Abstract:The lignin-based char-forming agent (MLig) containing silica element and carbon-carbon double bond was successfully synthesized in one step using alkali lignin as template and γ-methacryloxypropyl trimethoxy silane as modifier. The results of thermogravimetric analysis (TGA) show that MLig has the better thermal stability and charring ability, which is significantly better than the unmodified alkali lignin. MLig was used as car-forming agent for the preparation of intumescent flame retardant polypropylene composites (MLig/IFR/PP). The flame retardancy, thermal stability and mechanical properties of flame retardant polypropylene were investigated by limiting oxygen index analyzer, vertical burning analyzer, thermogravimetric analyzer and electronic universal analyzer. The results show that when the mass fraction of flame retardant is 30% and the mass ratio of MLig to pentaerythritol is 1:3, the limiting oxygen index (LOI) value of MLig/IFR/PP could reach 32% and vertical burning UL-94 is over V-0 rating, which are significantly better than intumescent flame retardant polypropylene with unmodified lignin (Lig/IFR/PP). Meanwhile, the flame retardancy of MLig/IFR/PP is still better than Lig/IFR/PP with 30% flame retardant when the total mass fraction of flame retardant added is reduced to 25%. In addition, the thermal stability and mechanical properties of MLig/IFR/PP are improved compared with Lig/IFR/PP, in which the impact strength is improved by more than 80%. It can be seen that the lignin-based car-forming agent has good application prospects in the field of intumescent flame retardant polymers.