Triblock SEBS/DVB crosslinked and sulfonated membranes: Fuel cell performance and conductivity

A set of styrene-ethylene-butylene-styrene triblock copolymer (SEBS) membranes with 10 or 25 wt% divinyl-benzene (DVB) as a crosslinking agent were prepared and validated. Physicochemical characterization revealed suitable hydrolytic and thermal stability of photo-crosslinked membranes containing 25 wt% DVB and post-sulfonated. These compositions were evaluated in H₂/O₂ single cells, and electrical and proton conductivities were furtherly assessed. The membranes with the milder post-sulfonation showed greater proton conductivity than those with excessive sulfonation. In terms of electrical conductivity, a universal power law was applied, and the values obtained were low enough for being used as polyelectrolytes. At the analyzed temperatures, the charge transport process follows a long-range pathway or vehicular model. Finally, fuel cell performance revealed the best behavior for the membrane with 25 wt% DVB, photo-crosslinked during 30 min and mild sulfonated, with a promising power density of 526 mW·cm⁻². Overall, the results obtained highlight the promising fuel cell performance of these cost-effective triblock copolymer-based membranes and indicate that higher sulfonation does not necessarily imply better power density.     

Water state in chemically and physically crosslinked chitosan membranes

Chemically and physically crosslinked chitosan membranes were prepared by treating chitosan (Ch) with glutaraldehyde (GA) and sulfuric acid (SA). FTIR and XRD results were employed to confirm the formation of covalent and ionic crosslinks between Ch, GA, and SA. The states of water in non‐crosslinked and covalently and ionically crosslinked chitosan membranes containing different amount of water were investigated by low temperature differential scanning calorimetry measurements. The equilibrium swelling in water was examined gravimetrically. Two types of water were found in the polymer samples, i.e., freezing water and non‐freezing water. The effect of crosslinking process on water state and water uptake was analyzed. The water uptake decreased after chitosan crosslinking with GA, but significantly increased after later crosslinking with SA. The amount of non‐freezing water was generally smaller in crosslinked membranes. An impact of molecular and supermolecular structure on water uptake and state of water in non‐crosslinked and crosslinked chitosan membranes was discussed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1707–1715, 2013     

Characterization,separation performance,and model analysis of STPP‐chitosan/PAN polyelectrolyte complex membranes

Polyelectrolyte complex membranes (PCMs) were prepared using sodium tripolyphosphate (STPP) solution surface‐crosslinking chitosan/polyacrylonitrile (PAN) composite membranes. Fourier transform infrared (FTIR) was used to characterize the surface‐crosslinking. The effects of different surface‐crosslinking time on morphologies, element distribution, and crystal structures were investigated by scanning electron microscopy (SEM), energy dispersion of X‐ray (EDX), and X‐ray diffraction (XRD). The effect of crosslinking ratio on swelling ratio was analyzed. The separation performances of PCMs in terms of permeation flux and separation factor were measured by dehydrating ethyl acetate aqueous solutions. A kinetic model of crosslinking reaction was proposed to investigate the effect of crosslinking agent concentration and surface‐crosslinking time on the crosslinking ratio of PCMs. It was found that the membrane possessed the excellent performance when surface crosslinked for 15 min. The permeation flux and separation factor were 336 g/(m² h) and 6270 in 97 wt % ethyl acetate aqueous solution at 313 K. The crosslinking ratio of PCM exponentially increased as time increased, while linearly increased as concentration and diffusion coefficient of crosslinking agent STPP solution increased. And the effect of crosslinking agent concentration on crosslinking ratio was inversely proportional to surface‐crosslinking time. The experimental results matched well with the kinetic model when STPP concentration was lower than 5 wt %. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of glutaraldehyde crosslinked chitosan nanofiltration membrane

In this article, we prepare chitosan (CS) membrane on polyacrylonitrile (PAN) ultrafiltration membrane, and utilize the protonated amine group (? NH₃⁺) on the CS to retain γ‐aminobutyric acid (GABA) in a solution with a pH condition below the amino acid isoelectric point, so as to separate the amino acid from a mixture with sodium acetate that simulates the amino acid fermentation broth. To improve the acid resistance of the composite membrane, we chelate the amine groups on the CS by copper sulfate first, then crosslink the hydroxyl groups in glutaraldehyde solution, and remove the copper ion in hydrochloric acid finally to release the amine groups. This crosslinked CS/PAN composite membrane achieves 95% GABA rejection in pH 4.69 solution under the operation pressure of 0.2 MPa, while over 90% of the sodium acetate permeates the membrane. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Diffusional properties of chitosan hydrogel membranes

