Marat O. Gallyamov

Expanded polystyrene (EPS) is costly to reprocess, occupies substantial landfill space, and presents significant challenges for reuse. The development of innovative methods for EPS recycling is therefore a promising area of research. This study explores the possibility of fabricating a dense foamed matrix from EPS and using it to produce strong acid cation (SAC) exchange resins for water purification. As an alternative to dissolution-based recycling, we propose a physical, environmentally friendly method involving the saturation of the pristine EPS matrix with CO₂ and its mixtures (modifying agents) under pressure. This approach enables the formation of a dense porous system while eliminating the need for subsequent solvent removal and cleaning. The modified EPS demonstrates a several-fold increase in density compared to the initial material and an SSA = 50–60 m²/g according to CO₂ sorption measurements. The ability to tailor pore size and density simply by varying the modifying agent, pressure, and exposure time was investigated. Structural analysis via SEM as well as N₂ and CO₂ sorption measurements revealed that the modification process critically dictates the pore architecture: treatment with pure CO₂ and a CO₂ + H₂ mixture resulted in the formation of meso- and macropores while preserving the presence of micropores in the material. FTIR spectroscopy and EDS analysis were employed to study the sulfonation of EPS and its resulting cation-exchange capacity. The kinetics of cations’ sorption was studied using capillary electrophoresis, and the static equilibrium ion exchange capacities were determined for both unmodified sulfonated EPS and modified sulfonated EPS towards Na⁺ and Ca²⁺ ions at various salinities of the model solutions. The resulting resins exhibited high sorption capacities, achieving 0.7–1.4 eq L⁻¹ for Na⁺ and 0.3–1.0 eq L⁻¹ for Ca²⁺ ions, while the sulfonated sample treated with the CO₂ + H₂ mixture exhibited the highest equilibrium capacity. The proposed methodology is relevant to both water purification and plastic waste recycling.

In this paper we study in detail the products formed during the process of water-assisted thermal oxidative decomposition (TOD) of polypropylene in the presence of pressurized oxygen. A set of techniques has shown that the main decomposition product in such a process is acetic acid with small amounts of other carboxylic acids (formic, propionic, succinic). The kinetics of carboxylic acid formation is studied by means of gas chromatography–mass-spectrometry as well as capillary electrophoresis, and the possible mechanisms behind the products formation are discussed. The role of water is considered based on the results obtained from substituting H₂O with D₂O in TOD. Compositions of residual oligomeric fractions as well as gas products are analyzed.

In this work, the electrophoretic deposition (EPD) of uniform and mechanically stable chitosan/poly(ethylene glycol) (PEG) films from a biphase H₂O/CO₂ medium under high pressure was proposed. This solvent has a pronounced sterilizing ability and spontaneously self-neutralizes during decompression, becoming a fully biocompatible medium. In such a medium, chitosan aggregates much less than in traditional acid solutions, which allows greater electrophoretic mobility of the macromolecules during EPD of the coating and contributes to an increase in the efficiency of the coating application. The addition of PEG improves the insufficient mechanical strength of the chitosan films, increasing their hardness and adhesion to the substrate. The average peel strengths were 0.15 ± 0.09 N mm^-1 for the chitosan coating and 0.7 ± 0.2 N mm^-1 for the chitosan/PEG composite. The interaction of chitosan and PEG, which form intermolecular complexes due to hydrogen bonding, was studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, and X-ray photoelectron spectroscopy methods. The contact angles of water droplets on the obtained coatings are in the optimal range for bone cell proliferation: 35-85°. High biocompatibility of the coatings was confirmed by evaluating the cytotoxicity using the methyl-thiazol tetrazolium assay with C2C12 osteo-like cells. The coatings show good corrosion resistance due to their high adhesion to metal. Composite coating demonstrated a shift in the corrosion potential toward positive values by 0.1 V, and a drop in corrosion current density by an order of magnitude as compared to the bare titanium substrate. The morphology of the coatings was evaluated by atomic force microscopy, scanning electron microscopy, and profilometry methods, and it was shown that the addition of PEG leads to a significant decrease in the coating thickness (2 μm), while increasing the uniformity. The roughness of the coatings is in the submicron range.

