The use of a mixed coupling agent system to improve the performance of polypropylene-based composites reinforced with short-glass-fibre mat

In order to improve the mechanical properties of composites consisting of polypropylene reinforced with mats of short glass fibres, the fibre surface was treated with a silane coupling agent, N-β(N-vinylbenzylaminoethyl)-γ-aminopropyl trimethoxy silane hydrogen chloride (STS), and a titanate coupling agent, isopropyltriisostearoyl titanate (TTS). The flexural properties and the impact absorption energy of these composites were measured as a function of coupling agent concentration. STS-only treatment of the fibre surface enhanced the flexural strength and the flexural modulus of the composite, while TTS-only treatment decreased the flexural strength and the flexural modulus. The improved flexural properties of the composite brought about by the STS-only treatment were obtained at the cost of its impact absorption energy, whereas TTS-only treatment showed the inverse characteristics. However, in a mixed coupling agent system, the impact absorption energy of the composite was improved without a reduction in the flexural properties. A morphological study of the fracture surfaces of the composite after impact testing, void content measurement and single-fibre fragmentation test were also carried out to understand the interfacial phenomena of the surface treated composites.