BLEACHING OF NONWOOD PULPS - CAN SODIUM-HYDROXIDE BE REPLACED WITH SODIUM-CARBONATE IN THE ALKALINE EXTRACTION OF NONWOOD PULPS

The use of sodium carbonate (Na2CO3) in the alkaline extraction of bamboo (Phyllostachys bambusoides) and eucalyptus (Eucalyptus. tereticornis) kraft pulps was examined. Used alone, Na2CO3 is not a viable alkaline-extraction chemical. However, pulps extracted with a 50:50 ratio of Na2CO3 and caustic soda (NaOH) were comparable with pulps extracted with NaOH alone. The NaOH and Na2CO3 should be charged sequentially, with the NaOH charged first to maintain high alkalinity during the critical initial phase of the alkaline extraction, where most of the lignin is removed. The Na2CO3 is best added during the residual phase of the process.