Preparation and characterization of inorganic hollow fiber membranes

Inorganic hollow fiber membranes were prepared by spinning a polymer solution containing suspended aluminum oxide (Al₂O₃) powders to a hollow fiber precursor, which is then sintered at elevated temperatures. In spinning these hollow fiber precursors, polyethersulfone (PESf), N-methyl-2-pyrrolidone (NMP), and polyvinyl pyrrolidone (PVP) were used as a polymer binder, a solvent, and an additive, respectively. The inorganic hollow fiber membranes prepared were characterized using scanning electron microscope (SEM), gas permeation techniques Coulter porometer, and gravimetric analysis. Some primary factors affecting the structure and performance of the membranes such as the sintering temperature and the ratio of the aluminum oxide to the PESf polymer binder were studied extensively. The prepared inorganic membranes show an asymmetric structure, which is similar to the conventional polymeric membranes prepared from the same phase-inversion technique. The inorganic hollow fiber membrane with a higher porosity and better mechanical strength could be prepared by blending the spinning solution with a smaller amount of aluminum oxide powder.     

Ceramic asymmetric hollow fibre membranes—One step fabrication process

Ceramic hollow fibre membranes which have an asymmetric structure have been prepared in one step, using an immersion induced phase inversion technique. With this method, membranes with a high surface area per unit volume ratio can be produced, while production cost is dramatically reduced. Yttria-stabilised zirconia (YSZ) is selected as a membrane material, as it is relatively inexpensive and has superior mechanical strength as well as oxygen ion conducting properties. Therefore, both the porous and non-porous membranes prepared from the YSZ have potential applications. For example, the porous YSZ membranes can be used for fluid separations in harsh environments where normal polymeric membranes cannot be sustained, while the non-porous YSZ membranes can be applied as a solid electrolyte in electrochemical devices such as solid oxide fuel cells, oxygen pumps and chemical gas sensors.Gas permeation analysis suggests that non-porous YSZ hollow fibre membranes can be prepared at sintering temperature of 1400 °C or greater, below which the membrane contains pores. Pore sizes of the YSZ porous membrane prepared fall into the pore size range of ultrafiltration membranes. However, the surface porosities of the membranes prepared from two-population sized particles at sintering temperatures of 1200 °C and 1400 °C are around 5000 m⁻¹ and 300 m⁻¹, respectively. The former is comparable to polymeric membranes, while the latter is an order of the magnitude smaller.     

Y2O3/ZrO2中空纤维陶瓷膜的制备与表征

本文结合相转化技术和干湿法纺丝工艺制备了以YSZ(以摩尔分数为8%的Y2O3稳定的ZrO2)为原料的中空纤维陶瓷膜, 考察了YSZ粉体的粒度分布和形貌, 并研究了YSZ中空纤维陶瓷膜的气密性、 孔特性、 机械性能、 微观结构及晶型变化等.     

Synthesis of fullerenol-derived elastomers and conductive elastomers

Utilization of polyhydroxylated C₆₀ in a condensation reaction with diisocyanated oligo(tetramethylene oxide) led to the successful fabrication of elastomeric poly(urethane-ether) networks. These polymer networks exhibit interesting thermal behavior at low temperatures, improved tensile strength and elongation at ambient temperatures, and enhanced thermal mechanical stability at high temperatures. Design of conducting elastomers was made by carrying out an in situ polymerization of conductive polymer precursors in an interpenetrating fashion at the near-surface of polyhydroxylated C₆₀-hypercrosslinked elastomers. Results demonstrated that elastomers with an appreciable conductivity while retaining desirable elastic properties of the network can be achieved. The room-temperature conductivity of polyaniline interpenetrated (IPN) conducting elastomer was found to be 2.0 Scm⁻¹. The tensile strength and elongation at break of one conductive IPN elastomer was found to be 20 MPa and 480%, respectively. Interestingly, the strain dependent conductivity of these conducting elastomers was found to increase progressively above 200% of elongation. These results demonstrated, for the first instance, conductivity measurements of organic conducting elastomers at an elongation length of higher than 300%, showing a r.t. conductivity of >4.0 Scm⁻¹.     

