Two-Ply Composite Membranes with Separation Layers from Chitosan and Sulfoethylcellulose on a Microporous Support Based on Poly(diphenylsulfone-N-phenylphthalimide).

Two-ply composite membranes with separation layers from chitosan and sulfoethylcellulose were developed on a microporous support based on poly(diphenylsulfone-N-phenylphthalimide) and investigated by use of X-ray diffraction and scanning electron microscopy methods. The pervaporation properties of the membranes were studied for the separation of aqueous alcohol (ethanol, propan-2-ol) mixtures of different compositions. When the mixtures to be separated consist of less than 15 wt % water in propan-2-ol, the membranes composed of polyelectrolytes with the same molar fraction of ionogenic groups (-NH3⁺ for chitosan and -SO3- for sulfoethylcellulose) show high permselectivity (the water content in the permeate was 100%). Factors affecting the structure of a non-porous layer of the polyelectrolyte complex formed on the substrate surface and the contribution of that complex to changes in the transport properties of membranes are discussed. The results indicate significant prospects for the use of chitosan and sulfoethylcellulose for the formation of highly selective pervaporation membranes.

Effect of Hydroxyl-Containing Fragments on the Structure and Properties of Membrane-Forming Polyamide-Imides.

The structural features and thermophysical and transport properties of dense nonporous membranes of the casting type from (co)polyamide-imides synthesized by the polycondensation of the diacid chloride of 2-(4-carboxyphenyl)-1,3-dioxoisoindoline-5-carboxylic acid and diamines 5,5'-methylene-bis (2-aminophenol) (DADHyDPhM) and 4,4'-methylenebis(benzeneamine) (DADPhM), taken in molar ratios of 7:3, 1:1, and 3:7, have been studied. The effect of hydroxyl-containing modifying fragments of dihydroxy diphenylmethane introduced in various amounts into the main polymer chain on the pervaporation properties of the formed films is discussed. It has been shown that the presence of the residual solvent N-methyl-2-pyrrolidone in the films not only has a plasticizing effect on the characteristics of film membranes but also promotes the preferential transmembrane transport of polar liquids, primarily methanol (permeation rate over 2 kg for a copolymer with a ratio of DADHyDPhM:DADPhM = 7:3). The removal of the residual solvent from the polymer film, both thermally (heating to 200 °C) and by displacement with another solvent as a result of sequential pervaporation, led to a significant decrease in the rate of transfer of polar liquids and a decrease in the selectivity of the membrane. However, the dehydrocyclization reaction resulted in more brittle films with low permeability to penetrants of different polarities. The results of our comprehensive study made it possible to assume the decisive influence of structural changes in membranes occurring in connection with the competitive formation of intra- and intermolecular hydrogen bonds.

Effect of Phase Heterogeneity on the Properties of Poly(vinyl alcohol)-Based Composite Pervaporation Membranes.

The structure, thermophysical characteristics, and pervaporation properties of composite membranes based on poly(vinyl alcohol) (PVA) are studied in dependence of the film preparation conditions. It is shown that the nature of the supramolecular organization of the composite polymer film determines which of the components of the separated mixtures of toluene and heptane predominantly penetrate through the corresponding pervaporation membrane. The observed structural effects can become more pronounced if the second component of a polymer mixture is purposefully selected (in this case, poly(N,N-dimethylaminoethyl methacrylate) instead of poly(acrylic acid)) or a nano-sized filler that can be well dispersed in the polymer matrix is introduced. Multi-wall carbon nanotubes are introduced into binary PVA-containing polymer blends. The influence of these fillers on the structure and transport properties of the obtained membranes is studied.

New Membrane-Forming Aromatic Co-Poly(amide-imide)s: Influence of the Chemical Structure on the Morphological, Thermal and Transport Properties.

Polymer film membranes are used to solve specific separation problems that dictate structural requirements. Structural and morphological parameters of film membranes based on glassy polyheteroarylenes can be controlled in the process of preparation from solutions that opens up prospects for obtaining structured membranes required for targeted separation. In the case of aromatic poly(amide-imide)s, the possibility of controlling film formation and structure virtually has not been studied. In the present work, a series of homologous co-poly(amide-imide)s differing in the number of repeating units with carboxyl-substituted aromatic fragments was synthesized by polycondensation. Comparative analysis of the processes of formation of membranes with different morphologies based on these polymers under equal conditions was performed. New information was obtained about the influence of the amounts of carboxyl groups and the residual solvent on structural properties of asymmetric membranes. The influence of these factors on transport properties of dense membranes under pervaporation conditions was studied. It was demonstrated that in the case of carboxyl-containing poly(amide-imide)s, the domains formed during film preparation had a significant effect on membrane properties.

Animal Cellulose with Hierarchical Structure Isolated from Halocynthia aurantium Tunic as the Basis for High-Performance Pressure-Resistant Nanofiltration Membrane.

