Biobased Natural Rubber Latex Adhesives Reinforced by Grafting-Coordination Hybrid Networks for Enhanced Durability and Multifunctionality

Developing high-performance biobased adhesives with robust interfacial bonding and environmental durability is essential for sustainable composite engineering. In this study, a grafting-coordination hybrid strategy is proposed to construct a multiscale reinforcement network within natural rubber latex (NRL). Alkali lignin (AL) was first covalently grafted onto NRL chains to improve compatibility and backbone rigidity, followed by the incorporation of a tannic acid-Fe3+-chitosan (TA/Fe/CS) nanosuspension to introduce dynamic metal-phenolic coordination and hydrogen-bond interactions. The hierarchical network significantly densified the amorphous structure, enhanced interfacial cohesion, and improved thermal stability. As a result, the optimized NRL-g-AL-TA/Fe/CS adhesive achieved a shear strength of ∼1.5 MPa, long-term adhesion stability for 21 days, and reliable bonding from −18 to 100 °C. The water-borne formulation exhibited a low VOC emission of 7.99 mg/m2, dominated by low-toxicity esters, and demonstrated strong antibacterial activity (>93% inhibition) and moderate biodegradability (42.33% mass loss after 90 days). This grafting-coordination approach provides an effective pathway for engineering multifunctional, durable, and environmentally benign NRL-based adhesives for wood bonding and flexible composite applications.