Oxygen selective ceramic hollow fiber membranes

Oxygen ion conducting Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ hollow fiber membranes with o.d. 1.15 mm and i.d. 0.71 mm were fabricated using a sequence of extrusion, gelation, coating and sintering steps. The starting ceramic powder was synthesized by combined EDTA–citrate complexing followed by thermal treatment at 900 °C. The powder was then dispersed in a polymer solution, and extruded through a spinerette. After gelation, an additional thin coating of the ceramic powder was applied on the fiber, and sintering was carried out at 1190 °C to obtain the final ceramic membrane. The fibers were characterized by SEM, and tested for air separation at ambient pressure and at temperatures between 700 and 950 °C. The maximum oxygen flux measured was 5.1 mL/min/cm² at 950 °C.     

A simple approach to porous low-temperature-sintering BaTiO3

Porous tetragonal BaTiO 3 ceramic was successfully prepared by a combination of hydrothermal and low-temperature-sintering method.The hollow TiO2@BaCO 3 as the sintering precursor was synthesized via a simple hydrothermal method,and then porous BaTiO 3 was generated by calcining the hollow TiO2@BaCO 3 precursor at 900 ℃ without additive.The hollow TiO2@BaCO 3 structure plays two important roles in the preparing of the porous BaTiO 3 ceramic.First,the TiO2@BaCO 3 hollow structure provides high surface areas and increases the contact points between BaCO 3 and TiO2,which can reduce the sintering temperature of the BaTiO 3 ceramic.Second,the cavity of the ordered arranged TiO2@BaCO 3 hollow sphere shows important influence on the porous structure,and the pore size of the as-prepared porous BaTiO 3 ceramic can be tuned from several nanometers to hundreds nanomters by changing the sintering temperature.The formation mechanism of the porous BaTiO 3 ceramic was proposed.     

Effect of the preparation conditions on the formation of asymmetric poly(vinylidene fluoride) hollow fibre membranes with a dense skin

Integrally skinned asymmetric poly(vinylidene fluoride) hollow fibre membranes were prepared and characterized. The effects of phase inversion methods (dry-wet or wet) and spinning conditions, such as the type of solvent (NMP, DMAc), the concentration of polymer in dope solution, temperature of the external coagulation bath and the composition of the inner coagulant on the morphology and on the formation of a dense skin layer were investigated. The structure of the membranes was analyzed by scanning electron microscopy and the gas permeation properties with six different gases (He, H₂, N₂, O₂, CH₄ and CO₂) were measured at 25 °C to confirm the integrity of the selective skin layer. Under the proper conditions highly selective and permeable PVDF hollow fibre membranes were thus obtained by dry-wet spinning of a 30 wt.% PVDF solution in DMAc, using hot water (50 °C) as the external coagulant and a bore fluid of pure water as the internal coagulant. The best membrane had a selective outer skin with an effective thickness of approximately 0.2 μm. The ideal selectivity of the hollow fibres approached or even exceeded the intrinsic ideal selectivity of a dense PVDF film, for instance the selectivity for He over N₂ was 86.2 for the hollow fibre, whereas it was 83.5 for a dense PVDF reference film. DSC and FT-IR/ATR analysis indicated a higher fraction of the β-crystal phase in the selective skin and a high overall crystallinity than in the melt-processed film. The latter explains the relatively high selectivity and low permeability of the membranes. Intrinsic polymer properties make the membranes also suitable for vapour transport than for gas separation.     

Preparation of a Conducting Flexible Material from Silane Coupling Agent and Hydroxyl Terminated Polybutadiene Rubber by Hydrolysis and Condensation

Abstract

Synthesis and characterization of a flexible polymer produced from silane coupling agent (SCA) and hydroxyl terminated polybutadiene (HTPB) were performed. Mechanical properties of chemically and electrochemically prepared conducting composites synthesized from this polymer were investigated. Conductivities of the composites were also measured. Polypyrrole enhanced the mechanical properties of the chemically prepared conducting composite. Doping with iodine greatly changed the conductivity of the composite. However, the change in mechanical properties and the conductivities of the electrochemically prepared composite were not as significant when compared with the electrochemically prepared polypyrrole. Among the composites, a chemically prepared composite was highly flexible like rubber. However, the electrochemically produced composite possesses two orders of magnitude higher conductivity. Also, this composite revealed higher tensile strength and elasticity with respect to pristine polypyrrole.     

