Construction of Eco-Friendly and Water-Resistant Peanut Protein Wood Adhesive through Multiple Cross-Linking Strategies

Due to the finite nature of fossil resources and increasing environmental regulations on formaldehyde emissions, as well as growing public health concerns, China's wood industry is in urgent need of developing environmentally friendly wood adhesives derived from renewable natural resources. The utilization of vegetable protein as a raw material for wood adhesives shows great potential; however, its limited bond strength and water resistance hinder its extensive application in the production of wood composites. The objective of this investigation was to enhance the adhesion and water resistance properties of peanut protein-based adhesive through the incorporation of formaldehyde-free urea-glyoxal (UG) resin into the curing system. The optimal adhesive composition ratio was systematically investigated to achieve the highest performance. The results demonstrate that UG resin undergoes a co-condensation reaction with the protein molecules, resulting in the formation of an imine bridge during the hot pressing process. The solidified adhesive forms a densely packed and water-resistant structure through both covalent and noncovalent interactions. Among them, PP20-UG30-2.2 binder exhibits superior bonding performance, with respective bonding strengths of 1.62 (dry strength), 1.39 (cold water strength), 1.32 (hot water strength), and 0.3 MPa (boiling water strength). This not only surpasses China's national standard requirements (>= 0.7 MPa) but also outperforms most plant protein-based wood adhesives. In general, the successful combination of UG resin and peanut protein has demonstrated a synergistic effect, surpassing the sum of their individual contributions. This advancement has significantly propelled the progress and utilization of high-performance water-resistant wood adhesives based on plant proteins.