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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 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.

Fibers of bacterial cellulose were obtained for the first time from solutions in N-methylmorpholine N-oxide (NMMO) by using the concept of solid-phase dissolution of bacterial cellulose. The mechanism of solid-phase dissolution of bacterial cellulose in NMMO is examined with due regard to the structural and morphological characteristics of native bacterial cellulose. By investigating the structure of the fibers it was possible to reveal the different orientation of the main diffraction planes of the outer shell and inner part of the fiber reflecting the structural aspect of the shell–core morphology. The fibrillar morphology of the fiber was established by scanning electron microscopy. The thermal characteristics of the fibers of bacterial cellulose differ radically from the characteristics of fibers of plant origin in the preponderance of condensation processes that produce exo effects on the thermograms and lead to increase of the carbon residue. The mechanical characteristics of the obtained fibers were characterized.

The process of film formation including the initial treatment of thin layers of cellulose solutions in N-methylmorpholine N-oxide with isobutanol followed by washing with water is investigated in detail, and the structural and morphological features of the obtained films are examined. The phase state of the N-methylmorpholine N-oxide–isobutyl alcohol system is studied by differential scanning calorimetry and optical interferometry, and a diagram describing the crystalline equilibrium and allowing determination of the temperature–concentration “window” of compatibility of components is constructed. The dependence of viscosity of N-methylmorpholine N-oxide solutions in isobutanol on temperature confirms the phase composition of the system. The process of film formation is modeled by analyzing the diffusion zone of the cellulose solution–isobutyl alcohol system. The IR study of the interaction of N-methylmorpholine N-oxide containing 13.3% water with isobutanol shows that the affinity of isobutanol for water is much higher than that for N-methylmorpholine N-oxide. For this reason, when the spinning solution is brought in contact with isobutanol, the redistribution of water between the interacting components occurs and the structure of the heterogeneous gel-like complex cellulose–N-methylmorpholine N-oxide–isobutanol “is frozen,” as proved by the X-ray diffraction study of the films. Complete removal of the solvent and isolation of cellulose from this film proceed only upon subsequent washing with water. The X-ray diffraction and optical interferometry study of the effect of temperature on the interaction of a hot cellulose solution with cold isobutanol suggests that at room temperature the film obtained from solution contains inclusions of the vitrified N-methylmorpholine N-oxide. Under isothermal conditions (at a temperature of 90°С), the rate of interdiffusion grows appreciably and the solution preserves the homogeneous structure. Thus, the precipitation of cellulose from the bicomponent solvent N-methylmorpholine N-oxide–water upon contact first with isobutanol and then with water proceeds via two stages: initially the system undergoes phase separation and a concentrated solution is formed in the isobutanol-N-methylmorpholine N-oxide blend, from which cellulose precipitates upon interaction with water. When the process of primary interaction of the solution with alcohol is conducted under the conditions of compatibility of isobutanol with N-methylmorpholine N-oxide, a more homogeneous morphology of the films can be obtained.

Solid–state dissolution in N–methylmorpholine N–oxide was used to obtain solutions of mixtures derived from cellulose and various organosilicon additives, namely, tetraethoxysilane, vinyltriethoxysilane, and bis (trimethylsilyl)acetylene. Optical study of the phase composition and morphology of these solutions showed that they are two–phase emulsions with a rather broad size distribution of particles of the dispersed phase. The nature of the flow of the mixed systems in continuous and dynamic deformation when the rheological behavior is monotypic depends to a certain extent on the nature of the organosilicon additive. Dry wet–jet spinning was used to obtain composite fibers. The structure and morphology of these fibers were studied as well as their mechanical and thermal properties. Analysis of the x–ray patterns diffractograms of the cellulose and composite fibers showed that the introduction of organosilicon additives into the cellulose matrix leads to less structural ordering of the cellulose. The mechanical characteristics of the composite fibers show some decrease in the strength and deformation characteristics with an increase in the elastic modulus in comparison with the cellulose fibers. Heat treatment of the cellulose and composite fibers up to 1000°C revealed a significant increase in the mass of carbon residue, whose amount depends on the type of additive.

