Discriminating the brightness stability of cellulosic pulp in relation to the final bleaching stage

The reasons for the improved brightness stability of pulp bleached in the final stage with hydrogen peroxide than with chlorine dioxide have been studied. UV–vis Diffuse Reflectance and UV Resonance Raman micro-spectroscopy @ 325 nm were employed to evaluate the chromophores formation/degradation in fully bleached eucalypt kraft pulp while applying a final chlorine dioxide or a hydrogen peroxide bleaching stages. Spectroscopic data were coupled to wet chemistry and mass spectrometry analyses of degradation products arisen during hydrothermal ageing of bleached pulps. The complementary analyses have revealed the important role of partially oxidised carbohydrates and of the residual xylan–lignin complex in ageing reactions. The leaching of degradation products from pulp during the final bleaching stage, rather than specific oxidation patterns of pulp polysaccharides with the bleaching agent was suggested to be a crucial factor predetermining the extent of brightness reversion of pulp.