The fractional characterisation of polysaccharides and lignin components in alkaline treated and atmospheric refined wheat straw

Abstract

Same amounts of lignin (20%) and hemicelluloses (50%) were dissolved in the chosen two treatment regimes (pretreatment and alkaline refining, PTAR, and atmospheric refining and posttreatment, NRPT). Nearly all of the p-coumaric acid and 65% ferulic acid were released in the PTAR process, while only 52% p-coumaric acid and 32% ferulic acid were released during the NRPT regime. No evident direct relationship between the solubilisation of lignin and release of ferulic/p-coumaric acid was observed. Xylose was found to be the major sugar constituent in all the hemicellulose fractions and the hydrolysates of the PTAR or 1.5% NaOH posttreatment after neutral refining. The predominant freecomponents of the hydrolysates in the alkali-labile monomers of lignin were found to be ferulic and p-coumaric acid, which together comprised 80–90% of the total free phenolic acids and aldehydes liberated in the alkaline medium. The major phenolic products of the alkaline nitrobenzene oxidation of lignin from the residues of PTAR or NRPT were syringaldehyde and vanillin, while p-hydroxybenzoic acid, vanillic and syringic acid appeared as major phenolic monomers in the oxidised mixture of residual lignin in extracted hemicelluloses and cellulose.