlpart B

14 Characterization

15 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

16 First Filtration 100μm

17 Second Filtration 50μm

18 Maximum Filtration 20μm

19 Characterization Environmental Scanning Electron Microscopy Able to characterize microcapsules from first filtration, microcapsules from multiple filtrations, and silane washed microcapsules embedded in polyurethane

20 ESEM First Filtration

21 ESEM Maximally Filtrated

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23 Microcapsule Shell Wall Our results Brown s Group at UIUC Brown [1] 2 um

24 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

25 Tensile Test Results - Virgin Polyurethane Results Units Average Values Std Dev Width in Thickness in Peak Load lb 63 4 Peak Stress psi Pk Ld % 4 11 Break Load lb 63 4 Break Stress psi Break % 4 11 Break in-lb Yield Load lb Yield Stress psi Yield % 4 11 Yield in-lb Modulus psi Tensile Strength (avg.) = 3154 psi (22 MPa) - Mfr reported vaule = 5000 psi (34 MPa) Modulus (avg.) = 98,000 psi (676 MPa)

26 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) Units Virgin PU average values PU with microcapsules Thickness in Izod Value ASTM Resultant D256 Izod Standard Average Tensile ft-lbs/in. Test Methods for Determining the Izod Pendulum Impact Resistance of Plastics

27 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

28 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

29 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.

30 References 1. Brown, et al. In situ poly(urea-formaldehyde) microencapsulation of dicyclopentadiene. Journal of Microencapsulation. 20.6: (2003). 2. White, et al. Autonomic healing of polymer composites. Nature. 409, (2001). 3. Humble, R.W., Dicylclopentadiene: A New Resin System for Making Composite TankStructures, 36th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, July 2000, Huntsville, Alabama, AIAA

31 Week by Week Project Schedule Research- Materials Used Presentation/Paper Calculations Visual- Simulation Testing/Characterization Prelim Testing of Host Fabrication- In Lab Fabrication- Research Research- Optimization Research- Crack Propagation Activity

32 Budget Materials Category Supplier Item Cost Shipping Total Cost MATRIX TAP Plastics PU and supplies ship? Polytek PU ship? Physics store1 acrylic sheets Physics store2 acrylic sheets Machine shop 1 Sheet Mold for dogbones approx Machine shop 2 Izod mold approx Physics store3 Screws (still need receipt) Physics store 4 zip disk and CD-R MICROCAPSULES Chem store chemicals and supplies Fisher Resorcinol, 100g approx; ship? Sigma EDA Sigma TDI Sigma Silane Fisher Scandium Triflate ship? Fisher Caprolactone ship? Fisher 1-ocatanol ship? Fisher PVA ship? Chem store petri dishes and beakers Chem store books, towels Chem store slides Composite Chem store bottles, weighing paper Characterization Equip ESEM FTIR Izod Tensile 2 hours? 1 hr?

33 Fabrication

34 Izod Mold Drawing

35 Tensile Specimen Mold

36 Interfacial Polymerization From p. 270, Controlled Particle, Droplet, and Bubble Formation

37 Summary of Procedure as Adapted from UIUC Group 1. Add 50 ml of 2.5 wt% EMA copolymer solution to 200 ml DI water in 1000 ml RT while agitating. 2. Dissolve 5.00 g urea, 0.50 g ammonium chloride and 0.50 g resorcinol in the EMA solution. 3. Raise ph to 3.5 by drop-wise addition of 10% NaOH solution 4. Add drops of 1-octanol 1 to eliminate surface bubbles 5. Add slow stream of 60 ml DCPD to form emulsion 6. Stabilize for 10 minutes 7. Add g (11.7mL) of 37 wt% formaldehyde solution to beaker. 8. Cover and heat emulsion to 55 C (target T). Agitate for 4 h while maintaining temperature. Switch off mixer and hotplate, and cool to ambient temperature. 9. After cooling, wash, filter, and separate microcapsules.

38 Tensile Test Results - Virgin Polyurethane Results Units Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average Values Std Dev Width in Thickness in Peak Load lb Peak Stress psi Pk Ld % Break Load lb Break Stress psi Break % Break in-lb Yield Load lb Yield Stress psi Yield % Yield in-lb Modulus psi

39 Izod Impact Testing Virgin PU Units Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average Values Std Dev Thickness in Izod Value Resultant Izod Average ft-lbs/in PU w/ microcapsules Sample 6 Thickness in Izod Value Resultant Izod Average ft-lbs/in. 0.24