一种低熔点芳香酯型液晶环氧树脂的合成与固化

本文合成了一种低熔点的芳香酯型液晶环氧树脂双4-环氧丙氧基乙氧基邻甲基对苯二酚酯(MPEPEB),并用IR、EA、1H-NMR、DSC和POM对其结构和性能进行了表征,结果表明MPEPEB在78.7℃～133.9℃之间为向列型液晶,并在降至-50℃后仍能保持液晶态。DSC研究表明,比较升温固化与等温固化的数据表明固化速率,不仅是反应温度和反应程度的函数,同时还与反应历程有关。固化后的体系具有较低的玻璃化温度,并且室温下保留的液晶结构在升温至86℃～88℃时消失。     

Thermophysical properties of carbon/graphite fibers and MOD-3 fiber-reinforced graphite

The flash method is extended to measure directly the thermal diffusivity of graphite/carbon fiber in unidirectionally fiber-reinforced composites and also in fiber bundles. The thermal diffusivity was measured using both composities and fiber bundles for Morganite II and Thornal 50 S graphite fiber and for composite samples containing PX 505 carbon fiber. In addition, the thermal diffusivity of Morganite II and Thornel 50 S graphite fiber was calculated from the effective thermal conductivity of composite samples measured by an absolute method. The thermal diffusivity of MOD-3 fiber-reinforced graphite was measured and the results were used to compute the thermal conductivity in the three orthogonal directions.     

Graphite-liquid-vapor triple point pressure and the density of liquid carbon

A detailed experimental investigation of the graphite-liquid-vapor triple point using a 400 W Nd:YAG continuous-wave laser as the heat source was completed and the triple point pressure accurately placed at 107 ± 2 atm (10.8 ± 0.2 MPa). Both X-ray diffraction and detailed microstructure of the recrysallized graphite were obtained to confirm melt. Careful experimental procedures were employed to address some of the remaining uncertainties in previous carbon triple point studies. These included accurate pressure measurements combined with apparatus designed to minimize pressure excursions. Also systematic melt experiments were completed in helium and argon as a function of sample size and laser power density to assure that sufficient power was available to produce melt at the triple point pressure and to prove, for the first time, that only carbon vapor was present at the sample surface during melting. Maximum mass loss rates were measured and used to confirm that non-equilibrium pressure excursions were experimentally insignificant. The presence of a bright laser-generated vapor or particle plume interfered with the temperature measurement and prevented the determination of the carbon triple point temperature. Finally, the density of liquid carbon near the triple point was calculated by quantitatively measuring the void fraction and density of the recrystallized melt. This density was found to be 1.37±0.06 g/cm³.     

Apparatus for determination of the wiley melting point

Summary A mechanically stirred Wiley Melting Point bath apparatus is described, which makes the Wiley Melting Point more accurate and reproducible, permits more determinations to be run at one time, and is less time-consuming than the hand-agitation procedure of the A.O.C.S. Method.     

A review on the mechanical and electrical properties of graphite and modified graphite reinforced polymer composites

Carbon materials particularly in the form of sparkling diamonds have held mankind spellbound for centuries, and in its other forms, like coal and coke continue to serve mankind as a fuel material, like carbon black, carbon fibers, carbon nanofibers and carbon nanotubes meet requirements of reinforcing filler in several applications. All these various forms of carbon are possible because of the element's unique hybridization ability. Graphene (a single two-dimensional layer of carbon atoms bonded together in the hexagonal graphite lattice), the basic building block of graphite, is at the epicenter of present-day materials research because of its high values of Young's modulus, fracture strength, thermal conductivity, specific surface area and fascinating transport phenomena leading to its use in multifarious applications like energy storage materials, liquid crystal devices, mechanical resonators and polymer composites. In this review, we focus on graphite and describe its various modifications for use as modified fillers in polymer matrices for creating polymer-carbon nanocomposites.     

Phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) from I: A proposition for the ferroelectric Curie point

A phase transition at a temperature immediately below the melting point of poly(vinylidene fluoride) form I has been found by means of differential scanning calorimetry (d.s.c.) and infra-red (i.r.) vibrational spectroscopy. An endothermic d.s.c. shoulder has been observed at a temperature about 10°C below the melting point, in the vicinity of which the i.r. crystalline trans bands decrease in intensity steeply and the crystalline gauche bands increase in intensity, indicating the conformational change from all-trans to T₃GT₃G type. These observations have been found to be detectable more clearly for samples subjected to the poling treatment under a d.c. high voltage. The transition shows the characteristic behaviour essentially identical to those observed for ferroelectric copolymers of vinylidene fluoride and trifluoroethylene, except for the irreversibility of the structural change, suggesting that the phase transformation revealed here may be a ferroelectric-to-paraelectric phase transition of polar form I crystal and the the Curie point may be about 172°C. It is consistent with Micheron's measurement of the temperature dependence of the dielectric constant. Other structural changes in the form I sample occurring in the temperature range from 20° to 170°C have also been discussed based on the i.r. spectral measurements.     

Effect of liquid fat on melting point and polymorphic behavior of cocoa butter and a cocoa butter fraction

The polymorphic behavior of cocoa butter and a high-melting fraction of cocoa butter (CBF) was investigated by differential scanning calorimetry. The effect of liquid fat on melting point and polymorphic behavior was established for six mixtures: 83.5% cocoa butter and 16.5% of a low-melting fraction of cocoa butter (CBF-LM), 90% cocoa butter and 10% olive oil, and four mixtures of CBF and olive oil containing 10%, 20%, 30%, and 50% olive oil. Six polymorphs were found for cocoa butter and at least five for CBF. The melting points for cocoa butter and CBF were 35 and 38 C, respectively. Addition of CBF-LM to cocoa butter reduced the observable polymorphs to four and the melting point to 32.5 C. In cocoa butter, 10% olive oil reduced the observable polymorphs to three and the melting point to 31.5C. Similarly, 10% olive oil in CBF reduced the observable polymorphs to three and the melting point to 37 C. Amounts of 20%, 30%, and 50% olive oil in CBF reduced the polymorphs to two and the final melting point to 34.5, 33, and 32 C, respectively. Possible explanations for the observed polymorphic behavior are advanced. Changes in the rates of tempering of cocoa butter and CBF on addition of various amounts of liquid fat are discussed.     

Scaling of the viscoelasticity of highly filled carbon black polyethylene composites above the melting point

Different types of linear low-density polyethylene and ethylene butylacrylate copolymers were mixed with various types of carbon black in amounts between 25 and 40% by weight. Viscoelastic properties were measured using dynamic mechanical analysis applying a frequency sweep. Typically, the complex modulus approaches asymptotically a constant value at small frequencies, which is referred to as ‘yield modulus’. These results were analysed using a scaling approach according to which the complex modulus and the frequency are normalised by the yield modulus and the quotient of the yield modulus and the polymer viscosity, respectively. Thus a master curve is achieved for nearly all samples independent of the polymer and carbon black type and loading. A similar scaling behaviour has been observed earlier for differently concentrated suspensions of carbon black in Newtonian liquids, but not for filled polymers and different carbon blacks. Thus, contributions from polymer and carbon black to the compounds' viscoelastic properties are discussed.     

Thermodynamic properties of carbon up to the critical point

Thermodynamic data on solid, liquid, and gaseous carbon have been carefully selected from the literature or estimated, and vapor pressure have been calculated up to the critical point. Using certain assumptions about the properties of liquid carbon and nonideal gas corrections for carbon vapor, our calculations show the triple point and critical point to be 4765 and 6810°K, respectively, with critical density 0·64 g/cm³, and critical pressure 2200 atm. The dominant vapor species above ～ 2000°K is C₃, while C₇ is also of importance from 4500 to 6810°K. Coexistence curves which summarize the densities and enthalpies of solid, liquid, and vapor carbon are plotted. The density of liquid carbon is assumed to be 20% less than that of graphite at the triple point. The enthalpy of fusion is given as 30 kcal/g-atom C. Sublimation enthalpies are found to be 50–66 kcal/g-atom C at 3000–4765°K, and vaporization enthalpies about 20 kcal/g-atom C at 4765–6000°K.     

