Abstract
Two series of rigid and flexible polyurethane foams were prepared with two types of silica fillers. The density of the flexible foams was 60 kg/m 3 and that of rigid 30 kg/m3. The fillers were micro-silica of the average particle size of 1.5 mm 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 either rigid or 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 was not changed by nano-silica concentrations up to 20%. 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.
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