Effect of Topological Structure of Cellulose on the Processes of Acetylation and Nitration

Abstract

Cellulose esters are actively used in the production of new by-products, drugs, and materials. Plant raw materials are the main source for the production of cellulose derivatives. The production of cellulose by microbial synthesis is also becoming promising. Despite similar pathways of microfibril biosynthesis, cellulose samples of plant and bacterial origin differ in a number of structural features. The aim of this work is to evaluate the influence of the topological structure of cellulose of plant and bacterial origin on the acetylation and nitration processes. Cotton and kraft cellulose were used as samples of plant cellulose. Bacterial cellulose was obtained in the laboratory using a mixed community of microorganisms under static conditions on synthetic glucose media. Nitration of cellulose samples was carried out with a mixture of concentrated sulfuric and nitric acids; and the degree of substitution was calculated from the nitrogen content determined by the ferrosulfate method. The IR spectra of samples of the original cotton cellulose, as well as nitrates of bacterial and cotton cellulose, were recorded on a Vertex-70 infrared Fourier spectrometer in the range of wave numbers 4000…400 cm–1. Cellulose acetylation was carried out in supercritical carbon dioxide by direct acetylation in an SFE-5000 supercritical fluid extraction system, Thar Process. The content of bound acetic acid in cellulose acetate was determined titrimetrically and then the degree of substitution was calculated. Fibers of plant cellulose and fibrils of bacterial cellulose were visualized by electron and atomic force microscopy. The yield of nitrate from pure cotton cellulose was 160 %, i.e., the degree of substitution was 2.20. Cellulose nitrate obtained from bacterial cellulose under similar conditions had a degree of substitution of 1.96. A new method of direct acetylation of lyophilically dried preparations of bacterial cellulose in supercritical carbon dioxide was proposed, which allows the process to be carried out without acid catalyst and at reduced consumption of acetylating agent. Acetylation of plant kraft cellulose showed a degree of substitution of 2.40, for bacterial cellulose – yield of diacetyl cellulose with the content of acetyl groups 50 %, this corresponds to the degree of substitution of 2.10. The obtaining of esters is due to both topochemical features of microfibrils and crystallinity of the material. For citation: Vashukova K.S., Terentyev K.Y., Chukhchin D.G., Ivakhnov A.D., Poshina D.N. Effect of Topological Structure of Cellulose on the Processes of Acetylation and Nitration. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 6, pp. 176–189. (In Russ.). https://doi.org/10.37482/0536-1036-2023-6-176-189