Recent advances in polymer and polymer composite membranes for reverse and forward osmosis processes

Semipermeable membranes are the core elements for membrane water desalination technologies such as commercial reverse osmosis (RO) process and emerging forward osmosis (FO) process. Structural and chemical properties of the semipermeable membranes determine water flux, salt rejection, fouling resistance, and chemical stability, which greatly impact energy consumption and costs in osmosis separation processes. In recent years, significant progress has been made in the development of high-performance polymer and polymer composite membranes for desalination applications. This paper reviews recent advances in different polymer-based RO and FO desalination membranes in terms of materials and strategies developed for improving properties and performances.     

Polymer-water interaction and its relation to reverse osmosis desalination efficiency

Water and salt sorption and the homogeneity of water distribution have been determined in various polymers and compared with their reverse osmosis desalination properties. A general relationship between the polymer water sorption, the water distribution in the polymer matrix, and the membrane water- and salt-permeabilities has been determined, which indicates that the uniformity of water distribution in the polymer is an important parameter controlling reverse osmosis desalination efficiency.     

Polymers for enhanced oil recovery: A paradigm for structure–property relationship in aqueous solution

Recent developments in the field of water-soluble polymers aimed at enhancing the aqueous solution viscosity are reviewed. Classic and novel associating water-soluble polymers for enhanced oil recovery (EOR) applications are discussed along with their limitations. Particular emphasis is placed on the structure–property correlations and the synthetic methods. The observed rheological properties are conceptually linked to the polymer chemical structure (1) and topology (2). In addition, the influence of external parameters, e.g. temperature, pH, salt, and surfactant, on the rheological behavior is reviewed. Progress booked in deeper understanding of the structure–property relationship is thoroughly discussed. Furthermore, a critical overview of the synthetic methods as well as of the solution properties of these polymers is provided. In this respect the influence of “internal” (i.e. chemical structure) and “external” (vide supra) factors on these properties provide a conceptual toolbox for the rationalization of the response of water-soluble polymers to external stimuli. In turn, such rationalization constitutes the basis for the design of new polymeric structures for EOR applications.     

Syntheses and the Main Properties of Fiban Fibrous Ion Exchangers

The works on synthesis and main properties of fibrous ion exchangers are reviewed in the paper. The main attention is paid to the FIBAN materials found practical applications in water treatment and air purification processes. The following methods for preparation of ion exchange fibers have been considered: mechanical mixing of inert fiber‐forming polymer solutions or melts with finely dispersed ion‐exchangers with their following spinning into fibers; preparation of composite fibers containing polymeric reinforcement in the polyelectrolyte body; spinning of specially prepared polymers containing ionizable groups and having fiber‐forming properties; grafting of ionogenic polymers (or polymers in which ionogenic groups can be introduced after grafting) onto polymer chains of the existing polymer fiber; polymer analogues conversion of existing polymeric fibers by introducing in their structure ionizable functional groups. Conditions for preparation of ion exchange fibers with high exchange capacity, optimal swelling and acceptable mechanical properties have been outlined.     

Gas and water vapour transport in a polyketone terpolymer

Gas and water vapour transport properties of a polyketone terpolymer (0.93/0.07/1 ethylene/propylene/carbon monoxide) have been investigated and related to the polymer structure. Permeability tests have been performed at several temperatures (from 25 to about 65°C) with five different gases (oxygen, nitrogen, methane, ethane and carbon dioxide), evaluating permeabilities, diffusivities and solubilities. Their dependence on temperature was interpreted on the basis of apparent activation energies of permeation and diffusion (E_P and E_D) and of heats of solution (ΔH_S). The investigated polymer was found to be rubbery at the test temperatures (glass transition temperature is about 17°C), but the detected permeabilities are comparable to those of the glassy polymers widely used for packaging applications. Data obtained in this investigation on samples exposed to moulding temperatures (240°C) for 3 min were compared to gas permeation data (presented in a previous paper) obtained for samples exposed at that temperature for 33 min in order to assess possible effects on gas transport properties. Water vapour transport was analysed by performing both sorption (35, 34, 55 and 65°C) and permeation (35°C) experiments at several activities. The analysis of sorption isotherms revealed the occurrence of water clustering, which was confirmed by a reduction of water diffusivity as a function of water concentration in the polymer.     

