Deep eutectic solvents, uses thereof, and method for preparing a lignin prepolymer based on the deep eutectic solvents

The present invention relates to a deep eutectic solvent (DES) comprising at least one carboxylic acid which comprises at least two carboxylic acid functional groups and has a number of carbon atoms in the range of from 4 to 10; at least one alcohol which comprises at least two alcohol functional groups, and which is selected from the group consisting of alcohols having a number of carbon atoms in the range of from 2 to 12 carbon atoms, polyethylene glycol and polypropyleneglycol; and water in an amount of from 10 to 50 wt.% of the total weight of the deep eutectic solvent. It is also related to the use of these deep eutectic solvents of the invention, as solvents for solubilising lignin from a lignin material or for preparing a lignin prepolymer. Furthermore, it is related to a process for preparing a lignin prepolymer which involves the use of the deep eutectic solvents of the invention, as well as to the lignin prepolymer as such and its uses for producing films, coatings, insulating foams, adhesives, binders, composites or for fibre sizing or for radical curing.