Lignin isolation

Table 3. Yields of Lignin Isolated from Sound and Decayed White Scots Pine (98).

Table 4. Comparison of Lignins Isolated from Sound and from Decayed (Lenlinus lepideus) White Scots Pine (79).

Thus, most of the degradative reactions of polymeric lignins suggested previously by the analysis of decayed lignin isolated from decayed wood by white-rot fungi were catalyzed by lignin peroxidase. 

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. 

The lignin isolated from white birch after steaming was ozonized. The ozonized lignin was soluble in epoxy resins at 120°C. It was also found that free carboxyl groups (introduced by ozonization) react with epoxide only by heating. Previous developmental work on the blending of lignin with epoxy resin has been reported by Ball and his co-workers (3). They synthesized... 

Figure 4. Gel permeation chromatograms of lignin isolated from birch and its ozonized lignins. Sample 0 untreated lignin 1 ozonized lignin No. 1 2 ozonized lignin No. 2 3 ozonized lignin No. 3.

The results of elementary analyses of lignin isolated from fresh (2, 3) and rotted straw and data for different types of coals and humic acids isolated from these and from chernozem are shown in Table III to illustrate further steps of coalification. The following points should be noted ... 

Searching for evidence on the nature of the bond, we conducted a spectroscopic study of lignins isolated from wood by ethanolysis (P) and found, as expected, that 0-keto groups did not appear in the lignins until... 

In this work we have, in a preliminary way, extracted periodate lignin by the continuous dioxane-dimethoxypropane-HCl procedure and obtained only about 11% of a soluble material which had the same infrared spectral characteristics as the lignin isolated from wood. The gel-like residue showed evidence of having undergone the same reaction but remained insoluble. This seemed to indicate that the reaction alone was not enough to confer solubility. 

Despite the anomalies, one key point does emerge when this work is compared with alcoholysis studies. Ethanolysis lignin has a much higher ethoxyl content than diethoxypropane lignin (spruce ethanolysis lignin contains 14.6% ethoxy (J, < )), and this is additional proof that lignin isolated by acetals is different from lignin isolated by alcohols. 

Chemical Shift Values for Hydrol Lignins. Lignins isolated by hydrogenolysis contain structural features not present initially, and it was necessary to determine the values for chemical shifts for the new types of protons. This was done using 8 values from the literature (/, 2, 5) from spectra of model compounds prepared in this study of the guaiacyl and syringyl type, substituted with Ci, C2, and C3 hydrocarbon side chains,... 

Potutkin and associates (14) report changes in the lignin isolated from hot-pressed particleboards compared to that from raw birchwood from which the boards were made. Lignin isolated from boards pressed at 180C showed increased infrared absorption at 800 cirri and 1300-1500 cm"1, which is interpreted to indicate condensation and demethoxylation, respectively. An appearance of a new band at 1370 cm""1 is assigned to aryl-alkyl ether bonds formed by reactions of lignin with other wood breakdown products to yield pseudolignin. 

Extraction of lignocellulosic materials with dioxane has been used for quite some time as a method for lignin isolation at atmospheric pressure (1) or, as recently reported, at high pressure and with supercritical C02 mixtures (2-5). In this case, it was possible to extract from wood lignin oligomers with a low degree of chemical modification, hemicelluloses were also depolymerized and extracted, but cellulose remained without significant mass losses. 

Lee ZZ, Meshitsuka G, Cho NS, Nakano J (1981) Characteristics of milled wood lignins isolated with different milling times Mokuzai Gakkaishi 27 671-677... 

All residual lignins isolated by the enzymatic method are contaminated with enzymes to varying extents. This is especially true for the residual lignins isolated from semi-bleached pulps (Jiang et al. 1987). The contamination can be largely removed by the following procedure ... 

Contamination by enzymes is a main drawback of the procedure, especially in the isolation of residual lignin from semi-bleached pulps. The contaminants cannot be completely removed by the purification procedure described above. Consequently, it is important to determine the nitrogen content of the residual lignin. Typical values of nitrogen content are 2.5% and 7.3% before purification and 0.6% and 2.3% after purification for residual lignins isolated from an unbleached and a semi-bleached southern pine kraft pulp, respectively (Jiang et al. 1987). 

Jiang J-E, Chang H-m, Bhattacharjee SS, Kwoh DLW (1987) Characterization of residual lignins isolated from unbleached and semi-bleached softwood kraft pulps. J Wood Chem Techno 1 7 81-96... 

Bartuska VJ, Maciel GE, Bolkers HI, Fleming Bl (1980) Structural studies of lignin isolation procedures by nC NMR Holzforschung 34 214-217 Dixon WT, Schaefer J, Sefcik MD, Stejskal EO, McKay RA (1981) Quantitative chemical composition of materials such as humic soils, lignins, and coals by high-resolution carbon 13 NMR J Magn Reson 45 173-176... 

Figure 6.4.4 and Table 6.4.2 provide gas chromatographic and gas chromatographic-mass spectral information relating to the thioacidolysis products derived from an extractive-free wheat straw and the corresponding lignin isolated by alkali (Scalbert 1984). 

---