Hydrophobic Fiber Research Articles

Preparation and Characterization of Hydrophobic Porous Yttria-stabilized Zir-conia Hollow Fiber for Water Desalination

Porous yttrium-stabilized zirconia (YSZ) hollow fibers with an outer diameter of 1.92 mm, membrane thickness of 0.21 mm were prepared by a combined technique of phase inversion and sintering. The hollow fiber possessed a sandwich structure with long-finger like voids near the inner and outer walls and a thin porous sponge-like layer in the center. The porosity and average pore size of the YSZ hollow fiber were determined to be 54% and 0.56 m, respectively. The surface of the hollow fiber was converted from hydrophilic to hydrophobic by grafting with fluoroalkylsilane (FAS). The as-prepared hydrophobic YSZ hollow fiber exhibited desired water desalination performance operating in the vacuum membrane distillation (VMD). A water flux as high as 48.3 L/(m 2 h) was attained with a salt rejection of over 99.7% by exposing the shell side of the fiber to an aqueous

Novel PVDF hollow fiber membranes for vacuum and direct contact membrane distillation applications

Microporous, hydrophobic hollow fiber membranes were prepared from polyvinylidene fluoride (PVDF) under different processing conditions and by changing the composition of the polymeric dope. In particular, different additives were incorporated into the dope (Polyvinyl Pyrrolidone and Maleic Anhydride) and the molecular weight and the concentration of PVDF polymer into the dope solution (medium and high Mw, 15–18wt.%) were varied, in order to obtain fibers with different morphologies. The prepared membranes were characterized in terms of morphology, mechanical properties, bubble point, overall porosity, pore size distribution and thickness. Comparison between their performance in membrane distillation (MD), working under vacuum and direct contact configurations was also performed. The trans-membrane flux obtained was related to the membrane properties, which are function of the operating spinning conditions and the polymeric dope composition. This systematic investigation is an attempt to establish a correlation between the MD performance (in terms of trans-membrane flux) and the hollow fiber preparation conditions (polymeric dope composition and spinning conditions).

Cellulosic Substrates for Removal of Pollutants from Aqueous Systems: A Review. 3. Spilled Oil and Emulsified Organic Liquids

Water-insoluble oils, including crude petroleum and a wide variety of refined organic liquids, can cause major problems if spilled or leaked to aqueous environments. Potential environmental damage may be reduced if the spilled oil is promptly and efficiently removed from the water. This article reviews research that sheds light on the use of cellulose-based materials as sorbents to mitigate effects of oil spills. Encouraging results for oil sorption have been reported when using naturally hydrophobic cellulosic fibers such as unprocessed cotton, kapok, or milkweed seed hair. In addition, a wide assortment of cellulosic materials have been shown to be effective sorbents for hydrocarbon oils, especially in the absence of water, and their performance under water-wet conditions can be enhanced by various pretreatments that render them more hydrophobic. More research is needed on environmentally friendly systems to handle oil-contaminated sorbents after their use; promising approaches include their re-use after regeneration, anaerobic digestion, and incineration, among others. Research is also needed to further develop combined response systems in which biosorption is used along with other spill-response measures, including skimming, demulsification, biodegradation, and the use of booms to limit the spreading of oil slicks.

Super-hydrophilic electrospun nylon-6/hydroxyapatite membrane for bone tissue engineering

The present study was aimed at designing a novel bimodal fiber diameter distributed electrospun hydroxyapatite/nylon-6 (HAp/N6) biocomposite nanofiber mat for bone tissue engineering. The manufacturing of pure N6 fibers and biocomposite fibers was explored by an electrospinning process. The synthesized HAp/N6 composite mats were characterized by XRD, TGA, FE-SEM, EDS, and TEM analyses and water contact angle measurements. The results revealed that fibers of distinct sizes (nano and true-nano scale) were obtained with the addition of a wide range (1–10wt.%) of HAp. Conversion of pristine hydrophobic N6 fibers (130.3°) to super-hydrophilic (0°) composite fibers by simple blending of different amounts of HAp with N6 solution prior to electrospinning could make N6 more biocompatible for hard tissue engineering. Biomineralization was carried out by immersing the composite into simulated body fluid for different lengths of time. Results showed that the nanocomposite had a better ability to form apatite layers on the surface of the fibers compared to the pristine fibers. Therefore, our results suggest that this newly developed HAp/N6 hybrid scaffold may have potential for bone tissue engineering.

