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Nucleating agent crystallization behavior of PBT

Author: MuXingWen
Tutor: LiGuiJuan
School: Changchun University of
Course: Materials Science
Keywords: DBS YS-688 PTT/PBT blends non-isothermal crystallization crystallization kinetics
CLC: TQ323.4
Type: Master's thesis
Year: 2010
Downloads: 117
Quote: 1
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Abstract

The actual processing of polymer materials is often under non-isothermal conditions, and there are close relations between the crystallization behavior during polymer processing and the quality of the products, so the study of non-isothermal crystallization dynamics has great practical significance. Service performance of a polymer is affected by the crystallization process, therefore, studying various parameters in polymer crystallization and knowing the factors influencing them can provide a scientific basis for optimizing forming conditions. Non-isothermal crystallization refers to the crystallization process in which the temperature changes. Compared with the isothermal crystallization process, the non-isothermal crystallization process is closer to actual production, easier to be realized in experiments, and, in theory, permits obtaining more information. In order to choose a suitable processing condition and prepare good performance materials, people pay more attention to the non-isothermal crystallization dynamics of a polymer.The crystallization behavior and crystal morphology of DBS/PBT and YS-688/PBT have been investigated by means of wide angle X-ray diffraction (WAXD) and polarized light microscopy (PLM). The results show that the DBS, YS-688 did not changed the crystal patterns of PBT, they crystallized individually. However, DBS, YS-688 play a role of heterogeneous nucleation in promoting the crystallization of PBT, with crystal number increased, size smaller.The modified Avrami, Mo and Kissinger models, were applied to investigate the non-isothermal melt crystallization process of Dibenzylidene Sorbitol (DBS)/Poly(butylene terephthalate) (PBT) blends by DSC measurements. It was found that the modified Avrami model can describe the non-isothermal melt crystallization processes of DBS/PBT blends fairly well. It was found that the cooling rates and the blend composition affect the crystallization for blends according to Mo crystallization kinetics parameters, Mo model shows that F(T) increases with increasing crystallinity, indicating that the needed cooling rate when it reached a certain crystallinity increased in unit time, the crystallization rate of DBS/PBT blends is faster than the crystallization rate of pure PBT, and the crystallization rate of the DBS/PBT blends with 0.5% DBS is fastest. Kissinger model showed that the crystallization activation energy of DBS/PBT blends is lower than the activation energy of pure PBT, the crystallization activation energy of the DBS/PBT blends with 0.5% DBS is the lowest.It was found that the modified Avrami model can describe the non-isothermal melt crystallization processes of YS-688/PBT blends fairly well. It was found that the cooling rates and the blend composition affect the crystallization for blends according to Mo crystallization kinetics parameters, Mo model shows that F(T) increases with increasing crystallinity, indicating that the needed cooling rate when it reached a certain crystallinity increased in unit time, the crystallization rate of YS-688/PBT blends is faster than the crystallization rate of pure PBT, and the crystallization rate of the YS-688/PBT blends with 0.5% YS-688 is fastest. Jezrony model shows that Zc decreases with increasing cooling rate, indicating that the crystallization rate of YS-688/PBT increases with increasing cooling rate. The crystallization rate of the DBS/PBT blends with 0.5% YS-688 is fastest.Macro-kinetic models, namely the modified Avrami, Ozawa, Mo, and Kissinger models, were applied to investigate the non-isothermal melt crystallization process of PTT/PBT blends by DSC measurements. It was found that the modified Avrami model can describe the non-isothermal melt crystallization processes of PTT/PBT blends fairly well. When the cooling rates range from 5 to 20℃/min, the Ozawa model could be used to satisfactorily describe the early stage of crystallization. However, the Ozawa model didn’t fit the polymer blends in the late stage of crystallization, because it ignored the influence of secondary crystallization. Under the conditions of the non-isothermal melt crystallization, it was found that the cooling rates and the blend composition affect the crystallization for blends according to Kissinger crystallization kinetics parameters. The crystallization kinetics constant Ka increases with increasing cooling rate, indicating the crystallization rates of PTT, PBT, and PTT/PBT blends were improved. The crystallization kinetic activation energy parameters are good agreement with the results from isothermal crystallization processes of the polymer blends. The crystallization activation energy of PTT/PBT blends is higher than the activation energy of PTT and PBT.

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