阅读说明：本技术 一种用于生物基高分子材料的磷氮阻燃剂的制备方法 (Preparation method of phosphorus-nitrogen flame retardant for bio-based high polymer material ) 是由 许月婷 赵莉莉 何志松 于 2021-01-11 设计创作，主要内容包括：本发明涉及化工领域,具体关于一种用于生物基高分子材料的磷氮阻燃剂的制备方法；本发明的一种用于生物基高分子材料的磷氮阻燃剂的制备方法,本发明提供了一种适用于生物基高分子材料的阻燃剂,该种阻燃剂是在聚磷酸铵表面接枝了生物基材料,具有其他阻燃剂与生物基高分子材料间所不具有的优良的分散性和相容性,不仅可以发挥碳源作用,还能更好的促进阻燃作用的发挥,阻燃更加高效；本发明的阻燃剂制备工序绿色环保,不涉及到任何有毒试剂,对环境相当的友好。(The invention relates to the field of chemical industry, in particular to a preparation method of a phosphorus-nitrogen flame retardant for a bio-based polymer material; the invention provides a preparation method of a phosphorus-nitrogen flame retardant for a bio-based polymer material, and provides a flame retardant suitable for the bio-based polymer material, wherein the flame retardant is formed by grafting a bio-based material on the surface of ammonium polyphosphate, has excellent dispersibility and compatibility which are not possessed by other flame retardants and the bio-based polymer material, can play a role of a carbon source, can better promote the play of a flame retardant role, and is more efficient in flame retardance; the preparation process of the flame retardant is environment-friendly, does not relate to any toxic reagent, and is environment-friendly.)

1. A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4-12.2 parts of casein into 200 parts of disodium hydrogen phosphate solution with the mass part of 2.5% -5.8%, stirring and mixing for 30-60min, then regulating the pH value of 10-15% phytic acid solution of 100-180 parts by mass with sodium hydroxide solution to 8.5-9.5, slowly adding into the reaction kettle, controlling the addition within 10-40min, then controlling the temperature to be 40-60 ℃, stirring and reacting for 60-120min, then adding 1.2-1.8 parts of metal salt into the reaction kettle, stirring for reaction for 120-180min, adding 65-78 parts of modified ammonium polyphosphate into the reaction kettle, controlling the temperature to be 50-70 ℃, stirring for reaction for 1-5h, and then cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

2. The method for preparing the phosphorus-nitrogen flame retardant for the bio-based polymer material according to claim 1, wherein the method comprises the following steps: the preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 60-68 parts by mass of ammonium polyphosphate into 200-80 parts by mass of 70-80% aqueous solution of an organic solvent, controlling the temperature to 65-80 ℃ under the protection of nitrogen, stirring and mixing for 30-60min, slowly adding 6-18 parts by mass of sulfanilic acid into a reaction kettle within 20-40min, controlling the temperature to 70-80 ℃, stirring and reacting for 5-10h, filtering after the reaction is finished, washing with the organic solvent, and drying; and then, under the protection of nitrogen, slowly adding the obtained product into 200-300 parts of 20-30% ethylene glycol diglycidyl ether solution by mass, controlling the adding to be finished within 60-120min, then controlling the temperature to be 40-75 ℃, stirring for reaction for 2-6h, cooling to room temperature after finishing the reaction, filtering, washing at one place, and drying to obtain the modified ammonium polyphosphate.

3. The method for preparing the phosphorus-nitrogen flame retardant for the bio-based polymer material according to claim 2, wherein the method comprises the following steps: the organic solvent is ethanol or isopropanol.

4. The method for preparing the phosphorus-nitrogen flame retardant for the bio-based polymer material according to claim 1, wherein the method comprises the following steps: the modified ammonium polyphosphate is solid powder with 300-400 meshes.

5. The method for preparing the phosphorus-nitrogen flame retardant for the bio-based polymer material according to claim 1, wherein the method comprises the following steps: the metal salt is nickel nitrate or nickel sulfate or ferric nitrate.

