Crystallization kinetics of new copoly(ethylene terephthalate-imide)s

Crystallization kinetics of copoly(ethyleneterephthalate-imide)s (PETIs) of various imide contents were studied by the DSC technique. The results of isothermal and nonisothermal crystallization kinetics studies showed a consistent trend in that the crystallization of all copolyesterimides comprised a primary stage and secondary stage, and that the crystallization mechanism was a three-dimensional growth with athermal nucleation. The crystallization rate of PETIs first increased and then decreased as the content of imide units in the copolyesterimides increased. This indicates that the imide units in the copolymer decreased the chain-packing regularity of poly(ethylene terephthalate) (PET) and the same units also enhanced the copolymer chain rigidity. The copolyesterimide with 0.2 mol% imide unit content showed a dramatic increase of the crystallization rate, and exhibited the highest crystallization rate of all the studied compositions. Studies of isothermal and nonisothermal crystallization kinetics, showed that small amounts of imide units in the the backbone act as nucleating agents during the crystallization process of copolyesterimides.     

聚对苯二甲酸丙二醇酯的结晶性能研究

采用热台偏光显微镜和DSC差示扫描量热仪对PET、PTT和PBT的结晶性能进行了研究。实验得到的结果是:PBT具有极强的结晶能力。在相同的△T下,PTT的结晶诱导期和球晶出现的时间比PET短,球晶的生长速率也比PET快;同时,在相同的△T下,PTT的总结晶速率大于PET。PET和PTT在较高的温度下等温结晶时倾向于异相成核,而随着等温结晶温度的降低,开始倾向于均相成核。     

研究高聚物结晶动力学的等速升温 DSC 方法

本文把等温 Avrami 方程推广应用于等速升温的非等温结晶过程。从推广的方程可得到Avrami 方程能得到的结晶动力学参数,如 Avrami 指数 n、复合结晶速度常数 K 和结晶半衰期t_(1/2)。等速升温方法可克服用 DSC 进行等温扫描时在实验上的不足,具有实验简单、获取的结晶信息量较大的特点。用 DSC 对 PET 树脂进行了等速升温结晶和等温结晶实验,并分析了实验结果。结果表明,由升温 DSC 方法得到的 n 和 t_(1/2)比等温方法稍大,K 则稍小。等温结晶结果与非等温结晶结果稍有不同的原因之一可能是这两种结晶过程的结晶机理有差别。等温结晶结果与非等温结晶结果的一致性是令人满意的。     

Crystallization of running filament in melt spinning of polypropylene

The crystallization kinetics of the running filament in melt spinning have been studied for three cases: isothermal crystallization of an isotropic melt, non-isothermal crystallization of an isotropic melt, and non-isothermal crystallization of a non-isotropic melt. Both the temperature and the orientation dependences of nucleation rate and growth rate are estimated for polypropylene. Calculated curves for non-isothermal crystallization of a non-isotropic melt with partial high orientation closely approximate the experimental data. In particular, the experimental data are best explained by crystallization with two-dimensional growth. The crystallization processes in melt spinning may be governed by localized molecular orientation of the supercooled melt in the initial stage.     

Effect of high content of carbon black on non-isothermal crystallization behavior of poly(ethylene terephthalate)

With the aid of co-rotating twin screw extruder, poly(ethylene terephthalate) (PET)/carbon black (CB) masterbatches were fabricated through melt-compounding using a separate feeding and metering technique and their homogeneous dispersion morphologies were confirmed by scanning electron microscopy and transmission electron microscopy. Moreover, the ultimate content of CB in the masterbatches was verified via thermogravimetric analysis method. The non-isothermal crystallization process of pristine PET and PET/CB masterbatch were investigated by differential scanning calorimetry and the different methods such as Jeziorny modified Avrami equation, Ozawa equation, and the method developed by Mo were employed to analyze their non-isothermal crystallization kinetics. The results show that CB particles uniformly dispersed in PET matrix act as heterogeneous nucleating agents, while crystallization activation energy (ΔE) of PET/CB masterbatch is much greater than that of virgin PET according to Kissinger formula, Takhor model, and Augis-Bennett model. Whereas, the results obtained from the above mentioned three methods simultaneously demonstrate the addition of CB greatly increases crystallization temperature and crystallinity and accelerates crystallization rate. The results reveal that crystal growth has little effect on the crystallization rate and crystal nucleation dominates the crystallization process of PET/CB masterbatch containing very high CB loading (20 wt%).     

