Determination of Target Delignification Rate of Kraft Bamboo Pulp in Two Stages Oxygen Delignification

The effects of oxygen delignification parameters on the delignification rate and viscosity reduction rate,and the relation between delignification rate and the contents of α-cellulose,pentosan and ash contents of the oxygen delignified pulps were investigated in this paper.It was found that the proper target delignification rate was approximately 68% after optimization of two stages oxygen delignification.The corresponding alkali charge(as NaOH),oxygen pressure,reaction temperatures and durations for two stages oxygen delignification were 3.0%,0.9 MPa,80℃,40 min and 2.0%,0.3 MPa,100℃,60 min,respectively.Although pentosan content of oxygen delignified pulps decreased once beyond this target delignification rate,the increase of α-cellulose content was not significant while the viscosity reduction rate was obviously increased.Moreover,it was also found that,when the total alkali charge of two stages oxygen delignification was higher than 5.0%,the decrease rate of viscosity would be accelerated correspondingly at the transition point of delignification rate of approximately 64%.Therefore,to avoid the significant reduction of pulp viscosity but simultaneously increase the delignification rate of kraft bamboo pulps in two stages oxygen delignification,the total alkali charge(as NaOH) of two stages oxygen delignification should not be higher than 5.0%.