Preparation and properties of geopolymer/soy protein isolate composites by in situ organic-inorganic hybridization: A potential green binder for the wood industry

Geopolymers have the potential to be used as environmentally friendly construction materials and binders. In this study, green geopolymer/soy protein isolate (SPI) composites were hybridized in situ by forming in situ SPI resin in metakaolin-based geopolymer. Preheating treatment accelerated the setting reaction but reduced the density and mechanical strength of the geopolymer/SPI composites. High flexural strength and interfacial compatibility between the in situ SPI resin and geopolymer were detected in the geopolymer/SPI composites with low SPI loadings (≤5 wt%). Reduced flexural strength and poor compatibility were observed when SPI content was greater than 10 wt%. Bonding of the geopolymer/SPI composites as a green binder for wood was also examined by studying the interfacial morphology and shear strength between the wood and the geopolymer/SPI binder. The interface formed via mechanical occlusion and the diffusion of compounds between wood and the geopolymer/SPI binder. Robust mechanical bonding was observed between the wood and the geopolymer/SPI binder when the addition of SPI was low (1 and 5 wt%). However, the bonding strength declined as SPI content increased to 10 and 20 wt%. This study elucidated the effects of in situ organic-inorganic hybridization of protein on geopolymers. The obtained composites can potentially be used as a green adhesive resource in the wood industry.