Lignin in pulping

Since there are numerous types of structural units in lignin, it is highly unlikely that a single technique will be sensitive to all of them. In addition to the standard analytical techniques, we have been applying Raman spectroscopy to the studies of lignin in pulps. This report focuses primarily on Raman spectroscopic studies of mechanical pulps. Previously, we applied this technique to the studies of celluloses, chemical pulps, and wood. 

We also verified PEG etherification of all three model compounds using simple solubility tests. Guaiacol, acetoguaiacone, and dehydrodiisoeugenol have limited solubilities in water while the PEG-modified products were completely water-soluble. This observation not only confirms the existence of a chemical bond between PEG and the models, but it also gives support to the concept that attachment of PEG to lignin in pulp will increase its hydrophilicity. 

Sjostrom, E., and Enstrom, B. (1966). Spectophotometric determination of the residual lignin in pulp after dissolution in cadoxen. Sven. Papperstidn. 69, 469-476. 

Henriksen A, Kesler RB (1970) The Nu-number, a measure of lignin in pulp Tappi 53 1131-1140... 

Loras V, Loschbrandt F (1956) Gravimetric and absorptiometric determination of lignin in pulp and wood Nor Skogind 10 1-12... 

Marton J, Sparks HE (1967) Determination of lignin in pulp and paper by infrared multiple internal reflectance Tappi 50 363-368... 

Schoning AG, Johansson G (1965) Absorptiometric determination of acid-soluble lignin in semichemical bisulfite pulps and in some woods and plants Sven Papperstidn 68 607-613 Schultz TP, Templeteon MC, McGinnis GD (1985) Rapid determination of lignocellulose by diffuse reflectance Fourier transform infrared spectrometry Anal Chem 57 2867- 2869 Sjostrom E, Enstrom B (1966) Spectrophotometnc determination of the residual lignin in pulp after dissolution in cadoxene Sven Papperstidn 69 469-476... 

Fiserova M, Suty L (1980) Comparative studies on milled wood lignins and cellulolytic enzyme lignin of beech wood (Fagus silvatica L ) Cellul Chem Technol 14 243-252 Glasser WG, Barnett CA (1979) The structure of lignins in pulps II A comparative evaluation of isolation methods Holzforschung 33 78-86... 

Glasser WG, Morohoshi N (1979) The structure of lignins in pulps The distribution of interunit linkages Tappi 62(12) 101-105... 

Several methods of estimating the sulfonate content of lignin in pulp simply measure total sulfur content and assume that all the sulfur is present in sulfonate groupings. 

The most convenient method of obtaining a direct measure of the sulfonate content of lignin in pulp has proven to be conductometric titration (Katz et al. 1984). The preferred method for analysis of total sulfur in lignin in pulp is combustion followed by ion chromatography (Douek and Ing 1989). 

The total acid group content of the pulp is calculated in the same manner using the second end point B in the above equation. The difference between total and sulfonic acid contents corresponds to the carboxylic acid content of the pulp. The sulfonic acid content of lignin in pulp is obtained by dividing the sulfonic acid content of pulp by the sum of Klason and acid-soluble lignin contents expressed as a percentage. 

Methods that attempt to directly measure the sulfonate content of lignin in pulps must overcome the challenge of distinguishing sulfonate from accompanying carboxylate groups. One such method (Sjostrom and Enstrom 1966, Sjostrom et al. 1965) is based on the concept that, under acidic conditions, benzidinium ions form salts only with the sulfonate groups. The pulp is saturated with an aqueous solution of benzidine hydrochloride and washed with water to remove excess reagent the benzidinium ions are eluted with hydrochloric acid and determined by UV spectrophotometry. 

M Halttunen, J Vydrykka, B Hording, T Tamminen, D Batchelder, A Zimmerman, and T Vuorinen. Study of Residual Lignin in Pulp by UV Resonance Raman Spectroscopy. Holrforschung 55 631-638, 2001. 

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