Lignin‐derived flame retardant for improving fire safety and mechanical properties of polypropylene

Abstract In this work, the self‐assembled lignin‐based flame retardant (LMA) was grafted with γ‐aminopropyltriethoxysilane (APTES) to obtain a novel type of silicon‐containing intumescent flame retardant (LK), which can be applied on polypropylene (PP) to obtain flame retardant PP (PP‐LK). Furthermore, low cost flame retardant PP biocomposite (PP/M/L) with high lignin content were prepared by compounding lignin, LK and PP. The developed PP‐LK and PP/M/L exhibited significant excellent flame retardancy, smoke suppression and mechanical properties. In particular, the UL‐94 test achieved V‐0, and the limit oxygen index (LOI) increased from 17.9% of PP to 28.3% of PP‐LK, and 27.2% of PP/M/L, respectively. Meanwhile, tensile strength and Young's modulus increased by 6.3% and 19.64% for PP‐LK and PP/M/L, respectively. Especially, the tensile strength of PP with 15% LK and 25% lignin achieved 30.88 MPa, and the Young's modulus reached 1415 MPa. The excellent carbonization properties of PP‐LK illustrated that the lignin component of LK had excellent carbonization ability. The prepared LK provided a novel strategy to improve the fire safety and cost of PP, and wide the applications of lignin.