Hydrophobic Fiber Research Articles

Highly porous PVDF hollow fiber membranes for VMD application by applying a simultaneous co-extrusion spinning process

Highly porous polyvinylidene fluoride (PVDF) hollow fiber membranes are of great interest for membrane contactor applications such as sea water desalination by membrane distillation in order to enhance the flux of the process. For the first time in this paper, porous hydrophobic PVDF asymmetric hollow fiber membranes with a high outer surface porosity for use in vacuum membrane distillation (VMD) were successfully fabricated by applying a simultaneous co-extrusion spinning process through the non-solvent induced phase separation (NIPS) method. In this approach, five kinds of dual-layer composite membranes were prepared by employing different inner and outer polymer dopes. Single-layer membrane was also fabricated through the conventional dry-jet wet phase inversion method. Results revealed that the introduction of the simultaneous co-extrusion spinning process greatly increased the outer surface porosity of the dual-layer composite membranes. It was also observed that the VMD flux of the dual-layer membranes spun through the simultaneous co-extrusion spinning process was 54% higher than the single-layer membrane fabricated by the conventional dry-jet wet phase inversion method. A VMD flux as high as 61.8kg/(m2h) at 70°C was obtained for the novel dual-layer composite membranes.

Effect of fiber natures on the formation of “solid bridge” for preparing wood sawdust derived biomass pellet fuel

Four different types of fibers including rice straw, wheat straw, rubber leaf and nylon were added into wood sawdust to prepare renewable biomass pellets (BPs) at room temperature. The effects of these fiber natures on the physical properties of BPs were investigated by characterizing the elongation, particle density, abrasive resistance and impact resistant index. Experimental results showed that the addition of rice straw and rubber leaf possessed a positive effect on the physical properties of BPs while the addition of wheat straw and nylon had a negative effect. The positive effect of the former can be attributed to the strengthened bonds in the BPs by the intertwining action of a “solid bridge” between these linear hydrophilic fibers and wood sawdust. The negative effect of the latter is due to the repelling role between the hydrophobic fiber and hydrophilic wood sawdust to arrest the formation of their “solid bridge”. Therefore, the added fiber natures highly influenced the formation of a “solid bridge” that determined the physical properties of BPs derived from wood sawdust.

Functionalization of flat sheet and hollow fiber microfiltration membranes for water applications.

Functionalized membranes containing nanoparticles provide a novel platform for organic pollutant degradation reactions and for selective removal of contaminants without the drawback of potential nanoparticle loss to the environment. These eco-friendly and sustainable technology approaches allow various water treatment applications through enhanced water transport through the membrane pores. This paper presents "green" techniques to create nanocomposite materials based on sponge-like membranes for water remediation applications involving chlorinated organic compounds. First, hydrophobic hollow fiber microfiltration membranes (HF) of polyvinylidene fluoride were hydrophilized using a water-based green chemistry process with polyvinylpyrrolidone and persulfate. HF and flat sheet membrane pores were then functionalized with poly(acrylic acid) and synthesized Fe/Pd nanoparticles. Surface modifications were determined by contact angle, surface free energy and infrared spectroscopy. The synthesized nanoparticles were characterized by electronic microscopy, X-ray spectrometry and image analysis. Nanoparticle sizes of 193 and 301 nm were obtained for each of the membranes. Depending on the concentration of the dopant (Pd) in the membrane, catalytic activity (established by trichloroethylene (TCE) reduction), was enhanced up to tenfold compared to other reported results. Chloride produced in reduction was close to the stoichiometric 3/1 (Cl-/TCE), indicating complete absence of reaction intermediates.

Surface modified PVDF nanofiber supported thin film composite membranes for forward osmosis

Hydrophilic electrospun nanofiber supported thin film composite (TFC) membranes have recently been considered for forward osmosis (FO). Our previous work has shown that the high degree of swelling in hydrophilic nanofibers compromises fiber strength and membrane integrity. To reduce swelling, we propose to modify a non-swelling hydrophobic fiber to make it hydrophilic and fully wettable without negatively impacting the mechanical properties of the material. The method chosen for this work involves the interfacial polymerization of 1,6-hexane diamine and adipoyl chloride to form nylon 6,6 directly onto electrospun PVDF fibers. The result is a dual benefit of hydrophilization and strengthening of nanofibers to improve their wettability. The modified nanofibers exhibited significantly lower swelling propensity than intrinsically hydrophilic nylon 6,6 nanofibers due to the hydrophobic core fiber, and are thus able to retain strength in an aqueous environment. These modified PVDF supports were used in making TFC membranes that exhibited excellent flux performance and one of the lowest structural parameters reported in open literature.

