Physicochemical characterization of alkaline and ethanol organosolv lignins from oil palm (Elaeis guineensis) fronds as phenol substitutes for green material applications

- Lignins were isolated with Kraft, soda and aqueous ethanol pulping from OPF.
- Spectral analyses revealed that Kraft and soda lignin samples comprised mainly of phenolic OH.
- Organosolv lignin comprised mainly of primary and secondary aliphatic OH functional groups.
- Syringyl (S) units were more favorable to be degraded compared with the guaiacyl (G) units.
- Physicochemical properties of OPF lignin suggest that it could serve as a green phenol substitutes.

In the present work, lignin isolation and physicochemical features from oil palm fronds (OPF) black liquor using Kraft, soda and organosolv pulping have been studied. The characterization of lignin samples by means of FTIR, 1H and 13C NMR has shown that different types of hydroxyl functional groups were obtained from different delignification processes. It was revealed that the lignin samples contained substantial amounts of non-condensed guaiacyl and syringyl unit with fewer p-hydroxyphenyl units. The GSH molar ratio of Kraft, soda and organosolv lignin was assigned to 26:51:21, 21:49:30 and 23:67:10, respectively, upon quantification. The significant differences in the physicochemical features of the lignin isolated with alkali and organosolv treatments may be of great interest as a promising alternative for its revalorization.