Hardwoods lignin

Table 1. Types and Frequencies of Interunitary Linkages in Softwood and Hardwood Lignins (Number of Linkages per 100 Units)...

Akiyama, T. Goto, H. Nawawi, D. S. Syafii, W. Matsumoto, Y. Meshitsuka, G. Erythro/threo ratio of P-O-4-structures as an important structural characteristic of lignin. Part 4 variation in the erythro/threo ratio in softwood and hardwood lignins and its relation to syringyl/guaiacyl ratio. Holzforschung 2005, 59, 276-281. 

Table 7. Comparison of the Native and Enzymatically Liberated Hardwood Lignins (64)...

It weis found that hardwood lignins yielded both guaiacyl and syringyl units on oxidation, whereas softwood lignins yielded only guaiacyl units. Hibbert and co-workers (20), (21) distinguished perennial plant lignins... 

Stamm, Seme and Harris 104) in 4932 indicated that hardwood lignins gave a maximum absorption peak at 274-276 mp, and softwood lignins gave maxima at 284-285 mp. 

Figure 3.2 The main linkage types in softwood and hardwood lignin.

Table 3.1 Frequency of occurrence of bond, types A-1 (see Figure 3.2) in softwood and hardwood lignin.

Hardwoods appear to have a much higher content of such aryl-glycerol-p,y-diaryl ethers because of the more restricted possibilities for condensations in the aromatic ring of sinapyl-type units owing to their two methoxyl groups. This is reflected in the greater susceptibility of hardwood lignins to mild hydrolysis (see Section I). 

The initially formed phenoxy radicals randomly combine to form a variety of bonds. Scheme 8.20 shows major linkages between units in softwood lignin. Hardwood lignins are similar, but contain varying quantities of the 3,5-dimethoxylated aromatic rings. 

This study describes the application of differential vis-cometry as a GPC detector to the problem of determining molecular weight distributions of acetylated hardwood lignins in tetrahydrofuran. Molecular weight distributions of ball-milled, organosolv, alkali-extracted/mild acid hydrolyzed, and alkali-extracted/steam exploded aspen lignins were estimated using universal calibration. 

This study reports the first application of universal calibration via HPSEC-DV to four acetylated hardwood lignins obtained from aspen (Pop-ulus tremuloides) wood meal by ball milling and solvent extraction steam explosion followed by alkaline extraction organosolv pulping followed by water extraction of the associated sugars and dilute sulfuric acid hydrolysis followed by sodium hydroxide extraction. 

When a new method is reported for synthesis of polymers, in a short time it is also tried on lignins. New lignin-based raw materials are also constantly appearing the use of steam exploded hardwood lignin for making plywood adhesives has recently been explored by Gardner and Sellers (64) and found promising in this intensively competitive area. 

Thermogravimetric weight loss for the OSL is similar to that of kraft lignin. Except for a slightly elevated methoxyl content, the NMR and degradation results in Table II are within the expected range for a hardwood lignin. 

This might be explained with failure to crosslink sufficiently. Sano et al. have also reported that phenolysis of hardwood lignin sulfonates enhances adhesion properties (22). It is thus clearly demonstrated that the introduction of phenol into lignin improves adhesion properties. 

The hardwood lignin model 13 was reacted in acidic aqueous dioxane to afford dimers, trimers, tetramers or higher oligomers (Fig. 4A). 

The etherified hardwood lignin model II reacted at a similar rate as the phenolic model indicating the etherification of the phenolic group has a small effect on the reaction rate. When this reaction was repeated at 55°C with an excess formaldehyde, some mefa-hydroxymethylated products were obtained (Fig. 4B). 

The soda/AQ hardwood lignin is constituted of both guaiacyl (2) and syringylpropanoid (3) units, of which the former have been condensed extensively during pulping (17). This is indicated by the low number of unsubstituted 5-positions (Table II). 

Figure 1 shows the variation by C-13 NMR in the lignin samples (a) EXWL (b) EXBWL and a kraft hardwood lignin (c) TomL. Partial C-13 spectra of lignin acetates showing the carbonyl region are illustrated in Figure 2. Molecular weight measurements were determined using the size exclusion chromatograms shown in Figure 3. The data are summarized in Table I.

This research was undertaken to study aqueous alkaline reactions of monomeric structures, similar to polymeric wood constituents, from which color would be formed. Since hardwood pulps were of the greatest immediate interest, the reaction of syringyl alcohol, representing the hardwood lignin structure, in aqueous alkaline solution at room temperature has been studied extensively up to the present time, but the reactions of vanillyl alcohol and a-methylvanillyl alcohol, representing the softwood lignin structure, have also been studied to some extent under the same reaction conditions. 

Color Characteristics of the Reaction Mixtures. Initial experiments in air involving the reactions of syringyl alcohol, vanillyl alcohol, and a-methylvanillyl alcohol with alkali showed both visually and spectro-photometrically that the reaction mixture of syringyl alcohol, the hardwood lignin model, and alkali was more intensely colored than either of the reaction mixtures of the guaiacyl compounds and alkali. 

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