6. The method for preparing the phosphorus-nitrogen flame retardant for the bio-based polymer material according to claim 1, wherein the method comprises the following steps: the sodium hydroxide solution accounts for 5-10% by weight.

7. The method for preparing the phosphorus-nitrogen flame retardant for the bio-based polymer material according to claim 1, wherein the method comprises the following steps: the phosphorus-nitrogen flame retardant is added into the bio-based polymer material in a melt blending mode.

Technical Field

The invention relates to the field of chemical industry, in particular to a preparation method of a phosphorus-nitrogen flame retardant for a bio-based polymer material.

Background

The flame retardant property is an important component of the comprehensive properties of the material, but the high flammability is determined by the long carbon chain of the high molecular material. Not only limits the application field of the material, but also must be careful in the use of the material in the existing application range to strictly prevent the occurrence of fire.

CN104532588A discloses a composite intumescent flame retardant, which consists of 50-65% of acid source, 10-20% of gas source, 15-20% of carbon source and 10-20% of smoke suppressant by weight percentage, wherein: the acid source is at least one of ammonium polyphosphate, melamine phosphate and melamine polyphosphate, wherein the ammonium polyphosphate is crystal II type ammonium polyphosphate with the average polymerization degree of more than 1000; the gas source is at least one of melamine and dicyandiamide; the carbon source is at least one of pentaerythritol and dipentaerythritol; the smoke suppressant is at least one of magnesium hydroxide, aluminum hydroxide and zinc borate. The invention also discloses a preparation method of the composite intumescent flame retardant.

CN106243387B provides a preparation method of a heat-conducting flame retardant, which comprises the following steps: (a) weighing a main material, an auxiliary material and a first auxiliary agent, and mixing the main material, the auxiliary material and the first auxiliary agent at a first temperature to obtain a prefabricated body, wherein the main material comprises spherical magnesium hydroxide and a fibrous structure, and the mass ratio of the spherical magnesium hydroxide to the fibrous structure is 5: 1-20: 1; (b) and modifying the prefabricated body at a second temperature by using a second auxiliary agent and drying to obtain the heat-conducting flame retardant. The invention also provides a heat-conducting flame retardant.

CN110114352A relates to flame retardants comprising triazine compounds: r ═ phosphites substituted with alkyl, functionalized alkyl, aryl, functionalized aryl, except for alkyl or aryl substituted with halogen; r ═ alkylene, arylene, alkoxy, or aryloxy, all unsubstituted or functionalized except for halogen substitution; x1 and X2 ═ heteroatoms, X1 ═ X2 or X1 ≠ X2, as well as the specific triazine compounds themselves.

The application of bio-based polymer materials is more and more extensive, for example, polylactic acid materials are all involved in the aspects of fiber fabrics, packaging materials, 3D printing and the like; the LOI value of polylactic acid is only about 20 percent, and the polylactic acid belongs to flammable polymers. In addition, the melt dripping phenomenon is severe when polylactic acid is burned. In a fire, the fire passing area is increased by the drops with flames, so that the rapid development of fire conditions is caused, and the fire extinguishing difficulty of firemen is greatly increased; the first way to improve the flame retardant property of the bio-based polymer materials such as polylactic acid is to add some traditional additives, such as metal hydroxide, inorganic flame retardant, organic phosphorus system, intumescent flame retardant system, etc. into the material matrix by physical mixing. However, the flame retardant efficiency of the single element flame retardant additive is often not comparable to that of halogen, the flame retardant effect is not satisfactory, and the formation of molten drops during combustion cannot be effectively improved.

Disclosure of Invention

In order to solve the problems, the invention provides a preparation method of a phosphorus-nitrogen flame retardant for a bio-based polymer material.

