Valorization of Kraft Lignin by mechanochemical processing with sodium percarbonate

Lignin is a highly underused resource. The complex and heterogeneous structure poses a challenge to industry and science. Problems are high polydispersity, high-molar-mass and insufficient functional groups. In this article, we present a mechanochemical one-pot reaction that depolymerises high-molecular-mass fractions by environmentally friendly hydrogen peroxide oxidation and introduces new carbonyl functionalities into the lignin framework. First, kraft lignin was ground using sodium percarbonate (SPC) and sodium hydroxide (NaOH) in a ball mill at different time intervals. After acidic work-up, the samples were analysed by infrared spectroscopy (IR), size exclusion chromatography (SEC), dynamic vapour sorption (DVS), and small angle X-ray scattering (SAXS). Already after 5 minutes, a reduction from the mass average molecular weight (Mw) of 47% and an increased carbonyl absorption by a factor of 2 can be observed. DVS data show a ~2.8-fold increase in water adsorption and provide information about the adsorption mechanism caused by the chemical modification. SAXS data show that there is no significant surface area increase of the lignin particles when additives are used, supporting the hypothesis that the increased adsorption performance is caused by chemical modification. A principal component analysis (PCA) gives additional insight into the IR spectra and SAXS parameter correlations. Refining of industrial lignin to produce homogeneous fractions with enhanced surface properties is essential for high-value applications