Preparation and characterization of new micro-composites derived from polyamide and silica sol

Abstract

New class of inorganic-organic hybrid micro-composites were prepared by the introduction of different proportions of colloidal silica particles into the polyamide matrix. Poly(phenyleneterephthalamide) was prepared by reacting a mixture of m- and p-phenylenediamines with terephthaloyl chloride in dimethyl acetamide. Colloidal silica particles were obtained separately through sol-gel process by controlling the hydrolysis and condensation steps using tetraethoxysilane, ethanol, fuming HCl and water. Various proportions of the resulting sol were mixed with the polymer solution. 1% aminophenyltrimethoxysilane was added as a coupling agent in each case. Films were cast by evaporating the solvent and these films up to 5% wt. silica were yellow, tough and transparent, whereas the films with 7.5% wt. silica or more were off-white in color and opaque. Mechanical properties of these films were analyzed. The values of tensile strength, maximum strain at rupture, initial modulus and toughness were initially found to increase and then decrease with further addition of silica. The maximum tensile stress was observed with 5% wt. silica (204 MPa) and tensile modulus was found in the range of 2.70 to 3.74 GPa at 25°C. Dynamic mechanical thermal analysis was carried out on the samples and the tanä data showed an increase in Tg with increase in silica contents. The storage modulus was found to be in the range of 9.55 to 10.25 GPa at 100°C.