共查询到18条相似文献,搜索用时 684 毫秒
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间规1,2-聚丁二烯的非等温结晶动力学 总被引:8,自引:1,他引:7
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. 相似文献
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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 总被引:2,自引:0,他引:2
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。 相似文献
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低密度聚乙烯/乙丙烯三元共聚(LDPE/EPO)共混体系的结晶动力学 总被引:2,自引:0,他引:2
用DSC方法研究了LDPE/EPO共混体系的等温及非等温结晶动力学,对LDPE/EPO共混体系的等温结晶动力学研究表明,共混物是三维生长的异相成核,共混物在各个结晶温度下的结晶过程都是以方式K_g(Ⅱ)进行的.采用联系Avrami方程和Ozawa方程导出的新非等温结晶动力学方程,处理了LDPE/EPO共混体系,得到了非等温结晶过程的一些基本参数,新方程很好地描述了此共混体系的非等温结晶动力学过程. 相似文献
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用DSC法研究了苯乙烯-丙烯等规立构嵌段共聚物的非等温结晶动力学。结果表明:冷却速率在5~20℃/min范围内,共聚物的非等温结晶动力学参数能很好地符合Avrami动力学方程,非等温结晶速率常数与冷却速率有关,动力学结晶能力则同时受到冷却速率和共聚物组成比的影响。文中还讨论了在非等温结晶条件下共聚物的结晶成核和生长方式与共聚物组成和结构的关系。联合Avrami方程和Ozawa方程推导的非等温结晶动力学方程较好地描述了iPS-b-iPP嵌段共聚物的非等温结晶动力学过程。 相似文献
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采用示差扫描量热仪(DSC) 研究了具有生物相容性及可降解性P(BHB-CL)超支化共聚酯的非等温熔融结晶过程, 分别采用Avrami 方程、Ozawa 方程和Mo方程对P(BHB-CL)共聚酯的非等温动力学数据进行比较分析, 计算了相关的非等温结晶动力学参数, 并利用Kissinger方程计算其非等温结晶活化能. 结果表明, Mo方程更适合描述P(BHB-CL)共聚酯的非等温结晶过程. 相似文献
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PET/PEN/DBS共混物非等温结晶动力学研究 总被引:1,自引:0,他引:1
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. 相似文献
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利用差示量热扫描热分析仪(DSC)测得了不同降温速率下聚乙交酯(PGA)的非等温结晶的温度-热焓曲线。分别通过Ozawa法、Jeziorny法和莫志深法对PGA的非等温结晶机理进行了分析。Ozawa法结果表明:在给定的温度范围内,Ozawa法并不适用于描述PGA的非等温结晶行为;Jeziorny法结果表明:不同降温速率下,PGA结晶过程的Avrami指数(n)接近4,PGA非等温结晶为均相成核、晶粒三维增长的过程;莫志深法结果表明:Avrami指数与Ozawa指数的比值(a)基本无变化,动力学参数f(T)随降温速率增加逐渐增大,即在更快的降温速率下,PGA结晶更充分,可获得更高的结晶度。通过Kissinger方程计算得到的PGA结晶扩散活化能为-66.9kJ/mol。 相似文献
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用差示扫描量热分析研究了间规聚苯乙烯(sPS)的非等温结晶及其动力学,并分别用Ozawa和Jeziorny两种方法来处理sPS的非等温结晶数据.结果表明,在25~40℃/min的冷却速率范围内,sPS的半结晶时间随冷却速率增大而呈指数式下降,sPS非等温结晶过程遵循Ozawa动力学方程,但不符合Jeziorny方法中的Avrami动力学方程.所得到的sPS非等温结晶Avrami指数n在36~41之间,高于等温结晶时的n值 相似文献
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E. Dargent A. Denis C. Galland J. Grenet 《Journal of Thermal Analysis and Calorimetry》1996,46(2):377-385
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. 相似文献
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Nilay K. Pramanik Ramsankar Haldar Utpal K. Niyogi MD. Sarwar Alam 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(4):296-307
The non-isothermal crystallization kinetics was studied by differential scanning calorimetric analysis on nylon 66 and e-beam irradiated nylon 66 at different cooling rates. The Modified Avrami equation, the Ozawa equation and the Combined Avrami-Ozawa equation were applied to study the kinetics of non-isothermal crystallization of nylon 66. The crystallization behavior of pristine nylon 66 polymer was compared with that of e-beam irradiated nylon 66 and observed that the kinetics of non-isothermal crystallization of nylon66 was affected largely upon e-beam irradiation. E-beam irradiation not only decreased the crystallization temperature of nylon 66, but influenced the mechanism of nucleation and crystal growth and reduced the overall crystallization rate of nylon 66 also. The crystallization activation energy calculated by the Kissinger method for irradiated nylon 66 was lower than that of pristine nylon 66. 相似文献
