Advances in Lignin Chemistry, Bonding Performance, and Formaldehyde Emission Reduction in Lignin‐Based Urea‐Formaldehyde Adhesives: A Review

Lignin, a complex biopolymer derived from plant biomass, has attracted significant attention in both academic research and industry due to its potential to revolutionize formaldehyde‐based adhesives by reducing their emissions, a critical concern in the wood industry. In the realm of wood adhesives, the integration of lignin has seen significant progress in recent years, where it is utilized either as a partial replacement for traditional synthetic resins or as a modifier to enhance adhesive properties. This has led to notable improvements in both environmental impact and adhesive performance, contributing to developing more sustainable and eco‐friendly wood composite materials. This review provides an in‐depth exploration of the recent advancements in the rapidly growing field of lignin‐based Urea‐Formaldehyde (UF) adhesives, spanning from fundamental research to practical applications. The initial sections of this paper offer an updated overview of lignin, covering its chemical structure, properties, extraction methods, and various chemical modifications, with a focus on its potential in adhesive applications. The review concludes with a detailed discussion of the economic and environmental advantages, alongside the challenges and future directions for integrating lignin into UF adhesive technology. In summary, lignin's incorporation into UF adhesives presents a transformative approach to achieving low formaldehyde emissions.