Preparation of a long-term mildew resistant and strong soy protein adhesive via constructing multiple crosslinking networks

Developing strong soy protein-based adhesive (SPA) to replace harmful formaldehyde-based resins in the wood-based panel industry is a hot research. However, the lack of long-term antibacterial and antifungal properties of SPA significantly impacts its durable bonding performance and limits application. The commonly used anti-mold agents often decrease the protein compatibility and strength. Inspired by the robust and resilient dissipative matrix found in slug mucus, a green and sustainable adhesive with long-term antibacterial, antifungal properties, and excellent bonding performance was prepared using classic self-assembly and building toughened crosslinked networks. Specifically, caffeic acid and L-arginine were grafted onto tubuchitosan via acylation to prepare a chitosan with strong cationic graft modification (CCL), which combined with self-made triglycidylamine as a crosslinking agent to synergically strengthen the adhesive network. The SPA demonstrated excellent antibacterial properties against Staphylococcus aureus (20 mm) and Escherichia coli (19 mm). The prepared plywood and liquid/cured adhesive showed effective antifungal periods of 30, 80, and 120 days, respectively. Moreover, the incorporation of CCL significantly enhanced the dry and wet shear strengths of the prepared plywood to 2.73 MPa and 1.86 MPa, respectively. And a dry shear strength of 2.10 MPa and a wet shear strength of 1.53 MPa maintained even after a 30-day antifungal observation period, which still meet the interior use plywood requirement (≥0.7 MPa). The corresponding plywood after placing 30 days (1.46 MPa) is obviously higher than E0 level (0.05 mg/m3, GB18580-2017, Climate chamber method) of melamine-urea–formaldehyde resin (0 MPa after ten days). This study provides a straightforward and effective strategy for developing high performance and durable bio-based composite material, including adhesive, film, hydrogel.