INCREASING WATER RESISTANCE IN BIODEGRADABLE THERMOPLASTIC FILMS FROM CARIOCA BEAN STARCH USING SODIUM TRIMETAPHOSPHATE-MODIFIED STARCH

The growing environmental concern associated with the accumulation of plastic waste from conventional materials has driven the search for sustainable and biodegradable alternatives for packaging applications. In this context, biopolymers, particularly starch, stand out as promising raw materials due to their abundance, renewability, and biodegradability. However, the use of native starch in the production of thermoplastic materials presents limitations, such as low mechanical resistance and high-water solubility. To overcome these limitations, chemical modifications, such as crosslinking with sodium trimetaphosphate (STMP), have been employed, promoting the formation of crosslinks between polymer chains and improving structural properties and water resistance. In addition, processing techniques such as thermomechanical extrusion followed by hot pressing enable the production of materials with properties similar to conventional plastics. Therefore, this study aimed to develop thermoplastic films based on native carioca bean starch and to evaluate the effect of adding 15% STMP-modified starch on the properties of the resulting materials. The produced films were characterized in terms of water solubility, contact angle, and soil biodegradability. The solubility results showed a significant reduction in water affinity, decreasing from 94% in the control film to 17% in the film containing modified starch, corresponding to a reduction of approximately 77%. Complementarily, contact angle analysis indicated an increase in surface hydrophobicity, with values of 67° for the control film and 98° for the film containing modified starch. This behavior is directly related to the reduced interaction between the material and water, corroborating the solubility results and indicating improved moisture resistance. In the biodegradability analysis, all films were completely degraded within 21 days, with the control film degrading in 15 days, while the film containing modified starch showed complete degradation in 21 days. These results indicate that the addition of STMP-modified starch increased water resistance while maintaining the biodegradable nature of the material, although with a slight increase in degradation time. Thus, the developed films show potential for application as biodegradable materials, with properties that can be tailored according to the intended use.