Bio-modified pineapple fibre/vinyl ester composites with Citrus limetta pectin: surface treatment and mechanical properties

This study investigates the enhancement of interfacial adhesion and mechanical performance of pineapple fibre/vinyl ester composites through bio-modification using Citrus limetta pectin. Both fibre and filler were surface-treated with 3-aminopropyltrimethoxysilane (3-APTMS). Two composite systems were developed: unaged (VP, VP11, VP12, VP13) and thermally aged (VP1, VP21, VP22, VP23), subjected to 60 °C for 30 days. Among the formulations, the composite containing 3 vol. % pectin (VP12) exhibited the highest shear performance, with lap shear strength of 22.6 MPa and rail shear strength of 24.3 MPa. It also showed superior fatigue resistance with 24,711 cycles at 25% UTS, 21,711 cycles at 50% UTS, and 18,741 cycles at 75% UTS. The 5 vol. % pectin composite (VP13) demonstrated improved creep resistance with lower strain values over time, indicating enhanced dimensional stability under sustained loading. The thermally aged composite (VP23) showed increased water absorption of 0.40%, indicating partial degradation of interfacial bonding. Scanning electron microscopy (SEM) analysis was used to examine fracture mechanisms, revealing the influence of surface treatment, filler dispersion, and thermal ageing on interfacial integrity and failure behaviour.