Hydrophobic Fiber Research Articles

Hydrophobic and Hydrophilic Hollow Fiber Membranes for Co2 Stripping via Gas-Liquid Membrane Contactor

Hydrophobic and Hydrophilic Hollow Fiber Membranes for Co2 Stripping via Gas-Liquid Membrane Contactor

An Amphiphilic Acrylic Copolymer/Montmorillonite Nanocomposite

A bi-component copolymer/layered silicate nanocomposite was synthesized by way of a two-stage radical copolymerization of emulsion intercalation and solution intercalation, using acrylates, methacrylic acid and acrylamide as monomers. The water-based product was designed with a structure of a hydrophobic copolymer dispersed in an aqueous copolymer solution to meet needs of warp sizing agents on adhesiveness to hydrophobic and/or hydrophilic fibers, appropriate glass transition temperature, as well as water-solubility. XRD patterns for the product films showed an exfoliated structure of montmorillonite (MMT) in the part of soluble acrylic copolymer as the MMT content equal to or less than 7%, while in the part of emulsion copolymer alone or the product as a whole, the MMT showed an intercalated structure. Determination of DSC indicated that chemical bondings occured between the hydrophobic and hydrophilic components, which guaranteed storage stability of the system and water-solubility of the sizing film, and that there were threeTgs corresponding to the emulsion copolymer, solution copolymer and the interfacial copolymer between the two phases. All theTgs increased with increasing content of the MMT in the composites.

A Study on Process Parameters for Imparting Hydrophobic Effect on Cotton Fiber with CF<sub>4</sub>-Plasma Treatment

The acquisition of hydrophobic surface offering liquid repellency is exploitable for diverse applications. This study examined the possibility of developing hydrophobic cotton fiber by employing atmospheric pressure plasma technique which is an environmentally friendly approach. We seek to determine a controlled hydrophobic modification of textile materials through the optimization of the fabrication process. A hydrophobic surface modification of cotton fabric was conducted with atmospheric pressure plasma using tetrafluoromethane (CF4) as the reactive gas. The resultant hydrophobic behavior was quantified macroscopically by a wetted area measurement. To control the degree of modification of the substrate, an orthogonal experimental design technique was utilized. The optimum process conditions were established based on the reduction of the wetted area of the plasma-modified fabrics.

Effect of spinning conditions on the structure and performance of hydrophobic PVDF hollow fiber membranes for membrane distillation

Microporous hydrophobic poly(vinylidene fluoride) (PVDF) hollow fibers were prepared via dry-jet wet phase-inversion method using N,N-dimethylacetamide (DMAc) as solvent, LiCl and PEG-400 as non-solvent additives in the polymer dopes. The effects of various preparation conditions, including the concentration of polymer and additives, bore liquid temperature, air gap, take-up speed and dope extrusion rate on the morphology and properties of membrane were studied. The prepared membranes were characterized through scanning electron microscopy (SEM) observation, gas permeation measurement, and tensile property test. The permeate flux of membrane in both vacuum membrane distillation (VMD) and direct contact membrane distillation (DCMD) for desalination was tested. It is found that the permeation property of membrane is mainly determined by membrane porosity, especially effective porosity. The formation of the sponge structure reduced VMD flux more fiercely than DCMD flux. Under the synergetic effect of PEG-400/LiCl, high permeate flux and relatively high mechanical strength of membrane can be simultaneously achieved. There exist the best ranges of bore liquid temperature and of air gap distance for relatively high permeate flux of membrane.

Hydrophobic photonic crystal fibers

We propose and demonstrate hydrophobic photonic crystal fibers (PCFs). A chemical surface treatment for making PCFs hydrophobic is introduced. This repels water from the holes of PCFs, so that their optical properties remain unchanged even when they are immersed in water. The combination of a hollow core and a water-repellent inner surface of the hydrophobic PCF provides an ultracompact dissolved-gas sensor element, which is demonstrated for the sensing of dissolved ammonia gas.

