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采用差示扫描量热(DSC)法对聚萘二甲酸乙二醇酯(PEN)的非等温冷结晶动力学进行研究;通过改变升温速率,讨论了PEN冷结晶起始温度与峰顶温度之间存在差值的原因;对比了两种不同的冷结晶起始点的确定方法对冷结晶动力学常数的影响。结果表明:以DSC曲线偏离基线作为PEN冷结晶的起始点,得到的表观Avrami指数很大;用基线延长线与DSC曲线的切线的交点作为冷结晶的起始点和结束点,得到的表观Avrami指数为2.55,且不随升温速率的变化而变化,与等温熔融热结晶方法得到的结果接近,具有相似的结晶生长方式。 相似文献
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采用熔融结晶法对甲醇合成油分离得到质量分数62.3%的均四甲苯富集液进行分离提纯以获得高纯度的均四甲苯副产品。实验中比较了静态结晶和鼓泡结晶的提纯效果,考察了鼓气速率、降温速率、结晶终温、结晶恒温时间、发汗终温和发汗恒温时间等操作参数对结晶过程的影响。最终确定了适宜的操作条件为速率比0.75 L/(h·g)、降温速率0.1℃/min,结晶恒温时间1.5 h和发汗恒温时间2 h。对不同质量分数的富集液进行结晶和发汗实验,得到以结晶终温和发汗终温为变量的操作平衡曲线。对质量分数为62.3%的原料通过三级结晶分离提纯,就可以获得99%以上的均四甲苯产品。通过实验与计算结果表明,本文计算模型与实验数据吻合较好,可以满足工程需要。 相似文献
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改善聚乙醇酸(PGA)的结晶性能有利于拓宽其应用领域。采用差示扫描量热仪和偏光显微镜研究市售成核剂TMC-300对PGA非等温结晶和等温结晶行为的影响规律,并利用Avrami方程研究其等温结晶动力学。结果表明,TMC-300的加入能够提高PGA熔融结晶温度和结晶度,最佳质量分数为0.8%。在此添加量下,TMC-300能使PGA在195~205℃下的半结晶时间缩短、结晶速率提高,Avrami指数n变化不明显。结合晶体形貌,说明PGA在等温结晶过程中呈异相成核的三维球晶生长方式,TMC-300的加入不会改变其结晶的生长维数,但能明显减小晶体尺寸。 相似文献
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成核剂对PET/PEN共混体系非等温结晶的影响 总被引:1,自引:0,他引:1
采用差示扫描量热法(DSC)研究了三种成核剂苯甲酸钠(SB)、1,3∶2,4-二亚苄基-D-山梨醇(DBS)、碳酸钙(CaCO3)对聚对苯二甲酸乙二醇酯(PET)/聚2,6-萘二甲酸乙二醇酯(PEN)共混体系的非等温结晶动力学的影响。结果表明,在PET/PEN/成核剂共混体系的非等温熔融结晶过程中,随着冷却速率的升高,结晶起始温度、终止温度、结晶峰温度都向低温方向移动,成核剂的加入使得不同速率下PET/PEN的结晶温度明显提高,结晶更为容易,SB、CaCO3、DBS均起到了较好的成核作用。由于次级结晶的存在,采用Ozawa法不能很好地描述PET/PEN/成核剂共混体系的非等温熔融结晶过程;莫志深法能较好地描述体系的非等温熔融结晶过程。 相似文献
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采用差示扫描量热仪和偏光显微镜,对未加成核剂和加入2种不同成核剂A、B的聚甲醛(POM)进行非等温结晶测试、等温结晶动力学研究,得到了在各种条件下的Avrami方程参数(K和n)、半结晶时间(t1/2)及结晶形态。研究表明,POM结晶过程为异相三维生长过程,2种成核剂均能使POM结晶速度加快,缩短了结晶时间,成核剂B效果好于成核剂A。 相似文献
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聚碳酸酯(PC)热结晶十分困难,但在某些溶剂诱导作用下,其结晶能力能得到显著提高。且诱导剂的种类、溶度参数和极性等物化性质的不同,其诱导 PC 结晶的能力与形态也不同。从溶剂分子在聚合物内的扩散动力学、诱导结晶行为与特性、诱导结晶形态、诱导结晶机理及应用前景等方面对溶剂诱导 PC 结晶的研究工作和理论进展进行了综述。 相似文献
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王锦燕;孙玉周;李冬霞 《中国塑料》2011,25(8):14-18
介绍了有关聚合物流动诱导结晶的研究工作,以及剪切诱导条件下结晶动力学、结晶形态学和结晶对材料流变参数的影响这三方面的主要研究模型,并进行了比较和讨论。 相似文献
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硫氮玻璃的析晶性能与结构分析 总被引:3,自引:0,他引:3
通过对二元(Ge-S)和三元(As-Ge-Se)系统硫系基玻璃和引入Si3N4的硫氮玻璃试样析晶性能的比较,对硫氮玻璃的析晶行为与其结构之间的关系进行了较深入的探讨。试验结果表明,随着Si3N4的引入,硫系玻璃的析晶温度得以提高或伴随析晶放热峰的消失。这表明氮原子的引入加强了硫系基玻璃微观结构的连缀度,使硫氮玻璃的析昌能力有所下降。此外还在经过析晶热处理的硫氮玻璃试样的XRD中发现两个新衍射峰,且 相似文献
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杨柳 《现代塑料加工应用》2007,19(2):34-36
利用差示扫描量热仪(DSC)研究了茂金属线性低密度聚乙烯(mLLDPE)和传统线性低密度聚乙烯(LLDPE)的非等温结晶行为。采用Jeziorny法和莫志深法对所得的数据进行了分析。结果表明,采用莫志深法处理数据可得到较好的线性关系,且mLLDPE在相同的相对结晶度下的结晶速率低于LLDPE。 相似文献
