An investigation of fibre sizing on the interfacial strength of glass-fibre epoxy composites

The fibre surface coating (or sizing) is one of, if not the, most crucial components involved in the manufacture of glass-fibres and plays a key role in determining the profitability, processability and both long- and short-term performance of the ultimate composite product. Given the importance of the fibre sizing to the optimisation of the interface, where the silane is the key component for interfacial strength, there is a critical need to improve our understanding of how this region is affected by fibre sizing. This paper focuses on an investigation into the role of a number of silanes typically used in fibre sizings in determining the interfacial shear strength (IFSS) of glass-fibre epoxy composites. The microbond test was used to characterise the effect of the fibre sizing on the IFSS. The work was conducted using silane- coated bare glass-fibres, silane-only sized fibres and fully-sized commercial fibres. It was found that sizing the fibres with silane increased the IFSS (with little significant difference between silanes), more so than with the fully-sized fibres. It was however considered that this apparent increase in IFSS may in fact be as a result of increased fibre tensile strength or an artefact of residual stress and static friction.