Bleaching
Also: bleaching, ECF, TCF, elemental chlorine free, totally chlorine free
Chemical removal of residual lignin from chemical pulp to produce white pulp. ECF (chlorine dioxide) and TCF (oxygen, ozone, peroxide) are the two major systems.
Chemical pulps leave the digester brown, containing 2 to 5% residual lignin. Bleaching selectively removes this lignin to produce white pulp. ECF bleaching uses chlorine dioxide (ClO2) as the primary oxidant and dominates globally (~90% of world bleached chemical pulp).
TCF bleaching uses only oxygen, ozone, and hydrogen peroxide. It produces somewhat lower brightness and slightly weaker pulp, but eliminates chlorinated byproducts entirely. Scandinavian markets have high TCF adoption; most other regions are ECF.
Related
- Kraft pulp. Chemical pulp produced by cooking wood chips with sodium hydroxide and sodium sulfide. The dominant pulp process globally.
- AOX. A regulatory parameter measuring chlorinated organic compounds in pulp mill effluent. Tracked to monitor ECF bleaching emissions.