This study focuses on the separation and characterisation of components from agricultural residues by novel methods. Four environmentally friendly methods were investigated for separation of hemicelluloses, cellulose and lignin as follows:
(1) Alkaline peroxide extraction, which released about 80% of original hemicelluloses and lignin from dewaxed oil palm frond fibre, maize stems, and barley, wheat, rice and rye straws, and all the hemicellulosic preparations are much lighter in color as compared to the hemicelluloses extracted with alkali in the absence of peroxide; (2) Nitric-acetic
acids method, in which the treatment with 80% acetic acid and 8.5% nitric acid as a catalyst at 125°C for 20 min resulted in over 96% original hemicelluloses and approximately 98% original lignin degradation, yielding the cellulose (37 .5%, dry
material weight) approaching 96% purity; (3) Organosolv treatment, in which a formic acid/acetic acid/water (30/60/10, v/v/v) system and cyanamide activated hydrogen peroxide bleaching were found to be the most effective in removal of hemicelluloses and delignification from the straw and did not have any undesirable effects on cellulose properties such as its intrinsic viscosity; (4) Steam explosion treatment. The processing of wheat straw by steam explosion pre-treatment and sequential alkaline peroxide posttreatment allowed the fractionation of the three main polymers present in the
lignocellulosic matrix with reasonable yields and purity, and appeared to be a promising technique for practical application of this by-product.
Original lignin and hemicelluloses were sequentially extracted with high yield/purity, using acidic dioxane/water solution and dimethyl sulfoxide, from ball-milled wheat straw. The acidic dioxane lignin fraction was distinguished by high P-O-4 structures and by low amounts of condensed units (P-5, 5-5', and P-1). Hemicelluloses contained arabinoxylans as the major polysaccharides, which were substituted by a-Larabinofuranose, 4-O-methylglucuronic acid, acetyl group (DS = 0.1), and xylose at 0-3 and/or 0-2 of xylans. It was found that arabinoxylans formed cross-links with lignins via ferulates by ether form, glucuronic acid by ester form, and arabinose/xylose by both ether form and glycosidic bonds, respectively, in the cell walls of wheat straw. Diferulates were also incorporated into cross-links between lignin and hemicelluloses as
well as lignification of wheat straw cell walls.
Study on modification of hemicelluloses showed that succinoylation of hemicelluloses with succinic anhydride by using NBS as a catalyst in DMF/LiCl system was an efficient chemical modification for obtaining the polymers with carboxylic groups. The total degree of substitution can be simply controlled by the reaction conditions. The preferred reaction parameters that resulted in the highest degree of substitution were as follows: 6: 1 reactant molar ratio, 50°C, 5 h, 2.0 % NBS.