Effect of Over‐Mercerization on the Interfacial Bonding and Mechanical Integrity of Bamboo Fiber/Epoxy Composites

Abstract

Owing to its exceptional mechanical performance, biodegradability, and abundant availability, bamboo fiber has emerged as a compelling sustainable alternative to synthetic reinforcements. This study systematically investigates the coupled effects of sodium hydroxide (NaOH) concentration (5 wt.% and 10 wt.%) and immersion duration (24 and 72 h) on the extraction efficacy of bamboo fibers and the subsequent performance of their derived epoxy composites. Woven bidirectional bamboo mats were integrated into an epoxy matrix utilizing a classic hand lay‐up technique, followed by a comprehensive evaluation of their physico‐mechanical, chemical, and morphological characteristics. Analytical results reveal that the composite reinforced with fibers treated at 5 wt.% for 24 h (5Na24) achieved optimum mechanical properties, driven by effective surface fibrillation and enhanced interface compatibility. Conversely, extending the alkali exposure to 72 h (5Na72) induced severe over‐mercerization, micro‐pitting, and structural degradation, culminating in a 61% reduction in tensile strength relative to the optimum condition. X‐ray diffraction (XRD) and Fourier‐transform infrared spectroscopy (FTIR) confirmed the structural transformation of cellulose paradigms and the removal of amorphous hemicellulose and partial lignin fractions. Furthermore, water absorption kinetics followed a Fickian diffusion model, where the hydrophobic characteristics were strongly dominated by the treatment duration; the (5Na72) specimen exhibited the lowest overall moisture uptake due to the extensive depletion of hydrophilic hydroxyl sites. Ultimately, these findings demonstrate that optimizing alkali extraction metrics is paramount to balancing structural integrity and interfacial bonding in sustainable engineering biocomposites.