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Crystallization of calcium carbonate by gas-liquid and liquid-liquid reactions in a continuous MSMPR crystallizer was conducted over a wide range of suspension densities. The effects of operating factors and reaction mechanism on the cyrstallization kinetics were investigated. The crystallization kinetics for both reaction systems are correlated by the power law model and these correlations depend on the suspension density regions. The kinetic orders in the power law model are correlated with carbonate alkalinity irrespective of the reaction mechanism and the suspension density. 相似文献
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Phase morphological effect on crystallization kinetics in various nanoconfined spaces in a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer with a PEO volume fraction of 37 vol% was investigated. The phase morphology was characterized by small-angle X-ray scattering and transmission electron microscopy techniques. When the sample was cast from chloroform solution and annealed at 150 °C, a double gyroid (DG) phase was obtained. After it was subjected to a large-amplitude reciprocating shear, the sample transformed to an oriented hexagonal cylinder (Hex) phase. To obtain a lamellar confined geometry, lamellar single crystals were grown from dilute solutions. The crystallization in the lamellar (Lam) phase was one-dimensionally (1D) confined, while it was two-dimensionally (2D) confined in the DG and Hex phases, although they had different structures. Differential scanning calorimetry (DSC) was employed to study the crystallization kinetics using the Avrami analysis for these three nanoconfined geometries. Heterogeneous nucleation was found in all three samples in the crystallization temperature (Tc) regions studied. DSC results indicated that the crystallization kinetics in the Lam phase was the fastest, and the PEO crystals possessed higher thermodynamic stability than in the DG and Hex phases. For the crystallization kinetics in two 2D-confined phases, at low Tc (<35 °C) the PEO crystallization rates in the DG and Hex phases were similar, while at high Tc (>35 °C) the PEO crystallization was slower in the DG phase than in the Hex phase. The Avrami exponent n-values for the DG and the Hex samples were similar (∼1.8), yet the values of lnK in the DG phase were smaller than those in the Hex phase. This suggested that the linear growth rate was slower in the DG phase than in the Hex phase due to continuous curved channels in the DG phase. 相似文献