Oxygen and ozone delignification of high kappa number sulphur-free soda hardwood pulps-pulp and papermaking properties

Soda birch pulps cooked to kappa numbers 35 and 50 were delignified using oxygen and ozone. The following process modifications were studied: 1) Medium kappa number (35) soda cooking followed by oxygen/ozone delignification and final bleaching: O-O-A/D-Eop-D-P and O-Z-D-Eop-D-P. 2) High kappa number (50) soda cooking followed by oxygen/ozone delignification and final bleaching: O-Z-D-Eop-D-P and O-O-Z-D-Eop-D-P. The results showed that stopping the soda cook at higher kappa number than in traditional cooking and continuing the delignification with oxygen and ozone would be a promising process alternative to obtain paper grade pulp with adequate properties and sulphur free lignin as a by-product