Multi-scale interface engineering based on wood surface delignification enables high-performance, flame-retardant and low-formaldehyde emission geopolymer-based wood composites

Alkali-activated geopolymer-based wood composites are promising for structural building materials and interior decoration because of their high dry bonding strength, low formaldehyde emission, and flame retardancy. However, the high brittleness of geopolymers and their poor compatibility with wood result in poor wet bonding strength, which limits their application. Organic–inorganic hybrid modification can improve bonding strength, but it requires a high content of petroleum-based polymers. This reduces the flame-retardant, low-emission, and low-carbon advantages of inorganic geopolymers. In this study, a wood surface chemical pretreatment strategy was developed to enhance adhesive penetration and interfacial bonding. Alkaline sulfite treatment partially removed hemicellulose and lignin from the wood surface, opened the multiscale structure of the wood, and promoted geopolymer penetration into wood. With a low content of organic polymer, the geopolymer-based wood composite achieved high bonding strength, low formaldehyde emission, and flame retardancy. The geopolymer-based wood composite showed a 101% increase in wet bonding strength (compared with GP-PFA@SDW0), reaching 1.8 MPa. It also exhibited a 25% reduction in total heat release (compared with PF@SDW3) and a 24 h formaldehyde emission of 0.093 mg/L. This work provides a practical strategy for developing high-performance, good flame-retardant, and low formaldehyde emission geopolymer-based wood composites.