PTT/PET共混体系晶体形态与结晶性能的研究

用差示扫描量热仪(DSC)、广角X射线衍射(WAXD)和正交偏光显微镜研究了聚对苯二甲酸丙二酯(PTT)和聚对苯二甲酸乙二酯(PET)共混体系的晶体形态与结晶性能.结果表明,共混体系结晶性能与PTT的含量有关.PET的加入,使共混体系的球晶尺寸减小.球晶完善性降低.当PTT含量为40wt%～60wt%时,共混物分别出现了双重熔融峰和双重结晶峰.双重熔融峰是加热过程中熔融重结晶造成的,双重结晶峰说明不完善的晶体产生的次级结晶.     

PC/PET/EPDM共混体系的结晶与熔融行为

本文用解偏振光法与DSC法分别测定并研究了PC/PET/EPDM共混体系的结晶速度、结晶度、Avrami指数(n)和熔融温度及其影响因素,共混物中PET的结晶速度、结晶度均随PC含量增加而下降;EPDM用量不超过10%时,可提高PET的结晶速度,但不影响结晶度和成核与增长方式,n值不变。当EPDM为5%时,结晶速度呈现极大值。经退火处理的共混物呈现熔融双峰,PC量增加,高温熔融峰略移向高温方向;热处理温度升高或时间延长,则低温熔融峰移向高温方向。     

聚对苯二甲酸1,3-丙二酯的自晶种成核等温结晶动力学

研究了自晶种成核对聚对苯二甲酸1,3-丙二酯(PTT)结晶行为的影响.示差扫描量热结果表明,经过自晶种成核处理后,PTT的结晶温度明显增加.应用Avrami方程分析了PTT等温结晶动力学,Avrami指数n的平均值为3.34,表明初级结晶为三维球晶生长.自晶种成核导致结晶活化能和链折叠功减小,促进PTT的结晶.     

聚对苯二甲酸乙二酯溶剂诱导结晶研究——Ⅱ.表层与断面结构形态形成的探讨

溶剂诱导结晶的结构形态与热结晶的有很大差别.本文应用偏光显微镜,小角激光光散射,电子扫描显微镜,进一步研究了形态及其形成,证明球形堆砌状结构仅在表层形成.在断面能观察到三层的结构形态和溶剂扩散前沿,并据此测定了溶剂扩散动力学,表明符合Fick方程,溶剂在表层和内部扩散过程不同,是表里形态结构各异的原因.     

聚对苯二甲酸乙二酯的玻璃化转变和结晶化的正电子湮没研究

研究了聚对苯二甲酸乙二酯的玻璃化转变和结晶过程对正电子湮没寿命谱的影响.结果表明,结晶过程对正电子湮没的长寿命组份τ_3的寿命值不敏感,用这种方法测得的“T_g”不随结晶度而变化,而长寿命组份的相对强度则随结晶度的增加而减小.     

变温红外法研究聚对苯二甲酸乙二酯分子链的松弛运动及其构象转变

在30～170 ℃范围内逐渐升温过程中,用红外光谱仪原位检测无定形聚对苯二甲酸乙二酯（PET）薄膜红外光谱图的变化情况。通过特征谱带吸光度与温度的变化特点,研究了PET分子链在热变化过程中的松弛运动及冷结晶过程中分子链的构象变化。实验结果表明在冷结晶过程中,随PET结晶的不断完善,对应左右式(gauche)构象的吸收峰减弱,对应反式(trans)构象的吸收峰增强,并计算出CH2面外摇摆振动结晶前和结晶后反式构象和左右式构象的相对百分含量随温度的变化关系,以及玻璃化转变和冷结晶的温区范围。     

