Abstract
Multiple melting endotherms of poly(ethylene terephthalate) (PET) were investigated with differential scanning calorimetry (DSC), Fourier transition infrared spectroscopy (FT-IR) and temperature modulated DSC (MDSC) by examining PET samples subjected to special schemes of crystallization and annealing treatment at different temperatures. Upon one-step and two-step annealing, a series of multiple minor peaks in the PET were demonstrated by DSC. FT-IR showed that the multiple endothermic minor peaks were due to melting of imperfect crystals during crystallization. From MDSC curves direct evidence can be obtained for explanation the multiple melting mechanisms in these cold crystallized polymers. The morphology and melting mechanism of semicrystalline polymers depend on the thermal history of crystallization or annealing. When the sample is crystallized at an isothermal temperature or at multiple ascending temperatures, the hypothesis of melting of original low-temperature crystals and reorganization (recrystallization) into high-melt crystals during DSC scanning has been found responsible for the observed multiple melting behavior; when the sample is isothermally crystallized and annealed at multiple descending temperatures, the proposal of multiple morphologies is more responsible for the multiple melting peaks.
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Wang, Y., Lu, J. & Shen, D. Calorimetric and Infrared Spectroscopic Analysis of Multiple Melting Endotherms of Poly(ethylene terephthalate). Polym J 32, 560–566 (2000). https://doi.org/10.1295/polymj.32.560
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DOI: https://doi.org/10.1295/polymj.32.560