Academician N.S. Enikolopov’s method of mechanochemical solid-phase modification of polymers under conditions of intensive shear deformation has resolved one of the most important issues in cellulose processing, its dissolution. The resulting method of solid-phase dissolution in N-methylmorpholine Nрoxide (MMO) has afforded highly concentrated solutions of cellulose and a series of synthetic polymers, as well as mixed solutions based on them in a wide range of concentrations. It has been shown for the first time that the highly concentrated phase (cellulose concentration up to 45

Eco-unfriendliness of viscose process − the main producer of tire cord from wood cellulose − does not meet the growing need for creation of “green” tires. Alongside viscose cord fiber, production of a new cord fiber, Lyocell, from wood cellulose by eco-clean NMMO process is developing. Technical fibers were obtained from high-molecular flax cellulose by the method of its solid-phase dissolution in N-methylmorpholine-N-oxide. Comparative studies of the structure and mechanical and thermal properties of flax fibers and industrial cord fibers showed correspondence of their properties and that the stiffness of the flax fiber is almost 30

Mixed 18% solutions of cellulose and PAN terpolymer containing methyl acrylate and methylsulfonate comonomers in N -methylmorpholine-N-oxide have been obtained over the entire range of compositions. All the obtained systems based on cellulose and PAN are biphasic, and the morphological features of the emulsions change from highly dispersed isotropic to fibrillar depending on the phase composition and the intensity of the deformation effect. At high shear stresses that emerge during preparation of the solutions in an extruder, all emulsions are characterized by the same microheterogeneous morphology, which is transformed into fibrillar by deformation. An IR spectroscopic study has established that in the preparation process, specific interactions occur between the functional groups of macromolecules of the cocomponents, leading to the formation of PAN/cellulose associates, which undergo hydrophobic repulsion along the interfaces. It is this process that initiates the fibrillation of the cellulose solution phase in the presence of a PAN solution during deformation. The rheological behavior of mixed solutions over the entire range of concentrations in continuous and dynamic modes at temperatures of 110–130°C is a direct consequence of the phase composition and morphological transformations occurring during deformation. Emulsion compositions characterized by viscoelastic properties that make it possible to successfully form composite fibers have been chosen.

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.

Optical interferometry has been employed to study the mass exchange processes that accompany the dissolution of PAN ternary copolymer and to determine limiting copolymer concentrations in solutions in different crystal hydrate forms of N-methylmorpholine-N-oxide (NMMO). Turbidity spectra, interferometry, and optical microscopy have been used to study the effect of the nature of a precipitant on the phase transformations in the system during solution coagulation and to find the precipitation numbers upon the addition of water and aqueous NMMO solutions (20–50 wt

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.

The production of long flax fiber for the subsequent production of textile yarn is accompanied by the formation of a significant amount of waste—noils, which is a mechanical mixture of long and short flax fibers and shives. Comparative studies of the structure and chemical composition of the fibrous fraction of noils and shives were carried out using IR spectroscopy. The solubility of shives and flax noils in N-methylmorpholine-N-oxide (NMMO) was studied, a comparative analysis of the rheological behavior of solutions of flax and wood cellulose was carried out and the optimal temperature–concentration conditions for obtaining flax fibers from noils were determined. It was shown for the first time that using the method of solid-phase activation of the cellulose-solvent system makes it possible to obtain fibers in a short period of time (no more than 10 min). The structure of both the raw material and the resulting fibers was studied by X-ray diffraction analysis. The thermal properties of a new type of cellulose fibers was evaluated. The complex of the conducted studies allows us to consider flax fibers from noils along with flax fibers from long-staple flax, as a real alternative to fibers from wood pulp.

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.

A method was developed for the preparation of new hydrated cellulose fibers from flax cellulose solutions in N-methylmorpholine-N-oxide using the method of solid-phase activation of cellulose-solvent system. The solubility of flax cellulose in this solvent was examined, a comparative analysis of the rheological behavior of flax cellulose and wood cellulose solutions was carried out, and the temperature and concentration conditions for the production of hydrated cellulose fibers were optimized. X-ray diffraction and IR–Fourier spectroscopic analyses revealed a more pronounced structural ordering of the fibers formed from flax cellulose compared with those obtained from Baikal wood cellulose. The mechanical characteristics of the new fibers conform to the level of commercial hydrated cellulose samples, so flax cellulose may be considered an alternative source of raw materials for obtaining hydrated cellulose fibers suitable as carbon fiber precursors.

The kinetics of dissolution of an acrylonitrile copolymer in various crystal hydrates and in a 12% cellulose solution in N-methylmorpholine-N-oxide in a wide temperature range is studied by optical microscopy. The rate and features of the dissolution process are determined by the hydrated form of the solvent. The activation energy of dissolution of the systems under study is calculated using the first-order kinetics. The kinetic characteristics of dissolution of polyacrylonitrile and cellulose in N-methylmorpholine-N-oxide can be used as a basis for finding the optimal temperature–time parameters for the process of obtaining joint solutions of polyacrylonitrile and cellulose, as well as new composite precursors of carbon fibers.

