Means towards optimal brightness stability

Brightness stability of both mechanical and chemical pulps is considered, and possible means to control discoloration reactions are addressed. As a new approach to retard the yellowing tendency of mechanical pulps, an enzymatically assisted bonding of inert compounds to the reactive sites of mechanical pulp is introduced. Promising results have been obtained by treatment of bleached mechanical pulps with laccase and linoleic acid. The brightness stability of chemical pulp, on the other hand, is largely determined during pulp processing, and especially bleaching. The efficient removal of hexenuronic acids (HexA) and residual lignin, as well as the role of final bleaching stage in ECF sequence in respect of pulp carbonyl groups are very important.