1. Lignocellulosic materials

Lignocellulose is a renewable organic material and is the major structural component of all plants. Lignocellulosic wastes are produced in large amounts by many industries including those of forestry, pulp and paper, agriculture, and food. Such wastes are also present in mu-nicipal solid waste (MSW), and animal wastes [1-6]. These potentially valuable materials were treated as waste in many countries in the past, and still are today in some developing counties, which raises many environmental concerns [7,8]. Lignocellulose consists of three major compo-nents: cellulose, hemicellulose and lignin. In addition, small amounts of other materials such as ash, proteins and pectin can be found in lig-nocellulosic residues in varying degrees based on the source [9]. Cellulose, the major constitu-ent of all plant material and the most abundant organic molecule on Earth, is a linear biopoly-mer consisting of anhydroglucopyranose-molecules (glucose) connected by β-1,4-glycosidic bonds. Coupling of adjacent cellulose chains via hydrogen bonds, hydrophobic interac-tions and Van der Waal’s forces results in the parallel alignment of crystalline structures known as microfibrils [10]. Unlike cellulose, hemicelluloses are heterogeneous polymers of pentoses (including xylose and arabinose), hex-oses (mainly mannose, less glucose and galac-tose) and sugar acids. The highly variable com-position of hemicelluloses is dependent on its plant source [11,12]. Lignin, the second-most abundant biopolymer on Earth and a heteroge-neous polymer in lignocellulosic residues, is the only naturally synthesised polymer with an aro-matic backbone. It generally contains three pre-cursor aromatic alcohols including coniferyl al-cohol, sinapyl and p-coumaryl [13]. These pre-cursors form the guaiacyl- (G), syringyl- (S) and p-hydroxyphenyl (H) subunits in the lignin mole-cule, respectively [14]. The subunits ratio, and consequently, the lignin composition, varie