lignin


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Related to lignin: hemicellulose

lignin

(lĭg`nĭn), a highly polymerized and complex chemical compound especially common in woody plants. The cellulose walls of the wood become impregnated with lignin, a process called lignification, which greatly increases the strength and hardness of the cell and gives the necessary rigidity to the tree. It is essential to woody plants in order that they stand erect.

Lignin

 

a complex polymeric compound contained in the cells of vascular plants. It is one of the lining substances of the sheath of plant cells. The deposition of lignin in the cell membranes produces lignification of the cells and increases their strength. The wood of deciduous trees contains 20–30 percent lignin; that of coniferous varieties, up to 50 percent. Lignin has not been found in lower plants (algae and fungi or mosses). The ultrastructure of lignified cell membranes may be compared to the structure of reinforced concrete: the microfibrils of cellulose correspond in their properties to the reinforcement rods, and the lignin, which has high compressive strength, corresponds to the concrete. The chemical composition of lignin has not been conclusively established. The lignin molecule consists of the products of polymerization of aromatic alcohols, and the basic monomer is coniferyl alcohol:

Lignin is an amorphous substance, yellowish brown in color; it is insoluble in water and organic solvents. It is stained by basic dyes and yields color reactions characteristic of phenols. The biosynthesis of lignin has not been completely studied. Its precursor is shikimic acid, which is also the case for a number of other aromatic compounds in plants. The formation of lignin takes place through the following basic stages: shikimic acid phenylalanine → cinnamic acid → ferulic acid → coniferyl alcohol → lignin.

REFERENCES

Kretovich, V. L. Osnovy biokhimii rastenii, 5th ed. Moscow, 1971.
Frey-Wyssling, A., and K. Mühlethaler. Ul’trastruktura rastitel’noi kletki. Moscow, 1968. (Translated from English.)
Biokhimiia fenol’nykh soedinenii. Edited by J. Harborne. Moscow, 1968. (Translated from English.)
N. D. GABRIELIAN
Lignin is produced in industry as a by-product of the production of cellulose (sulfate lignin, ligninsulfonic acids) and the hydrolysis of plant materials (hydrolytic lignin). Lignin is a valuable chemical raw material; as yet, far from complete use is being made of it. Sulfate lignin can be used as a strengthener in synthetic rubber and as a plasticizer in ceramic production. Ligninsulfonic acids are used as inexpensive strengtheners and binders in foundry work and as additives to the charge in cement production. Hydrolytic lignin is used in the production of lignite, active carbon, and porous brick and for the evolution of nitrolignin, which decreases the viscosity of clay mortars used in drilling.

REFERENCES

Nikitin, N. I. Khimiia drevesiny i tselliulozy. Moscow-Leningrad, 1962.
Brauns, F. E., and D. A. Brauns. Khimiia lignina. Moscow, 1964. (Translated from English.)
Khimiia drevesiny. Edited by B. L. Browning. Moscow, 1967. (Translated from English.)
A. N. KISLITSYN
In medicine, “lignin” or “wood wool” is the name for very thin corrugated sheets produced from the wood of coniferous trees by mechanical and chemical processing and used as surgical dressings.

lignin

[′lig·nən]
(biochemistry)
A substance that together with cellulose forms the woody cell walls of plants and cements them together.
(materials)
A colorless to brown substance removed from paper-pulp sulfite liquor.

lignin

1. An organic substance in wood that, with celluloses, forms the principal constituent of wood tissue.
2. A crystalline product recovered from paper pulp; used in the manufacture of plastics, as a binder in wood chipboard, and for anticorrosive coatings.
References in periodicals archive ?
However, after reproducing starch: lignin films according to the process of Vengal & Srikumar [1] it was found that lignin was not present in the starch: lignin films.
All the three components present in lignocellolosic biomass (bagasse) forms a very complex structure whereas lignin consisting of monomeric subunit act as a cement to hold in place to cellulose fibrils and hemicellilose backbone, resulting in a strong and impermeable structure.
The extracted sample was then subjected to analysis of its [alpha]- cellulose, klason lignin and holo cellulose content.
Currently, AST's Organosolv lignin is being used by several research teams at various universities, including University of Washington, Mississippi State University, University of Wisconsin, University of Minnesota, and Washington State University, for various research projects.
It will now act as the non-exclusive sales agent for Sappi Biotech's Hansa lignin products, manufactured at the Sappi Tugela Mill in both liquid and powder formats.
Lignin: After the removal of cellulose,the remaining residue contained lignin and silica.
Kalliola concludes, "The promising results of applying the alkali-02 oxidized lignin for concrete plasticizing encourage continuing the investigations.
Annually around 20 billion tons of lignin are produced.
To provide a more comprehensive and consistent account than most multi-authored books, these authors planned and wrote a reference on lignin and lignans as renewable sources of chemicals.
Particularly, the conjugated units in lignin were probably related to oxidation at [+ or -]-position of side-chain of lignin during hot press.