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4-12.2 parts of casein into 200 parts of disodium hydrogen phosphate solution with the mass part of 2.5% -5.8%, stirring and mixing for 30-60min, then regulating the pH value of 10-15% phytic acid solution of 100-180 parts by mass with sodium hydroxide solution to 8.5-9.5, slowly adding into the reaction kettle, controlling the addition within 10-40min, then controlling the temperature to be 40-60 ℃, stirring and reacting for 60-120min, then adding 1.2-1.8 parts of metal salt into the reaction kettle, stirring for reaction for 120-180min, adding 65-78 parts of modified ammonium polyphosphate into the reaction kettle, controlling the temperature to be 50-70 ℃, stirring for reaction for 1-5h, and then cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 60-68 parts by mass of ammonium polyphosphate into 200-80 parts by mass of 70-80% aqueous solution of an organic solvent, controlling the temperature to 65-80 ℃ under the protection of nitrogen, stirring and mixing for 30-60min, slowly adding 6-18 parts by mass of sulfanilic acid into a reaction kettle within 20-40min, controlling the temperature to 70-80 ℃, stirring and reacting for 5-10h, filtering after the reaction is finished, washing with the organic solvent, and drying; and then, under the protection of nitrogen, slowly adding the obtained product into 200-300 parts of 20-30% ethylene glycol diglycidyl ether solution by mass, controlling the adding to be finished within 60-120min, then controlling the temperature to be 40-75 ℃, stirring for reaction for 2-6h, cooling to room temperature after finishing the reaction, filtering, washing at one place, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is ethanol or isopropanol.

The modified ammonium polyphosphate is solid powder with 300-400 meshes.

The metal salt is nickel nitrate or nickel sulfate or ferric nitrate.

The sodium hydroxide solution accounts for 5-10% by weight.

The phosphorus-nitrogen flame retardant is added into the bio-based polymer material in a melt blending mode.

The invention provides a preparation method of a phosphorus-nitrogen flame retardant for a bio-based polymer material, and provides a flame retardant suitable for the bio-based polymer material, wherein the flame retardant is formed by grafting a bio-based material on the surface of ammonium polyphosphate, has excellent dispersibility and compatibility which are not possessed by other flame retardants and the bio-based polymer material, can play a role of a carbon source, can better promote the play of a flame retardant role, and is more efficient in flame retardance; the preparation process of the flame retardant is environment-friendly, does not relate to any toxic reagent, and is environment-friendly.

The modified ammonium polyphosphate is grafted to an ammonium polyphosphate chain by using sulfanilic acid and ammonium polyphosphate to perform an ion exchange reaction, then ethylene glycol diglycidyl ether is reacted and grafted with a sulfonic group, and the reaction mode is controlled to ensure that an epoxy bond is reserved and provide an active site for grafting a bio-based material to the surface of the ammonium polyphosphate; the casein contains more amino groups, has stronger electrostatic action with phosphate groups in phytic acid, reacts with active sites on the surface of the modified ammonium polyphosphate after the two groups of biological materials react, is grafted to the surface of the modified ammonium polyphosphate to form a shell-core structure, and has a coating effect on the flame retardant.

Drawings

FIG. 1 is a Fourier infrared spectrum of the novel flame retardant for polylactic acid prepared in example 2:

at 1146cm^-1An absorption peak of a carbon-nitrogen single bond in the vicinity of 2929cm^-1The expansion absorption peak of carbon-hydrogen bond is present nearby and is 881cm^-1A symmetric telescopic absorption peak of a phosphorus-oxygen single bond is present nearby and is 1236cm^-1A telescopic absorption peak of phosphorus-oxygen double bonds exists nearby, so that the pyrrole-based modified organophosphorus compound participates in the reaction; at 1458cm^-1An antisymmetric telescopic absorption peak of carbonate exists nearby, which indicates that hydrotalcite participates in the reaction; at 740cm^-1A stretching absorption peak of silicon-carbon bond exists nearby, which indicates that allyl triethoxysilane participates in the reaction; at 1656cm^-1An absorption peak of carbon-nitrogen double bond exists nearby, which indicates that the 1-vinyl-3-butylimidazole bromide salt participates in the reaction.

