**2.2 Hemicellulose**

Hemicellulose is the second highest heterogeneous polymer comprises of various sugars molecules i.e. galactans, glucuronoxylan, glucomannan, and low amounts of other polysaccharides. The other sugars molecules are glucans, xylans, galactans, arabinans and mannans exist in the hemicellulose molecule. The glucans, galactans, arabinans and mannans are linked togather with β-1,4 linked backbone. In the hemicellulose polymer, xylan contains 1–4 linkages of xylopyranosyl units attached with α-4-O-methyl-D-glucuronopyranosyl branch chain of glucose connected to other xylose carbon sugar monomers [23]. Notably at ordinary temperature, the hemicellulose is also insoluble in water. It is soluble in acidic solution, and the solubility increase with concnetration of acid and temperature. Naturally, hemicellulose has various size, shape, low polymerization in structure and is not crystalline owing acetyl groups in the polymer. The hemicellulose make a strong backbon in plant biomass by crosslinkg with non-covalent bonds cellulose micro-fibril chains [23].
