The structural characterization and antioxidant properties of oil palm fronds lignin incorporated with p-hydroxyacetophenone

Abstract

This study reports on the effects of unmodified autohydrolyzed ethanol organosolv lignin (AH EOL) and modified autohydrolyzed ethanol organosolv lignin on the structural characteristics and antioxidant properties upon incorporation of p-hydroxyacetophenone (AHP EOL). The lignin samples isolated from black liquor of oil palm fronds (OPF) were evaluated and compared using various complementary analyses; FTIR, ¹H and ¹³C NMR spectroscopy, 2D-NMR spectroscopy (HMBC and HSQC), CHN, GPC, HPLC and thermal analyses (TGA and DSC). Chemically modified organosolv lignin (AHP EOL) provided lignin with lower molecular weight (M_w), which has smaller fragments that leads to higher solubility rate in water in comparison to unmodified organosolv lignin, AH EOL (D_{AHP EOL}: 19.8% > D_{AH EOL}: 14.0%). It was evident that the antioxidant properties of modified organosolv lignin has better reducing power in comparison to the unmodified organosolv lignin. Therefore, the functionalization of lignin polymers enhanced their antioxidant properties and structural features towards a various alternative approach in lignin-based applications.

Keywords: Antioxidant; Oil palm fronds; Organosolv lignin.