Effects of xylanase treatment on fibre morphology in totally chlorine freebleaching (TCF) of Eucalyptus pulp

The effects of xylanase on pulp properties and fibre morphology in a TCF (t otally chlorine free) bleaching sequence has been studied. Enzymatic treatm ent is usually applied after oxygen delignification, but in this paper the effect of xylanase treatment before the oxygen delignification bleaching st age was studied. The application of xylanases in TCF bleaching of Eucalyptu s kraft pulps enables the production of fully bleached pulps with high brig htness (90% ISO) and viscosity (above 800 mL/g). The optimal NaOH charge in the oxygen delignification stage was studied. Xylanase treatment improves the accessibility of the bleaching chemicals to the fibres. The improvement of 'bleachability' produced by the enzyme reduces the quantity of ozone ne eded in subsequent bleaching stages. SEM (scanning electron microscopy) per formed after oxygen delignification showed notable changes on fibre surface s. (C) 1999 Elsevier Science Ltd. All rights reserved.