The Chromophores Remaining After Bleaching to Moderate Brightness

Abstract

A pine kraft pulp was bleached to 84% ISO brightness with an ECF DoEpD1 and a TCF OQ(PO)ZQ(PO) sequence. Both bleached pulps were subjected to ClO₂, H₂O₂, and NaBH₄. EPR analyses confirmed that the ECF pulp contained more quinone groups than the TCF pulp which contained more quinone–phenol groups. The colored compounds present at the end of the ECF bleaching sequence were less conjugated than the colored compounds present at the end of the TCF sequence. UV resonance Raman analyses performed on these pulps highlighted the differences between ECF and TCF bleached pulps, the latter containing more aromatics relative to C˭O groups. The bleachability of pulps impregnated with p‐benzoquinone, a quinone model, and alizarin, a quinone–phenol model, were compared with the ECF and TCF pulps. The quinone impregnated pulp behaved like the ECF pulp, whereas the quinone–phenol impregnated pulp behaved like the TCF pulp.

Keywords:

• Wood kraft pulp
• ECF pulp
• TCF pulp
• Quinone–phenol groups
• Bleaching
• Chromophores

Acknowledgments

The authors would like to acknowledge M. André Jeunet (UJF, France) for the EPR analyses and Prof. T. Vuorinen (HUT, Finland) for UV Raman analyses.