Ozone Bleaching: The Role Of Hexenuronic And Muconic Acids On Pulp Viscosity

摘要

An oxygen delignified eucalyptus (Eucalyptus grandis x Eucalyptus urophylla hybrid) was treated with ozone (Z)followed with an alkaline extraction (E).The implementation of a mild acidolysis stage (90°C, pH 3) ahead of Z to partially eliminate the hexenuronic acid groups had a marked beneficial effect on both the efficiency of ZE and the pulp viscosity after ZE. Splitting ZE in two phases (ZE) (ZE) with a washing step between the two (ZE) dramatically improved the efficiency of the bleaching process but also reduced the viscosity loss. These results would be due to the fact that OH radicals are formed when ozone reacts with the hexenuronic and muconic acids, which has been demonstrated by ESR spectroscopy carried out on model compounds. This finding makes it possible to design TCF bleaching sequences with a much lower impact on pulp viscosity.