PVA/TEOS crosslinked membranes incorporating zinc oxide nanoparticles and sodium alginate to improve reverse osmosis performance for desalination

Pure water is becoming less available with increases in world population, so seawater desalination is becoming more important. For efficient seawater desalination, this paper proposes a novel mixed matrix membrane (MMM) based on the deposition of a poly(vinyl alcohol) (PVA) nanofibrous active layer on a 3-triethoxysilylpropylamine-functionalized cellulose acetate substrate. The active layer is fabricated by utilizing a tetraethyl orthosilicate–crosslinked PVA incorporating zinc oxide nanoparticles (ZnO-NPs) and sodium alginate (NaAlg). The overall reverse osmosis performance of the MMMs is enhanced by the infusion of ZnO-NPs and NaAlg in PVA; we find the optimum concentration for the best performance to be ZnO-NPs at 0.1 wt % and NaAlg at 0.01 wt %. In terms of permeation flux, salt rejection, salt passage, stability, long-term rejection, membrane antifouling, reusability, and chlorine resistance, the proposed MMMs are examined using a dead-end reverse osmosis filtration setup. The results show that the active layer achieves an optimal permeation flux of 34.6 L/m² h, a natural sea salt rejection of 97%, and a chlorine resistance of 93%, suggesting that the proposed MMMs can be useful for seawater desalination. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47559.     

Poly(ethylene glycol) crosslinked sulfonated polysulfone composite membranes for forward osmosis

Forward osmosis (FO) membranes were prepared by a coating method with poly(ethylene glycol) crosslinked sulfonated polysulfone (SPSf) as a selective layer. The poly(ether sulfone)/SPSf substrate was prepared by phase inversion. The composite membranes were characterized with respect to membrane chemistry (by attenuated total reflectance/Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy), hydrophilicity (by static contact angle measurement), and surface morphology (by scanning electron microscopy and atomic force microscopy). The FO performance was also characterized. The effects of the crosslinker concentration on the hydrophilicity and FO performance were investigated. The crosslinked membrane exhibited a high hydrophilicity with a lowest contact angle of 15.5°. Under FO tests, the membranes achieved a higher water flux of 15.2 L m^?2 h^?1 when used against deionized water as the feed solution and a 2 mol/L sodium chloride (NaCl) solution as the the draw solution. The membranes achieved a magnesium sulfate rejection of 96% and an NaCl rejection of 55% when used against a 1 g/L inorganic salt solution as the feed solution and a 2 mol/L glucose solution as the draw solution. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43941.     

Ionic conductivity and related properties of crosslinked chitosan membranes

Crosslinked chitosan membranes were prepared with a relatively low degree of crosslinking with epichlorohydrin and glutaraldehyde as crosslinking agents under heterogeneous and homogeneous conditions, respectively. The tensile properties, crystallinity, swelling index, and ionic conductivity of the crosslinked membranes were investigated. A significant decrease in the crystallinity and a large change in the swelling ratio of the crosslinked membrane were observed. In comparison with the uncrosslinked chitosan membrane, when the chitosan membrane was crosslinked with an appropriate degree of crosslinking under homogeneous conditions, its ionic conductivity after hydration for 1 h at room temperature increased by about one order of magnitude. In addition, with a lower concentration of the crosslinking agent, the tensile strength and breaking elongation of the crosslinked membrane were almost unchanged. Moreover, up to a critical value, the tensile strength of the membrane increased gradually, and the breaking elongation decreased slowly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 306–317, 2003     

Thermal,mechanical, and dielectric behaviors of crosslinked linear low density polyethylene/polyolefin elastomers blends

Crosslinked linear low density polyethylene (XLPE) containing polyolefin elastomers (POE) has been evaluated. The blends with different dicumyl peroxide (DCP) and POE contents have been prepared and processed by compression molding. A series of the samples obtained have been investigated by gel content determination, scanning electron microscopy (SEM), different scanning calorimetry (DSC), mechanical, and dielectric behaviors measurements. The results obtained clearly show the relevant influence of the POE content, as well as of the DCP content, which tends to enhance crosslinking. As expected, the toughness of XLPE is improved by using adequate content of POE, and the blends exhibit a much more similar tensile behavior to that of elastomer. In addition, the results indicate that the blends possess the excellent dielectric behaviors, such as dielectric constant and dissipation factor. The crystallinity of the blends decreases as the DCP and POE contents increase. The melting temperature of the blends also decreases with the increase of DCP content, while POE content has few influences on the melting temperature of the blends. The SEM images strongly reveal that the blends are partially compatible, and the POE can be dispersed well in the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1920–1927, 2007     

