Pore structure of gel chitosan membranes. III. Pressuredriven mass transport measurements

The capillary pore model of water-swollen gels was used to interpret pressure-driven mass transport properties of gel chitosan membranes. Pure water hydraulic permeability coefficients, L_p, and rejection coefficients, R, of 13 solutes ranging in molecular radius from 2.4 Å (methanol) to 16 Å (polyethylene glycol 6000) were measured for an untreated chitosan membrane, for two chitosan membranes crosslinked with glutaraldehyde of concentrations 0.01 and 0.1% and coated with a protein, and for comparison for a commercial Cuprophan membrane. Pore radii of the membranes were determined from these results by three methods: (1) L_p method that uses water hydraulic permeability coefficient, (2) σ method that uses reflection coefficients, and (3) P/L_p method that uses water diffusive permeability coefficient and water hydraulic permeability coefficient.     

Pervaporation and properties of chitosan-poly(acrylic acid) complex membranes

Polyelectrolyte complex membranes between chitosan as a cationic polyelectrolyte and poly(acrylic acid) as an anionic species were prepared by blending two polymer solutions in different ratio. Characterization of chitosan-poly(acrylic acid) complex membrane was investigated by Fourier transform-infrared (FT-IR), wide angle X-ray diffractometer, dielectric analyzer. Their mechanical properties were studied by universal testing machine. The swelling of polyelectrolyte membranes was studied. Thermal properties of polyelectrolyte membranes from chitosan and poly(acrylic acid) by varying blend ratios showed a shift in transition temperatures of polyelectrolyte complexes. Polyelectrolyte complex membranes from chitosan and poly(acrylic acid) had pH sensitive characteristics as determined by FT-IR studies and swelling behaviors. Pervaporation performances were investigated with various organic mixtures; water-ethanol, water-isopropanol, methanol-methyl t-butyl ether mixtures. An increase of poly(acrylic acid) content in the polyelectrolyte complex membranes affected the swelling behavior and pervaporation performance of water-ethanol mixture. Permeation flux decreased and the water concentration in the permeate was close to 100% upon increasing the feed alcohol concentration.     

磺化聚醚醚酮与壳聚糖共混制备直接甲醇燃料电池用质子交换膜

给出了不同磺化度下的磺化聚醚醚酮(SPEEK)用作质子交换膜的一系列性能,另外提出了一种新型的酸碱共混质子交换膜,其中,磺化聚醚醚酮和壳聚糖分别被选为酸性、碱性高分子电解质,并对所制备的质子交换膜的相关性能如质子传导性,甲醇渗透性,吸水率以及膜溶胀性、热稳定性等进行了表征,结果表明此种新型复合膜尽管在质子传导性能方面有所下降,阻醇性能改变不大,但是膜溶胀性和吸水率方面有了较大的改善.磺化度为71.4%的SPEEK与壳聚糖以5∶1摩尔比共混制备的质子交换膜,其性质可以与商品化的Nafion 117相媲美,有望在甲醇燃料电池中得到应用.     

Separation of chitosan by degree of acetylation using simple free solution capillary electrophoresis

Chitosan is a biopolymer of increasing significance, as well as a renewable and sustainable material. Its main molecular characteristics are molar mass and degree of acetylation (composition). Precise average degrees of acetylation were measured by quantitative ¹H solution-state NMR spectroscopy. While number-average degrees of acetylation had already been determined by ¹H NMR spectroscopy, weight-average degrees of acetylation are also determined and may be more relevant for some properties, such as mechanical properties. We report the first separation of chitosan according to its degree of acetylation using free solution capillary electrophoresis. Capillary electrophoresis separates chitosan in the ‘critical conditions’: the molar mass plays little role and the separation is by the degree of acetylation. It characterises the heterogeneity of chitosan samples in terms of composition (dispersity of the distribution of degrees of acetylation). This heterogeneity (broad distribution of degrees of acetylation) cannot be neglected contrary to a common assumption found in the literature. This fast and easy separation will allow establishing a structure–property relationships.