单轴取向聚对苯二甲酸乙二酯非等温结晶动力学研究

采用等速升温DSC方法对单轴取向聚对苯二甲酸乙二酯 (PET)的结晶过程进行了研究 ,发现单轴取向PET的冷结晶峰表现为多重结晶峰 .等温DSC方法的研究结果进一步证实结晶重峰的存在 .为此 ,本文提出了一种依据非等温DSC曲线解析高聚物结晶动力学参数的新方法 .对单轴取向PET的研究结果表明 ,与其他方法相比较 ,由新方法计算出的理论曲线与实验数据能更好地吻合 .单轴取向PET的总的结晶过程由三个子结晶过程组成 .根据不同拉伸比 ,各个子过程的Avrami指数和质量分数的变化 ,对结晶机理进行了解释 .与各向同性PET样品相比 ,单轴取向PET在低温部分的结晶速率明显增快     

取向非晶态聚对苯二甲酸乙二酯(PET)膜的结晶

采用小角和广角X-散射法比较了未拉和热拉PET膜在结晶性能方面的差别,热拉试样在分子链段的小尺度范围内基本上是无规取向,而在分子链的大尺度范围内却是高度取向的。研究结果表明:热拉PET膜的结晶诱导期较短,长周期发展得较快,结晶后小角X-线散射表现出明显的各向异性,在热处理过程中先出现显著的热收缩,随后又表现出结晶伸长现象,这些都和未拉试样有明显的差别。     

PET/PEN/DBS共混体系结构与形貌的研究

共混是改善聚合物性能的一种简单而又行之有效的方法,PET和PEN均为结晶性聚酯,由于PEN合成原料的影响,致使PEN的价格较高,但性能比PET优良,通过二者的共混,既可以提高PET的性能,又可以降低PEN成本,有关PET／PEN共混体系的研究已引起人们的关注,而对于共混体系结晶形态和结晶条件的研究较少,由于成核剂能够提高结晶速率,减小球晶尺寸,因此本文对PET／PEN／DBS共混体系中,组分组成的影响及不同结晶条件下共混物的结晶形貌进行研究。     

成核剂和促进剂对聚对苯二甲酸乙二酯结晶的影响

研究了一种成核剂和结晶促进剂及其混合物对聚对苯二甲酸乙二酯（ＰＥＴ）结晶过程和熔融行为的影响．结果表明,成核剂的引入降低了ＰＥＴ的结晶成核界面自由能,起到促进ＰＥＴ结晶成核的作用,从而加快了ＰＥＴ的结晶速度．而结晶促进剂对ＰＥＴ的结晶速度影响很小,不能促进ＰＥＴ的成核结晶,但能使ＰＥＴ结晶更完善,使ＰＥＴ的结晶度提高．当两者并用时,ＰＥＴ由熔体降温的结晶行为主要由成核剂控制,而成核促进剂的作用不明显．     

Role of the Confined Geometry on the Crystallization of Poly（ethylene terephthlate） Ultrathin Films

The reflection-absorption infrared (RAIR) was employed to study the crystallization kinetic of poly (ethylene terephthalate) (PET) ultrathin films. During isothermal crystallization the thinner PET film shows a slower kinetic compared with the thicker film. Moreover, the final crystallinity of films with various thickness was found decrease with thickness. The result of fitting our data to Avrami equation showed that the Avrami exponents decrease with film thickness.     

Isothermal and non-isothermal crystallisation kinetics of pCBT and PBT

The crystallisation behaviour of in situ polymerised cyclic butylene terephthalates (pCBT) and poly(butylene terephthalate)s (PBT) were studied by differential scanning calorimetry (DSC) both under isothermal and non-isothermal conditions. The crystallisation was analysed by adopting the Avrami, Ozawa and Kissinger methods for the isothermal and non-isothermal crystallisations, respectively. An Avrami exponent n between 2 and 3 was found for the pCBTs whereas the exponent ranged between 3 and 4 for the PBTs. The Ozawa exponent m varied for all materials between 2 and 3. Differences in the crystallisation kinetics were also reflected in the related activation energy data.     