氧化铁包覆云母对聚对苯二甲酸乙二醇酯非等温结晶动力学的影响

以氧化铁包覆云母为成核剂,对聚对苯二甲酸乙二醇酯（PET）进行成核改性,采用差示扫描量热法分别研究了不同降温速率下PET和PET/氧化铁包覆云母复合材料的非等温结晶行为,用Jeziorny法和莫志深法对非等温结晶过程进行了分析,并用Flynn-Wall-Ozawa法计算其活化能。结果表明：氧化铁包覆云母对PET具有异相成核的作用,可明显提高PET的结晶速率;与Jeziorny法相比,莫志深法可较好描述PET和PET／氧化铁包覆云母复合材料的非等温结晶过程。进一步分析表明,氧化铁包覆云母的加入并没有明显改变PET基体的成核机理和生长方式,但降低了PET的结晶活化能,从而提高了PET的结晶性能。     

水溶性聚酯的结晶性能研究

研究了水溶性聚酯(W SPET)切片的结晶性能,并与常规聚酯(PET)切片相对比。结果表明W SPET切片与PET切片具有相同的非等温结晶行为,在非等温条件下的结晶机理以异相成核为主,在有限的三维体积中生成球晶,但W SPET切片的结晶速率明显慢于PET切片,结晶能力明显弱于PET切片。     

Kinetics of non-isothermal cold crystallization of uniaxially oriented poly(ethylene terephthalate)

The non-isothermal equation was extended to describe non-isothermal cold crystallization kinetics of oriented polymers. The validity of the equation was examined by using a DSC crystallization curve of oriented poly(ethylene terephthalate) (PET) fibers with a constant heating rate. The double cold crystallization peaks appeared in the DSC curve. The relative degrees of crystallinity at different temperatures were analyzed by using the equation. The results show that the value of the Avrami exponent near to 1 at lower temperatures implies the bundle-like crystal growth geometry and the value of the Avrami exponent near to, 2, at higher temperatures implies the higher dimension crystal growth geometry. The first crystallization process crystallizes at faster rate than that of the isotropic sample, while the second process crystallizes at slower rate than that of isotropic sample. If a simple single process model was used, the value of the Avrami exponent, 0.77, was obtained. The result shows the simple single process model cannot describe the processes of crystallization of oriented PET fibers satisfactorily.     

Effects of oxidative functionalized and aminosilanized carbon nanotubes on the crystallization behaviour of polyamide-6 nanocomposites

The purpose of this study is to investigate effects of oxidative functionalized and aminosilanized carbon nanotubes on the (1) isothermal and (2) non-isothermal crystallization kinetics of polyamide-6 by DSC analyses, and (3) crystal structure of injection molded specimens by XRD analyses. Nanocomposites were compounded by using melt mixing technique via twin screw extrusion. Due to basically very effective heterogeneous nucleation effect, both increasing amount and surface functionalization of carbon nanotubes by oxidation and aminosilanization resulted in higher relative crystallinity for all three cases. The increases were as much as 40 % for the isothermal and non-isothermal crystallization, and it was up to more than two times in the injection molding. Crystallization parameters and Avrami constants indicated that crystallization rate increases in isothermal crystallization while it decreases in non-isothermal crystallization due to the delayed conformational mobility of polymer chains via physical hindrance of carbon nanotubes. Parameters also revealed that growth mechanism of crystallites might change during isothermal crystallization while there was no significant change during non-isothermal crystallization. XRD deconvolution analyses indicated that during injection molding, due to the constraints of carbon nanotubes only α-crystal structure was formed.     

不同二氧化钛含量的PET非等温结晶动力学研究

用DSC、非等温结晶动力学方法研究了PET切片中不同二氧化钛含量对其结晶性能的影响。结果表明:适量的二氧化钛在聚合过程中起成核剂作用,随着切片中二氧化钛含量的增加,聚合物结晶速度加快,质量分数超过0.33％时,对熔体成核结晶有阻滞作用。结晶能力在冷却速率和二氧化钛含量变化时基本不变,说明二氧化钛的加入对聚合物的结晶能力影响不大。不同二氧化钛含量不同冷却速率的Avrami指数平均值都在4.0以上,可以认为结晶以均相成核为主,三维生长。     

DSC studies on the crystallization characteristics of poly(ethylene terephthalate) for blow molding applications

The crystallization behavior of blow-molded PET bottles, which helps determine the product's transparency, was investigated by DSC dynamic cooling experiments that simulated the cooling that occurs in the injection blow-molding manufacturing process. Dynamic cooling crystallization of PET optimized the conditions for keeping crystallinity to a minimum during the production of PET bottles. The kinetic parameters of non-isothermal crystallization behavior were determined, which indicate that the competing processes of nucleation and the growth of PET spherulites during the cooling process are the controlling factors for the degree of crystallinity in the final product. In addition, DSC measurements were employed to obtain information on related aspects, such as the ease of crystallization from glassy and molten states and the crystallinity in the products. An Avrami equation was used for the calculations of the crystallization kinetic parameters.     

