Effect of chemical and physical branching on rheological behavior of polylactide

This study was aimed at improving the process rheology of polylactide (PLA) melts by means of two strategies. First, PLAs of different branched structures, i.e., star shaped, comblike, and hyper branched, were synthesized and blended with a linear grade analog. Shear and extensional flow rheometry tests were performed on pure materials and their blends to evaluate their rheological properties. It was shown that the presence of branched poly(L-lactide) (PLLA) increased the shear thinning, shear and extensional viscosity, and elastic modulus of linear PLLA at the same time; the star shaped PLLA providing the most significant change. Second, poly(D-lactides) (PDLA) with similar molecular architectures were synthesized to have a double branching effect. In addition to the presence of branched architecture, physical cross-links due to the stereocomplex formation exist between PLLA and PDLA chains. Based on the rheological characterizations in shear and extensional mode, a greater improvement in PLA melt rheological properties was observed for blends containing stereocomplex structure as compared to linear/branched enantiopure blends.