EFFECTS OF METAL-IONS AND STABILIZERS ON PEROXIDE DECOMPOSITION DURING BLEACHING

A mathematical model has been formulated to allow the total peroxide c onsumption during bleaching of a mechanical pulp to be represented by two separate components; peroxide consumed in reactions with the pulp and peroxide decomposed in metal catalysed reactions. Using this model s it is possible to determine the extent of metal catalysed peroxide d ecomposition in the presence of pulp. This method enables the effects of transition metal ions and stabilisers during bleaching to be studie d directly. The use of constant pH conditions facilitates the direct c omparison of the results obtained during bleaching with those obtained for analogous systems in the absence of pulp. The presence of pulp ca n exert a significant influence on the behaviour of transition metal i ons and stabilisers towards peroxide decomposition. It appears that bo th the lignin and cellulose components can be responsible for the modi fications in the catalytic behaviour observed in the presence of pulp. The effects of stabilisers on the rates of metal catalysed peroxide d ecomposition during bleaching cannot be predicted by studies conducted in the absence of pulp.