国外复合材料用高级增强纤维的发展现状

本文综述了国外碳纤维、陶瓷、聚芳酰胺、超高分子量聚乙烯、液晶聚合物纤维的发展现状,包括它们的生产能力、消费情况、性能特点,主要生产国和生产公司、产品牌号以及应用领域等,并指出了其生产进展和发展动向。     

Semiflexible random thermotropic copolymers from 8‐(3‐hydroxy phenyl) octanoic acid and 3‐chloro‐4‐hydroxy benzoic acid/3,5‐dibromo‐4‐hydroxy benzoic acid

Two series of semiflexible random thermotropic copolymers containing 8‐(3‐hydroxy phenyl) octanoic acid (HPOA) with either 3‐chloro‐4‐hydroxy benzoic acid or 3,5‐dibromo‐4‐hydroxy benzoic acid were prepared by melt polycondensation techniques. The copolyesters were characterized with Fourier transform infrared spectroscopy, dilute solution viscometry, hot‐stage polarized light microscopy, differential scanning calorimetry, thermogravimetric analysis, and wide‐angle X‐ray diffraction. Studies revealed that the amount of HPOA as a disruptor incorporated into the backbone of substituted 4‐hydroxy benzoic acids had a detrimental effect on the liquid‐crystalline behavior. Mesophase‐transition temperatures were observed between 210 and 250°C, and the optical textures were of typical nematic phases. The degree of crystallinity decreased with an increase in the HPOA content. The thermal stability of the copolymers was in the range of 310–370°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Mixtures of tertiary amine functionalized azo-containing mesogens with acid-functionalized polymers

A tertiary amine functionalized 4-nitro-4′-alkoxy azobenzene mesogen with a 10 or 12 carbon spacer (azo-nN) was synthesized and complexed in equimolar proportions with poly(acrylic acid) (PA-H) and poly(sulfonic acid) (PSS-H), and investigated by thermogravimetric analysis, differential scanning calorimetry, polarizing optical microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The neat azo-nN is characterized by a partial bilayer S_A mesophase at higher temperatures, and a highly ordered phase, in which the molecules are stacked orthogonally in bilayers, at lower temperatures. As supported by infrared analysis, for the azo-nN/PA-H mixture, the complexation is partial while for the same azo-nN/PSS-H mixture, complete proton transfer occurs. When the azo-nN is blended with the PA-H, regarded as a weak acid, a biphasic system is generated and the thermotropic behavior of neat mesogen is not significantly affected. In contrast, by mixing the same mesogen with a PSS-H (regarded as a strong acid), the thermotropic behavior is significantly influenced: the complexation generated a partial or interdigitated smectic A or tilted smectic C lamellar phase.     

A sensitivity analysis of the linear complementarity programming model: Appalachian steam coal and the natural gas market

There have been extensive attempts in recent years to perform spatial equilibrium analysis of commodity markets, particularly that of energy. Most of these attempts have been based on linear programming transportation models, and more recently quadratic programming models. Unfortunately, neither of these modelling approaches can deal with the case of multi-commodity analysis with non-symmetric regression coefficients. In this paper, we overcome this problem by employing the linear complementarity programming model. In addition, we show how the model can be applied to coal and gas energy flows within a single region. Future potential applications of the model are also implied.     

新型液晶PVDF合金的研究

本文系统地研究了液晶聚合物(LCP)与PVDF合金共混体系的组成及加工工艺条件对共混物制件性能的影响。并用SEM观察了合金的形态结构。结果表明:在液晶含量10%左右时,加工温度为210℃,合金的拉伸强度最高,磨耗量最低,体系分散均匀并形成了较多的微纤结构。     

空间相关信道下基于线性星座的预编码技术

文中首先介绍基于MIM0系统的开环预编码技术,重点讨论如何采用线性星座预编码(LCP)方法对多天线系统进行预处理,使多天线系统获得较高的分集增益与编码增益.然后,对LCP预编码系统在空间相关信道下的差错性能作深入分析,分别对弱相关信道与强相关信道两种不同情况下的LCP预编码性能展开详细讨论.最后,用MATLAB软件进行仿真试验,将经过酉星座旋转处理的预编码系统与V-BLAST多天线传输系统作比较,得出不同相关信道下预编码系统的比特差错概率,并验证相应结论.     

