Aldehyde-amine crosslinked starch-based high-performance wood adhesive

Manufacturing green and sustainable bio-based adhesives is an effective strategy to alleviate both serious energy and environmental issues. Herein, based on the aldehyde–amine covalent reaction between dialdehyde starch (DAS) and polyamine (PA_6N), a hyperbranched crosslinked starch-based adhesive was prepared, which overcomes the disadvantage of poor water resistance of conventional starch-based adhesive. The imine groups (C = N) and aminal groups (N–C–N) produced by the reaction of dialdehyde starch and polyamines stably “weld” the molecular chains of dialdehyde starch and polyamine. In addition, the dense cross-linking network formed by the molecular chains stacking and entanglement also plays a crucial role in enhancing the water resistance of the adhesives. The FTIR, XPS, and ¹³C NMR indicated that the imine and aminal covalent bonds were formed between the starch molecular chain and the polyamine. The dry bonding strength of the modified starch adhesive reached 2.12 MPa, which was increased by 162% compared to the natural starch adhesive. The wet strength of the adhesive after 63 °C of hot/boiling water soaking for 3 h broke from 0 to 1.92/1.34 MPa. The proposed DAS-PA_6N starch-based adhesive has the advantages of low cost, high performance, and green sustainability, suggesting broad application prospects in aldehyde-free bio-based wood adhesives.