Mechanical performance enhancement of cassava starch and açaí residue films through optimized hydroxypropylation reaction

full factorial design of experiments (DoE) combined with a random forest (RF) algorithm was applied to optimize the hydroxypropylation reaction by evaluating the effects of propylene oxide/hydroxyl groups molar ratio (PO/OH), AR percentage, and reaction temperature. Hydroxypropylation significantly improved film flexibility even at 7.5 wt% glycerol amount, from around 6% to 13%, while AR incorporation maintained tensile strength and Young's modulus similar to the control sample, of around 6 MPa and 250 MPa, respectively. The optimized films also exhibited thermal stability comparable to that of native starch films with maximum decomposition rate at around 250 °C and rapid disintegration under soil burial conditions, occurring within 1 day. Statistical analysis and machine learning consistently indicated that higher molar ratio and fiber content favor enhanced mechanical performance. Overall, the results demonstrate that optimized hydroxypropylation enables the production of starch-based films with improved properties, reduced synthetic plasticizer content, and potential for agro-industrial waste upcycling following green chemistry principles.