Lignin fractions

The conclusion that solid-state spectra provide evidence for a lignin-carbohydrate complex is of special interest. Solid-state spectra of lignin fractions obtained by ball milling and extraction with dimethyl sulfoxide exhibit carbohydrate signals and vice... 

The use of the lignin fraction is much more cumbersome currently the best-known chemical of a real commercial importance is vanillin, which is obtained by oxidation of the black liquor. Another example is a product called spray-dried lignosulfonate (as sodium salt) obtained from the older, acidic sulfite pulping process. It is sold as a commercial product primarily as a concrete additive for enhanced strength. Since the cement industry is one of the big contributors of carbon dioxide emissions (due to the production of calcium oxide from calcium carbonate), the use of this renewable, wood-derived product not only is fossil-carbon neutral in itself but also reduces carbon dioxide emission due to the diminished need for cement in large infrastructures made of concrete. 

Finally, in order to establish unequivocally the identity of the native and residual lignin of white Scots pine wood, the sound wood was first extracted with ethyl alcohol to remove the native lignin fraction. The extracted wood was then decayed by means of the brown rot fungi,... 

Comparisons made between unpurified spruce milled-wood lignin fractions and unfractionated poljrmers made from coniferjd alcohol alone already revealed the great qualitative similarity between natural and biosynthetically duplicated lignins [see, for example, K. Freudenberg in 94), pp, 125—126]. When a purified lignin fraction is compared tvith an identical fraction made from a mixture of all three -coumaryl alcohols, the resemblance is of course much greater. 

Whatman filter paper 4 were examined for the distribution of lignin fractions (oligolignols), produced during the pretreatment. The results given in Table 4 at 0 time (uninoculated) indicated that the solubilized lignin just after pretreatment and prior to its fermentation with P. sajor-caju contained oligolignols of different MW. 

L.) was also found, and was readily distinguishable by a brittleness of the culm which appeared only after maturity of the plant. This mutant had a lower cellulose content, and this difference was assumed to be related to the brittleness of the culm (24). Significant differences were also found in the extractability of the lignin fractions and associated phenolic acids (25-26), suggesting that lignin formation was also affected. 

Figure 5. Composite MWD diagram showing the calculated distributions of four of the five master fractions obtained from preparative chromatography of organosolv aspen lignin (fraction number 4 to 1 from left to right). The Mw values for the master fractions from left to right are 1,110, 1,310, 2,420, and 8,050, respectively. The insert shows the elution profile of organosolv aspen lignin from the YMC preparative /z-Styragel column (5 x 200 cm). The 30 fractions collected were pooled into the five master fractions shown.

Table IV. Mn of Black Cottonwood Alkali Lignin Fractions in Different Solvents and at Several Temperatures...

In order to overcome the solubility limitation typical of lignin fractions, chemical modifications have been envisaged. Obviously only those methods giving nearly quantitative recovery are adequate for the purpose of measuring Mn- Table V shows results related to the acetylation technique where only a slight increase in M is observed as expected. 

Table V. Mn of Spruce Alkali Lignin Fractions Before and After Acetylation (in 2-methoxyethanol at 60°C)...

Tables VI and VII give results corresponding to two series of lignin fractions obtained with a flow-through reactor (3). (The units for dn/dc and A2 are respectively ml.g-1 and mole.ml.g-2). These results show that LALLS allows the determination of low Mw values. The dn/dc values differ from sample to sample but vary only slightly for a given set of fractions. The second virial coefficient exhibits no definite trend. Negative values indicate perhaps some association effects but light scattering alone is not sufficient to ascertain this point.

Table VI. LALLS Results on Acidic Organosolv Lignin Fractions from Black Cottonwood...

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

Although the use of lignin as an additive to polyurethanes is not new (15-20), even the most judicious selection of lignin isolation or modification schemes has not allowed researchers to overcome the incorporation limit of 25 to 40 weight percent of lignin as an active component in polyurethanes. Solvent fractionation allows for the isolation of lignin fractions with well defined solubilities and functionalities (21,22). Both of these features are critical for the practical inclusion of lignin into liquid polyol systems. 

Nitrogen values more than triple on adding ammonium nitrate. The mor the straw is rotted, the less nitrogen can be hydrolyzed with hydrochloric acid. A part of the nitrogen in the lignin fractions is fixed as a-amino nitrogen. The quantity decreases from 60% of total nitrogen content in fresh straw to about 20% in rotted straw. A remarkable decrease could be observed for the methoxyl content. This fact can be explained by an enzymatic demethylation process. 

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