Detailed Description

The invention is further illustrated by the following specific examples:

putting polylactic acid and the flame retardant prepared in each embodiment into an oven at 80 ℃ for baking for 24 hours to remove moisture adsorbed on the surface, putting the polylactic acid and the flame retardant into a double-screw extruder for melting and blending, granulating, and then carrying out hot-pressing melting in a vulcanizer to prepare a test sample strip; simultaneously preparing a blank sample; the amount of the flame retardant added was 5.5%. The test specimens were evaluated for flame level by means of a limiting oxygen index instrument, model JF-3 of Jiangning, Nanjing, according to the provisions of ISO 4589. The material used has dimensions of 100x10x3 (+ -0.1) mm³. The final result takes the critical volume fraction of oxygen as the limiting oxygen index value. The composite was evaluated for fire rating by means of a vertical fire determination apparatus, Nanjing Jiangning CZF-5, according to the regulations of ISO 9773. The material used has a size of 125x13x3.2 (+ -0.1) mm³. Five replicates of each formulation were run and their burn times were recorded.

Example 1

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4kg of casein into 200kg of 2.5% disodium hydrogen phosphate solution in parts by weight, stirring and mixing for 30min, then adjusting the pH value of 100kg of 10% phytic acid solution to 8.5 by using sodium hydroxide solution, slowly adding the solution into a reaction kettle, controlling the addition within 10min, controlling the temperature to be 40 ℃, stirring and reacting for 60min, then adding 1.2kg of metal salt into the reaction kettle, continuously stirring and reacting for 120min, adding 65kg of modified ammonium polyphosphate into the reaction kettle after the addition, controlling the temperature to be 50 ℃, stirring and reacting for 1h, cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 60kg of ammonium polyphosphate into 200kg of 70% organic solvent aqueous solution in parts by mass, stirring and mixing for 30min under the protection of nitrogen, controlling the temperature to 65 ℃, then slowly adding 6kg of sulfanilic acid into a reaction kettle within 20min, controlling the temperature to 70 ℃, stirring and reacting for 5h, filtering after the reaction is finished, washing with the organic solvent, and drying; and then slowly adding the obtained product into 200kg of 20% ethylene glycol diglycidyl ether solution under the protection of nitrogen, controlling the adding time to be 60min, controlling the temperature to be 40 ℃, stirring for reaction for 2h, cooling to room temperature after the reaction is finished, filtering, washing, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is ethanol.

The modified ammonium polyphosphate is solid powder with 300 meshes.

The metal salt is nickel nitrate.

The sodium hydroxide solution accounts for 5% by weight.

Example 2

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 10.6kg of casein into 230kg of disodium hydrogen phosphate solution with the mass fraction of 3.8%, stirring and mixing for 40min, then adjusting 140kg of phytic acid solution with the mass fraction of 12% to the pH value of 9 by using a sodium hydroxide solution, slowly adding the solution into a reaction kettle, controlling the adding within 30min, controlling the temperature to be 50 ℃, stirring and reacting for 90min, then adding 1.5kg of metal salt into the reaction kettle, continuously stirring and reacting for 150min, adding 70kg of modified ammonium polyphosphate into the reaction kettle, controlling the temperature to be 60 ℃, stirring and reacting for 3h, cooling to the room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 64kg of ammonium polyphosphate into 240kg of aqueous solution of 75% organic solvent in parts by mass, stirring and mixing for 40min under the protection of nitrogen, controlling the temperature to be 75 ℃, then slowly adding 12kg of sulfanilic acid into a reaction kettle within 30min, controlling the temperature to be 75 ℃, stirring and reacting for 8h, filtering after completion, washing with the organic solvent, and drying; and then slowly adding the obtained product into 240kg of 25% ethylene glycol diglycidyl ether solution under the protection of nitrogen, controlling the adding to be finished within 90min, controlling the temperature to be 55 ℃, stirring for reacting for 4h, cooling to room temperature after the reaction is finished, filtering, washing, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is isopropanol.