Evolution of the morphology of cellulose solutions in N-methylmorpholine-N-oxide during coagulation with a “soft” coagulant, isobutyl alcohol, at different temperatures is considered. Using optical interferometry and transmitted and scanning electron microscopy the mechanism of phase separation of the system to form a polymer phase is studied depending on the temperature of alcohol. It is shown that, in the case of a room temperature coagulant, a heterogeneous film with a droplet texture enlarging over thickness appears along the precipitation front. At a high temperature of alcohol the coagulation of the solution occurs in two stages. At the first stage the penetration of the coagulant into the jet of spinning solution leading to the formation of vacuoles occurs. The phase separation of the solution proceeds within the vacuoles as microreactors to form a polymer-concentrated shell and a polymer-diluted phase in the vacuole cavity. At the second stage the coagulant diffuses through the vacuole shell into the bulk of the solution and causes its uniform coagulation. The process of vacuole formation is visualized. The transverse cleavage of the film is analyzed by energy dispersive X-ray spectroscopy. The difference in the content of C, N, and O atoms on the walls of vacuoles and in the region of a film with a uniform cellular morphology is established.

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.

Bacterial cellulose as polysaccharide possessing outstanding chemical purity and a unique structure compared with wood cellulose, attracts great attention as a hydrocolloid system. It was shown, that at intense mechanical action on a neat bacterial cellulose film in presence of water, the gel-like dispersions are obtained. They retain stability in time (at least, up to several months) and temperature (at least, up to 60 °C) without macro-phase separation on aqueous and cellulose phases. The main indicator of the stability is constant viscosity values in time, as well as fulfilling the Arrhenius dependence for temperature dependence of viscosity. Flow curves of diluted dispersions (BC content less than 1.23%) show strong non-Newtonian behavior over the entire range of shear rates. It is similar with dispersions of micro- and nanocrystalline cellulose, but the absolute viscosity value is much higher in the case of BC due to more long fibrils forming more dense entanglements network than in other cases. Measuring the viscosity in increase and decrease shear rate modes indicate an existence of hysteresis loop, i.e., thixotropic behavior with time lag for recovering the structural network. MCC and NCC dispersions even at cellulose content more than 5% do not demonstrate such behavior. According to oscillatory measurements, viscoelastic behavior of dispersions corresponds to gel-like systems with almost total independence of moduli on frequency and essentially higher values of the storage modulus compared with the loss modulus.

Replacing the aqueous coagulation bath with an alcoholic one during spinning cellulose fibers (films) from solutions in N-methylmorpholine-N-oxide leads to a radical restructuring of the hydrogen bonds net of cellulose and, as a result, to a change in the structure and properties of the resulting material. By the method of optical interferometry, it was possible to identify the intrinsic features of the interaction of the solvent and isomeric alcohols and to construct phase diagrams of binary systems describing the crystalline equilibrium. Knowledge of the phase states of the system at different temperatures renders it possible to exclude the process of solvent crystallization and conduct the spinning in pseudo-homogeneous conditions. The structure and morphology of samples were studied using X-ray diffraction and scanning electron microscopy methods for a specific coagulant. When the solution under certain conditions is coagulated at contact with alcohol, the solvent may be in a glassy state, whereas, when at coagulation in water, an amorphous-crystalline structure is formed. The structural features of cellulose films obtained by coagulation of solutions with water and alcohols help to select potential engineering or functional materials (textile, packaging, membranes, etc.), in which their qualities will manifest to the best extent.

The process of solid-phase dissolution of polyacrylonitrile copolymer containing ionic sulfo groups in an electron-donating solvent, N-methylmorpholine-N-oxide, is studied depending on its crystal hydrate form and preparation conditions. Optical studies of the transition of solid-phase copolymer–solvent systems to a viscous flow state make it possible to construct solubility curves and reveal stages of morphological transformations during dissolution, explaining their nature. Solid-phase mixed systems are studied by IR spectroscopy, and interactions of the functional groups of the copolymer with various crystal hydrates of the solvent are analyzed both during standard mechanical mixing and mechanochemical activation under intense shear deformation, which predetermines the formation of solid solutions.

A new method is developed for the production of composite fibers based on cellulose and vinyltriethoxysilane and formed from N -methylmorpholine- N -oxide solutions. Introduction of the organosilicon additive promotes the activation of cellulose pyrolysis processes, and its choice relies on the presence of a double bond in vinyltriethoxysilane, which can be opened when the temperature rises. Mixed solutions are emulsions with labile droplets of the organosilicon liquid that easily change their shape under deformation. The study of the rheological behavior of the mixed solutions of cellulose with vinyltriethoxysilane reveals an unusual character of a change in viscosity with the concentration of vinyltriethoxysilane—with a minimum at 10–15%. From joint solutions by the dry-jet wet method, composite fibers are spun in an aqueous coagulation bath at a rate of 50–70 m/min. The study of their thermal properties shows that in thermolysis vinyltriethoxysilane additives catalyze condensation processes in cellulose and lead to an increase in char yield. Using IR spectroscopy, the combined chemical transformations of cellulose and vinyltriethoxysilane at all stages of the heat treatment of composite fibers up to 1200°C are analyzed for the first time. It is found that during thermolysis the chemical interaction of vinyltriethoxysilane with cellulose occurs and carbon fibers “crosslinked” by silicon carbide fragments are formed.