Thermal and mechanical properties of aramid-based titania hybrid composites

Abstract

The sol-gel process has been used to prepare various types of aramid-titania hybrid materials. Specifically, a mixture of m- and p-phenylenediamines was reacted with terephthaloyl chloride to produce linear polyamide chains in a dimethylacetamide solvent. Various proportions of tetrapropylorthotitanate (TPOT) were added, and its subsequent hydrolysis-condensation in the polymer solution produced a titania (TiO 2 ) network in the aramid matrix. Thin films prepared from these materials were tested for their tensile strength, which was found to decrease with increasing proportions of titania. To remedy this through chemical bonding between the matrix and the inorganic network, a slight excess of terephthaloyl chloride or 1,3,5-benzenetricarbonyl chloride was added near the end of the polymerization reaction. These aramid chains were thus end-capped with single or double carbonyl chloride groups. This allowed the chains to be further modified, with aminophenyltrimethoxysilane end caps. Chemically bonding the titania network to the aramid chains was then achieved by in situ hydrolysis-condensation of TPOT along with that of aminophenyltrimethoxysilane. In this way, thin transparent and tough films could be obtained with up to 30 wt % titania. The values of the tensile strength in the case of bonded hybrid materials increased with the addition of titania, and the polyamide system with nonlinear end groupings showed larger increases than did those with the linear chains ends. The systems with linear and nonlinear aramid chain ends were able to withstand maximum tensile stresses of the order of 193 and 246 MPa, respectively. This is presumably due to the extensive bonding between the polymeric chain ends and the inorganic phases as compared to the unbonded system. The thermal decomposition temperature of these composites was found to be in the range of 500-600°C and the overall weight loss was found to be minimized in an inert atmosphere.