Removal of total petroleum hydrocarbon from water using attapulgite fiber silica aerogel composite

Composite hydrophobic attapulgite fiber silica aerogels (AF-SAs) were prepared by modifying aerogels with AF. AF-SA composites with various fiber contents were prepared using a sol–gel method. The composite containing 0.30 g of added fiber was a typical nanoporous material; it had a specific surface area of 594.08 m2/g, a porosity of 75.00%, a pore volume of 2.15 cm3/g, and an average pore diameter of 84.74 nm. The kinetics of total petroleum hydrocarbon (TPH) adsorption onto AF-SAs was second order, and the isothermal adsorption of TPH conformed to the Langmuir adsorption model. The TPH adsorption capacity of an AF-SA, calculated using the Langmuir equation, was 5.00 g/g. Alkanes and aromatic hydrocarbons were both strongly adsorbed. The main adsorption mechanisms involved physical and chemical processes. The physical processes involved monolayer and multilayer adsorptions. Chemical adsorption occurred mainly after adsorption of TPH onto the AF-SA. The adsorption process was additionally assessed by monitoring the positions and areas of the Fourier-transform infrared absorptions of the main components (silicate, attapulgite, and functional groups of the surface-modification agent) of the composite materials.

Concentrating aqueous urea solution by using continuous-effect membrane distillation

In order to remove and recover urea from its dilute aqueous solutions, e.g., wastewater drained from urea synthesis plants, continuous-effect membrane distillation (CEMD) process providing an extremely high thermal efficiency was investigated to concentrate aqueous solution containing urea. By using an air-gap membrane distillation module fabricated with both porous hydrophobic hollow fibers and dense-wall hollow fibers, the CEMD operation-mode can easily realize the direct recovery of condensation heat of the permeate to preheat the cold feed in situ within a single module. A series of experiments were conducted to evaluate the performance of CEMD process in terms of permeation flux (Jw), gain output ratio (GOR) and rejection factor (Rf) under various operating conditions, such as the feed-in concentration, cold feed-in temperature, heated feed-in temperature and feed flow rate. The maximum values of GOR=14.0, Jw=6.8Lh−1m−2 and Rf=99.99% were achieved respectively. When a feed solution of 1.0wt% urea was used as a sample wastewater, the feed could be at least concentrated to 40wt% with high values of GOR, Jw and Rf. The experimental data showed that the mild operation condition could also help to avoid the urea loss from its thermal hydrolysis. A brief theoretical model was introduced and used to discuss experimental results.

Preparation and characterization of hydrophobic cotton fiber for water/oil separation by electroless plating combined with chemical corrosion

Preparation and characterization of hydrophobic cotton fiber for water/oil separation by electroless plating combined with chemical corrosion

Enhanced performance of a biomimetic membrane for Na2CO3 crystallization in the scenario of CO2 capture

Membrane assisted crystallization (MACr) offers an innovative platform for crystallizing Na2CO3, allowing its reuse after CO2 capture from flue gases by an alkaline solution (i.e., NaOH). In this study, the biomimetic aquaporin Inside™ membrane AIM60 was employed to enhance water removal, facilitating Na2CO3 crystallization. The water channel in the active layer, comprising aquaporin proteins, and the strong wettability of membrane substrate assist a better performance. For instance, the water flux of AIM60 membrane for concentrating a 1.89molL−1 Na2CO3 solution (osmotic pressure of 94.8bar) in forward osmosis (FO) mode was 6.62Lm−2h−1 and 3.25Lm−2h−1 in pressure retarded osmosis (PRO) mode when a 5.13molL−1 NaCl solution (osmotic pressure of 304.9bar) was employed as the draw solution. This demonstrates that the AIM60 FO membrane outperformed the previously reported dense reverse osmosis membrane (0.21Lm−2h−1 in FO mode and 0.16Lm−2h−1 in PRO mode) and a porous hydrophobic hollow fiber membrane (0.08Lm−2h−1) under the same operating conditions.Crystallization utilizing the AIM60 membrane in an osmotic crystallizer was achieved without noticeable membrane scaling or degradation. Furthermore, a proper control of the supersaturation level induces crystallization of Na2CO3·10H2O crystals with a purity of 99.94%. Hence, the aquaporin Inside™ FO membrane may be a promising alternative to existing methods for Na2CO3 crystallization for its application in a CO2 capture scenario.

