Comparative physicochemical characterization of organosolv lignin from palm kernel shell extracted using different organic solvents.

The organosolv lignin of palm kernel shell (PKS) was prepared by three different organic solvents (polyethylene glycol (PEG), tetrahydrofuran (THF), and formic acid (FA)) with a 70% mixture of solvents in water, using 2% w/w H2SO4 as a catalyst at 190 °C for 1 h. The results showed that the lignin extraction yields were in the range of 21.8-54.6%w/w as well as the total lignins with >97% and remaining composition of 0.26-0.34% total sugar and 0.05-0.64% ash content were observed from all fractionated lignins. PEG-lignin achieved the highest lignin properties like molecular weight (4355 g/mol), particle size distribution with 48.5 and 210.6 μm of D50 and D90, respectively, aliphatic hydroxyl content (5.21 mmol/g) from 31P NMR compared to the other lignins, leading to suitability for application in carbon fiber, insulating, and cosmetic. While the lowest lignin properties like molecular weight (1664 g/mol), the glass transition temperature (Tg) (92.81 °C), the total low aliphatic and phenolic hydroxyl content (0.35 and 1.10 mmol/g) opposite to the highest carboxylic hydroxyl content (0.6 mmol/g) were observed from the FA-lignin, resulting in utilization for precursors as antioxidant for bio-composites. THF-lignin showed the highest glass transition temperature (125.33 °C) and phenolic hydroxyl content (5.58 mmol/g) but the lowest particle size distribution (2.8 and 6.6 μm of D50 and D90, respectively) and 50% inhibitor concentration (IC50) (9.13 mg/mL), suggesting its use as bio-additive in adhesive. This study highlights the potential of organosolv lignin fractionated with various organic solvents for diverse industrial applications in next generation biorefineries.