N, P and Si type synergistic lignin-based flame retardant as well as preparation method and application thereof

The invention provides an N, P and Si type synergistic lignin-based flame retardant and a preparation method and application thereof. The preparation method comprises the following steps of dissolving a flame retardant intermediate DOPO in a solvent, adding a silane coupling agent and an acid-binding agent, cooling the mixture, and conducting stirring until the mixture is completely dissolved, so as to obtain a solution A; adding carbon tetrachloride into the solution A, and controlling the reaction temperature to obtain a solution B; raising the temperature of the solution B, enabling the solution B to fully react, washing a reaction product until white flocculent solids are separated out, and drying the washed product to obtain a faint yellow product C; dissolving industrial lignin and the product C in absolute ethyl alcohol, controlling the reaction temperature, and conducting stirring and reacting to obtain a brown product D; carrying out suction filtration on the product D, and conducting washing to remo