Extended Oxygen Delignification of Pine Kraft Pulp

The research deals with the issue of how the conditions of the oxygen delignification process (that is, the removal of residual lignin from pulp fibres with oxygen in alkaline medium) affect pulp properties. The investigation refers in particular to the effect of the amount of added NaOH, the time and the temperature of the oxygen delignification process of normal pine sulphate pulp (kappa number 31.5) on its kappa number, yield and the strength properties of the pulp. Similarly, we investigated the effect on these indices of the initial and inter-stage pulp treatment with peracetic acid, depending on its amount and the pH of the medium. It has been stated that delignifying pine kraft pulp with oxygen only to the level of kappa number <10 is difficult and results in an excessive decrease in pulp yield. Initial treatment of this pulp with peracetic acid in amounts of 0.33 and 0.66% A.O. prior to pulp treatment with oxygen in alkaline media enables it to be delignified to kappa number 7.5-9, with the yield higher by 0.5-1.4 % than that of pulp delignified with oxygen alone. Pulp delignified with oxygen and using the peracetic acid pre-treatment also restores higher viscosity, tear index, and fibre strength in comparison with pulp delignified with oxygen alone.