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

In this work, the self-assembled lignin-based flame retardant (LMA) was grafted with gamma-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.