Low Ecological Impact Lignin-Based Flame Retardants for Polyurethane Foams

The flammability of polyurethane is a great safety hazard, threatening both lives and goods. Recognizing this, efforts to enhance the fire resistance of polyurethanes can be pursued through various routes. Depending on the classes and applications of polyurethanes, fire retardation can be achieved by incorporating flame retardants or modifying the polymer structure. In response to growing environmental concerns, lignin is an abundant and renewable resource, which has been employed to develop effective flame-retardant polyurethanes, with a simultaneous focus on reducing their ecological impact. Lignin, characterized by its aromatic and phenolic structure, naturally can act as a reactive fire retardant for polyurethanes. Nevertheless, diverse chemical modifications of lignin have been explored to further enhance its fire resistance. This review highlights advancements in the design of phosphorus- and/or nitrogen-containing lignin-based reactive flame retardants tailored for bio-based polyurethanes.