Recent advances in transforming agricultural biorefinery lignins into value-added products

Each year, agricultural residues such as stalks, husks, and pits/nutshells from food crop harvesting are available on a gigatonne scale worldwide. While biorefinery routes have been used convert agricultural residue carbohydrates into value-added products (e.g., bioethanol, biochemicals), the lignin, comprising 20–50% of the dry mass of agricultural residues, remains largely underutilized. Therefore, there is an urgent need to explore the utilization of agricultural biorefinery lignins for value-added products. In this review, we briefly introduce the origins of agricultural lignins, discuss their structural differences, and compare them with the more commonly studied wood lignins. We highlight in greater detail the recent advances in using agricultural lignins as macromonomers/fillers for polymer syntheses that include epoxies and polyurethanes. The use of agricultural lignins as carbon-rich precursors for the preparation of carbon fibers, supercapacitor electrodes, and carbon foams are also discussed, as well as their use for other applications such as additives for fertilizer release control and UV-shielding. Altogether, this review provides key developments in the progress made to date for agricultural lignin utilization that may help promote future innovation in the field.