Design and Synthesis of Stereoblock Polylactic Acid with High Oxygen and Water Vapor Barrier Performances

Polylactic acid (PLA), derived from renewable resources, has good biodegradability and mechanical properties. However, poor water vapor and oxygen barrier properties limit its wide application in packaging. In this work, we designed and then synthesized a series of PLA, including C16-PLLA(x)-b-PDLA(y) block polymers and C16-PDLA(y)-b-PLLA(x) block polymers by a two-step-controlled ring-opening polymerization reaction of L-lactide or D-lactide. The synthetic routes, chemical and aggregate structures, thermal and tensile properties, and barrier performances of the synthesized PLA samples were investigated. The synthesized block-structured PLA contained only crystallites of the stereocomplex form and was thermally stable at almost the same level as homopolymerized PLA of comparable molecular weight, and its melting point increased by more than 40 degrees C. The block PLA films showed an increased tensile strength and elongation at break with increasing molecular weight and exhibited brittle fracture as homopolymerized PLA did. In barrier performance tests, the block PLA films outperformed the homopolymerized and solution-blended stereocomplex PLA films in terms of water vapor and oxygen barrier. This study will provide new ideas for the development of new PLA materials with enhanced gas barrier performance based on PLA itself.