As lignin is a polymer formed from its phenolic monomer radicals by purely chemical radical coupling reactions, the breadth of options for ‘designing’ the composition and structure of lignins is unparalleled. New phenolic monomers can be introduced into the polymer, and new ‘natural’ lignin monomers are constantly being discovered; we predict that there will be at least one new class of monomers discovered before this ACS meeting! Inspired by Nature’s incorporation of the non-lignin-pathway flavonoid, tricin, into monocot lignins, and hydroxystilbenes into palm endocarp lignins, researchers can now also contemplate plants in which the lignins incorporate valuable components that can be subsequently retrieved from ‘waste’ streams. Caffeyl alcohol-derived lignin polymers represent a class of ‘ideal lignins’ for conversion to monomeric phenolic commodity chemicals in high yield. Moreover, lignins have now been successfully ‘redesigned’ to contain readily chemically cleavable ester bonds in the polymer backbone, facilitating improved industrial processing – for example, chemical pulping, or pretreatment options for the saccharification of wall polysaccharides to sugars for liquid biofuels production. In addition to the apparent necessity to modify our stance on just what defines a plant lignin, and to speculate on the limits to what constitutes a lignin monomer, we appear to be entering a reinvigoration period for lignin research aimed at its manipulation for improved utilization and value.

Redefining and redesigning lignin

2019 Fall National Meeting

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