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Keywords:

  • atomic force microscopy (AFM);
  • biopolymers;
  • crystallinity;
  • differential scanning calorimetry (DSC);
  • differential thermal calorimetry;
  • orientation;
  • polyesters;
  • polylactide;
  • X-ray;
  • X-ray diffraction

Abstract

Uniaxial deformation of amorphous L-polylactic acid films was performed at two different temperatures at which thermal degradation was minimal, 70 °C or Tg + 10 and 90 °C or Tg + 30. Samples were annealed postdeformation for long times (either 15 or 45 min) to approach equilibrium conditions. Samples deformed and annealed at 70 °C showed low crystallinity and poor crystalline order or crystal size, as determined by wide-angle X-ray diffraction. At 90 °C, high crystallinity and order parameters were observed. In addition, once the oriented chains had crystallized at this temperature, nonoriented chains also underwent crystallization, and a small fraction of nonordered crystal phase was therefore observed after long annealing times. These observations are explained on the basis of different morphologies in samples drawn at the two temperatures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013