Direct fluorination of polymers—From fundamental research to industrial applications

In this paper fundamental features and industrial applications of the direct fluorination of polymers are reviewed. Direct fluorination of polymers (i.e. treatment of a polymer surface with gaseous fluorine and its mixtures) proceeds at room temperature spontaneously and can be considered as a surface modification process. The author of the current paper and his co-authors have studied the direct fluorination of more than 20 polymers (polystyrene, poly(ethylene terephthalate), poly(2,6-dimethyl-1,4-phenylene oxide), polymethylmethacrylate, low density polyethylene (2 types), high density polyethylene (6 types), polyvinyltrimethylsilane, poly(4-methyl-pentene-1), polyimide Matrimid^® 5216, polysulfones, polyetheretherketone, polycarbonatesiloxane, polysulfone–polybutadiene block-copolymers, polypropylene, polyvinylfluoride (PVF), polyvinylidenefluoride (PVDF), etc.). A large variety of experimental methods, such as FTIR spectroscopy, visible and near UV spectroscopy, Electron Spin Resonance spectroscopy, laser interference spectroscopy, refractometry, electron microscopy, method of surface energy measurement, gas chromatography, method of measurement of permeability of liquids through polymer materials, etc. was applied. Fundamental features of the direct fluorination, such as influence of treatment conditions (composition of the fluorinating mixture, fluorine partial pressure, temperature and fluorination duration) on the rate of formation, chemical composition, density, refraction index and surface energy of the fluorinated layer, kinetics of formation of radicals during fluorination and their termination, texture of fluorinated layer, etc. were studied. On the base of obtained experimental data a theoretical model of the direct fluorination of polymers was developed. It was demonstrated experimentally, that the direct fluorination can be effectively used to enhance commercial properties of polymer articles, such as barrier properties of polymer vessels, bottles and packaging, gas separation properties of polymer membranes and mechanical properties of polymer-based composite materials. Data on a fundamental research and commercial applications provided by other research groups are reviewed.     

反渗透膜脱硼技术研究进展

硼是生命体中必不可少的微量元素,但是摄入过量的硼会危害动植物的生长发育。在现有脱硼技术中,反渗透膜脱硼被认为最具应用前景,但受硼酸分子的分子直径小和不带电荷等影响,反渗透膜对硼的脱除仍不能满足实际要求,因此制备高脱硼反渗透膜具有重要意义。本文综述了近年来反渗透膜脱硼技术的研究进展,重点阐述了提高反渗透膜脱硼率的机制,主要思路包括优化反渗透膜结构和利用硼酸特殊性质;改善反渗透膜脱硼性能的有效途径包括开发新型膜材料,优化界面聚合工艺和物理化学法改性等;制备高脱硼反渗透膜的主要障碍是水硼传输的trade-off现象和缺少针对水和硼传输的模型。另外,硼酸分子具有独特的物理化学性质,可以借助硼酸分子研究聚酰胺反渗透膜的网络结构、水硼在膜内的传输机制和引起trade-off现象的因素。     

Physicochemical processes occurring during the formation of cellulose diacetate membranes. Research of criteria for optimizing membrane performance. IV. Cellulose diacetate-acetone-organic additive casting solutions

Asymmetric membranes were prepared from cellulose diacetate using a mixture of acetone and formamide, DMF, DMSO, NMP, dioxane or acetic acid as a basic solvent and water as the precipitation agent. The membrane water flux and salt rejection were determined by reverse osmosis tests. The change in mobility of the polymer chains during the evaporation and coagulation phases was studied by fluorescence depolarization. The main parameters such as casting solution composition, evaporation time, water concentration required for polymer precipitation, speed of coagulation and their effect on membrane structure and performance are discussed.     

