RESUMO
Organosolv lignins obtained from Eucalyptus grandis, sugarcane bagasse and Picea abies by Acetosolv, Formacell and Organocell processes were characterized, fractionated and converted to hydroxymethylated and oxidized products. The reactivity of lignins with formaldehyde did not improve significantly with the fractionation. Both eucalyptus Acetosolv (EAc) and eucalyptus Formacell (EFo) lignins retained high heterogeneity in relation to the molecular weight distribution but not in relation to structural units. The temperatures of the exothermic peaks and the apparent activation energies for the cross-linking are different for hydroxymethylated lignins and phenol, with similar cure temperatures of the resols. Chemical oxidation using cobalt(II) and manganese(II) salts furnished oxidized lignins with improved chelating properties. These chelating agents can remove up to 14% of Mn present in pulps, decreasing the peroxide consumption in the bleaching process. The products obtained can be also used as oxidized phenols and controlled-release matrices. Oxidation of Acetosolv bagasse lignin with polyphenol oxidase furnishes lignins with chelating capacity 110% higher than that of original lignin.