Large-scale synthesis of hollow carbon fibers with ultra-large diameter by thermally controlled pyrolysis

Hollow carbon fibers (HCF) with ultra-large diameter have been synthesized and the versatility to convert them into the corresponding carbon-based composites has been demonstrated. The hollow carbon fibers were fabricated by thermal controlled carbonization of electrospun polyacrylonitrile fibers. For the existence of inorganic silica shell during pyrolysis, heat release will be blocked at the boundary, driving the polyacrylonitrile precursor fiber to form hollow structure. The diameter of the as-prepared hollow carbon fibers can exceed 150 nm. Sol-gel-derived Fe₃O₄ nanoparticles can grow on the outer-surface and the inner-surface of hollow carbon fibers. The microwave absorption performance of ternary HCF@Fe₃O₄@PPy composite is testified and the values of reflection loss exceeding −10 dB can be obtained in the frequency of 3.3-11.3 GHz. The large diameter of hollow carbon fibers can have inner and outer interfaces in the corresponding composites, which make them great potential for a variety of applications in future.     

Separation of NaCl, glycin from collagen solution by the thermal sensitive polyurethane membrane

A novel thermal sensitive polyurethane (TSPU) membrane with a thermal switch was prepared via wet phase inversion technique and used for separation of NaCl, glycin from collagen solution. From Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD), it was found that the TSPU showed segmented structure (i.e. the hard segment and soft segment) and independent phase transition temperatures (the phase transition temperature of the soft segment defined as switch temperature, T_s). Scanning Electron Microscope (SEM) and Atom Force Microscope (AFM) were employed to study the morphology structures of membranes, the results indicated that the membrane showed relative dense surfaces (or skin) and porous cross sections, which controlled their selectivity and permeation. The porosity of membrane measured by the mass loss of wet membrane after drying revealed that when the temperature varied ± 10 °C around the T_s, the porosity of membranes increased from 51.7% to 73.3%, showing a significant improvement to thermal stimuli. When this TSPU membrane was used for separation of NaCl, glycin from collagen solution, we found the ions of Na⁺ and Cl⁻ could permeate the TSPU membrane at any temperature, and higher temperature resulted in higher penetration rate. Whilst the penetration of glycin relied on the temperature variation, that is, a barrier effect at lower temperature (T < T_s) and higher permeation fluxes at higher temperature were observed. Typically, when the temperature exceeded the T_s, the permeation flux of glycin increased markedly, showing sensitivity to thermal stimuli. Collagen, due to its large molecule size, could not permeate the TSPU membrane in all temperature range. As a result, molecules of NaCl, glycin and collagen with different size could be selectively separated by TSPU membrane driven by the temperature.     

Pervaporative dehydration of diethylene glycol through a hollow fiber membrane

In this study, the pervaporative dehydration of diethylene glycol (DEG) through a commercial hollow fiber membrane was investigated at various feed temperatures in the range of 333–363 K with feeds containing 0.5–2.0 wt % water. Unlike the usual pervaporative dehydration process in which water is less volatile than the organic solvent, the feed mixture used in this study contained the organic component DEG, which is less volatile than water, resulting in unique permeation behaviors. The permeation behaviors of the individual components were investigated as functions of the feed temperature and feed composition. In particular, the effect of the low vapor pressure characteristics of DEG was investigated. Semi‐empirical equations for predicting the individual component fluxes and separation factor were quantified directly from actual dehydration pervaporation of DEG. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of polysulfone hollow fiber affinity membrane modified with mercapto and its recovery properties. I. Synthesis and preparation of hollow fiber matrix membrane

