From technical lignin to native lignin: Depolymerization, functionalization, and applications

Lignocellulose as a form of biomass is inedible. It represents a renewable feedstock for the synthesis of chemicals and materials. Its utilization has become an area of growing interest. Of lignocellulose components, lignin is comparatively under-explored and under-utilized, despite its abundance. This Focus Review recognizes this missed opportunity and presents a concise overview on some of the most recent progress involving the generation and application of functional materials derived from lignin. Between the two commonly encountered forms of lignin, technical lignin is a by-product of the paper production industry and is highly processed under harsh conditions. As such, it has generally been used for filler and resin materials. By comparison, native lignin is rich in chemical functionalities and holds great promise for downstream chemical synthesis. In recognition of these potentials, “lignin-first” strategies have emerged to directly convert native lignin to building blocks rich in functional groups, such as alcohols and carbonyls, while maintaining the integrity of the aromatic structures in lignin. The lignin-first strategy complements the already well explored field of technical lignin utilization. These chemoselective, lignin-first methods promise routes to native lignin valorization into high-value building blocks while keeping cellulose and hemicellulose intact and, therefore, are particularly appealing. This Focus Review first recognizes the importance of the traditional strategies for technical lignin utilization and highlights some of the newest developments. It then puts an emphasis on these lignin-first approaches for improved native lignin utilizations.