Fractionation kraft lignin

J Nakano, Y Izuta, T Orita, H Hatakeyama, K Kobashigawa, K Teruya, S Hirose. Thermal and mechanical properties of polyurethanes derived from fractionated kraft lignin. Sen-I Gakkaishi 53 416 22, 1997. 

Norgren, M., Lindstrom, B. Physico-chemical characterization of a fractionated kraft lignin. Holzforschung 54, 528-534 (2000)... 

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. 

Figure 8. Kraft lignin fractionation into two subsets of species during desalting by elution with aqueous 35% diaxane through Sephadex LH20 of an initially 4.5 gL 1 sample solution at 2.3 M ionic strength containing 0.32 M aqueous NaOH.

Figure 13. Comparison of weight-average molecular weights for component subsets B ( ) and C ( ) with those for complete paucidisperse fractions ( 0) isolated from Sephadex G100/0.10 M aqueous NaOH elution profile of the dissociated kraft lignin sample precipitated upon acidification to pH 3.0 after 2000 h at 0.50 gL 1 in 0.10 M aqueous NaOH.

Figure 14. Variation with molecular weight exhibited by ratios of absorbance values at 230 and 300 nm for paucidisperse kraft lignin fractions in aqueous 0.10 M NaOH from ( ) associated sample after 385 h at 180 gL 1 in 1.0 M ionic strength aqueous 0.40 M NaOH (O) original preparation ( ) dissociated sample precipitated upon acidification to pH 3.0 after 2000 h at 0.50 gL"1 in aqueous 0.10 M NaOH.

Figure 8. Fractionation of pine kraft lignin by preparative reversed-phase liquid chromatography.

Figure 9. Molar mass distribution of pine kraft lignin (fractions 1-IV in Figure 8).

Every year the U.S paper industry produces over 33 million metric tons of kraft lignin (1). Most of this biomass is burned as fuel but small amounts are used as binders, asphalt additives, or cement additives. Larger fractions of this waste would be used in other industrial or commercial processes if an economical way existed to convert lignin into a marketable product with sufficient profit margin to compensate for the loss of the fuel. 

We observed in a previous investigation of PU s derived from a kraft lignin (KL)-polyether triol-diphenylmetane diisocyanate (MDI) system (Yoshida, H. Morck, R. Kringstad, K. P. Hatakeyama, H., submitted to J. Appl Polym. Set.) that KL fractions of low molecular weight yielded more flexible and less crosslinked PU s than the medium and high molecular weight KL fractions. This was attributed to the lower functionality of the low molecular weight KL fractions. 

Kraft Lignin. A softwood kraft lignin (KL) was isolated from a partly evaporated, industrial kraft black liquor by precipitation through the addition of dilute sulfuric acid as described elsewhere (7). The lignin was thereafter fractionated by successive extraction with organic solvents (7). The KL fraction used in the present investigation was the second of five fractions obtained (propanol soluble - methylene chloride insoluble). 

Middle molecular weight fraction of kraft lignin Propylene oxide triol with a M , of 600 C 194... 

Two lignin preparations were used in these experiments, milled wood spruce lignin (M.W.L.) prepared according to Bjorkman (< ), and a kraft pine lignin fraction. Both preparations were characterized earlier (M.W.L., (/, 8) kraft lignin (26)). Some pertinent data are given in Table I. 

Figure 2. Oxidation of kraft lignin fractions in dilute aqueous alkali dissolved in 0.2N NaOH) 2 mole equivalents alkali based on MW 1000) 70°C.

Kraft Lignin Fractions. 5 grams were dissolved in 50 ml. 0.2N NaOH, corresponding to 2 mole equivalents alkali per 1000 grams lignin. 

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