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The research investigates the thermal behavior of mixed systems based on natural and artificial cellulose fibers used as precursors for carbon nonwoven materials. Flax and hemp fibers were employed as natural components; they were first chemically treated to remove impurities and enriched with alpha-cellulose. The structure, chemical composition, and mechanical properties of both natural and viscose fibers were studied. It was shown that fiber properties depend on the fiber production process history; natural fibers are characterized by a high content of impurities and exhibit high strength characteristics, whereas viscose fibers have greater deformation properties. The thermal behavior of blended compositions was investigated using TGA and DSC methods across a wide range of component ratios. Carbon yield values at 1000 °C were found to be lower for blended systems containing 10–40% by weight of bast fibers, with carbon yield increasing as the quantity of natural fibers increased. Thus, the composition of the cellulose composite affects carbon yield and thermal processes in the system. Using the Kissinger method, data were obtained on the value of the activation energy of thermal decomposition for various cellulose and composite systems. It was found that natural fiber systems have three-times higher activation energy than viscose fiber systems, indicating their greater thermal stability. Blends of natural and artificial fibers combine the benefits of both precursors, enabling the deliberate regulation of thermal behavior and carbon material yield. This approach opens up prospects for the creation of functional carbon materials used in various high-tech areas, including thermal insulation. 

Betulin is a promising natural organic substance due to its antibacterial, fungicidal, and antitumor properties, as are their derivatives. The particle size of betulin can reach several tens of micrometers, and its thickness is several microns. There are various ways of processing betulin, but the most promising are solution methods (applying thin layers, impregnation, etc.). Application or impregnation of various materials is carried out using betulin; however, currently known solvents do not allow obtaining solutions with the necessary content of it. Since a number of direct solvents are already known for betulin, which provides only low-concentration solutions, the use of complex systems based on two solvents can become the optimal solution to the problem. The literature data show that the use of mixtures of solvents allows for the preparation of homogeneous solutions, for example, for natural polymers like cellulose, etc. This approach to obtaining solutions has become the basis for the processing of betulin. The use of a mixed solvent based on ethanol and DMSO for the preparation of betulin solutions has been proposed for the first time. The solubility of betulin in a mixture system with a ratio of components of 50 wt.% to 50 wt.% was studied, and a solubility curve was plotted. It is shown that the use of a two-component solvent makes it possible to transfer up to 10% of betulin into solution, which is almost twice as much as compared to already known solvents. The rheological properties of the obtained solutions have been studied. The viscosity of betulin solutions in a complex solvent depends on its content and temperature, so for 7% solutions at 70 °C, it is approximately 0.008 Pa*s. Applying betulin to the surface of the cardboard increases its hydrophobic properties and repellency.