Filip Ublekov

In this work, composites based on thermosetting polymers (epoxy, polyester and vinylester resins) are presented, in which carbon particles and cenospheres are embedded. The influence of combinations of multi-walled carbon nanotubes (MWCNTs) and cenospheres, as well as amorphous carbon and cenospheres, on the mechanical properties and electromagnetic attenuation in (part of) the X-band range (812 GHz) of the developed composites has been studied. It has been established that the used combinations of carbon particles and cenospheres have the greatest positive effect on the mechanical properties of the composites based on vinylester resin. The developed materials demonstrate effectiveness for electromagnetic protection in the X-band range. The combination of a polymer matrix and appropriate fillers leads to significant attenuation of the radio frequency signal. The presented composites are suitable materials for integration into various defense systems—from coatings to structural elements with functional purposes.

Viruses cause a great number of infectious diseases with medical, veterinary, agricultural, social and economic impact. Their unique mechanisms to spread, overcome and resist the existing countermeasures require innovative and smart antiviral strategies such as the effective disinfection of enclosed environments with ensured broad-spectrum efficacy and minimized risks associated with handling liquid biocides. Formic acid (FA) is a well-established natural acaricide used in beehives with an antiviral potential; however, its application in a liquid form is hindered by severe corrosiveness and rapid, uncontrolled evaporation. This study describes a novel formulation of FA, using a cryogel carrier for achieving a vapor-phase inactivation of viruses, thus eliminating the need for direct contact between the disinfectant and the pathogen. Firstly, a poly(N-isopropylacrylamide) (PNIPAm) cryogel was synthesized by a procedure involving cryogenic treatment, photochemical crosslinking, and freeze-drying, and then the cryogel was swollen with 65% FA or _ddH₂O as a control. After an exposure of a panel of animal and human viruses to FA, evaporated by the polymer carrier for time intervals between 15 min and 12 h, they were neutralized completely as follows: Poliovirus (PV) as a surrogate for major bee viral pathogens for 60 min by 5.1 ∆lg; Feline calicivirus (FCV) for 60 min by 5.3 ∆lg; Adenovirus 5 (AdV5) for 12 h by 4.0 ∆lg; and Influenza virus A (IAV) for 15 min by 5.1 ∆lg. Results were recorded after titration, 48–72 h incubation, cytopathic effect estimation and NR uptake assay. Our results suggest that 65% FA, when delivered via the PNIPAm cryogel matrix, acts as a powerful agent for fumigation-like disinfection. This “dry” delivery strategy offers significant practical advantages: it eliminates the need for open liquid containers, prevents spill-related hazards, and provides an alternative for controlled, long-term release of active vapors.

Natural zeolites—clinoptilolite from Golobradovo and mordenite from Lyaskovets deposits, Bulgaria—were used for the preparation of zeolite-supported CeO₂@Polybenzimidazole (PBI) hybrid materials, incorporating green-synthesized ceria using Veronica officinalis L extract. In order to prepare the hybrid composites, the zeolites/CeO₂ were surface-impregnated with an ethanolic KOH solution of meta-PBI, which served as a dispersant medium. The composites were investigated by WDXRF, PXRD, FTIR, POM, and TG. The materials were tested in the photocatalytic degradation of 5 ppm Reactive Black 5 dye under UV light. The higher degree of degradation (98%) was achieved using mordenite/CeO₂@PBI as the photocatalyst compared to the clinoptilolite/CeO₂@PBI (14%).

In this work, the mechanical properties of composites with a polymer matrix and reinforced with carbon particles have been studied. It has been established that the obtained engineering materials have increased elastic and plastic characteristics. The thermosetting polymers used are epoxy, polyester, and vinylester resins. The carbon particles are carbon nanotubes and waste carbon from the plasma decomposition of methane in the production of green hydrogen. The carbon particles used are in an amount of 1 wt% and 2 wt% of the weight of the composite, and they are not subjected to pre-treatment (modification). The studied composites are used in shipping, automotive, and aviation technology, and the presence of carbon particles in them is a prerequisite for improving their anti-radar properties.