Pervaporation separation of ethanol/water mixture using modified zeolite filled PDMS membranes

In this article, the composite polydimethylsiloxane (PDMS) membranes supported by cellulose acetate (CA) microfiltration membrane were successfully prepared by adding modified zeolite particles with a silane coupling agent, NH₃–C₃H₆–Si(OC₂H₅)₃. The sorption and diffusion behaviors of ethanol and water in the films were studied. The results showed that with the increase in the modified zeolite content, the solubility selectivity increased, but the diffusion selectivity first increased, then decreased. The effects of modified zeolite content and feed temperature on the pervaporation performance of the composite membranes in 10 wt % ethanol/water mixture were also investigated. When modified zeolite loading was 20 wt %, for 10 wt % ethanol/water mixture at 40°C, the permeate flux was 348.7 g·m^?2·h^?1, the separation factor was 14.1, and the permeate separate index was 4568, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41897.     

Morphology and mechanical properties of pullulan/poly(vinyl alcohol) blends crosslinked with glyoxal

We prepared pullulan/poly(vinyl alcohol) (PVA) blend films by casting the polymer solution in dimethyl sulfoxide. Their morphology and mechanical properties were investigated. Scanning electron micrographs revealed that the pullulan was immiscible with PVA over the entire composition range. The tensile strength and modulus of the blend films were lower than those predicted by the upper bound composite equation. To improve the mechanical properties, we investigated the reaction of the 40/60 blend with glyoxal. The infrared spectral change and the increase in the glass‐transition temperature (corresponding to the PVA component) accompanying the reaction indicated that crosslinking with glyoxal had proceeded. The crosslinked films were homogeneous and had higher tensile strengths and moduli than the simple blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2273–2280, 2001     

Characterization and gas‐permeation properties of crosslinked diacetylene‐containing polymer membranes from ferulic acid

Thermally and UV crosslinked poly[propargyl(3‐methoxy‐4‐propargyloxy) cinnamate] (PPOF) were investigated in terms of their physical, thermal, optical, and gas‐permeation properties. The crosslinked membranes had high gel contents because of the formation of a diacetylene network. The wide‐angle X‐ray diffraction patterns showed that all of the membranes were amorphous in structure, regardless of the type of crosslinking reaction. The membrane density increased after the crosslinking reaction; this suggested that the free volume of the crosslinked membrane was lower than that of the untreated membranes. Drastic color changes in the membranes were also observed because of the highly conjugated crosslinked network of diacetylene. In addition, the conjugation caused by diacetylene crosslinking led to visible absorption within the range 400–600 nm. The gas permeation of the crosslinked membrane was reduced compared with that of the untreated membranes. In particular, the gas permeability of the thermally crosslinked membrane was lower than that of UV‐irradiated membrane. On the basis of this result, the degree of crosslinking by thermal treatment was higher than that of UV irradiation. Hence, the crosslinked PPOF membranes showed improved gas‐barrier properties due to the high conjugation of the crosslinked diacetylene network induced by thermal treatment and UV irradiation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Chlorine-resistance of reverse osmosis (RO) polyamide membranes

Polyamide (PA) reverse osmosis (RO) membranes suffer performance decay when exposed to oxidizing species, limiting their lifetime and increasing operation costs. This article aims at reviewing the effect of chlorine species on the performance and characteristics of PA-membranes. Experimental evidence supporting different competing mechanisms for chlorine-polymer interaction will be presented, together with the influence of operational parameters. Additionally, an overview of different modification methods that exist to render PA-membranes more chlorine-resistant is given.     

