Phase Transition and Melt-Recrystallization Behavior of Poly(Butylene Adipate) Investigated by Simultaneous Measurements of Wide-Angle X-Ray Diffraction (WAXD) and Differential Scanning Calorimetry (DSC)

Simultaneous measurements of wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) were carried out to investigate the phase transition and melting behaviors of poly(butylene adipate) (PBA). Thermal expansion changes along the a and b axes of the β form unit cell are different from each other during the heating process. At the beginning of the β to α(H) (high-temperature α phase) phase transition, the β phase melts very fast, while the recrystallization of the α(H) phase is delayed and slowed. With the further increment of the temperature, the melting rate of the β phase slows down, while the recrystallization of the α(H) phase accelerates. The diffraction peak intensity ratios of the β(020):β(110) and α(H)(020):α(H)(110) diffraction peaks during the first heating process have similar value. However, the above value is different from the value of α(020):α(110) during the following melt-crystallization process. This difference comes from the different orientations of the crystal lattices of the α and α(H)(β) crystals to the substrate plane, which indicates that the α(H) phase inherits the orientation of the β phase during phase transition and the orientation of α(H) form crystals is different from the α form crystals that crystallized from the melt.