# Application of Thermochemical Method to Determine the Crystallinity Degree of Cellulose Materials
## 3 Results  
The X-ray diffraction pattern of the cotton cellulose (CC) was typical of natural cellulose containing a crystalline allomorph of CI with characteristic peaks at 2\(\Theta\) angles of 14.9, 16.5, 22.7, and 34.7\({}^{\circ}\) due to X-ray diffraction from planes of the CI-crystalline lattice with Miller indices of (1\(\overline{1}\)0), (110), (200), and (004), respectively [30] (Figure 1, X-pattern 1). The diffraction patterns of the isolated and bleached wood pulps (KP and SP) were similar to those of cotton cellulose, with the difference that the intensity of the peaks was slightly less and their width was somewhat larger. As a result, the samples of wood pulps showed a lesser CrI value than CC (Table 1). On the other hand, acid hydrolysis of cotton cellulose to obtain MCC led to an enhancement in the intensity of the CI peaks and an increase in CrI value due to the partial removal of the amorphous fraction from the original CC during hydrolysis (Figure 2, X-ray pattern 1). After the mercerization of cotton cellulose or sulfite pulp, the diffraction pattern of CI allomorpht turned into a diffraction pattern characteristic of CII allomorph, which contains peaks at 2\(\Theta\) angles of 12.4, 20.5, 22.0, and also 34.6\({}^{\circ}\)[31] (Figure 1, X-pattern 2). In addition, the intensity of these peaks was lower than the peaks of the original CI samples, which is caused by partial decrystallization during mercerization. The least structurally ordered was a sample of viscose rayon fibers, the CII diffraction pattern of which had low intensive and broad peaks (Figure 2, X-ray pattern 2). Figure 1: X-ray patterns of original (**1**) and mercerized (**2**) CC. Thus, the comparative analysis showed that the MCC sample was the most crystalline and the VF sample was the most amorphous. However, this comparative assessment is not enough to judge the true crystallinity degree of cellulose samples. For this purpose, special studies were carried out, described below. As is known from chemical thermodynamics, liquid water and equilibrium saturated water vapor have the same chemical potential. This means that such an absorbent as cellulose will absorb the same equilibrium amount of water from the liquid phase as from the saturated vapor phase, having relative vapor pressure \(\rm P/P_{o}=1\). It is also known that cellulose crystallites are inaccessible to water molecules and their absorption occurs only by amorphous domains of this biopolymer [21; 22; 23]. Moreover, the interaction of cellulose with liquid water is accompanied by an exothermic thermal effect, such as wetting enthalpy [15; 21; 22; 23]. Thus, the lower the crystallinity degree (X) and the higher the amorphicity degree (Y = 1 - X), the greater will be the absorption value (\(\rm A_{o}\)) of saturated water vapor and the higher will be the exothermic wetting enthalpy (\(\rm\Delta H_{w}\)) of the cellulose sample. This provides a linear correlation, \(\rm\Delta H_{w}=k\)\(\rm A_{o}\), from which one can find also the maximum wetting enthalpy value (\(\rm\Delta H_{w,a}\)) for completely amorphous cellulose. Then, the crystallinity degree (X) expressed in mass fractions for various cellulose samples can be calculated by the equation:  
\[\rm X=1-(\rm\Delta H_{w}/\rm\Delta H_{w,a}) \tag{2}\]  
To implement such an algorithm, it was necessary to determine the \(\rm A_{o}\) value for various cellulose samples. For this purpose, sorption isotherms of water vapor (WV) were studied in a wide range of relative vapor pressures, \(\rm P/P_{o}\). It was found that these isotherms for various cellulose materials have a sigmoid shape and belong to type II (see, e.g., Figure 3). Isotherms of this type have an initial steep stage, after which a gradual and then accelerated increase in sorption is observed, and, finally, at high relative vapor pressures, a sharp rise in the sorption of WV occurs.