Flame retardants

1. A flame retardant comprising:

rice husk comprising silica and lignin, wherein the rice husk is micronized to an effective size, wherein the effective size of the rice husk is about 1 μm to about 750 μm,

and wherein the lignin and the silica are chemically modified, wherein:

lignin chemical modification comprises the addition of a moiety selected from the group consisting of chlorine, iodine, fluorine, phosphoric acid esters, sulfhydryl groups, sulfate groups, organic carbonate, and inorganic carbonate, and silica chemical modification comprises the addition of a functional group selected from the group consisting of an amine group, a hydroxyl group, a silane, isocyanate, vinyl, siloxane, thiol, sulfate, phosphine, and phosphate.

2. The flame retardant of claim 1 , wherein the flame retardant is in the form of a dry powder, a wet slurry, or a liquid.

3. The flame retardant of claim 1 , further comprising a propellant.

4. The flame retardant of claim 3 , wherein the propellant includes an inert gas.

5. The flame retardant of claim 4 , wherein the inert gas includes at least one of:

carbon dioxide; or

nitrogen.

6. A composition comprising a substrate and the flame retardant of claim 1 .

7. A flame retardant comprising:

chemically modified rice husk, wherein the chemically modified rice husk includes:

silica, wherein the silica has been chemically modified with the addition of a functional group selected from the group consisting of:

an amine group;

a hydroxyl group;

a silane;

isocyanate;

vinyl;

siloxane;

thiol;

sulfate;

phosphine; and

phosphate; and

lignin, wherein the lignin has been chemically modified with the addition of a moiety selected from the group consisting of:

chlorine:

iodine;

fluorine;

phosphoric acid esters;

sulfhydryl groups;

sulfate groups;

organic carbonate; and

inorganic carbonate; and

wherein the chemically modified rice husk is micronized to an effective size, wherein the effective size of the chemically moditfied rice husk is between 10 μm to about 750 μm.

8. The flame retardant of claim 7 , wherein the effective size of the chemically modified rice husk is about 50 μm.

9. The flame retardant of claim 7 , wherein the functional group is selected from the group consisting of:

an amine group;

a hydroxyl group; and

a silane.

10. The flame retardant of claim 7 , wherein the functional group is selected from the group consisting of:

isocyanate;

vinyl; and

siloxane.

11. The flame retardant of claim 7 , wherein the functional group is selected from the group consisting of:

thiol;

sulfate;

phosphine; and

phosphate.

12. A flame retardant comprising:

chemically modified rice husk, wherein the chemically modified rice husk includes:

silica, wherein the silica has been chemically modified by reaction with 3-hydroxypropyltrimethoxysilane; and

lignin, wherein the lignin has been chemically modified by the addition of a moiety selected from the group consisting of phosphoric acid esters, sulfhydryl groups, sulfate groups, organic carbonate, and inorganic carbonate,

wherein the chemically modified rice husk is micronized to an effective size and wherein the effective size of the chemically modified rice husk is about 1 μm to about 750 μm.

13. The flame retardant of claim 12 , wherein the reaction between the silica and 3-hydroxypropyltrimethoxysilane results in a functional group that includes silicon hydroxide.

14. The flame retardant of claim 12 , wherein the moiety is a phosphoric acid ester.

15. The flame retardant of claim 12 , wherein the moiety is selected from the group consisting of:

sulfhydryl groups; and

sulfate groups.

16. The flame retardant of claim 12 , wherein the moiety is selected from the group consisting of:

organic carbonate; and

inorganic carbonate.