In Order to improve delignification and reduce viscosity drop on medium consistency ozone bleaching, bleaching conditions and bleaching methods were investigated.
The results may be summarized as follows :
(1) The lower pH conditions on ozone bleaching made better delignification until lower kappa number and the bleached pulp had better resistance against alkali.
(2) It was confirmed that manganese inside pulp could be strikingly washed out by sulfuric acid solution.
(3) With removal of ozone oxidation products on multistage ozone bleaching, delignification was improved.
(4) By sequential changing of pulp consistency (in this experiment, pulp was bleached at 15% pulp consistency initially and at 8% pulp consistency finally), we obtained a bleachability that pulp could be bleached with higher bleaching velocity initially and lower viscosity drop finally.
And in order to find alkaline decomposition and the color reversion properties, OZEP, OZD and OZ-bleached pulp were compared.
The results may be summarized as follows :
(1) OZ-pulp has declined resistance against alkali. The viscosity drop of OZEP pulp bleached under alkaline conditions was much higher than that of OZD pulp bleached under weak acidic conditions.
(2) The color reversion of OZEP-bleached pulp and OZD-bleached pulp was lower than that of OZ-bleached pulp. The color reversion of OZEP-bleached pulp was lowest.
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