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991.
Paulo Cardoso Jaime Silva Maria Conceição Paiva Ferrie van Hattum Senentxu Lanceros‐Mendez 《Journal of Polymer Science.Polymer Physics》2012,50(17):1253-1261
The electrical properties and dispersion of vapor‐grown carbon nanofibers (VGCNF) and multiwalled carbon nanotubes (MWCNT)—epoxy resin composites are studied and compared. A blender was used to disperse the nanofillers within the matrix, producing samples with concentrations of 0.1, 0.5, and 1.0 wt % for both nanofillers, besides the neat sample. The dispersion of the nanofillers was qualitatively analyzed using scanning electron microscopy, transmission optical microscopy, and grayscale analysis. The electrical conductivity and the dielectric constant were evaluated. The percolation threshold of MWCNT epoxy composites is lower than 0.1 wt % while for VGCNF lies between 0.1 and 0.5 wt %. The difference on the dispersion ability of the two nanofillers is due to their intrinsic characteristics. Celzard's theory is suitable to calculate the percolation threshold bounds for the VGCNF composites but not for the MWCNT composites, indicating that intrinsic characteristics of the nanofillers beyond the aspect ratio are determinant for the MWCNT composites electrical conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
992.
Résumé Une nouvelle façon de repérer la gélification d'une résine thermodurcissable est proposée, à partir de mesures rhéologiques. Le point de gel est relié à une diminution de la vitesse de croissance du module visqueux observée sur les courbes expérimentales en cours de cinétique à température constante. Les temps de gel obtenus sont du même ordre que ceux donnés par les autres méthodes rhéologiques, mais font cependant apparaître des différences sensibles. Le temps de gel obéit à une loi d'Arrhénius en fonction de la température de cuisson.Le module visqueux au point de gel et, par conséquent la viscosité en ce point, varient avec la température. Il en est de même pour le facteur de perte tan . Par contre, le module élastique au point de gel se conserve quelle que soit la température. Ces résultats ont été obtenus sur deux formulations de résine: DGEBA (n = 0) – mPDA et DGEBA (n = 0) – DDM à la stoechiométrie.
A new method of characterizing gelation of a thermosetting resin from rheological measurements is proposed. Gelation is associated with a reduction in the speed of growth of the viscous modulus which is observed on the experimental curves during isothermal kinetics. Times of gelation obtained in this way are of the same order of magnitude as those found with other rheological methods, however distinct differences are observed. These times follow the Arrhenius' law as a function of the processing temperature.The viscous modulus at the gelation point and, as a consequence, the viscosity at this point, vary with temperature. This comes also true for the loss factor tan . In contrast, the elastic modulus at the gelation point does not change with the temperature. These results were obtained with two resin formulas: DGEBA (n = 0) – mPDA and DGEBA (n = 0) – DDM in stoechiometric concentration.相似文献
993.
994.
Yanbing Wang Chenguang Zhou Hao Yan Zhixiong Huang 《Journal of Macromolecular Science: Physics》2014,53(5):813-819
Chlorinated butyl rubber composites were prepared by a compounding and vulcanizing process using phenolic resin (PF) as the vulcanizing agent and carbon black as filler. Instead of using the conventional vulcameter method to determine the vulcanizing parameters, the vulcanization temperature and time were obtained by differential scanning calorimetry (DSC) and tensile testing, respectively. Dynamic mechanical analysis (DMA) showed that, higher PF content resulted in higher E′ and lower tanδ, and variations of E′ and tanδ with temperature were consistent with the time-temperature equivalence principle. It is proposed that chlorinated butyl rubber using phenolic resin as the vulcanizing agent could be used as potential damping materials in the temperature range 20–100°C and frequencies 0.1–100 Hz. 相似文献
995.
为充气靶丸的精密装配提供有效的胶斑定位检测方法,研究了具有荧光特性的环氧胶黏剂,通过环氧胶黏剂与香豆素和JS-064荧光染料的相容性及荧光性的研究,探索其适用于靶丸装配和检测的添加工艺。分别测定了入射波长和适用于工艺的激发波长,研究了荧光强度与香豆素浓度的关系以及固化剂对荧光强度的影响。并确定了无水乙醇减小表面张力的工艺方法。结果表明:香豆素的激发波长为274nm,入射波长为519nm;荧光染料的激发波长为435nm,适用于胶斑定位检测的激发波长为365nm;香豆素能很好地溶于固化剂176中,有淡蓝色荧光,而荧光染料均匀分散于胶黏体系,且荧光性能良好。 相似文献
996.
