Preparation and characterization of electrospun,biodegradable membranes

Nonwoven, biodegradable membranes fabricated by electrospinning have recently attracted a great deal of attention for biomedical applications. In this study, microporous, nonwoven membranes of poly(L ‐lactide) and its copolymers and blends were fabricated through electrospinning. The structures and morphologies of the electrospun membranes were investigated with scanning electron microscopy, differential scanning calorimetry, and X‐ray diffraction. Different polymer membranes, incorporated with carmofur, were fabricated, and their drug release profiles were investigated. Scanning electron microscopy images showed that the fiber diameters were down to the nanometer range. The diameters and morphologies of thenanofibers depended on processing parameters such as the solution properties (concentration and polymer molecular weight), applied electric voltage, solution feeding rate, and needle diameter. Differential scanning calorimetry showed that the crystallinity of the electrospun membranes was lower than that of the cast film. For all the membranes incorporated with the drug, there was a burst release in the first 10 h of incubation in phosphate‐buffered saline at 37°C. Poly(glycolide‐co‐lactide) membranes showed faster and more complete drug release than poly(L ‐lactide), and this could be attributed to its faster degradation. The incorporation of polylactide–poly(ethylene glycol) could shorten the drug release time. A combination of suitable degradable biomaterials with an appropriate electrospinning process could be useful in the fabrication of a new kind of membrane suitable for different biomedical applications such as tissue engineering and drug delivery. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of polymerization conditions on the viscosity and yield of poly(phenylene sulfide ether)

High molecular weight poly(phenylene sulfide ether) (PPSE) was successfully synthesized by reaction of 4,4′‐dihydroxy diphenyl sulfide with 4,4′‐dichloro diphenyl sulfide in N‐methyl‐2‐pyrrolidone (NMP). The influence of polymerization conditions on the intrinsic viscosity and yield of PPSE was investigated and the optimized reaction condition was concluded. Reactions at about 180°C for 6 h along with sodium benzoate as an additive and monomer concentration of 0.588 mol/L NMP were found to produce the highest intrinsic viscosity (0.55 dL/g). Longer reaction time and/or higher temperature reduced the intrinsic viscosity and yield of the resulting product, probably due to side reactions, such as reductive dehalogenation and chemical degradation. X‐ray diffraction indicated that the polymer possessed of orthorhombic cell and had a high crystallinity of 65.8%. The high molecular weight PPSE is a crystalline polymer with T_m of 252°C and T_mc of 224°C. The polymer shows good chemical resistance, but is soluble in organic amide, halo‐hydrocarbon and oxohydrocarbon solvent at a temperature over 150°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Mechanical and morphological properties of epoxy resins modified by poly(phthalazinone ether sulfone ketone)

A series of blends have been prepared by adding a novel thermoplastic poly(phthalazinone ether sulfone ketone) (PPESK) in varying proportions to diglycidyl ether of bisphenol A epoxy resin (DGEBA) cured with p‐diaminodiphenylsulfone (DDS). All the blends showed two‐phase structures characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Addition of the PPESK resulted in great enhancement of glass transition temperatures (T_g) both in the epoxy‐rich phase and in the PPESK‐rich phase by reason of the special structure of PPESK. There was moderate increase in the fracture toughness as estimated by impact strength. Fracture mechanisms such as crack deflection and branches, ductile microcracks, ductile tearing of the thermoplastic, and local plastic deformation of the matrix were responsible for the increase in the fracture toughness of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Amorphous carbon-matrix composites with interconnected carbon nano-ribbon networks for electromagnetic interference shielding

Carbon-matrix composites with self-assembly interconnected carbon nano-ribbon networks were fabricated using natural and inexpensive rice husks by impregnating the rice husks with transitional metal solutions and sintering. The nano-structure of the composite was characterized using transmission electron microscopy. The electromagnetic interference shielding effectiveness of the composite was evaluated in the frequency range of 30 kHz–1.5 GHz. The electrical conductivity was measured as a function of the sintering temperature. These characteristics were compared with those of carbon-matrix composites without nano-ribbon networks.     

Cure behavior and thermal stability analysis of multiwalled carbon nanotube/epoxy resin nanocomposites

As‐received multiwalled carbon nanotubes (MWCNTs) were first treated by a 3 : 1 (v/v) mixture of concentrated H₂SO₄/HNO₃ and further functionalized by ethylenediamine/dicyclohexylcarbodiimide/tetrahydrofuran solution. MWCNT/epoxy nanocomposites were prepared. Their cure behaviors were investigated by dynamic differential scanning calorimetry. Quantitative analysis of the activation energy as a function of the degree of curing was carried out by the Flynn‐Wall‐Ozawa method. The fitted multiple regression equations for values of the activation energy of different systems were obtained. MWCNTs have the retardation effect on the cure reaction of epoxy resin, while the functional groups on the surface of amine‐modified MWCNTs could accelerate the cure reactions. Thermal stability was studied by thermogravimetric analysis. The filling of amine‐modified MWCNTs is beneficial to lower the cure activation energy and improve thermal stability of the nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

基于FEM的承受附加载荷的法兰连接安全评价

在考虑垫片力学性能的非线性和非保守的基础上,建立了承受附加载荷高温螺栓法兰连接结构的有限元分析方法.运用APDL和UIDL开发了基于ANSYS环境的法兰连接结构强度和紧密性分析模块,实现了连接系统的参数化建模及程序化计算.提出了基于紧密性的承受附加载荷螺栓法兰连接的安全评价方法,并以某铂重整装置接管法兰连接为对象,验证了有限元分析和安全评价方法的可行性,确定了该连接的安全操作条件.研究结果为承受附加载荷的螺栓法兰连接系统的安全评价和结构设计提供了借鉴.     

低碳钢回火过程中Cu、Nb析出的相互作用

研究了两种不同成分的低碳钢在600 ℃条件下经不同时间回火处理后的硬度变化,并对600 ℃回火18 h的样品析出物进行组织观察、TEM观测及粒度统计。结果表明：C-Nb钢和C-Cu-Nb钢在600 ℃条件下,短时间回火硬度趋势相反,长时间回火硬度趋势平缓,说明Cu和Nb的析出过程独立存在,析出时间和规律不同;Cu-Nb钢中Nb析出物颗粒尺寸明显大于C-Nb钢,说明Cu的添加促进了Nb析出物的长大。     

DZ40M钴基合金铝化物涂层的循环氧化

以新型定向凝固钴基高温合金ＤＺ４０Ｍ为基体,研究其低压化学气相沉积铝化物涂层的循环氧化行为,发现该涂层具有较高的抗循环氧化性能,涂层与基体结合良好。涂层退化主要是由外表面氧化膜的愈合消耗Ａｌ源所造成,沉积渗剂中加入Ｔｉ可加速涂层的退化。     

表面状态对轿车用新型齿轮钢疲劳寿命的影响

较详细地研究了表面应力状态和表面光洁度等对汽车用齿轮的疲劳寿命的影响规律。实验发现,随着喷丸形成的表面应力增大,齿轮疲劳寿命显著增加,而且表面光洁度的改善也能明显提高齿轮的疲劳寿命。     

内电解法处理工业废水

用内电解法对印染废水、靛蓝生产废水、电镀废水及炼油厂含油废水进行了试验,结果表明,CODCr的去除率可达50％－70％,色度、硝基苯、酚、重金属离子及油的去除率可达90％以上。