Fabrication of magnesium bentonite hollow fibre ceramic membrane for oil-water separation

In this study, low-cost magnesium bentonite (MB) was used for the fabrication of bentonite hollow fibre (BHF) membrane with high pure water flux. MB powder was initially characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), particle size distribution (PSD) analyser, Brunnauer -Emmett- Teller (BET) method, and field emission scanning electron microscope (FESEM). The BHF membrane obtained was then fabricated through dope suspension mixing, phase inversion and sintering process. The dope suspension was prepared by mixing MB, dispersant, polymer binder, and solvent using a planetary ball mill. While the spinning process was carried out at the extrusion rate of 8 mL/min, a fluid bore rate of 10 mL/min and air gap of 5 cm, and this was followed by sintering operation at 950 °C, 1000 °C, 1050 °C, and 1100 °C. The resulting BHF membrane was characterized by scanning electron microscopy (SEM) and XRD; the porosity test, water flux and oil rejection were also examined. The SEM surface morphology of BHF at sintering temperature of 950 °C showed spongy-like and nested macrovoids structure; the porosity was 49.09% with a mean pore size of 3.9 µm. The performance test on the bentonite-based hollow fibre membrane showed that the membrane prepared at 20 wt% and sintering temperature of 1000 °C, which induced high and stable permeate water flux and oil rejection of BHFC membrane were 544 L/m² h and 97%, respectively. The results have shown that the presence of magnesium in bentonite can enhance and promote the needed support material for the fabrication of hollow fibre ceramic membrane.     

Ionic liquid as hollow fibre membrane carrier for extraction of fluoroquinolone antibiotics in milk coupled with high-performance liquid chromatography quantification

A new hollow fibre liquid phase microextraction technology with an ionic liquid as the carrier was developed to determine the fluoroquinolone antibiotics in milk. In this technology, a porous polypropylene hollow fibre was filled with aqueous ionic liquid and the extraction efficiency of different factors, such as the type of hollow fibre membrane carrier, the pH and ionic strength of the donor solution, the pH of the acceptor solution, the stirring rate and the extraction time, were investigated. The optimised extraction condition was: [OMim][BF₄] impregnated in the pores of the hollow fibre; 0.1?mol?L^?1 of Na₂HPO₄ (pH 11.0) as the acceptor solution was injected into the lumen of the hollow fibre; 0.1?mol?L^?1 H₃PO₄ (pH 5.0) was used as the donor solution; 600?rpm was selected as the stirring rate; 120?min was the optimum extraction time. The proposed method provided very high factors with 130-fold, 156-fold and 116-fold enrichment of ofloxacin, ciprofloxacin and enrofloxacin, respectively.     

Acid–gel-immobilized,nanoporous composite,protonic membranes as low cost system for Direct Methanol Fuel Cells

An alternative, low cost, proton conducting electrolyte, designed for low and intermediate temperature DMCF and formed by new type of nanoporous, composite membrane in which sulphuric acid is immobilized by gelification, is here reported. The membrane is based on a polyvinylidene fluoride polymer matrix containing dispersed SiO₂ ceramic powder at nanoparticles size. The stability of the immobilized sulphuric acid gel combined with the favorable swelling effect of the extended membrane porosity give to the membrane a high proton conductivity, a low methanol crossover and a satisfactory thermal stability. Good performances both at room and intermediate temperatures are showed by Direct Methanol Fuel Cells which use this system as separator.     

Reactive Template Synthesis of Polypyrrole Nanotubes for Fabricating Metal/Conducting Polymer Nanocomposites

Unique nanocomposites of polypyrrole/Au and polypyrrole/Pt hybrid nanotubes are synthesized employing polypyrrole (PPy) nanotubes as an advanced support by solution reduction. The conducting polymer PPy nanotubes are fabricated by using pre‐prepared MnO₂ nanowires as the reactive templates. MnO₂ nanowires induce the 1D polymerization of pyrrole monomers and the simultaneous dissolution of the templates affords the hollow tube‐like structure. The loading content of metal nanoparticles in the nanocomposites could be adjusted by simply changing the amount of metal precursors. This work provides an efficient approach to fabricate an important kind of metal/conducting polymer hybrid nanotubes that are potentially useful for electrocatalyst and sensor materials.     

