Structural characterization of technical lignins for the production of adhesives:: Application to lignosulfonate, kraft, soda-anthraquinone, organosolv and ethanol process lignins

The aim of this study is to completely characterize technical lignins so they can be incorporated into phenolic resins such as phenol-formaldehyde. Technical lignins such as Kraft (KL), lignosulfonate (LS), soda-anthraquinone (SAL), organosolv (OSL) and ethanol process lignins (EPL) were characterized by elemental analysis, functional groups analysis, molecular weight distribution, Mannich reactivity and other techniques. Results from elemental analysis (% nitrogen), ash content and polysaccharides show that all these lignins have a high level of purity after treatment except for lignosulfonate, which has a high ash content, and ethanol process lignin, which has a high nitrogen content. We discuss the results of the functional analysis and molecular weight distribution (M-w, M-n, M-w/M-n) for all lignins in order to select a good lignin for adhesive production. After characterizing the lignins, we provide an approximate C-9 formula and active reaction sites for each lignin. Our study of lignin reactivity by Mannich reactivity and UV-spectroscopy shows that Kraft and soda-anthraquinone lignins are more reactive towards modification than the others studied. These lignins may be good raw material for lignin derivatives such as lignin-based phenol-formaldehyde resins. (C) 2005 Elsevier B.V. All rights reserved.