Properties and pervaporation performance of poly(vinyl alcohol) membranes crosslinked with various dianhydrides

In this work, three dianhydrides with similar chemical structures, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), 4,4′‐oxydiphthalic anhydride (ODPA), and pyromellitic dianhydride (PMDA), are employed for the crosslinking modification of poly(vinyl alcohol) (PVA) membranes for ethanol dehydration via pervaporation. The changes in crosslinking degree, surface hydrophilicity, and glass‐transition temperature are investigated and compared. Compared to the pure PVA membrane, all crosslinked membranes show higher fluxes but lower separation factors, because of the higher fractional free volume and the lower hydrophilicity by the crosslinking of the PVA matrix, respectively. In addition, all crosslinked PVA membranes exhibit similar flux, and the separation factor presents a decreasing order of PVA/PMDA‐2 > PVA/ODPA‐2 > PVA/BTDA‐2, which is in the reverse order of their hydrophilicity, probably because of the reduction in the swelling resistance. With the PMDA content increasing from 0.01 to 0.04 mol/(kg PVA) in the PVA/PMDA crosslinked membranes, the crosslinking degree is enhanced and the hydrogen bonding is weakened, resulting in a flux increase from 120.2 to 190.8 g m^?2 h^?1, but the separation factor declines from 306 to 58. This work is believed to provide useful insight on the chemical modification of PVA membranes for pervaporation and other membrane‐based separation applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46159.     

Preparation and characterization of poly(ethylene glycol) crosslinked chitosan films

Poly(ethylene glycol) (PEG) crosslinked chitosan films with various PEG to chitosan ratio and PEG molecular weight were successfully prepared via the epoxy‐amine reaction between chitosan and PEG‐epoxy. The thermal and mechanical properties and swelling behavior were studied for the PEG crosslinked chitosan films. The mechanical strength of chitosan films were greatly enforced by the introduction of PEG‐epoxy, achieving an elongation of about 80%. It was found that the crosslinked chitosan films form hydrogel in water, achieving a swelling ratio higher than 20 times of original weight. The swelling behavior of chitosan films relied greatly on the molecular weight of the crosslinker PEG‐epoxy and the weight percent of PEG‐epoxy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Quaternized poly (2,6-dimethyl-1,4-phenylene oxide) crosslinked by tertiary amine and siloxane for anion exchange membranes

A series of tertiary amine and siloxane crosslinked composite anion exchange membranes were prepared by incorporating 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane (EHTMS) and N,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHDA) into N-Methyldiethanolamine (MDEA)-functionalized poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) backbone via sol-gel process. The resultant membranes named as AEM-X (X = 1, 2, 3, 4), which own a three-dimensional (3D) cross-linking structure, exhibit superior swelling resistance, mechanical properties, even the thermal stability is up to 220°C. Compared with AEM-1 (contains no crosslinker), the swelling ratio of AEM-2 obviously decreases by 10.2% at 80°C, while the OH⁻ conductivity of AEM-2 has a merely 1.9% decline (20.6 mS cm⁻¹) at 80°C and can maintain 67% of its initial value in a 2 M aqueous NaOH at 80°C for 240 h. The simultaneous introduction of inorganic siloxane and organic linear crosslinker provides a new idea for the preparation of anion exchange membranes with largely improvement in dimensional stability and alkali resistance while the ionic conductivity is kept at comparatively high level.     

Effects of maleic anhydride grafted polyethylene on rheological,thermal, and mechanical properties of ultra high molecular weight polyethylene/poly(ethylene glycol) blends

Ultra‐high molecular weight polyethylene (UHMWPE) has gained considerable fame due to its excellent wear and mechanical properties, though the inferior processability has restricted its further extensive applications. In this study, a combination of UHMWPE and poly(ethylene glycol) (PEG) was considered based on the recent reports, and aiming to further exploit the potential of PEG that acts as processing aid, and also to obtain greater enhanced processability along with other properties, the effects of incorporating maleic anhydride grafted polyethylene (MAPE) was thoroughly investigated. Rheological tests revealed a further significant reduction in melt viscosity of UHMWPE/PEG blends after MAPE introduced, showing a potential of better processability, while the flexural strength and toughness of UHMWPE blends experienced a satisfying increase without any obvious compromises in other mechanical properties. A slight improvement of thermal stability in UHMWPE ternary blends along with an increase of vicat softening temperature were characterized by thermal tests, while the crystallinity of UHMWPE was diminished after the introduction of MAPE. Morphology analysis indicated that better dispersion and decreased size of PEG particles were achieved in UHMWPE matrix when MAPE was incorporated, which confirmed the improved interfacial interactions and other reinforcements obtained in UHMWPE/PEG/MAPE blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42701.     

