# Application of Thermochemical Method to Determine the Crystallinity Degree of Cellulose Materials
## 4 Discussion  
From Figure 5, it follows that the wetting enthalpy is a linear function of maximum absorption value:  
\[\Delta\rm H_{w}=k\cdot A_{o} \tag{4}\]  
where coefficient k = \(-\)336 J/g. Then, using the maximum moisture absorption value, A\({}_{\rm o,a}\) = 0.5 (g/g), found for completely amorphous cellulose (Table 2), one can calculate the numerical value of the maximum wetting enthalpy, \(\Delta\rm H_{w,a}\), for such an amorphous cellulose sample, as follows:  
\[\Delta\rm H_{w,a}=k\cdot A_{o,a}=-336\times 0.5=-168\ (J/g) \tag{5}\]  
It should be noted that the direct experimental determination of the numerical value of \(\Delta\rm H_{w,a}\) is impossible due to the crystallization of amorphous cellulose during contact with water [34; 35], which distorts the true value of the maximum wetting enthalpy. \begin{table}
\begin{tabular}{c c c} \hline
**Sample** & **A\({}_{o}\), g/g** & \(-\Delta\)H\({}_{w}\), J/g** \\ \hline CC & 0.144 \(\pm\) 0.002 & 46.5 \(\pm\) 0.2 \\ MCC & 0.125 \(\pm\) 0.003 & 42.2 \(\pm\) 0.2 \\ CCM & 0.226 \(\pm\) 0.005 & 75.6 \(\pm\) 0.5 \\ KP & 0.174 \(\pm\) 0.003 & 58.5 \(\pm\) 0.3 \\ SP & 0.183 \(\pm\) 0.004 & 62.1 \(\pm\) 0.4 \\ SPM & 0.236 \(\pm\) 0.005 & 78.9 \(\pm\) 0.3 \\ VF & 0.310 \(\pm\) 0.004 & 104.2 \(\pm\) 0.5 \\ AC & 0.500 * & 168 * \\ \hline \end{tabular}
\end{table} 
Table 2: Maximum moisture absorption and wetting enthalpy for cellulose samples. Figure 5: Dependence of wetting enthalpy on maximum moisture absorption value for various cellulose samples. Substituting the obtained \(\Delta\)H\({}_{\rm w,a}\) value (\(-168\) J/g) into Equation (2), one can calculate the thermochemical degree of crystallinity (X) for any cellulose sample (Table 3). In addition, the degree of cellulose amorphicity (Y) can be also calculated, as follows:  
\[\rm{Y=1-X=\Delta H/\Delta H_{w,a}} \tag{6}\]  
Using the literature data on the wetting enthalpy of CC and VF samples [21; 22; 23], it can be calculated by Equation (2) that the X value of these samples is 0.72 \(\pm\) 0.01 and 0.39 \(\pm\) 0.01, respectively. These independent studies confirm the X values of the cellulose samples obtained in this research, which indicates the reliability and reproducibility of the thermochemical method. As can be seen from the results, the thermochemical method provides the determination of the crystallinity degree of cellulose with a standard deviation (SD) of no more than \(\pm\)0.01. In contrast to the thermochemical method, the existing methods used currently for assessing the cellulose crystallinity by CrI, such as WAXS, solid-state \({}^{13}\)C NMR, FTIR, Raman spectroscopy, etc., have 3 to 10 times greater SD values. In addition, the CrI value is poorly reproducible. A comparison of the determined X values with the CrI values for various cellulose samples showed that the relative deviation (RD) of the CrI value from the real X value is large, from 15% for CC to 42% for VF (Table 3). [PERSON] and coauthors found [14] that values of CrI for cotton cellulose obtained by means of different measurement techniques of WAXS can vary in the wide range; using these data, it can be calculated that the average relative deviation of CrI from the real degree of crystallinity is 15%. Such large discrepancies indicate that such a parameter as the crystallinity index estimated by different methods and techniques, as a rule, cannot characterize the real content of crystallites in cellulose samples. In some cases, CrI measured by the same method and technique can be used only for a comparative assessment of the crystallinity of cellulose samples. On the other hand, the obtained degree of crystallinity or amorphicity describes the real supramolecular structure and provides a prediction of various important characteristics of cellulose samples. It is known that many physical, physicochemical, and chemical properties of crystalline and amorphous cellulose differ significantly [2; 3; 27; 36].