Mechanical Properties of Mullite–Corundum Composites Prepared from Bauxite

Mullite–corundum composites have been prepared by reaction sintering of Indian bauxite having considerable amount of impurities and silica sol. The effect of changing mullite phase proportion on the mechanical properties (i.e., flexural strength, elastic modulus, hot modulus of rupture, thermal shock resistance) of prepared composites has been studied. Flexural strength and elastic modulus increase with increasing free corundum phase content in the composites. Hot modulus of rupture for the sample containing only mullite phase increases with increasing test temperature over entire temperature range. Theoretical thermal shock resistance parameters R and R? are well supported by experimental thermal shock data.     

静电纺丝法制备聚合物功能纤维的研究进展

静电纺丝是一种可以直接、连续制备聚合物纳米纤维的新方法。通过静电纺丝法制备的直径在几纳米到几百纳米的纤维在很多领域都有潜在的应用。简单介绍了静电纺丝的原理、发展以及在各领域的应用前景,综述了静电纺丝纤维作为功能材料在吸附过滤、导电导热和保温隔热等方面的应用,并对静电纺丝技术在制备聚合物纳米纤维功能材料方面的发展前景作出了展望。     

Electrospun Silica—Polybenzimidazole Nanocomposite Fibers

A new route for the manufacturing of silica/poly(benzimidazole) (PBI) nanocomposites fibers is described. PBI was synthesized via melt polycondensation and polycondensation in poly(phosphoric acid). Solutions of PBI and silica nanoparticles in N,N‐dimethylacetamide (DMAc) were electrospun to fibers and non‐wovens. The resulting materials were analyzed by ATR‐IR spectroscopy, small‐angle X‐ray scattering (SAXS) and nitrogen sorption measurements. The non‐wovens could be processed towards dense, cross‐linked membranes by hot pressing and treatment with p‐xylylene dichloride.

     

Fibers from urea–formaldehyde resins

The preparation of fibers from aqueous urea–formaldehyde resins has been investigated; a dry spinning process has been developed based on the extrusion of catalyzed resin into a drying chamber at 180–220°C, producing a multifilament yarn at spinning speeds of up to 600 m/min. A range of UF filaments was produced with diameters between 10–70 μm; the tenacities of spun filaments were 6–10 cN/tex, initial moduli were 220–340 cN/tex, and elongation at break was 4–10%. The best tensile properties resulted from conditions that produced the smallest diameter fibers. Postspin heat treatment improved the tenacity to 14 cN/tex and the elongation to 20%. Spinnability improved with increased viscosity of the spinning solution and increased cell temperature, while tenacity and elongation increased with increasing cell temperature and spinning stretch. A correlation was found between TGA weight loss (between 105 and 200°C) and fiber tenacity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 64–74, 2000     

Phase Evolution,Microstructure, and Mechanical Properties of Alumina–Mullite–Zirconia Composites Prepared by Iranian Andalusite

This paper investigates the effects of Iranian andalusite and short milling times on alumina–mullite–zirconia composites. Andalusite powder was added at 0, 2.5, 5, and 10 wt% to an alumina–zircon mixture and the raw materials were milled for 1 or 3 h. The sintering of samples was carried out at the temperatures of 1550°C, 1600°C, and 1650°C for 3 h. Microstructural changes, phase composition, physical properties, and mechanical strength of the sintered composites were characterized by scanning electron microscopy, X‐ray diffraction, density, and strength measurement tests. Results show that andalusite promoted the decomposition of zircon and accelerated the reaction sintering of alumina–zircon, which leads to the formation of much more mullite phase and improvements to the composites’ thermal shock resistance up to about 50%.     

