聚苯硫醚及其聚醚砜共混物结晶动力学的研究

本文采用DSC方法,研究了聚苯硫醚及其聚醚砜共混物的等温结晶动力学。结果表明,经α-氯代萘处理后的聚苯硫醚原粉结晶速率常数有明显提高;聚苯硫醚/聚醚砜共混物的Avrami指数较纯聚苯硫醚低,共混物的结晶速率常数随共混组成变化出现最低值;共混物存在明显的二次结晶现象,t_(?)与t_(max)之间存在线性关系。     

一种研究聚合物非等温结晶动力学的方法

作者基于多年对聚合物结晶动力学方面研究的工作积累,联合Avrami方程和Ozawa方程,提出了一种研究聚合物非等温结晶动力学的新方法.该方法既克服了使用Ozawa方程所获得的数据点过少,常常出现非线性,不能获得可靠的动力学参数的缺点,又克服了使用经Jeziorny修正的Avrami方程所获得的表观Avrami指数无法准确预测非等温过程成核生长机理的缺点.该方法已成功用于多种聚合物体系,被国内外学者引用数百次,已成为研究聚合物非等温结晶动力学一种有效方法.     

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     

Crystallization kinetics and multiple melting phenomena of a flame‐retardant phosphorus containing copolyester

Melt, cold isothermal crystallization kinetics, and multiple melting phenomena are investigated by differential scanning calorimetry (DSC) for a flame‐retardant phosphorus containing copolyester. The crystallization kinetics was investigated by the Avrami equation. The Avrami exponent is about 2.6 for melt crystallization and about 2 for cold crystallization. The crystallization activation energy for melt crystallization and for cold crystallization is −64.7 and 145.5, respectively. Three melting endotherms are found in the DSC scan, and they are explained in terms of secondary crystallization, primary crystallization, and recrystallization during the scan. A strong evidence of a two‐stage crystallization mechanism was also observed in the DSC isothermal experiment and X‐ray diffraction. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2269–2277, 1999     

去氢枞酸类成核剂改性聚丙烯的非等温结晶动力学研究

对以去氢枞酸盐为成核剂的聚丙烯非等温结晶动力学进行了研究，用修正Avrami方程的Jexiorny法和莫志深法进行处理。结果表明：修正Avrami方程的Jeziorny方法和莫志深法都适用于去氢枞酸类成核剂改性的聚丙烯的非等温结晶动力学。在同样的降温速率下纯聚丙烯的t1/2比成核聚丙烯的t1／2要长，当降温速率为20K/min时，纯聚丙烯和成核聚丙烯的t1/2分别为0．78min和0．51min。同时从莫志深法得到的F(T)结果可以看出，达到相同的结晶度时纯聚丙烯所需的降温速率要大于成核聚丙烯所需的降温速率，说明成核剂的加入提高了聚丙烯的结晶速率。从Jeziorny法求出的纯聚丙烯和成核聚丙烯的Avrami指数分别为4．46和2．77，表明成核剂改变了聚丙烯的结晶成核和生长方式。     

聚十二烷二元酸丁二酯及其共聚酯的结晶行为研究

聚十二烷二元酸丁二酯是长碳链脂肪族聚酯中的一种新的聚合物材料．近年来，随着对环境问题的日益重视，利用脂肪族聚酯容易水解的特性，开发生物降解脂肪族聚酯材料的研究得到广泛开展．目前脂肪族二元酸酯的研究大多是围绕聚丁二酸酯、聚乙二酸酯及其共聚酯这一类降解速度较快的材料进行的．虽然这些聚酯已有部分商品化，但远远不能满足对特定降解速率材料的需求．长碳链脂肪族聚酯由于其具有类似PE的结构特征，又兼具聚酯的结构特征，有望在可降解包装材料、书籍装订、服装用热熔胶等方面获得广泛的应用．     

间规1,2-聚丁二烯的非等温结晶动力学

结合Avrami和Ozawa方程,构筑了一个新的聚合物非等温结晶动力学方程.以铁催化体系间规1,2聚丁二烯(st- 1,2PB)为例,将新方法与其他常用的Jeziony和Ozawa方法的处理结果进行比较.发现由Jeziony方法分析得到的表观Avrami指数不能直接用于预测st -1,2PB的非等温结晶机理.由Ozawa方法分析实验数据,得到的线性关系很差,因此也很难得到可靠的动力学参数.而采用新方法可得到一系列线性关系较好的直线.根据新参数a与表观Avrami指数n和Ozawa指数m的关系,st -1,2PB的结晶机理可以预测且与等温方法获得的结果有可比性.这种新方法已应用于聚醚酮、聚酰胺、聚烯烃、烷基取代聚噻吩、聚(β-羟基丁酸酯)及其共混物等多种聚合物体系中.     

