Informing the valorisation of lignin for sustainable chemical feedstocks by lignin radical chemistry

Lignin is a complex biopolymer that has attracted increasing attention as a potential renewable feedstock for low molecular weight chemicals. However, the complex composition of lignin is having significant impact on reactivity and analysis. Significant efforts are being made to exploit lignin beyond burning the waste of the paper industry for fuel. In a world of dwindling petrochemical feedstocks developing renewable sources for precursors of fine chemicals has to be a strategic priority. Lignin is known to polymerise in the plant by a radical mechanism and depending on source of wood and subsequent treatment large concentrations of stable radicals persist in lignin.(1) Nevertheless, the presence of a substantial radical content is often ignored in the chemical breakdown and analysis of lignin. The Westwood group has significant experience in the fractionation and valorisation of lignin and the Bode group specialises in the study of radicals and other paramagnetic systems with electron paramagnetic resonance spectroscopy. We have recently found that fractions from acetylated lignin show a correlation between radical content and solvent polarity for extraction. Additionally, the radical content reduced upon solubilisation of the crude lignin by acetylation.(2) Recent evidence by others shows that the type and amount of radical strongly depends on the source prior to the treatment of wood and lignin.(3) This project will establish the use of electron paramagnetic resonance (EPR) spectroscopy as key technique informing lignin fractionation and valorisation. It will be demonstrated that the decline in radical content accurately monitors the acylation success. This will in turn allow identifying different topologies of lignin with linear structures more susceptible to acetylation than branched ones. Finally, monitoring the fate of the lignin radicals during functionalisation will inform approaches to efficient monomerization of lignin.
Research training comprises of chemistry laboratory training functionalising and fractionating lignin and analysing the products with common biophysical and physicochemical techniques applicable to (bio)polymers (mainly NMR and chromatography) and analysis of the radical content and type of radicals by conventional and advanced EPR spectroscopy as abundantly applied to biopolymers in recent years.