Investigation of properties of fiber/matrix interphase formed due to the glass fiber sizings

Sizings on glass fibers consist of a silane-based network that is chemically bound to the fiber and other compounds that are adsorbed onto the glass surface. Formation of interphase involves dissolution of adsorbed species and inter-diffusion of these compounds and resin monomers into the interphase region and chemical reaction of available functional groups. All these phenomena occur at the presence of the silane-based network. In this study, the effects of the silane-based network on the properties of the interphase region are investigated for an epoxy/amine resin system and compatible sized glass fibers. The composition of the sizing material bound to glass was determined using nuclear magnetic resonance (NMR) spectroscopy. Based on this information, model interphase materials were synthesized that were a blend of an epoxy/amine matrix and inclusions. The inclusions consist of an interpenetrating network of silane-based polymer and epoxy/amine thermoset that represents the interphase material formed during processing. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) techniques were used to characterize the glass transition temperature and flexural modulus of the model materials. The properties of the model interphase material were obtained using the DMA results and established micromechanics models. The results show that the glass transition temperature of the model interphase is about −5°C, and its flexural storage modulus at room temperature is about 50% of that of the bulk matrix. This work has also shown that a reduction in the cross-link density of the bound network might significantly reduce the modulus within the interphase region by a factor of 5 to 8.