Several kinds of chloromethyl polysulfones (CMPSF) with different chlorinity and reactive groups were synthesized by Friedel‐Crafts reaction, which could be utilized as reactively matrix membrane materials. The CMPSF hollow matrix membranes were prepared with phase inversion by utilization of the CMPSF/additive/DMAC casting solution and CMPSF as membrane materials. The rheological behavior of CMPSF/additives/DMAC spinning casting solution was studied. The experimental results showed that the spinning casting solution was a pseudoplastic fluid, the apparent viscosity of the spinning casting solution decreased with the increase of shearing rate, and the viscous flow activity energy of the spinning casting solution was inclined to unchange at high shearing rate. The effects of composition of spinning casting solution and process parameters of dry–wet spinning on the structure of CMPSF hollow fiber matrix membrane were investigated. The pore size, porosity, and water flux of membrane decreased with the increase of additive content, bore liquid, and dry spinning distance. With the increase of extrusion volume outflow, the external diameter, wall thickness, and porosity of the hollow fiber matrix membrane increased, but the pore size and water flux of the membrane decreased. It was also found that the effects of internal coagulant composition and external coagulant composition on the structure of CMPSF hollow fiber matrix membrane were different. The experimental results showed that thermal drawing could increase the mechanical properties of CMPSF hollow fiber matrix membrane and decrease the pore size, porosity, and water flux of the CMPSF hollow fiber matrix membrane, and the thermal treatment could increase the homogeneity and stability of the structure of the CMPSF hollow fiber matrix membrane. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 758–771, 2006     

Porous hollow fibers with controllable structures templated from high internal phase emulsions

A technique to fabricate hollow fibers with porous walls via templating from high internal phase emulsions (HIPEs) has been demonstrated. This technique provides an environmentally friendly process alternative to conventional methods for hollow-fiber productions that typically use organic solvents. HIPEs containing acrylate monomers were extruded into an aqueous curing bath. Osmotic pressure effects, manipulated through differences in salt concentration between the curing bath and the aqueous phase within the HIPE were used to control the hollow structures of polyHIPE fibers. The technique was used to produce porous fibers (with millimeter-scale diameters and micron-scale pores) having a hollow core (with a diameter of 50%–75% of the fiber diameter). Two potential applications of the hollow fibers were demonstrated. In vitro drug release studies using these hollow fibers show a controlled release profile that is consistent with the microstructure of the porous fiber wall. In addition, the presence of pores in the walls of polyHIPE fibers also enable size-selective loading and separation of functional materials from an external suspension.     

Processing of multilayered filament composites by melt blown spinning

Newly designed layer multiplying blocks are introduced in the process line of a melt blown spinning machine. The layer multiplying blocks have the capability to produce filament composites up to 1025 layers. Multilayer filament composites of polypropylene (PP) with poly(caprolactone) (PCL), a water soluble polyester or poly(l ‐lactic acid) are successfully produced in the form of nonwovens. Selected samples of PP/PCL are delaminated using the following methods: semi‐crystalline PP/PCL samples are soaked in chloroform and agitated, and amorphous PP/PCL samples are subjected to mechanical stress in the axial spinning direction. Results show the possibility to create thin ribbons with extremely high surface area. The produced nonwovens and ribbons are characterized by field emission scanning electron microscopy and by differential scanning calorimetry. The extremely high surface area ribbons can be applied in different fields where high surface area is required, such as filtration, energy applications, catalysis, or tissue engineering. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40786.     

The effect of the production method on the mechanical strength of an alumina porous hollow fiber

The mechanical strength of inorganic porous hollow fibers is an important property and is strongly affected by the production method. Three production methods for fibers are compared: non-solvent induced phase separation (NIPS), bio-ionic gelation with an internal multivalent ion source (BIG-I), and with an external ion source (BIG-E). The BIG-E fibers show insufficient mechanical integrity for strength analysis. Fibers prepared via BIG-I have a larger bending strength compared to fibers prepared using NIPS or BIG-E, combined with a larger scatter in their strength data. The large scatter likely originates from surface deformations present in the fiber wall, which can be reduced by further optimization of the production method. Statistical models are fitted to the measured strength data. The NIPS and BIG-I production methods yield fibers of which the strength distribution follows the Weibull model, presuming failure occurs at the weakest link.     

