Highly strengthened mechanical, morphological, IR vibrational and optical properties of rationally tailored wheat starch–chitosan blends crosslinked with dual UV/acetic acid system for sustainable green packaging

Through this study, wheat starch/chitosan composite (SCB) films were successfully developed via a UV/acetic acid-assisted solution−casting approach with varying chitosan ratios. Tensile testing shows that stress at break remains nearly unchanged at lower chitosan content (10–30 wt%) but increases abruptly beyond 30 wt%, reaching an optimum value at 50 wt% due to intensified hydrogen bonding and cross-linking between chitosan NH₃⁺ and starch OH⁻ groups. Strain at break follows a similar trend, with markedly elevated elongation and elasticity. Young’s modulus exhibits the highest rigidity at 50 wt%, while stiffness decreases thereafter, consistent with enhanced elastic deformation. Morphological analysis reveals that chitosan incorporation transforms starch films from brittle, cracked surfaces to densely compact structures with fewer pore defects, resulting in superior adhesion and integrity. UV–vis results show improved UV shielding, higher transparency, and tunable absorption, while FTIR analysis confirms only physical interactions with no new bonds formed between the components. Overall, chitosan incorporation significantly fortifies the SCB films by improving mechanical strength, structural stability, and optical performance, extending their application as green, multifunctional materials for sustainable packaging, coatings, and wastewater treatment.