Fabrication of Aligned Poly(L‐lactide) Fibers by Electrospinning and Drawing

A new target collector was designed for taking up aligned nanofibers by electrospinning. The collector consists of a rotor around which several fins were attached for winding electrospun filaments continuously in large amounts. The alignment of the nanofibers wound on the collector was affected by the electrospinning conditions, such as the needle‐to‐collector distance and the applied voltage, but not by the rotation speed of the collector. At a voltage of 0.5 kV · cm^?1, about 60% of the fibers were found to be aligned within an angle of ± 5° relative to the rotational direction of the collector. The fiber alignment was improved to 90% by drawing the fiber bundle 2–3 times at 110 °C. The drawing was also effective for crystal orientation of the fibers as revealed by WAXD. The drawn fibers show improved mechanical properties.

     

硼氢化钠还原法从化学镀镍废液中回收镍

针对化学镀镍废液中存在大量可再生利用的金属镍资源,采用正交实验法和TEM,XRD,XRF等分析手段,系统研究了化学镀镍废液中镍离子硼氢化钠催化还原回收工艺。实验结果表明:回收工艺中各因素对产量影响的显著性顺序为硼氢化钠的体积浓度、反应温度、pH值、KH570的质量浓度;不同分散剂对回收产物产量和粒度影响不同,其中,使用KH570得到的回收产物的产量最大,粒度分布也较集中。推荐化学镀镍废液较优回收工艺为:硼氢化钠140mL/L,KH5703g/L,温度40℃,pH值5。按该工艺所回收的产物平均粒径为70nm,含有镍、硼和磷等元素,并且由镍-硼和镍-磷非晶态合金组成,处理后废液中镍离子的质量浓度低于1mg/L,其回收率接近100%。     

Electrospinning of Tough and Elastic Liquid Crystalline Polymer–Polyurethane Composite Fibers: Mechanical Properties and Fiber Alignment

Tough and elastic microfiber composites composed of an elastic polyurethane (Hydrothane) and a liquid crystalline polymer (Vectran) are fabricated via electrospinning. The composite fibers (HVC) are examined as a function of the mixing ratio of the polymers and evaluated on the bases of fiber formation, morphology, thermal properties, mechanical performance, and fiber alignment. The fiber diameters of the HVCs decrease as the content of Vectran increases. When the fibers are aligned via a rotating target, they have even smaller diameters and increased uniformity than when a static target is employed. Surprisingly, the aligned fibers’ mechanical properties are different than those of random orientation; the HVC fibers of random orientation display increases in strength, toughness, and elastic modulii when increasing amounts of Vectran are incorporated in the fibers. The aforementioned mechanical properties of the aligned fibers decrease somewhat as the content of Vectran is increased. Further, the durability of the aligned fibers is examined by extensional durability tests over ten cycles. The tests indicate that the HVC fibers are very durable and can function as tunable, tough, and elastic fibrous polymer scaffolds and have potential applications in high‐performance composites, polymeric filtration devices, and fibrous bioengineering materials.     

用水合肼还原法从化学镀镍废液中回收镍

化学镀镍废液量大,且含有镍和磷等资源,废液处理关系到资源循环利用与环境保护的问题.研究了以水合肼为还原剂回收化学镀镍废液中镍的工艺.实验结果表明,在初始化学镀镍废液中pH=6.5、水合肼质量浓度为20mL/L、θ为85 ℃,反应t为1.5h,废液的镍回收率可达98.5％ ～98.9％,残液中ρ(Ni2+)为71.7 ～ 94.1 mg,/L,析出的产物为黑色微粒,ω(镍)为90.5％ ～91.5％,ω(磷)为7.9％ ～8.5％.     

静电纺丝法制备La0.96Mn0.96O3纤维

以聚乙烯吡咯烷酮(PVP) 为络合剂与Mn(CH3COO)2和La(NO3)3·6H2O反应制得前驱体溶液,用静电纺丝法制备了PVP/ Mn(CH3COO)2 ·La(NO3)3纤维,经煅烧得到具有微孔结构的La0.96Mn0.96O3纤维.对所制备纤维采用红外光谱分析( IR) 、X 射线衍射(XRD) 分析、扫描电镜(SEM)等手段进行了表征.结果表明:煅烧前后纤维的性质和形貌发生很大变化.     

