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 methylsilic one preceramic polymer and a polyurethane, exhibit excellent mechanical pro perties. The thermal evolution of process to produce from the foamed blend (weight ratio of 1 to 1) to ceramic foam was investigated from room tempera ture to 1400 degreesC. Firstly, the methylsilicone preceramic polymer was c haracterized with various techniques. Secondly, the weight decrease and the degradation gas from the unpyrolyzed foamed blend, the phase morphology ch ange, the compositional change, and the dimensional change were investigate d. The main variation of characteristics of the foamed blend was observed i n the temperature range 400 to 600 degreesC, where the largest weight loss occurred in TGA, for most of the measurements. At these temperatures, the d ecomposition of the polyurethane phase is mostly completed, and the polymer -to-ceramic conversion of the silicone resin is under way. The phase-morpho logical analysis surprisingly showed that the polyurethane was dispersed as particles in a methylsilicone preceramic polymer matrix, although original ly polyurethane was intended to be used as a sacrificial template matrix. T he polyurethane domain particles gradually aggregated and tended to disappe ar as the temperature increased, and the ceramic foam walls and struts appe ared to be dense (for pyrolysis temperature < 1400 degreesC). These feature s can be explained assuming that the preceramic polymer matrix deformed dur ing the decomposition of the polyurethane and the polymer-to-ceramic conver sion. (C) 2001 Kluwer Academic Publishers.