Improving thermal stability of starches native cross-linked with citric acid as a compatibilizer for thermoplastic starch/polylactic acid blends

Abstract This study aimed to enhance compatibility and thermal stability between thermoplastic starch (TPS) and polylactic acid (PLA) by incorporating citric acid-grafted starch (CA–Starch) at different concentrations (1 and 5%) with varying degrees of substitution for starch derived from sweet potatoes and yams (DY). Blends were produced using a constant TPS/PLA weight ratio of 60:40, both with and without a compatibilizer. The blending process was carried out using a torque rheometer under two distinct conditions. The results exhibited reduced particle sizes in TPS 60 /PLA 40 /CA–Starch blends, as evidenced by SEM images displaying improved interaction and smoother surfaces. Significantly, one of the properties that experienced substantial improvement was the compatibility between TPS and PLA, as indicated by reduced phase segregation within the blends. This improvement manifested in enhanced surface morphology, smaller particle sizes, and greater homogeneity in the blends. Additionally, an enhancement in thermal properties, particularly thermal stability, was observed with higher CA content. This study underscores that the incorporation of CA–Starch not only enhances compatibility but also improves thermal stability in TPS 60 /PLA 40 blends, offering potential for the development of biocompatible materials with superior performance. Graphical abstract