Fractionation of lignin

The present paper describes the fractionation of lignin sulfonates and kraft lignin by gel permeation chromatography (GPC) and the method developed and used for several years at the Finnish Pulp and Paper Research Institute. 

Elution of Lignin Sulfonates with Water. As can be seen from Figures 1, 2, 3, and 4, the fractionation of lignin sulfonates on elution with water through Sephadex G-50 and G-75 takes place in such a way that the logarithms of... 

Figure 1. Fractionation of lignin sulfonates in spent sulfite liquor on Sephadex G-50. Eluent water. (Reprinted with permission from ref. 1. Copyright 1969 Wiley.)...

Figure 5. Fractionation of lignin sulfonates on elution through Sephadex G-75. Eluent 0.5M NaCl, 0.1M Tris-HCl (pH 8).

Schuerch C (1952) The solvent properties of liquids and their relation to the solubility, swelling, isolation and fractionation of lignin J Am Chem Soc 74 5061-5067 Scott JAN, Procter AR, Fergus BJ, Goring DAI (1969) The application of ultraviolet microscopy to the distribution of lignin in wood Description and validity of the technique Wood Sci Technol 3 73 - 92... 

Acidify the filtrate in Step 3 to pH 10.5 and repeat Steps 3 and 4 to recover a second fraction of lignin. 

Crosslinking in Water at pH >7. Resin cure in aqueous alkali is common practice for phenolics (44) Although most isolated lignins have satisfactory solubility in aqueous alkali, phenolation has been found to enhance the tolerance of phenolic resins to the addition of macromolecular fractions of lignin (4,45-47)-Improved miscibility and reactivity both account for this phenomenon. 

Reslurry the filter cake in distilled water and under good stirring acidify the slurry to pH 2 with 20% sulfuric acid. Centrifuge off the precipitated lignin. After several washings with water at pH 2, air dry the recovered lignin. Acidify the filtrate in Step 3 to pH 10.5 and repeat Steps 3 and 4 to recover a second fraction of lignin. 

X Pan, D Lachenal, C Lapierre, B Monties. Structure and reactivity of spruce mechanical pulp lignins Part II. Organosolv fractionation of lignins in a flow-through reactor. J Wood Chem Technol 12 279-298, 1992. 

FIGURE 5.40 Age of the organic matter is reflected by the changes in the relative fractions of lignin and cellulose content. (Adapted from DeBusk and Reddy, 1998.)... 

The molecular weight distribution (data plotted in Figure 5.14) shows that the HPH process under the condition described above extracts the lower molecular weight fraction of lignin present in biomass. 

Polar solvent extraction of sapwood, heartwood, or rhytidome (outer bark) yields a pale tan- to brown-colored solid, which is insoluble in water and in less polar solvents such as diethyl ether or dichloromethane. Proximate analysis, methoxyl content, color reactions, and infrared spectra (32) are so close to those of lignin to have lead F. E. Brauns and others in the 1940s to believe that this material was a low molecular weight fraction of lignin. Later on, Hergert (21) showed that this material was present in relatively large amounts in heartwood and only in very small quantities in sapwood. It must, therefore, be formed biosynthetically in the same way as other heartwood extractives since solubility characteristics alone would preclude translocation from the sapwood or the cambium. 

Ma and Burken (2002) also found that wood-water partitioning depended mainly on the fraction of lignin when evaluating the sorption of trichloroethylene (TCE), 1,1,2,2-tetrachloroethane, and carbon tetrachloride to poplar tree cores. 

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