PEROXIDE BLEACHING OF EUCALYPTUS-REGNANS COLD CAUSTIC SODA CHEMIMECHANICAL PULPS

The bleaching response of Eucalyptus regnans cold caustic soda chemimechanical pulps has been studied in the presence of alkaline hydrogen peroxide. Samples of pulp were obtained from trees in Tasmania, from different locations and with ages ranging from 10 to 120 years. No simple overall correlation between tree age and initial pulp brightness or brightness gain could be found under conventional bleaching conditions. Experiments were made under constant pH conditions and peroxide concentration to separate effects due to behaviour of chromophores present and the differing rates of peroxide decomposition due to catalytic properties of transition metal ions. The influences of addition of magnesium and silicate, as well as pulp concentration have also been studied. Results have been considered in the context of proposed kinetic models for peroxide bleaching. Factors other than the intrinsic reactivity of the chromophores play a role in determining the final brightness achieved. In particular extraneous material in the bleaching liquor may exert an influence on the rate of chromophore creation processes, possibly through radical induced mechanisms.