Ethylene glycol/deep eutectic solvents in reactive lignin isolation: from wood delignification to lignin nanoparticles

Abstract

Deep eutectic solvents (DES) have recently demonstrated their potential in lignocellulosic biomass fractionation owing to their action on multiple fronts. DES acidity enhances the delignification of biomass resulting in an implemented isolation of biomass polymeric constituents via hydrolytic processes. The use of an additional reacting agent favours the solvation of lignin via the formation of novel ether bonds implementing the yield in soluble materials. The present effort is focused on the fractionation of birch wood by a DES system (chloro-choline, oxalic acid) supplemented with ethylene glycol as active reacting component with the object of isolating ethylene-glycol-functionalized lignins. The newly lignin derived material was used in the synthesis of nanoparticles (EG-LNPs). The effect of temperature, extraction time, and the composition of DES system on the yield and structure of the isolated lignins were carefully evaluated via the use of spectroscopic and chromatographic techniques and compared with samples isolated by a conventional acidolysis process. Differences in terms of molecular weight, hydroxyl groups contents, and bonding patterns were highlighted. Finally, EG-LNPs from DES-EG-lignin isolated under different conditions were prepared via the use of the hydrotropic method. EG-LNPs were characterised by ζ-potential and dynamic light scattering to evaluate their colloidal stability and size distribution.