RESUMEN
Morphological transformations in emulsions of cellulose and polyacrylonitrile (PAN) ternary copolymers containing acrylonitrile, methyl acrylate, and methylsulfonate comonomers in N-methylmorpholine-N-oxide were studied over the entire range of concentrations depending on temperature and intensity of the deformation action. Based on the morphological and rheological features of the system, the temperature-concentration range of spinnability of mixed solutions was determined, and composite fibers were spun. The fibers are characterized by a heterogeneous fibrillar texture. Studies of the structure of the fibers, carried out using X-ray diffraction analysis, revealed a decrease in cellulose crystallinity with an increase in the content of PAN. The study of the thermal properties of the obtained fibers, carried out using DSC, and chemical transformations in them in a wide temperature range by high-temperature diffuse reflection IR spectroscopy made it possible to reveal a new intense exothermic peak on the thermograms at 360 °C, which according to the IR spectra corresponds to the transformation of intermacromolecular physical interactions of the PAN and cellulose into covalent bonds between polymers. In addition, the ester groups found during the thermal treatment of the PAN part of the composite fibers in the pyrolysis zone can have a key effect on the process of their further carbonization.
RESUMEN
An original method is proposed for preparing highly concentrated solutions of PAN copolymer in N-methylmorpholine-N-oxide (NMMO) and forming membranes for nanofiltration from these solutions. The high activity of the solvent with respect to the polymer provides short preparation time of spinning solutions in comparison with PAN solutions obtained in other solvents. The use of the rheological approach made it possible to find the optimal concentration for obtaining membranes. The formation of PAN membranes from the obtained solutions is proposed by the rolling method. The morphology of the formed membranes depends on the method of removing the precipitant from the sample. The features of the formed morphology of PAN membranes were studied by scanning electron microscopy. It was revealed that the use of water as a rigid precipitant leads to the formation of a homogeneous and symmetric morphology in the membrane. The average pore sizes in the membrane have been obtained by porosimetry. The study of the separating properties of PAN membranes revealed noteworthy values of the permeability and rejection for the anionic dyes Orange II and Remazol Brilliant Blue (74 and 97%, respectively). The mechanical properties of PAN membranes from solutions in NMMO are not inferior to analogs formed from commercially used direct solvents.
RESUMEN
The work is focused on the study of the influence of the cellulose type and processing parameters on the structure, morphology, and permeability of cellulose films. The free volume of the cellulose films was evaluated by the sorption of n-decane, which is a non-solvent for cellulose. The structural features of the membranes and their morphology were studied using X-ray diffraction, IR spectroscopy, SEM, and AFM methods. The characteristic features of the porous structure and properties of cellulose films regenerated from cellulose solutions in the N-methylmorpholine-N-oxide (NMMO) and cellophane films were compared. Generally, cellulose films obtained from solutions in NMMO have a higher permeability and a lower rejection (as measured using Orange II dye) as compared to cellophane films. It was also found that the cellulose films have a higher ultimate strength and modulus, whereas the cellophane films are characterized by higher elongation at break.
RESUMEN
The evolution of structural-morphological transformations of cellulose membranes obtained from solutions in N-methylmorpholine-N-oxide through various temperature isobutanol coagulation baths and subsequent treatment with water and their transport properties were studied. Using SEM, it was found that during coagulation in water and drying of the membranes, a uniform monolithic microheterogeneous texture was formed. The replacement of an aqueous precipitation bath with an isobutanol one leads to the formation of a porous structure with wide pore size and shape distributions. With an increase in precipitant temperature in the as-formed membrane, transverse tunnel cavities are formed with respect to the membrane-forming axis, which collapses when the membrane is washed with water, forming a dense texture with a non-uniform membrane volume. The mechanical properties of the obtained membranes were determined and a mechanism is proposed that allows their values to be correlated with structural-morphological and transport properties.
