Lignin as a green and multifunctional alternative to phenol for resin synthesis

Phenolic resins (PRs) are being widely used in many fields such as molding plastics, foams, coatings, and semiconductor packaging owing to their good properties including corrosion resistance, heat resistance, flame resistance, and electrical insulation properties. However, the traditional phenolic resins industry depends very heavily on petroleum as a source of phenol raw material, which is under the influence of petroleum reserves. In recent years, many studies have been conducted to develop cheap, abundant, renewable, and high-performance alternatives to phenol for the production of PR. Lignin, as the most abundant natural polyphenol, has similar chemical structures to that of phenol. Lignin has received increasing attention as a potential feedstock for renewable fuels and chemical production. The substitution of lignin for phenol can not only reduce the costs of PRs but also increase their performance, such as low-toxicity residues and environmental friendliness. This paper reviews the recent progress in lignin activation and modification for lignin-based phenolic resin (LPR) synthesis, highlights the different lignin modification methods, compares the performance of different LPR products, and summarizes their applications in adhesives, foams, molding powders, micro/nano-spheres, and other advanced materials. Finally, this review puts forward the current challenges and potential future prospects for LPR materials.