Mechanically improved superhydrophobic nanofibrous polystyrene/high-impact polystyrene membranes for promising membrane distillation application

Robust membranes for commercial applications of membrane distillation (MD) are nearly the Achilles ankle of the process. Despite from high hydrophobicity requirements of the MD membranes, they must have enough mechanical and thermal stabilities. In this regard, flexible, superhydrophobic, and high-productive nanofibrous membranes were fabricated using mixed dope solutions made of polystyrene (PS) and high-impact PS (HIPS) through the electroblowing process. Although the PS nanofibers can be designed to have hierarchically rough surfaces to show superhydrophobicity, the inherent brittleness of this polymer still remains a big issue for practical application for a longer period of time. Upon adding HIPS into the PS-containing dope solution, the rigid PS membrane turned into a more flexible one with improved elongation at break from 5.83% to 14.89%. Also, excellent direct contact membrane distillation performance was achieved using high saline (up to 150 g/L) and 0.1 mM sodium dodecyl sulfate/35 g/L NaCl feed solutions during 96 and 24 h, respectively. Superhydrophobicity (˃160°) and high LEP value (up to 173.2 kPa) gifted membranes with outstanding wetting resistance. Our proposed procedure can pave the route for the facile fabrication of robust MD membranes using cost-effective materials and a high-throughput fabrication process.     

Preparation and characterization of braided tube reinforced polyacrylonitrile hollow fiber membranes

Polyacrylonitrile (PAN) and polyester (PET) braided hollow tube that used as a special reinforcement are braided from their filaments via two‐dimensional weaving techniques. PAN braided tube reinforced homogeneous PAN hollow fiber membranes and PET braided tube reinforced heterogeneous PAN hollow fiber membranes are prepared by concentric circles squeezed‐coated spinning method. As for PAN hollow fiber membrane, the effects of PAN concentration on the performance of the prepared hollow fiber membranes are investigated in terms of pure water flux, protein rejection, mechanical strength, and morphology observations by a scanning electron microscope (SEM). The interfacial bonding state of the braided tube reinforced PAN hollow fiber membranes is studied by constant speed stretching method. Results show that the breaking strength of two‐dimensional braided tube reinforced PAN hollow fiber membranes is higher than 80 MPa. The structure of separation surface is similar to the structure of an asymmetric membrane. With the increase of polymer concentration, the membrane flux decreases while the retention rate of BSA increase. The membrane porosity and maximum pore size have the same decreasing tendency as the increase of PAN concentration. The results also show that the interfacial bonding state of the PAN two‐dimensional braided tube reinforced homogeneous PAN hollow fiber membranes is better than that of the PET two‐dimensional braided tube reinforced heterogeneous PAN hollow fiber membranes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41795.     

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     

Superhydrophobic polytetrafluoroethylene nanofiber membranes prepared by vacuum sintering and their application in vacuum membrane distillation

Electrospinning-sintering is a general strategy to fabricate polytetrafluoroethylene (PTFE) nanofibrous membranes. In this study, vacuum atmosphere was created in the sintering process to obtain pure PTFE fibers. The effect of vacuum pressure on fiber morphology and material component of the sintered membrane was investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) characterization. A proper vacuum condition was believed to be beneficial to decrease poly(vinyl alcohol) residual and creating nanosize structures on the fiber surface, as porous, which contributes to a secondary roughness, while insignificantly influence membrane strength. As a result, the prepared membrane was superhydrophobicity with enhanced liquid entry pressure value. The anti-wetting property of the vacuum sintered membranes was further evaluated by vacuum membrane distillation process, and ensured the superior wetting resistance of the vacuum sintered PTFE membranes.     

Fabrication and characterization of hydrophobic PVDF hollow fiber membranes for desalination through direct contact membrane distillation

The mixture of inorganic salt LiCl and soluble polymer polyethylene glycol (PEG) 1500 as non-solvent additive was introduced to fabricate hydrophobic hollow fiber membrane of polyvinylidene fluoride (PVDF) by phase inversion process, using N,N-dimethylacetamide (DMAc) as solvent and tap water as the coagulation medium. Compared with other three membranes from PVDF/DMAc, PVDF/DMAc/LiCl and PVDF/DMAc/PEG 1500 dope solution, it can be observed obviously by scanning electron microscope (SEM) that the membrane spun from PVDF/DMAc/LiCl/PEG 1500 dope had longer finger-like cavities, ultra-thin skins, narrow pore size distribution and porous network sponge-like structure owing to the synergistic effect of LiCl and PEG 1500. Besides, the membrane also exhibited high porosity and good hydrophobicity. During the desalination process of 3.5 wt% sodium chloride solution through direct contact membrane distillation (DCMD), the permeate flux achieved 40.5 kg/m² h and the rejection of NaCl maintained 99.99% with the feed solution at 81.8 °C and the cold distillate water at 20.0 °C, this performance is comparable or even higher than most of the previous reports. Furthermore, a 200 h continuously desalination experiment showed that the membrane had stable permeate flux and solute rejection, indicating that the as-spun PVDF hollow fiber membrane may be of great potential to be utilized in the DCMD process.     

