Upgrading Natural Peach Gum into Biobased Adhesives: Low Curing Temperature, Universal Adhesion, and Flame Retardancy

Despite the natural abundance of peach gum (PG), its efficient and large-scale utilization remains limited. Inspired by the Maillard reaction, this study successfully developed a high-performance PG-based wood adhesive through controlled acid degradation of PG and a subsequent reaction with a polyamine polymer. The three-layer plywood bonded with the resulting adhesive exhibited a hot-water shear strength of 0.94 MPa after hot-pressing at 120 °C, meeting the requirements for Type II plywood according to the Chinese National Standard (GB/T 9846-2015), and maintained durable adhesion in warm water (60 °C) for up to 120 days. Even after 12 h of exposure to harsh environments, including acidic (pH = 5) and alkaline (pH = 9) conditions, acetone, ethanol, and simulated seawater, the bonding strength remained around 1.0 MPa. Moreover, the adhesive displayed broad and superior bonding performance toward diverse substrates such as composites and metal and nonmetal substrates, with bonding strengths ranging from 2.02 to 17.01 MPa. Additionally, the adhesive exhibited a limiting oxygen index of 30.6%, indicating favorable flame retardancy. This work provides a viable route for the high-value and scalable utilization of PG in wood adhesives and offers an environmentally friendly alternative to conventional formaldehyde-based resins for the wood industry.