Conformational Energy Settled Crystallization Behaviors of Poly(l-lactic acid)

Polymer crystallization is crucial to the properties of polymers, which are determined by thermal dynamics and kinetics. The formation of polymorphism has turned out to be very important for applications of poly(l-lactic acid) (PLLA), because it has evolved into a competitive commodity material over the past decade. In the in situ wide-angle X-ray scattering study, it shows the growth of α-crystal of thermally treated PLLA at Tc = 80 and 90 °C, which was considered only appropriate for the crystallization of its δ-form. A part of α-embryos and the locally ordered structures developed for the α-crystal may adjust their chain conformations from getting adapted to the crystallization of the δ-crystal, while the others continue to grow in their own α-form. Two crystal forms crystallize on different dynamic pathways, and the δ-form should be an independent crystal, better identified as the “δ-” instead of the previous “α′-”.