DELIGNIFICATION OF PLANT RAW MATERIALS UNDER MICROWAVE IRRADIATION. IR SPECTRA AND ORDERING INDICES OF THE CELLULOSE

Abstract

The effect of plant raw materials delignification with an 18% solution of peracetic acid under microwave irradiation at a frequency of 2450 MHz on the degree of ordering of the cellulose supramolecular structure was studied. The samples of the obtained cellulose were characterized by FTIR spectroscopy. It was found that microwave heating reduces the rate of ordering of the cellulose supramolecular structure in the process of delignification of wood and straw of annual plants with peracetic acid. In general, the delignification products obtained under microwave irradiation with a treatment time of 30 min are characterized by lower values of the ordering index (0.64–0.79) compared to cellulose samples obtained using heating by thermal conductivity (water bath, 100 °С) at processing time 60 min (0.70–0.86). The IR spectra of cellulose samples obtained with the use of heat conduction heating are characterized by a slightly higher intensity of the band at 1372 cm-1 in comparison with the delignification products obtained under microwave irradiation. It has been shown that the degree of ordering of the cellulose supramolecular structure under the studied delignification conditions is determined by the peculiarities of the composition of the feedstock and the polysaccharides supramolecular organization in the native state. For cellulose obtained from wood and straw, different dependences of the values of the ordering index on the heating method and the residual content of hemicelluloses are characteristic.