Structural characteristics of lignin extracted from Jordanian olive cake using different fractionation conditions

The chemical structure and properties of lignin-derived from lignocellulosic olive mill waste (Jeft) were investigated. Alkali and dioxane lignins were evaluated regarding the achieved high delignification and high purity of the extracted lignins. The results declared that the major constituents of olive cake are extractives, cellulose, hemicelluloses, and lignin. Furthermore, the olive cake has low relative crystallinity and the ash content does not exceed 2%. The yields of Alkali and Dioxane lignins were 15.3 +/- 0.34, and 1.4 +/- 0.43%, respectively. For the elucidation of structural features of lignin molecules, lignins samples were also subjected to UV spectroscopy and (HNMR)-H-1 analysis. The analysis showed that the treatment under acidic condition did not significantly attack the beta-aryl ether structure (beta-O-4), while the alkali treatment shows an extensive cleavage of the beta-aryl-ether linkage with the degradation of ester resulting in a structural alteration of lignin. High Delignification is achieved by dioxane process through progressive enrichment of carboxylic acid group in isolated lignin; also dioxane isolation has little influence on the structure of isolated lignin. Moreover, the results confirmed that Alkali and Dioxane lignin were guaiacyl-syringyl lignin, typical of hardwood lignins.