Synthesis of a Novel Lignin‐Based Intumescent Flame Retardant and Its Application in the Flame Retardancy of Polypropylene

ABSTRACT Designing char‐forming agents as multifunctional components provides a practical direction for developing intumescent flame‐retardant materials with excellent fire safety. In this work, a novel bio‐based macromolecular charring agent (NL‐OH) was synthesized by chemically modifying lignin with pentaerythritol (PER) and melamine (MEL) and compounded with ammonium phosphate (APP) at an optimal ratio of 5:4 to construct an intumescent flame‐retardant system (IFRR) for polypropylene (PP). The flame retardancy and mechanism of the fabricated composites were evaluated using LOI, UL‐94, TGA, CCT, TG‐FTIR, and other techniques. With the synergy between NL‐OH and APP, PP composites exhibited outstanding LOI values of 32.9%, significant char‐forming ability of 10.71% of char residues, and notable reductions in the peak heat release rate (PHRR) and peak smoke production rate (PSPR) by 46.9% and 80.9%, respectively. NL‐OH functioned as both a charring and blowing agent, promoting the formation of an expanded and continuous char layer that effectively insulates heat and suppresses flammable gas release, contributing to the overall fire safety of the material. This study aligns with international efforts toward sustainable and eco‐friendly flame‐retardant technologies, which provide a theoretical basis for the construction of a dual‐source charring agent.