Disruption of Escherichia coli Amyloid-Integrated Biofilm Formation at the Air–Liquid Interface by a Polysorbate Surfactant

Functional amyloid fibers termed curli contribute to bacterial adhesion and biofilm formation in Escherichia coli . We discovered that the nonionic surfactant Tween 20 inhibits biofilm formation by uropathogenic E. coli at the air-liquid interface, referred to as pellicle formation, and at the solid-liquid interface. At Tween 20 concentrations near and above the critical micelle concentration, the interfacial viscoelastic modulus is reduced to zero as cellular aggregates at the air-liquid interface are locally disconnected and eventually eliminated. Tween 20 does not inhibit the production of curli but prevents curli-integrated film formation. Our results support a model in which the hydrophobic curli fibers associated with bacteria near the air-liquid interface require access to the gas phase to formed strong physical entanglements and to form a network that can support shear stress.

Ultrafiltration and osmotic evaporation applied to the concentration of cholupa (Passiflora maliformis) juice

Cholupa it's an exotic fruit that has excellent organoleptic characteristics but highly sensitive to thermal treatments. Fruit was harvested in commercial fields and for each process stage, the following physicochemical parameters were analyzed: soluble solids, pH, total solids, viscosity, and turbidity. Was used a Pellicon2® ultrafiltration system (10 kDa) with flat membranes and filtration area 0.5 m2, osmotic evaporator had a polypropylene hydrophobic hollow fiber module MD020CP2N® with area 0.104 m2. Prior to ultrafiltration, in order to obtain a higher permeate flow, juice was subjected to enzymatic treatment with commercial mixtures, found that doses of Maxoliva® (50 µl/100g) and Rapidase® (40 µl/100g) are best treatment, which had a significant effect (P<0.05) reducing the viscosity and increase soluble solids; in clarification process by ultrafiltration, permeate flux rate has a behavior that fulfills Darcy law, with 19.4 and 6.0 l m-2 h-1, as maximum and minimum, respectively. Finally, osmotic evaporation process produce a concentrate of 65.15±0.36 oBrix with homogeneous appearance, dark yellow color, which when it's reconstituted dissolves easily in water. The results show that ultrafiltration and osmotic evaporation proved to be effective and synergistic technologies to get a good quality concentrate, that preserve much original characteristics of juice. This is the first work reported about cholupa juice processing.

Studies on Surface Hydroxypropylation and Swellability of Bacterial Cellulose

Bacterial Cellulose (BC) consisting of hydrophobic ultra-fine fibers was produced by Acetobacter xylinum. Hydroxypropyl bacterial celluloses (HPBC) were synthesized by surface modification of nano-fibrils via hydroxypropylation using two modifier systems, sodium hydroxide/ propylene oxide as system (I) and sodium hydroxide/urea/propylene oxide as system (II) respectively. The equilibrium swelling ratio (ESR) of HPBC was studied. ESR of HPBC obtained from system (I) was significantly higher than that obtained from system (II). The maximum ESR of HPBC was nearly 70 times larger than that of air dried BC and 10 times larger than that of freeze dried BC.

A novel heat-resistant organic matrix adhesive for hydrophobic silica aerogels composites and 1Cr18Ni9Ti steel bonding

The novel organic matrix adhesive was used to join hydrophobic mullite fiber reinforced silica aerogels (HMF/SA) composites and 1Cr18Ni9Ti steel. It was prepared using silicone resin (SR) as a matrix, Al, low melting point glass (GP), ZnO and Fe2O3 powders as inorganic fillers, γ-aminopropyltriethoxysilane (γ-APS) as curing agent and dibutyltin dilaurate (DBTDL) as catalyst. The curing mechanism and character of the adhesive were studied, as well as the bonding mechanism of the adhesive. The tensile shear strength of the adhesive was investigated after heat-resistant experiment in atmosphere surroundings. Results showed that the adhesive could be cured at room temperature through polycondensation reaction using γ-APS. The adhesive had a good wettability with HMF/SA composites and 1Cr18Ni9Ti steel, and established strong adhesion between both of them. The adhesive could be resistant to 750°C with satisfactory bonding strength (4.68MPa). The optimized ratio of inorganic fillers had important influences on the bonding properties of the adhesive. Al took an important effect in giving a strong refractory ceramic bond to the adherends. Failure mode of joint was substrate failure due to the high chemical bonding force between the adherends.

