Cyclic organic carbonates as reagents for the functionalization of lignins and hemicelluloses
Cyclic organic carbonates are non-toxic components with high boiling and flash points and can be used as polar aprotic solvents or reagents to access new biobased and environmentally friendly polymer building blocks. This work focused on the use of different cyclic carbonates to extend the functionalities of lignins and hemicelluloses. Lignin polyols were successfully synthesized by an efficient, nontoxic and solvent free oxyalkylation procedure using commercially available organic carbonates (ethylene (EC), propylene (PC), butylene (BC) and glycerol carbonate (GC)). The applicability of oxyalkylation to a set of lignins from hardwood, softwood and annual plants and different processes (organosolv, kraft, soda) was investigated. To broaden the range of applications for lignin a simple environmentally friendly procedure was developed to prepare cyclocarbonated lignins, which could be used as synthons for the preparation of nonisocyanate polyurethanes. Since a growing interest in utilization and derivatization of hemicelluloses has emerged during the last decades the ability of propylene (PC) and vinyl ethylene carbonate (VEC) to etherify xylans was tested and the structure of products was analysed.