Analytical methods for determining functional groups in various technical lignins

Abstract In this paper we compare various analytical methods for determining functional groups in technical lignins of five different origins: kraft, sulfite, soda/anthraquinone, organosolv and ethanol process lignins. These lignins were characterized in terms of methoxyl, phenolic and aliphatic hydroxyl, carbonyl, carboxyl and sulfonate groups. The analytical methods used were: gas chromatography, aminolysis, UV-spectroscopy, 1 H and 13 C NMR spectroscopy, the oximating method, FTIR spectroscopy, acid number determination, and non-aqueous and aqueous potentiometry. The statistical comparison of the various analytical methods for hydroxyl groups (phenolic and aliphatic) shows that the results obtained are not fully comparable. Aminolysis and non-aqueous potentiometry are assumed to be the most reliable for phenolic hydroxyl. We observed the same trend for the methods for carbonyl groups and selected the oximating method as reliable for determining total carbonyl. The results for the methods used for carboxylic groups showed correspondence at a significance level of 0.05. We selected aqueous and non-aqueous titration as being reliable for the lignins studied. We also compare all the commercial lignins in terms of functional groups. Finally, by completely characterizing the functional groups of various technical lignins, we have established the most complete representative expanded formula C 9 for each lignin under study.

[1]  Ronald E. West,et al.  Solar Energy Research Institute , 2003 .

[2]  K. Lundquist.  Proton (1H) NMR Spectroscopy , 1992 .

[3]  Richard J.A. Gosselink,et al.  Characterisation of structure-dependent functional properties of lignin with infrared spectroscopy , 2004 .

[4]  Stephen Y. Lin,et al.  Methods in Lignin Chemistry , 1992, Springer Series in Wood Science.

[5]  D. Robert,et al.  Quantitative Estimation of Hydroxyl Groups in Milled Wood Lignin from Spruce and in a Dehydrogenation Polymer from Coniferyl Alcohol Using 13C NMR Spectroscopy , 1984 .

[6]  G. Vázquez,et al.  The Influence of Pulping Conditions on the Structure of Acetosolv Eucalyptus Lignins , 1997 .

[7]  M. Snijder,et al.  Characterisation and application of NovaFiber lignin , 2004 .

[8]  O. Faix,et al.  Fourier Transform Infrared Spectroscopy , 1992 .

[9]  P. Griffiths.  Fourier Transform Infrared Spectrometry , 2007 .

[10]  A. Nadif,et al.  Analytical protocols for characterisation of sulphur-free lignin , 2004 .

[11]  O. Faix,et al.  Determination of Carbonyl Groups of Six Round Robin Lignins by Modified Oximation and FTIR Spectroscopy , 1998 .

[12]  E. Jong,et al.  Co-ordination network for lignin—standardisation, production and applications adapted to market requirements (EUROLIGNIN) , 2004 .

[13]  Wolfgang G. Glasser,et al.  Recent Industrial Applications of Lignin: A Sustainable Alternative to Nonrenewable Materials , 2002 .

[14]  J. Salvadó,et al.  Structural characterization of technical lignins for the production of adhesives: Application to lignosulfonate, kraft, soda-anthraquinone, organosolv and ethanol process lignins , 2006 .

[15]  Y. Lai.  Determination of Phenolic Hydroxyl Groups , 1992 .

[16]  Ģ. Zaķis.  Functional analysis of lignins and their derivatives , 1997 .