Diffusion of Aggressive Media in Hydrophilic Polymers

Abstract

The simultaneous sorption and diffusion of acid and salt in polyvinylalcohol are considered under conditions of polymer swelling. Obtained data on water sorption by PVA show an anomalous mechanism of the transport of solvent in this kind of polymer. The analysis of equilibrium sorption of an acid-salt mixture shows that interactions of polymer OH groups with hydrogen ions of hydrogen chloride lead to a decrease in salt solubility in the polymer. The theory of Donnan equilibrium was used to solve the problem of the sorption of the acid-salt mixture as well as to create the boundary conditions for a proposed mathematical model of the transport of the buffer mixture.

Methods of determining parameters of the buffer mixture transport in hydrophilic polymers have been created and physicochemical characteristics of investigated multicomponent system are calculated on the basis on these methods.     

Influence of processing history on water and salt transport properties of disulfonated polysulfone random copolymers

Disulfonated poly(arylene ether sulfone)s are high glass transition temperature polymers, and their water and salt transport properties depend sensitively on thermal processing history. In this study, films of a 32 mol% disulfonated poly(arylene ether sulfone) random copolymer (BPS-32), polymerized in the potassium counter-ion form, were acidified using solid state and solution routes. The resulting acid counter-ion form materials were then converted to sodium, potassium, and calcium counter-ion forms via ion exchange. Additionally, several films were subjected to various thermal treatments in the solid state. Water uptake as well as water and NaCl permeability of these BPS-32 films were measured. Acidification via immersion of BPS-32 films in boiling sulfuric acid solution increased water uptake, and water and salt permeability increased. Exposure of samples to elevated temperature also influenced transport properties. For example, immersing BPS-32 films in boiling water for 4 h increased water sorption by 50%, water permeability by 2.3 times, and NaCl permeability by 8 times. The counter-ion form of the sulfonated polymer influenced the polymer’s transport properties, but these effects were weaker than the effect of thermal treatment. Generally, the BPS-32 samples prepared with different processing histories followed a trade-off between water/salt permeability selectivity and water permeability. These results suggest that, like many other glassy polymers, thermal processing history influences small molecule transport in these materials.     

Hydroresin dispersions: tailoring morphology of latex particles and films

Hydroresin dispersions are a new class of emulsifier free polyacrylate secondary dispersions. They are prepared by the emulsification of self-emulsifying polymer blends in water. The blends typically consist of two polymers, one is a salt group containing copolymer, the other is a hydrophobic polymer without salt groups. The particle diameters can be controlled by the amount of salt group containing polymer and the concentration of salt groups in this polymer. One advantage over conventional secondary dispersions is the fact that they are not only water dilutable but free of organic solvents. Another advantage is the extremely low content of hydrophilic salt groups in the resulting polymer mixture, which leads to very hydrophobic films. The application properties of these aqueous systems are more similar to those of organic polymer solutions than to conventional emulsion polymers. Applications of these surfactant free binders are in areas such as solvent face road marking paints and corrosion protection coatings without active pigments. The technique for the preparation of hydroresin dispersions is also useful for the creation of latex particles with core-shell structures. Two examples are given, which differ in the glass transition temperature of both the cores and the shells. From these dispersions, films with defined morphology can be prepared. A blending of the polymers with hydrophobic low molecular weight compounds, before the emulsification step, is also possible. It can be used for the incorporation of additional functions into the latex particles. As an example, the loading of latexes with a hydrophobic fluorescent dye is given.     

