Types of Lignin

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FIGURE 6.1. Wood and its composition (Hanshekar, H. Fiechter, A. Advances in Bio-chemicai Engineering/Biotechnology, 27 (1983) 119-178. 

FIGURE 6.2. SEM images in hardwoods (oak, left) and softwoods (pine, right) (Wikimedia Commons). 

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In solution, lignin is most conveniendy analyzed quaUtatively and quantitatively by uv spectroscopy. Typical absorptivity values, D, at 280 nm for milled wood (MW) lignins and other types of lignins are Hsted ia Table 4. These values are used for quantitative determination of the lignins ia suitable solvents. 

Fig. 2.2 A. Chemical structure of the three types of lignin monomer units H, p-hydroxyphenyl- G, guaiacyl and S, syringyl. Note the methyl groups (boxed) in the methoxy moieties of the G and S monomers. B. Pie chart showing the proportions of pine xylem ESTs that putatively encode enzymes of Ci metabolism, glycolysis, and the TCA cycle.

Symbol of Sample Type of Lignin Acceptor Type Reaction Time, h mmol NPCI2 Acceptor Yield of Product3, g P % S Cl... 

Symbol of Sample Symbol of Initial Product Type of Lignin Used Type of Modifying Compound Yield of Product3, g Chemical Content. P S % Cl Infrared Frequency of P-N Unit, crn l... 

Symbol of Sample Type of lignin P Content, X Temperature of Maximum Rate of Mass Loss, °C Range of Temp. of Max. Rate of Mass Loss, °C 100°C Percentage of Mass Loss at Different TemDeratures 200°C 300°C 400°C 500°C 600°C... 

Sample P Content, Type of Lignins % Temperature kJ/mol Range, °C... 

Application of several types of lignin sulfonates as carriers in connection with reactive herbicides (21-23) permits the development of effective controlled release (CR) preparations. The properties of chemically bound lignin 2,4-D-based herbicides are summarized in Table XI. 

Guaiacylglycerol-/3-coniferyl ether is a dimeric decomposition product of coniferous lignin dehydrodivanillin may be also formed by dimerization of vanillin after formation from lignin. Among the lignin decomposition products are mono-, di- and triphenol derivatives which are derived from the different types of lignin of needle trees, deciduous trees, or graminees. 

The most significant conclusion that may be drawn from these results is that palladium-charcoal exhibits similar catalytic properties as does Raney nickel if used under similar conditions. The same types of lignin hydrogenolysis products are obtained, and as before the major fraction under neutral conditions is the phenylpropanol derivative, dihydro-coniferyl alcohol. With a minimum temperature ca. 150°C. required for any reaction to occur and an optimum temperature ca. 195°C. for maxi-... 

Fig. 4.1.8. Triangular coordinate system displaying the three types of lignin (C, GS, and HGS) in realtion to the composition of the lignins (H, G, and S units expressed as mol % and the methoxyl contents as the number/100 phenylpropane units). According to Faix 1991...

The value of kML is likely to be in the vicinity of 1.7 for mature normal softwoods (Saka et al. 1982). However, compression (Westermark 1985) and juvenile woods (Donaldson and Ryan 1987) are reported to have a different correction factor. This may be due to the fact that such abnormal softwoods contain different types of lignins in both the secondary wall and middle lamella regions. 

Note 2. The absorptivity values depend on the type of lignin and solvent. It is important to use an appropriate value for the lignin sample under study. The values listed in Table 5.1.3 are for general reference only. 

Benzaldehydes (lg, 2g, 3g) are liberated in the same way but originate in part from other sources (cf. Fig. 6.1.2). The presence of benzoic acids (lh, 2h, 3h) and ferulic acid (1 j) can be explained by hydrolysis of ether or ester linkages. p-Flydroxybenzoic and p-coumaric acids (3h and 3j, respectively) are attached to certain types of lignins by ester linkages and their occurrence in the acidolysis mixtures is, in these cases, at least primarily due to the hydrolysis of these linkages. 

Obst JR, Sachs IB, Kuster TA (1988) The quantity and type of lignin in tyloses of bur oak (Quercus macroscarpa) Holzforschung 42 229-231... 

Periodate lignin may be another type of lignin preparation representative of whole lignin in wood [46]. Wood meal suspending in water with a small amount of acetic acid is treated with sodium metaperiodate at room temperature, by which vic-glycol structures in carbohydrates are cleaved to give aldehydes. After the subsequent reduction of aldehydes to alcohols, carbohydrates are readily hydrolyzed even at room temperature in a mild acid condi-... 

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