Preparation of polysulfone hollow fiber affinity membrane modified with mercapto and its recovery properties. II. Preparation of PSF‐SH hollow fiber affinity membrane for recovery of Hg2+

A high qualified polysulfone hollow fiber affinity membrane modified with mercapto as chelating groups was prepared by phase inversion technology using chlormethyl polysulfone (CMPSF) as membrane matrix materials, through the reaction between thiourea and CMPSF hollow fiber matrix membrane to afford the methyl isothiourium polysulfone and was then alkaline hydrolyzed. The adsorption isotherms of the hollow fiber affinity membrane chromatography for Hg²⁺ were determined, and the effects of mobile phase conditions and the operating parameters on removal performance of the hollow fiber affinity membrane chromatography for Hg²⁺ were also investigated. The experimental results showed that adsorption isotherms of Hg²⁺ could be described by the Langmuir isotherm. Addition of NaCl into feed solution for the increase of ionic strength was harmful for the removal of Hg²⁺. The recovery of Hg²⁺ decreased at low pH and the optimum range of pH was from 5.0 to 7.0. The feed concentration had a remote effect on recovery of Hg²⁺ at the specified loading amount of Hg²⁺, and the Hg²⁺ could be removed from different concentration feed solution by the hollow fiber affinity membrane chromatography. The increase of feed flow rate led to slight decrease of recovery of Hg²⁺ at the specified loading amount of Hg²⁺. The hollow fiber affinity membrane chromatography could be operated at height feed flow rate and a large scale removal of Hg²⁺ could be realized. With the increase of load amount, Hg²⁺ recovery decreased, but the saturation degree of hollow fiber affinity membrane chromatography increased. According to required recovery of Hg²⁺ and the saturation degree of membrane chromatography, the optimum loading amount of Hg²⁺ should be selected in the actual removal of Hg²⁺. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4795–4803, 2006     

Desalination with a cascade of cross‐flow hollow fiber membrane distillation devices integrated with a heat exchanger

Cost‐efficient desalination technology was developed successfully by integrating a countercurrent cascade of the novel cross‐flow direct contact membrane distillation (DCMD) devices and solid polymeric hollow fiber‐based heat exchange devices. Simulations have been carried out for the whole DCMD cascade to project values of gained output ratio (GOR) as a function of the number of DCMD stages as well as other important factors in the cascade vis‐à‐vis the temperatures and flow rates of the incoming hot brine and cold distillate streams. The simulation results were verified with experimental results from cascades consisting of two to eight stages. The numerical simulator predicts a GOR of 12 when unequal flow rates of the incoming brine and distillate streams are used. An artificial sea water was concentrated eight times successfully when a countercurrent cascade composed of four stages of the DCMD modules and a heat exchanger was used during the DCMD process. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Preparation of porous hollow fiber membranes with a triple‐orifice spinneret

A triple‐orifice spinneret has been applied for the preparation of hollow fiber microfiltration membranes with a high surface porosity. Considering the general rules of diffusion induced phase separation, a low polymer concentration is required at the outer layer to obtain a highly interconnected open‐porous structure. Therefore, by using N‐methylpyrrolidone (NMP) as the external liquid at the outside orifice of the spinneret, a highly porous surface can be obtained. For a polymer solution containing a low molecular weight additive and with an initial concentration close to the cloud point, this technique shows slightly improvement on the pure water and gas fluxes since the major resistance of the membrane is located at the substructure and the inner skin. However, for a solution containing a high molecular weight additive and with an initial concentration far from the cloud point, a porous shell surface is obtained, resulting in a significant improvement in water flux. The effect of various external liquids on the morphology has been investigated as well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2151–2157, 2003     

Effect of diluent on poly(ethylene‐co‐vinyl alcohol) hollow‐fiber membrane formation via thermally induced phase separation

Poly(ethylene‐co‐vinyl alcohol) hollow‐fiber membranes with a 44 mol % ethylene content were prepared by thermally induced phase separation. A mixture of 1,3‐propanediol and glycerol was used as the diluent. The effects of the ratio of 1,3‐propanediol to glycerol in the diluent mixture on the phase diagram, membrane structure, and membrane performance were investigated. As the ratio increased, the cloud point shifted to lower temperatures, and the membrane structure changed from a cellular structure due to liquid–liquid phase separation to a particulate structure due to polymer crystallization. Better pore connectivity was obtained in the hollow‐fiber membrane when the ratio of 1,3‐propanediol to glycerol was 50:50, and the membrane showed about 100 times higher water permeability than the membrane prepared with pure glycerol. For the prepared hollow‐fiber membrane, the solute 20 nm in diameter was almost rejected. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 219–225, 2005     

Improved spinnerette design for extrusion of polymeric large internal diameter hollow fiber membranes

