Chlorine Dioxide Bleaching of Soda Rapeseed Pulp

Abstract

Soda pulp cooked from rapeseed straw (Brassica napus L. convar. napus, winter line genotype Labrador) was subjected to a four-stage elemental chlorine-free bleaching under laboratory conditions. The bleaching sequence comprised three chlorine dioxide stages. The alkali extraction enhanced with hydrogen peroxide addition followed the first chlorine dioxide delignification. For comparison, kraft pulp cooked from a blend of spruce and pine was subjected to the same bleaching sequence D0EPD1D2. After each bleaching step, the optical and strength properties were measured. The preliminary results showed that bleachability of soda rapeseed pulp was lower in comparison with kraft softwood pulp for D0EPD1P bleaching sequence. The final brightness of 83.5 % ISO and 87.8 % ISO was achieved for soda and kraft pulps, respectively. However, the bleaching had a negative impact on the strength of soda rapeseed fibres. The zero-span breaking length decreased from 4.0 km to 3.3 km for unbleached and bleached soda pulps, respectively, while, for kraft softwood pulp, a decrease in fibre strength was not found.