Preparation,characterization and properties of β-chitin and N-acetylated β-chitin

Free amino groups in β-chitin from squid pen were acetylated to obtain N-acetylated β-chitin. After careful control of degree of acetylation, thermal and mechanical properties of β-chitin and N-acetylated β-chitin were compared. The structural differences of β-chitin and N-acetylated β-chitin were characterized by Fourier transform infrared (FTIR) and wide-angle x-ray diffraction (WAXD) analysis. The results indicated that the crystallinity of N-acetylated β-chitin was higher than that of β-chitin and N-acetylated β-chitin exhibited characteristics similar to α-chitin. Equilibrium water content (EWC) of β-chitin reached to about 50% and this hydrophilic nature was assumed to be caused by a relatively weak hydrogen bonding force of β-chitin with parallel main chains. On the other hand, EWC of N-acetylated β-chitin was 40% due to the introduction of ordered structure. β-chitin and N-acetylated β-chitin have the tensile strength of 0.4 and 0.7 Mpa in the swollen state, respectively. Viscoelastic properties and thermal relaxation behaviors were investigated by dynamic mechanical thermal analysis (DMTA). DMTA spectra of these samples showed that α-transition peaks of β-chitin and N-acetylated β-chitin were observed at 170 and 190°C, respectively. These relaxation peak maxima were assigned to be their glass transition temperature. In addition, a second relaxation peak of β-chitin resulting from acetamide groups was found at 112°C and a broad relaxation peak of N-acetylated β-chitin at around 81–100°C. As a result of thermogravimetric analysis, 10% weight loss temperatures of β-chitin and N-acetylated β-chitin were 270 and 285°C, respectively. © 1996 John Wiley & Sons, Inc.     

Bioactive molecules immobilized to liposome modified albumin-blended chitosan membranes—Antithrombotic and permeability properties

The search for a nonthrombogenic membrane having high permselectivity to be used for hemodialysis applications continues to be a field of extensive investigation. A series of membranes was prepared by air drying the thin layers of albumin: chitosan [a (1 → 4)-2-amino-2-deoxy-β-d-glucan] blends in a ratio of 7:3 (chitosan:albumin). The albumin blended chitosan membranes showed high permeability properties for low molecular weight compounds. Nonthrombogenic albumin: chitosan blended membranes were derived by immobilizing bioactive molecules like PGE₁, hirudin, heparin, or AT-III on liposome modified membranes, via the carbodiimide functional moiety. Such novel membranes demonstrated good permeability properties for small molecules and showed dramatic reduction in platelet attachment; though they exhibited variable degrees of wettability. The interfacial changes arising from surface modifications did not cause any significant interference with their permeability and mechanical properties.     

Gas permeation through water-swollen hydrogel membranes

This work deals with water-swollen hydrogel membranes for potential CO₂ separation applications, with an emphasis on elucidating the role of water in the membrane for gas permeation. A series of hydrogel membranes with a wide range of water contents (0.9–10 g water/g polymer) were prepared from poly(vinyl alcohol), chitosan, carboxyl methyl cellulose, alginic acid and poly(vinylamine), and the permeation of CO₂, H₂, He and N₂ through the membranes at different pressures (200–800 kPa) was studied. The gas permeabilities through the dry dense membranes were measured as well to evaluate the resistance of the polymer matrix in the hydrogel membranes. It was shown that the gas permeability in water-swollen membrane is lower than the gas permeability in water, and the selectivity of the water-swollen membranes to a pair of gases is close to the ratios of their permeabilities in water. The permeability of the water-swollen membranes increases with an increase in the swelling degree of the membrane, and the membrane permeability tends to level off when the water content is sufficiently high. A resistance model was proposed to describe gas permeation through the hydrogel membranes, where the immobilized water retained in the polymer matrix was considered to form transport passageways for gas permeation through the membrane. It was shown that the permeability of hydrogel membranes was primarily determined by the water content in the membrane. The model predictions were consistent with the experimental data for various hydrogel membranes with a wide range of water contents (0.4–10 g water/g polymer).     

