Bio-based sorbitan monooleate as a dual-function crosslinker for strong and water-resistant polyurethane adhesives

The development of sustainable, high-performance adhesives has remained a challenge, hindered by the intrinsic trade-off between eco-friendliness and robust functionality, required for demanding applications. This is particularly true for waterborne polyurethane (WPU) adhesives, whose use in the plywood industry is limited by insufficient mechanical strength and poor water resistance. In this study, a bio-based molecule sorbitan monooleate (SP) was introduced as a dual-function crosslinker to enhance the mechanical and hydrophobic properties of WPU wood adhesives. The unique molecular structure of SP, featuring synergistic polyhydroxyl groups and a long hydrophobic oleic acid chain, was precisely engineered to construct a dense (215.06 mol/m³) three-dimensional network within the WPU matrix, abbreviated as WPU-SP_x. This molecular-level design by introducing biomolecule SP yield a dramatic, synergistic enhancement of the final plywood composite's properties. Compared to the unmodified WPU group, the static bending strength and bonding strength of the optimized WPU-SP_x plywood was enhanced by 435.7 % and 299.0 %, respectively. Concurrently, the WPU-SP_x plywood composite exhibited exceptional dimensional stability against moisture, with its delamination rate and volumetric expansion suppressed to a mere 3.92 % and 0.52 %, demonstrating a remarkable improvement over the unmodified WPU group. This study validates a novel concept where bio-based molecules with designed functionalities can simultaneously enhance the mechanical and hydrophobic properties of polymer networks, offering a scalable and green strategy to generation advanced sustainable materials that meet industrial performance demands.