Water binding properties of hydrogel polymers for reverse osmosis and related applications

Differential scanning calorimetry (DSC) has been used in the study of a series of hydrogels in an attempt to correlate water binding and transport properties. DSC and oxygen transport studies were carried out on a series of styrene-2-hydroxyethyl methacrylate copoly-mers. The transport of dissolved oxygen through those copolymers that contained no freezing water was found to be negligible in comparison to those in which both freezing and non-freezing water was present. This correlates well with the observation that the dense layer of asymmetric cellulose acetate reverse osmosis membranes was found to contain little or no free water. On this basis, the use of DSC in the design of a hydrogel that contains little or no freezing water (to promote salt rejection) with a reasonably high total water content (to maximise water flux) for use in reverse osmosis, is described. The resultant copolymer of acrylamide, methacrylic acid and styrene has a total equilibrium water content (30 per cent) that is twice that of a typical dense cellulose acetate used in reverse osmosis and a very low (< 1 per cent) freezing water content. Examination of the fine structure of the melting endotherms and freezing exotherms associated with various hydrogels shows several interesting features which are interpreted in terms of the existence of a continuum of water states. These range from water that is unaffected by its polymeric environment to water (on average two or less molecules per monomer repeat unit) that is hydrogen bonded to functional groups in the polymer.     

Radiopaque miscible systems composed of poly(methyl methacrylate) and transition and nontransition metal salts: Spectroscopic,thermal, and radiographic characterization

The preparation of miscible systems containing poly(methyl methacrylate) and cupric nitrate, manganese chloride, praseodymium chloride, and uranyl nitrate is described. The salt was dissolved in the monomer, which was subsequently polymerized. The heavy metal salts impart radiopacity to these plastics and this renders them useful for X-ray imaging in applications such as medical implants. The polymer–salt systems are characterized on the basis of their infrared spectra, thermal, and radiographic properties, and the formation of complexes between the cations and the carbonyl function of the polymer is discussed. The glass transition temperatures of the salt-containing polymers are higher than those of the salt-free polymers, the elevation being dependent on the nature and concentration of the metal salt. Miscible PMMA–uranyl nitrate systems are transparent, glassy plastics and approximately 11 wt % of uranyl nitrate hexahydrate imparts a radiopacity equivalent to that of aluminum.     

Ionic reverse osmosis membranes of grafted polyethylene

Membranes of graft copolymers of polyethylene with poly(sodium styrene sulfonate), poly(4-vinylpyridinium methyl bromide), and poly(sodium acrylate) were prepared by using the technique of peroxide grafting. The reverse osmosis characteristics of the membranes were examined as a function of grafting yield. In these membranes, the grafting can be considered as a process of introducing ionic sites, and it depends on the conditions of the grafting reaction, such as monomer concentration and temperature. However, the overall reverse osmosis characteristic is not only dependent on the number of ionic sites introduced but also on the swelling capability of the membrane. Consequently, the salt rejection of grafted membrane of a fixed graft yield depends on the conditions of the grafting reaction. All grafted membranes which have grafting yields above a certain value behave as normal ionic polymer membranes, and their interrelationship of salt rejection and water permeability follow the general dependence found for ionic polymer membranes.     

Studies on effect of irradiation on semipermeable membranes

The effect of γ irradiation on reverse osmosis (RO) semipermeable membranes has been studied in order to evaluate their performance under the radiation environment arising in the processing of various streams in nuclear industry by reverse osmosis process. Both cellulosic and noncellulosic membranes in dry as well as wet conditions were used. A Co⁶⁰ source was used for γ doses from kilorads to megarads. The transport properties, namely, salt retention and water flux of membranes determined before and after irradiation, suggested deterioration in the membrane properties due to irradiation. The tensile strength and viscosity of membrane polymer also suggested membrane degradation. Differential scanning calorimetry was taken to look into any structural changes in the membrane polymer as a result of irradiation. IR spectra and X-ray of membrane polymer was also undertaken to understand the changes on the molecular level.     

Grafting of hyperbranched polymers: From unusual complex polymer topologies to multivalent surface functionalization

In this feature article, the grafting of hyperbranched polymers to different substrates is reviewed. Both grafting onto macromolecules with different topologies (homogeneous grafting) and the resulting complex polymer architectures containing highly branched segments as well as their applications are discussed. In the second part grafting of hyperbranched polymers on surfaces, i.e., planar surfaces and spherical particles (heterogeneous grafting), with respect to specific applications, such as bio-repellent surfaces or soluble carbon nanotubes is described. In all cases, the one-step synthesis and the resulting highly branched topology of the hyperbranched building blocks is beneficial for the convenient introduction of a large number of functional groups to the substrates. These multifunctional hybrid materials open interesting options for applications, e.g., for highly functional nanoparticles or nanocomposites.     