Effect of dope flow rate on the morphology,separation performance,thermal and mechanical properties of ultrafiltration hollow fibre membranes

We have determined the effects of dope extrusion speed (or shear rate within a spinneret) during hollow fibre spinning on ultrafiltration membrane's morphology, permeability and separation performance, and thermal and mechanical properties. We purposely chose wet-spinning process to fabricate the hollow fibres without drawing and used water as the external coagulant in the belief that the effects of gravity and elongation stress on fibre formation could be significantly reduced and the orientation induced by shear stress within the spinneret could be frozen into the wet-spun fibres. An 86/14 (weight ratio) NMP/H₂O mixture was employed as the bore fluid with a constant ratio of dope fluid to bore fluid flow rate while increasing the spinning speed from 2.0 to 17.2 m/min in order to minimise the complicated coupling effects of elongation stress, uneven external solvent exchange rates, and inner skin resistance on fibre formation and separation performance. Hollow fibre UF membranes were made from a dope solution containing polyethersulphone (PES)/N-methyl-2-pyrrolidone (NMP)/diethylene glycol (DG) with a weight ratio of 18/42/40. This dope formulation was very close to its cloud point (binodal line) in order to speed up the coagulation of nascent fibres as much as possible so that the relaxation effect on molecular orientation was reduced. Experimental results suggested that a higher dope flow rate (shear rate) in the spinneret resulted in a hollow fibre UF membrane with a smaller pore size and a denser skin due to a greater molecular orientation. As a result, when the dope extrusion speed increased, pore size, water permeability, CTE and elongation of the final membranes decreased, but the separation performance, storage modulus, tensile strength and Young's modulus increased. Most surprisingly, for the first time, we found that there was a certain critical value, when the dope extrusion rate was over this value, the final fibre performance could not be influenced significantly. The results suggested that it was possible to dramatically enhance the production efficiency of hollow fibre UF membranes with the same fibre dimension and similar separation performance by the method proposed in this paper.     

Study on the effect of spinning conditions and surface treatment on the geometry and performance of polymeric hollow-fibre membranes

Hollow-fibre membranes were prepared by the wet-dry spinning technique from polyether sulfone (PES). The effect of spinning conditions such as the flow-rate of the internal coagulant and the flow-rate, composition and temperature of the polymer solution on the geometry and performance of hollow fibres was studied. In particular, five different ratios of pore former/polymer covering the range 0.2–1.0 were investigated while the polymer content was kept constant. Since the viscosity of the spinning dope affects the morphology of the hollow-fibre membrane, hollow fibres were prepared at different temperatures of the spinning dope from 25 to 60°. By scanning electron microscopy (SEM) two layers sandwiching a finger-like cavity structure were observed. Also, the surface on the bore side of the hollow fibre was modified by grafting polyethylene glycol (PEG) with γ-ray irradiation to improve the ultrafiltration performance.     

Apparent shear strength of hybrid glass fibre reinforced composite joints

The incorporation of nano or micro ceramic particles into fibre reinforced composites (FRC) to enhance their stiffness and durability has been widely investigated. This mechanism has been attributed to the increase in stiffness of the polymeric matrix phase and shear strength of FRCs due to the presence of particles at the interlaminar regions. In order to elucidate such effect, hybrid single-lap joints consisted of ceramic particles and glass fibre reinforced composites were evaluated to better assess the mechanical interlocking effect provided by silica and cement inclusions. A full factorial design (2³) was performed to identify the effect of the type of particle (silica and cement), particle weight fraction (2.5 and 5 wt%) and glass fibre grammage (200 and 600 g/m²) on the apparent shear strength and adherent strength of single-lap joints under tensile loading. The ceramic particle inclusions led to increased apparent shear strength and adherent strength. The inclusion of 5 wt% ceramic particles into 600 g/m² cross-ply glass fibre composites enhanced both adherent and apparent shear strengths.     

Co-Electrospun BaTiO3 Hollow Fibers Combined with Sol-Gel Method

BaTiO₃ xerogel hollow fibers have been prepared firstly by co-electrospinning the sol precursor, and the polycrystalline BaTiO₃ ceramic hollow fibers were obtained after calcination at 1000°C. The obtained hollow fibers made up of well-crystallized nanocrystals were about 400 nm to several micrometers in outer diameter. The hollow BaTiO₃ fibers have been detected by means of SEM, TG, DSC, FTIR, and XRD techniques.     

