On the importance of the structural composition of pulp for the selectivity of ozone and chlorine dioxide bleaching

From the literature it is known that both chlorine dioxide and ozone not on ly degrade lignin but also react with hexenuronic acid (HexA). In the prese nt article, this knowledge is further developed, asking not if but rather u nder which circumstances these bleaching agents react with the different st ructures present in the pulp. The results show that, whereas chlorine dioxi de prefers to react with lignin, ozone preferentially reacts with HexA. Thi s finding is used to explain several anomalies seen between the actions of the two chemicals, e.g. regarding brightness increase and selectivity. More over, it is concluded that, especially for hardwood, a (DZE) stage shows ma ny benefits over a (ZDE) stage, even when all the chlorine dioxide has reac ted to completion before ozone addition, i.e. the explanation here is not t he normally encountered synergism between chlorine dioxide and ozone.