Synthesis and Characterization of Polyelectrolyte Complex N-Succinylchitosan-chitosan for Proton Exchange Membranes

Synthesis of acid-base complex membrane is one of method to improve the proton conductivity in proton exchange membrane for fuel cell applications. In this study, acid-base complex membrane was synthesized based on N-succinylchitosan-chitosan complexes. The N-succinylchitosan was blended with chitosan in acetic acid at various substitution degree of N-succinylchitosan with weight ratio of N-succinylchitosan of 80% w/w. The acid-base complex membranes were cast from the polymer solution and dried by evaporation. The properties of the membranes such as water uptake, ion exchange capacity, proton conductivity, and mechanical strength were analyzed. It was observed that the increase of substitution degree of N-succinylchitosan tends to increase the proton conductivity. The optimum performance of membrane unit is attained by the substitution degree of N-succinylchitosan of 0.72, which is reflected by its ion exchange capacity of 3.45 meq/g and proton conductivity of 7.35 × 10^-2 S cm^-1, respectively. Blending of N-succinylchitosan and chitosan also improved the mechanical strength of the membranes. These results imply that this type of polyelectrolyte complex membrane is a good candidate for proton exchange membrane in fuel cell applications.     

Ionic conductivity and tensile properties of hydroxyethyl and hydroxypropyl chitosan membranes

Hydroxyethyl chitosan and hydroxypropyl chitosan were prepared through the reaction of alkali‐chitosan with 2‐chloroethanol and propylene epoxide, respectively. Fourier transform infrared and ¹³C NMR measurements were made to examine the substitution on the chitosan unit. According to a comparison of the peak areas between the modified chitosan and unmodified chitosan and the integration of peak areas of ¹H NMR spectra, for both modified chitosans, the maximum degree of substitution was less than 25%. The ionic conductivity and mechanical properties of modified chitosan membranes were investigated. In comparison with the unmodified chitosan membrane, hydrated hydroxyethyl and hydroxypropyl chitosan membranes with a higher degree of substitution showed an increase in ionic conductivity of about one order of magnitude; moreover, the crystallinity of hydroxyethyl and hydroxypropyl chitosan membranes was remarkably reduced, and their swelling indices increased significantly. However, these modified membranes did not exhibit significant changes in their tensile strength and breaking elongation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1379–1397, 2004     

Blended chitosan and polyvinyl alcohol membranes for the pervaporation dehydration of isopropanol

Homogeneous membranes were prepared by casting the solution of blended chitosan and polyvinyl alcohol (PVA) on a glass plate. The percent weight of chitosan in the membrane was varied from 0 to 100%. The membrane thickness was in the range of 15–30 μm. The membranes were heat treated at 150 °C for an hour. After that the membranes were crosslinked by glutaraldehyde and sulfuric acid in acetone aqueous solution. The membranes were tested at 30–60 °C for dehydration performance of 50–95% isopropanol aqueous solutions. At around 90% of isopropanol in the feed mixture, permeate flux increased whereas the percent of water in permeate tended to decrease when the feed temperature increased for all membranes, except that the water content in permeate from the membrane containing 75 wt.% chitosan remained constant. The swelling degree in water and the total flux increased with increasing chitosan content in membranes. The effect of temperature on permeate flux followed the Arrhenius relationship. The permeate flux decreased when isopropanol in the feed increased for all membranes. However, water content in permeate and isopropanol concentration in the feed formed complex relationship for different chitosan content membranes. Sorption did not appear to have significant effects on separation. The membrane containing chitosan 75% performed the best. For a feed solution containing 90% isopropanol at 60 °C, the permeate flux was 644 g/m² h with water content of nearly 100% in the permeate. At 55% isopropanol in the feed at 60 °C, the permeate flux was 3812 g/m² h. In the range of 55–95% of isopropanol in the feed, the water content in permeate was more than 99.5%. This membrane showed very excellent performance with good mechanical strength. It is promising to develop this membrane for industrial uses.     

壳聚糖-纤维素硫酸钠聚电解质复合物膜对药物表观渗透系数的测试

药物渗透系数是考察复合物膜的药物释放性能的重要参数. 本文以溶解性不同的两种药物扑热息痛和5-氨基水杨酸(5-ASA)为模型药物研究了其在壳聚糖-纤维素硫酸钠聚电解质复合物膜中的渗透性能. 结果表明：壳聚糖-纤维素硫酸钠聚电解质复合物膜的渗透性能与其溶胀性能密切相关;复合物膜中壳聚糖和纤维素硫酸钠的配比、相对分子量和pH值对膜的渗透性能和溶胀性能影响显著,以扑热息痛作为模型药物研究了壳聚糖-纤维素硫酸钠聚电解质复合物膜在模拟胃肠液中对药物的渗透性能. 通过调整该复合物膜的配方,可以使该膜分别实现胃、小肠和结肠定位释药的目的.     

