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Doctor of Philosophy (PhD)
Polymer Science and Engineering
Year Degree Awarded
Month Degree Awarded
Alan J. Lesser
Polymer and Organic Materials
A new approach to toughen anionically polymerized polyamide 6 (aPA6) was applied using reaction induced phase separation (RIPS). This method solved issues with particle dispersion, mixture viscosity, and additive concentration common with conventional rubber toughening thereby making it an ideal candidate for fiber reinforced aPA6 reaction injection molding (RIM). Octamethylcyclotetrasiloxane (D4) was used as a functional additive that undergoes RIPS during aPA6 polymerization and polymerizes to polydimethylsiloxane (PDMS). Controlled phase separation, modulus retention, and increased crystallinity were achieved at low additive concentrations. Optimal properties were achieved with 2 wt% D4. Fracture energy was measured at high stress concentrations and low loading rates as well as low stress concentrations and high loading rates. Approximately a 3-fold increase in nonlinear fracture toughness with compact tension testing and a 2-fold increase in Izod impact energy were achieved. The fracture mechanism was extensively investigated considering material morphology and fracture properties. Additional siloxane, silane, and hydrocarbon additives were identified for further investigation. Phenyl siloxane and hydrocarbon polymers were particularly promising. D4 was also used as a RIPS toughening additive in epoxy systems.
Superheated water was investigated as a processing aid in conventional aliphatic polyamide systems at elevated pressures. Polyamides investigated include polyamide 6 (PA6), polyamide 6,6 (PA66), polyamide 6,12 (PA612), and polyamide 12 (PA12). Polyamide melting and crystallization temperatures were severely reduced with superheated water. For example, the melting temperature of PA6 was depressed from 206°C to 153°C in the presence of superheated water. A relationship between amide group density and thermal transition temperature reduction was observed. With this method, low density foams and high density phase separated materials were created. In situ observations of polyamides melting at low temperatures were made and used to estimate the diffusion coefficient of superheated water in PA6. Low temperature extrusion was performed with PA6 and superheated water at temperatures as low as 180°C and mixture viscosity was estimated. A 20 fold depression in viscosity was observed at 240°C with superheated water. Additional superheated liquids and polymers were identified for further investigation. Particularly, superheated water, alcohols, and siloxanes were studied with polyamides, polyesters, polyolefins, polyethers, and fluoropolymers.
Evans, Gregory Connor, "Engineering Polymers through Impact Modification and Superheated Liquid Processing" (2016). Doctoral Dissertations. 740.