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Recovered fibers are reused for manufacturing bright paper after deinking and fiber decolorization. This second process generally starts with an alkaline hydrogen peroxide (H 2 O 2 ) stage, referred to as P. However, the color-stripping effect of P is often limited due to the low reactivity of H 2 O 2  on the azo groups of dyes. The purpose of this study was to improve the removal of these azo dyes by H 2 O 2 . A bleached kraft pulp was dyed with a model azo dye and submitted to activated H 2 O 2  bleaching. Phenanthroline and copper(II)-phenanthroline (Cu-Phen) served as activating compounds. The color-stripping trials were carried out at weak or conventional alkaline pH. The results were mainly evaluated in terms of dye removal index and degree of polymerization of cellulose. The theoretical composition of Cu-Phen in the bleaching conditions was calculated by means of the geochemical software PHREEQC. The results show that Cu-Phen was able to activate H 2 O 2  color stripping, although it was accompanied by additional cellulose degradation. Moreover, the color stripping was more effective under alkaline conditions, in which case CuPhen(OH) 2  would be present. Two hypotheses are proposed to explain this activated decolorization: a free radical mechanism and the influence of CuPhen(OH) 2  as an activating species.

Activated hydrogen peroxide decolorization of a model azo dye-colored pulp