Polyvinyl alcohol solvent-free adhesives for biomass bonding via rapid water activation and heat treatment

Bio-based adhesives have attracted significant attention from both academia and industry owing to their environmental friendliness and sustainability. However, conventional bio-based adhesives are predominantly solvent based, leading to major challenges, such as high viscosity and low solid content. In this context, this study presents the preparation of high-performance polyvinyl alcohol (PVA) solvent-free adhesives (PSFAs). These adhesives are prepared through a straightforward solution-casting method and exhibit substantial scalability, demonstrated herein by the production of a 1.1 m long sample. Following a rapid water activation (∼3 s), PSFAs show excellent adhesion capability, exhibiting excellent adhesive bonding performance with wood. Heat treatment initiates the formation of dual cross-linking networks between PVA chains, encompassing both chemical covalent bonds and physical hydrogen bonds, which leads to strong cohesion with the material. The wet strength of PSFAs reaches 2.25 MPa, exceeding that of the GB/T 9846-2015 standard (0.70 MPa) by more than two-fold. Moreover, PSFAs demonstrate exceptional durability and universality, enabling the preparation of diverse high-performance biomass composite materials. Compared to commercial adhesives, PSFAs are shown to be competitive across various dimensions, including adhesive preparation, wet bonding performance, cost-effectiveness, transportation, and storage time. In addition, the entire process of PSFAs only employs materials and chemicals recognized as safe in food by the US Food and Drug Administration (FDA). This study introduces a novel and promising approach for the development and application of environmentally friendly bio-based adhesives.