Chitosan membranes were prepared by a solvent evaporation technique, followed by crosslinking with glutaraldehyde and coating with BSA. The effects of crosslinking and BSA coating on the pore structure of such prepared hydrogel chitosan membranes were determined. The diffusion rates of 12 non‐electrolytes ranging in molecular radius between 2.5 and 14 Å through the membranes were measured, and the results were interpreted in terms of the capillary pore model and free volume model of solute diffusional transport through hydrogel membranes. Glutaraldehyde crosslinking was found to reduce the membrane water content and consequently the membrane pore size and surface porosity, whereas further BSA coating brought about the opposite effect. The latter effect lessened with an increase in glutaraldehyde pretreatment of the membranes. The optimal chitosan membrane preparation, compromising between the solute flux and membrane stability and durability was obtained when the membranes were crosslinked with glutaraldehyde at concentrations between 0.01 and 0.1% (w/w). The knowledge of transport properties and of physical strength of the membranes is of importance for the development of chitosan‐based controlled release systems. © 2001 Society of Chemical Industry     

Ionic conductivity of chitosan membranes

Chitosan membranes with various degrees of deacetylation and different molecular weights (MW) were prepared by film casting with aqueous solutions of chitosan and acetic acid. Ultraviolet (UV) spectrometry and infrared (IR) spectrometry were used to determine the degree of deacetylation (DDA) of chitosan. The viscosity-average MW of chitosan was measured in an aqueous solvent system of 0.25 M CH₃COOH/0.25 M CH₃COONa. The intrinsic ionic conductivities of the hydrated chitosan membranes were investigated using impedance spectroscopy. It was found that the intrinsic ionic conductivity was as high as 10⁻⁴ S cm⁻¹ after hydration for 1 h. The tensile strength and breaking elongation of the membranes were evaluated according to standard ASTM methods. The crystallinity and swelling ratio of the membranes were examined. A tentative mechanism for the ionic conductivity of chitosan membranes is also suggested.     

Synthesis and investigation of desalinating,antibacterial, and mechanical properties of tetraethylorthosilicate crosslinked chitosan/polyethylene glycol (PEG-300) membranes for reverse osmosis

Solution casting method was used to synthesize chitosan (CS)-based membranes for reverse osmosis (RO) using PEG-300 and tetraethylorthosilicate as a crosslinker. Their salt rejection (%) and permeate flux (mL/h.m²) was measured by using lab scale RO plant. FTIR spectroscopy reveals interactions between CS and PEG by shifting of  OH peak from 3237 cm⁻¹ to lower wavenumber in modified membranes. SEM results showed pores in modified membranes while pure CS membranes had uniform nonporous and dense microstructure. DMA results demonstrated that the addition of PEG lowers the T_g value up to 6.5%. Water content of membranes increases up to 82.63% as the amount of PEG increases owing to its hydrophilic nature. The bacterial killing ability showed that the modified membranes possess good antibacterial activity against Escherichia coli in comparison to the control film. The permeation results revealed that salt rejection and flux of the modified membranes increased up 60% and 86.36 mL/h.m², respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48870.     

Phosphonic acid functionalized siloxane crosslinked with 3‐glycidoxyproyltrimethoxysilane grafted polybenzimidazole high temperature proton exchange membranes

Phosphonic acid functionalized siloxane crosslinked with 3‐glycidoxypropyltrimethoxysilane (GPTMS) grafted polybenzimidazole (PBI) membranes are prepared by sol–gel process. The structure of the membranes is characterized by Fourier‐transform infrared spectroscopy and X‐ray diffraction spectroscopy. SEM images of the membranes show that the membranes are homogeneous and compact. The crosslinked membranes exhibit excellent thermal stability, chemical stability and mechanical property. The proton conductivity of the crosslinked membranes increases by an order of magnitude over range of 20 °C to 160 °C under anhydrous condition, which can reach 3.15 × 10^?2 S cm^?1 at 160 °C under anhydrous condition. The activation energy of proton conductivity for membranes decreases with increase of PBI, because the formation of hydrogen bond network between the phosphonic acid and the imidazole ring can enhance the continuity of hydrogen bond in the membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44818.     