Nonequilibrium nanoblend membranes for the pervaporation of benzene/cyclohexane mixtures

Immiscible blends of polymers were cast from solution, and the rate of evaporation was controlled relative to the rate of phase separation to produce different morphologies; upon crosslinking, stable nonequilibrium nanoblends were realized. This process of forced assembly produced useful membrane materials that could be designed for solubility selectivity with the group contribution methodology. Crosslinked ternary blends of nitrile butadiene rubber (NBR), poly(methyl methacrylate) (PMMA), and a tercopolymer of ethylene oxide/epichlorohydrin/allyl glycidyl ether (Hydrin) were examined for use in the separation of benzene from cyclohexane by pervaporation. For a 50 : 50 wt % benzene/cyclohexane feed, blend 811 (containing 80 wt % NBR, 10 wt % Hydrin, and 10 wt % PMMA) gave a separation factor of 7.3 and a normalized flux of 28 kg μm/m² h; such a performance is unmatched in the literature, with the flux being very high for the reported separation factor. Among the samples tested, the flux of the membrane increased as the amount of NBR in the ternary blend decreased; however, the separation factor was not largely affected. Blended samples showed no sign of deformation after 48 h at the operating temperature as compared to pure NBR, which did show evidence of creep. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of porous poly(vinylidene fluoride) membranes for dehumidification with poly(ethylene glycol) as an additive

Porous poly(vinylidene fluoride) (PVDF) membranes for dehumidification were prepared from a PVDF/dimethylformamide/water system by phase inversion with poly(ethylene glycol) (PEG) as an additive at various concentrations (1.2, 1.8, and 2.4%) and with various molecular weights (1000, 2000, and 6000). The surface morphologies of the resultant membranes were characterized with scanning electron microscopy and atomic force microscopy, and the pore diameter, porosity, and pore size distribution of the membranes were also determined by a gas‐sorption method. The influence of the concentration and molecular weight of PEG on water‐vapor transport through the membranes was evaluated. The moisture‐transport property of the membranes was improved significantly with increases in the concentration and molecular weight of PEG, and a membrane with good moisture permeability was obtained with 2.4% PEG‐6000 as an additive. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Surface and mechanical properties of microporous membranes of poly(ethylene glycol)-polydimethylsiloxane copolymer/chitosan

Poly(ethylene glycol)-polydimethylsiloxane (PEG-PDMS) block copolymers were prepared via a condensation reaction between PEG diacid and PDMS diol. PEG diacid was synthesized from the reaction between hydroxy-terminated PEG and succinic anhydride. PDMS diol was prepared from the ring-opening polymerization of octamethylcyclotetrasiloxane (D₄) followed by hydrosilylation with allyl alcohol. The copolymers were incorporated into chitosan in order that good water swellability and wettability of chitosan were retained due to hydrophilic PEG blocks, whereas PDMS block in the copolymers functioned as a toughening modifier. Percent crosslinking of 66-84 was observed once 5-10 wt% of the copolymers was incorporated. As compared to the unmodified sample, the copolymer-containing chitosan exhibited the decreases in both water contact angles and the rate of water vapor permeability. The studies on tensile properties indicated that incorporation of copolymers into chitosan improved the flexibility of the films.     

Thermal and mechanical properties of silane‐grafted water crosslinked polyethylene

The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, with 0.10 phr of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5‐Dimethyl‐2,5‐di (tert‐butyl‐peroxy)‐hexane (DHBP), it was found that the grafting effect was improved; however, as Di(2‐tert‐butylperoxypropyl ‐(2))‐benzene (DIPP) or excess DHBP was used, LLDPE was supposed to cause self‐crosslinking, which reduced the grafting effect of silane and was invalid in the processing of extrusion. In this study, vinyl trimethoxysilane (VTMS) was grafted onto various polyethylenes (HDPE, LLDPE, and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to crosslink utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to crosslink during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for crosslinked LDPE and LLDPE. Mechanical and thermal properties of the crosslinked PE are much better than that of uncrosslinked PE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2383–2391, 2005     

Solvent and pH resistance of surface crosslinked chitosan/poly(acrylonitrile) composite nanofiltration membranes