Cyanobacterial CO2biofixation in batch and semi-continuous cultivation, using hydrophobic and hydrophilic hollow fiber membrane photobioreactors

The performance of hollow fiber membrane photobioreactors (HFMPB) for the growth of Synechococcus elongatus at various CO2 concentrations (0.04% (ambient air), 10% and 15%) and medium re-circulation flow rates (34.4, 60 and 86.6 mL/min) was studied. Cultivation was carried out at both batch and semi-continuous modes in HFMPBs containing neat and hydrophilized in-house fabricated poly propylene (PP) membranes at a fixed light intensity of 3000 lux and temperature of 27oC. Cyanobacterium showed better growth at 10% CO2 at an initial pH = 8.2 using BG11 medium in both cultivation modes and modules. Maximum biomass concentration, CO2 biofixation and specific growth rates equal with 2.1 g L–1, 2.08 g L–1d–1 and 1.76 d–1 were obtained for non-wetted membranes, respectively. Comparing the performance of both modules showed that the impact of cultivation mode on the CO2 biofixation rate and CO2 removal is more influential than the impact of mass transfer resistance in membrane contactors. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd

Polystyrene‐b‐poly(2,2,2‐trifluoroethyl acrylate)‐b‐polystyrene copolymers: Synthesis and fabrication of their hydrophobic porous films, spheres, and fibers

ABSTRACTNew block copolymers Polystyrene‐b‐poly (2,2,2‐trifluoroethyl acrylate)‐b‐Polystyrene (PS‐PTFEA‐PS) with controlled molecular weight (Mn=5000‐11000 g⋅mol−1) and narrow molecular weight distribution (Mw/Mn=1.13‐1.17) were synthesized via RAFT polymerization. The molecular structure and component of PS‐PTFEA‐PS block copolymers were characterized through 1H NMR, 19F NMR, GPC, FT‐IR and elemental analysis. The porous films of such copolymers with average pore size of 0.80‐1.34 μm and good regularity were fabricated via a static breath‐figure (BF) process. The effects of solvent, temperature, and polymer concentration on the surface morphology of such film were investigated. In addition, microstructured spheres and fibers of such block copolymers were fabricated by electrospinning process and observed by scanning electron microscopy (SEM). Furthermore, the hydrophobicity of porous films, spheres, and fibers was investigated. The porous film showed a good hydrophobicity with the water‐droplet contact angles of 129°, and the fibers showed higher hydrophobicity with the water‐droplet contact angles of 142°. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 678–685

High-performance supercapacitor of electrodeposited porous 3D polyaniline nanorods on functionalized carbon fiber paper: Effects of hydrophobic and hydrophilic surfaces of conductive carbon paper substrates

Although polyaniline (PANI) was electrodeposited on various conductive substrates for use as the pseudocapacitor electrodes, the effect of carbon paper surfaces has not yet been investigated. In this work, PANI was electrodeposited on two carbon surfaces including hydrophobic carbon fiber paper (CFP) and hydrophilic functionalized CFP (f-CFP). f-CFP with a bulk conductivity of 2.03mS/cm having hydroxyl and carboxyl groups on its surface can significantly enhance the charge storage performance of the PANI/f-CFP pseudocapacitors due to its high surface ionic conductivity. The symmetric pseudocapacitors of PANI/f-CFP in aqueous and organic electrolytes exhibit much higher areal capacitance, power and energy than those of PANI coated on the hydrophobic surface of CFP. The areal capacitance of a half-cell PANI/f-CFP electrode in 1M H2SO4 (aq.) is 704mF/cm2 (1323F/g_PANI) at 10mV/s. A symmetric organic-based PANI/f-CFP pseudocapacitor at an areal power of 240μW/cm2 (a specific power of 351W/kg_PANI) has an areal energy of 102μWh/cm2 (a specific energy of 149Wh/kg_PANI). At a lower areal energy of 2.0μWh/cm2 (3Wh/kg_PANI), the device has higher areal power of 2660μW/cm2 (3881W/kg_PANI). The stability of the device tested by galvanic charge–discharge over 2500 cycles is over 97% capacitance retention.

