Rethinking Lignin: a renewable feedstock for the synthesis of eco-friendly resin and sustainable materials

Lignin is the second most abundant natural polymer on earth, standing out due to its cost-effectiveness. The production per year is approximately 50-70 million tons, and it is expected to double before 2030. Lignin, long dismissed as a low-value by-product, has attracted renewed scientific interest, and it has been used in the preparation of adhesives, surfactants, fillers, anti-microbial agent, adsorbents, and for many biomedical and biotechnological applications.1 The most common methodologies for lignin extraction, namely Kraft and soda processes involve harsh chemical processes, leading to the separation of a chemically altered polymer. These methods have a negative impact on the environment, and recently, new sustainable procedures have been developed for a greener extraction of lignin. Deep eutectic solvents (DES) extraction represents a valuable alternative to traditional processes, as DES are non-toxic, can be easily recovered and re-use, and they exhibited remarkable delignification efficiency.2 In this work, we employed dry seed hard shells, a by-product from agri-food industry as source of lignin. The polymer was recovered with a green process based on the use on NAtural DES (NADES) in combination with ultrasonic technology. The lignin obtained has been employed for the synthesis of more sustainable resins as safer aldehydes were used as alternative to the cancerous formaldehyde. Lignin was also employed for the development of 100% natural-based nano delivery system. Finally, as possible application for water remediation, the natural polymer was assessed for its adsorption capabilities in the removal of synthetic dyes from water. In these studies, ATR-FTIR, NMR and DLS were mainly employed for structural characterization.