The resistance of novel surface crosslinked Chitosan/poly(acrylonitrile) (PAN) composite nanofiltration (NF) membranes to pH and organic solvents was studied with respect to the effects of crosslinking parameters, namely, glutaraldehyde concentration and crosslinking time. The pH resistance was determined by permeation of aqueous acidic (pH 2.5) and basic (pH 11) solutions as well as swelling studies in the pH range of 2.5–11. The solvent resistance was determined by swelling, immersion, and permeation studies with several industrially important organic solvents, namely methanol, ethanol, iso‐propanol, methyl ethyl ketone, ethyl acetate and hexane. It was observed that the crosslinked composite membranes maintain the permeate fluxes for test solvents for 2 h of continuous operation without any significant change in flux. SEM studies on membrane samples after immersion as well as permeation with the above‐mentioned solvents indicated that the membrane morphology was maintained. The results are explained in terms of solvent–membrane polar and hydrophobic interactions, using solubility parameters of membrane and solvents and dielectric constants of solvents. Pure water flux and polyethylene glycol transmission data indicated that at pH 2.5 and 11, the membrane stability increased with increasing glutaraldehyde concentration and was much better at pH 11 than at pH 2.5. All surface crosslinked membranes showed reduced swelling between pH 4–10. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1782–1793, 2000     

Structure and properties of new reversibly crosslinked iPP/LDPE blends

Reversibly crosslinked blends of isotactic polypropylene and low density polyethylene (iPP/LDPE) were prepared in the presence of crosslinking agents using reactive extrusion. The structure and properties of the modified blends were investigated by means of wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and macro- and micro-mechanical measurements. The crystallinity of the modified samples (LDPE, iPP, and their blends) does not seem to be so much affected by the crosslinking process. Results show that the microhardness of the iPP/LDPE blends notably increases with the iPP content. The micromechanical properties of the modified blends only improve slightly as a consequence of the crosslinking process. In the iPP samples, and also in the iPP/LDPE blends, this process gives rise to the appearance of new, crystalline ethylenic chains, as evidenced by the calorimetric measurements. Furthermore, the impact strength of the modified materials is improved as compared with that of the original ones, while some of the crosslinked blends show a ductile fracture behavior. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal,mechanical, and surface characterization of starch–poly(vinyl alcohol) blends and borax‐crosslinked films

Starch–poly(vinyl alcohol) (PVA) blends with different compositions were prepared and crosslinked with borax by in situ and posttreatment methods. Various amounts of glycerol and poly(ethylene glycol) with a molecular weight of 400 were added to the formulations as plasticizers. The pure starch–PVA blends and the crosslinked blends were subjected to differential scanning calorimetry, thermogravimetry, and X‐ray photoelectron spectroscopic studies. Broido and Coats–Redfern equations were used to calculate the thermal decomposition kinetic parameters. The tensile strengths and elongation percentages of the films were also evaluated. The results suggested that the glass‐transition temperature (T_g) and the melting temperature strongly depended on the plasticizer concentration. The enthalpy relaxation phenomenon was dependent on the starch content in the pure blend. The crosslinked films showed higher stability and lower T_g's than pure PVA and starch–PVA blends, respectively. High‐resolution X‐ray photoelectron spectroscopy provided a method of differentiating the presence of various carbons associated with different environments in the films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1313–1322, 2005     

Relationship between the cell structure and mechanical properties of chemically crosslinked polyethylene foams

The main objective of this work was to study the effect of the controlling parameters on the morphology and mechanical properties of the peroxide crosslinked low‐density polyethylene foams. The relationship between the morphology and mechanical properties was also considered. Using different Dicumyl peroxide (DCP) and azodicrbonamide (ADCA) concentrations, various foams with different cell structures were prepared. Gel content and density of the foams were measured according to the standard methods. The morphology was examined using SEM technique. The mechanical properties of the foams were evaluated by means of compression and creep recovery tests. The results showed that the gel content and the density are mainly controlled by DCP and ADCA concentration, respectively. The results also showed that the cell size distribution is mainly controlled by DCP concentration. Increasing of DCP increased the gel content and decreased the cell size and cell size distribution. Foam density was mainly controlled by ADCA concentration, whereas the morphology was less affected with ADCA concentration. The foams with small cell size and narrow cell size distribution showed higher mechanical strength and lower plastic strain. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012