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971.
972.
A heavy Iraqi residue was thermally cracked using a soaker visbreaking process at temperatures between 435 and 480 °C, with a range of residence times of 43–109 s in the coil and 151–379 s in the soaker. The pressure was kept constant at 7 bar. Visbroken products were characterized, evaluated and fractionated into light, middle and heavy cuts. The stability of the visbroken products was compared with that of the original feedstock. Also an activation energy was calculated for the visbreaking process and related to the severity of the process. The results obtained show that the conditions used were not severe and could be applied to obtain a required conversion depending on the uses of the products. 相似文献
973.
Atsuhiko Yamanaka Tooru Kitagawa Masayuki Tsutsumi Toshihiro Kashima Hiroyuki Fujishiro Kimiko Ema Yoshinobu Izumi Shigehiro Nishijima 《应用聚合物科学杂志》2004,93(6):2918-2925
High strength polyethylene fiber (Toyobo, Dyneema® fiber: hereinafter abbreviated to DF) has a negative thermal expansion coefficient. Relation between fiber structure and thermal strain of DF used as reinforcement of DF reinforced plastic (DFRP) for cryogenic use was investigated. The crystallinities and orientation angles of several kinds of polyethylene fibers having different modulus from 15 to 134Gpa (herein after abbreviated to DFs) were measured by NMR and X‐ray. We obtained the parameters of the mechanical series‐parallel model composed of crystal and amorphous by crystallinity and modulus. Thermal expansion coefficients of DFs were estimated by mechanical series‐parallel model. All DFs having different modulus showed negative thermal expansion coefficients in the temperature range from 180 to 300K, and absolute values of those markedly increased by increasing tensile modulus of DF. The estimated thermal expansion coefficients showed negative values, and thermal strains showed a similar curve to observed ones mostly. Average thermal expansion coefficients in the temperature range from 180 to 300K estimated by mechanical model agreed with the observed ones. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2918–2925, 2004 相似文献
974.
Double‐shell‐structured microcapsules encapsulating phase‐change materials (micro‐PCMs) with an average diameter of 5–10 μm were successfully fabricated with a melamine–formaldehyde resin as the coating material. The mechanical properties of the obtained piled micro‐PCMs, tested under compression, were evaluated with a pressure sensor. Typical stress–strain curves showed that both the single‐shell‐ and double‐shell‐structured microcapsules had yield points and maximum point pressures. The morphological changes in the shell surface confirmed the existence of yield points by scanning electron microscopy. When the pressure was beyond the yield point, the microcapsules showed conventional plastic behavior, and the double‐shell structure was more mechanically stable than the single‐shell one. Differential scanning calorimetry analysis results revealed that the properties of the phase‐change materials experienced no variation after coating with a single‐shell‐ or double‐shell‐structured polymer. Thermogravimetric analysis showed that the double‐shell‐structured micro‐PCMs experienced a weight loss of only about 5% from 86.3 to 232°C but did so more rapidly from 232 to 416°C. Thermoregulation was determined with periodical heating and cooling tests. The data showed that the micro‐PCMs changed temperature in a narrow range of 20–25°C with a time lag of 20 min to reach the maximum or minimum temperature in comparison with a reference temperature of 18–28°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1295–1302, 2007 相似文献
975.
高固体分丙烯酸树脂相对分子质量的研究 总被引:1,自引:0,他引:1
采用溶液聚合法合成高固体分丙烯酸树脂,用凝胶渗透色谱(GPC)法分析引发剂的种类和用量、反应温度及聚合工艺对丙烯酸树脂的相对分子质量及其分布的影响。结果表明,选用偶氮二异丁腈和过氧化苯甲酰两种引发剂进行复配可提高聚合物的相对分子质量;采用“饥饿态”聚合工艺进行聚合反应可有效控制聚合物的相对分子质量,且相对分子质量分布均匀,分散度小于2;当引发剂用量为2%,在110℃的反应条件下制得的丙烯酸树脂的综合性能优异,固含量超过70%,相对分子质量可达4万。 相似文献
976.
以TiO2 ZrO2 P2O5为复合成核剂,采用传统熔融冷却法获得了高ZnO含量的Li2O-A l2O3-SiO2系统的基础玻璃。通过差热分析确定了该玻璃的热处理条件、晶化性能,利用梯温炉实验、X射线衍射分析和扫描电镜对晶化试样的物相和微观结构进行了研究,讨论了热处理制度对玻璃的析晶及热膨胀系数的影响。研究结果表明:含10%(质量分数)ZnO的LAS系统样品玻璃最佳核化温度为(710±2)℃,玻璃的晶化活化能E为(275±2)kJ/mol,晶化指数n为3.11±0.2,样品玻璃在较低温度下失透,并且随着晶化温度升高,样品的热膨胀系数加大。 相似文献
977.
978.
979.
Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.
Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes. 相似文献
980.
分别以烷基化剂溴代十二烷、溴代十四烷、溴代十六烷与二苯醚反应,制得系列烷基二苯醚产品。通过正相高效液相色谱法监测烷基系二苯醚曲合成,优化其合成工艺。色谱条件为:色谱柱,C18 kromasil(5μm,250×4.6mm);流动相,体积比V正己烷:V异丙醇=18:1;流速,1mL/min。最佳合成工艺为:各反应物的摩尔比n二苯醚:n催化剂:n澳代烷=1:2:5;反应温度为75℃。反应时间为6h。双十二烷基二苯醚、双十四烷基二苯醚、双十六烷基二苯醚的产率分别为79.62%、72.38%、66.83%。 相似文献