Structural and morphological evolution of polyacrylonitrile (PAN) samples from starting powder of a ternary copolymer to fibers produced from concentrated solutions of PAN in N-methylmorpholine-N-oxide (NMMO) was studied using x-ray diffraction for the first time. X-ray exposures in transmission and reflection geometries allowed the structures of outer and inner parts of the PAN fibers to be differentiated. It was shown that a shell—core structure formed in the precipitation bath during fiber spinning. A comparison of x-ray diffraction patterns of fibers spun using the NMMO process and industrial samples spun from DMSO and aqueous sodium thiocyanate solutions did not reveal fundamental structural differences.

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.

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 &deg, 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.

The combined solutions of cellulose and PAN in N-methylmorpholine-N-oxide at total polymer contents of 18 and 25% are obtained by solid-phase dissolution. The investigation of phase composition and morphology of these systems via optical methods shows that the solutions of cellulose and PAN in N-methylmorpholine-N-oxide are incompatible and form emulsions. The action of deformation on the emulsions leads to the appearance of orientational effects. If PAN predominates in droplets of the dispersed phase of cellulose solutions, this leads to the formation of fibrillar structures under shear stress, while in the case of PAN dispersion medium double emulsions are formed, in which internal droplets of the cellulose solution are most easily extended under shear. The rheological behavior of the combined systems is the direct consequence of structural-morphological transformations proceeding during deformation of the system. An analysis of the morphological and rheological features of heterophase systems reveals the concentration interval for the moldability of composite fibers from spinning emulsions.

Carbon—silicon-carbide fibers were produced from cellulose and triethoxyvinylsilane and spun using the solid-phase NMMO-process. Scanning and transmission electron microscopy studies, energydispersive x-ray spectrometry, and x-ray structure analysis of composite carbon fibers established and identified the structure and morphology of carbon fibers that varied from an isotropic shell to regularly organized lamellae of graphite-like layers of the fiber core. Distributions of chemical elements were plotted. The nano-sized dimensions of silicon-carbide regions in the carbon fibers were determined.

Composite fibers were prepared by solid-state dissolution of cellulose in N-methylmorpholine-N-oxide with added tetraethoxysilane (TEOS). It was shown that adding TEOS to the cellulose matrix increased up to 16% the fiber carbon residue during heat treatment. Bonds formed between Si and C during their high-temperature treatment according to IR spectra of the composite cellulose fibers. The thermal behavior of the fibers was studied using TGA and TMA. The fiber morphology and the structure of the Si-containing additive particles were examined using SEM and TEM. The mechanical properties of carbon fibers prepared from cellulose-hydrate and composite fibers were compared.

Highly concentrated solutions of acrylonitrile copolymers (PAN) in N-methylmorpholine N-oxide (NMMO) were obtained via the solid-phase activation method. Specific interactions in the system at different stages of the dissolution process starting from solid-state activation and finishing with a transition to a viscous state were studied by IR spectroscopy, polarizing microscopy, interferometry and rheology. It was shown that the crucial factor determining a possibility of dissolution is the complex formation between carboxyl groups in the copolymer and the electron-donor N → O group in the solvent. This complex arises during the process of solid-phase activation of PAN and crystalline NMMO, which thereafter melts and transforms into a homogeneous solution having viscoelastic behavior. In the temperature range of 130–135 °C, irreversible chemical transformations take place in the solutions due to the coherent interaction between nitrile groups; these reactions lead to the formation of cyclic structures and conjugated sequences in the PAN chains. Rheological properties follow this process via specific viscosity and viscoelasticity evolution in time.

A method for producing cellulose-based composite fibers with the addition of tetraethoxysilane (TEOS) with a high degree of dispersion of the additive in the cellulose matrix through a “solid phase” dissolution step of the cellulose in N-methylmorpholine-N-oxide (NMMO) is proposed. Investigation of the phase state and morphological features of mixtures of cellulose solutions with TEOS additives in NMMO has shown that in the entire range of concentrations studied, the solutions are biphasic emulsions, and their dispersity and the shape of dispersed phase droplets depend on the prehistory of solution preparation. It is established that the rheological behavior of cellulose solutions with TEOS additives varies depending on the amount of the additive. A theory about a mechanism for changing the rheological behavior of cellulose solutions with TEOS is formulated. X-ray diffraction analysis, scanning and transmission microscopy and IR spectroscopy were used to characterize the structure and morphology of composite fibers. The mechanical properties of composite cellulose fibers with TEOS are investigated.