In modern life, people face a wide number of sticky problems when adhesion is highly undesirable: water and dirt stick to clothes, useful materials stick to the walls of their containers and cannot be fully used, water sticking and freezing on airplane wings affects handling and can be dangerous, biological liquids can stick and form clots inside medical devices threatening patients' lives, etc. Slippery liquid-infused porous surfaces (SLIPSs) with pressure stable omniphobicity could help to solve these issues. Lubricant depletion from porous surface and subsequent degradation of omniphobic properties is the major problem for SLIPS. It could be resolved by attaching flexible, liquid-like sidechains to the polymer matrix. Understanding the relationship between the structure of such polymer films and wetting effects is therefore of great importance. The present work is devoted to the study of droplet pinning on crosslinked polydimethylsiloxane (PDMS) polymer films with varied amounts of attached flexible PDMS sidechains and clarification of the relationship between slippery and viscoelastic properties of the films. An one-stage approach to the synthesis of such slippery coatings on smooth and porous substrates in "eco-friendly" pressurized CO₂ solutions is proposed. Pinning force and Young's modulus (E) of the films on silicon substrates with variation of the grafted sidechains amount (x) are measured. The non-monotonic dependence of the pinning force on the amount of sidechains is obtained: the pinning force decreases at small x values (region I) and starts to increase at higher x (region II). The effects of the grafted sidechains amount, as well as matrix softening, are discussed for each case. It is demonstrated that the proposed method of film synthesis allows one to obtain thin, uniform coatings on fabrics without gluing the fibers. Such coatings with an optimal amount of PDMS sidechains demonstrate decreased sliding angles for droplets of water and aqueous alcohol solutions, as compared to PDMS coatings without grafted sidechains. The proposed technique may be of interest for deposition of coatings on porous surfaces having a complex morphology, such as textiles, aerogels, porous electrodes, etc.

The main challenge of modern polymer science is to search for ways of further development of polymer civilization, which obviously includes living organisms on the Earth, without harmful consequences for civilization and the planet in its entirety. The review considers approaches to handle the problem of environmental accumulation of plastic waste. Promising trends in the development of polymer technologies, which can significantly reduce the amount of waste produced, are highlighted. Separate Sections address original methods of additive manufacturing technologies, such as the extrusion printing technique to produce multilayer films, 3D printing by using high-temperature polyimide materials, new functional siloxane oligomers and hydrogels for medical uses. Much attention is paid to the development and applications of biodegradable materials in medicine, packaging industry and agriculture. An analysis of the European strategy for plastics and plastic disposal demonstrates that it has a number of limitations due to high energy requirements and changes in Earth's carbon balance. The modern approach to plastic waste management free from these shortcomings is briefly outlined. Bibliography — 1233 references.

The main known patterns of thermal and/or catalytic destruction of high-molecular-weight organosilicon compounds are considered from the viewpoint of the prospects for processing their wastes. The advantages of using supercritical fluids in plastic recycling are outlined. They are related to a high diffusion rate, efficient extraction of degradation products, the dependence of solvent properties on pressure and temperature, etc. A promising area for further research is described concerning the application of supercritical fluids for processing the wastes of organosilicon macromolecular compounds.

Methods for creating various 3D morphologies of composites based on chitosan and copper nanoparticles stabilized by it in carbonic acid solutions formed under high pressure of saturating CO₂ were developed. This work includes a comprehensive analysis of the regularities of copper nanoparticles stabilization and reduction with chitosan, studied by IR and UV-vis spectroscopies, XPS, TEM and rheology. Chitosan can partially reduce Cu²⁺ ions in aqueous solutions to small-sized, spherical copper nanoparticles with a low degree of polydispersity; the process is accompanied by the formation of an elastic polymer hydrogel. The resulting composites demonstrate antimicrobial activity against both fungi and bacteria. Exposing the hydrogels to the mixture of He or H₂ gases and CO₂ fluid under high pressure makes it possible to increase the porosity of hydrogels significantly, as well as decrease their pore size. Composite capsules show sufficient resistance to various conditions and reusable catalytic activity in the reduction of nitrobenzene to aniline reaction. The relative simplicity of the proposed method and at the same time its profound advantages (such as environmental friendliness, extra purity) indicate an interesting role of this study for various applications of materials based on chitosan and metals.

This review considers the key advantages of using supercritical carbon dioxide as a solvent for systems with organosilicon compounds. Organosilicon polymeric materials synthesis as well as the creation and modification of composites based on them are discussed. Polydimethylsiloxane and analogues used as polymerization stabilizers and nucleation promoters in pore formation processes are analyzed as well.