Surface characteristics of ionically crosslinked chitosan membranes

In this study, homogenous dense chitosan membranes were prepared by solution‐casting procedure. Then the membranes were ionically crosslinked by sulfuric acid. The surfaces of chitosan membranes before and after crosslinking were characterized by using FTIR‐ATR, X‐ray photoelectron spectroscopy (XPS), and atomic‐force microscopy (AFM) techniques. The XPS data suggest that the surface composition of crosslinked membrane does not change significantly with respect to uncrosslinked membrane and the most important evidence is a certain amount of sulfur, coming from the crosslinker. The result from FTIR‐ATR data shows the effectiveness of the crosslinking procedure by the shift in amide I and amide II bands. The investigation of membrane surfaces by AFM indicates that the crosslinking procedure modifies the surface morphology of chitosan. After crosslinking, the surface topography becomes more homogenous and relatively flat. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Propranolol hydrochloride release behaviour of crosslinked chitosan membranes

Chitosan membranes of 20 μm thickness were prepared by a solvent evaporation technique and crosslinked with different concentrations of glutaraldehyde to obtain membranes of various degrees of crosslinking. These membranes were characterized by thermogravimetric (TG) analysis, differential scanning calorimetry (DSC) and tensile strength studies. The effect of crosslinking on the permeability of membranes to propranolol hydrochloride was evaluated by permeation studies conducted in static glass diffusion cells. A decrease in the thermal stability of chitosan membranes due to crosslinking was observed. The tensile strength of the membranes was improved by crosslinking. The introduction of crosslink points within the membrane reduced its permeability to propranolol hydrochloride as evidenced by decreased permeability and diffusion coefficients. Permeability studies revealed the operation of a pore mechanism in the transport of hydrophilic agents such as propranolol hydrochloride through chitosan and crosslinked chitosan membranes.     

二元醇共价交联羧基化石墨烯复合膜和正丁醇脱水性能

以二元醇(乙二醇、1,3-丙二醇和1,4-丁二醇)为交联剂,通过抽滤的方式在涂覆盐酸多巴胺的聚醚砜(PES)支撑层上制备了共价交联的羧基化石墨烯/聚醚砜(CG/PES)复合膜。稳定性测试证明盐酸多巴胺的涂覆和二元醇的交联显著提高了分离层和支撑层以及CG纳米片间的结合力。采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱仪和水接触角测试仪对复合膜的物化性质和微观形貌进行了表征。结果表明,所得复合膜的分离层连续无缺陷,厚度在60～64nm之间。二元醇与CG纳米片上的羧基成功发生反应,将CG纳米片锚固在一起。交联剂的引入没有大幅降低亲水性且实现了对分离层层间距的有效调控,随二元醇分子尺寸增加,所得复合膜的层间距由0.761nm提高到0.778nm。CG/PES复合膜对正丁醇/水混合物具有优良的渗透汽化分离性能。在料液温度为50℃、料液中水的质量分数为10%时,三种交联剂所得复合膜的渗透通量分别达到0.79kg/(m²·h)、0.87kg/(m²·h)和0.96kg/(m²·h),而分离因子比未交联的复合膜高一个数量级。15天的...     

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.     

Gas‐separation properties of amine‐crosslinked polyimide membranes modified by amine vapor

The modification of a polyimide (PI) membrane by aromatic amine vapor was performed in this work to increase the crosslinking of the membrane and to study the effect on gas permeability and the corresponding selectivity. The single‐gas permeability of the membranes at 35 °C was probed for H₂, O₂, N₂, CO₂, and CH₄. From the relationship between the combinations of gases and ideal permselectivities, this study showed that amine‐crosslinked PI membranes tended to increase gas permselectivities exponentially with the increasing difference in gas kinetic diameter. Moreover, this study illustrated that the permeability of the membranes was influenced by the formation rate of amine‐crosslinked networks or chemical structures after the reaction. The membranes had the highest level of permselectivities among crosslinked PI membranes for O₂/N₂, and the H₂/CH₄ permselectivity increased 26 times after vapor modification. Furthermore, the modification method that used aromatic amine vapor produced thin and strongly modified layers. These findings indicate that modification is an advantageous technique for improving gas‐separation performance, even considering thinning. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44569.     

Optimization of the properties of chitosan lactate/hyaluronan film

Polyelectrolyte complexes represent attractive class of polymer‐based materials, finding an irreplaceable role in biomaterial preparation for tissue engineering or drug delivery beads. Mechanical properties, physical properties, and enzymatic degradation of the film prepared from chitosan lactate/hyaluronan polyelectrolyte complex, crosslinked with starch dialdehyde derivatives, were studied to optimize its composition. This work represents an example demonstrating how a minor modification of the modified complex composition changes final properties of the prepared film and emphasizes enormous variations in complex formation by crosslinking. To obtain sufficiently useful information, experimental design was employed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1413–1419, 2006     

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.     

