Robust and high barrier thermoplastic starch – PLA blend films using starch-graft-poly(lactic acid) as a compatibilizer

Abstract

This work reports the design of a single-layer robust and good barrier sustainable films by using graft polymer compatibilizers. A starch-graft-poly(lactic acid) (St-PLA) copolymer was synthesized and its efficacy as a compatibilizer of thermoplastic starch (TPS)/PLA blends was studied in detail. The St-PLA copolymer is synthesized using a tin(II) 2-ethylhexanoate initiator, employing ring-opening surface graft polymerization. The microstructure and morphology development of the blends are studied using a polarized optical microscope (POM), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and rheology investigations. Results indicate that the addition of the St-PLA at 2.5 wt% and 5 wt% in the TPS/PLA blend via a melt extrusion process has tremendously improved the compatibility of TPS/PLA blends. Moreover, the PLA crystal spherulite size demonstrates considerable reduction with the addition of the St-PLA compatibilizer despite maintaining similar melt processing parameters. As a result of the improvement in microstructure and morphology changes, the compatibilized blends exhibit outstanding oxygen barrier and thermomechanical properties. Thus, the compatibilization effects provided by St-PLA offer a non-reactive approach to improve the overall morphology and physical properties of the immiscible TPS–PLA blends. Such blend can be used as a single layer flexible packaging material and allows repeated recycling.