Using green γ-valerolactone/water solvent to decrease lignin heterogeneity by gradient precipitation

Lignin heterogeneity, involving complex structure and high polydispersity, is a key challenge that restricts its value-added applications. Fractionation of heterogeneous lignin into several homogeneous subdivisions is an attractive and practical strategy to overcome this limitation. In this work, γ-valerolactone (GVL), a sugar-derived product, was used as a green solvent for lignin fractionation when mixed with water. The enzymatic hydrolysis lignin (EHL) was subdivided into three different fractions (F1, F2, and F3) by dissolving it completely in 60% aqueous GVL and then following gradient precipitation in 40%, 30%, and 5% aqueous GVL solutions, sequentially. Detailed characterization techniques were conducted to provide a comprehensive evaluation of the three obtained lignin fractions. Moreover, the proposed fractionation mechanism was further investigated on the basis of Kamlet–Taft parameters. The gel permeation chromatography (GPC) analyses showed that the three fractions presented lower polydispersi...