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     

Preparation of a sodium alginate–poly(vinyl alcohol)–chitosan bipolar membrane and its application in the electrogeneration of ferrate(VI)

A sodium alginate (SA)–poly(vinyl alcohol) (PVA)–chitosan (CS) bipolar membrane (BPM) was prepared by a paste method with PVA, SA, and CS as starting materials and modified by Fe³⁺ and GA as a crosslinking agent. The morphology, functional groups, and physical properties of the film were studied by scanning electron microscopy, IR spectroscopy, and tensile testing, respectively. The SA–PVA–CS BPM was used as a separator in the electrolysis cell for electrogenerated ferrate(VI). The results show that the SA–PVA–CS BPM possessed reasonable physical and electrochemical properties. The SA–PVA–CS BPM not only prevented ferrate(VI) from diffusing into the cathode room but also played an important role in the supply of OH^? consumed during the electrogenerated ferrate(VI) process. Compared with the traditional method of preparing ferrate(VI), electrodialysis with the BPM (SA–PVA–CS) had the further advantage of lower alkali and energy consumption. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Fabrication and properties of superabsorbent complex gel beads composed of hydrolyzed polyacrylamide and chitosan

A novel method for preparing complex beads composed of hydrolyzed polyacrylamide (HPAM) and chitosan, based on the electrostatic attraction between ? COO^? of HPAM and Al³⁺ and between ? COO^? and ? NH₃⁺ of chitosan, was established. In the two‐stage crosslinking process, first Al³⁺ was used as a crosslinking agent for the crosslinking of HPAM molecules, which were used as the skeleton structure of the gel beads. In the second stage, chitosan diffused into the skeleton structure. The gel beads were characterized with scanning electron microscopy, inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. There was a chitosan component in the gel beads, and these gel beads had porous and rough surfaces. The swelling properties of the HPAM–chitosan gel beads were measured in water, in acidic, neutral, and alkaline buffers, and in different saline solutions. The swelling ratio was as high as 3675 g/g in water and 170 g/g in a 0.15 mol/L NaCl solution. The beads showed pH sensitivity in buffers of different pH values and salt sensitivity in different saline solutions. The order of the equilibrium absorbency of the gel beads in different saline solutions was Na⁺ > K⁺ > Mg²⁺ > Ca²⁺ > Al³⁺. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High flux and rejection with chiral chitosan composite nanofiltration membranes: Preparation and characterization

Two series of novel composite nanofiltration (NF) membranes were prepared by the overcoating of polysulfone ultrafiltration membranes with a mixture of chitosan and chitosan derivatives modified with two different chiral compounds. The two chiral compounds and their chitosan derivatives were characterized by IR spectroscopy, differential scanning calorimetry, and polarimetry. The structure of the membrane was characterized by scanning electron microscopy (SEM). The rejection and flux of the composite NF membranes were strictly related to the chiral compound grafted to chitosan and its composition in the mixture. An extremely high rejection, 98.23%, was observed with P_2–3 of the polymer (P₂) composite NF membrane, and the flux remained as high as 351 L m^?2 h^?1 at 0.4 MPa with 1000 mg/L NaCl. These results, together with SEM and IR images of the composite NF membrane, indicated that the chiral compound structure was crucial for the structure and function of the composite membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and properties of chitosan/acidified attapulgite composite proton exchange membranes for fuel cell applications

A composite proton exchange membrane chitosan (CS)/attapulgite (ATP) was prepared with the organic–inorganic compounding of ATP and CS. The composite membranes were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). The mechanical properties, thermal stability, water uptake, and proton conductivity of the composite membranes were fully investigated. The composite membranes exhibited an enhanced mechanical property, dimensional and thermal stability compared to CS membrane, owing to the interface interaction between ATP and CS. The maximum tensile strength of 53.1 MPa and decomposition temperature of 223.4°C was obtained, respectively. More importantly, the proton conductivity of the composite membrane is also enhanced, the composite membrane with 4 wt% ATP content (CS/ATP-4) exhibited the highest proton conductivity of 26.2 mS cm⁻¹ at 80°C with 100% relative humidity, which is 25.1% higher than pure CS membrane. These results may explore a simple and green strategy to prepare CS-based PEMs, which have a great potential in the application of proton exchange membrane fuel cells.