Recycling Bleach Technologies
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When faced with bleaching recycled fibers, the technologist must consider the usual factors associated with the bleaching of virgin fibers plus additional factors introduced by recycling. The lignin content of the furnish and the products to be made determine whether delignifying or lignin-preserving agents are to be used. Factors introduced by recycling include mixed lignin contents, dyes , residual ink particles and carrier chemicals, contaminants, color reversion, and hornification (which affects accessibility of chromophores to bleaching reagents). In addition, the technologist must be concerned with the environmental impact of the bleaching operation. Dithionite and formamidine sulfinic acid are effective lignin-preserving reductive bleaching agents for recycled fibers. Hydrogen peroxide is an effective lignin-preserving oxidative agent, but heavy metals and enzymes catalyze its decomposition. Chelating agents have an important role in decreasing metal content. For some delignification and effective removal of organic chromophores, oxygen and ozone show promise. Research on the use of oxygen-based oxidative bleaching agents is intense because of their favorable environmental attributes.
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