Vanillin cross-linked hydrogel membranes interfacial reinforced by carbon nitride nanosheets for enhanced antibacterial activity and mechanical properties

Biopolymer based hydrogels are highly adaptable, compatible and have shown great potential in biological tissues in biomedical applications. However, the development of bio-based hydrogels with high strength and effective antibacterial activity remains challenging. Herein, a series of Vanillin-cross-linked chitosan nanocomposite hydrogel interfacially reinforced by g-C₃N₄ nanosheet carrying starch-caped Ag NPs were prepared for wound healing applications. The study aimed to enhance the strength, sustainability and control release ability of the fabricated membranes. Starch-caped silver nanoparticles were incorporated to enhance the anti-bacterial activities The fabricated membranes were assessed using various characterization techniques such as FT-IR, XRD, SEM, mechanical testing, Gel fraction and porosity alongside traditional biomedical tests i.e., swelling percentage, moisture retention ability, water vapor transmission rate, oxygen permeability, anti-bacterial activity and drug-release of the fabricated membranes. The mechanical strength reached as high as 25.9 ± 0.24 MPa for the best optimized sample. The moisture retention lied between 87–89%, gel fraction 80–85%, and water vapor transmission up to 104 ± 1.9 g/m²h showing great properties of the fabricated membrane. Swelling percentage surged to 225% for blood while porosity fluctuated between 44% ± 2.1% and 52.5% ± 2.3%. Oxygen permeability reached up to 8.02 mg/L showing the breathable nature of fabricated membranes. The nanocomposite membrane shown excellent antibacterial activity for both gram-positive and gram-negative bacteria with a maximum zone of inhibition 30 ± 0.25 mm and 36.23 ± 0.23 mm respectively. Furthermore, nanoparticles maintained sustainable release following non-fickian diffusion. The fabricated membrane demonstrated the application of inorganic filler to enhance the strength of biopolymer hydrogel with superior properties. These results envisage the potential of synthesized membrane to be used as wound dressing, artificial skin and load-bearing scaffolds.     

Structure of N-alkyl chitosan membranes on water-permselectivity for aqueous ethanol solutions

N-Alkyl chitosans with different numbers of carbons and degrees of substitution of the N-alkyl group were prepared. The water-permselectivity for aqueous ethanol solutions through the N-alkyl chitosan membranes in evapomeation were studied. The permeation rate and separation factor for water-permselectivity were significantly influenced by the number of carbons in the N-alkyl group, in particular, one N-alkyl chitosan membrane showed a maximum in the permeation rate and separation factor. The degree of substitution in the N-alkyl group little affected the permeation rate, but significantly changed the separation factor. The characteristics of permeation and separation for an aqueous ethanol solution through the N-alkyl chitosan membranes with different N-alkyl groups and different degrees of substitution of the N-alkyl group are discussed from the viewpoints of physical and chemical structures of their membranes, such as, density, crystallinity, surface free energy and degree of swelling of the membrane.     

New breathable and waterproof coatings for textiles: effect of an aliphatic polyurethane on the formation of PEEK-WC porous membranes

PEEK-WC is an amorphous polyetheretherketone with high chemical stability, excellent thermal resistance and significant solubility in various solvents. It has been used to prepare flat membranes by the phase inversion technique. The water vapour permeability through a porous PEEK-WC film was 1350 g/m² day at 26 °C and its liquid entry pressure (LEP) of water equivalent to a column of 2.0 m. These values were remarkably improved by addition of an aliphatic ether polyurethane (PU) into the PEEK-WC/DMF dopes: the water vapour flux was increased up to 2000 g/m² day and the LEP was equivalent to 12.5 m. This improvement is correlated to the different structure of the membranes: a spongy, porous and almost symmetric structure for the PEEK-WC/PU membranes, and an asymmetric structure with fingers for PEEK-WC membrane. The presence of PU influences also the mechanical properties of the blend membranes. The role of the PU on the resulting membrane morphology is rationalised on the basis of the mechanism of phase separation.     

