测定高聚物动力学结晶能力的非等温DSC方法

研究了从非等温ＤＳＣ结晶曲线计算高聚物动力学结晶能力的方法．从高聚物非等温结晶动力学微分方程出发导出了计算高聚物动力学结晶能力的新方程．以含有不同催化剂的聚对苯二甲酸乙二酯为例，对其结晶进行了测试与计算．发现合理地选定最快结晶速率温度是计算动力学结晶能力的关键．本方法所得动力学结晶能力能正确反映高聚物的整体结晶信息     

高聚物非等温结晶动力学

由于等温ＤＳＣ法测定结晶动力学参数在实验上存在着一定的局限性，这些缺点可通过非等温ＤＳＣ法来克服。本文基于上述观点介绍了高聚物非等温结晶动力学的理论和实验方法，并对影响动力学过程的一些因素进行了讨论，对非等温结晶动力学的最新情况及发展倾向，应用情况作了介绍。     

测定高聚物结晶动力学参数的非等温理论和方法

对测定高聚物结晶动力学参数的非等温结晶理论和等速变温ＤＳＣ方法进行了讨论，文中包含了作者在此领域研究工作的最新进展。     

固相缩聚PET等温结晶动力学

高聚物等温结晶动力学方面的研究者甚多,由熔融缩聚制备的不同分子量PET的等温结晶动力学及几种不同缩聚催化体系固相缩聚PET的等温结晶动力学已有报道.本文采用一个修正的Avrami方程对固相缩聚PET样品进行系统的等温结晶动力学研究.     

聚合物结晶动力学

本文介绍了聚合物等温及非等温结晶动力学过程的理论和实验方法，对影响动力学过程的一些因素进行了讨论。     

取向聚对苯二甲酸乙二酯纤维的非等温结晶动力学

取向聚对苯二甲酸乙二酯纤维的非等温结晶动力学张志英，赵家森（天津纺织工学院材料科学系天津３００１６０）关键词取向高聚物，聚对苯二甲酸乙二酯，非等温结晶，结晶动力学研究高聚物结晶动力学常用的等温方法有光透射法、密度法、显微镜法、Ｘ－射线衍射法、差示扫描...     

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     

PET/PEN/DBS共混物非等温结晶动力学研究

采用DSC方法, 用修正的Avrami, Ozawa, Ziabicki宏观动力学模型描述PET/PEN/DBS[PET: 聚对苯二甲酸乙二醇酯; PEN: 聚2,6-萘二甲酸乙二醇酯; DBS: 1,3∶2,4-二(亚苄基)-D山梨醇]共混物的非等温熔融结晶过程, 研究结果表明, 修正的Avrami模型能很好地描述此共混物非等温结晶过程. 冷却速率在5-20 ℃/min范围内, Ozawa方程能很好地描述初期结晶过程, 但结晶后期由于忽略次级结晶而不适宜. 由Ziabicki结晶动力学参数可知, 该共混物的结晶随着成核剂DBS含量的增加而降低, 结晶速率随着成核剂DBS含量的增加而提高. 在非等温结晶条件下, 共混物结晶同时受到冷却速率和共混物组成的影响, 与共混物非等温结晶过程的有效能垒分析结果基本一致.     

尼龙1010非等温结晶动力学与机理研究

尼龙１０１０非等温结晶动力学与机理研究朱诚身，王经武，李卓美（郑州大学材料工程系郑州４５００５２）（中山大学高分子研究所广州５１０２７５）关键词尼龙１０１０，非等温结晶动力学，结晶机理，动力学结晶能力尼龙１０１０的结晶动力学，无论是等温还是非等温，研...     

高聚物的非等温结晶动力学——从不同速率的升温或降温DSC曲线解析结晶动力学参数

根据等温DSC法,测定结晶动力学参数在实验上存在着一定的局限性,结晶太快或太慢都难于获得可靠的结果,这就限定了能测定的温度区间。可见,等温DSC法测定结晶动力学参数具有获得的信息量少,结晶起始点难以确定,费时等缺点。这些缺点可通过等速变温DSC法来克服。然而,通过等速变温DSC法测定结晶动力学参数的方法至今还不完善。例如Ozawa曾基于Evans理论把Avrami方程推广于非等温结晶,从Ozawa方程通过等速变温DSC曲线可得到表征结晶机理的函数Avrami ＄数。和冷却结晶函数。Ozawa方法的不足是从其冷却结晶函数不能解析出表征结晶速率的参数。     

