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In the paper, wheat straw was rapidly liquefied in the mild condition. The optimum liquefaction effect was obtained at steam-explosion pre-treatment of wheat straw, liquefaction temperature of 140 °C, solvent/wheat straw ratio of 6:1, glycol (EG):glycerol = 5, sulfuric acid of 5%, and wheat straw of water content of 150%. During the liquefaction, cellulose, semi-cellulose and lignin are decomposed, which results in changes of hydroxyl value, acid value, viscosity and weight-average molecular weight of the reaction system. The liquefaction product was used to prepare polyurethane foam. Compared with the normal PUF, the foam had similar mechanical properties and better water absorption and biodegradability. 相似文献
114.
This article describes the fundamental foaming mechanisms that governed the volume expansion behavior of extruded polypropylene (PP) foams. A careful analysis of extended experimental results indicated that the final volume expansion ratio of the extruded PP foams blown with butane was governed by either the loss of the blowing agent or the crystallization of the polymer matrix. A charge coupling device (CCD) camera was installed at the die exit to carefully monitor the shape of the extruded PP foams. The CCD images were analyzed to illustrate both mechanisms, gas loss and crystallization, during foaming at various temperatures, and the maximum expansion ratio was achieved when the governing mechanism was changed from one to the other. In general, the gas loss mode was dominant at high temperatures and the crystallization mode was dominant at low temperatures. When the gas loss mode was dominant, the volume expansion ratio increased with decreasing temperature because of the reduced amount of gas lost. By contrast, when the crystallization mode was dominant, the expansion ratio increased with increasing temperature because of the delayed solidification of the polymer. The processing window variation with the butane concentration, the change in the temperature ranges for the two governing modes, and the sensitivity of melt temperature variations to the volume expansion ratio are discussed in detail on the basis of the obtained experimental results for both branched and linear PP materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2661–2668, 2004 相似文献
115.
为了提高轿车侧面耐撞性,设计耐撞性能强的B柱成为主要课题之一.目前的优化方法很难将B柱侵入量和侵入速度同时控制在理想范围内.因此,提出泡沫铝材料填充在汽车B柱内代替B柱加强板的方法,缓冲侧面碰撞冲击.通过建立泡沫铝有限元模型与材料特性分析,确定仿真泡沫铝主要材料参数.进而根据中国新车评价规程C-NCAP要求,建立轿车整车侧面碰撞有限元模型,采用LS-DYNA软件进行仿真分析.结果表明,泡沫铝填充后的B柱侵入量和侵入速度都有明显降低.泡沫铝材料塑性变形和整体弯曲变形能够吸收1.51kJ的能量,是B柱加强板的3倍.填充泡沫铝前后仿真结果表明,轿车B柱填充泡沫铝是一种提高轿车侧面耐撞性的方法. 相似文献
116.
Changes in the liquid hold-up, ?, and the diameter of d, of a foam that are induced by perforated plates (PPs) and the contribution of PPs to foam-breaking were studied. A foaming system containing a dilute detergent solution in a column with mechanical agitation fitted with a rotating-disk foam-breaker (MFRD) was used. After the foam passed through the PPs, ? and d decreased and increased, respectively. The use of PPs to achieve a maximum reduction in ? and a maximum increase in d is confirmed. It is also demonstrated that use of PPs contributes not only to improving the foam-breaking performance of the MFRD, but also to power savings. 相似文献
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Scanning Electron Microscopic (SEM) studies were carried out on the failure surface of syntactic foam material tested in a short beam three point bend test (SBT) by employing 21 × 15 × 3 mm3 dimension bearing specimens. The syntactic foams were fabricated using glass microballoons in epoxy binder. The failure of the tensile, compression, and shear dominated regions were studied by SEM at different magnifications. The tensile region had characteristic features, such as partial debonding of the microballoons from the matrix and cracking of glass microballoons, apart from matrix cracking and some river pattern features. The compression side was characterized by crushing and collapsing of microballoons, resulting in accumulation of debris with no apparent river pattern for matrix‐rich regions. The midway positions of the SBT failed surface comprised of deformation bands in the matrix and occasional debonding of microballoons. The morphology recorded in the tensile and compression regions corroborated well with the results obtained on these foam samples in those specimens that were subjected to pure uniaxial tension and compression, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 673–679, 2005 相似文献
119.
全水发泡硬质聚氨酯泡沫塑料技术研究进展 总被引:12,自引:1,他引:12
对CFC 11发泡替代技术中全水发泡技术路线进行了分析 ,指出水作为发泡剂存在的优点与不足。着重阐述了全水发泡中几种主要因素如水的用量、聚醚多元醇性质和结构以及异氰酸酯指数对泡沫性能的影响 ,并对国外近些年来全水发泡用聚醚多元醇研究现状进行了详细论述 相似文献
120.
半球型动压气体轴承陀螺电机设计及性能测试 总被引:1,自引:0,他引:1
针对高精度三浮陀螺用半球型动压气体轴承陀螺电机的启停寿命问题,对半球型动压气体轴承的设计理论以及保证轴承在电机工况下能可靠启停的一些关键技术进行研究.其中轴承间隙和螺旋槽结构参数是影响轴承可靠启停以及其力学性能的关键因素,将螺旋槽结构参数作为变量,通过改变变量参数来分析轴承力学指标的变化趋势,得出螺旋槽各关键参数与轴承刚度的关系曲线;通过有限元法仿真分析并校核了电机在工况下轴承的稳定性,证明了轴承间隙参数设计合理.在此基础上研制了半球型动压气体轴承陀螺电机样机,并进行专项的电机启停寿命试验,启停次数满足陀螺不少于3 000次指标要求,满足高精度三浮陀螺的使用要求. 相似文献