Study of ECF and TCF bleaching of birch kraft pulp

Raw material for pulp and paper making is becoming short increasingly. Therefore, developing raw material for paper making industry is very important. Both hardwood and annual plants can be used as raw material for papermaking, but hardwood is more appropriate to be used for large-scale paper mill than annual plants because it can be collected and transported easily by mechanized means. Hardwood pulp has advantages of better runnability on paper machine, better printability of the formed paper and other apparent qualities. Hardwood resource is rich in China. There is brilliant prospect for plantation for rapid growth tree. It is necessary and possible to accelerate the exploitation of hardwood for papermaking. Birch is one of main hardwood in the north China. Cooking and bleaching of the birch were studied in this paper. The birch from the northeast China was pulped by kraft process and bleached with ECF and TCF sequence. The birch chip was cooked with 15-dm(3) cooker in laboratory and pulp was bleached. In this paper, oxygen delignification, hydrogen peroxide bleaching, chlorine dioxide bleaching, oxygen delignification of hydrogen peroxide reinforcement and pretreatment with activator following oxygen delignification were investigated. High brightness of the pulp could be obtained by ECF bleaching. The brightness of the pulp bleached using OpD(1)ED(2) sequence could reach to 86.2%(ISO), using OpD(1)EpD(2) sequence 87.6%(ISO) and using OpD(1)EpP sequence more than 88%(ISO). The brightness of the pulp bleached by TCF bleaching, Op(AQ)Pp sequence could reach to more than 80%(ISO).