反渗透膜的研究进展与展望

反渗透具有低能耗、高效率等突出优点,是目前应用最为广泛的分离技术之一。反渗透膜的性能是影响反渗透过程效率的决定因素,反渗透膜的研制一直是国内外膜领域的研究热点。特别是近年来,石墨烯、碳纳米管等新型材料展现出优异的水传递行为,成为新型反渗透膜材料的研究热点。本论文回顾了反渗透膜的研制发展历程,介绍了不同单体通过界面聚合反应成膜的研究进展,综述了国内外新型混合基质膜和无机分子筛反渗透膜材料及其成膜研究,最后提出了新型反渗透膜的研究方向。     

THERMODYNAMIC MODELING OF SOLUTE TRANSPORT THROUGH REVERSE OSMOSIS MEMBRANE

A new thermodynamic model is developed for water and solute transports through reverse osmosis membranes. The model is featured with rigorous derivations in theoretical development and clearly defined parameters for membrane transport properties. The new model can correctly describe not only the dependence of salt rejection on pressure and salt concentration, but also the non-linearity between water flux and pressure. Comparisons of model simulations with the reported reverse osmosis experiments demonstrate that the parameters in the new model are concentration-independent. This study shows that water and salt transports through reverse osmosis membranes can be satisfactorily described with irreversible thermodynamics.     

Antibacterial activity of natural polymer gels and potential applications without synthetic antibiotics

Antibiotics' use has increased, resulting in disadvantages like patients' drug resistance. Consequently, urgent action is required to develop a new generation of antibacterial agents. Most antibacterial platforms still require a modification with further antibacterial agents (e.g., antibiotics) for adequate antibacterial efficiency. Thus, a nonantibiotic methodology is immediately needed. Furthermore, bactericidal agents used for this purpose are usually based on metal nanoparticles, carbon materials, and polymers. Still, chemicals, antibiotics, and biocides lead to environmental damage. Therefore, the help of biocompatible yet durable materials and polymers is highly appreciated. In addition, if a polymer is not biodegradable, it will remain in the environment for more than one hundred years due to its low degradation rate. Moreover, non-biodegradable polymers are harmful to in vivo applications. Hence, the use of biodegradable and non-toxic materials has received many considerations. Over the last few years, the design and synthesis of new polymer gels have gained increasing attention. A polymer gel, also known as a hydrogel, is a three-dimensional and cross-linked network filled with water or other liquid solvents. Besides, the hydrogels supercritical drying method results in aerogels, and the freeze-drying method generates cryogels, where their porous and sponge-like structures are preserved. Additionally, antibacterial polymer gels are a new generation of polymers considered attractive due to their unique properties. The most recent studies and the latest innovations in polymer gels and hybrid polymers with intrinsic antibacterial properties were discussed in the present review. The reviewed studies from 2015 to April 2022 showed a tremendous revival in research about biopolymer hydrogel, aerogel, and cryogel as antibacterial agents.     

DNA compaction by nonbinding macromolecules

Compaction of DNA by nonbinding macromolecules such as uncharged flexible polymer chains and negatively charged globular proteins is thought to have various applications in biophysics, for example in the formation of a nucleoid structure in bacteria. A simple experimental model that has been very well studied is the classic DNA ??-condensation induced by polymers and salt. In recent years, compaction of DNA by nonbinding macromolecules has been reconsidered under conditions that are closer to the biophysical applications, in various respect. This work is reviewed here. Topics that are considered are: DNA compaction by nonbinding globular proteins, the influence of DNA binding proteins and DNA topology on ??-condensation, and finally, the impact of confinement on DNA ??-condensation.