Thermal evolution of a silicone resin/polyurethane blend from preceramic to ceramic foam

Ceramic foams, prepared by the pyrolysis of a foamed blend of a methylsilicone preceramic polymer and a polyurethane, exhibit excellent mechanical properties. The thermal evolution of process to produce from the foamed blend (weight ratio of 1 to 1) to ceramic foam was investigated from room temperature to 1400°C. Firstly, the methylsilicone preceramic polymer was characterized with various techniques. Secondly, the weight decrease and the degradation gas from the unpyrolyzed foamed blend, the phase morphology change, the compositional change, and the dimensional change were investigated. The main variation of characteristics of the foamed blend was observed in the temperature range 400 to 600°C, where the largest weight loss occurred in TGA, for most of the measurements. At these temperatures, the decomposition of the polyurethane phase is mostly completed, and the polymer-to-ceramic conversion of the silicone resin is under way. The phase-morphological analysis surprisingly showed that the polyurethane was dispersed as particles in a methylsilicone preceramic polymer matrix, although originally polyurethane was intended to be used as a sacrificial template matrix. The polyurethane domain particles gradually aggregated and tended to disappear as the temperature increased, and the ceramic foam walls and struts appeared to be dense (for pyrolysis temperature <1400°C). These features can be explained assuming that the preceramic polymer matrix deformed during the decomposition of the polyurethane and the polymer-to-ceramic conversion.