A comprehensive review on sustainable lignin extraction techniques, modifications, and emerging applications

Lignin is the second most abundant naturally occurring biopolymer and presents a sustainable and renewable alternative to non-renewable aromatic polymers. Its inherent properties have sparked significant interest in the synthesis of high-value products and platform chemicals, including phenolic bioactive compounds, eco-friendly antioxidants, bio-based plastics, composites, and adhesives for non-formaldehyde wood resins and packaging applications. Lignin can be obtained from various lignocellulose biomass and various processes such as pulp production and second-generation bioethanol production. Recently, various extraction methods, such as the use of solvents including ionic liquids, deep eutectic solvents, and organo-solvents, have been developed to produce lignin with desirable characteristics. The extraction of lignin with the required properties is crucial for its suitability for various applications, and the source and the extraction methods employed influence the quality of lignin. After extraction, lignin undergoes various chemical modifications to enhance its potential for transformation into value-added products. This article provides a comprehensive overview of lignin sources, extraction methods, modification technologies and diverse industrial applications. The review also discusses the future potential of lignin in the transition towards a more sustainable and bio-based economy.