Unsupported electrospun membrane for water desalination using direct contact membrane distillation

In this project, an unsupported electrospun poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) membrane was used for water desalination using direct contact membrane distillation (DCMD). The membrane was electrospun using a laboratory-scale machine with multiple nozzles that was developed in-house. Critical process parameters, including the applied voltage and polymer concentration, were optimized to obtain bead-free electrospun membranes with fiber diameters less than 300 nm. To improve the membrane thermal stability and performance, the selected electrospun membrane was heat-pressed at 160°C. The untreated and heat-pressed membranes were tested in a DCMD setup at different feed temperatures (60, 70, and 80°C) and feed flow rates (0.4, 0.6, and 0.8 L/min), while maintaining the permeate temperature and flow rate at 20°C and 0.2 L/min, respectively. The modified electrospun membrane exhibited a very high permeate flux (>37.5 kg/m²/h) and a salt rejection rate of 99.99% at a feed temperature of 70°C. The performance of the heat-pressed unsupported PVDF-HFP electrospun membrane was nearly identical to a commercially available polytetrafluoroethylene (PTFE) supported membrane. These promising results demonstrate that relatively low-cost electrospun membranes can be easily produced and successfully used in DCMD to minimize the capital cost and increase the energy efficiency of the process.     

Preparation and properties of polytetrafluoroethylene/CaCO3 hybrid hollow fiber membranes

A novel method of preparing polytetrafluoroethylene (PTFE) hollow fiber membrane was presented by utilizing poly (vinyl alcohol) (PVA) can form a gel of two dimensional complex compounds with Boric acid (H₃BO₃). Effects of H₃BO₃ on PTFE nascent hollow fiber were investigated, and the results showed that the introduction of H₃BO₃ effectively reduced the addition of PVA. The configuration named “fibril” formed between PVA and H₃BO₃ could be observed in nascent hollow fiber by SEM (Scanning electronic microscopy). Furthermore, Calcium carbonate (CaCO₃) particles (60 nm～ 90 nm) were introduced into PTFE matrix. The interfacial microvoids (IFMs) which were different from the PTFE sintering or node‐fibril network structure were obtained. The assumption of the IFMs formation was proposed in this study. Effects of CaCO₃ amount and draw ratios on structure and properties of hybrid hollow fiber membranes were analyzed, and the SEM results showed that the IFMs quantity and diameter improved with draw ratio increasing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

CuO‐filled aminomethylated polysulfone hybrid membranes for deep desulfurization

CuO‐filled aminomethylated polysulfone hybrid membranes were prepared for sulfur removal from gasoline. The as‐prepared membranes were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X‐ray diffraction (XRD). The separation performance of the hybrid membranes was evaluated by pervaporation (PV) separation of n‐heptane/thiophene binary mixture. CuO‐filling leads to a decrease in permeation flux. The sulfur‐enrichment factor increased first and then decreased with increasing CuO loading, and it is worth noting that there is a rebound in enrichment factor above 8 wt % CuO loading. Influencing factors such as nitrogen content, feed temperature, sulfur content, and various hydrocarbons on membrane PV performance were also evaluated. Permeation flux of 23.9 kg·μm·m^?2·h^?1 and sulfur‐enrichment factor of 3.9 can be achieved at 4 wt % CuO loading in PV of n‐heptane/thiophene binary mixture with 1500 μg·g^?1 sulfur content. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3718–3725, 2013     

Formation of bicontinuous,hydrophobic nylon 12 membranes via cold-solvent-induced phase separation for membrane distillation application