Structure-property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units III. Preparation and properties of semi-permeable membranes for water desalination by reverse osmosis separation performance

Flat sheet asymmetric reverse osmosis membranes were successfully prepared from N,N-dimethylacetamide (DMAc) solutions of a series of novel wholly aromatic polyamide-hydrazides that contained different amounts of para- and meta-phenylene rings. These polyamide-hydrazides were synthesized by a low temperature solution polycondensation reactions of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl dichloride [TCl], isophthaloyl dichloride [ICl] or mixtures of various molar ratios of TCl and ICl in anhydrous DMAc as a solvent. All the polymers have the same structural formula except of the way of linking phenylene units inside the polymer chains. The content of para- to meta-phenylene moieties was varied within these polymers so that the changes in the latter were 10 mol% from polymer to polymer, starting from an overall content of 0-100 mol%. All the membranes were characterized for their salt rejection (%) and water permeability (cm³ cm⁻² day⁻¹) of 0.5 N aqueous sodium chloride feed solution at 3924 kPa operating pressure. The effects of polymers structural variations together with several processing parameters to achieve the best combination of high selectivity and permeability were studied. Effects of various processing parameters of the membranes on their transport properties were investigated by varying the temperature and period of the solvent evaporation of the cast membranes, coagulation temperature of the thermally treated membranes, annealing of the coagulated membranes, casting solution composition, membrane thickness and the operating pressure. During the thermal treatment step, the asymmetric structure of the membranes with a thin dense skin surface layer supported on a more porous layer was established. The former layer seems to be responsible for the separation performance. The results obtained showed that membrane performance was very much influenced by all of the examined processing variables and that membranes with considerably different properties could be obtained from the same polymer sample by using different processing parameters. Thus, the use of higher temperatures and longer exposure times in the protomembrane forming thermal treatment step would result in a membrane of lower solvent content and with a thicker skin layer and consequently led to higher salt rejection at lower water permeability. Most significantly, the membrane properties clearly depended on the polymer structure. Under identical processing condition, substitution para-phenylene rings for meta-phenylene ones within the polymer series resulted in an increase in salt rejection capability of the membranes. This may be attributed to an increase in their chain symmetry associated with increased molecular packing and rigidity through enhanced intermolecular hydrogen bonding. This produces a barrier with much smaller pores that would efficiently prevent the solute particles from penetration. Coagulation temperature controls the structure (porosity) of the membrane particularly its supported layer and consequently its water permeability. Moreover, annealing of the prepared membranes in deionized water at 100 °C was found essential for useful properties in the single-stage separation applications, which required optimum membrane selectivity. Upon annealing, the membrane shrinks resulting in reducing its pore size particularly in the skin layer and consequently improving the salt rejection. Addition of lithium chloride to the casting solution produced a membrane with increased porosity and improved water permeability. Salt rejection capability of the membranes is clearly affected by the applied pressure, reaching its maximum at nearly 4000 kPa. Furthermore, the water permeability is inversely proportional to the membrane thickness, while the salt rejection is not substantially influenced.     

Blend membranes from cellulose/konjac glucomannan cuprammonium solution

The blend membranes were prepared from cellulose/konjac glucomannan (KGM) cuprammonium solution by coagulating with aqueous 10 wt% NaOH solution, 20°C and 40°C water, respectively. Miscibility, pore morphology, structure, water permeability and mechanical properties of the blend membranes were investigated. The complex forms of cellulose/KGM in the mixed solutions, the effect of various coagulants and the percent content of KGM (w_KGM) on the structure and properties of the blend membrane are discussed. SEM and mechanical relaxation analysis indicate that the blend membranes are miscible in the range of 0–30 wt% of w_KGM. When w_KGM was smaller than 20 wt%, the tensil strength of the blend membrane coagulated by alkali aqueous solution was enhanced, corresponding to homogeneous structure and small pore size. However, blend membranes having a larger pore size (366 nm by SEM) and water permeability (560 ml/m² h mmHg) were obtained by coagulating the cellulose/KGM (70:30) cuprammonium solution with 40°C water, where ca. 20% of KGM as pore former were removed from the membrane.     

