Improving the performance of geopolymer-based wood adhesives using a green mechanochemical strategy

Geopolymers are a new type of inorganic polymeric cementitious material with excellent properties such as flame retardancy and thermal stability. In this work, an environmentally friendly geopolymer-based adhesive was prepared using a one-step mechanochemical method, and the geopolymer-based adhesive was used to develop a low-cost, aldehyde-free, and highly flame-retardant plywood. Mechanical ball milling generated high temperatures through the collision of the agate balls and the material, which facilitated the polymerization reaction of the geopolymer. This method increased the viscosity of the adhesive and enhanced the "riveting" of the mechanical interlocks between the geopolymer and the wood. When the solid-liquid ratio of the synthetic geopolymer was 2.2, the bonding strength of the plywood developed using the adhesive prepared by the mechanochemical method was 43.0% higher than that of the plywood developed using the electromechanical stirring method, reaching 0.735 MPa, while in compliance with the GB/T 9846-2015 (China) standard for Class II plywood. In addition, the geopolymer-based adhesive had excellent thermal stability, and its mass retention rate was as high as 86.8% after treatment at 800oC. Meanwhile, the geopolymer-based adhesive endowed the flammable plywood with flame-retardant properties, and the heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of the plywood were as low as 275.9 kW/m2, 27.4 MJ/m2 and 0.84 m2, respectively. Therefore, geopolymer-based adhesives show great potential in replacing traditional aldehydebased adhesives in plywood production, providing a new idea for quick, green, and efficient preparation of inorganic adhesives with excellent bonding properties.