Interfacial adhesion: improving the mechanical properties of silicon nitride fibre - epoxy polymer composites

Abstract

In this work silicon nitride (Si3N4) fibres, with diameters D50 = 300 nm, were successfully functionalised with a monolayer of γ-glycidoxypropyl trimethoxysilane (GPS) coupling agent. The surface modification was used as a method to enhance the dispersion and interfacial adhesion of the fibres in epoxy polymer composites. It is well known that strong interfacial adhesion between dispersed inorganic fibres and a polymer matrix improves the mechanical properties of the composite by providing an effective stress-transfer pathway between the matrix and the fibres. The functionalised Si3N4 fibres were dispersed into a commercial epoxy resin via tumble-mill mixing and ultra-sonication. Setting was initiated via addition of a poly-amine hardener and the composites were cured at room temperature for 24 hours. The fractured surfaces of the cured composite materials were analysed via SEM imaging and the mechanical properties of the composites were tested. The GPS-Si3N4 composites were shown to have improved bonding at the interface, which resulted in enhanced mechanical properties compared to the unfunctionalised Si3N4 composites, with improved tensile strengths and hardness values. This study shows the importance of achieving a strong interphase region between the surface of a fibre and the polymer matrix in fibre-reinforced polymer composites.