Bleaching of Soda Rapeseed Pulp with Chelation and Acid Stages

Abstract

Soda pulp cooked from rapeseed straw was subjected to the totally chlorine-free bleaching using hydrogen peroxide and peractic acid as bleaching agents. The five-stage bleaching sequence, Q1Q2EpPaaP, containing two chelation stages, as well as four-stage sequence, AEpPaaP, with an acidic stage were applied to investigate the properties of bleached soda pulp, namely its brightness and tensile strength. For comparison, once-dried kraft softwood pulp, as well as never-dried oxygen-predelignified kraft softwood pulp and sulphite spruce pulp were bleached under the same process conditions. The results obtained showed that totally chlorine-free bleaching did not bring the sufficient bleaching effect for soda rapeseed pulp. The brightness of 54 % ISO achieved for the AEpPaaP bleaching sequence was lower comparing to that for kraft and sulphite pulps.