A mathematical model has been formulated to allow the total peroxide consumption 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 models it is possible to determine the extent of metal catalysed peroxide decomposition in the presence of pulp. This method enables the effects of transition metal ions and stabilisers during bleaching to be studied directly. The use of constant pH conditions facilitates the direct comparison of the results obtained during bleaching with those obtained for analogous systems in the absence of pulp. The presence of pulp can exert a significant influence on the behaviour of transition metal ions and stabilisers towards peroxide decomposition. It appears that both the lignin and cellulose components can be responsible for the modifications in the catalytic behaviour observed in the presence of pulp. The effects of stabilisers on the rates of metal catalysed peroxide decomposition during bleaching cannot be predicted by studies conducted in the absence of pulp.
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