The Properties of Birch Bark Affecting the Separation of Birch Bark from Bast

The article considers the problem of using birch bark in the Russian Federation, where significant reserves of this raw material are used mainly as solid fuel. The methods of studying the grinding and separation of birch bark, as well as the extraction of biologically active substance – betulin – from birch bark are presented. The literature review has revealed: the importance of separating the bark into bast and birch bark; the dependence of the separability of bast and birch bark on the moisture content of birch bark, the degree of grinding, etc.; the need to study the properties of birch bark. The dependencies of the density of birch bark and bast on moisture content, of the yield of birch bark on the degree of grinding, as well as the kinetic curves of water absorption at different temperatures have been obtained. It has been established that when the moisture content of the grinded bark is more than 35 %, the gravitational separation of birch bark from bast occurs in an aquatic medium. These dependencies will make it possible to optimize the bark moistening process. Based on the study of the properties of bark, birch bark and bast, it is recommended to carry out separation in 2 stages: mechanical and hydrostatic separation. An analysis of the results of the study of the properties of birch bark affecting the separation of birch bark from bast has shown the feasibility of grinding the bark in a hammer grinder with a rotor speed of 1500 rpm with a material moisture content of 42–52 % for 45–90 s with further classification of the grinded particles into 3 fractions: large with particle sizes of more than 2 mm with a predominant content of birch bark; fine with particles of less than 1 mm with a predominance of bast in the composition; medium with particle sizes of 1–2 mm with more than 30 % birch bark. Birch bark from the medium fraction should be separated by gravitational sedimentation in water for 3–10 min. The identified optimal operating parameters for separating birch bark from bast make it possible to obtain final products, in particular betulin, of higher quality.