On lignin reactions in TCF kraft pulp bleaching

Industrial bleaching of Kraft pulps is performed with chlorine (Cl-2), chlorine dioxide (ClO2) and oxygen-based bleaching agents - molecular oxygen (O-2), hydrogen peroxide (H2O2), ozone (O-3) and peracids. Chlorine bleaching is polluting, since it produces large quantities of chlorinated organics. Chlorine dioxide replaces elemental chlorine and has the advantage or being a very selective delignifying agent, while the disadvantage Of its utilization ill Kraft Pulp bleaching is that, apart from the high production costs of ClO2, chlorinated organics arc still produced, even if at lower levels. This is why, From all environmental point of view, Totally Chlorine Free (TCF) bleaching seems more attractive. Lignin fragmentation is a direct result of the species present ill oxygen-based bleaching systems, including ozone (O-3), molecular oxygen (O-2), Superoxide radical (O-2(center dot-)), hydrogen peroxide (H2O2), perhydroxyl radical (HOO center dot) and hydroxyl radical (HO center dot). The Study discusses the action of oxygen-based delignification and of the bleaching reagents oil residual lignin.