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The 2D X‐ray diffraction pattern of the uniaxially oriented mesophase, prepared by stretching the amorphous sample around T _g, is shown in Figure 6.2a. The pattern is very broad and diffuse. The relative content of the mesophase increases with an increase of tensile drawing ratio of the original amorphous sample [54]. The X‐ray data analysis revealed that the oriented mesophase contains the conformationally disordered 10/3 helical chains, which are gathered together to form the small domains of about 30 Å (c‐axis) × 20 Å (lateral direction) size with low correlation between them [5]. By heating, the mesophase undergoes the stepwise disorder‐to‐order phase transformation to the δ and α forms [5] (refer to Section 6.3.1). These transitions were proposed to occur, not by the solid‐to‐solid process, but by the melt‐recrystallization process, although not yet confirmed [55].

FIGURE 6.9 Comparison of the observed X‐ray diffraction profiles with those calculated for the structure model 2 of the β form.

Source: Reproduced from Wang et al., Macromolecules 2017, 50, 3285–3300.