Chemical and chemi-mechanical pulping of rapeseed straw

Abstract

Firstly, batch soda pulping of rapeseed straw (species Brassica napus L. convar. napus) was conducted without and with addition of anthraquinone as a catalyst in the cooking liquor. To characterize the chemical composition of rapeseed straw, cellulose, holocellulose, lignin, ash, and extractives were determined. For selected samples of pulp, degree of polymerization, as well as strength properties of soda and soda-AQ pulps were measured. The presence of anthraquinone in cooking liquor accelerates delignification, however, for a given H-factor, lower kappa number and total yield were achieved, compared with cooking without anthraquinone. Also, anthraquinone in cooking liquor had a positive effect upon the decrease of rejects, mainly at a lower H-factor. Secondly, pulping of rapeseed straw using sodium sulphite, blend of sodium sulphite and caustic soda and caustic soda via cold processes were conducted. The influence of varying charges of chemicals on strength properties of handsheets were studied. Moreover, the effect of adding mechanical and chemi-mechancial pulp to secondary fibres upon strength charactersitics of handsheets were determined. The results revealed that the caustic soda pulping has greater effect on bending stiffness and bending modulus of handsheets in comparison with neutral sulphite and alkaline sulphite pulping. The addition chemi-mechanical pulp and mechanical pulp into secondary fibres reduced the bending stiffness while, 25 % of chemi-mechanical pulp addition with secondary fibres increased the bending modulus of handsheets obtained from cold pulping processes. Thirdly, the mechanical and chemi-mechanical pulp was treated with various enzymes. Among all enzymes utilized, the straw treated with BLX 13839 showed higher bending stiffness for handsheets having basis weights of about 260 g m-2 and 520 g m-2. Similarly, the bending modulus of elasticity was the highest for the pulp leached with BZM 2555 for both levels of basis weights.