A novel fractionation process for lignin with temperature-induced self-assembly

The complex chemical structure and broad molecular weight distribution of lignin lead to heterogeneity and unsatisfactory performance, essentially restricting its high-value utilization. A novel lignin fractionation process is proposed here to solve this problem and overcome the shortcomings of common fractionation methods. Using enzymatic hydrolysis lignin (EHL) as raw material, five lignin fractions were obtained by cooling precipitation in the ethanol/water mixed solvent. Their chemical structure and physicochemical properties were compared. All lignin fractions presented reduced heterogeneity compared to the EHL and a gradual decrease of molecular weights accompanied by increasing hydrophilic group content. In addition, temperature-induced self-assembly for forming lignin colloidal spheres co-occurred during cooling precipitation. Interestingly, a fraction with light color and high UV-blocking activity was obtained. By combining this color-light sample with pure hand cream, a lignin-based sunscreen was prepared, which had a 40 % higher sun protection factor (SPF) than EHL sunscreen.