Study of heat effects of topochemical esterification of cellulose

This research studied the heat effects of topochemical esterification of cellulose, namely, nitration and acetylation. Depending on the conditions, the esterification process can occur in two main topochemical directions: bulk and local. In a bulk process, the reagent reacts with both amorphous domains (ADs) and crystallites (CRs) of cellulose. However, in local esterification, the reagent reacts with the most accessible ADs only, whereas CRs remain almost unreacted. It has been established that the bulk nitration of cellulose to a substitution degree (DS) of 1.5 is endothermic and determined primarily by the temperature-entropy component of the Gibbs potential. However, the reaction of bulk nitration of cellulose to higher DP values becomes exothermic; thus, the feasibility of this reaction is determined by the enthalpy component of the Gibbs potential. Unlike nitration, the bulk acetylation of cellulose is always an exothermic process, regardless of the achieved degree of substitution; therefore, this esterification process can probably be implemented due to the reaction enthalpy's predominant contribution to the Gibbs potential. In the case of local esterification of ADs, the main contribution to the negative Gibbs potential is made by the exothermic enthalpy of the reaction. Besides, the local acetylation is more exothermic than the local nitration process. Since the locally substituted esters are copolymers of amorphous hydrophobic ester and crystalline cellulose, these esters should be significantly less hydrophilic than cellulose. Therefore, it can be expected that local esterification will find a wide practical application for the inexpensive hydrophobization of various cellulose materials.