Experiments were conducted to develop lightweight composites based on thermosetting polymers with cenosphere fillers. Cenospheres are rich in Al and Si particles and are known as low-density aluminosilicate CFA microspheres. The production of a polymer-based structural material (composite) with reduced weight and good mechanical properties, in which a waste product polluting the environment is used as a filler, is a current engineering task. Epoxy, polyester and vinylester resins were used, as well as different filler concentrations (cenospheres – 5 wt.%, 10 wt.% and 15 wt.%). The mechanical properties of the developed composites were studied. It was found that the use of cenospheres positively affects the mechanical properties of the vinylester resin, while in the case of other thermosetting plastics an increase in some of the mechanical characteristics was registered.

We examined the amorphocrystalline structures of polyethylene glycol 400 (PEG-400) using thermogravimetric, calorimetric, X-ray phase analysis, dielectric and IR spectroscopies. The physical properties of such a system are affected by the presence of water, due to the formation of the hydration shell. When the amorphic-crystalline PEG-400 is heated, it undergoes first low-temperature and then high-temperature dielectric relaxation. We demonstrate that the low-temperature dielectric relaxation is due to conformational motion of the PEG molecule’s HO–CH2–CH2– end groups. In contrast to that, the high-temperature relaxation is due to the conformational motion in the central parts of the PEG molecule, due to the motion of local topological defects along the backbone of the molecule.

Supercapacitors are advanced energy storage devices renowned for their rapid energy delivery and long operational lifespan, making them indispensable across various industries. Their relevance has grown in recent years due to the adoption of environmentally friendly materials. One such material is bacterial nanocellulose (BNC), produced entirely from microbial sources, offering sustainability and a bioprocess-driven synthesis. In this study, BNC was synthesized using a symbiotic microbial community. After production and purification, pristine BNC membranes, with an average thickness of 80 microns, were impregnated with an alkali-alcohol meta-polybenzimidazole (PBI) solution. This process yielded hybrid BNC/PBI membranes with improved ion-transport properties. The BNC membranes were then doped with a 6 M KOH solution, to enhance OH− conductivity, and characterized using optical microscopy, ATR FT-IR, XRD, CVT, BET analysis, and impedance spectroscopy. Both BNC and BNC/PBI membranes were tested as separators in laboratory-scale symmetric supercapacitor cells, with performance compared to a commercial Viledon® separator. The supercapacitors employing BNC membranes exhibited high specific capacitance and excellent cycling stability, retaining performance over 10,000 charge/discharge cycles. These findings underscore the potential of BNC/KOH membranes for next-generation supercapacitor applications.

Solid-state supercapacitors with gel electrolytes have emerged as a promising field for various energy storage applications, including electronic devices, electric vehicles, and mobile phones. In this study, nanocomposite gel membranes were fabricated using the solution casting method with perfluorosulfonic acid (PFSA) ionomer dispersion, both with and without the incorporation of 10 wt.% montmorillonite (MMT). MMT, a natural clay known for its high surface area and layered structure, is expected to enhance the properties of supercapacitor systems. Manganese oxide, selected for its pseudocapacitive behavior in a neutral electrolyte, was synthesized via direct co-precipitation. The materials underwent structural and morphological characterization. For electrochemical evaluation, a two-electrode Swagelok cell was employed, featuring a carbon xerogel negative electrode, a manganese dioxide positive electrode, and a PFSA polymer membrane serving as both the electrolyte and separator. The membrane was immersed in a 1 M Na₂SO₄ solution before testing. A comprehensive electrochemical analysis of the hybrid cells was conducted and compared with a symmetric carbon/carbon supercapacitor. Cyclic voltammetric curves were recorded, and galvanostatic charge–discharge tests were conducted at various temperatures (20, 40, 60 °C). The hybrid cell with the PFSA/MMT 10 wt.% exhibited the highest specific capacitance and maintained its hybrid profile after prolonged cycling at elevated temperatures, highlighting the potential of the newly developed membrane.