Crystallization of PLLA in linear PLLA and star-shaped PLLA blends

The crystallization behaviors of poly(L-lactic acid) (PLLA) in linear PLLA and star-shaped PLLA blends were studied. Especially, the crystallization behaviors of α and α' crystals of PLLA were investigated. Usually, a tightly packed α form crystal of PLLA will be formed at high crystallization temperature (> 120 °C) and a loosely packed α' form crystal will be formed at low crystallization temperature (< 90 °C). Meanwhile, α and α' form crystals will coexist at moderate crystallization temperature (120 ∼ 90 °C). Star-shaped PLLA with three arms was blended with linear PLLA by solution casting. The core unit of star-shaped PLLA could be considered as impurity and was expelled from PLLA crystal lamellae during the crystallization. Thus the crystallization was impeded. Also, it caused the difficulty to form stable nuclei and required longer induction time to crystallize. However, star-shaped PLLA had varying level of influence on the crystallization of α and α' and it results in the change of cocrystallizati...