Composite fibers were obtained from highly concentrated solutions of cellulose and polyacrylonitrile (PAN) copolymers in N-methylmorpholine-N-oxide (MMO). The processes of co-dissolving cellulose and PAN in MMO and the rheological properties of the resulting composite solutions were examined. It was shown that introduction of PAN into the cellulose matrix affects the structurization processes. Specifically, an increase of the PAN content in the cellulose matrix affects the thermal behavior and mechanical properties of the composite fibers.

The influence of precipitation and conditioning baths of various natures and compositions on the structure, morphology, and properties of cellulose-hydrate films produced by solid-state dissolution of cellulose in the direct solvent N-methylmorpholine-N-oxide was studied. The structure-morphology transformations occurring in freshly formed cellulose films due to various conditionings and their influence on the physicomechanical properties of the finished films were demonstrated and analyzed for the first time.

Combined solutions of cellulose and an acrylonitrile-based copolymer in N-methylmorpholine-N-oxide have been prepared for the first time, new composite fibers have been formed, and the properties of the solutions and fibers under standard conditions and during thermal treatment have been studied. On the basis of studying the phase state and morphological peculiarities of combined cellulose solutions with polyacrylonitrile additives, it has been shown that the completed solutions make emulsions in the entire range of investigated concentrations. The rheological behavior of combined solutions changes with temperature. With the use of IR spectroscopy methods, it has been found that the addition of polyacrylonitrile to cellulose results in the association of nitrile groups with hydroxyl groups of cellulose, which favors the cyclization of CN groups during heating and the appearance of polyconjugated bonds in polyacrylonitrile chains. Thermal transformations of cellulose and polyacrylonitrile in the course of mixed-fiber carbonization have been studied via DSC and TGA. It has been shown that polyacrylonitrile inhibits the dehydration processes in cellulose and reduces the intensity of the peak due to the first stage of the structural rearrangement, i.e., acts as a “catalyst” of pyrolysis.

This research examines the possibilities of regulating the structure of cellulose precursor fibers spun from solutions in N-methylmorpholine-N-oxide when replacing aqueous coagulation baths with thermodynamically softer alcohol baths at different temperatures. The fibers were spun by the dry jet&ndash, wet method in isobutanol coagulation baths with a temperature of 25 &deg, C and 70 &deg, C. The study of the phase state of the solvent&ndash, coagulant system using viscometry and point cloud methods revealed the temperature-concentration regions of the single-phase and two-phase states of the system. Using elemental analysis, DSC (differential scanning calorimetry) and XRD (X-ray diffraction) methods, it was shown that just spun fibers, due to the presence of a residual amount of solvent and coagulant in them, regardless of the temperature of the precipitator, have an amorphous structure. Additional washing with water completely washed away the solvent and coagulant as well, however, the structure of cellulose changes slightly, turning into a defective amorphous-crystalline one. A relationship was found between the phase composition, structure, and properties of just spun fibers and precursors washed with water. Thus, the loss of structural ordering of both just spun and washed cellulose fibers leads to a decrease in strength characteristics and an increase in deformation. The thermal behavior of the fibers is determined by their phase composition. Fibers just spun into hot alcohol containing a coagulant and traces of solvent acquire thermal stability up to 330 &deg, C. During the pyrolysis of the obtained precursors up to 1000 &deg, C, the value of the carbon yield doubles. The amorphized structure of the obtained fibers allows us to consider it as a model when analyzing the transformation of the structure of precursors during thermolysis.

