Long-term Moisture Degradation of Rubber/Bamboo-Epoxy Composites

This study presents a layered approach to understanding the environmental degradation of bamboo/epoxy/rubber bio-composites, focusing on the coupled effects of moisture diffusion, thermal exposure, and mechanical loading. Inspired by the structural concept of a conventional table tennis racket, a hybrid laminate assembly was developed using unidirectional bamboo fibers embedded in an epoxy matrix, with rubber skin layers introduced for enhanced damping and flexibility. The long-term durability of the composite was assessed through a combination of experimental investigation, analytical modeling, and environmental aging protocols. Moisture uptake behavior was characterized under three exposure conditions: 60% RH, 83.5% RH, and full water immersion at 30°C. Bamboo/epoxy composite substrate followed Fickian diffusion, while rubber layers exhibited Sequential Dual Fickian (SDF) behavior. Anisotropic absorption was observed, with longitudinal bamboo direction showing significantly higher uptake. Mechanical performance under compression was evaluated before and after aging, revealing the synergistic effects of hygrothermal and mechanical degradation. To capture this behavior, a hygro-thermomechanical extension of laminate theory was developed, enabling layer-wise prediction of stress distribution and diffusion kinetics under coupled environmental conditions. The findings offer new insights into the multi-physics degradation mechanisms of natural fiber composites and provide a framework for the design of durable, bio-inspired structural materials for sustainable engineering applications.