Effect of feed concentration in solvent/anti-solvent precipitation fractionation of lignin: Impact on lignins structure-property correlations

Technical lignins are relatively heterogeneous and structurally not fully understood, which hinders their commercialization. This study involves the precipitation fractionation of organosolv (OS) lignin into different molecular weight (MW) classes by stepwise addition of an anti-solvent in acetone/water mixtures with varying feed lignin concentrations of 5, 10, and 15 wt% in the lignin/solvent mixture. Characterization of the obtained lignin fractions by SEC-MALS, TM-DSC, and 31P NMR revealed MW classes in a broad range from 2050 to 26500 g mol−1, glass transition temperatures between 68 and 201 °C and the presence of different amounts of hydroxyl groups. The results verify that besides the acetone/water gradient, the lignin concentration has a major influence on the fractionation outcome. We demonstrate the significant impact of different OS lignin concentrations on the solubility of such polydisperse system and hereby establish an additional way to tune the molecular weight of lignin fractions and their related physico-chemical properties.