Hygrothermal Ageing of Glass and Carbon Fibre Composites Manufactured Using Different Resin Systems

This study investigates the degradation mechanisms of glass-fibre- and carbon-fibre-reinforced polymer (GFRP and CFRP, respectively) composites fabricated either with epoxy, vinyl-ester, or bio-epoxy resins under a hygrothermal environment. Composite laminates were manufactured using the vacuum-assisted resin infusion technique and exposed to high moisture and elevated in-service temperatures of 23 °C (room temperature), 40 °C and 60 °C for up to 125 days. Changes in the physical, microstructural, chemical and mechanical properties were then assessed. CFRP and GFRP composites showed distinct differences in their hygrothermal ageing depending on the resin system used in the manufacturing. CFRP composites consistently demonstrated higher stability than GFRP composites. Epoxy resin exhibited high resistance to water absorption and hydrolysis under hygrothermal exposure. After 125 days at 60 °C, glass/epoxy (GE) and carbon/epoxy (CE) composites retained 79.0% and 72.1% of their tensile strength and 46.9% and 72.6% of their interlaminar shear strength (ILSS), respectively. Vinyl-ester composites showed high mechanical retention, with glass/vinyl-ester (GV) and carbon/vinyl-ester (CV) retaining 70.8% and 83.1% of tensile strength and 67.5% and 80.3% of ILSS, respectively. Despite this mechanical stability, evidence of hydrolysis indicated ongoing chemical degradation of the vinyl-ester resin under prolonged hygrothermal exposure. In contrast, bio-epoxy composites exhibited relatively low overall durability. Glass/bio-epoxy (GB) retained 126.5% tensile strength and 68.8% ILSS, whereas carbon/bio-epoxy retained 61.0% tensile strength and 44.3% ILSS after 125 days at 60 °C. Overall, fibre and resin types were found to have a significant effect on the hygrothermal ageing of polymer composites.