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141.
改性淀粉与丙烯酸接枝共聚物的合成及应用性能 总被引:18,自引:2,他引:18
研究经过热处理的改性淀粉与丙烯酸的接枝共聚反应。接枝共聚产物在 790cm-1、85 0cm-1(物理改性淀粉的特征吸收峰 )和 172 0cm-1(聚丙烯酸的特征吸收峰 )处的红外光谱验证了接枝共聚反应的发生。探讨了引发剂过硫酸铵浓度、丙烯酸浓度、反应温度和反应时间等因素对接枝率和接枝效率的影响。当 ρ(淀粉 ) =70 g/L、t =6 0℃、反应时间为 3h、c〔(NH4) 2 S2 O8〕 =3 0× 10 -3 mol/L、c(丙烯酸 ) =0 4 2mol/L时 ,合成胶粘剂的初粘力为 10 0 % ,吸水率为 15 0 14 % ,吸油率为 2 0 6 % ,其压制的纸板冲击强度为 3 2 5kN/m ,拉伸强度为 3 75MPa ,与纯淀粉粘接剂相比较 ,所压制纸板的应用性能得到较大的改善。 相似文献
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In this article, the polycondensation of terephthaloyl chloride and p-phenylenediamine was systematically studied, including the liquid–crystalline state of the solution and the spinning of poly(1,4-phenyleneterephthalamide) (PPTA). High-molecular-weight PPTA with εinh = 5–7 was prepared and the main factors influencing the solution polycondensation of 1,4-phenylenediamine with terephthaloyl chloride were studied in detail. Experimental results showed that the water content of the reaction system, reactant concentration, and volume ratio of mix solvents have a great influence on the inherent viscosity of the poly(1,4-phenyleneterephthalamide) obtained. The highest εinh was obtained at 0.3M/liter reactant concentration in a mixed solvent ratio HMPA/DMAC of 4/1 (by volume), at 0.35M/liter reactant concentration in a mixed solvent of HMPA/NMP = 7/3, and at 0.5M/liter of reactant concentration in a mixed solvent of HMPA/THF = 9/1. The water content must be controlled to less than 100 ppm in the polymerization system. In the early stage of the polycondensation process, the εinh of the polymer obtained increased rapidly with time. The system gelled within 2 or 3 min, while the monomer conversion reached about 100%. However, the reaction of polycondensation continued after gelation and the εinh of the polymer increased appreciably. We have studied the viscosity behavior at 20–155°C for the anisotropic solution of PPTA in 100% sulfuric acid (εinh of PPTA 2.5–4.9). Experimental results showed that, at low concentrations the viscosity of isotropic solution increases with the increase of polymer concentration to reach a maxium near the critical polymer concentration, beyond which the solution changes to an anisotropic liquid–crystalline solution. The appropriate spinning region was obtained as shown in the phase diagram determined by viscosity, degree of depolarization anisotropy, and region of thermal depolymerization. Fibers of PPTA with high modulus and high tenacity were obtained by dry-jet wet spinning. The fibers obtained have a tenacity of ~22 g/denier, a modulus of ~600 g/denier, and elongation at break ~3.5%. 相似文献
145.
Hong-Bing Tsai Da-Kong Lee Hsien-Wen Chen Jia-Yeh Chang Jung-Liang Liu Chih-Huey Chang I-Chung Du Sheng-Yuan Lei Jiang-Wen You 《Journal of Polymer Research》1996,3(1):59-63
The liquid crystalline transitions of two kinds of smectic polyesters with different molecular weights were investigated by DSC, polarized microscopy and X-ray diffraction. The molecular weight affects the transitions significantly for these two kinds of polyesters. With a high enough molecular weight, both poly (pentamethylenep,p-bibenzoate) and poly(hexamethylenep,p-bibenzoate) exhibit an enantiotropic smectic phase, but the two endothermic transition peaks of the DSC heating curve seem to overlap. The polyesters tend to exhibit a monotropic smectic phase as the molecular weight decreases. From the DSC cooling curve, the isotropic-smectic transition can be seen more clearly. As the molecular weight decreases, the smectic order decrease significantly. The molecular weight affects the transitions in a different way for these two different kinds of polyesters. 相似文献
146.
Pt/γ-Al2O3 catalysts were prepared by two different impregnation methods and characterized by XRD, TEM, and CO chemisorption. The Pt particle sizes ranged in 2.4–23.3 nm for these 5.0 wt% Pt/γ-Al2O3 catalysts. The catalysts were also characterized by FT-IR spectroscopy using CO as a probe molecule before and after the chiral modification with cinchonidine. Two IR bands (2078 and 2060 cm-1) due to CO linearly adsorbed on the Pt/γ-Al2O3 catalyst, calcined at 500 °C before reduction in sodium formate solution were observed, whereas only one IR band at ~2070 cm-1 was observed for other catalysts. A red shift of the IR band was observed after chiral modification of all the catalysts, except the one with the largest Pt particle size and lowest Pt dispersion. The catalytic performance of the cinchonidine-modified Pt/γ-Al2O3 catalysts was tested for the enantioselective hydrogenations of ethyl pyruvate and ethyl 2-oxo-4-phenylbutyrate (EOPB). A 95% ee value was obtained for the ethyl pyruvate hydrogenation and about 83% ee was achieved for the enantioselective hydrogenation of EOPB under the optimized preparation and reaction conditions. It is deduced that the interaction of Pt with γ-Al2O3 is a crucial factor for obtaining high activity and that the adsorption abilities (adsorption of reactant, solvent and chiral modifier molecules) of the catalyst surface affect the catalytic performance significantly. 相似文献
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主要研究了LTE系统下行链路中的载波同步,分析了基于PSS相关估计和基于CP的ML估计两类传统频偏估计算法。针对后者抗多径能力不足、抗极性反转能力差和估计范围较小的缺陷,提出了一种改进频偏估计算法。该算法在利用CP数据进行ML频偏估计时去掉一部分受符号干扰的数据,以减少多径影响;利用PSS相关估计结果的极性信息,对算法估计结果进行修正,扩大频偏估计范围和提高抗极性反转能力。仿真结果表明:改进算法相对于原算法在多径环境下具有更好的估计性能;当频偏|εF|接近0.5时能够抵抗极性反转具有较高的鲁棒性,当|εF|〉0.5时原算法失效而改进算法仍能够保持较高的估计性能。 相似文献
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150.
One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this
work, titanium dioxide (TiO2) nanoparticles having enhanced surface area were synthesized under the interference of SiO2. The mixed oxide, SiO2-TiO2 (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO2 nanoparticles were added into the TiO2 sols after hydrolysis. After condensation and calcination heat treatment, the SiO2-TiO2 nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO2, the SiO2 was removed subsequently by aqueous NaOH solution. The TiO2 products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for
chemical analysis (ESCA), and by N2 adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO2 after calcination at 400∘C and the average pore diameter was about 7 nm. The porous TiO2 products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples
were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ∼43 nm remained
constant upon calcinations from 500 to 700∘C. The specific surface area was increased up to 66% compared to regular TiO2 samples that were prepared by the similar sol-gel procedure. The porous TiO2 nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation. 相似文献