The modified ammonium polyphosphate is solid powder with 400 meshes.

The metal salt is nickel sulfate.

The sodium hydroxide solution accounts for 10% by weight.

Example 3

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 12.2kg of casein into 250kg of 5.8% disodium hydrogen phosphate solution in parts by weight, stirring and mixing for 60min, then adjusting the pH value of 180kg of 15% phytic acid solution to 9.5 by using sodium hydroxide solution, slowly adding the solution into a reaction kettle, controlling the adding within 40min, controlling the temperature to be 60 ℃, stirring and reacting for 120min, then adding 1.8kg of metal salt into the reaction kettle, continuously stirring and reacting for 180min, adding 78kg of modified ammonium polyphosphate into the reaction kettle after the adding, controlling the temperature to be 70 ℃, stirring and reacting for 5h, cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 68kg of ammonium polyphosphate into 300kg of aqueous solution of 80% organic solvent in parts by mass, stirring and mixing for 60min under the protection of nitrogen, controlling the temperature to 80 ℃, then slowly adding 18kg of sulfanilic acid into a reaction kettle within 40min, controlling the temperature to 80 ℃, stirring and reacting for 10h, filtering after the reaction is finished, washing with the organic solvent, and drying; and then slowly adding the obtained product into 300kg of 30% ethylene glycol diglycidyl ether solution in parts by mass under the protection of nitrogen, controlling the adding to be finished within 120min, controlling the temperature to be 75 ℃, stirring for reacting for 6h, cooling to room temperature after the reaction is finished, filtering, washing, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is isopropanol.

The modified ammonium polyphosphate is solid powder with 400 meshes.

The metal salt is ferric nitrate.

The sodium hydroxide solution accounts for 10% by weight.

The limiting oxygen index and the burning time of the flame retardant prepared in the above examples applied to the polylactic acid material are shown in the following table:

	limiting oxygen index	Burning time(s)
			Blank experiment	19.8	Complete combustion
Example 1	35.3	3.6
			Example 2	36.2	2.7
Example 3	38.4	1.9

Comparative example 1

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4kg of casein into 200kg of 2.5% disodium hydrogen phosphate solution in parts by weight, stirring and mixing for 30min, then adjusting the pH value of 100kg of 10% phytic acid solution to 8.5 by using sodium hydroxide solution, slowly adding the solution into a reaction kettle, controlling the addition within 10min, controlling the temperature to be 40 ℃, stirring and reacting for 60min, then adding 1.2kg of metal salt into the reaction kettle, continuously stirring and reacting for 120min, adding 65kg of ammonium polyphosphate into the reaction kettle after the completion, controlling the temperature to be 50 ℃, stirring and reacting for 1h, cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The modified ammonium polyphosphate is solid powder with 300 meshes.

The metal salt is nickel nitrate.

The sodium hydroxide solution accounts for 5% by weight.

Comparative example 2

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4kg of casein into 200kg of 2.5% disodium hydrogen phosphate solution in parts by weight, stirring and mixing for 30min, then adjusting the pH value of 100kg of 10% phytic acid solution to 8.5 by using sodium hydroxide solution, slowly adding the solution into a reaction kettle, controlling the addition within 10min, controlling the temperature to be 40 ℃, stirring and reacting for 60min, then adding 1.2kg of metal salt into the reaction kettle, continuously stirring and reacting for 120min, adding 65kg of modified ammonium polyphosphate into the reaction kettle after the addition, controlling the temperature to be 50 ℃, stirring and reacting for 1h, cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 60kg of ammonium polyphosphate into 200kg of 70% organic solvent aqueous solution in parts by mass, stirring and mixing for 30min under the protection of nitrogen, controlling the temperature to 65 ℃, then slowly adding 6kg of sulfanilic acid into a reaction kettle within 20min, controlling the temperature to 70 ℃, stirring and reacting for 5h, filtering after the reaction is finished, washing with an organic solvent, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is ethanol.

