(144h) Reactivity-Based Fractionation of Lignins Via Reversible Conjunction to Polymeric Amines

Fractionation is a necessary step in the process of upgrading lignins to synthetic materials. Existing methods for separating lignin fractions based on differences in solubility or molecular size generate polymer mixtures with heterogeneous physiochemical properties, which are not suitable for use in high-value plastics or composites.

We demonstrate the utility of catalytic oxidation as an approach to partially depolymerizing lignins from diverse sources including raw biomass, enzymatic lignin, and fungal decay lignin. The resulting lignin fragments contain reactive carbonyl groups (i.e. aldehydes and ketones), which conjugate reversibly with primary amines. Using an amine-functionalized polymer as the conjugating reagent, we are able to isolate lignin fractions that are enriched in carbonyl structures. Recovery and reuse of the conjugating reagent are achieved via acid-catalyzed hydrolysis of amine-carbonyl adducts.