Synthesis and pyrolysis of a novel preceramic polymer PZMS from PMS to fabricate high‐temperature‐resistant ZrC/SiC ceramic composite

As a valuable ultra‐high‐temperature ceramic (UHTC), ZrC was introduced to SiC ceramic for the preparation of high‐temperature‐resistant ZrC/SiC composite by a polymer‐derived method through the reaction between Cp₂Zr(CH=CH₂)₂ and polymethylsilane (PMS). The composition, structure, element distribution and pyrolysis process of the preceramic polymer polyzirconomethylsilane (PZMS) were investigated by nuclear magnetic resonance, infrared, gel permeation chromatography, X‐ray photoelectron spectroscopy, energy‐dispersive X‐ray spectroscopy, scanning electron microscopy and thermogravimetric analysis. The obtained ZrC/SiC ceramic composites had very good high‐temperature resistance with a weight loss of 7.1% after being subjected to temperatures ranging from 1200 to 2200°C, as the introduction of ZrC prevented the fast growth of crystalline β‐SiC. The ceramic composites prepared by this method were homogeneous with well‐distributed element components, and the ceramic yield reached as high as 78.4%. Copyright © 2013 John Wiley & Sons, Ltd.     

Cu2O亚微米空心球的低共熔溶剂辅助合成与表征

以低共熔溶剂(DESs)/H2O混合溶剂为介质成功制备了形貌均一、尺寸小且稳定性高的亚微米Cu2O空心球。采用扫描电镜、透射电镜和X射线衍射等方法表征了所制备样品的形貌、尺寸和结构。同时,研究了温度、p H、聚乙烯吡咯烷酮(PVP)用量等因素对样品尺寸、形貌及纯度的影响。结果表明,制备高纯Cu2O空心球的优化工艺条件为40℃、p H=11和PVP用量0.9g。混合溶剂中DESs的存在对提高所制备Cu2O样品的纯度、形态均一性和稳定性以及缩小颗粒的尺寸起到了重要作用。     

Transient thermal response of phase change material embedded with graphene nanoplatelets in an energy storage unit

This research was focused on the preparation of mixed metal oxide pigments doped with terbium ions with the general formula of Sn_0.752Co_0.08P_0.16Tb_0.008O₂. These pigments were synthesised by solid-state reactions at high calcination temperatures. The temperature range was chosen from 1350 to 1500 °C. The goal was to develop conditions for the synthesis of this type of pigments and to determine the influence of terbium ions on the colour properties of these compounds. All prepared pigments were applied into the organic matrix and into the ceramic glaze. Thermal behaviours of the reaction mixtures were investigated using differential thermal and thermogravimetric analysis. Synthesised Sn_0.752Co_0.08P_0.16Tb_0.008O₂ pigments were compared with concurrently prepared pigment Sn_0.760Co_0.08P_0.16O₂ depending on the calcination temperature with respect to the colour properties in CIE L*a*b* colour space, furthermore from the point of particle size distribution and phase composition. All compounds provided blue–violet hues that are stable in ceramic glazes.     

Uniaxial tensile tests and dynamic mechanical analysis of satin weave reinforced epoxy shape memory polymer composite

The utilization of epoxy shape memory polymer composite (SMPCs) as engineering materials for deployable structures has attracted considerable attention in recent decades due to high strength and satisfactory stiffness in comparison with shape memory polymers (SMPs). Knowledge of static and dynamic mechanical properties is essential for analyzing structural behavior and recovery properties, especially for new epoxy SMPCs. In this paper, a new weave reinforced epoxy shape memory polymer composite was prepared with satin weave technique and resin transfer molding technique. Uniaxial tensile tests and dynamic mechanical analysis were carried out to obtain basic mechanical properties and glass transition temperatures, respectively.The tensile strength and breaking elongation of warp specimens were comparable with those of weft specimens. The increment of elastic modulus and hysteresis loop areas became smaller with loading cycles, meaning that cyclic tests could obtain approximate stable mechanical properties. For dynamic mechanical properties, glass transition temperature (T_g) obtained from storage modulus curves was lower than that determined from tan delta curves and T_gs in the warp and weft directions were similar (29.4 °C vs 29.7 °C). Moreover, the storage modulus in response to T_g was two orders of magnitude less than that with respect to low temperature, which demonstrated the easy processibility of epoxy SMPCs near glass transition temperature. In general, this study could provide useful observations and basic mechanical properties of new epoxy SMPCs.