For obtaining high brightness pulp, O
2, O
3 and H
2O
2 bleaching and subsequent ClO
2 bleaching have been carried out with two sorts of unbleaching pulp obtaind by alkali-oxygen pulp-ing process with pulping condition (I) and (II) from rice straw. And the effects of those bleaching was evaluated on the basis of brightness and paper strength of pulp obtained by oxidative bleaching and by subsequent ClO
2 bleaching.
(1) The both unbleached pulps were possible to obtain more higher brightness with O
3 bleaching, but paper strength, especially tear factor were decreased remakably.
(2) The unbleached pulp obtained with pulping condition (I) were increased generally 5 points of brightness with O
2 and H
2O
2 bleaching, but the unbleached pulp obtained with pulping condition (II) were not improved thier brightness with those bleaching.
(3) The bleached pulp of brightness over 80% were obtained from O
3 bleached pulp and commercial Cl
2 treated pulp with one stage bleaching. But paper strength of the former had showed remakable low value and it was necessitated to investigate appropriate protector for O
3 bleaching.
(4) For obtaining the bleached pulp over 80% brightness from pulp obtained with O
2 bleaching, two stage ClO
2 bleaching were required, but paper strength of obtained pulp were maintained same strength with original pulp. And the pulps obtained with H
2O
2 bleaching and subsequent two stage ClO
2 bleaching were not attained to brightness over 80%.
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