Comparative studies of the structure and thermal behavior of cellulose and composite precursors with additives of silyl-substituted acetylene and alkoxysilanes were carried out. It is shown that the introduction of silicon-containing additives into the cellulose matrix influenced the thermal behavior of the composite fibers and the carbon yield after carbonization. Comparison of the activation energies of the thermal decomposition reaction renders it possible to determine the type of additive and its concentration, which reduces the energy necessary for pyrolysis. It is shown that the C/O ratio in the additive and the presence of the Si&ndash, C bond affected the activation energy and the temperature of the beginning and the end of the pyrolysis reaction.

For the first time, graphitized fibers from Lyocell cellulose precursors spun from solutions prepared via the solid-phase dissolution method in N-methylmorpholine-N-oxide were obtained. Carbonization was performed up to processing temperature of 2400 °C. Comparative studies of cellulose precursors and carbon fibers, carried out by means of scanning and transmission electron microscopy, X-ray and thermal analysis, allowed us to establish the structural-morphological features and thermophysical properties of carbon fibers. It is shown that graphitized fibers consist of randomly arranged regular lamellae of graphite-like layers. Using transmission electron microscopy, the interplanar distance between the layers (d002) was estimated to be ∼ 0.341 nm. Graphitization of the fibers leads to content of carbon ∼99.75% and oxygen ∼0.25% and to reach the tensile strength up to 1.5 GPa.

The structure and rheological behavior of cellulose solutions in the high-polarity donor solvent N-methylmorpholine-N-oxide containing particles of layered aluminosilicates of various natures, namely, natural hydrophilic montmorillonite (Cloisite Na+) and hydrophobized montmorillonite (Cloisite 20A), are studied. The rheological properties of the mixed systems cellulose-N-methylmorpholine-N-oxide-Cloisite Na+ and cellulose-N-methylmorpholine-N-oxide-Cloisite 20A are similar, although their structures are different. This similarity may be explained by the fact that the highly developed structure of the cellulose matrix phase resulting from strong interactions between polar components of the system exerts the decisive effect on the character of flow of mixed solutions. Therefore, the filler assumes the minor role. The concentration dependences of solution viscosity turn out to be atypical when the content of moisture in Cloisite 20A is increased above the equilibrium value and when M2Cloisite Na+ nanoparticles modified in a certain manner are introduced into cellulose solutions.

Highly concentrated solutions of cellulose and solutions of cellulose blends with synthetic polymers are prepared via the solid-phase dissolution of cellulose in N-methylmorpholine-N-oxide. The phase state and morphological features of these solutions are studied via DSC and polarization microscopy, and their rheological behavior is considered. Evolution in the structure of cellulose in these systems is investigated at all stages during spinning of oriented fibers from solutions. It is first shown that the addition of synthetic polymers to cellulose makes it possible to control processes of cellulose structuring; to stop them at the stage of mesophase formation; and, thus, to avoid further perfection of the structure and formation of the crystalline phase of cellulose.

For the first time the composite fibers based on cellulose with additives of vinyltriethoxysilane (VTEOS) have been obtained. The choice of the additive was justified by the chemical structure of the VTEOS, namely the Si-C links content and the low C/O ratio. Composite fibers were prepared from solid phase pre-solutions of cellulose with VTEOS in N-methylmorpholine-N-oxide (NMMO). An investigation of the rheological behavior of the filled cellulose solutions with VTEOS showed a slight effect of the additive on the viscosity properties of the system. Introduction of 5% of VTEOS to cellulose does not lead to significant structural changes and, as a result, mechanical properties of the fibers. The thermal behavior of composite fibers differs from cellulose fibers.

Phase state and morphological features of solutions of cellulose blends with rigid-chain thermotropic LC copolyesters and isotropic poly(m-phenyleneisophthalamide) in the highly polar donor solvent N-methylmorpholine-N-oxide are studied by DSC and polarization microscopy. The ternary phase diagram for the cellulose-copolyesters-N-methylmorpholine-N-oxide system is constructed. Rheological characteristics of the prepared solutions are studied using capillary and rotary rheometers under the regimes of continuous and periodic shear deformation. Rheological characteristics of cellulose solutions with copolyesters in N-methylmorpholine-N-oxide with their different phase states are shown to change in accordance with the traditional mechanism of flow for solutions with high specific interactions between their components. However, the character of the rheological behavior of mixtures of cellulose with poly(m-phenyleneisophthalamide) in N-methylmorpholine-N-oxide primarily stems from structural-morphological transformations in solutions taking place upon deformation.