Self-Propelled Droplet Removal from Hydrophobic Fiber-Based Coalescers.

Fiber-based coalescers are widely used to accumulate droplets from aerosols and emulsions, where the accumulated droplets are typically removed by gravity or shear. This Letter reports self-propelled removal of drops from a hydrophobic fiber, where the surface energy released upon drop coalescence overcomes the drop-fiber adhesion, producing spontaneous departure that would not occur on a flat substrate of the same contact angle. The self-removal takes place above a threshold drop-to-fiber radius ratio, and the departure speed is close to the capillary-inertial velocity at large radius ratios.

Study on vacuum membrane distillation (VMD) using FEP hollow fiber membrane

Poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP) hydrophobic hollow fiber membranes were prepared through melt spinning method. The performances and structures of membrane samples with different stretching ratios were investigated. It can be seen that the increased stretching ratios (nascent, 50%, 100% and 150%) brought about obvious interfacial microvoids (IFMs) which improved the membrane's porosity, while decreased the liquid entry pressure (LEP) and mechanical strength. In addition, the FEP hollow fiber membranes exhibited strong hydrophobicity, excellent chemical and thermal stability owing to its perfluoro structure. Therefore, the performances of membrane samples were measured by vacuum membrane distillation (VMD) using alkaline aqueous with high temperature. The results showed that the FEP hollow fiber membranes' salt rejections achieved as high as 99.0%. In addition, the MD flux, salt rejection and mechanical strength kept stable in the strong alkaline aqueous (NaOH concentration of 300g/L, 80°C) through a long term operation of 48h. However, the compared poly(vinylidenefluoride) (PVDF) hollow fiber membrane exhibited weak alkaline and thermal endurance with obvious decrease of mechanical strength and salt rejection. Therefore, this study indicated that the obtained FEP hollow fiber membrane could be used in the VMD which exhibited satisfying salt rejection.

Oil sorption behaviors of porous polydimethylsiloxane modified collagen fiber matrix

ABSTRACTA facial and cost‐effective synthesis method of converting the leather protein solid wastes into a value‐added collagen matrix oil sorbent is successfully established for the first time. Hide powder fiber (HPF) was firstly prepared by using the pre‐tanned fleshing wastes from the leather industry, and then cross‐linked with epoxy‐terminated polydimethylsiloxane (PDMS) to produce hydrophobic collagen fiber, which was verified by the FT‐IR spectrum and contact angle analysis. Subsequently, a series of porous PDMS modified collagen‐based sorbents with roughness surface was successfully fabricated by solvent‐ and freeze‐drying methods respectively. The oil sorption capacity, sorption saturated time and retention capacity of the prepared sorbents was investigated. Combined with the SEM images, liquid displacement method and contact angle analysis, the results revealed that oil sorption capacities of the sorbent with lower pore size, higher porosity and rougher surface for silicone oil, motor oil and vegetable oil were approximate to 13.60, 12.50, and 11.92 g/g, respectively. Additionally, the sorption of oils is a quasi‐instantaneous process and also showed excellent oil retention capacity. It exhibited acceptable oil sorption performances as compared to commercial biomass sorbents. These findings indicated its potential as an eco‐friendly oil sorbent material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42727.

