Optimization of Morphology of Polyimide–Silica Hybrids in the Production of Matrices for Carbon Fibre Composites

Abstract

Hybrids of polyimide and silica have been produced from solutions via the sol–gel process. Compatibilization of the organic phase, originating from a polyamic acid and the inorganic phase, based on alkoxysilane solutions of tetraethoxysilane (TEOS), was achieved through the use of an epoxy-functional trialkoxysilane coupling agent, γ-glycidyloxypropyltrimethoxysilane (GOTMS). The use of GOTMS brings about the intimate inter-dispersion of the two phases, which results in the formation of nano-sized co-continuous domains. The materials were evaluated by a variety of techniques, including differential scanning calorimetry, thermogravimetric analysis, electron microscopy and dynamic mechanical tests. The gelation characteristics of the precursor solutions, the mechanical and thermal properties of the resulting hybrids as matrices for carbon fibre composites were used as parameters to assess the compatibilization efficiency. The results show notable improvements in the thermal stability and mechanical properties of hybrids over those of the base polymer. Above the optimum concentration of the coupling agent, however, properties were found to deteriorate owing to a diluting effect by the aliphatic component in its structure, as well as to the reduction in the degree of imidization of the polymeric component.