Synthesis of a new compatibilisant agent PVC‐g‐MA and its use in the PVC/alfa composites

AbstractThe main objective of this research was to synthesize a new compatibilisant agent (PVC‐g‐MA), which was grafted from the maleic anhydride on the PVC chains. The presence of maleic anhydride grafting on PVC was made evident by infrared analysis. PVC‐g‐MA was used like compatibilisant to solve the problem of the incompatibility between the hydrophobic polymeric matrix (PVC) and hydrophilic fiber (alfa). Composites samples were prepared with different alfa fiber loading (10, 20, and 30 wt %) and incorporating PVC‐g‐MA (1, 3, and 5 wt %) or PP‐g‐MA (3 wt %). The tensile properties, the thermal stability and the morphology of the composites were investigated. The result indicated that the PVC‐g‐MA increased the interfacial adhesion between the fibers and the polymer matrix and this effect was better than that obtained for the maleated‐polypropylene‐coupled composites. Microstructure analysis of the fractured surfaces of MAPP modified composites confirmed improved interfacial bonding. The addition of alfa and PVC‐g‐MA increased the thermal stability of the composites. The temperature of degradation of the polymer matrix increased about 16°C in comparison to the noncoupled composite, indicating that PVC‐g‐MA improved the thermal stability of the polymer. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Controlling the moisture absorption capacity in a fiber-reinforced thermoplastic starch using sodium trimetaphosphate

A novel biodegradable material derived from thermoplastic potato starch was prepared with intended uses in high moisture environments where its high water sorption characteristics are beneficial, such as wound dressing, transdermal patches or food packaging. A modified composite was prepared for this purpose by reactive extrusion whereby potato starch and 2.5–25% (w/w) sisal cellulose fibers were compounded together in the presence of 2.7% (w/w) sodium trimetaphosphate. The fibers were included to increase the wet strength of the material. A low degree of substitution (0.088–0.113) was sought by bound phosphate groups with anionic character in order to overcome a reduction in moisture absorption capacity resulting from fiber incorporation, yet being insufficient to cause embrittlement via crosslinking. The results showed the approach has sufficient merit to minimize the influence of the hydrophobic fibers on the water absorption capacity of the starch material but adhering to so low of a degree of substitution could not fully prevent a reduction. The results also suggested that the fibers may have participated in the crosslinking reaction.

Analysis of trace amounts of chlorobenzenes in water samples: An approach towards the automation of dynamic hollow fiber liquid-phase microextraction

We have combined dynamic hollow fiber liquid-phase microextraction with GC and electron capture detection for the quantitative determination of five chlorobenzenes in water samples. Extraction is based on an automated dynamic extraction device called TT-tube extractor which consists of a polypropylene hollow fiber mounted inside a stainless steel tube. Toluene is used as the extraction solvent that fills the lumen and pores of the hydrophobic fiber and flows through the lumen of the fiber using a programmable syringe pump. The type of organic solvent, ionic strength, diameter of the TT-tube, sample volume, and the times for extraction and dwelling were optimized. Under optimum conditions, the method gives limits of detection as low as 10–100 ng L−1, a linear dynamic range of 0.05–100 μg L−1, and relative standard deviations of <7% (n = 6). The preconcentration factor can be as large as 562–973. In an example for a practical application, the chlorobenzenes were successfully determined in environmental aqueous samples. The hollow fiber membrane can be used at least 20 times without any carry-over or loss in extraction efficiency. The system is inexpensive and convenient, and requires minimal manual handling.

Hydrogel–electrospun fiber composite materials for hydrophilic protein release

Although hydrogels are widely used in controlled-release systems, obtaining extended, uniform drug release with little initial burst has been challenging. However, recently researchers have shown that combining hydrogels with another drug delivery material can dramatically improve release kinetics. Here we describe a novel hydrogel-based composite material that exhibits stable, near-linear, sustained release of a model hydrophilic protein (e.g., bovine albumin serum, BSA) for over two months with a significant reduction in initial burst release (7% vs. 20%). The composite is comprised of poly(ε-caprolactone) (PCL) electrospun fiber mats coupled with poly(ethylene glycol)-poly(ε-caprolactone) diacrylate (PEGPCL) hydrogels through photo-polymerization. It is believed that the additional diffusion barrier provided by hydrophobic electrospun fiber mats reduces hydrogel swelling and water penetration rates and increases the diffusion path length, resulting in delayed, more uniform drug release. Further, released proteins remain bioactive as demonstrated by PC12 cell neurite extension in response to released nerve growth factor (NGF). The use of electrospun fiber mats to modulate hydrogel drug release provides a new method to control release kinetics of hydrophilic proteins, reducing burst release and extending the release duration.