Influence of different polyesters and their molecular weight on the textural and electrooptical behavior of polymer‐dispersed liquid crystals

The textural and electrooptical behavior of a nematic liquid crystal (LC) dispersed in a flexible and rigid polyester was studied. The dispersion of LC in the polymer matrix and light transmission through the polymer‐dispersed liquid crystal (PDLC) is governed by the nature of the polymer, its molecular weight, and the applied voltage. It was observed that the transmission of light and the dispersion of LC maximizes their respective values at the minimum molecular weight irrespective of the nature of the polymer and at the maximum voltage. The reason is the predominance of chain alignment over entanglement at the minimum molecular weight. As molecular weight increases, the transmission of light as well as the dispersion of LC in the polymer may increase or decrease depending on the predominance of chain entanglement or chain alignment. The alignment of LC droplets in the direction of the applied voltage is increased by an increase in the applied voltage, causing enhancement of the light transmission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 284–289, 2003     

Effect of nano‐silica filler on the rheological and morphological properties of polypropylene/liquid‐crystalline polymer blends

A fumed hydrophilic nano‐silica‐filled polypropylene (PP) composite was blended with a liquid‐crystalline polymer (LCP; Rodrun LC5000). The preblended polymer blend was extruded through a capillary die; this was followed by a series of rheological and morphological characterizations. The viscosity of the PP matrix increased with the addition of the hydrophilic nano‐silica. At shear rates between 50 and 200 s^?1, the composite displays marked shear‐thinning characteristics. However, the incorporation of LC5000 in the PP composite eliminated the shear‐thinning characteristic, which suggests that LC5000 destroyed the agglomerated nano‐silica network in the PP matrix. Although the viscosity ratio of LCP/PP was reduced after the addition of nano‐silica fillers, the LCP phases existed as droplets and ellipsoids. The nano‐silicas were concentrated in the LC5000 phase, which hindered the formation of LCP fibers when processed at high shear deformation. We carried out surface modification of the hydrophilic nano‐silica to investigate the effect of modified nano‐silica (M‐silica) on the morphology of the PP/LC5000 blend system. Ethanol was successfully grafted onto the nano‐silica surface with a controlled grafting ratio. The viscosity was reduced for PP filled with ethanol‐M‐silica when compared to the system filled with untreated hydrophilic nano‐silica. The LC5000 in the (PP/M‐silica)/LC5000 blend existed mainly in the form of fibrils. At high shear rates (e.g., 3000 s^?1), the LC5000 fibril network was formed at the skin region of the extrudates. The exclusion of nano‐silica in the LC5000 phase and the increased viscosity of the matrix were responsible for the morphological changes of the LCP phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1484–1492, 2003     

Studies on morphology,mechanical, thermal,and rheological behavior of extrusion‐blended polypropylene and thermotropic liquid crystalline polymer

Polypropylene (PP) was melt‐blended in a single‐screw extruder with a thermotropic Vectra B‐950 liquid crystalline polymer (LCP) in different proportions. The mechanical properties of such blends were compared in respect of their Young's moduli, ultimate tensile strength (UTS), percent elongation at break, and toughness to those of pure PP. The thermal properties of these blends were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphology was studied by using a polarizing light microscope (PLM) and a scanning electron microscope (SEM) while the rheological aspects of the blends and the pure PP were studied by a Haake Rheowin equipment. Mechanical analysis (tensile properties) of the blends showed pronounced improvement in the moduli and the UTS of the PP matrix in the presence of 2–10% of LCP incorporation. TGA of all the blends showed an increase in the thermal stability for all the blends with respect to the matrix polymer PP, even at a temperature of 410°C, while PP itself undergoes drastic degradation at this temperature. DSC studies indicated an increase in the softening range of the blends over that of PP. Morphological studies showed limited mixing and elongated fibril formation by the dispersed LCP phase within the base matrix (PP) at the lower ranges of LCP incorporation while exhibiting a tendency to undergo gross phase separation at higher concentrations of LCP, which forms mostly agglomerated fibrils and large droplets. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 767–774, 2003     

Relationship between processing,microstructure, and mechanical properties of injection molded thermotropic LCP

A commercial thermotropic liquid crystalline polymer (LCP), Vectra A950, was injection molded into rectangular sheets of thickness ranging from 1 to 4 mm. By changing the thickness of the mold, the shear rate experienced by the TLCP melt in the mold could be varied. The 1‐mm test sample was highly anisotropic while that with larger thickness (4 mm) was less anisotropic. X‐ray diffraction profile at various depths for each of the test sample corresponded to the degree in the fiber orientation present in the test samples. The anisotropy can be described macroscopically by measuring the tensile strength and modulus in the longitudinal and transverse direction. The ratio between the longitudinal and transverse property decreases proportionally to the thickness of the test sample. This reduction corresponded to the reduction in the shear field as the thickness of the mold was increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1713–1718, 2003