Combined Effects of Cellulose Bleaching, Silane Treatment, and Stacking Sequence on the Mechanical, Fatigue, and Creep Behavior of Pineapple Fiber Reinforced Vinyl Ester Composites

The development of sustainable polymer composites requires natural reinforcements with high cellulose content, improved interfacial compatibility, and enhanced long term mechanical performance. In the present investigation, pineapple fiber and cellulose extracted from Nelumbo nucifera were employed as reinforcements for vinyl ester composites. The cellulose was isolated through sequential alkali treatment followed by high content bleaching to remove residual lignin and hemicellulose, producing highly purified cellulose suitable for composite reinforcement. Subsequently, both the pineapple fiber and the bleached cellulose were subjected to combined alkali and 3 aminopropyltrimethoxysilane (3 APTMS) treatments to improve the reinforcement matrix interface. Composite laminates were fabricated using the hand layup technique with a 0 ° /45 ° /90 ° stacking sequence and evaluated through tensile, flexural, impact, hardness, fatigue, and creep tests, while the fracture behaviour was examined using scanning electron microscopy.The experimental results demonstrated that the synergistic effect of high content cellulose bleaching, combined alkali silane surface modification, and the optimized stacking sequence significantly improved the mechanical and time dependent behaviour of the developed composites. Among the fabricated laminates, MV5, reinforced with 40 vol.% alkali silane treated pineapple fiber and 2 vol.% alkali silane treated bleached cellulose, exhibited the optimum performance, achieving a tensile strength of 186.8 MPa, flexural strength of 163.5 MPa, impact strength of 5.3 J, hardness of 101 Shore D, and fatigue lives of 32,145, 31,567, and 30,824 cycles under 25%, 50%, and 75% of the ultimate tensile strength, respectively. The laminate containing 4 vol.% treated bleached cellulose (MV6) exhibited the highest creep resistance, recording the lowest creep strain values of 0.0038, 0.0191, and 0.0394 after 5000 s, 10,000 s, and 15,000 s, respectively. Fractographic observations confirmed improved reinforcement matrix adhesion, reduced fiber pull out, and delayed crack propagation due to the combined chemical treatments.The findings demonstrate that high content cellulose bleaching, followed by combined alkali silane surface modification and an optimized laminate stacking sequence, provides an effective route for developing lightweight, high performance, and environmentally sustainable vinyl ester composites for automotive, transportation, construction, and other structural engineering applications.