Water dynamics inside a cathode channel of a polymer electrolyte membrane fuel cell

The present study focuses on the investigation of water dynamics inside a polymer electrolyte membrane fuel cell using two different modelling approaches: Eulerian two-phase mixture and volume of fluid interface tracking models. The Eulerian two-phase mixture model has provided overall information of species distribution inside a fuel cell and identified that the liquid water usually accumulates under the land area. The volume of fluid interface tracking model has then been implemented to investigate the emergence of water droplets from the gas diffusion layer into the cathode channel and the subsequent removal of water from the channel. Further, the effects of the location of water emergence in the cathode channel on the dynamic behavior of liquid water have been investigated. The present study shows that the water emerging into the channel near the side walls greatly reduces the surface water coverage of the channel. In order to control the water path into the channel near side walls, a further discussion has been provided that a gas diffusion layer design based on hydrophilic fibres distributed inside a hydrophobic fibre matrix could provide a precisely controlled water path through the gas diffusion layer.

Generation of Dean vortices and enhancement of oxygen transfer rates in membrane contactors for different hollow fiber geometries

This work aimed to study the enhancement of oxygen transfer rates in hollow fiber membrane contactors by applying Dean vortices. Systematic investigations of how the geometric parameters, like curve diameter, helical pitch or geometric shape, and flow rates affect the mass transport were done to assess the potential for membrane contactors. The membrane was a hydrophobic microfiltration hollow fiber (polypropylene). Helical, meander and twisted formed hollow fibers with fiber lengths from 5 to 30cm and curvature diameters between 5 and 19mm were constructed. The oxygen transfer rates per membrane area were investigated. The curved hollow fibers show a linear dependence between Dean number and enhancement factor and an increase of transfer rates up to an enhancement factor of 2.4. For the meander shaped fibers a critical Dean number/range between 10–20 was found, where the mass transport enhancement is adjusted rapidly to those of helical hollow fibers. Also the mass transfer in packed membrane modules was investigated, taking into account the theoretical packing densities of the different fiber geometries. It was found that a volumetric enhancement of gas transfer rates for helical and meander formed fibers can only be improved applying very small curvature diameters less than 4mm.

Membrane Condenser as a New Technology for Water Recovery from Humidified “Waste” Gaseous Streams

The potentialities of a membrane condenser for the selective recovery of evaporated wastewater from industrial gases have been investigated in the present paper. Membrane modules have been prepared and their performance has been evaluated in an artificial flue gas stream. A simulation study of the process has been carried out for predicting the membrane-based process performance. The achieved results indicate that a 20% water recovery (the amount to make the plant self-sufficient) can be achieved with temperature reductions less than 5 °C if flue gas is in common conditions (i.e., 50 °C < T < 90 °C and 90% < RH < 100%). To verify the results achieved by the simulation analysis a membrane module with microporous hydrophobic PVDF hollow fibers has been built, and its performance has been evaluated by feeding an artificial flue gas stream. The experimental results showed good agreement with the simulation ones, obtaining deviations less than 2.24%.

Quantitative Analysis of Amyloid-Integrated Biofilms Formed by Uropathogenic Escherichia coli at the Air-Liquid Interface

Bacterial biofilms are complex multicellular assemblies, characterized by a heterogeneous extracellular polymeric matrix, that have emerged as hallmarks of persistent infectious diseases. New approaches and quantitative data are needed to elucidate the composition and architecture of biofilms, and such data need to be correlated with mechanical and physicochemical properties that relate to function. We performed a panel of interfacial rheological measurements during biofilm formation at the air-liquid interface by the Escherichia coli strain UTI89, which is noted for its importance in studies of urinary tract infection and for its assembly of functional amyloid fibers termed curli. Brewster-angle microscopy and measurements of the surface elasticity (Gs′) and stress-strain response provided sensitive and quantitative parameters that revealed distinct stages during bacterial colonization, aggregation, and eventual formation of a pellicle at the air-liquid interface. Pellicles that formed under conditions that upregulate curli production exhibited an increase in strength and viscoelastic properties as well as a greater ability to recover from stress-strain perturbation. The results suggest that curli, as hydrophobic extracellular amyloid fibers, enhance the strength, viscoelasticity, and resistance to strain of E. coli biofilms formed at the air-liquid interface.

