ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
ABSTRACT
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.
Subject(s)
Chitosan/chemistry , Polysaccharides/chemistry , Alginates/chemistry , Anions , Hot Temperature , Hyaluronic Acid/chemistry , Microscopy, Electron, Scanning , Static Electricity , Thermodynamics , Thermogravimetry , X-Ray DiffractionABSTRACT
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.