Electrospinning of poly(dimethyl siloxane) by sol–gel method

Crosslinked poly(dimethyl siloxane) (PDMS) fibers were fabricated by electrospinning in combination with a sol–gel process followed by heat treatment. Before and after heat treatment, the changes in the chemical and thermal properties of the electrospun PDMS fibers were examined by differential scanning calorimetry (DSC), equilibrium swelling tests, and contact angle measurements. There was no significant change in morphology and average diameter of the as‐spun PDMS fibers after heat treatment. The tensile properties of the as‐spun PDMS fibers mat increased with increasing heat treatment temperature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polypyrrole‐Fe3O4 Magnetic Nanocomposite Prepared by Ultrasonic Irradiation

Summary: Ultrasonic irradiation was employed to prepare polypyrrole (PPY)/Fe₃O₄ magnetic nanocomposite by chemical oxidative polymerization of pyrrole in the presence of Fe₃O₄ nanoparticles. This approach can solve the problem in the dispersion and stabilization of inorganic nanoparticles in polymer. The structure and properties of PPY/Fe₃O₄ nanocomposite were characterized by TEM, XPS, FT‐IR, TG, and XRD. PPY deposits on the surface of Fe₃O₄ nanoparticles while Fe₃O₄ nanoparticles are dispersed at the nanoscale by ultrasonic irradiation, which leads to the formation of polypyrrole‐encapsulated Fe₃O₄ composite particles. The doping level of PPY in PPY/Fe₃O₄ nanocomposite is higher than that of neat PPY. The composites possess good electrical and magnetic properties. With the increase in the Fe₃O₄ content, the magnetization increases and the conductivity first increases and then decreases. When the Fe₃O₄ content is 40 wt.‐%, the conductivity reaches a maximum value of 11.26 S · cm^?1, about nine times higher than that of neat PPY, and the saturation magnetization is 23 emu · g^?1. Also, the introduction of Fe₃O₄ nanoparticles enhances the thermal stability of PPY/Fe₃O₄ composite.

Conductivity of PPY/Fe₃O₄ composite at different Fe₃O₄ content.     

Mechanical and Magnetic Properties of Novel Yttria-Stabilized Tetragonal Zirconia/Ni Nanocomposite Prepared by the Modified Internal Reduction Method

Dense ceramic/metal nanocomposite has been fabricated by internal reduction method, which includes a two-step process: sintering of ceramic–metal oxide solid solution and subsequent heat treatment in a reducing atmosphere to precipitate metal nanoparticles. This novel technique has been applied to yttria-stabilized tetragonal zirconia (Y-TZP) and nickel oxide (NiO) system to fabricate Y-TZP/Ni nanocomposite. Dense Y-TZP and 0.3 mol% NiO solid solution ceramic was successively prepared by the pressureless sintering, and Y-TZP/Ni was fabricated by the internal reduction treatment. The obtained Y-TZP/Ni nanocomposite possessed characteristic intragranular nanostructure with nano-sized metallic Ni particles of around 20 nm. Fracture toughness of both the solid solution and nanocomposite was remarkably improved because of the solid solution of NiO into Y-TZP and resultant destabilization of the tetragonal phase, and the Y-TZP/Ni nanocomposite was still destabilized by the remaining nickel solution after the reduction. The nanocomposite exhibited ferromagnetism, while the Y-TZP–NiO solid solution had diamagnetic nature. Comparison of saturation magnetization values revealed that 39.5 at.% of introduced nickel was reduced to metallic nanoparticle, proving the existence of residual NiO solute in zirconia that contributed to higher toughness value than the monolithic Y-TZP. It is concluded that the introduced internal reduction method is a suitable process to achieve multifunctional ZrO₂/Ni nanocomposite with high toughness and coexistent magnetic characteristic.     