Hydraulic and osmotic permeabilities of water and water/sucrose solutions through cellophane membranes

Measurements were made of different transport phenomena in cellophane membranes, using a specially designed device. The aqueous, hydraulic permeability was studied over a range of temperatures between 30 and 50°C. The hydraulic permeability/temperature relationship was found to be linear. The use of sucrose solutions of equal concentration in the two phases on either side of the membrane produced a considerable variation in the hydraulic permeability when the solution concentrations were greater than 0.1 M. Osmotic flow experiments were carried out for sucrose/water solutions, and the coefficient of osmotic permeability was found to be independent of the solution concentrations separated by the membrane within the range of concentrations studied (up to 0.2 M). The equivalent pore radius was calculated for the membranes used; these values are higher than that of the molecular diameter of water. The reflection coefficient was calculated for one of the membranes used and a value of 0.077 was obtained.     

Synthesis and properties of sulfonated and crosslinked poly[(vinylidene fluoride)-graft-styrene] membranes

Crosslinked proton exchange membranes were prepared by electron beam grafting of styrene with divinylbenzene, DVB, or bis(vinyl phenyl)ethane, BVPE, on to poly(vinylidene fluoride), PVDF, followed by sulfonation. The area and thickness increase, crystallinity and mechanical properties of the membranes were investigated. All these properties were influenced by the crosslinker structure and its concentration. The crosslinkers increase the final degree of grafting. For noncrosslinked membranes it was about 80% and with 10% of BVPE crosslinker about 180% after 8 hr. The area increase with grafting is very similar for the noncrosslinked membranes and the differently crosslinked membranes, but the crosslinkers reduce swelling for sulfonated membranes swelled in boiling water. DVB reduces swelling more than BVPE. With grafting, the crystallinity of the PVDF phase decreases; with 10% BVPE the decrease is smallest and with 10% DVB largest. The mechanical properties of the sulfonated swelled membranes decrease with the degree of grafting, for a 10% DVB crosslinked membrane the strength decreases to zero at degrees of grafting higher than 75%. © 1998 John Wiley & Sons, Ltd.     

多羧基酞菁铜、乙酰基二茂铁改性CMC/CS双极膜的制备及表征

柔性链高分子聚乙二醇(PEG)分别与阳离子交换膜层羧甲基纤维素钠(CMC)、阴离子交换膜层壳聚糖(CS)共混以增强界面的相容性和膜的机械性能.以金属有机高分子多羧基酞菁铜(CuPc)改性CMC、乙酰基二茂铁改性CS,采用流延法制备了CuPc-mCMC/mCS双极膜.双极膜溶胀性和热重分析结果表明膜改性后稳定性能得到提高.膜交流阻抗、I-V工作曲线的测定结果表明该双极膜阻抗及工作电压均较小.双极膜经改性具有较高的离子渗透性能。     

Poly (caprolactone)/poly (ethylene glycol) pervaporation blend membranes: Synthesis,characterization, and performance

Poly (caprolactone) membranes with addition of different poly (ethylene glycol) concentrations were prepared for separation of water/isopropanol azeotropic mixture by pervaporation process. Different characterization tests including Fourier transform infrared, scanning electron microscopy, water contact angle, and thermogravimetric analysis were carried out on the prepared membranes. In addition, the effect of poly (ethylene glycol) PEG content on the swelling degree and the performance of the prepared membranes in pervaporation process were investigated. According to the obtained results, all the membranes were water selective and the blend membrane containing 3 wt% PEG exhibited the best pervaporation performance with a water flux of 0.517 kg/m² hour and separation factor of 1642 at the ambient temperature. Hydrophilicity improvement of the blend membranes was confirmed by constant decrease in water contact angle of the membranes as PEG content increased in the casting solution. Scanning electron microscopy cross‐sectional images indicated that the blend membranes containing PEG had a closed cellular structure. Furthermore, mechanical and thermal properties of the membranes decreased by adding PEG.