Multifunctional reinforcement of bio-based water-borne wood coatings via chitosan/calcium bentonite/linseed oil hybrid system: A response surface optimization approach

This study aimed to optimize water-borne wood coating formulations using chitosan, calcium bentonite, and linseed oil as bio-based additives. Eighteen experimental runs were designed using Box–Behnken Design (BBD) and Response Surface Methodology (RSM) via Design-Expert, with each additive evaluated at three concentration levels of 0%, 1%, and 2%. The quadratic RSM model for coating thickness showed a high coefficient of determination (R2 = 0.9584), with an adjusted R2 of 0.9050, an F-value of 17.93, and a model p-value of 0.0005, indicating statistically significant model performance. The optimized formulation, identified as Run 7 and containing 1 wt.% of each additive, was comprehensively characterized in terms of coating thickness, color, gloss, adhesion (ASTM D3359), pencil hardness (ASTM D3363-22), water absorption, contact angle, FT-IR, and DSC analyses. The optimized formulation exhibited improved adhesion resistance and a low water absorption value of 10.7% compared with the reference coating. FT-IR analysis confirmed the incorporation of the additives into the coating matrix, while DSC analysis showed that the optimized formulation exhibited a higher glass transition temperature (187 °C) than the reference coating (182 °C). Overall, the results showed that the incorporation of bio-based additives such as chitosan, calcium bentonite, and linseed oil can improve selected performance characteristics of bio-based coatings.