Towards lignin-based functional materials in a sustainable world

In light of the incessant consumption of raw materials in the world today, the search for sustainable resources is ever pressing. Lignin, the second most naturally abundant biomass, which makes up 15% to 35% of the cell walls of terrestrial plants, has always been treated as waste and used in low-value applications such as heat and electricity generation. However, its abundance in nature could potentially solve the problem of the rapidly depleting resources if it was successfully translated into a renewable resource or valorized to higher value materials. Advanced lignin modification chemistry has generated a number of functional lignin-based polymers, which integrate both the intrinsic features of lignin and additional properties of the grafted polymers. These modified lignin and its copolymers display better miscibility with other polymeric matrices, leading to improved performance for these lignin/polymer composites. This review summarizes the progress in using such biopolymers as reinforcement fillers, antioxidants, UV adsorbents, antimicrobial agents, carbon precursors and biomaterials for tissue engineering and gene therapy. Recent developments in lignin-based smart materials are discussed as well.