Self-Healing Polymers: Applicable to Polyurethanes? ENMA 490 Capstone Design Course Melissa Considine Erin Dreyer Paul Freese Paul Ledwith Joanna Meador
Contents • • • • • • •
Motivation Materials Selection Fabrication Characterization Future Work Conclusions Acknowledgements
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
Crack initiation site
Materials Selection
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: 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 • 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 mL Part A – 6 mL Part B
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 Our results
Brown’s Group at UIUC 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 W idth Thickness Peak Load Peak Stress %Strn @ Pk Ld Break Load Break Stress %Strn @ Break Energy @ Break Yield Load Yield Stress %Strain @ Yield Energy @ Yield Modulus
Units in. in. lb psi % lb psi % in-lb lb psi % in-lb psi
Average Values Std Dev 0.125 0 0.16 0 63 4 3154 181 4 11 63 4 3154 181 4 11 3 0.1 63.1 4 3153.8 181 4 11 3 0.1 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) Virgin PU average values Thickness 0.44969 Izod Value 1 0.2896 ASTM D256Izod “Standard Tensile Test Methods Resultant Average ft-lbs/in. 0.562 for Determining the Izod Pendulum Impact Resistance of Plastics” Units in.
PU with microcapsules 0.46275 0.149 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.
References 1. 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-20003676
Week by Week Project Schedule Presentation/Paper Visual- Simulation Calculations Testing/Characterization Prelim Testing of Host Fabrication- In Lab
Fabrication- Research Research- Optimization Research- Crack Propagation Research- Materials Used 8
9
10
11
12
Activity
13
14
15
16
Budget Materials Category MATRIX
MICROCAPSULES
Supplier
Item
TAP Plastics Polytek Physics store1 Physics store2 Machine shop 1 Machine shop 2 Physics store3 Physics store 4
PU and supplies PU acrylic sheets acrylic sheets Sheet Mold for dogbones Izod mold Screws (still need receipt) zip disk and CD-R
Chem store
chemicals and supplies Resorcinol, 100g
Fisher Sigma Sigma Sigma Fisher
EDA TDI Silane Scandium Triflate
Fisher
Caprolactone
Fisher
Shipping Total Cost 114.5 65 25.76 30.6 50 80 4.99 11.83
0 0 0 0 0 0
114.5 65 25.76 30.6 50 80 4.99 11.83
123.02
0
123.02
26 26.7 25.2 75.9 48.6
2.61 7.46 7.43
11.08
Chem store
0 0 0
Chem store
bottles, weighing paper
8.22
0
8.22
Chem store
Characterization Equip ESEM FTIR
approx approx
13.14 ship?
1-ocatanol PVA petri dishes and beakers books, towels slides
Chem store
ship? ship?
26 approx; ship? 29.31 32.66 83.33 48.6 ship?
13.14 8.55 18 11.08 37.06 13.22
Fisher
Composite
Cost
8.55 ship? 18 ship? 37.06 13.22
2 hours? 1 hr?
Izod Tensile
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. 2. 3. 4. 5. 6. 7. 8. 9.
Add 50 ml of 2.5 wt% EMA copolymer solution to 200 ml DI water in 1000 ml beaker @ RT while agitating. Dissolve 5.00 g urea, 0.50 g ammonium chloride and 0.50 g resorcinol in the EMA solution. Raise pH to 3.5 by drop-wise addition of 10% NaOH solution Add 1-2 drops of 1-octanol to eliminate surface bubbles Add slow stream of 60 ml DCPD to form emulsion Stabilize for 10 minutes Add 12.67 g (11.7mL) of 37 wt% formaldehyde solution to beaker. 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. After cooling, wash, filter, and separate microcapsules.
Tensile Test Results - Virgin Polyurethane Results W idth Thickness Peak Load Peak Stress %Strn @ Pk Ld Break Load Break Stress %Strn @ Break Energy @ Break Yield Load Yield Stress %Strain @ Yield Energy @ Yield Modulus
Units in. in. lb psi % lb psi % in-lb lb psi % in-lb psi
Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average Values Std Dev 0.125 0.125 0.125 0.125 0.125 0.125 0 0.160 0.160 0.160 0.160 0.160 0.160 0 59.7 60.4 64.6 67.7 59.6 62.4 4 2987 3020 3230 3387 2977 3120 181 27.9 4 4 3.9 4.1 8.8 11 59.7 60.4 64.6 67.7 59.6 62.4 4 2987 3020.2 3230.2 3387.3 2977.5 3120 181 27.9 4 4 3.9 4.1 8.8 11 3.05 2.95 3.07 3.06 2.92 3.0 0.1 59.7 60.4 64.6 67.7 59.6 62.4 4 2987 3020.2 3230.2 3387.3 2977.5 3120 181 27.9 4 4 3.9 4.1 8.8 11 3.1 2.9 3.1 3.1 2.9 3.0 0.1 13224 93635 101705 104195 91373 80826 38169
Izod Impact Testing Virgin PU Thickness Izod Value 1 Resultant Izod Average
Units in.
Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Average Values Std Dev 0.45660 0.44385 0.45680 0.44790 0.44330 0.44969 0.00664 0.280 0.299 0.335 0.258 0.276 0.290 0.029 ft-lbs/in. 0.53 0.59 0.66 0.49 0.54 0.56 0.07
PU w / microcapsules Thickness Izod Value 1 Resultant Izod Average
Sample 6 in. ft-lbs/in.
0.46275 0.149 0.24
