Alkali–sulfite–thermal microstructural engineering of thin-walled sympodial bamboo for high-performance epoxy composites: From interfacial synergy to mechanical excellence

The industrial utilization of small-diameter sympodial bamboo is severely limited by its thin culm walls, low processing yield, and poor interfacial compatibility with polymer matrices. Herein, we report a combined alkali–sulfite–thermal treatment that simultaneously tailors the hierarchical microstructure and surface chemistry of Bambusa textilis fibers, thereby substantially improving their composite performance. Compared with pristine bamboo, the modified bamboo strips exhibit a 58.4% increase in tensile strength, reaching 651.5 MPa, and a 47.3% increase in modulus, reaching 26.8 GPa. These improvements are attributed to the selective removal of hemicellulose and lignin, densification of the fiber cell walls, and increased cellulose crystallinity. Fabricated by vacuum infusion followed by hot-press molding, the resulting bamboo filament/epoxy resin composites exhibit a porosity of only 2.41%, corresponding to an 85.2% reduction relative to the untreated control. They achieve tensile and flexural strengths of 418.5 MPa and 444.9 MPa, respectively, representing increases of 35.2% and 21.3%. Notably, their tensile strength approaches the intrinsic tensile strength of bulk Bambusa textilis , marking a substantial advance in the performance of bamboo-reinforced epoxy composites. Comprehensive interfacial analyses, including wettability measurements, fiber bundle pull-out tests, and fractographic observations, reveal a dual strengthening mechanism involving (i) micromechanical interlocking enabled by rough, microporous surface structures and (ii) interfacial bonding arising from reactions between exposed hydroxyl groups and epoxy moieties. This study establishes a robust structure–property–processing relationship for the valorization of underutilized bamboo resources and provides a viable route toward sustainable, high-performance structural composites for load-bearing and wind-energy applications.