Application of thermochemical methods for the study of cellulose and cellulose esters

In this research, the enthalpy of the interaction of cellulose and cellulose esters with various polar liquids was studied. Besides, the standard enthalpies of combustion and formation of cellulose and its esters were determined. It was shown that the absolute value of the standard exothermic enthalpy of the interaction of cellulose with the polar liquids is an indicator of the accessibility of the supramolecular structure for these liquids. It has been also established that the interaction enthalpy of cellulose materials with water, i.e., wetting enthalpy, is directly proportional to the content of non-crystalline domains and inversely proportional to the degree of cellulose crystallinity. In the case of cellulose esters, the wetting enthalpy characterizes their substitution degree and hydrophobicity, which are the higher, the lower the absolute value of the exothermic wetting enthalpy. The determination of the standard enthalpies of combustion and formation of cellulose and the melting heats of crystallites was carried out to evaluate the relative thermodynamic stability of CI, CII, CIII, and CIV crystalline forms and amorphous cellulose. For esters of cellulose, it was shown that an increase in the degree of substitution contributes to enhancing the exothermic enthalpy of the formation; thus, the esterification of cellulose is thermodynamically favorable.