The modified ammonium polyphosphate is solid powder with 300 meshes.

The metal salt is nickel nitrate.

The sodium hydroxide solution accounts for 5% by weight.

Comparative example 3

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4kg of casein into 200kg of 2.5% disodium hydrogen phosphate solution in parts by weight, stirring and mixing for 30min, then adjusting the pH value of 100kg of 10% phytic acid solution to 8.5 by using sodium hydroxide solution, slowly adding into a reaction kettle, controlling the adding within 10min, controlling the temperature to be 40 ℃, stirring and reacting for 60min, then adding 65kg of modified ammonium polyphosphate into the reaction kettle, controlling the temperature to be 50 ℃, stirring and reacting for 1h, cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 60kg of ammonium polyphosphate into 200kg of 70% organic solvent aqueous solution in parts by mass, stirring and mixing for 30min under the protection of nitrogen, controlling the temperature to 65 ℃, then slowly adding 6kg of sulfanilic acid into a reaction kettle within 20min, controlling the temperature to 70 ℃, stirring and reacting for 5h, filtering after the reaction is finished, washing with the organic solvent, and drying; and then slowly adding the obtained product into 200kg of 20% ethylene glycol diglycidyl ether solution under the protection of nitrogen, controlling the adding time to be 60min, controlling the temperature to be 40 ℃, stirring for reaction for 2h, cooling to room temperature after the reaction is finished, filtering, washing, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is ethanol.

The modified ammonium polyphosphate is solid powder with 300 meshes.

The metal salt is nickel nitrate.

The sodium hydroxide solution accounts for 5% by weight.

Comparative example 4

A preparation method of a phosphorus-nitrogen flame retardant for a bio-based high polymer material comprises the following specific preparation scheme:

adding 8.4kg of casein into 200kg of 2.5% disodium hydrogen phosphate solution in parts by weight, stirring and mixing for 30min, then adding 1.2kg of metal salt into a reaction kettle, continuously stirring and reacting for 120min, adding 65kg of modified ammonium polyphosphate into the reaction kettle after the reaction is finished, controlling the temperature at 50 ℃, stirring and reacting for 1h, then cooling to room temperature, washing the collected product with deionized water, and drying to obtain the phosphorus-nitrogen flame retardant for the bio-based high polymer material.

The preparation method of the modified ammonium polyphosphate comprises the following steps:

adding 60kg of ammonium polyphosphate into 200kg of 70% organic solvent aqueous solution in parts by mass, stirring and mixing for 30min under the protection of nitrogen, controlling the temperature to 65 ℃, then slowly adding 6kg of sulfanilic acid into a reaction kettle within 20min, controlling the temperature to 70 ℃, stirring and reacting for 5h, filtering after the reaction is finished, washing with the organic solvent, and drying; and then slowly adding the obtained product into 200kg of 20% ethylene glycol diglycidyl ether solution under the protection of nitrogen, controlling the adding time to be 60min, controlling the temperature to be 40 ℃, stirring for reaction for 2h, cooling to room temperature after the reaction is finished, filtering, washing, and drying to obtain the modified ammonium polyphosphate.

The organic solvent is ethanol.

The modified ammonium polyphosphate is solid powder with 300 meshes.

The metal salt is nickel nitrate.

The sodium hydroxide solution accounts for 5% by weight.

The limiting oxygen index and the burning time of the flame retardant prepared in the above examples applied to the polylactic acid material are shown in the following table:

	limiting oxygen index	Burning time(s)
			Comparative example 1	28.2	8.1
Comparative example 2	31.8	6.2
			Comparative example 3	34.1	4.8
Comparative example 4	32.4	5.6