## 3 Results
### Wettability  
Table 3 shows that the metal surface had a different hydrophilic behavior (\(\theta<90^{\circ}\)), depending on the type of liquid used. The contact angle for the CMC solution had the highest value in the series. A linear decrease in the contact angle values was observed up to the CMC 30 solution, where it slightly increased. From this moment, the contact angle values had a downward trend, reaching a minimum of 43.8\({}^{\circ}\) for CMC 50. From the data presented in Figure 5, it could be concluded that the wetting of the metal surface was very favorable for CMC 20 and CMC 40 liquids, and especially for CMC 50. These liquids formed a continuous thin liquid film on the hard surface. The CMC solution minimized the contact with the metal surface the most and had the lowest coefficient of friction. The contact angle is considered to be a method for characterizing the wettability of surfaces and, consequently, of the way that cooling liquids spread on a metal part [20]. The temperature of the CMC solution increased during the metal quenching process. For this reason, a process of degradation of the polymer solution occurred, which started with the breaking of the hydrogen bonds between the macromolecular chains, followed by the breaking of the covalent bonds in the basic chain (backbone) and, consequently, a decrease in the molecular mass [19; 21]. The acetal bond in polysaccharides is easily hydrolysable; the reaction is strongly favored by the presence of acidic or basic substances, but also of some natural enzymes (microbiological destruction). Depending on the stage of degradation and the fractions of reduced molecular mass, the solutions would have had different viscosities. Due to the depolymerization and decomposition processes of the cellulose solutions and also of the particles, resulting from the hardening of metals, the intermolecular interactions were different from case to case. It is, therefore, understandable why the CMC solutions had a different behavior in terms of surface wetting. Considering the variation in the contact angle--determined by the analysis of the samples from CMC  
Figure 5: The contact angles of water and carboxymethyl cellulose solutions on a metal surface. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **Water** & **CMC** & **CMC 10** & **CMC 20** & **CMC 30** & **CMC 40** & **CMC 50** \\ \hline Contact angle, & & & & & & \\ \(\theta\) & 63.7 \(\pm\) 2.9\({}^{\circ}\) & 74.3 \(\pm\) 2.9\({}^{\circ}\) & 61.2 \(\pm\) 2.3\({}^{\circ}\) & 48.4 \(\pm\) 2.8\({}^{\circ}\) & 57.1 \(\pm\) 0.3\({}^{\circ}\) & 56.8 \(\pm\) 0.9\({}^{\circ}\) & 43.8 \(\pm\) 3.6\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Mean values and standard deviation of contact angle (\({}^{\circ}\)) of the samples. 10-CMC 50, where, after CMC 30, a slight decrease in the hydrophobic properties was observed--and considering the even greater oxidation of the tempering medium if we exceeded 50 cycles, it could be concluded that the hydrophobic properties linearly decreased as the number of cycles increased. This conclusion was confirmed by the variation in other properties, such as pH. There was a correlation between the value of the contact angle and the pH of the solution; these two parameters had a similar variation, certainly determined by the different composition of the carboxymethyl cellulose solutions in separate stages of degradation [21]. The variation in the pH of NaCMC with heat treatment procedures was established and determined. The pH value decreased to a given point, after which the pH again took a high value and then decreased, demonstrating a different chemical composition of the CMC solution after the heat treatment. A strong change in the properties of the liquids was observed for the cooling liquid used with 20 thermal cycles.