| Summary: | 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 (<i>v</i>/<i>v</i>) acetone/water mixture. While the weight average molecular weight (M<sub>W</sub>) of lignin in comparison to the starting material was reduced by 82% after oxidation (T = 318 K, t = 1 h, c<sub>lignin</sub> = 40 g L<sup>−1</sup>, c<sub>H2O2</sub> = 80 g L<sup>−1</sup>, c<sub>NaOH</sub> = 2 mol L<sup>−1</sup>) and subsequent solvent fractionation (T = 298 K, t = 18 h, c<sub>cleavage product</sub> = 20 g L<sup>−1</sup>), the carboxyl group (–COOH) content increased from 1.29 mmol g<sup>−1</sup> up to 2.66 mmol g<sup>−1</sup>. 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<sub>W</sub> of 1607 g mol<sup>−1</sup>, a number average molecular weight (M<sub>N</sub>) of 646 g mol<sup>−1</sup>, a narrow polydispersity index of 3.0, and a high –COOH content of 2.96 mmol g<sup>−1</sup>. Application of these oligomeric lignin fragments in epoxy resins or as adsorbents is conceivable without further functionalization.
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