Improvement in the physical properties of poly(lactic acid)/thermoplastic starch blends using oligo(lactic acid)-grafted starch

General-purpose petroleum-derived plastic remains in the environment for long periods and has significant impacts on oceans and land. Biodegradable and biomass plastics are being developed around the world as countermeasures. A poly(lactic acid) (PLA)/thermoplastic starch (TPS) blend is a promising ecofriendly alternative to biodegradable plastic made from plants. However, owing to the hydrophilicity of starch and the hydrophobicity of PLA, phase separation occurs between PLA and starch. Furthermore, PLA/TPS blends have poor water resistance because of the presence of starch, limiting their applications. In this study, to improve the affinity of PLA for starch, oligo(lactic acid)-grafted starch (OLAgSt) was synthesized as a compatibilizer for PLA/TPS blends, and the effect of its addition to PLA/TPS blends was evaluated. OLAgSt with different OLA molecular weights and degrees of substitution (DS) were synthesized, and their effects on PLA/TPS were compared. The results indicated that OLAgSt functioned as a good compatibilizer, improving the dispersibility of TPS in PLA with 4 wt% OLAgSt added to PLA/TPS and improving the water resistance. Moreover, the OLA molecular weight of OLAgSt was greater than that of DS. These results are expected to facilitate the development of PLA/TPS applications in the food packaging and biomedical fields. Blends of poly(lactic acid) (PLA) and thermoplastic starch (TPS) are promising biodegradable plastics, although their poor compatibility results in poor physical properties. In this study, oligo(lactic acid)-grafted starch (OLAgSt) was synthesized and added to PLA/TPS blends as a compatibilizer, and the physical properties of the obtained blends were evaluated. OLAgSt was synthesized by ring-opening polymerization of L-lactide using the hydroxy group of tapioca starch as an initiator. OLAgSt not only enhanced the dispersion of TPS within PLA, but also improved the biodegradability of the blend in a seawater environment.