Clean bleaching of larch dissolving pulp used for viscose fiber

Two-stage oxygen delignification(O1/O2)and chlorine dioxide-based bleaching sequence(D0ED1P,where D was chlorine dioxide bleaching,E alkaline extraction and P hydrogen peroxide bleaching)was employed to bleach pre-hydrolyzed larch kraft pulp.The dosage effect of sodium hydroxide(NaOH)in O1 stage,chlorine dioxide(ClO2)in D0 one and hydrogen peroxide(H2O2)in P one on pulp properties was investigated.The results showed that high efficiency of oxygen delignification can be achieved in two-stage delignification,and the Kappa reduction of 76.4% was gained at optimal amount 2.5% and 0.5% NaOH in O1 and in O2 stages respectively.The dissolving pulp with alpha cellulose 94.1%,pentosan 2.86%,polymerization degree 511 and ISO brightness 87.2% can be prepared by D0ED1P bleaching for the oxygen-delignification pulp at optimal chemicals dosage.It has been proved that the bleaching technology proposed in this paper is reliable.The clean bleaching sequence could be used to remake the traditional CEHP bleaching(C chlorine,E alkaline extraction,H hypochlorite and P hydrogen peroxide bleaching)with the advantage of investment saving due to reuse of original apparatus and pipelines.In addition,the content of absorbable organic halides(AOX)generated during bleaching was just 0.96 kg·(t pulp)-1,only about ten percent of the AOX generated in traditional CEHP bleaching,giving better environmental benefit.