Flame-retardant modified intermediate prepared by grafting of alkali lignin and undecylenic acid

The invention discloses a preparation method and application of an intermediate product for improving the flame retardant property of alkali lignin. The intermediate is a grafted product of undecylenic acid and alkali lignin, is used as a grafted product prepared from alkali lignin and undecylenic acid, and is characterized in that a short chain with carbon-carbon double bonds is introduced into along-chain macromolecule of alkali lignin, so that an effective site is provided for subsequent access of flame retardants with rich electrons, such as dicyandiamide. The preparation method is simpleand easy to implement; and the undecylenic acid monomer is grafted on the lignin to form the undecylenic acid grafted lignin compound, the undecylenic acid molecular chain structure is simple, and subsequent improvement operation is facilitated. And the final intermediate uses the environment-friendly, renewable, cheap and easily available alkali lignin as the preparation raw material, thereby reducing the use of petroleu