Oxalate : a microbial metabolite of interest for the pulping industry

Oxalate is a common metabolite produced by almost all plant-pathogenic fungi. The degradation of cell wall from poplar and spruce chips by oxalate is reviewed. Sugars constituting hemicelluloses were found to be the major target of oxalate. The examination of the cell wall ultrastructure of wood chips by transmission electron microscopy (TEM) after polysaccharide staining showed a characteristic fading of the staining of the SI/S2 and S2/S3 transition areas, supporting the idea that reactivity and organization of polysaccharides had changed after the oxalate treatments. Finally, all these changes enhanced the ability of the wood chips to be defiberized by a mechanical process (RMP), as well as the further refining of the pulps. By examining the surface of poplar fibres, it became apparent that fracture areas during the RMP process had moved toward the S2 layer, explaining why defibering and refining occurred more easily, with less energy input in the process.