The structure and transport properties of the new Cellokon-AKH membrane based on animal cellulose obtained from tunic of ascidian Halocynthia aurantium were studied. The results of scanning electron microscopy (SEM), FTIR spectroscopy, and the X-ray diffraction data revealed significant differences in the structure and morphology of upper and lower surfaces of this layered film membrane based on animal cellulose. It was shown that the membrane surface is a network of intertwined cellulose fibers, with both denser and looser areas present on the lower surface compared to the completely uniform morphology of the main part of the upper surface. The hierarchical structure of tunicin-based outgrowths evenly distributed over the upper surface was determined and analyzed. The 3D visual representation of the surface structure was performed with the surface reconstruction technique using scanning electron microscope images. A surface model was calculated from the aligned images based on the photogrammetric approach. The transport properties of samples with different prehistory with respect to ethanol, water, and their mixtures of different compositions were studied depending on the pressure. Representing an alcohol-containing gel film in its original state, as solvents are removed, the membrane transforms into a low-permeability fibrillary organized selective film. The obtained results confirmed the possibility of using Cellokon-AKH (dried form) for the filtration of substances with a molecular weight of more than 600 Da in various media. Further study of this new material will allow to get closer to understanding the structure of the studied seabed inhabitants and to use these natural resources more efficiently.

Thermal Properties and Structural Features of Multilayer Films Based on Chitosan and Anionic Polysaccharides.

This study investigates the thermal and structural properties of multilayer composites based on chitosan (CS) and polyanions with different functionalities, including sodium sulfoethyl cellulose (SEC), sodium alginate (ALG), and sodium hyaluronate (HA). Unlike polyelectrolyte complexes (PECs) obtained by polymer mixing, the formation of a PEC layer by a process of layer-by-layer deposition of oppositely charged polymers is accompanied by the transformation of the CS polymorphic state, and this affects the relaxation and thermal properties of the resulting multilayer composite. X-ray diffraction analysis showed that the formation of the PEC layer in the CS/SEC multilayer film is accompanied by crystallization of the CS chains and the formation of a predominantly anhydrous CS modification. Thermogravimetric analysis of the CS/SEC film registers a high-temperature peak associated with the thermal decomposition of crystalline CS in the PEC composition. According to the dynamic mechanical analysis, the CS/SEC composite was characterized by a single glass transition temperature, indicating a strong interaction between the layers when using SEC (a strong acid salt) as the counterion to CS. For multilayer composites with weak polyacid salts (ALG and HA), the crystallization of CS in the PEC layer is weaker, as reflected in the thermal degradation of these films. A high-temperature peak is recorded in the thermal decomposition of CS/HA and is absent in the case of CS/ALG. Dynamic mechanical analysis of the CS/ALG composite showed two glass transition temperatures close to those of the original polymers, indicating weak PEC formation. The CS/HA composite showed an intermediate response. Thus, the effect of the PEC layer on the properties of the poly-layer composites decreases in the order CS/SEC > CS/HA > CS/ALG.

Pervaporation membranes of a simplex type with polyelectrolyte layers of chitosan and sodium hyaluronate.

Self-supporting multilayer films containing a polyelectrolyte complex (PEC) were prepared by the sequential layering of sodium hyaluronate (HA, MW 5.4 × 104) and chitosan (CS, MW 1.6 × 105, the degree of deacetylation 0.80) in different orders. Imaging with low-voltage scanning electron microscopy (LVSEM) showed that the CS/HA films had a multilayer structure, while X-ray diffraction (XRD) indicated significant structuring of the CS layer near the PEC-CS region. Analysis of the thermal properties of the CS/HA films revealed differences in the structural organization and morphological features of the polymer layers and high thermal stability of the PEC layer. Testing of the transport properties of the CS/HA film in pervaporation (PV) separation using different compositions of ethanol-water mixtures indicated that the multilayer membrane was selective across a wide range of concentrations in the feed. Separation of an azeotropic ethanol-water mixture containing 5 wt% water yielded a permeate consisting of about 100 wt% water. LVSEM revealed that the membrane microstructure changed during the PV process due to membrane swelling and changes in the arrangement of the macromolecules during transport of the penetrant. The results support the use of CS/HA composite films as highly effective PV membranes. In addition to pervaporation separation, CS/HA multilayer films can also be used for drug delivery, tissue engineering, and wound healing applications.

Pervaporation multilayer membranes based on a polyelectrolyte complex of λ-carrageenan and chitosan.

A polyelectrolyte complex (PEC) was prepared from chitosan (CS) and λ-carrageenan (λ-CAR) using a layer-by-layer deposition of polyion solutions on a plated nonporous support. This material was then used as a multilayer membrane for the pervaporation separation of aqueous ethanol solutions. The fabricated complex film (25-30µm thick) was a multilayer system (λ-CAR-PEC-CS) containing a polycation CS (MW 3.1×105, DDА 0.93), a polyanion λ-CAR (MW 3.5×105, extracted from the alga Chondrus armatus), and a PEC layer formed between the two polyion layers. X-ray diffraction indicated a significant structuring of the film in the region of the composite PEC-CS bilayer. The structural and morphological characteristics of the CS surface in the multilayer membrane, as revealed by atomic force microscopy, were close to the characteristics of the dense CS film. However, this structure changed following pervaporation (i.e., the distinct spherical structures on the surface disappeared). Similarly, the initially loose surface of λ-CAR in the composite changed to an ordered domain after pervaporation. The transport properties of the pervaporation membranes were tested by examining the separation of ethanol-water mixtures of different compositions. The flux increased with an increase in the weight percentage of water in the feed mixture, but the separation capacity of the membrane was unchanged. In a range of feed concentrations of 50-94wt%, the membrane mainly releases water with a corresponding concentration in the permeate of 99.9-99.8wt% and substantial fluxes of 0.003-1.130kgm-2h-1 at 40°C. The obtained results indicate significant prospects for the use of non-gelling type CARs for the formation of highly effective pervaporation membranes.