# Application of Thermochemical Method to Determine the Crystallinity Degree of Cellulose Materials
###### Abstract  
Currently, to characterize the crystallinity of cellulose, such an estimated parameter as the crystallinity index is used, measured by various methods and techniques. The main purpose of this article was to develop a thermochemical method for determining the real degree of crystallinity (X) of cellulose based on the measurement of the enthalpy of wetting. Various cellulose samples, such as MCC, pure cotton cellulose, bleached wood pulps, mercerized celluloses, and viscose rayon fibers, were used. For these samples, the exothermic wetting enthalpy (\(\Delta\)H\({}_{\rm w}\)), the maximum amount of sworbed moisture (A\({}_{\rm o}\)), as well as the X-ray index of crystallinity (Crl) were studied. The dependence of \(\Delta\)H\({}_{\rm w}\) on A\({}_{\rm o}\) was linear and can be expressed by the equation: \(\Delta\)H\({}_{\rm w}\) = k A\({}_{\rm o}\), where the coefficient k = \(-\)336 (J/g). After substituting the theoretical value A\({}_{\rm o,a}\) = 0.5 (g/g) into this equation, the numerical value of maximum wetting enthalpy \(\Delta\)H\({}_{\rm w,a}\) = \(-\)168 (J/g) for completely amorphous cellulose was obtained. As a result, the equation for calculating the real crystallinity degree (X) expressed in mass fractions was derived: X = \(1-(\Delta\)H\({}_{\rm w}\)/\(\Delta\)H\({}_{\rm w,a}\)). Analysis of the obtained results showed that only the X parameter can characterize the real content of crystallites in cellulose samples, instead of the approximate Crl parameter. cellulose; thermochemical method; wetting enthalpy; degree of crystallinity; calculations +
Footnote †: journal: Applied  
[PERSON], [PERSON], [PERSON]. from the crystalline and amorphous domains. So, the study of microcrystalline cellulose Avicel PH-101 showed that the measuring of peak heights gave CrI 0.80-0.93, deconvolution of the peaks gave CrI 0.55-0.61, subtraction of amorphous scattering gave CrI 0.60-0.78, [PERSON]'s technique gave CrI 0.55-0.61, the technique of Jayme-Knolle gave CrI about 0.69, and the technique of Hermans-Weidinger gave CrI ranging from 0.63 to 0.82 [13; 14; 15]. Moreover, if one technique of the same method for the same sample (e.g., Avicel PH-101) is used, then the CrI value obtained by different researchers turns out to be poorly reproducible [13]. There are several main reasons for the large discrepancies in the values of the crystallinity indices when they are evaluated by different methods or by different measurement techniques of the same method. Firstly, it is due to the application of different calculating equations, mathematical functions, and software to calculate CrI. Secondly, it is due to the different experimental conditions of different methods. Thirdly, it is due to the use of inadequate structural models to evaluate the crystallinity of real cellulose samples. In addition, there are no standard protocols for preparing cellulose samples for the determination of their crystallinity. In particular, the value of the X-ray crystallinity index is affected by the type of crystalline allomorph, the size of crystallites, the distortions, and the texture of the sample [15]. Thus, it is not possible to conclude which of the currently used methods and/or measurement techniques of cellulose crystallinity is the most appropriate. Therefore, it is advisable to develop a new method operating on other principles, namely the thermochemical method based on the measurement of the wetting enthalpy of various cellulose samples. Unlike the methods discussed above, this thermochemical method is direct, simple, fast, reliable, and reproducible; furthermore, it does not require the use of special models, complex software, and calculations. Several terms are used to express the exothermic effect of the interaction between cellulose and water. This effect is called the \"heat\" or \"enthalpy\" of \"wetting\" or \"swelling\". In this article, the thermochemical term \"enthalpy of wetting\" (or \"wetting enthalpy\") will be used. The history of the study of the enthalpy of wetting covers more than 90 years.