Date of Award
Master of Science (MS)
Polysiloxanes are a class of materials that possess high temperature stability and the ability to remain flexible at extremely low temperatures. Their elastomers generally exhibit low strength and have poor mechanical properties unless reinforced with fillers. Reinforcement can be accomplished by compounding reinforcing silica fillers with polysiloxanes via twin-screw extrusion compounding that vigorously mixes the fillers into a polymer matrix. In this thesis, a lab-scale twin-screw extruder was utilized to compound thermoplastic materials to determine the effects of processing on thermoplastics material properties, as well as to determine the extruder’s compounding effectiveness. Processing via lab-scale twin-screw extrusion did not negatively affect the thermoplastic material properties. A thermoplastic and titanium dioxide formulation was effectively compounded, as well. Lab-scale twin-screw extrusion was also utilized to compound two model polysiloxanes (a vinyl-terminated polydimethylsiloxane (Gelest DMS-V31), and a vinyl-terminated diphenyl-dimethyl siloxane copolymer (Gelest PDV-0331)) and four experimentally-synthesized polysiloxane copolymers with three silica fillers (Hi-Sil™ 135, Hi-Sil™ 233D, and Cab-O-Sil M-7D ) to produce well-dispersed compounded materials.
The filled polysiloxanes were characterized by thermogravimetric analysis to evaluate the distribution of filler. Oscillatory rheometry and flow rheology were used to evaluate the yield stress and thixotropic behavior, respectively. Processing parameters, filler type, and amount of filler were evaluated in the polysiloxane formulations and compared to a commercial reference silicone to evaluate the formulations for their viability in applications that currently use the reference silicone resin.
Thermogravimetric analysis confirmed that the compounded materials possessed an even distribution of filler in most formulations. Thermal stability, yield stress, and thixotropic behavior of the filled materials were most dependent on the type and amount of filler used in each formulation, rather than chemical characteristics, including molecular weight and copolymer composition, of the polysiloxanes studied. Cab-O-Sil-filled materials resulted in the most thermally stable materials with the highest yield stress and the greatest degree of thixotropy. However, despite these properties, the Cab-O-Sil-filled materials are too stiff to replace the reference silicone. The Hi-Sil-233D-filled materials attained similar rheological properties to the reference silicone, and may be a more viable alternative in applications where the reference silicone is currently utilized.
Schwenker, Kyle W., "EFFECTS OF PROCESSING PARAMETERS ON PROPERTIES OF NOVEL SILICA-FILLED POLYSILOXANE MATERIALS" (2017). Electronic Theses & Dissertations. 217.