Spinnerettes for extrusion of large (～ 1 mm) internal diameter (i.d.) hollow fiber membranes must possess certain features to extrude fibers with the proper tensile and geometrical properties. Spinnerette designs that properly extrude small i.d. (< 200 μm) hollow fibers will produce large i.d. hollow fibers with low burst strengths because of poor flow patterns and insufficient time in the spinnerette to knit a strong seam interface. In this report, an alternative design is offered that provides much better fiber properties without creating high pressure drops or shear stresses at the spinnerette wall that would normally result in melt fracture. The equations that guide the presented spinnerette design are provided and the suggested design is successfully guided by the results. The new spinnerette design also has the feature of allowing rapid change of hollow fiber wall thickness by making the core fluid pin replaceable. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2157–2163, 2002     

Formation of continuous dense polymer layer at the surface of hollow fiber using a photografting process

The surface modification of a PES hollow fiber by UV photografting has been investigated in order to graft a dense polymer layer. The study focused on a UV photografting process, starting from a monomer solution, enabling the thickness and regularity of the grafted polymer to be followed. 2‐(Acryloyloxy)ethyl trimethylammonium chloride was polymerized on the surface of the PES membrane. Modified membranes were characterized by SEM, FTIR spectroscopy, and liquid and gas permeability. A dense layer of poly(2‐(acryloyloxy)ethyl trimethylammonium chloride) was obtained when a photoinitiator and a photocrosslinker were used. Polymerization of the ammonium material also occurred inside the pores of the membrane. With pretreatment and an increase of the irradiation time, the thickness of the grafted polymer decreased and gas permeability reached measurable levels. However, a CO₂/N₂ selectivity of around 1 was found which suggested the presence of defects in the grafted layer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41514.     

高固含量水性聚氨酯的合成及其成膜性能的研究

采用预聚体分散法制备出50%以上固含量的水性聚氨酯,考察了软链段分子链长及硬链段含量对聚氨酯相分离行为、热性能及力学性能等的影响。研究表明:硬链段含量、软链段链长的提高和离子基团的增加均有利于拉伸强度的提高。     

Dual-layer hollow fibers for gas separation processes produced by quadruple spinning

A novel quadruple spinneret to produce dual-layer hollow fiber membranes by simultaneous spinning of two polymer solutions, using the dual precipitation bath technique is proposed. Hollow fibers aimed at gas separation processes were prepared in extrusion system specifically designed and built for this purpose. A polyurethane polymer was selected as the selective layer (outer-layer), while polyethersulfone was defined as the support (inner-layer). Activated carbon powder was added into the PU solution for further improvement of the transport properties. The hollow fibers showed good adhesion between the polymer layers and a defect-free selective layer. Representative results include a CO₂/N₂ selectivity of 43.     

Metal‐chelated polyamide hollow fibers for human serum albumin separation

We modified microporous polyamide hollow fibers by acid hydrolysis to amplify the reactive groups and subsequent binding of Cibacron Blue F3GA. Then, we loaded the Cibacron Blue F3GA‐attached hollow fibers with different metal ions (Cu²⁺, Ni²⁺, and Co²⁺) to form the metal chelates. We characterized the hollow fibers by scanning electron microscopy. The effect of pH and initial concentration of human serum albumin (HSA) on the adsorption of HSA to the metal‐chelated hollow fibers were examined in a batch system. Dye‐ and metal‐chelated hollow fibers had a higher HSA adsorption capacity and showed less nonspecific protein adsorption. The nonspecific adsorption of HSA onto the polyamide hollow fibers was 6.0 mg/g. Cibacron Blue F3GA immobilization onto the hollow fibers increased HSA adsorption up to 147 mg/g. Metal‐chelated hollow fibers showed further increases in the adsorption capacity. The maximum adsorption capacities of Co²⁺‐, Cu²⁺‐, and Ni²⁺‐chelated hollow fibers were 195, 226, and 289 mg/g, respectively. The recognition range of metal ions for HSA from human serum followed the order: Ni(II) > Cu(II) > Co(II). A higher HSA adsorption was observed from human serum (324 mg/g). A significant amount of the adsorbed HSA (up to 99%) was eluted for 1 h in the elution medium containing 1.0M sodium thiocyanide (NaSCN) at pH 8.0 and 25 mM ethylenediaminetetraacetic acid at pH 4.9. Repeated adsorption–desorption processes showed that these metal‐chelated polyamide hollow fibers were suitable for HSA adsorption. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3346–3354, 2002     