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In this work, the non-isothermal crystallization kinetics of poly(ethylene glycol-co-1,4-cyclohexanedimethanol terephthalate) (PETG) random copolyesters with different compositions was first investigated from the glassy state. Regardless of the composition, the value of the Avrami exponent determined from Jeziorny theory was 2.1–2.4, depending on the heating rate, whereas the value of α (the ratio of the Avrami exponent to the Ozawa exponent) obtained from Mo's method was 1.3–1.6, depending on the relative crystallinity. These results indicated that the nucleation and growth mechanism of the PETG copolyesters were apparently identical to those of the poly(ethylene terephthalate) (PET) homopolymer. However, the cold crystallization rate was accelerated by increasing the heating rate, but retarded by incorporating the 1,4-cyclohexanedimethanol (CHDM) unit into the polymer backbone. Based on the crystallization rate coefficient (CRC) and the crystallization rate parameter (CRP) approaches, the cold crystallization rate was in the following order: PET > PETG(30/70) > PETG(85/15) > PETG(50/50) > PETG(70/30). 相似文献
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Hong-xiang Teng Wen-hong Tang Yi Shi Xi-gao Jin State Key Laboratory of Polymer Physics Chemistry Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing China Department of Chemistry Jilin University Changchun China 《高分子科学》2002,(4):339-345
Based on thermal analysis, the isothermal and nonisothemal crystallization kinetics of Ziegler-Natta catalyzedlinear low density polyethylene (Z-N LLDPE) and metallocene catalyzed LLDPE (m-LLDPE) were studied. Treating theresults with the Avrami equation and the Ozawa equation, the crystallization constant lgk and the Avrami exponent n wereobtained. Some other crystallization parameters were also discussed. According to the different characteristics of the chainstructures of Z-N LLDPE and metallocene LLDPE, their crystallizaton behaviors were analyzed. It is indicated that thehomogeneity and heterogeneity of the two polymers act in different way during the crystallization process of polymers,including the nucleation and the growth of crystals under various conditions. 相似文献
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Xu W. B. Zhai H. B. Guo H. Y. Zhou Z. F. Whitely N. Pan W.-P. 《Journal of Thermal Analysis and Calorimetry》2004,78(1):101-112
The non-isothermal crystallization kinetics of polyethylene (PE), PE/organic-montmorillonite (Org-MMT) composites were investigated
by differential scanning calorimetry (DSC) with various cooling rates. The Avrami analysis modified by Jeziorny and a method
developed by Mo were employed to describe the non-isothermal crystallization process of these samples very well. The difference
in the exponent n between PE and PE/Org-MMT nanocomposites, indicated that non-isothermal kinetic crystallization corresponded to tridimensional
growth with heterogeneous nucleation. The values of half-time, Zc and F(T) showed that the crystallization rate increased with the increasing of cooling rates for PE and PE/Org-MMT composites,
but the crystallization rate of PE/Org-MMT composite was faster than that of PE at a given cooling rate. The method developed
by Ozawa did not describe the non-isothermal crystallization process of PE very well. Moreover, the method proposed by Kissinger
was used to evaluate the activation energy of the mentioned samples. The results showed that the activation energy of PE/Org-MMT
was greatly larger than that of PE.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献