Effect of glass fibre sizing on the interfacial properties of composites produced using in-situ polymerised Polyamide-6 transfer moulding

The fibre-matrix interfacial properties of glass-fibre/polyamide-6 (GF/PA-6) composites produced by thermoplastic resin transfer moulding (TP-RTM) were investigated. Two different fibre sizings were compared, a specially-developed novel reactive fibre sizing and a standard silane glass fibre sizing. Scanning electron microscopy, atomic force microscopy and a number of mass-loss techniques were employed to study the form, distribution, quantity and degradation temperature of the fibre sizings. Activated PA-6 monomer precursor materials with viscosities of ∼10 mPa s were injected into the glass-fibre fabrics, contained between heated press platens, and polymerisation occurred in-situ within several minutes. Glass-fabric laminates with fibre volume fractions of ∼53% and low void content were produced at a pressure of ∼4 bar, with the low viscosity of the monomer negating the need for expensive high-pressure injection. Similar quality between the laminates was demonstrated by measuring density, thickness, fibre volume fraction, void content and fibre bundle distribution. Transverse mechanical properties of the composites reinforced with the novel reactive sizing were 20–28% higher than those with the standard fibre sizings, demonstrating improved fibre-matrix interfacial properties. Average mode I fracture toughness was also measured to be 10–30% higher than with the standard fibre sizing. Scanning electron microscopy and 3D depth composition were used to investigate fracture surfaces and determine the surface roughness. The novel reactive fibre sizing resulted in improved fibre-matrix adhesion and improved fracture toughness.