A series of blends were prepared by different ratios of polylactic acid (PLA) and thermoplastic polyurethane (TPU) with a crosslinking agent of dicumyl peroxide (DCP). This study focused on the crystal structure, morphology, crystallization, and melting behaviors of PLA/TPU blends using a wide angle x-ray diffractometer (WAXD), a polarizing optical microscope (POM) and a differential scanning calorimeter (DSC). A Modified Avrami equation was applied to analyze non-isothermal crystallization kinetics of PLA/TPU blends. Results show that the nucleation of PLA was enhanced by the added TPU. The spherulitic growth rate, crystallization rate, and crystallinity of the PLA/TPU blends increased with an increase of TPU content. WAXD results show that all of the crystal reflections of PLA/TPU blends related to those of PLA.
The crystallization regimes and spherulitic morphology of poly (trimethylene terephthalate/isophthalate) (TI) random copolyesters were studied in this work. A hot stage polarizing microscope was used to observe morphology and measure growth rate of the spherulite of TI copolyesters. Lauritzen-Hoffman secondary nucleation theory was applied to investigate crystallization kinetics and regimes of TI copolyesters. Results show that the spherulitic growth rate decreased with an increase in isophthalic acid content of the copolyesters. The analysis of Lauritzen-Hoffman secondary nucleation theory shows that regime I, II, and III were observed in TI11 and TI21. Regime III was observed in TI29. The spherulitic morphology of TI11, TI21, and TI29 changed from elliptical-shaped spherulite to irregular spherulite and then to normal spherulite at the regime transitions.
Poly(trimethylene terephthalate-co-isophthalate) (TI) copolyesters were synthesized using different ratios of isophthalic acid (IPA) and Terephthalic acid (TPA) with 1,3-propanediol (1,3-PDO). The compositions of TI copolyesters were analyzed using 1H nuclear magnetic resonance (NMR). Non-isothermal melt- and cold-crystallization and subsequent melting behaviors were investigated using differential scanning calorimetry (DSC). For TI0, TI10, and TI20, non-isothermal crystallization kinetics were analyzed using a modified Avrami equation. The results show that the reaction rate of TPA with 1,3-PDO was similar with that of IPA with 1,3-PDO in TI copolyesters. Crystallization exothermic peak and melting endothermic peak were not observed in DSC traces with an increase of the relative amount of PIP to 41%. The Avrami exponent n is in the range of 3.5-4.2 for melt-crystallized TI copolyesters and between 3.0-3.2 for cold-crystallized copolyesters. It suggests that the crystallization from melt state corresponds to thermal nucleation but the crystallization from glassy state originates from predeterminated nuclei.
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