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The extraction and characterization of defined and carboxyl-rich oligomeric lignin fragments with narrow molecular weight distribution is presented herein. With regard to the well-known pulp bleaching process, oxidative lignin depolymerization was investigated using hydrogen peroxide in an aqueous alkaline solution (i.e., at T = 318 K, t = 1 h) and subsequent selective fractionation with a 10/90 ( v / v ) acetone/water mixture. While the weight average molecular weight (M W ) of lignin in comparison to the starting material was reduced by 82% after oxidation (T = 318 K, t = 1 h, c lignin = 40 g L -1 , c H2O2 = 80 g L -1 , c NaOH = 2 mol L -1 ) and subsequent solvent fractionation (T = 298 K, t = 18 h, c cleavage product = 20 g L -1 ), the carboxyl group (-COOH) content increased from 1.29 mmol g -1 up to 2.66 mmol g -1 . Finally, the successful scale-up of this whole process to 3 L scale led to gram amounts (14% yield) of oligomeric lignin fragments with a M W of 1607 g mol -1 , a number average molecular weight (M N ) of 646 g mol -1 , a narrow polydispersity index of 3.0, and a high -COOH content of 2.96 mmol g -1 . Application of these oligomeric lignin fragments in epoxy resins or as adsorbents is conceivable without further functionalization.

Valorization of Lignin via Oxidative Depolymerization with Hydrogen Peroxide: Towards Carboxyl-Rich Oligomeric Lignin Fragments