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以对苯二甲酸(PTA)、乙二醇(EG)、异山梨醇(ISB)为原料,通过直接熔融缩聚法合成聚(对苯二甲酸乙二醇酯-co-对苯二甲酸异山梨醇酯)(PEIT)共聚酯。利用差示扫描量热法(DSC)研究了共聚酯的结晶行为,采用Avrami方程分析了共聚酯的等温结晶动力学。结果表明,PEIT共聚酯结晶行为受共聚组成和结晶温度影响。随着ISB用量的增加或结晶温度的降低,共聚酯半结晶周期t1/2增加、结晶速率变慢;ISB摩尔分数超过20%,共聚酯无法结晶。 相似文献
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提出了几种通过共聚改性提高聚酯冷结晶温度的方法,同时探索了缩聚工艺条件对聚酯结晶性能的影响,实验结果表明,通过降低缩聚初期的温度,可显著减慢聚酯的结晶速度。 相似文献
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提出了几种通过共聚改性提高聚酯冷结晶温度的方法,同时探索了缩聚工艺条件对聚酯结晶性能的影响.实验结果表明,通过降低缩聚初期的温度,可显著减慢聚酯的结晶速度. 相似文献
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用DSC法对三氧化二锑 (Sb2 O3)、氟钛酸钾 (K2 TiF6 )、钛酸四丁酯 (Ti(OC4 H9) 4)及乙二醇锑(S -2 4) 4种催化体系所得聚酯进行等温结晶研究 ,求得了结晶速率常数 (k)和Avrami指数 (n)。结果表明 ,锑系催化剂所得聚酯的结晶速度总体大于钛系催化剂所得聚酯 ,其中以Sb2 O3催化所得聚酯结晶速度最快 ,而Ti(OC4 H9) 4催化所得聚酯结晶速度最慢。DTA结果表明锑系催化剂所得聚酯冷结晶温度低于钛系催化剂所得聚酯 ,与结晶速度测试结果相一致。 相似文献
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Polyester/clay nanocomposites were prepared by melt compounding with different clay loadings. Comparing against neat polyester resins, the crystallization and multiple melting behavior of the nanocomposites was investigated by differential scanning calorimetry (DSC) and X‐ray diffraction (XRD). Nanoclay filler is an effective heterogeneous nucleating agent, as evidenced by a decrease and an increase in the crystallization temperature for both cold and melt crystallization of polyesters, respectively. The degree of crystallinity was found to increase with increasing clay content, due to heterogeneous nucleation effects by the addition of a nanofiller. For the annealed samples, multiple melting peaks were always observed for both neat polyester and its nanocomposites. The origins of the multiple melting behavior are discussed, based on the DSC and XRD results. Interestingly, an ‘abnormal’ high‐temperature endothermic peak (Tm, 3) at about 260 °C was observed when the nanocomposite samples were annealed at higher temperatures (eg ≥240 °C). The constrained polyester crystals formed within intercalated clay platelets due to confinement effects were probably responsible for this melting event at these higher temperatures. Copyright © 2004 Society of Chemical Industry 相似文献
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《国际聚合物材料杂志》2012,61(9):878-890
The thermal behavior of poly-L-lactide (PLLA) isothermal crystallization upon cooling from the melt was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and polarizing microscope (POM) by changing the crystallization temperature and time. It was indicated that 110°C should be a critical temperature for PLLA melting crystallization. The melting point of crystallized PLLA discontinuously changed with crystallization temperature, increased with temperature, but decreased at about 110°C, and thereafter again increased with higher crystallization temperatures. At 110°C a multiple endothermic peak was observed. PLLA crystals of higher perfection form when crystallized under higher temperature, which reflects the effects of high chain mobility in higher temperatures. During isothermal crystallization, PLLA crystallites become increasingly perfect, and thicken with prolonged time, leading to an increasing melting point. 相似文献
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Poly(ethylene terephthalate) (PET) is a widely used polyester, which can be crystallized from the melt over a wide range of supercooling conditions or, alternatively, quenched into the amorphous state and, subsequently, crystallized by thermal treatment above the glass‐transition temperature. It is well known that the crystallization of PET can be hindered by means of copolymerization or reactive blending. The incorporation of comonomeric units into the polymer backbone leads to an irregular chain structure and thereby inhibits regular chain packing for crystallization. The crystallization of PET copolyesters is strongly influenced by the chain microstructure regarding comonomer distribution, randomness and length of the crystallizable ethylene terephthalate sequences. This paper is mainly devoted to the thermally induced crystallization behaviour of PET and to reviewing the efforts that have been made in the last decade to modify the glass‐transition and melting temperatures, the crystallinity and the crystallization rate of this polyester. Furthermore, some illustrative experimental data obtained from isothermal and non‐isothermal crystallization of PET are included in this study. © 2003 Society of Chemical Industry 相似文献
