EFFECT OF INTERFACIAL SILANE NETWORK STRUCTURE ON INTERFACIAL STRENGTH IN GLASS-FIBER COMPOSITES

The effect of crosslinked structure of silane condensates on the interfacial strength between silane-treated glass fibre and epoxy resin was examined using a dialkoxysilane, gamma-aminopropyldimethoxymethylsilane (APDS), and a trialkoxysilane, gamma-aminopropyltrimethoxysilane (APTS). Glass fibres were treated with aqueous solutions of APDS, ATPS or mixtures of both to change the silane crosslink density, and then washed with methanol to leave only chemically bonded silane at the surface. As an index of interfacial strength, the interfacial stress transmissibility was determined using a modified single-filament test. The interfacial strength decreased in the order APDS, mixtures of APTS and APDS, and APTS, showing that siloxane crosslinking of the silane condensates reduces the interfacial strength. This result suggests that the crosslinked structure depresses the penetration of the resin into the interphase and hinders reaction between silane organofunctional groups and the resin. In addition, treatment of the glass fibre with the various APDS-APTS mixtures reduced the interfacial strength in all cases, compared with the strength after APDS treatment alone. This indicates that the silane interphases formed in the present system do not lead to the formation of interpenetrating networks with the resin molecules.