Reinforcement of silicone elastomers with treated silica xerogels: Silica-silicone IPNs

The use of silylated xerogels as reinforcing fillers in silicone elastomers was investigated. The silylated xerogels used in this study were mesoporou s solids with a high degree of surface treatment and an open, interconnecte d high porosity. Some macropores were also present in the original xerogel particle. During compounding the original size of the xerogel particles is reduced substantially by fracture through the macroporous regions. The meso porous regions of the xerogel are retained and exist as a uniform dispersio n of filler particles in the siloxane polymer phase. The absence of a bound rubber phase, and the presence of an open porosity in the xerogel suggests reinforcement occurs via a silica-silicone interpenetrating network. This creates additional chain restrictions which lead to increases in modulus an d other mechanical properties.