Preparation method of phenolic acid-based phosphorus-nitrogen flame retardant, phenolic acid-based phosphorus-nitrogen flame retardant and application of phenolic acid-based phosphorus-nitrogen flame retardant

Abstract

The invention discloses a preparation method of a phenolic acid-based phosphorus-nitrogen flame retardant, the phenolic acid-based phosphorus-nitrogen flame retardant and application of the phenolic acid-based phosphorus-nitrogen flame retardant, and the preparation method comprises the following steps: S1, dissolving a phenolic acid compound in absolute ethyl alcohol, adding 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, carrying out heating reaction, then cooling, carrying out reduced pressure distillation, washing with deionized water, filtering and drying to obtain a flame-retardant intermediate; and S2, dissolving the flame-retardant intermediate in the step S1 in an organic solvent, dropwise adding phosphonitrilic chloride trimer dissolved by the organic solvent, carrying out heating reaction, cooling, carrying out reduced pressure distillation, washing with deionized water, filtering, and drying to obtain the phenolic acid-based phosphorus-nitrogen flame retardant. According to the present invention, the natural renewable phenolic acid compound is adopted as the main raw material, the chemical structure of the phenolic acid compound contains phosphorus atoms of different valence states so as to simultaneously provide the condensed phase and gas phase flame retardation mechanism, and the structure contains the nitrogen element and the aromatic ring so as to be suitable for the efficient flame retardation treatment of the polylactic acid material, and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and specifically relates to a preparation method of a phenolic acid-based phosphorus-nitrogen flame retardant, the phenolic acid-based phosphorus-nitrogen flame retardant and applications thereof. Background Art

[0002] Polylactic acid (PLA) is a polymer formed by the dehydration condensation of -OH and -COOH in lactic acid molecules. As a biodegradable material, it has good processability, mechanical strength, biocompatibility, degradability and environmental friendliness, and has been widely used in drug delivery, chemical fiber textiles, packaging materials and agricultural production. However, polylactic acid is a flammable material with a limiting oxygen index of only about 19%, and obvious droplet phenomenon, which is easy to cause secondary fires, which greatly limits its further application and development. Therefore, it is particularly important to improve the flame retardant properties of polylactic acid.

[0003] In recent years, organic phosphorus or phosphorus nitrogen flame retardants have been widely used in halogen-free flame retardant polylactic acid materials due to their advantages of halogen-free, low toxicity and high flame retardant efficiency. The flame retardant mechanism of phosphorus flame retardants mainly includes condensed phase and gas phase flame retardant mechanisms. In the condensed phase, phosphorus flame retardants are thermally decomposed to form acidic compounds such as polymetaphosphoric acid, which catalyze the dehydration, cyclization and carbonization of polymers, and form a barrier carbon layer on the surface of the polymer to prevent heat and material exchange; in the gas phase, phosphorus flame retardants are thermally decomposed to form volatile PO free radicals, which can capture active hydrogen atoms and prevent the combustion chain reaction. At present, the development of phosphorus or phosphorus nitrogen flame retardants is mostly concentrated on compounds containing single-valent phosphorus elements. Their flame retardant mechanism is relatively simple, and there are problems such as low flame retardant efficiency and high addition amount (usually greater than 10%), which often have a certain impact on the mechanical properties of polylactic acid. In addition, the current synthesis of flame retardants mainly relies on petrochemical resources. Therefore, the development of efficient bio-based phosphorus nitrogen flame retardants has become an urgent need in the field of flame retardant polymer technology. Summary of the invention

[0004] In order to solve the deficiencies in the prior art, the present invention provides a preparation method of a phenolic acid-based phosphorus-nitrogen flame retardant, a phenolic acid-based phosphorus-nitrogen flame retardant and an application thereof. The phenolic acid-based phosphorus-nitrogen flame retardant provided by the present invention uses natural renewable phenolic acid compounds as main raw materials, and its chemical structure not only contains phosphorus atoms of different valence states, which can simultaneously exert condensed phase and gas phase flame retardant mechanisms, but also contains nitrogen elements and aromatic rings in the structure, and is suitable for efficient flame retardant treatment of polylactic acid materials.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The preparation method of the phenolic acid-based phosphorus-nitrogen flame retardant comprises the following steps:

[0007] S1. dissolving a phenolic acid compound in anhydrous ethanol, adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, heating to react, then cooling, distilling under reduced pressure, washing with deionized water, filtering, and drying to obtain a flame retardant intermediate;

[0008] S2, dissolving the flame retardant intermediate in S1 in an organic solvent, adding hexachlorocyclotriphosphazene dissolved in the organic solvent dropwise, heating to react, then cooling, distilling under reduced pressure, washing with deionized water, filtering, and drying to obtain a phenolic acid-based phosphorus-nitrogen flame retardant.

[0009] Preferably, the phenolic acid compound in S1 is any one of chlorogenic acid, caffeic acid and p-coumaric acid.

[0010] Preferably, the molar ratio of the phenolic acid compound to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in S1 is 1:1.

[0011] Preferably, the temperature range of the temperature-raising reaction in S1 is 70-80° C., and the time range of the temperature-raising reaction is 4-8 hours.

[0012] Preferably, the molar ratio of the flame retardant intermediate to hexachlorocyclotriphosphazene in S2 is in the range of 1:1 to 3:1.

[0013] Preferably, the organic solvent in S2 is any one of acetonitrile or tetrahydrofuran.

[0014] Preferably, the temperature range of the temperature-raising reaction in S2 is 60 to 80° C., and the time range of the temperature-raising reaction is 6 to 12 hours.

