Non-Chlorine Bleaching of Wood Pulps Mediated by Heteropolyoxometalates
Wood consists primarily of carbohydrates (cellulose and some hemicelluloses) and lignin. In the production of chemical pulps, used in the manufacture of high quality paper, most of the lignin is removed by reaction with alkaline sulfide. At the elevated temperatures used in pulping, chemical reactions of lignin give rise to highly colored conjugated aromatic structures that remain within the wood cell (fiber) walls. The purpose of bleaching is to degrade or remove these chromophores along with remaining lignin.