Bleaching lignin reactions

PI Gnnnarsson, SCH Ljnnggren. The kinetics of lignin reactions dnring chlorine dioxide bleaching. Part 1. Infinence of pH and temperature on the reaction of l-(3,4-dunethoxy-phenyl)ethanol with chlorine dioxide in aqneons solution. Acta Chem Scand 50 422-431, 1996. 

S Ljungren and E Johansson. The kinetics of lignin reactions during oxygen bleaching. Part 2. The reactivity of 4,4 -dihydroxy-3,3 -dimethoxystilbene and (l-aryl structures. Nord. Pulp Paper Res. J. 5 148-154, 1990. 

Formation and Elimination of Multiple Bond Functionalities. Reactions that involve the formation and elimination of multiple bond functional groups may significantly effect the color of residual lignin in bleached and unbleached pulps. The ethylenic and carbonyl groups conjugated with phenoHc or quinoid stmctures are possible components of chromophore or leucochromophore systems that contribute to the color of lignin. 

Further Preparative Reactions. When pulps are to be used in the production of materials that do not retain the original fiber stmcture, such as rayon or ceUulose acetate film, the lignin, hemiceUulose, and other components must be reduced to the lowest possible concentrations. A surfactant (ionic or nonionic) is often added during a hot, weakly alkaline extraction step after chlorination. Another approach, sometimes used in addition to the surfactant step, is to treat the pulp with 6—10% NaOH after most of the oxidative bleaching is finished. This treatment removes most of the hemiceUulose. In most purification plants the final stage includes use of sulfuric acid chelators are optional. 

Sodium chlorite has also been used for treatment and removal of toxic and odorous gases such as hydrogen sulfide and mercaptans. Chlorine dioxide from chlorite is also useful for microbial and slime control in paper mills and alkaline paper machine systems (164,165). The use of sodium chlorite in textile bleaching and stripping is well known. Cotton is not degraded by sodium chlorite because the oxidation reactions are specific for the hemiceUulose and lignin components of the fibers. 

The use of ceric ion initiation to graft polymers on to the surface of wood pulp fibres requires pre-bleaching of the fibres to remove most of the lignin (Mansour etal., 1982). The reaction requires acidic conditions, with a typical system utilizing ceric ammonium... 

Gierer, J., and H.-F. Htiber The Reactions of Lignin during Bleaching. Acta Chem. Scand. 18, 1237-1243 (1964). 

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