THERMAL AND MECHANICAL-PROPERTIES OF ARAMID-BASED TITANIA HYBRID COMPOSITES

The sol-gel process has been used to prepare various types of aramid-t itania hybrid materials. Specifically, a, mixture of m- and p-phenylen ediamines was reacted with. terephthaloyl chloride to produce linear p olyamide chains in a dimethylacetamide solvent. Various proportions of tetrapropylorthotitanate (TPOT) were added, and its subsequent hydrol ysis-condensation in the polymer solution produced a titania (TiO2) ne twork in the aramid matrix. Thin films prepared from these materials w ere tested for their tensile strength, which was found to decrease wit h increasing proportions of titania. To remedy this through chemical b onding between the matrix and the inorganic network: a slight excess o f terephthaloyl chloride or 1,3,5-benzenetricarbonyl chloride was adde d near the end of the polymerization reaction. These aramid chains wer e thus end-capped with single or double carbonyl chloride groups. This allowed the chains to be further modified, with aminophenyltrimethoxy silane end caps. Chemically bonding the titania network to the aramid chains was then achieved by in situ hydrolysis-condensation of TPOT al ong with that of aminophenyltrimethoxysilane. In this way, thin transp arent and tough films could be obtained with up to 30 wt % titania. Th e values of the tensile strength in the case of bonded hybrid material s increased with the addition of titania, and the polyamide system wit h nonlinear end groupings showed larger increases than did those with the linear chains ends. The systems with linear and nonlinear aramid c hain ends were able to withstand maximum tensile stresses of the order of 193 and 246 MPa, respectively. This is presumably due to the exten sive bonding between the polymeric chain ends and the inorganic phases as compared to the unbonded system. The thermal decomposition tempera ture of these composites was found to be in the range of 500-600 degre es C: and the overall weight loss was found to be minimized in an iner t atmosphere. (C) 1998 John Wiley & Sons, Inc.