Influence of sintering temperature on the morphology of ceramic hollow fibers prepared from niobium pentoxide

Ceramic hollow fibers were prepared by the phase inversion and sintering method using niobium pentoxide (Nb₂O₅) as an innovative starting material. X-ray diffraction and Raman analyses revealed the same monoclinic crystalline phase for the ceramic material, H-Nb₂O₅, at all the evaluated sintering temperatures. According to SEM images, the starting material was composed of polydisperse particles of irregular size and shape with sizes ranging from 12.5 to 89.7 μm. The increase in the sintering temperature caused particles agglomeration. In the hollow fiber precursor (without sintering), Nb₂O₅ grains were surrounded by the coagulated polymer. The polymeric phase was eliminated when the fibers were sintered at temperatures above 600°C. When sintered at 1350°C, the outer surface of the fiber presented elongated crystals of well-defined shape, while agglomerated round shape grains were observed at the inner surface of the fiber. Formation of these elongated crystals was probable due to the material sintering at high temperatures (up to 1350°C) for more than 300 minutes. This study demonstrated the potential for general applicability of niobium pentoxide to fabricate ceramic hollow fiber membranes.     

Formation Mechanism Analysis of Shear-Induced Microgel Filaments during Microfluidic Gelation

Dynamic microfluidic gelation enables the fabrication of bundle-structured multiple parallel microgel filaments from an aqueous two-phase system. The formation mechanism of shear-induced filaments from an alginate (Alg)/polyvinyl alcohol (PVA) blend is studied using red-colored PVA and a titanium alkoxide PVA crosslinker. Bundle-structured Alg microgel filaments are formed through contact with a Ca²⁺ crosslinker. In this process, the PVA acts as a sacrificial polymer to maintain the Alg gel filaments because approximately 90% of the red-colored PVA is released from the Ca²⁺-crosslinked Alg gel filaments into the wash water. In addition, the fabrication of PVA gel filaments shows that the sacrificial PVA is also transformed into fibrillar domains under shear. However, the filament structure cannot be formed from a single-phase PVA/Alg solution. These results clearly show that the bundle-structured gel filaments are maintained by preventing the fusion of filaments during gelation based on the tendency of the non-crosslinked filaments to cause splitting of the gelled filaments.     

Preparation and characterization of nanohydroxyapatite strengthening nanofibrous poly(L‐lactide) scaffold for bone tissue engineering

A biomimetic nanofibrous poly(L ‐lactide) scaffold strengthened by nanohydroxyapatite particles was fabricated via a thermally induced phase separation technique. Scanning electron microscopy results showed that nanohydroxyapatite particles uniformly dispersed in the nanofibrous poly(L ‐lactide) scaffold (50–500 nm in fiber diameter) with slight aggregation at a high nHA content, but showed no influence on the interconnected macroporous and nanofibrous structure of the scaffold. The nanofibrous poly(L ‐lactide) scaffold presented a specific surface area of 34.06 m² g^?1, which was much higher than that of 2.79 m² g^?1 for the poly(L ‐lactide) scaffold with platelet structure. Moreover, the specific surface area of the nanofibrous scaffold was further enhanced by incorporating nanohydroxyapatite particles. With increasing the nanohydroxyapatite content, the compressive modulus and amount of bovine serum albumin adsorbed on the surface of the nanofibrous composite scaffold were markedly improved, as opposed to the decreased crystallinity. In comparison to poly(L ‐lactide) scaffold, both the nanofibrous poly(L ‐lactide) and poly(L ‐lactide)/nanohydroxyapatite scaffolds exhibited a faster degradation rate for their much larger specific surface area. The culture of bone mesenchymal stem cell indicated that the composite nanofibrous poly(L ‐lactide) scaffold with 50 wt % nanohydroxyapatite showed the highest cells viability among various poly(L ‐lactide)‐based scaffolds. The strengthened biomimetic nanofibrous poly(L ‐lactide)/nanohydroxyapatite composite scaffold will be a potential candidate for bone tissue engineering. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013