ABSTRACT
Two series of polyurethane foams both rigid and flexible were prepared with two types of silica fillers. The density of the flexible foams was 60 kg/m3 and that of rigid 30 kg/m3. The fillers were micro silica, of the average particle size of 1.5 pm and nano-silica of the average particle size of 12 nm. The concentration of fillers varied from 0–20%. The micro-silica filler did not show any significant effect on density of both rigid and flexible foams. Nano-silica increased the density of both types of foams only at concentration above 20%. Nano-silica lowered the compression strength of both types of foams, at all concentrations while micro-silica exhibited the same effect at concentrations above 10%.
The hardness and compression strength in flexible polyurethane foams with nano-silica was increased and the rebound resilience decreased. Reduced density of foams filled with nano-silica was not changed up to 20% of the concentration. It is assumed that the nano-filler as an additional physical crosslinker increased modulus of the flexible segment in the polyurethane matrix, resulting in increased hardness and compression strength. The micro-filler in flexible foams lowered hardness, and compression strength, but increased rebound resilience.
Wide angle x-ray scattering (WAXS) showed amorphous morphology of both flexible and rigid foams filled with nano-silica. WAXS of the micro-silica filled foams showed the presence of randomly oriented crystalline quartz particles and the amorphous structure of the polymeric matrix.