Effect of enzymatic interesterification on the melting point of tallow-rapeseed oil (LEAR) mixture

To reduce the melting point of a tallow-rapeseed oil mixture, the triglyceride composition of the mixture was altered by enzymatic interesterification in a solvent-free system. The interesterification and hydrolysis were followed by melting point profiles and by free fatty acid determinations. The degree of hydrolysis was linearly related to the initial water content of the reaction mixture. The rate of the interesterification reaction was influenced by the amount of enzyme but not much by temperature between 50 and 70°C. The melting point reduction achieved by interesterification depended on the mass fractions of the substrates: the lower the mass fraction of tallow, the larger the reduction of the melting point.     

低熔点煤灰熔融温度调控研究进展

基于低灰熔点煤灰熔融温度的可控调整对煤的高效洁净转化意义重大,介绍了耐熔剂(Al_2O_3、SiO_2及TiO_2等单体耐熔剂和高岭土、硅基添加剂等复合耐熔剂)和配煤对低灰熔点煤灰熔融温度的影响规律,并从实验检测(XRD、SEM-EDX检测)和软件模拟(Fact Sage软件热力学计算和Gaussian量子化学计算)两方面综述了添加耐熔剂和配煤改变灰熔融温度的机理;阐述了支持向量机模型在煤灰熔融温度预测方面的应用。最后对提高低熔点煤灰熔融温度的研究方向提出了建议。     

人工神经网络建立超声耦合亚临界水提取数学模型

采用超声耦合亚临界水提取香菇多糖,用人工神经网络技术建立提取数学模型,以提取温度、提取时间、提取压力、料液比、超声功率作为网络输入,香菇多糖得率作为输出,首先对亚临界水提取和超声耦合亚临界水提取单因素条件下的香菇多糖得率进行模拟预测,然后利用Design-expert软件对影响因素进行优化实验,分别用响应曲面法和人工神经网络进行多糖得率的模拟预测对比,并对最优化条件进行实验验证。结果表明,人工神经网络拟合值与实验值能很好的吻合,其拟合效果在一定程度上优于响应曲面。     

Crystal structure, mesomorphic and emission properties of liquid crystals having a 7-(diethylamino)-3-phenylcoumarin core

Cholesteryl 4-(7-diethylamino-2-oxo-2H-1-benzopyran-3-yl)benzoate (1) had an enantiotropic cholesteric phase. The crystal structure of 1 has been determined by X-ray crystallographic analysis. The crystals of 1 had intermolecular CH...pi and CH...O interactions. 7-(Diethylamino)-3-phenylcoumarin derivatives (1) gave a strong emission band at 500 nm in the solid state when excited at 440 nm.     

Microstructure and tribological properties of in-situ TiC-C/Cu nanocomposites synthesized using different carbon sources (graphite,carbon nanotube and graphene) in the Cu-Ti-C system

For the first time, TiC-C/Cu nanocomposites were fabricated from a mixture of Cu, Ti and C powders by the use of different carbon sources (graphite, carbon nanotube (CNT) and graphene) through two-step high energy mechanical milling and in-situ synthesis by annealing, to study the effect of carbon source on phases formation and tribological properties. The results showed the presence of Cu as the matrix, TiC and unreacted carbon phases in the microstructure of sintered samples, and relatively uniform distribution of the reinforcement phase in the copper matrix was obtained. With the decrease of carbon source size, the density of sintered nanocomposites was reduced. It was revealed that using the CNT and graphene as carbon sources results in finer TiC nanoparticles, which considerably improves the tribological properties of the nanocomposite. Using CNT and graphene as carbon sources led to 15% and 49% reduction in wear volume loss and 16% and 6% decrease in friction coefficient respectively, in compassion to using graphite.     

Crystallization kinetics and multiple melting point phenomena of polybutylene naphthalate terephthalate (PBNT) copolyesters

The melting behavior and crystallization kinetics of PBNT copolyesters were studied using differential scanning calorimetry (d.s.c.). The Avrami exponent, n, increased from 2.5 to 3.0 with increasing of annealing temperature between 161 °C and 170 °C. The Avrami rate constant K increased with naphthalene content while activation energy decreased with naphthalene content. PBNT copolyesters showed three melting peaks, namely minor, lower and upper peaks respectively. The minor peak and lower peak grew with the increasing annealing temperature and holding time, while upper peak decreased. When scanning rate increased, minor peak and lower peak shifted to high temperature but upper peak decreased. Received: 22 April 1997/Revised: 24 June 1997/Accepted: 4 July 1997