Morphology and properties of compatibilized polylactide/thermoplastic starch blends

This paper investigates the properties and interfacial modification of blends of polylactide (PLA) and glycerol-plasticized thermoplastic starch (TPS). A twin-screw extrusion process was used to gelatinize the starch, devolatilize the water to obtain a water-free TPS and then to blend into the PLA matrix. The investigated TPS concentration ranged from 27 to 60 wt%. In the absence of interfacial modification, the TPS/PLA blend morphology observed through scanning electron microscopy was very coarse with TPS particles sizes between 5 and 30 μm. Interfacial modification was achieved by free-radical grafting of maleic anhydride (MA) unto the PLA and then by reacting the modified PLA with the starch macromolecules. Blends comprising MA-grafted PLA showed much finer dispersed phase size, in the 1-3 μm range and exhibited a dramatic improvement in ductility. The paper discusses the effects of two interfacial modification strategies on the blend morphology and tensile properties and investigates the compatibilization efficiency for glycerol plasticizer contents between 30 and 39 wt% and for starches from three different sources: wheat, pea and rice.