Phosphonate-substituted lignin as a flame retardant

1. A flame retardant comprising:

a lignin; and

a phosphorous containing component covalently bonded to the lignin, the phosphorous containing component comprising a compound of general formula:

wherein:

B is C 1 to C 18 open-chain hydrocarbyl or C 5 to C 20 carbocyclyl;

each X is, independently, phosphine, phosphine oxide, phosphinite, phosphonite, phosphinate, phosphonate, or phosphate, and

n is an integer of 2 to 8.

2. The flame retardant of claim 1 , wherein B is C 1 to C 18 alkyl, C 2 to C 18 alkenyl, or C 2 to C 18 alkynyl.

3. The flame retardant of claim 1 , wherein B is C 5 to C 20 cycloalkyl, or C 5 to C 20 aryl.

4. The flame retardant of claim 1 , wherein B comprises cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl, cyclopentyl-diene, benzyl, naphthyl, indenyl, or combinations thereof.

5. The flame retardant of claim 1 , wherein:

each X is substituted at one or more positions with a substituent R, wherein each R is independently selected from a group consisting of C 1 to C 18 alkyl, C 2 to C 18 alkenyl, C 2 to C 18 alkynyl, C 5 to C 20 cycloalkyl, and C 5 to C 20 aryl;

the flame retardant comprises about 0.1 wt % to about 50 wt % of the phosphorous containing component; and

the lignin comprises lignin sulfonates, Kraft lignins, soda lignins, organosolv lignins, softwood lignin, hardwood lignin, cellulosic grasses lignins, corn stover lignins, steam explosion lignins, or combinations thereof.

6. The flame retardant of claim 1 , wherein each X is independently

Z—(CH 2 ) m —

wherein:

Z is phosphine, phosphine oxide, phosphinite, phosphonite, phosphinate, phosphonate, or phosphate; and

m is an integer of 1 to 10.

7. The flame retardant of claim 6 , wherein each Z is independently substituted at one or more positions with a substituent R, wherein R is independently selected from a group consisting of C 1 to C 18 alkyl, C 2 to C 18 alkenyl, C 2 to C 18 alkynyl, C 5 to C 20 cycloalkyl, and C 5 to C 20 aryl.

8. The flame retardant of claim 6 , wherein B is C 5 to C 20 cycloalkyl, or C 5 to C 20 aryl.

9. The flame retardant of claim 6 , wherein B comprises cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl, cyclopentyl-diene, benzyl, naphthyl, indenyl, or combinations thereof.

10. The flame retardant of claim 9 , wherein each X is

11. The flame retardant of claim 6 , wherein B is C 1 to C 18 alkyl, C 2 to C 18 alkenyl, C 2 to C 18 alkynyl.

12. The flame retardant of claim 11 , wherein each X is

13. The flame retardant of claim 1 , wherein each X is

14. The flame retardant of claim 1 , wherein the phosphorous containing component comprises a compound of general formula:

wherein Y is a leaving group.

15. The flame retardant of claim 14 , wherein Y comprises hydroxyl, mesylate, tosylate, phosphite ester, or chlorosulfite.

16. The flame retardant of claim 15 , wherein each X is

17. The flame retardant of claim 16 , wherein B is C 1 to C 18 alkyl, C 2 to C 18 alkenyl, or C 2 to C 18 alkynyl.

18. The flame retardant of claim 16 , wherein B is C 5 to C 20 cycloalkyl, or C 5 to C 20 aryl.

19. The flame retardant of claim 16 , wherein B comprises cyclopentyl, cyclohexyl, cyclooctyl, cyclodecyl, cyclopentyl-diene, benzyl, naphthyl, indenyl, or combinations thereof.

20. A method for producing a flame retardant, the method comprising:

producing a reaction mixture by contacting a lignin having free hydroxyl groups with a solvent and a phosphorous containing compound to form a covalent bond between the lignin and the phosphorous containing compound, wherein the phosphorous containing compound includes a compound of general formula:

wherein:

B is C 1 to C 18 open-chain hydrocarbyl or C 5 to C 20 carbocyclyl;

each X is, independently, phosphine, phosphine oxide, phosphinite, phosphonite, phosphinate, phosphonate, or phosphate, and

n is an integer of 2 to 8; and

introducing a catalyst into the reaction mixture.

21. The method of claim 20 , wherein producing the reaction mixture comprises contacting the lignin having free hydroxyl groups with the solvent and a phosphorous containing compound of general formula:

wherein Y is a leaving group.

22. The method of claim 20 , wherein producing the reaction mixture comprises contacting the lignin having free hydroxyl groups with the solvent and a phosphorous containing compound of general formula:

wherein Y comprises hydroxyl, mesylate, tosylate, phosphite ester, or chlorosulfite.

23. The method of claim 20 , wherein producing the reaction mixture comprises contacting the lignin having free hydroxyl groups with the solvent and a phosphorous containing compound of general formula:

wherein:

Y comprises hydroxyl, mesylate, tosylate, phosphite ester, or chlorosulfite;

B is C 1 to C 18 alkyl, C 2 to C 18 alkenyl, C 2 to C 18 alkynyl, C 5 to C 20 cycloalkyl, or C 5 to C 20 aryl; and

each X is independently

Z—(CH 2 ) m —

wherein:

Z is phosphine, phosphine oxide, phosphinite, phosphonite, phosphinate, phosphonate, or phosphate; and

m is an integer of 1 to 10.

24. The method of claim 23 , wherein each X is

25. The method of claim 24 , wherein:

producing the reaction mixture comprises contacting the lignin having free hydroxyl groups with at least one solvent selected from dimethyl sulfoxide, dimethyl acetamide, 1,4-dioxane, 1-methyl-2-pyrrolidinone, pyridine, hexamethylphosphoramide, N-methylpyrrolidone, nitromethane, dimethylformamide, acetonitrile, sulfolane, or combinations thereof;

introducing the catalyst comprises introducing at least one catalyst selected from azopyridine, triphenylphosphine, diethyl azodicarboxylate, diisopropyl azodicarboxylate or combinations thereof; and

the method further comprises:

adding water to the reaction mixture to produce a precipitant;

filtering the precipitant from the reaction mixture;

heating the precipitant in a dilute base comprising about 1 wt. % to about 5 wt. % solution of sodium hydroxide;

adding an acid to the precipitant in the dilute base to neutralize the pH; and

dehydrating the precipitant to form a flame retardant powder.