Water-mediated self-bonding enables strong and reprocessable binderless bamboo composites

Bamboo is a rapidly renewable biomass resource with high specific strength and low density, offering strong potential for sustainable composite manufacturing. However, conventional bamboo composites rely on synthetic adhesives that may release volatile organic compounds, particularly formaldehyde. In this work, a mechanically robust binderless bamboo composite was developed through a water-mediated self-bonding strategy, where water acted as both a heat transfer medium and an interfacial activator. The effects of water acidity and hardness on interfacial bonding and mechanical performance were systematically investigated. Mildly acidic and mildly alkaline conditions promoted partial lignocellulose hydrolysis and exposure of hydroxyl groups, which enhanced hydrogen bonding and interfacial adhesion. Meanwhile, an appropriate Ca 2+ concentration further reinforced the interfacial network through coordination and ionic interactions. The optimized composite achieved a flexural strength of 61.75 MPa and an internal bond strength of 2.67 MPa. In addition, the reversible noncovalent bonding enabled wet pulping assisted recycling and reconstruction of waste composites, demonstrating closed-loop utilization. This study provides a sustainable binderless route to strong and reprocessable bamboo composites for biomass valorization.