The dissolution of thermotropic alkylenearomatic LC copolyesters and isotropic poly(m-phenyleneisophthalamide) in a high-polarity donor solvent, N-methylmorpholine-N-oxide, has been studied. It has been demonstrated that N-methylmorpholine-N-oxide shows high dissolving power with respect to hydrophobic synthetic polymers. In this case, the dissolution of the polymers is accompanied by the formation of crystal solvates of different compositions. With the use of polarization microscopy, DSC, and X-ray diffraction, the stages of formation of crystal solvates have been examined and the phase equilibrium in systems containing crystal solvates has been investigated. Special attention is given to the structural and morphological features of such heterophase systems.

The nature of the anisotropy of highly concentrated solutions of cellulose in MMO was investigated. The temperature-concentration intervals of the existence of nonequilibrium and thermodynamically equilibrium anisotropic states of cellulose in solutions of MMO were detected and determined. The proposed explanation of the specific features of the reaction of cellulose with MMO, which results in the formation of a mesophase, does not exhaust the group of problems of the mechanism of ordering of highly concentrated cellulose solutions and the structural characteristics of the liquid-crystalline phase formed. An examination of these questions requires conducting further detailed studies.

A scientific concept of solid-phase physicomechanical activation of cellulose with a direct solvent of the donor type, N-methylmorpholine N-oxide (MMO), the basis of new solid-phase MMO processing of wood cellulose into the new cotton-like fibre Orcel®, was elaborated. The high degree of crystallinity and orientation ensure the high physicomechanical properties of Orcel fibre.

The retention of more than 70 voltatile organic compounds of different classes was studied by steam chromatography using aqueous solutions ofN-methylmorpholineN-oxide as the stationary liquid phase (SLP). The effects of temperature and composition of the mobile phase on the retention factors (k) for polar and nonpolar sorbates were elucidated. An unusual order of elution of aliphatic alcohols was noted, namely,tert-butyl alcohol

The structural and phase transitions in formation of anhydrous MMO during vacuum drying of DH-MMO and MH-MMO were investigated. The characteristics of the structural changes in MH-MMO in repeated processing of the sample in a heating-cooling regime were determined.

The examined method of processing cellulose can be used to conduct solid-phase EDA-complexation of cellulose with high-melting MMO hydrates in conditions of the effect of shear strains and pressure. The method allows: expanding the concentration range of the solubility of cellulose in MMO to 50% and obtaining highly concentrated spinning solutions with a concentration of up to 30%; decreasing the duration of dissolution to 5–10 min; regulating the process of thermal degradation of MMO and cellulose: fabricating “Orcel®” fibre with a high degree of orientation and high strength and modulus of elasticity. The solid-phase amine oxide method of processing cellulose was developed by the contract group at the All-Russian Scientific-Research Institute of Polymer Fibres (VNIIPV): Candidate L. K. Golova (director), candidate N. V. Vasil'eva, Candidate L. K. Kuznetsova. Candidate T. A. Lyubova, Research Associate O. E. Borodina, and Research Associate T. B. Krylova with the participation of leading specialists at the Institute's BI Center (director of the Center, Candidate I. Z. Eifer). The studies of the properties and structure of Orcel® fibre were conducted by leading specialists at the Institute's BIFIM Complex (Professor M. M. Iovleva. Director). Candidates V. N. Smirnova, S. I. Banduryan, T. A. Belousova, L. P. Mil'kova, I. N. Andreeva, L. P. Konovalova, V. G. Brusentsova, Dr. A. T. Kalashnik, Research Associate G. Ya. Rudinskaya, and Dr. A. Sh. Goikhman.

The possibility of fabricating composite chitosan—cellulose films from mixed solutions of polysaccharides in MMO was demonstrated. Unoriented films of inhomogeneous phase composition exhibit elevated swelling in aqueous media (500-600%) and could be of great interest as separating membranes or film dressings.