Crystallization Kinetics of Polypropylene and Poly (butyl methacrylate-co-hydroxyethyl methacrylate) Blend

The crystallization kinetics of polypropylene and poly (butyl methacrylate-co-hydroxyethyl methacrylate) blend was investigated with differential scanning calorimetry. The isothermal crystallization analysis based on the Avrami theory indicated a heterogeneous nucleating effect from the copolymer. A systematic study of the nonisothermal crystallization kinetics was undertaken using the Avrami equation and its later modifications by Ozawa, Mo, and Zhang. The results demonstrated that the linear relationship failed in the different cooling rates because the Avrami method did not take into account that the crystallization temperature was lowered continuously. The Ozawa and Mo methods could be successful in describing the overall nonisothermal process of polypropylene and the blend. In addition, the nonisothermal crystallization energy values were estimated by the Kissinger and Freidman models. There are two mutually opposite effects on the crystallization behavior of the blend: nucleation ability and growth retardation.     

聚苯硫醚及其碳纤维复合材料结晶动力学的研究

用膨胀计法研究了聚苯硫醚及其碳纤维复合材料的结晶动力学行为。发现其碳纤维复合材料对Avrami方程有较明显的偏离。聚苯硫醚具有中等的结晶速率,与PE、PMO等高聚物比较,它的σσ_c值、堆砌系数K_c以及结晶动力学方程中的前置指数G_0值较低。G_0是决定高聚物结晶速率的主要因素,ρ_a/ρ_c(值较小的高聚物有可能出现较高的结晶速率。     

Crystallization kinetics study of poly(L‐lactic acid)/carbon nanotubes nanocomposites

Effects of carbon nanotubes (CNT) on the isothermal crystallization kinetics of poly(L ‐lactic acid) (PLLA) were quantitatively investigated using the Avrami equation and the secondary nucleation theory of Lauritzen and Hoffman. CNT via grafting modification with PLLA could well disperse in the PLLA matrix and give significantly enhanced crystallization rate and crystallinity of PLLA as analyzed by differential scanning calorimetry and polarized optical microscopy. Analysis of isothermal crystallization kinetics using the Avrami equation demonstrated that CNT significantly enhanced the bulk crystallization of PLLA. Analysis of spherulite growth kinetics using the secondary nucleation theory of Lauritzen and Hoffman found that CNT could expand the temperature range of the crystallization regime III of PLLA. Values of the nucleation constant (K_g) in crystallization regimes III and II of PLLA both increased with increasing CNT contents. The K_g III/K_g II ratios were found to be close to the theoretical value 2 but were not clearly found to depend on the CNT contents. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 983–989, 2010     

Isothermal crystallization kinetics,morphology, and thermal conductivity of graphene nanoplatelets/polyphenylene sulfide composites

Graphene nanoplatelets (GNP) and polyphenylene sulfide (PPS) were used as filler and matrix, respectively, to produce composites. The PPS/GNP thermal composites were prepared via a melt blending method. The effects of GNP on crystallization behavior and kinetics, morphology, and thermal properties of PPS/GNP composites were investigated. To determine the isothermal crystallization kinetics parameters and isothermal crystallization activation energy, the Avrami model was used to comparatively analyze the relevant DSC experimental data. The results show that GNP provides an obvious heterogeneous nucleation effect on PPS to accelerate the crystallization and decrease isothermal crystallization activation energy. Thermal conductivity values of PPS/GNP composites with various GNP contents revealed that GNP remarkably increases thermal conductivity of composites mainly via a layered dispersion in PPS matrix. Thermal conductivity also increased with increasing GNP content, which was further improved at elevated temperatures. The thermal conductivities of PPS composite containing 30 mass% of GNP were 1.156 and 1.350 W m^?1 K^?1 at 30 and 110 °C, respectively, indicating an increase of more than 3 times compared with the neat PPS.     

Non-isothermal crystallization kinetics of hot drawn polyester films

The non-isothermal crystallization kinetics of hot drawn poly(ethylene terephthalate) films were studied using the Kissinger and Ozawa equations. The influence of the initial drawing on the crystallization kinetics was investigated. The values of the apparent activation energy and of the Avrami exponent indicates that the nucleation and growth of crystallites depend greatly on the stress submitted to the samples.     

Nonisothermal bulk crystallization studies of high density polyethylene using light depolarizing microscopy

The quiescent nonisothermal bulk crystallization kinetics of two high-density polyethylene resins were investigated by a modified light-depolarizing microscopy (LDM) technique. The technique allows studies at average cooling rates up to 2500°C/min. The polymer was found to crystallize at a pseudo-isothermal temperature even at these very high cooling rates. The overall bulk crystallization rate increased rapidly as the cooling rate and supercooling increased. Crystallization kinetics was analyzed by Avrami analysis. Avrami exponents near 3 suggested spherical growth geometry and instantaneous nucleation at predetermined sites. Observation of spherulites by optical microscopy together with a number density of spherulites that changed little with increase in cooling rate or supercooling supported this model of crystallization behavior. Analysis of the half-time of crystallization based on the Lauritzen and Hoffman secondary nucleation theory indicated that the regime II-III transition was found to occur at a degree of supercooling of approximately 22°C. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 681–692, 1998     

Interpretation of the nonisothermal crystallization kinetics of polypropylene using a power law nucleation rate function

