Lignin

History: It is an organic substance that binds fibers and cells. Straw, plants, etc, for example. It is the second most abundant carbon source on earth. cellulose is #1. On average 45 million tons are produced each year. It is not scientifically possible to define the structure of it. Further, there are two categories: sulphur free and sulphur bearing. The sulphur free ones are not open for public purchase.

Lignin plays a crucial part in conducting water in [|plant] stems.



complex, irregular aromatic containing bipolymer cross-links the cellulose polymer chain; cross-linking produces a stiffer polymer Lignin is mainly derived form wood, part of the cell wall of plants and some types of algea Biological function of Lignin is that it fills the spaces between cell walls of plants

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Environmental Significance : Highly lignified wood is durable and therefore a good raw material for many applications. It is also an excellent fuel, since lignin yields more energy when burned than cellulose. Mechanical, or high-yield pulp used to make newsprint contains most of the lignin originally present in the wood. This lignin is responsible for newsprint's yellowing with age. Lignin must be removed from the pulp before high-quality bleached paper can be manufactured from it. In sulfite pulping, lignin is removed from wood pulp as sulfonates. These lignosulfonates have several uses:
 * Dispersants in high performance cement applications, water treatment formulations and textile dyes
 * Additives in specialty oil field applications and agricultural chemicals
 * Raw materials for several chemicals, such as vanillin, DMSO, ethanol, xylitol sugar, and humic acid
 * Environmentally sustainable dust suppression agent for roads

Structure
Lignin is a cross-linked racemic macromolecule with molecular masses in excess of 10,000 [|u]. It is relatively hydrophobic and aromatic in nature. The degree of polymerisation in nature is difficult to measure, since it is fragmented during extraction and the molecule consists of various types of substructures that appear to repeat in a haphazard manner. Different types of lignin have been described depending on the means of isolation. There are three monolignol monomers, methoxylated to various degrees: //p//-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. These lignols are incorporated into lignin in the form of the phenylpropanoids //p//-hydroxyphenyl (H), guaiacyl (G), and syringyl (S), respectively. Gymnosperms have a lignin that consists almost entirely of G with small quantities of H. That of dicotyledonous angiosperms is more often than not a mixture of G and S (with very little H), and monocotyledonous lignin is a mixture of all three Many grasses have mostly G, while some palms have mainly S. All lignins contain small amounts of incomplete or modified monolignols, and other monomers are prominent in non-woody plants. Thioglycolysis is an analytical technique for lignin quantitation. Lignin structure can also be studied by computational simulation
 * Fig. 1**: An example of a possible lignin structure
 * Fig. 2**: A small piece of lignin polymer
 * Fig. 3**: The three common monolignols: paracoumaryl alcohol (1), coniferyl alcohol (2) and sinapyl alcohol (3)
 * Fig. 4**: Polymerisation of coniferyl alcohol to lignin. The reaction has two alternative routes catalysed by two different oxidative enzymes, peroxidases or oxidases.