The crystallization of poly(lactic acid) (PLA) homo-crystallites (HC) and stereocomplex crystallites (SC) is quite complicated for the inducing and competing effects of SC on HC. Furthermore, carbon dioxide (CO2) would...

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Exploring the origin of multiple melting of thermoplastic polyurethane (TPU) is of great significance for comprehending the mechanism for its phase transition. Herein, the effects of two crystal forms (Form-I and Form-II) and crystal form transition on the melting behaviors and crystallization kinetics of TPU are reported. As the function of the crystallization temperature (T c ), Form-II and Form-I develop at T c ≥ 130 °C and T c ≤ 130 °C, respectively, which leads to distinct differential scanning calorimetry (DSC) melting curves of TPU. It is found that the repeated melting−recrystallization occurs during the melting of Form-I, which includes the crystal form transition of Form-I to Form-II, resulting in four melting peaks in the DSC heating curves of Form-I. The results reveal that the mesophase (Form-I) could transform into the stable crystal form (Form-II) through melting−recrystallization upon heating in TPU, and TPU has the ability to continuously reorganize the ordered structure upon heating. Meanwhile, the intervention of Form-I significantly increases the overall isothermal crystallization rates, and the motion ability of TPU molecular chains is the crucial factor affecting the generation of Form-I.

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