Effect of fibre-width distribution on ozone bleaching

The reaction of pulp fibres with ozone gas is rapid and follows a shrinking core reaction model. However model agreement with experimental data is goo d only up to approximately 60% delignification. the model departs fro the e xperimental data as delignification progresses further. Here we show that e xperimental data for high-consistency ozonation of kraft pulp can be accura tely modelled over the entire reaction period using a shrinking core model provided that the fibre wall thickness distribution of the pulp is accounte d for. By assuming that cellulose degradation occurs by radical attack in t he advancing reaction front and by direct attack behind the reaction front, this same model an be used to follow the loss of pulp viscosity throughout the course of ozonation.