Preparation, characterization and laboratory-scale application of modified hydrophobic aluminum oxide hollow fiber membrane for CO2 capture using H2O as low-cost absorbent

The objective of this work was to apply the modified hydrophobic metal oxide hollow fiber membrane in a laboratory-scale gas–liquid membrane contacting process for CO2 capture applications using H2O as low-cost absorbent at room temperature. With this aim, the porous aluminum oxide (α-Al2O3) hollow fiber membranes were prepared by a phase inversion spinning technique and a sintering method. In order to render the hydrophilic surface of prepared Al2O3 hollow fiber membrane without changing its physical properties, a fluoroalkylsilanes (FAS) film was used. The fluoroalkylsilanized Al2O3 hollow fiber membrane surface was studied by performing thermal gravimetric analysis (TG), scanning electron microscopy (SEM), X-ray diffractometer (XRD). In addition, the hydrophobicity nature of modified Al2O3 hollow fiber membrane surfaces was measured by water drop contact angle test and break through pressure measurement. This work, for what we believe to be the first time, has successfully realized a room-temperature laboratory-scale gas–liquid membrane contactors using a single fluoroalkylsilanized Al2O3 hollow fiber membrane for CO2 capture. According to the experimental results, the correlations between water and gas flow rate, and CO2 mass transfer through the modified hydrophobic Al2O3 hollow fiber membranes are given. In addition, a comparative review was made between our modified hydrophobic aluminum oxide and traditional polymeric hollow fiber membrane for application in the field of CO2 absorption in water. The results indicated that studied fluoroalkylsilanized Al2O3 hollow fiber membrane may be possible candidates for the development of new gas–liquid membrane contactors for CO2 capture.

Kinetic and equilibrium studies of hydrophilic and hydrophobic rice husk cellulosic fibers used as oil spill sorbents

In this work, rice husk cellulosic sorbents are produced by both chemical and biological pretreatment. The results indicate that the sorbent pretreated by sodium hydroxide (NaOH) and hydrogen peroxide (H2O2) contains up to 87.75% cellulosic concentration. Acetylated sorbents produced from both NaOH/H2O2 and Aspergillus flavus pretreated rice husks are compared with raw rice husk and non-acetylated rice husk sorbents for oil sorption capacities. By plotting oil uptake capacity against contact time, the optimum theoretical sorption capacity of acetylated chemical pretreated rice husk sorbent is 28.2g/g RMG 386 after 15min dripping. The sorption data shows that the modified rice husk sorbents achieve saturation after only 3–5min of contact with both RMG 386 marine diesel and corn oil. The experimental data of acetylated chemical pretreated rice husk sorbent is analyzed using the pseudo-first order, the pseudo-second order and the intraparticle diffusion models. The model results indicate that the pseudo-second order model accurately correlates with the oil sorption data. In terms of the equilibrium isotherm analysis, the Freundlich model provides the best fit to the experimental data. As a result, the acetylated rice husk sorbent has shown to significantly outperform the non-acetylated sorbent with a high oleophilic and hydrophobic capacity with up to 19.66g/g RMG 386 oil uptake capacity compared to 8.26g/g by the non-acetylated rice husk sample in an aqueous medium.

Novel membrane contactor for CO2 removal from flue gas by temperature swing absorption

Conventional processes for CO2 scrubbing from flue gas in a contactor using aqueous monoethanolamine (MEA) solution followed by steam-stripping with an intermediate heat exchanger for heating up the CO2-loaded absorbent and cooling down the regenerated absorbent increase the cost of electricity enormously. To reduce the cost, the absorbent mass has to be substantially reduced and the temperature swing range limited considerably so that cheaper utilities (hot water) are used. Membrane contactors are compact and highly attractive for non-dispersive CO2 absorption; we propose here a novel hollow fiber membrane contactor that integrates absorption and stripping using a nonvolatile reactive absorbent (e.g., 80% polyamidoamine (PAMAM) dendrimer generation 0 and 20% of an ionic liquid (IL)). We have carried out proof-of-concept experiments via a cyclic process and a novel device containing two commingled sets of hollow fibers. Through the bore of one set of porous hydrophobic hollow fibers, flue gas is passed; CO2 diffuses to the shell side to get reactively absorbed in the stagnant PAMAM dendrimer-IL on the shell side. After there is CO2 breakthrough at the other end of the porous hollow fibers, feed gas flow is shut down. Through the bore of the second set of hollow fibers having a solid wall impervious to H2O and common gases under the conditions used, hot water is next supplied to heat the shell-side liquid absorbent and strip the absorbed CO2. After a short period, stripped CO2 is withdrawn through the bores of the first set of porous hollow fibers. We describe the performance of this temperature swing membrane absorption (TSMAB) process here with absorption at 50°C and stripping between 85 and 97°C. Equilibrium CO2 absorption in the nonvolatile viscous mixed absorbent is as high as 6.37mmolCO2/g absorbent in the presence of moisture at 50°C. The CO2 absorption and regeneration behavior of the integrated device has been studied for this absorbent at various absorption and regeneration temperatures and device design changes needed have been discussed.