A nucleation rate function is proposed for use in analyzing the overall crystallization kinetics of polymers. This function allows for the possibility that the nucleation rate varies substantially during the crystallization. This feature is particularly useful in analyzing nonisothermal crystallization, but it can be used to analyze isothermal crystallization as well. The nucleation rate function was used in the derivation of a modified transformation kinetics equation of the Avrami type. The modified Avrami equation was found to be suitable for kinetics analysis for the data obtained from nonisothermal crystallization at rapid cooling rates. Kinetics parameters used to describe nonisothermal crystallization under rapid cooling rates are presented and discussed. These include crystallization induction time, plateau (crystallization) temperature, crystallization half-time, crystallization rate constant, Avrami index, and newly defined quantities called nucleation index, geometric index, and nucleation rate constant. The procedure used to obtain the nucleation rate constant and nucleation index for the nucleation rate function is described and illustrated by application to the analysis of the crystallization kinetics of polypropylene. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1077–1093, 1997     

Reflection–absorption infrared spectroscopy investigation of the crystallization kinetics of poly(ethylene terephthalate) ultrathin films

Reflection–absorption infrared spectroscopy was used to study the crystallization behavior of poly(ethylene terephthalate) (PET) ultrathin films. The crystallinity of ultrathin films was estimated by the fraction of trans conformers of PET. The isothermal and nonisothermal crystallization kinetics of ultrathin films with different thicknesses were investigated. The thinner PET film showed slower kinetics during isothermal crystallization than the thicker film. Moreover, the final crystallinity of films with various thicknesses were reduced with decreasing thickness. An Avrami equation was used to fit the acquired results. The Avrami exponents decreased with the film thickness. As for the nonisothermal crystallization, the cold‐crystallization starting temperature shifted to a lower temperature as the film thickness increased. The influence of the substrate on the crystallization kinetics of the films was also studied. The half‐crystallization times and final crystallinities of ultrathin films adsorbed onto a self‐assembled‐monolayer‐treated surface and an untreated substrate were clearly different, although their thickness dependence was similar. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4440–4447, 2004     

Crystallization kinetics for low‐ether‐content polyether–polyester block copolymers with amide linkages

A series of low‐ether‐content polyether–polyester block copolymers with amide linkages were synthesized. Their crystallization kinetics and mechanisms were investigated. The crystallization kinetics were analyzed via Avrami treatment; an average value of 1.8 for the Avrami index was thus obtained. Athermal nucleation was evidenced by observations of a linear boundary between impinged spherulites under polarized light microscopy and transmission electron microscopy. The development of spherulitic morphology with a hedgehog texture was attributed to the mechanism of lamellar branching. On the basis of the morphological observations and Avrami analysis, a crystallization mechanism through a heterogeneous nucleation process with homogeneous lamellar branching was proposed. No regime transition was found for polyether–polyesters in the examined temperature ranges, and the crystallization was identified as regime I kinetics on the basis of a Lauritzen Z test. The copolymerization of poly(ether amide)s with polyesters led to a significant suppression of the crystallization rate of polyester crystals. The suppression was explained as the result of a dilution effect in nucleation combined with an increasing nucleation barrier. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2469–2480, 2001     

Effect of silver nanoparticles on the morphology,crystallization, and melting behavior of polypropylene: A study on non-isothermal crystallization kinetics

The nanocomposites were prepared using melt intercalation method and the effects of the processing conditions on silver nanoparticles dispersion were investigated by transmission electron microscopy. Non-isothermal crystallization kinetics of virgin polypropylene (PP) and its nanocomposites have been evaluated using differential scanning calorimetric technique. The non-isothermal crystallization melt data were analyzed using macro kinetics equation with the help of Avrami, Malkin, and Mo’s models. The crystallization rate increased with the increasing of cooling rates for virgin PP and nanocomposite, but the crystallization of nanocomposite was faster than that of PP at a given cooling rate. The activation energy for non-isothermal crystallization of virgin polymer and nanocomposites based on Kissinger method has been determined to be 186 and 211 kJ/mol, respectively. Transmission electron microscopy analysis reveals balanced dispersion and presence of some silver nanoparticles aggregates, which act as a heterogeneous nucleating agent during the crystallization of the nanocomposite.     

Crystallization Kinetics of Polypropylene-polyethylene-based Copolymers

A crystallization kinetics analysis of several polypropylene-polyethylene (PP-PE), PP-rich copolymers was made by means of differential scanning calorimetry. The crystallization was studied via calorimetric measurements at different cooling rates. Several additives were added to the base material. Some test samples were subjected to artificial ageing processes. A modified isoconversional method was used to describe the crystallization process under non-isothermal conditions. The value of the Avrami parameter was determined for primary and secondary crystallization. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

苯乙烯-丙烯嵌段共聚物等温结晶动力学的研究

用DSC法研究苯乙烯-丙烯嵌段共聚物(iPS-b-iPP)的等温结晶动力学。结果表明,在所选择的结晶温度(127～132℃)范围内,共聚物很好地符合Avrami动力学方程;共聚物结晶温度、结晶速率、结晶成核和生长方式都与共聚物结构和组成比有关,随着嵌段共聚物中iPS段含量的增加,结晶速率和Avranu指数(n)明显降低。