Incorporation of wheat starch and coupling agents into poly(lactic acid) to develop biodegradable composite

Abstract

Composites of poly (lactic acid) (PLA)/wheat starch and PLA/wheat starch/methyldiphenyldiisocyanate, were prepared and characterised in this study. The effects of incorporating different coupling agents on the physical properties and morphology of the composites were studied. Extrusion technology and injection moulding techniques were used to prepare standard tensile and impact test pieces. Tensometry was used to investigate the tensile properties of the composites and impact testing using falling weight technique was used to investigate impact strength. To investigate the thermal behaviour of the composites, differential scanning calorimetry was employed. Water absorption properties of the composites were also investigated. Scanning electron microscopy was used to investigate the morphology of the composites. Starch can be incorporated in a PLA matrix at 10% level without difficulty in processing by extrusion followed by injection moulding to make shaped mouldings in the presence of MDI. With 10% wheat starch and 2% MDI, blends of wheat starch/PLA can reach the tensile strength, elongation, impact strength properties of raw PLA. In the presence of 2% MDI and 10% glycerol, blends of PLA and starch make an entirely flexible material.