Fractional isolation and structural characterization of mild ball-milled lignin in high yield and purity from Eucommia ulmoides Oliv

Sequential extractions of the mild ball-milled Eucommia ulmoides Oliv with 80% neutral dioxane, 75% dioxane containing 0.025 M HCl, 75% dioxane containing 0.1 M NaOH, 60% ethanol containing 0.5 M NaOH, 5% KOH, 5% NaOH, and 8% KOH at 75°C for 3 h released 91.3% of the original lignin. The results showed that the procedure for extracting lignin from the mild ball-milled wood with mild alkaline organic solvent was more efficient than the traditional method of neutral and mild acidic dioxane extractions. The structure of the seven lignin fractions were analysed using wet chemical analysis, such as alkaline nitrobenzene oxidation, FT-IR, and solution-state 1H, 13C, and 31P NMR techniques. It is clear that the sequential mild acidic and alkaline organic solvent extractions of the mild ball-milled E. ulmoides Oliv offered significant yield improvements over the traditional signal acidolysis procedure for isolating lignin from wood, and the alkaline organic solvent extraction led to more lignin release than that of the mild acidolysis. This new procedure proposed in this study could be used for the lignin structural analysis, whereby wood is mild ball-milled and successively extracted with both mild acidic and alkaline organic solvents as well as aqueous alkalis to produce lignin fractions with high yield and purity and representing the total lignin in wood.