Development of biodegradable films based on a ternary system of cassava starch–polyvinyl alcohol–sodium bentonite for applications in the preservation of tropical fruits

Abstract

The growing demand for sustainable materials has driven the development of biodegradable films for food packaging applications. In this study, thermoplastic films were prepared by the casting method using cassava starch (Manihot esculenta), polyvinyl alcohol (PVA), and sodium bentonite in mono- and ternary formulations. Key physical properties such as thickness, opacity, and water vapor permeability (WVP) were evaluated following standardized protocols. The results showed that the ternary films exhibited higher thickness values (125–128 µm) compared to the monocomponent ones (96–110 µm), reflecting the formation of a denser and more stable polymeric network. Regarding opacity, the formulations with a higher proportion of PVA (F4 and F5) were the most transparent (L* = 74.82–75.55), highlighting the ability of this polymer to form clear and homogeneous films. In contrast, starch-dominant films (F1 and F3) showed the lowest luminosity values (L* = 68.49–69.23), associated with starch retrogradation and the formation of semicrystalline domains that increase light scattering. WVP was significantly reduced in the ternary formulations (F4 = 13.25 g and F5 = 14.32 g), in contrast to the starch and pure PVA films (22.29–23.99 g). This behavior is attributed to the synergistic effect of PVA, which provides cohesion and homogeneity, and sodium bentonite, which increases tortuosity in the vapor diffusion path. In conclusion, cassava starch–PVA–sodium bentonite ternary films exhibited a favorable balance between transparency and barrier properties, establishing themselves as promising candidates for the sustainable preservation of tropical fruits.