Electromembrane Extraction from Biological Fluids

Electro-assisted extraction of ionic drugs from biological fluids through a supported liquid membrane (SLM) and into an aqueous acceptor solution was recently introduced as a new sample preparation technique termed electromembrane extraction (EME). The applied electrical potential across the SLM has typically been in the range of 1-300 V. Successful extractions have been demonstrated even with common batteries (9 V) instead of a power supply. The chemical composition of the SLM has been crucial for the selectivity and for the recoveries of the extraction. Compared to other liquid-phase microextraction techniques (LPME), extraction times have been reduced by a factor of 6-17, and successful extractions have been obtained at extraction times of 1-5 min, and even down to a few seconds with online microfluidic EME devices. The technique has provided very efficient sample clean-up and has been found well suited for the extraction of sample sizes in the low µL range. Extractions have been performed with both rod-shaped hydrophobic porous fibers and with flat hydrophobic porous sheets as SLM support. The technique has been successfully downscaled into the micro-chip format. The nature of the SLM has been tuned for extraction of drugs with different polarity allowing extractions to be tailored for specific applications depending on the analyte of interest. The technique has been found to be compatible with a wide range of biological fluids and extraction of drugs directly from untreated human plasma and whole blood has been demonstrated. EME selectively extracts the compounds from the complex biological sample matrix as well as allowing concentration of the drugs. With home-built equipment fully acceptable validation results have been obtained.

Influence of membrane morphology on characteristics of porous hydrophobic PVDF hollow fiber contactors for CO2 stripping from water

Wetting resistance and gas permeability are the main factors for membrane contactor applications, which can be optimized according to the membrane morphology. In present study, three different types of the membrane morphology were obtained via a dry–wet spinning technique. By measuring cloud point data and viscosity, the polymer dope composition was adjusted to produce the different morphologies. The membranes with large finger-like, small finger-like and almost sponge-like morphology were obtained. The plain PVDF membrane with large finger-likes morphology presented the higher N2 permeance, lower wetting pressure and larger mean pore size (0.08μm). By addition of phosphoric acid into the spinning dope, the prepared sponge-like morphology resulted in the high surface porosity with small pore sizes, which demonstrated good permeability and wetting pressure. It was found that the mean pore size measured by gas permeation method was approximately three times larger than those from FESEM examination. CO2 stripping from water was conducted through the gas–liquid membrane contactors. The membranes with smaller pore sizes and higher wetting pressure presented higher stripping performance. In conclusion, a structurally developed PVDF hollow fiber membrane for gas–liquid contactor applications can be achieved by controlling the membrane morphology.

Precise control of surface physicochemical properties for electrospun fiber mats by surface-initiated radical polymerization

Non-woven fiber mats were fabricated with the electrospinning method using poly(methyl methacrylate)-co-poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) in various solvents. The surface morphology of the electrospun fibers depended on the solvent vapor pressure and polymer concentration. Surface-initiated atom transfer radical polymerization (ATRP) with 3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate), 2-hydroxyethyl methacrylate or 2-(perfluorooctyl)ethyl acrylate generated surface-grafted polymers, as determined by X-ray photoelectron spectroscopy. Scanning electron microscopic observation revealed that the apparent fiber morphology did not change upon modification. The atomic force microscopic images of the grafted fiber cross-sections indicated that monomers and solvents penetrated slightly into the fibers and polymerization occurred at both internal and external initiation sites. Physicochemical properties, such as contact angle, hydrophobicity and hydrophilicity, and wettability, could be altered by the proper selection of substrates (spin-coated flat films or the variously prepared non-woven fiber mats). We have successfully prepared hydrophilic and hydrophobic fiber surfaces by a combination of the electrospinning protocol and surface-initiated ATRP. Functional non-woven fiber mats were prepared by combining the electrospinning method and surface-initiated atom transfer radical polymerization (ATRP). The surface-initiated ATRP of 3-(N-2-methacryloyloxyethyl-N,N-dimethyl) ammonatopropanesulfonate), 2-hydroxyethyl methacrylate and 2-(perfluorooctyl)ethyl acrylate proceeded successfully from the fiber surface of poly(methyl methacrylate)-co-poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) without any structural changes. A grafted layer after the surface-initiated ATRP was observed by atomic force microscopy. Static contact angles against water were also evaluated to discuss the relationship between the roughness of the electrospun non-woven fiber mats and wettability.