Preparation of Ultrafine Ethylene/Propylene/Diene Terpolymer Rubber Fibers by Coaxial Electrospinning

Elastomeric EPDM fibers with diameters of 200–400 nm are prepared by coaxial electrospinning of PVP/EPDM fibers, subsequent vulcanization of the polymers and finally removal of the outer PVP layer using ethanol. The initially applied PVP layer restricts the elastic recovery of the EPDM fibers. The crosslinking density of the EPDM fibers reaches 8.44 × 10^?5 mol · cm^?3. The original morphology of EPDM is preserved after removing the PVP layer. The ultrafine EPDM fibers are expected to be useful in many fields, such as brittle plastics toughening, as well as applications in extremely high or low temperatures.

     

Characterization of Phase Separation and Thermal History Effects in Magnesium Silicate Glass Fibers by Nuclear Magnetic Resonance Spectroscopy

Liquid–liquid immiscibility, leading to the separation of silica-rich and silica-poor domains, is a common phenomenon in binary silicate glasses, but can be difficult to detect and characterize when rapid cooling results in nano-scale domain dimensions. ²⁹Si nuclear magnetic resonance (NMR) spectroscopy can be very useful for detecting such phase separation, because the exclusion of paramagnetic impurity ions from the silica-rich regions can greatly slow their spin-lattice relaxation rates. Properly designed experiments can therefore largely isolate the NMR signals from high-silica and low-silica domains, and thus provide information about their proportions, compositions, and short- to intermediate-range structures. We demonstrate this approach here for fiber glasses that are predominantly magnesium, or calcium-magnesium silicates, with minor contents of alumina. For bulk compositions within the known region of stable liquid immiscibility, phase separation occurs even when extremely rapid cooling yields fibers less than 1 μm in mean diameter. Slower cooling increases the extent of separation, while the addition of small amounts of alumina reduces it.     

Development of Functional Polyurethane–ZnO Hybrid Nanocomposite Coatings from Thevetia peruviana Seed Oil

The present article reports eco‐friendly multi‐functional polyurethane–ZnO hybrid nanocomposite coatings obtained from Thevetia peruviana seed oil (TPSO). Initially, the polyols were prepared by treating TPSO with glycerol and the formation was supported by Fourier transform infrared (FT‐IR) and ¹H‐NMR studies. In the next stage, siloxane functionalized ZnO nanoparticles were added to the polyol mixture in different weight percentages (0, 1 and 2 %) and then treated with excess 4,4′‐diisocyanatodicyclohexylmethane (H₁₂MDI) in order to synthesize isocyanate terminated polyurethane nanocomposites. The polyurethane hybrids were then casted as thin films and cured under atmospheric moisture. After complete curing they were characterized by using FT‐IR, ¹H‐NMR, ¹³C‐NMR, X‐ray diffraction, scanning electron microscopy, thermogravimetric analysis, and dynamic mechanical thermal analysis techniques. The hybrid nanocomposites showed superior thermo‐mechanical and anti‐corrosive properties compared to pristine polyurethane. Also, due to the presence of nano ZnO in the polyurethane matrix, the composite coatings are showing excellent resistance towards various bacterial and fungal stains.     

Comparatively Thermal and Crystalline Study of Poly(methyl‐methacrylate)/Polyacrylonitrile Hybrids: Core–Shell Hollow Fibers,Porous Fibers,and Thin Films

The polyacrylonitrile/polymethyl‐methacrylate (PMMA/PAN) porous fibers, core–shell hollow fibers, and porous thin films are prepared by coaxial electrospinning, single electrospinning, and spin‐coating technologies, respectively. The different morphologies arising from different processes display great influences on their thermal and crystalline properties. The adding of PMMA causes porous structure due to the microphase‐separation structure of immiscible PMMA and PAN phases. The lower weight loss, higher degradation temperature, and glass‐transition temperatures of porous thin films than those of porous fibers and core–shell hollow fibers are obtained, evidencing that the polymer morphologies produced from the different process can efficiently influence their physical properties. The orthorhombic structure of PAN crystals are found in the PMMA/PAN porous thin films, but the rotational disorder PAN crystals due to intermolecular packing are observed in the PMMA/PAN porous fibers and core–shell hollow fibers, indicating that different processes cause different types of PAN crystals.