Bio-Based Brewer’s Spent Grain Particleboards: Effect of Rosin Coating and Wood Veneer Reinforcement on Structure and Properties

Brewer’s spent grain (BSG) is an abundant agro-industrial by-product with potential for manufacturing sustainable particleboards, although its relatively low cellulose content limits the mechanical performance of the resulting boards. In this study, particleboards were produced from BSG using a soybean protein concentrate (SPC)-based adhesive at three adhesive contents. In addition, rosin surface coating and wood veneer reinforcement were investigated as strategies to improve the performance of the boards. Physical and mechanical properties were evaluated according to American and European standards, while X-ray micro-computed tomography was used to analyze the structure of the panels. Increasing the SPC content significantly improved all mechanical and physical properties. Rosin coating further reduced water absorption and moisture diffusivity while improving the modulus of rupture, modulus of elasticity, and internal bond strength. X-ray micro-CT analysis revealed local density increases associated with rosin penetration into the board structure. The greatest improvement was achieved with wood veneer reinforcement particleboards, satisfying the H1-ANSI A208.1 and P2-EN312 minimum flexural requirements. Moreover, Digital Image Correlation (DIC) revealed that wood veneer reinforcement significantly altered the deformation and failure mechanisms. These results demonstrate that simple surface reinforcement strategies enable the production of bio-based particleboards with significantly improved performance.