Comparative studies of ash-AQ and soda-AQ lignins from oil palm EFB fibre

Three ash-AQ and three soda-AQ lignin preparations were obtained from the corresponding supernatants of black liquors after isolation of the polysaccharide degradation products and ash by precipitation at pH 3.0, 2.0, and 1.5, respectively. A comparison study of the lignin preparations was made in terms of yield, purity, content of associated polysaccharides, molecular weight, structural feature, and thermal stability. The yield of ash-AQ and soda-AQ lignins increased from 1.13 to 1.19 and 0.98 to 1.06 with decreasing precipitation pH from 3.0 to 1.5, respectively. Both of ash-AQ and soda-AQ lignins showed approximately molecular weights of M¯w, ranging between 3,580 and 3,930 g mol-1, and had a similarly structural features and almost same physico-chemical properties except for the more condensed structure in ash-AQ lignin preparations. The results obtained by alkaline nitrobenzene oxidation revealed that all the lignin preparations composed of large amounts of non-condensed syringyl units and small amounts of non-condensed guaiacyl units together with minor quantities of p-hydroxyphenyl units.