Developing a stable high-performance soybean meal-based adhesive using a simple high-pressure homogenization technology

Abstract Soybean meal (SM), a byproduct of bean oil production, was recycled to develop a bio-adhesive capable of replacing formaldehyde-based wood adhesives. However, SM's large particle size, uneven particle size distribution, and hydrophilic hydrogen bonds result in SM adhesives' exhibiting low adhesion stability and poor water resistance. Traditional chemical modification methods do not sufficiently mitigate these complications, and consequently SM adhesives must overcome some significant challenges before they can be considered for industrial application. In this work, we propose a simple, clean and physical high-pressure homogenization (HPH) technology in conjunction with eco-friendly cross-linking to develop a stable high-performance bio-based adhesive. Results showed that HPH treatment reduced the SM's particle size by 62% and increased the particle size distribution uniformity, which significantly enhanced the adhesive's bonding stability. Furthermore, many active functional groups inside the soy protein were simultaneously unmasked during HPH, which increased their reactivity with the cross-linker. This facilitated the formation of covalent bond complexes with a denser structure in the adhesive system, thereby improving the SM adhesive's water resistance. Specifically, after the HPH treatment, the resultant plywood's wet shear strength marked a 212% increase compared to that of untreated SM adhesive, which meets the requirements for indoor use. Moreover, this method has been successfully applied in pilot scale industrial production, and thereby shows broad prospects for practical application.