Enhanced properties of oil palm fronds (OPF) lignin fractions produced via tangential ultrafiltration technique

•Different OPF lignins were separated via ultrafiltration membranes.•Permeates produces lignin with smaller molecular weight and high phenolic OH content.•Better solubility of lignin permeates was observed.•The antioxidant activity of lignin permeates was better than the crude ones.

The present study sheds light on the structural characteristic and antioxidant properties of different oil palm fronds lignin fractions (kraft, soda and organosolv) separated via 5 kDa ultrafiltration membranes. The different permeates obtained have improved the physicochemical properties of lignin in terms of their specific molecular weight fragments, phenolic OH content (especially the phenolic S units) and solubility. It was found that the antioxidant activity of lignin permeates was better than the crude ones (highest oxygen uptake inhibition, OUI up to 83%) and was closely related to its average molecular weight and phenolic OH content. The ultrafiltration process allows the production of lignins with different chemical structures and antioxidant capacity, enhanced solubility and subsequently making it more adequate for commercial applications.