This paper presents a comprehensive analysis of the thermal stability and decomposition mechanisms of IPN hydrogels based on polyvinyl alcohol (PVA) and a copolymer network of poly(ethylene glycol) diacrylate–poly(ethylene glycol) methacrylate (PEGDA–PEGMA). Using thermogravimetric analysis (TGA/DTG) and multi-approach kinetic analysis (Friedman and Ozawa–Flynn–Wall isoconversion methods, nonparametric kinetics, Shestaka-Berggren model), the influence of composition on the processes of dehydration, thermal destruction, and the distribution of activation energy by degrees of conversion was investigated. The constructed three-dimensional kinetic “landscapes” made it possible to identify characteristic features of the behavior of various samples, including differences in the rate and mechanisms of destruction. It was found that an increase in the content of PVA enhances moisture binding and shifts the T_max of dehydration to higher temperatures, while an increase in the concentration of PEGDA forms a denser network that limits moisture retention and accelerates thermal decomposition. Calculation of diffusion coefficients using the Fick model showed a decrease in D with an increase in network density, which reflects an increase in resistance to moisture mass transfer. The combination of the data obtained demonstrates the multistage nature of thermal destruction and allows for the targeted selection of hydrogel compositions for biomedical, environmental, and materials science applications, including drug delivery systems, sorbents and heat-resistant coatings.

Modern tissue regeneration strategies rely on soft biocompatible materials with adequate mechanical properties to support the growing tissues. Polymer hydrogels have been shown to be available for this purpose, as their mechanical properties can be controllably tuned. In this work, we introduce interpenetrating polymer networks (IPN) hydrogels with improved elasticity due to a dual cross-linking mechanism in one of the networks. The proposed hydrogels contain entangled polymer networks of covalently cross-linked poly(ethylene glycol) methacrylate/diacrylate (PEGMA/PEGDA) and poly(vinyl alcohol) (PVA) with two types of physical cross-links—microcrystallites and tannic acid (TA). Rheological measurements demonstrate the synergistic enhancement of the elastic modulus of the single PEGMA/PEGDA network just upon the addition of PVA, since the entanglements between the two components are formed. Moreover, the mechanical properties of IPNs can be independently tuned by varying the PEGMA/PEGDA ratio and the concentration of PVA. Subsequent freezing–thawing and immersion in the TA solution of IPN hydrogels further increase the elasticity because of the formation of the microcrystallites and OH-bonds with TA in the PVA network, as evidenced by X-ray diffraction and ATR FTIR-spectroscopy, respectively. Structural analysis by cryogenic scanning electron microscopy and light microscopy reveals a microphase-separated morphology of the hydrogels. It promotes extensive contact between PVA macromolecules, but nevertheless enables the formation of a 3D network. Such structural arrangement results in the enhanced mechanical performance of the proposed hydrogels, highlighting their potential use for tissue engineering.

Научная новизна данного исследования заключается в комплексном анализе физических и химических свойств бурого угля Кузнецкого месторождения с применением современных методов исследования. Были систематизированы и представлены данные, касающиеся элементного состава, зольности, влажности и выхода летучих веществ данного угля. Особое внимание было уделено изучению влияния функциональных групп на реакционную способность угля, что ранее не было исследовано в столь детализированной форме для этого месторождения. Актуальность данного исследования заключается в глубоком и систематическом анализе свойств гуминовых кислот, полученных из бурого угля Кузнецкого месторождения, с применением современных аналитических методов. Впервые в рамках данного исследования были выявлены и охарактеризованы химические структуры гуминовых кислот, что позволяет глубже понять их состав и функциональные особенности. Использование таких методов, как инфракрасная спектроскопия и элементный анализ, термогравиметрический анализ дало возможность не только идентифицировать основные функциональные группы бурых углей и гуминовых кислот, но и определить их термическую стабильность и реакционную способность. Это позволяет оценить их потенциальное применение в различных отраслях, таких как агрохимия, экология и медицина. Таким образом, полученные результаты исследования являются значительным вкладом в область углехимии и экологии, а также могут послужить основой для дальнейших исследований и разработок в сфере применения гуминовых кислот как экологически чистых добавок и сорбентов.

Polyethylene glycol fumarate (PEGF) with controlled structural composition has been obtained for further synthesis of double network crosslinked hydrogels for biomedical applications. The copolymer has been synthesized by polycondensation reaction of fumaric acid and polyethylene glycol (PEG-600). Molecular weight of PEGF has been determined by gel permeation chromatography to be approximately 6000 Da with gel permeation chromatography. The polycondensation of fumaric acid and PEG-600 was studied throughout the reaction process. The structure of the reaction product has been evidenced using FTIR- and 1H NMR-spectroscopy. The quantitative ratios of the amount of –C=C– bonds and –COO groups to –C=O groups in the obtained PEGF have been estimated from IR-spectra for different synthesis time. The time-dependence of molar ratio of double bonds to methyl groups in PEGF has been obtained from corresponding 1H NMR-spectra. FTIR and 1H NMR-spectroscopy, both, demonstrate that after the end of reaction the unsaturated –C=C– double bonds remain in the structure of the macromonomer, that is essential for further preparation of cross-linked hydrogels. The addition of the tightly cross-linked network of polyvinyl alcohol leads to formation of highly tough biocompatible material for preparation of the artificial meniscus which can further be used as a solution n the treatment of diseases such as osteoarthritis.

This article presents the synthesis and comparative characterization of humic acids extracted from brown coal deposits of Kuznetsk and Kumuskuduk in Kazakhstan. Advanced analytical techniques, including infrared (IR) spectroscopy, elemental analysis, and thermogravimetric/differential scanning calorimetry (TGA/DSC), were employed to investigate the physicochemical and structural properties of the humic acids derived from these two distinct geological sources. The results revealed significant differences in elemental composition, particularly in carbon, oxygen, and hydrogen content, which were directly related to the geological and environmental conditions under which the coals were formed. Variations in the concentration of carboxyl and hydroxyl functional groups were also identified, influencing the sorption capacity, acidity, and complexation behavior of the humic acids. Thermal analysis demonstrated differing levels of thermal stability and decomposition patterns, reflecting the structural heterogeneity of the samples. This study highlights the importance of geological origin in determining the functional potential of humic substances and supports their application in environmental remediation, agriculture, and water purification.