Sustainable Polyvinyl Alcohol/Carnauba Wax Films: D-Optimal Formulation Optimization for Improved Water Resistance

This study developed and optimized a sustainable polyvinyl alcohol (PVA)/carnauba wax (CW) film formulation with improved water resistance using a D-optimal mixture–process design. PVA, CW, glycerol (GLY), stearic acid (SA), and polysorbate-20 were evaluated as formulation components, while water was considered a process variable. Twenty-three experimental formulations were generated within the predefined design space, and film water solubility was experimentally evaluated. The resulting model adequately described the relationship between formulation composition and water solubility (R2 = 0.887), demonstrating the applicability of statistical mixture design for sustainable polymer formulation. PVA exhibited a positive effect on water solubility, whereas CW reduced solubility through its hydrophobic contribution. Significant interactions between CW–SA and CW–polysorbate-20 further demonstrated the importance of component compatibility in controlling film water resistance. Numerical optimization identified a formulation containing 0.44 PVA, 0.2513 CW, 0.09 GLY, 0.09 SA, and 0.1287 polysorbate-20 with 75 mL of water. Experimental validation yielded a water solubility of 72.21%, compared with the predicted value of 66.72%. The findings demonstrate how mixture-based formulation optimization can support the development of functional sustainable polymer films while reducing reliance on trial-and-error approaches in materials development.