In this article, the spherulitic morphology and growth rate of the neat and plasticized poly(lactic acid) (PLA) with triphenyl phosphate (TPP) were compared and analyzed by polarizing optical microscopy with hot stage at a temperature range of 100À142 C. The spherulitic morphology of the neat PLA underwent a series of changes such as the typical Maltese Cross at less than 132 C, the disappearance of the Maltese Cross at 133 C, the irregular and distorted spherulites at higher than 134 and 142 C, respectively. For plasticized PLA, the spherulitic morphology exhibited the same changes as neat PLA, but these changes were shifted to lower temperature when compared with neat PLA. In the case of the spherulitic growth, neat PLA had the maximum value of 0.28 lm/s at 132 C, and plasticized PLA had higher values than that of neat PLA. Further analysis based on the LauritzenHoffman theory was presented and results showed that the values of nucleation parameter K g increased with TPP content. The crystallization behavior of PLA was analyzed by differential scanning calorimetry and wide-angle X-ray diffraction. The results showed that the degree of crystallinity of plasticized PLA markedly increased when compared with neat PLA sharply with the incorporation of plasticizer. The crystallization kinetics for the neat and plasticized PLA under isothermal crystallization at 114 C was described by the Avrami equation and the Avrami exponent is close to 2, implying that the crystallization mechanism did not change.

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Both poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) are fully biodegradable polyesters. The disadvantages of poor mechanical properties of PLA limit its wide application. Fully biodegradable polymer blends were prepared by blending PLA with PBAT. Crystallization behavior of neat and blended PLA was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and wide angle X-ray diffraction (WAXD). Experiment results indicated that in comparison with neat PLA, the degree of crystallinity of PLA in various blends all markedly was increased, and the crystallization mechanism almost did not change. The equilibrium melting point of PLA initially decreased with the increase of PBAT content and then increased when PBAT content in the blends was 60 wt % compared to neat PLA. In the case of the isothermal crystallization of neat PLA and its blends at the temperature range of 123-142 C, neat PLA and its blends exhibited bell shape curves for the growth rates, and the maximum crystallization rate of neat PLA and its blends all depended on crystallization temperature and their component.

The kinetics of neat poly(lactic acid) (PLA) and its composites with triphenyl phosphate (TPP) and/or talc crystallized nonisothermally at different cooling rates of 1, 2.5, 5, 7.5, and 108C/min was analyzed by differential scanning calorimetry and described by Avrami equation and combined Avrami-Ozawa equation. The results showed that talc acted as PLA nucleating agent accelerated crystallization rate by decreasing the crystallization half-time t 1/2 or rate parameter F(T), whereas TPP acted as PLA plasticizer decreased crystallization rate. For neat PLA and plasticized PLA, the average values of Avrami exponent n were almost close to each other, but added TPP decreased crystallization rate constant k. As for PLA composites with talc, the crystallization process was relatively complex, and was divided into three regimes. At a given cooling rate, the value of n 2 was almost larger than that that of n 1 or n 3 , whereas the value of k 2 was less than that of k 1 or k 3 . The effective activation energy DE x calculated from Friedman formula increased with the increase of relative crystallinity and TPP content, whereas decreased with the presence of talc. Wide angle X-ray diffraction verified that all samples crystallized nonisothermally in cooling rate range of 1-108C/min form a-form. POLYM. COMPOS.,