Modification of thermoplastic starch using oligo(lactic acid) via reactive extrusion method

A modified thermoplastic starch grafted with oligo(lactic acid) (OLA-g-TPS) was successfully prepared using the reactive extrusion method. The sugar palm (Arenga pinnata) starch was mixed with glycerol as a plasticizer at a weight ratio of 70/30 (starch/gliserol) and oligo(lactic acid) as the modifier for grafting thermoplastic starch. After the mixture was left for 24 hours, the mixture of sugar palm starch, glycerol, and oligo(lactic acid) was reacted in the extrusion. The reactive extrusion process was conducted at 140 °C at screw speeds of 50 and 80 rpm. The FTIR analysis confirms a new absorption peak at 1750 cm-1 from the C=O bond, indicating the ester linkage from the reaction product of the hydroxyl group from starch and the carboxyl group from the oligo(lactic acid). The 1H-NMR analysis confirms the new peak at 1.5-1.2 ppm from the CH3 of the oligo(lactic acid).