溶液间歇结晶过程成核与生长阶段的定量识别

为定量识别溶液间歇结晶过程中的成核和生长阶段,基于晶粒数目和粒度的变化对粒度分布(CSD)的二阶和三阶矩量影响程度的不同,定义并关联了无因次变量K和K^*.添加晶种KNO₃-H₂O溶液结晶过程模拟计算的结果表明,K和K^*值均呈先降后升的变化趋势,成核时单调下降,生长过程中单调上升;且K与K^*值较接近.测定了KNO₃-H₂O溶液自发成核结晶过程中溶液浓度和透光率的变化,用K^*判据定量识别出成核阶段和生长阶段,并与晶体线性生长速率模型检验的结果相吻合.K值的计算依赖于CSD和结晶动力学参数,而K^*作为成核和生长阶段的模型判据,由实验测定的溶液浓度和透光率计算得到.     

穿插程度对高分子链结晶初始阶段的影响

用分子动力学方法模拟了具有不同穿插程度的寡链凝聚体系结晶初始阶段的有序化过程. 链间穿插程度通过径向分布函数的统计进行表征. 模拟计算结果表明, 链间的穿插程度对体系的有序化过程具有明显的影响, 穿插程度越小的体系有序化越快, 形成的有序结构也更完整. 与实验结果的比较表明, 在聚合物粒子结晶的初始阶段, 体系由穿插引起的缠结就已经起到了作用.     

Spherulitic growth rates and morphology of absorbable poly(p‐dioxanone) homopolymer and its copolymer by hot‐stage optical microscopy

Hot‐stage optical microscopy was used to study the crystal morphology, nucleation, and spherulitic growth rates of poly(p‐dioxanone) (PDS) homopolymer and an 89/11 PDS/glycolide segmented block copolymer. A wide range of crystallization conditions were experimentally accessible, allowing the inspection of various morphological features and accurate estimations of characteristic growth parameters, including radial growth and nucleation rates. Although the regime analysis of the crystallization kinetics indicated no breaks in the growth rate curve, the isothermal data were in excellent agreement with the Hoffman–Lauritzen theory. Spherulitic growth rates obtained from optical measurements are compared with values of the half‐time of crystallization determined earlier by differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3073–3089, 2001     

Isothermal crystallization kinetics and spherulitic morphology of poly(4‐hydroxybutyric acid‐alt‐glycolic acid)

Isothermal crystallization behavior of a new regular polyester constituted by glycolic acid and 4‐hydroxybutyric acid units is studied by means of differential scanning calorimetry and hot‐stage optical microscopy. A wide range of crystallization conditions were experimentally accessible, allowing various morphological features to be observed and accurate estimates made of characteristic growth parameters, including radial growth and nucleation rates. Three‐dimensional spherulitic growth from heterogeneous nuclei is deduced from the Avrami analysis, whereas optical micrographs reveal two different spherulitic textures that agree with the existence of two crystallization regimes. These can be well distinguished from the breaks observed in the Lauritzen and Hoffman plots when the linear crystal growth rate or the overall crystallization rate is considered. Ringed and nonringed spherulites with negative and positive birefringence, respectively, can be obtained depending on crystallization conditions and regimes. The studied polyester shows rather complex melting behavior which is interpreted in terms of a recrystallization process involving the two different kinds of spherulites. This study allows polymorphism to be discounted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2640–2653, 2007     

New Developments in Crystallization Processing

The intention of this work presented is to introduce new processing principles for the crystallization of watery or fatty phases in food systems, and in particular to quantify the process — microstructure — product quality relationships for such food systems. The crystallization processes demonstrated in detail are high shear crystallization (i), spray crystallization (ii) and spray powder based seed crystallization (iii). Crystalline, semi-crystalline and/or amorphous structures were analysed by calorimetric, mechanical/rheological and microscopical methods. Quality aspects of the final food products, which are related to the structure of the crystalline and/or amorphous components, were investigated additionally.This revised version was published online in November 2005 with corrections to the Cover Date.     

