Biodegradable thermoplastic cassava starch/poly(butylene succinate) blends with citric acid: Characterization and evaluation of properties.

In environmental concerns and preservation, thermoplastic starch (TPS) emerges as a natural and biodegradable polymer. Its use has been accompanied by blending with biodegradable polyesters and/or chemical modification. In this process, organic acids are modifying agents acting on the properties of TPS once incorporated. Binary blends of thermoplastic cassava starch (70 wt%) and poly(butylene succinate) (PBS) (30 wt%) containing citric acid were prepared in the molten state using a Haake internal mixer and subsequently molded by thermal compression. The acid content ranged from 0 to 5 wt%. The molten-state behavior of the samples was investigated, along with their surface characteristics, morphology, microstructure, and optical properties. The torque required to process the starch decreased after incorporating PBS. Similarly, the presence of citric acid also had a significant effect on the processing behavior of the blend, contributing to a reduction in torque as the acid concentration increased, thereby facilitating the process. Simultaneously, the contact angle decreased in the acid-containing samples. XRD and SEM analyses revealed that the starch gelatinization process was incomplete. In particular, the composition with the highest citric acid content (5 wt%) showed improved dispersion and homogeneity between the polymeric phases of the blend. Notably, the coloration of the samples visibly changed with the addition of citric acid, indicating interaction between the acid and the TPS.