Preparation of an oxyalkylated lignin‐g‐polylactic acid copolymer to improve the compatibility of an organosolv lignin in blended poly(lactic acid) films

Abstract

AbstractTo improve the compatibility of an organosolv lignin (OL) in polylactic acid (PLA) blends, a green approach was pursued whereby the lignin was modified with propylene carbonate (PC) to increase its aliphatic hydroxyl content, and thereby, its reactivity. The oxyalkylated organosolv lignin (OOL, synthesized at 170°C) was analyzed by quantitative 31P NMR and showed the number of phenolic hydroxyls decreased from 4.73 to 0.16 mmol·g−1, and the number of aliphatic hydroxyls increased from 3.56 to 3.92 mmol·g−1. OOL‐g‐PLA copolymer (OOLPC) samples were prepared by graft polymerization of L‐lactide with the OOL and showed the molecular weights (Mn) to range from 12,343 to 16,834 Da, increasing with the lignin loading of the copolymer. Scanning electron microscope indicated that the graft copolymerization reaction between L‐lactide and the OOL afforded a copolymer that was compatible with PLA. The highest increase in elongation at break was 7.43% for the PLA blend films prepared with the OOLPC having a 5.0% loading of OOL; the tensile strength at this level of lignin loading was 12.03% lower. Introducing an OL into the blend films showed excellent ultraviolet absorption ability and thus the OOLPC could be used as a well‐dispersed UV‐blocking agent for biocompatible packaging materials.