Morphology, isothermal and non-isothermal crystallization kinetics of poly(methylene terephthalate)

The morphology of crystals, isothermal and non-isothermal crystallization of poly(methylene terephthalate) (PMT) have been investigated by using polarized optical microscopy and differential scanning calorimeter (DSC). The POM photographs displayed only several Maltese cross at the beginning short time of crystallization indicating that some spherulites had been formed. The crystal cell belonged to the Triclinic crystal systems and the cell dimensions were calculated from the WAXD pattern. The commonly used Avrami equation and that modified by Jeziorny were used, respectively, to fit the primary stage of isothermal and non-isothermal crystallization. The Ozawa theory was also used to analyze the primary stage of non-isothermal crystallization. The Avrami exponents n were evaluated to be in the range of 2-3 for isothermal crystallization, and 3-4 for non-isothermal crystallization. The Ozawa exponents m were evaluated to be in the range of 1-3 for non-isothermal crystallization in the range of 135-155 °C. The crystallization activation energy was calculated to be −78.8 kJ/mol and −94.5 kJ/mol, respectively, for the isothermal and non-isothermal crystallization processes by the Arrhenius’ formula and the Kissinger’s methods.     

Isothermal and nonisothermal crystallization kinetics of poly(propylene terephthalate)

The kinetics of crystallization of poly(propylene terephthalate) (PPT) samples of different molecular weights were studied under both isothermal and nonisothermal conditions. The Avrami and Lauritzen–Hoffmann treatments were applied to evaluate kinetic parameters of PPT isothermal crystallization. It was found that crystallization is faster for low‐molecular‐weight samples. The modified Avrami equation, and the combined Avrami–Ozawa method were found to successfully describe the nonisothermal crystallization process. Also, the analysis of Lauritzen–Hoffmmann was tested and it resulted in values close to those obtained with isothermal crystallization data. The nonisothermal kinetic data were corrected for the effect of the temperature lag and shifted alone with the isothermal kinetic data to obtain a single master curve, according to the method of Chan and Isayev, testifying to the consistency between the isothermal and corrected nonisothermal data. A new method for ranking of polymers, referring to the crystallization rates, was also introduced. This involved a new index that combines the maximum crystallization rate observed during cooling with the average crystallization rates over the temperature range of the crystallization peak. Furthermore, the effective energy barrier of the dynamic process was evaluated with the isoconversional methods of Flynn and Friedmann. It was found that the energy barrier is lower for the low‐molecular‐weight PPT. The effect of the catalyst remnants on the crystallization kinetics was also investigated and it was found that this is significant only for low‐molecular‐weight samples. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3775–3796, 2004     

Heterogeneous nucleation on the crystallization poly(ethylene terephthalate)

The crystallization behavior of poly(ethylene terephthalate) (PET) with disodium terephthalate (DST) as nucleating agent was investigated. A detailed analysis of the crystallization course from the melt was made with the Avrami expression. The results demonstrated that DST additive can promote the PET crystallization rate in its entire crystallizable temperature range, and the acceleration degree of DST decreases with increasing temperature after a temperature higher than 180 °C. The values of the Avrami exponent indicated that the crystallization mode in Avrami theory is not suitable for the crystallization of these polymers, and the mechanism of the heterogeneous nucleation on PET crystallization is discussed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2135–2144, 2003     

Isothermal crystallization studies of poly(butylene terephthalate) composites

Different crystallization kinetic models (Avrami and Tobin) have been applied to study the crystallization kinetics of virgin poly(butylene terephthalate) (PBT) and filled PBT systems under isothermal experimental conditions. The experimental data have been analyzed with a nonlinear, multivariable regression program. The kinetic parameters for the isothermal crystallization have been determined. The analysis results indicate that both models satisfactorily represent the isothermal crystallization kinetics. PBT crystallizes most slowly. The presence of nanoclays or nanofibers, added as fillers, enhances the crystallization rate of PBT composites. An analysis of the kinetic data with the Avrami and Tobin models has shown little change in the crystallization exponent compared with that of virgin PBT. The crystallization rate constant decreases with a rise in the temperature for the two models. This trend has been observed for similar polyester systems reported in the literature. The dispersion of the clay layers in the PBT nanocomposites has been characterized with wide‐angle X‐ray diffraction and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1344–1353, 2007     

