Reasons leading to the brightness ceiling in mechanical pulp peroxide bleaching were investigated with spruce thermomechanical pulp. During peroxide bleaching, new phenolic guaiacyl units, alpha-carbonyls and catechols were shown to be formed. All those are known precursors that can be converted to new coloured structures. High chemical charges, especially alkali, enhance formation of these precursors, and thereby limit brightness development. Contrary to the previously reported results on hardwood chemithermomechanical pulp, nitrogen pressurization had no beneficial effect on final brightness of spruce thermomechanical pulp, although it may slightly reduce formation of some colour precursors. The lower chromophore formation is probably obscured by the reduced lignin dissolution. During peroxide bleaching, naturally formed peracetic acid has no significant role in brightness development.
|Number of pages||7|
|Journal||Journal of Pulp and Paper Science|
|Publication status||Published - 2010|
|MoE publication type||A1 Journal article-refereed|