Cobalt(II) membrane-extraction by DP-8R/Exxsol D100 using pseudo-emulsion based hollow fiber strip dispersion (PEHFSD) processing

The transport of cobalt(II) from acidic sulphate solutions through PEHFSD was investigated using the extractant DP-8R in Exxsol D100. The acidic feed solution containing Co(II) was passed through the tube side, and pseudo-emulsions of DP-8R/Exxsol D100 and sulphuric acid was passed through the shell side in counter-current mode, using a single microporous hydrophobic polypropylene hollow fiber contactor for extraction and stripping. In PEHFSD the aqueous strip (sulphuric acid) solution was dispersed in the organic membrane solution in a reservoir tank with an impeller stirrer to form a strip dispersion. This pseudo-emulsion phase is circulated from the tank to the membrane module to provide a constant supply of the carrier solution to the membrane micropores. Several hydrodynamic and chemical parameters, such as variation in feed pH (3–7), cobalt concentration in feed (0.17–1.7 × 10 −3 M), carrier concentration (0.16–1.28 M), etc., were investigated. Mass transfer modelling was performed and the validity of the model was evaluated with experimental data. Moreover, the system was applied in the cobalt purification of synthetic lithium solutions derived from the processing of rechargeable batteries, with cobalt/lithium separation factor values around 25.

Two-Stage in Situ Intercalation Polymerization of Acrylic Copolymer/Montmorillonite Nanocomposites

An amphiphilic acrylic copolymer/montmorillonite nanocomposite was synthesized by way of a two-stage radical copolymerization of emulsion intercalation and solution intercalation, using acrylates, methacrylic acid, and acrylamide as monomers. The water-based product was designed with a structure of a hydrophobic copolymer dispersed in an aqueous copolymer solution to meet the needs of warp sizing agents on adhesiveness to hydrophobic and/or hydrophilic fibers, appropriate glass transition temperature, as well as water-solubility. XRD patterns and TEM observation for the product films showed an exfoliated structure of montmorillonite (MMT) in the part of soluble acrylic copolymer as the MMT content equal to or less than 7%, while in the part of emulsion copolymer alone or the product as a whole, the MMT showed an intercalated structure. Determination of DSC indicated that chemical bondings occurred between the hydrophobic and hydrophilic components, which guaranteed storage stability of the system and water-solubility of the sizing film, and that there were three T g s corresponding to the emulsion copolymer, solution copolymer and the interfacial copolymer between the two phases. All of the T g s increased with increasing content of the MMT in the composites. The elongation at break of the composite films increased with increasing MMT contents up to 3 wt % and then dropped down, and the tensile strength and abrasive resistance of the acrylic copolymer increased with content of the MMT.

Preparation and characterization of silica aquasols

Aquasols containing silica nanoparticles with diameters of 75 to 95nm were obtained directly by hydrolysis of 2wt.% tetraethoxysilane (TEOS) in water in the presence of a non-ionic surfactant. The reaction was catalyzed by hydrochloric acid, ammonia, or sodium hydroxide. The particle size, which mainly depends on the concentration of TEOS in water, was determined by dynamic light scattering (DLS). Whereas the catalysts have almost no influence on the particle size, they very strongly affect the morphology of the silica particles formed. The dried SiO2 particles obtained via the HCl-catalyzed reaction have film-forming properties and show no measurable BET surface area. SiO2 particles prepared with ammonia as catalyst form nanoporous films on glass, and the BET surface area of the freeze-dried particles is 540m2/g. Using sodium hydroxide as catalyst results in some agglomeration of uniform spherical particles with a BET surface area of 237m2/g. 29Si MAS NMR investigations of the freeze-dried particles provide information about the degree of condensation and the ratio of “free” hydroxyl groups. The silica aquasols described have a surprisingly high hydrophilizing effect on hydrophobic fibers (PP, PET). Silica nanoparticles of comparable diameters, prepared by the “Stöber method”, dispersed in alcohol do not show any hydrophilizing properties worth to mention.

