Dispersion of silica particles with hydrophilic surfaces into polymer

The dispersion of silica particles with hydrophilic surfaces into hydrophobic polymeric materials without any hydrophobic treatment has been investigated by the direct melt-compounding method. Loose agglomerates of silica fine particles with controlled mechanical strength were prepared from an aqueous colloidal silica solution. The shear stress acting on polyethylene-polyvinylalcohol random copolymer, polycarbonate, polystyrene, and polyfluoroethyene polymer melts was evaluated as a function of the melt-compounding condition. The shear stress was maximized in order to disintegrate the loose silica agglomerates and simultaneously disperse the primary silica particles in the polymer. For all the polymer matrices selected in the present study, well-dispersed silica particles were observed in the composites. This is in contrast to the conventional knowledge that particle dispersion largely depends on the compatibility of particles with the polymer matrix.