**2.2 Lignin**

Lignin is the second most common organic polymer. About 50 million tons of lignin is produced worldwide annually as residue in paper production processes. It consists of methoxylated phenyl propane structures. The biosynthesis of complex structure of lignin is thought to involve the polymerization of three primary monomers, monolignols: p-coumaryl, coniferyl, and sinapyl alcohols (Figure 3), which are linked together by different ether and carbon-carbon bonds forming a three-dimensional network. The monolignols are present in the form of p-hydroxylphenol, guaiacyl and syringyl residues in lignin structure. Lignin is non-toxic, inexpensive and abundantly available (Sena-Martins et al.; 2008). It is hydrophoebic, smaller in size and forms stable mixtures (Park et al.; 2008). It is used in dye dispersants, dispersants for crop protection products, to produce low molecular weight chemicals like dimethyl sulphoxide. It is also used as filler in inks, varnishes and paints (Belgacem et al., 2003) and as a dispersing agent in concrete, as binders for wood composites, chelating agents, for treating porous materials, in coatings and paintings (Stewart , 2008; Park et al., 2008; Mulder et al., 2011).
