The effect of silica nanoparticles obtained from different sources on mechanical properties of polyurethane nanocomposites

Abstract

Spherical silica particles were synthesized from two different sources, tetraethyl orthosilicate (TEOS) and sodium sili-cate obtained from wheat straw ash, respectively. In the first case, monodispersed and microporous silica particles with average particle size of 400 nm were prepared by hydrolysis and condensation of TEOS. In the second case, the silica particles were generated from supersaturated sodium silicate solution. The extraction of silicate solution from wheat straw ash (WSA) was performed by the multi-step sequential extraction using 2,5 mol/L NaOH. WSA silica particles were polydispersed and contain the primary silica particles with average size of ~250 nm and agglomerates obtained by aggregation of primary silica particles, with average size of ~1.5 mm and 5 mm. The silica particles obtained from WSA have the average pore size of 28.3 nm, total pore volume of 0.1638 cm 3 /g and average surface area of 23.131 m 2 /g. Flexible polyurethane/silica composites with my(TEOS silica and WSA silica) and different filler concentration were synthesized. Dispersion of silica fillers in polyol system preceded the mixing with isocyanate resulted in formation of cavities in polyurethane-silica composite. On the other hand, dispersion of TEOS silica filler into isocyanate which preceded the mixing with polyol system resulted in homogenous and compact composite. The application of silica filler obtained from TEOS at filler concentration of 4 wt.% increased Young's modulus for 20% relative to that of polyurethane without filler. On the other side, the application of WSA silica filler resulted in reduced Young' s modulus probably due to large silica aggregates.