Skinless nylon 12 microporous membranes were prepared via a cold-solvent-induced phase-separation process from a binary nylon 12–formic acid system. Through the incorporation of an aging step, polymer nucleation in the dope was enhanced, and the formed membranes exhibited a special particulate structure composed of interlocked sticklike or sheaflike crystallites, which coexisted with continuous microporosity. The crystallite size was affected by the polymer concentration in the dope and the aging time; for example, aging alone allowed for the reduction of the particle diameter from about 20 μm to about 1 μm. Because the membranes were skinless and hydrophobic (contact angles ≈ 105°), they were potentially appropriate for desalination via membrane distillation (MDi). For the case of desalting 3.5% NaCl_(aq) by means of direct-contact MDi, very high rejection ratios (∼99.6%) were achieved for all membranes under the operation conditions (temperature of the hot stream = 50°C, temperature of the cold stream = 20°C, and circulation rate = 0.7 L/min), whereas the highest permeation flux obtainable was 5.15 L/m² h. The membranes were strong, with tensile strengths ranging from 4.7 to 6.3 N/mm². Finally, we discovered a shift from α to γ structure as the dope polymer increased, whereas the crystallinity was about 27% in all cases. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47036.     

Preparation and properties of porous polytetrafluoroethylene hollow fiber membrane through mechanical operations

Porous polytetrafluoroethylene (PTFE) hollow fiber membranes were prepared from fine powder through a series of mechanical operations including paste extrusion, heat treatment, stretching and sintering. In contrast to conventional process, the heat treatment used in this study was performed at 200°C to 330°C (near the melting point) on the PTFE nascent hollow fiber (precursor of membrane). The results showed that the introduction of heat treatment step effectively improved the mechanical properties of precursors, the ultimate stress and strain increased observably with heat treatment temperature, which was beneficial to subsequently stretching precursors to make them porous. Furthermore, the morphological changes and improvement of membrane properties caused by stretching operation were investigated for porous PTFE hollow fiber membrane having finer pore size and higher porosity. The porous microstructure of nodes interconnected by fibrils varied depending on the stretching conditions, such as the stretching temperature, rate, and ratio. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42696.     

Preparation of a hydrophobically enhanced antifouling isotactic polypropylene/silicone dioxide flat‐sheet membrane via thermally induced phase separation for vacuum membrane distillation

Isotactic polypropylene (iPP) hydrophobic flat‐sheet membranes were fabricated for use in vacuum membrane distillation (VMD) through a thermally induced phase‐separation process with dispersing hydrophobically modified SiO₂ nanoparticles in the casting solution to achieve a higher hydrophobicity and to sustain a stable flux in VMD. The contact angle (CA) measurements indicated that the incorporation of nano‐SiO₂ into a casting solution mixture containing 20 wt % iPP had a 20.9% higher CA relative to that of SiO₂‐free membranes. The addition of nano‐SiO₂ also induced morphological changes in the membrane structure, including changes in the pore size distribution, porosity, and suppression of macrovoids. The pore size distribution of the iPP–SiO₂ membranes became narrower compared with that of the SiO₂‐free membranes, and the porosity also improved from 35.45 to 59.75% with SiO₂ addition. The average pore size and maximum pore size of the iPP–SiO₂ membranes both decreased. The ability of the membranes to concentrate an astragalus aqueous solution (a type of traditional Chinese medicine) with VMD was investigated. The surface hydrophobicity and antifouling performance of the iPP–SiO₂ membranes improved with nano‐SiO₂ addition to the membrane casting solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42615.     

Modeling and simulation for direct contact membrane distillation in hollow fiber modules

Direct contact membrane distillation (DCMD) offers an attractive operation for the separation of mixtures at atmospheric pressure with reasonable energy requirement. A new simultaneous heat and mass transfer model in DCMD in a hollow fiber configuration is presented. Flow regime in feed and permeate side, the variations of mean temperature and concentration along the membrane module, the length of the membrane, and various properties of membrane characteristics are taken into account in the present model. A system of nonlinear equations describing the DCMD process is solved numerically for each cell using the FSOLVE coding, which is a built‐in function in MATLAB^® to find the influence of the temperature and velocity of the feed and permeate streams, and the salt concentration of the feed along the module on the permeate flux. The predicted results by the new model show a good accord with a wide range of various experimental results available in the literature. © 2012 American Institute of Chemical Engineers AIChE J, 59: 589–603, 2013     

