Are silanes the primary driver of interface strength in glass fibre composites? : exploring the relationship of the chemical and physical parameters which control composite interfacial strength

It is probably not an overstatement to say that organosilanes are the most important chemicals used in the glass fibre, and consequently the composites, industry. One of the best-known assertions about silanes is that they promote chemical bonding across the fibre-matrix interface. This concept was fixed in the collective consciousness of the composites community early in its history when developments were focussed strongly on reactive matrices. Indeed, the chemical bridging mindset is strongly entrenched in the interface research community and extends to most other fibre-matrix combinations. However, the development of thermoplastic matrix composites raises questions about the simplistic chemical bridging model of silanes at the interface. A growing number of researchers have also commented on residual stress contributing to the stress transfer capability at the fibre-matrix interface. We will review experimental data on the temperature dependence of the apparent interfacial shear strength (IFSS) in glass fibre-polypropylene and of glass fibre-epoxy composites. This phenomenon is characterised by a large drop in IFSS when the test temperature is raised above the matrix glass transition temperature. These results can be shown to support the hypothesis that the apparent IFSS in composites can be largely explained by residual thermal stresses in the system