New perspectives in lignin valorization: Lignin-derived nanostructures

Lignin is undoubtedly one of the most interesting biomasses in terms of high added-value materials obtainable from its valorization. As by-product of pulp and paper industries and biorefineries, it is produced in large volumes and is readily available at low cost. The unlocking of its full potential is therefore of crucial importance in view of a sustainable growth based on circular economy paradigms. In this context, the generation of lignin-based nanomaterials is attracting considerable attention as the self-assembly characteristics of this biopolymer can be easily exploited, thus avoiding time- and resource-consuming functionalization or purification steps and, most importantly, preserving all its peculiar and unique features. In the last years, many researchers have devoted their efforts toward the development of more efficient and sustainable procedures for the synthesis of lignin-derived nanomaterials, also expanding the possible applications thanks to the easy tunability of their functional properties. In this contribution, the most important synthetic procedures for the obtainment of lignin nanoparticles, nanocapsules and nanofibers are critically revised and discussed, and the range of uses they have been tested for is presented.