电纺及疏水改性制备CA/SiNPs-FAS超疏水复合膜及膜蒸馏脱盐研究

以1-甲基-2-吡咯烷酮/丙酮为混合溶剂,无纺布为支撑层,采用静电纺丝技术与溶胶-凝胶方法,制备了醋酸纤维素/二氧化硅复合纳米纤维膜,并将其浸渍于全氟烷基硅烷/正己烷分散液中进行疏水化改性。利用场发射扫描电子显微镜、红外光谱仪、孔径分析仪、接触角测量仪器等表征了改性前后复合膜表面形貌、官能团变化、孔径分布及润湿性等膜性能参数并将其应用于连续性直接接触式膜蒸馏盐浓缩过程。结果表明,静电纺丝复合膜呈三维空间网状结构,且利用正硅酸乙酯生成的纳米二氧化硅颗粒内陷于醋酸纤维素纤维内部形成微米-纳米梯级分布。经全氟烷基硅烷修饰后,红外特征峰明显,复合膜水接触角最高可达156°,且对质量分数为5%的十二烷基硫酸钠液滴也同时展示出优良的抗润湿性能（接触角125°）。以60℃、35 g·L^-1的NaCl溶液为进料液进行持续性直接接触式膜蒸馏脱盐实验,当渗透温度为20℃时,各复合膜盐截留率均能达到99.99%以上,其中,CA/SiNPs-FAS膜通量可稳定在11.2 kg·（m²·h）^-1。     

Preparation of a cellulose acetate/organic montmorillonite composite porous ultrafine fiber membrane for enzyme immobilization

Four types of fibrous membranes based on cellulose acetate (CA)—CA membranes with nonporous fibers, CA/organic montmorillonite (O‐MMT) membranes with nonporous fibers, CA membranes with porous fibers, and CA/O‐MMT membranes with porous fibers—were prepared by electrospinning, and then, they were used for enzyme immobilization. The surface morphologies of the composite fibrous membranes were investigated with scanning electron microscopy and transmission electron microscopy. The optimum pH was 3.5 for all of the immobilized enzymes, and the optimum temperature was 50 °C. Compared with the free enzyme, the immobilized enzyme showed better stability for pH and temperature changes. Moreover, the addition of O‐MMT and the pores on the fibers improved the storage stability and the operational stability. Among the four kinds of fibrous membranes, the CA/O‐MMT membranes with porous fibers showed the best stability for the immobilized enzymes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43818.     

High performance synthetic paper used for color printing based on ultrahigh molecular weight polyethylene/SiO2 by using TIPS method

The production of traditional cellulose paper not only consumes lots of timber, but also brings about some environmental issues. Therefore, it is being increasingly replaced by synthetic paper. In this study, ultrahigh molecular weight polyethylene (UHMWPE)/SiO₂ synthetic paper with high application performance was prepared by the thermally induced phase separation method using mineral oil as diluent. The corresponding properties of synthetic paper, including surface morphology, overall porosity, tensile strength, thermal stability, acid and alkali resistance, whiteness, and inkjet print effect were investigated respectively. The results show that the overall porosity of UHMWPE/SiO₂ synthetic paper is above 45%, and the tensile strength exceeds 4.3 MPa. UHMWPE/SiO₂ synthetic paper also presents light weight, as well as good resistance to heat, acid and alkali. Meanwhile, the average whiteness of the samples is up to 91.8%. The sample K‐50, which contains 31.5 wt % SiO₂, takes on the best print performance caused by its dense surface and higher SiO₂ content. It is indicated that UHMWPE/SiO₂ synthetic paper has good market prospects in the color printing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41529.     

Preparation,characterization, and performance evaluation of coated PES polymer materials fabricated via dry/wet phase inversion technique

Sulfur dioxide (SO₂) is the major air pollutant which is emitted from the power plant. In this study, hollow fiber membrane (HFM) separation process is applied for the improvement of SO₂ removal efficiency in the post‐combustion gas. HFM was produced by dry/wet phase inversion method and then coated with Polydimethylsiloxane (PDMS). The membrane morphology and characterization were examined with help of scanning electron microscope (SEM), energy dispersion of X‐ray spectroscopy (EDX), Fourier transform infrared (FT‐IR) and atomic force microscopy (AFM). Polyethersulfone (PES) hollow fiber membranes were tested for the SO₂/N₂ binary mixed gas separation. Single gas permeance of SO₂, N₂, and binary mixture gas (200 ppm of SO₂) separation experiment was initiated to observe membrane behavior according to temperature and pressure difference and retentate flow rate. As a result, permeance of SO₂ was 24.9–47.4 GPU and selectivity of SO₂/N₂ was 1.6–4.2. From the mixture gas separation experiment, SO₂ removal efficiency increased according to stage cut and operating pressure. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39711.     

