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991.
992.
Molecular weight dependence of growth and morphology of spherulites of isotactic poly(butene-1), iPB-1, and those of the mixtures with atactic poly(butene-1), aPB-1, were examined by atomic force microscopy (AFM) and polarizing optical microscopy (POM) in order to examine the mechanism of the structural evolution by the branching and re-orientation of lamellar crystals at the growth front. The width of lamellar crystals and the characteristic size of the inner structure of spherulites decreased with increasing molecular weight. The result suggests that the mobility of the melt determines the sizes in spherulites and supports the growth front instability induced by a gradient triggering the branching. The sizes in the mixtures also decreased with increasing weight-averaged molecular weight, Mw. The size dependence in low Mw region, however, was too strong and that in high Mw was too weak in comparison with the predicted dependence for the prepared Mw. It has been concluded that the peculiar behaviors should be discussed with effective Mw influenced by the occurrence of separation and exclusion of non-crystallizing aPB-1 at the growth front. 相似文献
993.
直接酯化法合成了一系列聚对苯二甲酸乙二酯(PET)-间苯二甲酸双羟乙酯磺酸钠(SIPE)-聚乙二醇(PEG)共聚酯,以差示扫描量热分析法(DSC)研究了这些共聚酯及纯PET的熔融和结晶过程,并利用万能材料测试仪研究了纤维的力学性能。试验结果表明:加入SIPE和PEG后,共聚酯熔点(Tm)、玻璃化转变温度(T)g降低;随着PEG相对分子质量的增大,PET共聚酯的Tg、冷结晶温度(Tc)c、Tm、结晶温度降低(T)c,纤维的断裂强度和初始模量下降,断裂伸长率增加。 相似文献
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Jen‐Taut Yeh Yu‐Ching Lai Hai Liu Yao‐Chi Shu Chi‐Yuan Huang Kuo‐Shien Huang Kan‐Nan Chen 《Polymer International》2011,60(1):59-68
The influence of formation temperature on the ultradrawing properties of ultrahigh‐molecular‐weight polyethylene/carbon nanotube (UHMWPE/CNT) fiber specimens is investigated. Gel solutions of UHMWPE/CNT with various CNT contents were gel‐spun at the optimum concentration and temperature but were cooled at varying formation temperatures in order to improve the ultradrawing and tensile properties of the UHMWPE/CNT composite fibers. The achievable draw ratio (Dra) values of UHMWPE/CNT as‐prepared fibers reach a maximum when they are prepared with the optimum CNT content and formation temperature. The Dra value of UHMWPE/CNT as‐prepared fibers produced using the optimum CNT content and formation temperature is about 33% higher than that of UHMWPE as‐prepared fibers produced using the optimum concentration and formation temperature. The percentage crystallinity (Wc) and melting temperature (Tm) of UHMWPE/CNT as‐prepared fiber specimens increase significantly as the formation temperature increases. In contrast, Wc increases but Tm decreases significantly as the CNT content increases. Dynamic mechanical analysis of UHMWPE and UHMWPE/CNT fiber specimens exhibits particularly high α‐transition and low β‐transition, wherein the peak temperatures of α‐transition and β‐transition increase dramatically as the formation temperature increases and/or CNT content decreases. In order to understand these interesting drawing, thermal and dynamic mechanical properties of the UHMWPE and UHMWPE/CNT as‐prepared fiber specimens, birefringence, morphological and tensile studies of as‐prepared and drawn fibers were carried out. Possible mechanisms accounting for these interesting properties are proposed. Copyright © 2010 Society of Chemical Industry 相似文献
998.
We address in this article the mid‐term planning of chemical complexes with integration of stochastic inventory management under supply and demand uncertainty. By using the guaranteed service approach to model time delays in the flows inside the network, we capture the stochastic nature of the supply and demand variations, and develop an equivalent deterministic optimization model to minimize the production, feedstock purchase, cycle inventory, and safety stock costs. The model determines the optimal purchases of the feedstocks, production levels of the processes, sales of final products, and safety stock levels of all the chemicals. We formulate the model as a mixed‐integer nonlinear program with a nonconvex objective function and nonconvex constraints. To solve the global optimization problem with modest computational times, we exploit some model properties and develop a tailored branch‐and‐refine algorithm based on successive piecewise linear approximation. Five industrial‐scale examples with up to 38 processes and 28 chemicals are presented to illustrate the application of the model and the performance of the proposed algorithm. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
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