Hydroxymethylation and oxidation of Organosolv lignins and utilization of the products Adilson R. Gonc ßalves a, * , Priscila Benar a,b a Departamento de Biotecnologia ± FAENQUIL ± CP 116, 12.600-000 Lorena, SP, Brazil b Departamento de F  isica e Qu  imica ± ICI ± EFEI, CP 50, 37.500-000 Itajub a, MG, Brazil Received 22 June 2000; received in revised form 19 March 2001; accepted 25 March 2001 Abstract Organosolv lignins obtained from Eucalyptus grandis, sugarcane bagasse and Picea abies by Acetosolv, Formacell and Or- ganocell processes were characterized, fractionated and converted to hydroxymethylated and oxidized products. The reactivity of lignins with formaldehyde did not improve signi®cantly 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 dierent for hy- droxymethylated lignins and phenol, with similar cure temperatures of the resols. Chemical oxidation using cobaltII) and man- ganese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. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: Organosolv lignins; Hydroxymethylation of lignins; Oxidation of lignins; Resols; Chelating agents 1. Introduction Lignin samples directly extracted from the plant can be utilized with small changes in their structure. Lignins can enter the application process as a reagent and often react with other components of the product. The largest current application for unaltered lignin, is its use as a replacement of phenol in phenol±formaldehyde PF) adhesives or resins, which are used as 10% of the ply- wood and particle board Nimz, 1983). Lignins obtained as byproducts of Organosolv pulping processes have several advantages, since these lignins: a) are obtained from renewable sources, which can make the Organo- solv processes economically feasible; b) have an aro- matic and highly cross-linked structure, similar to the network of PF resins; c) can be used as macromolecular material without previous treatment Nimz, 1983). As a resin component, lignin can react with formal- dehyde and phenol by heating under alkaline conditions to produce a resol. In the ®rst step of the reaction, hy- droxymethyl groups are introduced into the lignin re- active positions, mainly into ortho-positions in relation to phenolic OH groups) of aromatic rings Fig. 1). When the temperature is increased, the hydroxymethyl groups react with free positions of other lignin units or phenol to form methylene bonds. At the cure temperature, a cross-linked network is formed and the adhesive be- comes a rigid material Pizzi, 1983). The reactivity of lignins during hydroxymethylation or cross-linking de- pends on their sources softwood, hardwood or grass), on the pulping conditions pH, temperature, pressure) and on the reaction conditions. Technical lignins have been used for partial replace- ment of phenol in resols, but at dierent percentages of substitution. Consequently, the resins obtained have dierent qualities and properties. Olivares et al. 1988) produced resins for particleboards replacing 20% of the phenol by a softwood kraft lignin after ultra®ltration. The mechanical and swelling properties of the particle- boards manufactured with this resin were better than those obtained with a conventional PF adhesive. Ac- cording to Klasnja and Kopitovic 1992), up to 50% substitution of the phenol by kraft lignin resulted in a liquid resin viscosity of 500 mPa s) with a satisfactory Bioresource Technology 79 2001) 103±111 * Corresponding author. Fax: +55-12-553-3165. E-mail addresses: adilson@debiq.faenquil.br A.R. Gonc ßalves), priscila@ici.efei.br P. Benar). 0960-8524/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0960-852401)00056-6