Crystal Evolution of Amorphous Poly(lactic acid) During Simultaneous Multi‐step Tensile Deformation and Annealing

Abstract

ABSTRACTThe cold‐crystallization and crystal evolution of amorphous poly(lactic acid) (PLA) are analyzed during multistep tensile deformation and annealing at 70°C using in situ synchrotron wide‐angle X‐ray scattering (WAXS) measurements. The 2D‐WAXS diffraction pattern reveals that the PLA crystalline structure forms perpendicular to the draw direction. The annealing process lets to a rearrangement of the crystalline structure, while the stretching causes crystal contraction. Both WAXS and FTIR analyses confirm that the crystals developed through stretching and annealing are in the α′‐form. The crystallinity of PLA increases with higher deformation strains and longer annealing times. The orientation degree of both crystalline and amorphous phases of PLA, as indicated by the Hermans orientation factor and dichroic ratio of 956 cm−1 band (evaluated by WAXS and polarized FTIR analysis, respectively) also increase. The enhanced cold‐crystallization ability of PLA is attributed to the synergistic effect of tensile deformation and annealing, rather than either technique alone. The unusual crystallization phenomenon observed during multistep tensile deformation coupled with annealing provides valuable insights into the crystallization and crystal evolution of PLA.