Comparative study of antibody immobilization mediated by lipid and polymer fibers

Antibody immobilization and function retention are important to a variety of applications, including proteomics, drug discovery, diagnostics, and biosensors. The present study investigates antibody immobilization mediated by cholesteryl succinyl silane (CSS) fibers, in comparison to hydrophobic polycaprolactone (PCL) fibers and hydrophilic plasma-treated PCL fibers. When incubated with a model protein, the formation of protein aggregates is observed on hydrophobic PCL fibers but not on the more hydrophobic CSS fibers, indicating that CSS fibers immobilize proteins through mechanisms other than hydrophobic interaction. When exposed to a limited amount of antibody, CSS fibers immobilize more antibodies than plasma-treated PCL fibers and no fewer antibodies than PCL fibers. The function retention of antibodies immobilized on the fibers is analyzed using a cell-capture assay, which shows that the antibody-functionalized CSS fibrous matrices capture 6- or 7-fold more cells than the antibody-functionalized PCL or plasma-treated PCL fibrous matrices, respectively. Data collected from the study show that the lipid fiber-mediated immobilization of antibody not only maintains the advantages of physical immobilization such as easiness and rapidness of operation but also improves function retention.

In situ synthesis of bacterial cellulose/polycaprolactone blends for hot pressing nanocomposite films production

A series of bacterial cellulose (BC)/polycaprolactone (PCL) nanocomposite films were successfully prepared by supplementation of the BC culture medium with variable amounts of PCL powder followed by hot-pressing of the BC/PCL mixtures obtained after incubation. PCL powder was fully incorporated into the BC network during its production and did not change the BC network morphology. The obtained films showed a homogenous distribution of PCL throughout the BC network, as well as good thermal stability (up to 200°C) and improved mechanical properties, when compared to pristine PCL. In addition, the intrinsic biodegradability and biocompatibility of the nanocellulose fibers and PCL opens the possibility of using this novel nanocomposite in the biomedical field and food packaging. The BC biosynthetic approach combined with the hot-pressing proved successful for the sustainable development of nanocomposites combining hydrophobic thermoplastic matrices and hydrophilic nanocellulose fibers, without the use of harmful organic solvents commonly used to dissolve this type of polymeric matrices.

Optimization of intrinsic and extrinsic tendon healing through controllable water-soluble mitomycin-C release from electrospun fibers by mediating adhesion-related gene expression

To balance intrinsic and extrinsic healing during tendon repair is challenging in tendon surgery. We hypothesized that by mediating apoptotic gene and collagen synthesis of exogenous fibroblasts, the adhesion formation induced by extrinsic healing could be inhibited. With the maintenance of intrinsic healing, the tendon could be healed with proper function with no adhesion. In this study, we loaded hydrophilic mitomycin-C (MMC) into hyaluronan (HA) hydrosols, which were then encapsulated in poly(L-lactic acid) (PLLA) fibers by micro-sol electrospinning. This strategy successfully provided a controlled release of MMC to inhibit adhesion formations with no detrimental effect on intrinsic healing. We found that micro-sol electrospinning was an effective and facile approach to incorporate and control hydrophilic drug release from hydrophobic polyester fibers. MMC exhibited an initially rapid, and gradually steadier release during 40 days, and the release rates could be tuned by its concentration. In vitro studies revealed that low concentrations of MMC could inhibit fibroblast adhesion and proliferation. When lacerate tendons were healed using the MMC-HA loaded PLLA fibers in vivo, they exhibited comparable mechanical strength to the naturally healed tendons but with no significant presence of adhesion formation. We further identified the up-regulation of apoptotic protein Bax expression and down-regulation of proteins Bcl2, collage I, collagen III and α-SMA during the healing process associated with minimum adhesion formations. This approach presented here leverages new advances in drug delivery and nanotechnology and offers a promising strategy to balance intrinsic and extrinsic tendon healing through modulating genes associated with fibroblast apoptosis and collagen synthesis.