This paper studies a two-stage oxygen-alkaline treatment and subsequent bleaching of softwood sulfate pulp obtained from healthy and deadwood of spruce and larch. Delignification was carried out at elevated temperature and pressure in an alkaline medium with the addition of hydrogen peroxide, after which the pulp was subjected to classic ECF cycles with chlorine dioxide, hydrogen peroxide and, if necessary, elemental chlorine. The selected and washed mass was ground to a specified degree of grinding and formed into laboratory sheets of standard density on a sheet-forming apparatus. The results showed that oxygen-alkaline pretreatment significantly reduces the residual lignin content, and subsequent bleaching cycles make it possible to obtain high-brightness pulp with minimal losses of cellulose and viscosity. The structural, morphological and mechanical characteristics of the obtained samples were studied. After a full bleaching cycle, the fibers become slightly shorter and thinner, their surface is leveled, the proportion of small fractions decreases, and the homogeneity of the structure improves. The resulting cellulose samples demonstrate mechanical characteristics that meet industrial requirements for high-quality printing and thin-layer paper grades.
Sevastyanova et al. (Thu,) studied this question.