Optimization of Dry and Wet Heat Transfer through Textile Structures

This work reports on research being carried out in the area of functional knitted fabrics with a special structure incorporating hydrophobic fibres near to the skin and suction channels of hydrophilic fibres to suck moisture from the skin on the hydrophilic layer away from the skin; in this way, comfort is maximised in active wear as the fabric does not feel wet near to the skin.

Highly Hydrophobic Electrospun Fiber Mats from Polyisobutylene-Based Thermoplastic Elastomers

This paper is the first report of electrospinning neat polyisobutylene-based thermoplastic elastomers. Two generations of these materials are investigated: a linear poly(styrene-b-isobutylene-b-styrene) (L_SIBS) triblock copolymer and a dendritic poly(isobutylene-b-p-methylstyrene) (D_IB-MS), also a candidate for biomedical applications. Cross-polarized optical microscopy shows birefringence, indicating orientation in the electrospun fibers, which undergo large elongation and shear during electrospinning. In contrast to the circular cross section of L_SIBS fibers, D_IB-MS yields dumbbell-shaped fiber cross sections for the combination of processing conditions, molecular weight, and architecture. Hydrophobic surfaces with a water contact angle as high as 146 ± 3° were obtained with D_IB-MS that had the noncircular fiber cross section and a hierarchical arrangement of nano- to micrometer-sized fibers in the mat. These highly water repellent fiber mats were found to serve as an excellent scaffold for bovine chondrocytes to produce cartilage tissue.

Application of hollow fiber membrane contactor for the removal of carbon dioxide from water under liquid–liquid extraction mode

In this study, we investigate the application of a hollow fiber membrane contactor operated in the LLE mode for the removal of dissolved CO 2 from water. The membrane contactor consists of hydrophobic polypropylene microporous hollow fibers. Experiments are performed to determine the extent of CO 2 removal from the feed water flowing through the lumens of the hollow fibers. The feed at different concentration levels of dissolved CO 2 was extracted using aqueous diethanolamine solution flowing on the shell side of the contactor. A mathematical model was developed, incorporating radial and axial diffusion of solute CO 2 in the lumen and its permeation through the pores of the membrane. The governing second order partial differential equation of species balance was numerically solved using the alternate direction implicit technique. The developed mathematical model was used to predict the concentration profiles of CO 2 and study its transport through water and membrane pores. The numerical value of the permeation coefficient obtained for CO 2 in the hollow fiber membrane was found to be in good agreement with the data in literature.

A novel approach to automation of dynamic hollow fiber liquid‐phase microextraction

An automated dynamic two-phase hollow fiber microextraction apparatus combined with high-performance liquid chromatography was developed for extraction and determination of chlorophenoxy acid (CPA) herbicides from environmental samples. The extraction device, called TT-extractor, consists of a polypropylene hollow fiber mounted inside a stainless steel tube by means of two tee-connectors in flow system. An organic solvent, which fills the lumen and the pores of the hydrophobic fiber, is pumped through the fiber repeatedly and the sample is pumped along the outer side of the fiber. The factors affecting the dynamic hollow fiber liquid-phase microextraction (DHF-LPME) of target analytes were investigated and the optimal extraction conditions were established. To test the applicability of the designed instrument, CPAs were extracted from environmental aqueous samples. The limits of detection (LODs) as low as 0.5 μg/L, linear dynamic range in the range of 1-100 μg/L and the relative standard deviations of <7% were obtained. The developed method can provide perconcentration factors as large as 230. A hollow fiber membrane can be used at least 20 times with neither loss in the efficiency nor carryover of the analytes between runs. The system is cheap and convenient and requires minimal manual handling.

Biomimetics of the extracellular matrix: an integrated three-dimensional fiber-hydrogel composite for cartilage tissue engineering

The native extracellular matrix (ECM) consists of an integrated fibrous protein network and proteoglycan-based ground (hydrogel) substance. We designed a novel electrospinning technique to engineer a three dimensional fiber-hydrogel composite that mimics the native ECM structure, is injectable, and has practical macroscale dimensions for clinically relevant tissue defects. In a model system of articular cartilage tissue engineering, the fiber-hydrogel composites enhanced the biological response of adult stem cells, with dynamic mechanical stimulation resulting in near native levels of extracellular matrix. This technology platform was expanded through structural and biochemical modification of the fibers including hydrophilic fibers containing chondroitin sulfate, a significant component of endogenous tissues, and hydrophobic fibers containing ECM microparticles.