Effect of the mass ratio of Fe3O4/PAA on separation properties and the extractive amount of Fe3O4 during the formation of Fe3O4‐PES ultrafiltration membranes

A series of Fe₃O₄‐PES ultrafiltration membranes with different mass ratios of Fe₃O₄ and PAA were prepared from suspensions, using the phase inversion process. The suspensions consisted of polyether sulfone (PES), dimethyl formamide, polyacrylic acid (PAA), and ferrosoferric oxide (Fe₃O₄). The separation properties of ultrafiltration membranes with different Fe₃O₄/PAA mass ratio were investigated by a cross‐flow experimental system. The Fe₃O₄/PAA mass ratio had little effect on the rejection of membranes to BSA. However, the pure water flux had a slight decline and then rised rapidly with the increase of Fe₃O₄/PAA mass ratio. An interesting phenomenon observed was that the Fe₃O₄ particles could diffuse into the nonsolvent bath during the formation of membrane, and the amount of Fe₃O₄ extracted into the nonsolvent bath nearly kept a constant mass ratio to PAA, even if the Fe₃O₄/PAA proportion was changed. The reasons of this interesting phenomenon were investigated. This result indicates that modified inorganic fillers may be used as the pore‐forming agent to prepare the porous membranes like the template leaching method. At the same time, this method does not use any strong acid or base. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of PVDF/CaCO3 composite hollow fiber membrane via a thermally induced phase separation method

The spinnabiliy of polyvinylidene fluoride (PVDF)/CaCO₃ microparticle dope solution were explored via a thermally induced phase separation process, and composite hollow fiber (CHF) membranes were prepared successfully. The experiment results showed that the self‐supporting property of CHF got improved after adding CaCO₃ at low concentration of PVDF, so the control of spinning process became easy. The effects of CaCO₃ on the structure and properties of hollow fiber membrane were investigated in terms of morphology, water flux, porosity, breakage strength, and crystallization. The results indicated that CHF presented a uniform bicontinuous structure. The permeability and porosity of CHF increased obviously when CaCO₃ was removed by acid, while the breakage strength decreased slightly. CHF presented a good drying stability. POLYM. COMPOS., 34:1204–1210, 2013. © 2013 Society of Plastics Engineers     

Synergetic effects of organic and inorganic additives on improvement in hydrophilicity and performance of PVDF antifouling ultrafiltration membrane for removal of natural organic material from water

Surrounding vegetation, animal, human and microbiological decomposition are the strong source of humic acid (HA) falling into the surface water bodies through rain runoff in the monsoon. HA contains various functional groups, such as carboxylic, phenolic, hydroxyl, and quinine, which are the major foulant. Contact of HA may have an adversarial health issue to human beings namely goiter, black foot, and cancer disease. The maximum permissible limit of HA in drinking water should be less than 2 ppm as per the Environmental Protection Agency (EPA). The membrane technology has prevailed a prominent place worldwide in chemical, water and wastewater treatment technologies. The proposed work is focused on the blending of organic-water soluble polymer polyethylene glycol 6000 as a pore-forming agent and inorganic salt lithium bromide (LiBr) as membrane morphology modifier with polyvinylidene fluoride host polymer in the N,N-Dimethylacetamide solvent. All fabricated membranes were characterized for functional groups and morphology. The total number of pores per unit surface area of membrane for membranes M-LiBr-0, M-LiBr-1, M-LiBr-2, and M-LiBr-3 are 2 × 10¹³, 2.3 × 10¹⁴, 2.7 × 10¹⁴ and 2.82 × 10¹⁴, respectively. The static water contact angle was decreased from 68.2° to 50.6° with an increase in the content of LiBr from 0 to 3 wt%. The order of pure water flux and hydraulic permeability of the membrane was M-LiBr-0 < M-LiBr-1 < M-LiBr-2 < M-LiBr-3. The HA rejection of the membrane was also increased from 90.13% to 96.24% with LiBr content due to a decrease in pore size of the membrane with the addition of LiBr content.     

Spray-coated PDMS/PVDF composite membrane for enhanced butanol recovery by pervaporation

In this study, spray-coating was used to prepare dihydroxypolydimethylsiloxane (PDMS) composite membranes with high flux and separation factor for biobutanol recovery from aqueous solution. A thin, smooth, and defect-free PDMS layer was prepared by spray-coating on polyvinylidene difluoride ultrafiltration membrane with little PDMS penetration. The effects of process parameters for membrane fabrication and pervaporation on membrane performance were investigated. A membrane with 2 μm active layer was obtained with a high flux of 1306.9 g/m² h. The optimal membrane with the highest pervaporation separation index (PSI) (19.15 kg/m² h) showed a total flux of 530.6 g/m² h and a separation factor of 36.1 at 37°C, and a PSI of 65.61 kg/m² h and a flux of 1927.0 g/m² h at 70°C. Membrane performance was affected by feed composition and temperature. Acetone-butanol-ethanol solution and fermentation broth gave lower butanol fluxes and separation factors compared to butanol model solution.