Characterization of thermal behavior and kinetics of crystallization of a thermotropic rigid-chain copolymer

Thermal analysis was employed to estimate the heat of transition, equilibrium melting temperature and surface free energy of a thermotropic liquid crystal copolyester resin (70 mol% p-hydroxybenzoic acid and 30 mol% 2,6-hydroxynaphthoic acid). Specific heats and melting and crystallization behavior were evaluated using differential scanning calorimetry (DSC). Experiments over a wide range of cooling rates indicate two different crystallization processes: a rapid crystallization process and a slow crystallization process. The kinetics of the rapid crystallization process were evaluated using a non-isothermal method. The analysis indicates that the rapid crystallization process can be suitably described by the non-isothermal Avrami equation. The Avrami exponent is found to be equal to 2, which is in agreement with the nucleation and growth mechanism of the rigid rodlike molecules. The kinetics of the slow crystallization process, which were studied using an isothermal method, indicate that the degree of crystallinity varies linearly with log(time). The equilibrium melting temperature for this process is found to be 372°C. The Arrhenius plot yields a linear relationship in the lower temperature range.     

Irregularly shaped DSC exotherms in the analysis of polymer crystallization

Summary This article details a study of irregularly shaped DSC exotherms of poly(3-hydroxybutyrate) (PHB) developed during isothermal and non-isothermal crystallization. Due to the extreme purity of the polymer, PHB crystallization is mainly initiated by homogeneous nucleation, with the formation of very large spherulites, especially under slow nucleation conditions. When the number of growing spherulites is low, the evolution of latent heat is very sensitive to every act of nucleation as well as to the space limitations in the process of growth, resulting in non-monotonous development of latent heat, with sudden increases and decreases in crystallization rates. This results in non conventional DSC exotherms, under given crystallization conditions, characterized by spikes or shoulders associated to nucleation of new spherulites.     

Crystallization kinetics and morphology of nylon 1212

The isothermal and non-isothermal crystallization processes of nylon 1212 were investigated by polarized optical microscopy. The crystal growth rates of nylon 1212 measured in isothermal conditions at temperatures ranged from 182 to 132 °C are well comparable with those measured by non-isothermal procedures (cooling rates ranged from 0.5 to 11 °C/min). The kinetic data were examined with the Hoffman-Lauritzen nucleation theory on the basis of the obtained values of the thermodynamic parameters of nylon 1212. The classical regime I→II and regime II→ III transitions occur at the temperatures of 179 and 159 °C, respectively. The crystal growth parameters were calculated with (100) plane assumed to be the growth plane. The regime I →II→ III transition is accompanied by a morphological transition from elliptical-shaped structure to banded spherulite and then non-banded spherulite. The development of morphology during isothermal and non-isothermal processes shows a good agreement.     

Crystallization morphology and crystallization kinetics of poly(lactic acid): effect of <Emphasis Type="Italic">N</Emphasis>-Aminophthalimide as nucleating agent

The effect of N-Aminophthalimide compound (NA-S) as nucleating agent on crystallization behavior and morphology of poly(lactic acid) was studied. With polarized optical microscope (POM), the unique phenomena of nucleation and epitaxial crystallization of PLA/NA-S system were observed. Dynamic morphology of crystallization was also studied by POM to investigate the relationship between growth behavior of PLA and nucleating agent. Isothermal and non-isothermal crystallization behavior of PLA were studied by differential scan calorimeter (DSC). When nucleating agent was added, a new peak appeared in wide angle X-ray diffraction (WAXD) compared with pure PLA, indicating the nucleating effect of NA-S on crystallization of PLA. All the results indicate that the nucleating agent of NA-S shows obvious nucleating effect on isothermal crystallization above 120 °C and in non-isothermal crystallization after it is added in PLA, that is, the induction crystallization time is reduced, the crystallization rate and nucleation density of PLA are increased.     

