Mildew resistant modified starch adhesive by soybean meal flour crosslinking with excellent bonding properties

Starch adhesives have gained popularity due to their unique properties, which include a range of raw materials, simplicity of separation and purification, high yield, non-toxicity, and biodegradability. However, starch-based adhesives have weaknesses such as poor bonding effectiveness, poor water resistance, and poor mildew resistance. This study aims to solve these shortcomings and make such adhesives useful in the wood processing industry. Sodium periodate was used on corn starch (US) to yield oxidized starch (OS) containing aldehyde groups, and afterwards mixing it with soybean meal flour (SF). Through a Schiff base reaction, addition reaction, and hydrogen bonding, a cross-linked network was formed, yielding a starch-based wood adhesive (OSSF). The dry shear strength, 24-h cold water (20 °C), 3-h hot water (63 °C) and 3-h boiling (93 °C) water soaking strength of the plywood bonded with this resin were respectively 2.0, 1.27, 1.15, and 0.92 MPa, which is better than the strength requirements of the GB/T 9846-2015 standard (≥0.7 MPa). Additionally, the OSSF adhesive showed good storage stability for 50 days without mildewing, with the hot water strength still satisfying the requirements of the standard. This offers a practical approach to creating starch-based wood adhesives that have low cost, high performance, and are environmentally friendly.