Lignin origin

The values allow a rough characterization of the DOM according to its genesis— for example, whether it is more allochtonous (plant and lignin origin) or more autochtonous (algae- and aquatic microorganisms-derived). 

Considering the ligno-holocellulosic composition of wood, it is not surprising that the liquor is divisible into a carbohydrate (neutral) fraction and an aromatic (acidic) fraction, the former of holocellulosic origin and the latter of lignin origin. 

Most of the research in the area of chemical modification of wood was conducted for improving either its dimensional stability or its biological resistance. Wood is made up primarily of cellulose, hemicellulose, and lignin. Originally, chemical modification of wood was a chemical reaction between some reactive part of a wood component and a simple chemical reagent to form a covalent bond between the two [1]. The most abundant reactive sites in wood are the hydroxyl groups. The major important types of covalent bonds formed by chemical modification of wood are ethers and esters. The treated wood must still possess the desirable properties of wood. Past research work on the chemical modification of wood was reviewed extensively in 1975 [1] and 1984 [2] by Rowell. 

Composition of Lignin Origin of the Monomeric Units Polymerization of Lignin Lignans Biosynthesis Biological Activity Neolignans... 

After the precipitation stage, the final powder from twin screw extmsion (92% dry matter), contains 91% organic matter. The global yield of this process is about 24 % of the potential in hemicelliiloses of wheat bran, if it is considered that arabinoxylans represents 60 % organic matter 26% protein and 5.3% lignin (originating from straw) (table 111). These results should be compared with extraction conditions in the stirred reactor, where the best results are obtained with a molar soda and a L/S ratio of 50. The chemical charge is reduced by a factor of 14 and the L/S ratio by a factor of 15 when twin-screw extruder is used. 

Mechanical pulps contain substantially all the lignin originally present in the wood. Considerable mechanical treatment is required to separate and prepare the fibers from wood (135). 

Paper pulp used to make newsprint contains most of the lignin originally present in the wood, together with the cellulose. The oxidation of lignin is responsible for newsprint s yellowing with age (Figure 6.3). 

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