PET/PP共混体系的熔融及非等温结晶行为

用熔融共混法制备了聚对苯二甲酸乙二醇酯(PET)/聚丙烯(PP)复合材料。对复合体系的形态结构、熔融及非等温结晶行为进行了研究。结果表明:两相界面或PP相对PET结晶无明显的异相成核效应;当PP为连续相时,已结晶的极性PET粒子对PP的异相成核作用较为明显;而当PP为分散相时,固态的PET在一定程度上阻碍了PP分子链的运动,促使PP结晶均相成核趋势增加。与纯PET或PP相比,共混体系中两组分结晶的完善程度都有所下降。     

SEBS-g-MAH对聚乙烯等温及非等温结晶动力学的影响

利用差示扫描量热法结合Avrami方程研究了苯乙烯-乙烯-丁烯-苯乙烯嵌段共聚物接枝马来酸酐(SEBS-g-MAH)对线型低密度聚乙烯(LLDPE)等温及非等温结晶动力学的影响。结果表明,热塑性弹性体SEBS及其接枝物的加入阻碍了LLDPE分子链的规则排列,影响了链段在结晶扩散迁移规整排列的速度,使得结晶速率变慢,对LLDPE晶体生长起了抑制作用;LLDPE/SEBS-g-MAH共混体系的半结晶时间t1/2和结晶活化能E明显增大,Avrami指数n对结晶温度有依赖性,kn值随温度的升高而减小。通过Jeziorny法对非等温结晶过程进行处理,试样的Avrami指数n值均在1.1~1.5,表明LLDPE的结晶成核机理和生长方式没有改变。     

Study on Crystallization Behavior of Solid-Phase Graft Copolymers of Polypropylene with Maleic Anhydride and Methyl Methacrylate

The isothermal crystallization behavior of neat polypropylene (PP) and solid-phase graft copolymers of PP with maleic anhydride and methyl methacrylate (PPMM) were compared by differential scanning calorimetry. The Avrami equation and Hoffman theory were applied to describe the isothermal crystallization kinetics. The results show that the fitted isothermal crystallization parameters are similar to the experimental data, and suggest that the Avrami equation is suitable to describe the isothermal crystallization process of PP and PPMM. The grafted side chains on PP can change the nucleation and growth of crystallization. They caused a decrease in the apparent crystallization activation energy and lateral surface free energy, and an increase in the nucleation rate. This was attributed to the grafted side chains not only acting as nucleating agent but also hindering the motion of the molecular chains and reducing the growing rate of crystallization.     

原位聚合二氧化硅改性聚酯的非等温结晶性能研究

用DSC方法研究了原位聚合制备的不同尺寸二氧化硅改性聚对苯二甲酸乙二醇酯(PET)冷结晶、熔融结晶过程中的非等温结晶动力学。结果表明,SiO_2的加入使聚酯的结晶能力增强;SiO_2粒径尺寸越小,在聚酯中起到成核剂的作用越明显,PET的结晶速度也越快,在结晶过程中形成的晶粒尺寸分布越窄。     

The nucleation, crystallization and dispersion behavior of PET-monodisperse SiO2 composites

To more accurately investigate the nucleation, crystallization and dispersion behaviors of silica particles in polymers, the composites of PET with monodisperse SiO₂-PS core-shell structured particles were prepared with SiO₂ size from 380 nm to 35 nm.For these SNPET samples, DSC results showed that the nucleation rate of silica particles increased as their size decreased, in which 35 nm SiO₂ particles produced the most obvious nucleation effect. At 2.0 wt.% load of 35 nm silica, Avrami equation proved that the isothermal crystallization rate G of SNPET was ca. 30% higher than that of pure PET and the crystallization activation energy for SNPET was −218.7 kJ mol⁻¹ lower than −196.1 kJ mol⁻¹ for PET. While, the non-isothermal crystallization ΔE for SNPET was −199.8 kJ mol⁻¹ lower than −185.5 for PET.On non-isothermal crystallization, Jeziorny equation presented the primary and secondary crystallization stages in PET and SNPET, in which nano SiO₂ accelerated the crystallization rate. Their Ozawa number m was from 2.1 to 2.7, which was smaller than that of Avrami number n.The nucleation and dispersion behaviors of SiO₂ particles were directly observed. POM results demonstrated that SNPET samples crystallized more quickly from melt and their crystallization rate increased as silica load increases but accelerated at 2-3 wt.%. The spherulites grew well in PET but their size was smaller in SNPET due to the silica barrier on their growth. SEM and TEM observed the homogeneous silica dispersion morphology and the vivid ordered patterns formed in SNPET. The monodisperse particles are highly expected to give more accurate and valuable references than multi-scale ones in obtaining novel advanced PET composites.