Desalination by air gap membrane distillation using a two hollow-fiber-set membrane module

Desalination by air gap membrane distillation (AGMD) combines in one device the processes of evaporation of water from hot brine through a porous hydrophobic membrane, condensation of the water vapor so generated on a cold condenser surface and recovery of heat in the condenser cooling liquid which may be the cold/cooled brine. Existing devices for AGMD are bulky due to the condenser arrangements adopted even though evaporation from brine may be carried out with porous hydrophobic hollow fibers. In this research we have developed a two-hollow-fiber-set based compact device where all such functions are combined in a compact device. The first fiber set consists of porous hydrophobic hollow fibers of either polypropylene (PP) or polyvinylidene fluoride (PVDF). The second set of hollow fibers is of solid PP through the bore of each such hollow fiber the cooling liquid is passed and on the outside surface of which water vapor condensation takes place. A number of modules having different packing densities of hollow fibers have been studied for desalination of brine containing 1% NaCl. The performances of such modules have been investigated for a range of feed brine temperatures as well as the flow rates of the two liquid streams, hot brine and the cooling liquid. Enhanced water vapor productivity was achieved in small laboratory devices suggesting potential for scale up.

Making Nano-Porous SiO&lt;sub&gt;2&lt;/sub&gt; Insulation through Filter-Pressing of Foamed Slurry

Nano-porous SiO2 insulation material was made from foamed aqueous slurry of nano-silica powder by filter-pressing. The foamed aqueous slurry mainly consists of hydrophobic SiO2 nano-particles, xonotlite whiskers and glass fiber. The latter two will enhance strength of the insulation material. Rheological properties of the foamed slurry with varying solid mass concentration were studied. The effect of forming pressure on the density and pore size distribution of the nano-porous silica material was investigated. It was found that the foamed slurry with solid concentration less than 17% behaves pseudoplastic as decreasing its apparent viscosity with increasing of shear rate during rheological testing. Homogeneous foamed slurry can be obtained when solid concentration in it is below 7%. Such slurry should be dewatered into solid concentration being of 10-15% before filter-pressing. Rigorously stirring of the concentrated slurry is required before pouring it into a mould, which leads to reducing the viscosity of the slurry and helps uniformly filling mould. During pressing the loading speed should be strictly controlled in order to reaching designed pore size distribution in SiO2 insulation material. The SiO2 insulation material with apparent density about 0.45g/cm3 and pore size mainly ranging from 10 to 50nm was obtained.

Effects of operational conditions on the removal of phenols from wastewater by a hollow-fiber membrane contactor

Abstract The removal of phenols from wastewater has been investigated under various operational conditions using hydrophobic hollow fiber membrane contactors. Experimental overall mass transfer coefficients were obtained in both handmade and Liqui-Cel modules. Model predictions based on a resistance in series model with solvent-filled membrane pores matched well with experimental values for tributyl phosphate/Shellsol extraction systems. However, the predictions were in poor agreement with experimental data obtained when 50% pentanol/xylene was used to treat industrial wastewater in the handmade module. Further analysis showed that the operational pressure on the aqueous side and the breakthrough pressure for the two solvents probably influenced the position of the interface within the membrane pores. This change in wetting patterns resulted in significant differences in mass transfer and solute recovery which can be accounted for by adjusting the position of the interface within the membrane fiber.

Preparation and Characterization of Amphiphilic Triblock Terpolymer-Based Nanofibers as Antifouling Biomaterials

Antifouling surfaces are critical for the good performance of functional materials in various applications including water filtration, medical implants, and biosensors. In this study, we synthesized amphiphilic triblock terpolymers (tri-BCPs, coded as KB) and fabricated amphiphilic nanofibers by electrospinning of solutions prepared by mixing the KB with poly(lactic acid) (PLA) polymer. The resulting fibers with amphiphilic polymer groups exhibited superior antifouling performance to the fibers without such groups. The adsorption of bovine serum albumin (BSA) on the amphiphilic fibers was about 10-fold less than that on the control surfaces from PLA and PET fibers. With the increase of the KB content in the amphiphilic fibers, the resistance to adsorption of BSA was increased. BSA was released more easily from the surface of the amphiphilic fibers than from the surface of hydrophobic PLA or PET fibers. We have also investigated the structural conformation of KB in fibers before and after annealing by contact angle measurements, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and coarse-grained molecular dynamics (CGMD) simulation to probe the effect of amphiphilic chain conformation on antifouling. The results reveal that the amphiphilic KB was evenly distributed within as-spun hybrid fibers, while migrated toward the core from the fiber surface during thermal treatment, leading to the reduction in antifouling. This suggests that the antifouling effect of the amphiphilic fibers is greatly influenced by the arrangement of amphiphilic groups in the fibers.

