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

The optimization of hydroxypropylated cassava starch (HPS) films reinforced with açaí residue (AR) for sustainable packaging applications using low glycerol content (7.5 wt%) is reported. A 2³ 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.