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熔融条件对聚醚醚酮结晶熔融行为的影响 总被引:2,自引:0,他引:2
用DSC法研究了熔融温度和熔融时间对聚醚醚酮地晶熔融行为的影响。实验表明,聚醚醚酮的结晶峰随熔融延长向高温移动,且峰形变窄,峰的强度增大,继续延长熔融时间,结晶峰降低,峰形变宽;熔融时间延长时,聚醚醚酮的玻璃化转变温度和冷结晶峰温度均提高,熔融峰强度减弱。熔融温度升高时,聚醚醚酮的结晶峰强度减弱,峰宽增强;而冷结晶温度提高。 相似文献
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Pitt Supaphol 《应用聚合物科学杂志》2001,82(5):1083-1097
The melting behavior of syndiotactic polypropylene (s‐PP) after isothermal crystallization from the melt state was studied using differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) techniques. Three melting endotherms were observed for isothermal crystallization at high degrees of undercooling. The minor endotherm, located closed to the corresponding crystallization temperature, was postulated to be the melting of the secondary crystallites formed at the crystallization temperature. The low‐temperature melting peak was found to be the melting of the primary crystallites formed, and the high‐temperature melting peak was a result of the melting of the crystallites recrystallized during a heating scan. The triple‐melting behavior observed in subsequent melting endotherms of s‐PP was therefore described as contributions from melting of the secondary crystallites and their recrystallization, partial melting of the less stable fraction of the primary crystallites and their recrystallization, melting of the primary crystallites, and remelting of the recrystallized crystallites formed during the heating scan. In addition, determination of the equilibrium melting temperature for this s‐PP resin according to the linear and nonlinear Hoffman–Weeks extrapolations provided values of 143.1 and 185.6°C, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1083–1097, 2001 相似文献
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Isothermal crystallization and subsequent melting behavior of five samples of syndiotactic polypropylene are presented. Crystallization studies were carried out in the temperature range of 60°C to 97.5°C using a differential scanning calorimeter (DSC). Subsequent DSC scans of isothermally crystallized samples exhibited double melting endotherms. The high melting peak was concluded to be the result of the melting of crystals formed by recrystallization during the reheating process. Overall crystallization kinetics was studied based on the traditional Avrami analysis. Analysis of crystallization times based on the modified growth rate theory suggested that, within the crystallization temperature range studied, the syndiotactic polypropylenes crystallize in regime III. Kinetic crystallizability parameters also were evaluated, and were found to be in the range of 0.41°C s−1 to 2.14°C s−1. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 44–59, 2000 相似文献
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Shu‐Ling Zhang Gui‐Bin Wang Zhen‐Hua Jiang Wei‐Chun Wu Rong‐Tang Ma Zhong‐Wen Wu 《应用聚合物科学杂志》2004,94(3):839-844
PA1010/TPU blends were prepared by melt blending. The melting, crystallization behavior, and isothermal crystallization kinetics were investigated using differential scanning calorimetry (DSC). The results showed that the DSC thermograms of blend samples exhibit double melting peaks. With increasing the TPU content, the position of the double melting peaks shifted to a lower temperature, and the total heat of fusion decreased. With increasing the heating rates, the position of the lower melting peak shifted to a higher temperature, while the position of the higher melting peak shifted to a lower temperature; however, the total heat of fusion remained almost constant. With prolonging the annealing time and increasing the crystallization temperature, the position of the lower melting peak shifted to a higher temperature, while the position of the higher melting peak almost did not change; however, the total heat of fusion increased. The addition of TPU could promote the crystallization of PA1010 but not affect the crystallization mechanism. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 839–844, 2004 相似文献