## 2 Materials and Methods
### Materials
#### 2.1.2 Heat-Accumulating Components  
Heat-preserving materials (HPMs) are characterized by phase change properties. Heat is spent on a phase change, which is often associated with the melting of the main constituent substance. Upon a reverse change in the temperature effect on the main active HPM, the substance is again solidified. These HPMs feature a fairly high specific energy [12]. HPMs of various types are widely used, including various phase change substances (PCMs), which are embedded in the dispersion form in the polymer matrix [13], as well as organic gels and hydrogels [14]. However, for the integration into textiles and further use in clothing, it is important to fix the volume of the active HPM size, shape, and resistance to establish contact with other fibrous components of materials. Therefore, PCM encapsulation methods, using covers of high molecular weight compounds, have become widespread for these purposes. A requirement of the heat accumulators with phase changes is the use of a special composition of the active substance for each of the required temperature values. Taken from the research and systematization of the temperature properties of modern PCMs [15; 16; 17], their systematization is given in Table 1.  
Our analyses of materials with a phase change (PCMs) showed that heat-preserving materials that can store heat within the temperature range of 20 to 40 \({}^{\circ}\)C have found the widest technological application in the form of microcapsules in fibrous materials. When the temperature rises above 35 or 40 \({}^{\circ}\)C, microencapsulated systems absorb heat; whereas, at temperatures below 20 \({}^{\circ}\)C, they release the absorbed heat into the environment. The melting point analyses of pure saturated hydrocarbons and their mixtures, as presented in Table 1, have allowed us to isolate substances--such as octadecane and its compounds (heneicosane-octadecane, docosane--octadecane, octadecane-heneicosane-palmitic acid), nonadecane, eicodecane, sodium sulfate decahydrate (Glauber's salt), heptadecane, and sodium sulfite heptahydrate--that, in terms of their temperature properties, most \begin{table}
\begin{tabular}{l l} \hline \hline  & **Mixture Composition** & **Melting Temperature, \({}^{\circ}\)C** \\ \hline Pentadecan & +9.9 \\ Dakotan & +44 \\ Heptadecan & +22 \\ Heneicosan & +40 \\ Octadecan & +26...+25.8 \\ Tetradecan & +27...+25.5 \\ Dakotan octadecan & + 31.2...+38.4 \\ Octadecan heneicosan & +35.0...+42.2 \\ Palmitic acid & +53.0...+80.0 \\ Nonadecane & +50...+55 \\ Aktekin & +48 \\ Heat-accumulating composition RU 2239647 [18] & +32.5 \\ Heat-accumulating composition RU 2190656 [19] & +33.4 \\ Sodium thiosulfate pentahydrate & +22...+36.1 \\ Sodium sulfate decahydrate (Glauber’s salt) & +58.0 \\ Sodium sulfite heptahydrate & +53.4 \\ Sodium carbonate decahydrate & +55.4 \\ Sodium acetate trihydrate & +52.6 \\ Paraffin & +25...+50 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Melting/stabilization temperature parameters of substances and materials with heat-preserving properties. correspond to the phase change thermal conditions and the characteristic temperature of the human body in heat-protective clothes. For the relevant temperature range, the materials that are being widely used in the world are Micronal(r) PCMs, which are based on microcapsules from a special group of paraffins and Glauber's salt, as developed and implemented by BASF [20]. Micronal(r) PCMs can be used in the dispersion of the microcapsules therein. A phase change (melting) of this material occurs at a temperature of +25 \(\pm\) 1 \({}^{\circ}\)C (the main peak) and another phase change (crystallization) occurs at +24 \(\pm\) 1 \({}^{\circ}\)C (the main peak); the melting heat is within the range of 10 to 35 \({}^{\circ}\)C \(\geq\) 97 J/g [20]. However, this material is currently adapted mainly for building materials.