Oxidation of spruce wood sawdust by MnO2 plus oxalate:: A biochemical investigation

This paper reports the modification/degradation of lignin within spruce sawdust by manganese complexes formed by the association of MnO2 and oxalate. The Mn oxidants formed are shown to modify both the chemical and physical properties of the wood cell wall. Scanning electron microscopy analysis of oxidized tracheids revealed a smoothing of the cell wall surface from the lumen side due to the removal of some material. Thioacidolysis analysis of the oxidized lignin showed reductions of up to 30% in the recovery of ether-linked guaiacyl monomers and up to 45% for the some dimers composing the polymer. The MnO2/oxalate system also slightly modified polysaccharides, corresponding to a 10% loss in weight of arabinose and glucose in the oxidized sample. However, no delignification occurred, according to the acid insoluble lignin content of spruce. Oxalic acid at pH 2.5 did not induce detectable changes in the chemical structures of the lignin or of the polysaccharides.