Crystallization kinetics of blends of two poly(lactic acid) grades with diverse stereoregularity and molar mass

The crystallization kinetics of binary blends of two poly(lactic acid) grades is detailed in this contribution. A poly(l-lactic acid) (PLLA) with a molar mass of around 120 kDa and containing 4% of D-isomers was blended by solution mixing with a PLLA of high stereoregularity and molar mass of 4 kDa. The blends are homogeneous in the melt and display a single, composition-dependent glass transition. Increasing concentration of the highly stereo-regular low-molar-mass polymer accelerates crystallization due to both faster nucleation and crystal growth. PLLA chains of the low-molar mass component start to crystallize at higher temperature than those of the high-molar mass component, acting as nuclei for the subsequent crystal growth that involves both species.