Bioactive Nano-Filters to Control Legionella on Indoor Air

Several factors affect the indoor air quality, among which ventilation, human occupancy, cleaning products, equipment and material; they might induce the presence of aerosols (or bioaerosols in the presence of biological components) nitrogen oxides, ozone, carbon monoxide and dioxide, volatile organic compounds, radon and microorganisms. Microbiological pollution involves hundreds of bacteria and fungi species that grow indoors under specific conditions of temperature and humidity. Exposure to microbial contaminants is clinically associated with allergies, asthma, immune responses and respiratory infections, such as Legionnaires Disease and Pontiac Feaver, which are due to contamination byLegionella pneumophila. Legionnaire's Disease has increased over the past decade, because of the use of central air conditioning. In places such as homes, kindergartens, nursing homes and hospitals, indoor air pollution affects population groups that are particularly vulnerable because of their health status or age, making indoor air pollution a public health issue of high importance. Therefore, the implementation of preventive measures, as the application of air filters, is fundamental. Currently, High Efficiency Particulate Air (HEPA) filters are the most used to capture microorganisms in ventilation, filtration and air conditioning systems; nevertheless, as they are not completely secure, new filters should be developed. This work aims to present how the efficiency of a textile nanostructure in a non-woven material based on synthetic textiles (high hydrophobic fibers) incorporating appropriate biocides to controlLegionella pneumophila, is going to be measured. These bioactive structures, to be used in ventilation systems, as well as in respiratory protective equipment, will reduce the growth of microorganisms in the air through bactericidal or bacteriostatic action. The filter nanostructure should have good air permeability, since it has to guarantee minimum flows of fresh air for air exchange as well as acceptable indoor air quality.

Preparation and properties of PVDF composite hollow fiber membranes for desalination through direct contact membrane distillation

► PVDF composite hydrophobic hollow fibers were prepared for membrane distillation. ► Influence of nano-particles on the membranes characteristics was investigated. ► The mechanical properties of the PVDF composite membranes were enhanced obviously. ► The spun fiber presented excellent performance stability and hydrophobicity. The polyvinylidene fluoride (PVDF) composite hydrophobic hollow fiber membranes were fabricated for membrane distillation through non-solvent induced phase inversion by dispersing hydrophobic modified calcium carbonate nano-particles in the PVDF casting solution and using the mixture of LiCl and polyethylene glycol (PEG) as non-solvent additive. The influence of nano-particles on the spun hollow fiber membrane characteristics was investigated. The addition of hydrophobic nano-particles could optimize the sandwich-like morphology, narrow the pore size distribution, improve the membrane porosity and increase the membrane surface roughness and contact angle to some extent. The nano-particles also enhanced the crystallinity degree and thermal stability of the hollow fiber. In addition, the composite membranes presented stronger mechanical properties compared to the fiber without particles. During the desalination process of 3.5 wt% sodium chloride solution, the maximum transmembrane permeate flux about 46.3 kg/m 2 h with a lower thermal loss was obtained from the composite fiber when the hot feed inlet temperature and the cold distillate inlet temperature were at 80.5 °C and 20.0 °C, respectively. Furthermore, the composite membrane exhibited satisfying performance stability compared with the pure PVDF membrane in the 30 days continuous desalination experiments, indicating that the as-spun composite fiber may be of great potential to be utilized in MD process for desalination.

Hydrophobic porous alumina hollow fiber for water desalination via membrane distillation process

Abstract This paper reports the development of hydrophobic porous alumina ceramic hollow fiber membranes for water desalination based on the membrane distillation process. The alumina hollow fiber with an average pore size of 0.7 μm was prepared by the phase inversion and sintering method. The surface of the hollow fiber was converted from hydrophilic to hydrophobic via grafting with fluoroalkylsilane (FAS). The water desalination performance of the as-prepared hydrophobic hollow fiber was tested using the vacuum membrane distillation method. By exposing the shell side of the fiber to an aqueous solution of 4 wt% NaCl at 80 °C and vacuuming the lumen side of the fiber to a pressure of 0.04 bar, a water flux of 42.9 L m−2 h−1 was attained with a salt rejection over 99.5%, which is comparable with the best performance of polymer membrane. The water flux and salt rejection was found to decrease slowly with time, but after water washing–drying the rejection was recovered completely, and the water flux largely. The hydrophobic ceramic hollow fiber membrane developed in this work is promising for practical applications.

Isothermal Ice Crystallization Kinetics in the Gas-Diffusion Layer of a Proton-Exchange-Membrane Fuel Cell

Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear ice-crystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. A validated rate expression is now available for predicting ice-crystallization kinetics in GDLs.