Isothermal crystallization kinetics and melting behaviour of PET/ATO nanocomposites prepared by in situ polymerization

Neat poly(ethylene terephthalate) (PET) and PET/antimony doped tin oxide (ATO) nanocomposites were prepared by in situ polymerization. The study of the isothermal crystallization behaviors of neat PET and PET/ATO nanocomposites was carried out using differential scanning calorimetry (DSC). The crystallization kinetics under isothermal conditions could be described by the Avrami equation. For neat PET and PET/ATO nanocomposites, the Avrami exponent n both decreased with increasing crystallization temperature. In addition, for the same crystallization temperature, the value of n increased with increasing ATO content. These suggested that the crystallization types related to the values of n in the Avrami theory could not be suitable for the crystallization of PET and its nanocomposites. The change of the n values indicated that the addition of ATO resulted in the increase of the crystallizing growth points. That is a heterogeneous nucleating effect of ATO on crystallization of PET. In the DSC scan after isothermal crystallization process, multiple melting behavior was found. And the multiple endotherms could be attributed to melting of the recrystallized materials or the secondary lamellae produced during different crystallization processes. The equilibrium melting temperature of PET in the nanocomposites increased with increasing the ATO content. Surface free energy of PET chain folding for crystallization of PET/ATO nanocomposites was lower than that of neat PET, confirming the heterogeneous nucleation effect of ATO.     

Isothermal crystallization kinetics of poly(trimethylene terephthalate) under the influence of self-seeding nucleation

The effect of self-seeding nucleation on the crystallization behavior of poly(trimethylene terephthalate) (PTT) was studied. Differential scanning calorimetry (DSC) indicated that the crystallization temperature of PTT notably increased after self-seeding nucleation. Avrami equation was applied in the analysis of the isothermal crystallization process of PTT. The resulting average value of the Avrami exponent at n = 3.34 suggests that primary crystallization may correspond to a three-dimensional spherulitic growth. Self-seeding nucleation, leading to a decrease in active energy for crystallization and chain folding work, promotes the overall crystallization process of PTT. Translated from Acta Polymerica Sinica, 2006, (3): 414–417 (in Chinese)     

Crystallization of polypropylene,nylon-66 and poly(ethylene terephthalate) at pressures to 200 MPa: Kinetics and characterization of products

The crystallization kinetics of polypropylene (PP), polyamide (PA66), and poly(ethylene terephthalate) (PET) were studied, using a pressure dilatometer (to 200 MPa) to follow the volume changes associated with the crystallization process. The commonly used Avrami equation fitted the isothermal/isobaric crystallization data of PP and PA66 well. The Avrami exponent n was between 1.3 and 1.7, independent of crystallization pressure and temperature. Lines of constant Avrami rate parameter Z in the P-T plane were essentially parallel to the pressure dependence of the melting points and crystallization temperatures. However, the Avrami equation was not suitable for PET. The Malkin, Dietz, and Kim equations provided better fits. The crystallization half-time of PET increased with pressure at constant supercooling, in contrast to PP and PA66, for which it remained essentially unchanged. X-ray diffraction, differential scanning calorimetry, and pressure dilatometry were used to study the effect of formation pressure on the crystal structure, the melting point, and the density of products which were crystallized for short times (minutes) at various temperatures and pressures. No new crystal structures were found for PA66 and PET, but a mixture of monoclinic and triclinic crystals existed in PP above a formation pressure of 50 MPa. The melting points increased with formation pressure for PET, but remained unchanged for PP and PA66. Density at ambient conditions decreased with formation pressure for PP, but increased for PET and PA66. © 1994 John Wiley & Sons, Inc.