Small- and wide-angle X-ray scattering study on α′-to-α transition of Poly(L-lactide acid) crystals

Abstract

We employed time-resolved simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) measurements in combination with a temperature-jump (T-jump) installment to investigate α′-to-α transition in poly(L-lactide acid) (PLLA) crystals during isothermal annealing at a high temperature. Upon heating in a short period (ca. 10s) to the annealing temperature 150 °C, the melting within the pre-existing α′-crystal domains before recrystallization into neighboring α-crystals was observed, appearing as discontinuous first order α′-to-α transition, which confirms the melting-recrystallization mechanism co-existing with continuous crystal perfection. Furthermore, during α′-to-α transition the loosely packed 10/3 helices of α′-crystals reorganized into the stable α-crystals by extending the lateral crystal sizes rather than the lamellar thickness. Based on our structural characterization, the microscopic mechanism of α′-to-α transition in PLLA crystals was proposed and approved by dynamic Monte Carlo simulations.