Chemical decomposition of an epoxy system made of tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) and 4,4′-diaminodiphenylsulfone (DDS) in supercritical 1-propanol was investigated under different reaction temperature and time. The GC–MS results suggested that the epoxy system was decomposed to the products including aniline, N-propylbenzenamine, and 4,4′-diaminodiphenylsulfone. The change of the products' yield with time was measured by GC. In addition, the formed chars were characterized by SEM, elemental analysis, Raman and XRD. The results implied the presence of some graphite microcrystals and disordered structure in the solid residue. Upon the addition of KOH, the Guerbet reaction of 1-propanol was promoted to generate more hydrogen. A possible free-radical reaction mechanism was proposed for the depolymerization of TGDDM/DDS epoxy resin. Hydrogenation of radicals had a promotion effect on thermolysis of TGDDM/DDS epoxy resin. 相似文献
997.
Wei-Can Zhang Gan-Zuo Li Jian-Hai Mu Li-Qiang Zheng Hao-Jun Liang Chi Wu 《Journal of Dispersion Science and Technology》2013,34(5):605-613
ABSTRACT The effect of benzyl alcohol on the micellar size and shape of CTAB in KBr solution has been investigated by means of viscosity, LLS (laser light scattering), and NMR measurements. The surfactant CTAB (cetyltrimethylammonium bromide) and KBr content are kept constant at 0.01 mol.L?1 and O.l?1 mol.. The data from the various techniques are quantitatively in agreement. The viscosity of 0.01 mol.L?1 CTAB/ 0.01mol.L?1 KBr micellar system has a marked maximum at benzyl alcohol content 0.6%(v/v), where the size of rod micelles are largest. The results from 'H-NMR spectra of CTAB molecules show that before the maximum viscosity, benzyl alcohol is located in the interfacial region of CTAB micelles in the presence of KBr salt. If more benzyl alcohol is added, it starts solubilizing in the palisades of the micelles. 相似文献
998.
Aniline–terephthalaldehyde resin p-toluenesulfonic acid (ATRT) salt was easily prepared by the reaction of aniline with 1.25 equiv of terephthalaldehyde in the presence of 1.0 equiv of p-toluenesulfonic acid at 75 °C for 24 h in EtOH. ATRT efficiently catalyzed the tetrahydropyranylation of alcohols and deprotection of tetrahydropyranyl (THP), triethylsilyl (TES), and tert-butyldimethylsilyl (TBDMS) ethers. Deprotection of dodecyl THP ether and dodecyl TBDMS ether catalyzed by ATRT proceeded faster than those by pyridinium p-toluenesulfonate (PPTS). ATRT was reused without significant loss of activities. 相似文献
999.
有机相中固定化脂肪酶催化合成植物甾醇酯 总被引:3,自引:0,他引:3
酶法合成植物甾醇酯具有反应条件温和、产物纯度和产量高等优点,但非水相酶催化的活性和稳定性普遍较低.本文以大孔树脂固定化脂肪酶为催化剂,并在催化过程中添加乳糖的类似物,构建了有机相高效合成植物甾醇酯的工艺过程.以酯化率为考察指标,对脂肪酶和反应溶剂进行筛选,对酯化条件进行优化,同时考察了糖的种类及添加量对酶催化性能的影响.结果表明,大孔树脂NKA吸附固定化的褶皱假丝酵母(Candida rugosa)脂肪酶(NKA-CRL)为最适宜的催化剂,以正己烷为反应介质,在酸醇摩尔比为2和添加酶蛋白质量7.5%的海藻糖的条件下,40°C反应10 h,酯化率达到96.6%.连续6次催化后,植物甾醇的酯化率仍维持在85.0%以上. 相似文献
1000.
Octa(aminophenyl)silsesquioxane (OAPS) was used as the curing agent of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin. A study on comparison of DGEBA/OAPS with DGEBA/4,4′-diaminodiphenyl sulfone (DDS) epoxy resins was achieved. Differential scanning calorimetry was used to investigate the curing reaction and its kinetics, and the glass transition of DGEBA/OAPS. Thermogravimetric analysis was used to investigate thermal decomposition of the two kinds of epoxy resins. The reactions between amino groups and epoxy groups were investigated using Fourier transform infrared spectroscopy. Scanning electron microscopy was used to observe morphology of the two epoxy resins. The results indicated that OAPS had very good compatibility with DGEBA in molecular level, and could form a transparent DGEBA/OAPS resin. The curing reaction of the DGEBA/OAPS prepolymer could occur under low temperatures compared with DGEBA/DDS. The DGEBA/OAPS resin didn’t exhibit glass transition, but the DGEBA/DDS did, which meant that the large cage structure of OAPS limited the motion of chains between the cross-linking points. Measurements of the contact angle indicated that the DGEBA/OAPS showed larger angles with water than the DGEBA/DDS resin. Thermogravimetric analysis indicated that the incorporation of OAPS into epoxy system resulted in low mass loss rate and high char yield, but its initial decomposition temperature seemed to be lowered. 相似文献