A crystalline paradise – three substances exhibiting the following crystallization modes: (1) conglomerate,kryptoracemic and unbalanced (2) conglomerate and kryptoracemic

The compound bis(ethylenediamine-N,N′)-(oxalato-O,O′)-cobalt biphenyl-4,4′-disulfonate hydrate, refcode TIQHOR, crystallizes with four Co(III) cations in the asymmetric unit. Another pair of compounds, rac-bis(ethylenediamine-N,N′)-(oxalato-O,O′)-cobalt(III) l-hydrogenaspartate, refcode VAGBOU, and tetra-ammine-(N-benzylethanediamine)-cobalt(III) trinitrate sesquihydrate, refcode ZIFHEB crystallize both as conglomerates and kryptoracemates. Their stereochemical characteristics are described, and the fact that they display more than one mode of crystallization in a single lattice, is illustrated numerically and visually.     

Fractionated crystallization of α‐ and β‐nucleated polypropylene droplets

A layer multiplying coextrusion process was used to produce multilayered polypropylene/polystyrene (PP/PS) films with various nucleating agents. When heated into the melt, the thin PP layers broke up into submicron PP droplets that exhibited fractionated crystallization. If the initial PP layers were 20 nm or less, the resulting droplets exhibited exclusively homogeneous nucleation. If a nucleating agent was added, the systematic departure from homogeneous nucleation provided insight into the nature of the heterogeneous nucleation. In this study, we used thermal analysis, atomic force microscopy (AFM), and wide angle X‐Ray scattering (WAXS) to examine the effect of two nucleating agents. We confirmed with WAXS and AFM that a soluble sorbitol nucleating agent for the PP α‐form operates in three concentration regimes as proposed in a previous study. Morphologically, homogeneous nucleation of the submicron droplets produced a granular texture. The correlation length from small‐angle X‐Ray scattering (SAXS) suggested that the grains contained 1–3 mesophase domains. Drawing on classical nucleation theory, the critical size nucleus of an individual mesophase domain was estimated to be about 2 nm³, which was considerably smaller than the mesophase domain. This pointed to mesophase crystallization that included the processes of nucleation and growth. Additional experiments were performed with nucleating agents for the PP β‐form. However, they were not effective in nucleating crystallization of the droplets, presumably because they were essentially insoluble in PP and the nucleating particles were too large to be accommodated in the PP droplets. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Kinetic study of the crystallization processes of some decorative ceramic glazes

A kinetic study of the crystallization processes was performed for some decorative ceramic glazes in the PbO-SiO₂-Na₂O-K₂O-CaO(BaO)-Al₂O₃-B₂O₃ system with addition of 10% TiO₂ and ZnO. The crystallization kinetics has been studied in non-isothermal conditions using DTA technique. The apparent activation energies of the crystallization processes were calculated using the Kissinger method. The main crystalline phase, which provides the decorative effect, is rutile. This has been identified by X-ray diffraction and it is clearly visible in the optical microscopy images taken in transmitted light, as needle-like or even prismatic crystals arranged in radial-fibrous aggregates.     

反式-/顺式-1,4-聚异戊二烯共混体系的结晶动力学

采用差示扫描量热(DSC)法对反式-/顺式-1,4-聚异戊二烯共混体系的等温及非等温结晶动力学进行了研究,分别采用Avrami方程和莫志深法对其动力学参数进行了解析.研究结果表明,在反式-/顺式-1,4-聚异戊二烯共混体系的等温及非等温结晶过程中,顺式-1,4-聚异戊二烯(CPI)组分的存在会降低反式-1,4-聚异戊二烯(TPI)组分的结晶速率;在等温结晶过程中,CPI组分会提高TPI组分自身的结晶度;而非等温结晶过程中,CPI则提高了共混物中β晶型的相对含量.     

Crystallization kinetics of the monoclinic modification of poly(3,3-dimethyl oxetane)

Poly(3,3-dimethyl oxetane) fractions ranging in number average molecular weights from 18500 to 130000 have been isothermally crystallized from the relaxed melt state in the temperature range from 12 to 44 °C, where only the monoclinic modification is formed. The influence of molecular weight and undercooling in crystallization kinetics has been analyzed. The level of crystallinity is very slightly dependent on molecular weight but the influence of this parameter on the time scale of the crystallization is relatively pronounced. The crystallization temperature coefficient was determined and it was found a constant value of the product of the interfacial energies in the range of molecular weights which has been analyzed. Growth rate measurements were carried out for fraction ¯M _n=130000 and it was found that the temperature coefficients for overall and growth rates are equal. Finally, the comparison of the experimental results for this polymer with those reported for poly(oxetane) shows two main differences: first, the crystallization rate is slower for poly(3,3-dimethyl oxetane) and second, the temperature coefficient is smaller for this polymer.