[0015] The invention also discloses a phenolic acid-based phosphorus-nitrogen flame retardant, which is prepared by the preparation method of the phenolic acid-based phosphorus-nitrogen flame retardant.

[0016] The invention also discloses the application of the phenolic acid-based phosphorus-nitrogen flame retardant in flame-retardant polylactic acid.

[0017] Preferably, in terms of mass percentage, the mass fraction of the phenolic acid-based phosphorus-nitrogen flame retardant in the flame-retardant polylactic acid is 1.5-2.5%.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects:

[0019] (1) The phenolic acid compounds in the present invention are products of secondary metabolism and widely exist in various plants in nature. Their structures contain not only phenolic hydroxyl groups, but also carboxylic acids, unsaturated double bonds, etc., such as chlorogenic acid, caffeic acid, and p-coumaric acid. They have high reactivity, which lays a foundation for their use as synthetic raw materials for flame retardants.

[0020] (2) In the present invention, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and hexachlorocyclotriphosphazene are flame retardant materials mainly based on gas phase flame retardant mechanism and condensed phase flame retardant mechanism, respectively. The active PH bond in the structure of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide reacts with the carbon-carbon double bond in the phenolic acid compound by addition reaction, and the P-Cl in the structure of hexachlorocyclotriphosphazene reacts with the phenolic hydroxyl group and the carboxyl group in the phenolic acid compound by nucleophilic substitution reaction, so as to prepare a phenolic acid-based phosphorus nitrogen flame retardant having both gas phase and condensed phase flame retardant mechanism;

[0021] (3) The phenolic acid-based phosphorus-nitrogen flame retardant prepared in the present invention uses natural renewable phenolic acid compounds as the main raw materials, does not contain halogens and metal elements, and its chemical structure not only contains phosphorus atoms of different valence states, but also can play a role in the condensed phase and gas phase flame retardant mechanism, making up for the low flame retardant efficiency of a single flame retardant mechanism, and contains nitrogen elements and aromatic rings in the structure, which is suitable for efficient flame retardant treatment of polylactic acid materials;

[0022] (4) The phenolic acid-based phosphorus-nitrogen flame retardant provided by the present invention uses natural renewable plant biomass as the main raw material, which reduces the consumption of petrochemical resources and belongs to a bio-based flame retardant;

[0023] (5) The phenolic acid-based phosphorus-nitrogen flame retardant provided by the present invention contains phosphorus elements of different valence states, which can exert both condensed phase and gas phase flame retardant mechanisms, have high flame retardant efficiency, and have good compatibility with polylactic acid, and are suitable for industrial production and promotion and application;

[0024] In summary, the present invention has the advantages of using natural renewable phenolic acid compounds as the main raw materials, and its chemical structure not only contains phosphorus atoms of different valence states, which can simultaneously exert the condensed phase and gas phase flame retardant mechanisms, but also contains nitrogen elements and aromatic rings in the structure, which is suitable for efficient flame retardant treatment of polylactic acid materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Video screenshots of the flame retardant polylactic acid provided in specific example 4 of the present invention and the polylactic acid provided in comparative example 3 during the vertical combustion test.

[0026] Figure 2 Scanning electron microscope images of the fracture surfaces of the flame-retardant polylactic acid provided in specific embodiment 4 of the present invention and the polylactic acid provided in comparative example 3 after mechanical property testing. DETAILED DESCRIPTION

[0027] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0028] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0029] Those skilled in the art will recognize that the chemical reactions described herein can be used to appropriately prepare many other compounds of the invention, and other methods for preparing the compounds of the invention are considered to be within the scope of the invention. For example, the synthesis of non-exemplified compounds according to the invention can be successfully accomplished by those skilled in the art through modification methods, such as appropriate protection of interfering groups, by utilizing other known reagents in addition to those described herein, or by making some conventional modifications to the reaction conditions. In addition, the reactions disclosed herein or known reaction conditions are also recognized to be applicable to the preparation of other compounds of the invention.

[0030] The raw materials used in the following examples of the present invention are as follows: phenolic acid compounds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, hexachlorocyclotriphosphazene, and organic solvents are all commercially available conventional products. Among them, polylactic acid was purchased from Total Energies Company of Thailand, with a brand name of LX-175 and a melt index of 6.2 g / 10 min (210° C. / 2.16 kg), wherein 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is abbreviated as DOPO, and hexachlorocyclotriphosphazene is abbreviated as HCCP.

[0031] The performance measurement methods involved in the following embodiments listed in the present invention are described as follows: the vertical combustion grade is obtained by testing with a CZF-2 vertical combustion instrument in accordance with GB / T 2408-2008; the limiting oxygen index is obtained by testing with a HC-2C oxygen index tester in accordance with GB / T 2406.1-2008; and the mechanical properties are obtained by testing with an Instron 3366 uniaxial tensile testing machine in accordance with GB / T 1040.2-2006.

[0032] Example 1

[0033] The preparation method of the phenolic acid-based phosphorus-nitrogen flame retardant of the present invention comprises the following steps:

[0034] S1. Dissolve a phenolic acid compound in anhydrous ethanol, add 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, heat the reaction, and then cool, distill under reduced pressure, wash with deionized water, filter, and dry to obtain a flame retardant intermediate, wherein the phenolic acid compound is any one of chlorogenic acid, caffeic acid, and p-coumaric acid, the molar ratio of the phenolic acid compound to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 1:1, the temperature range of the temperature reaction is 70 to 80°C, and the time range of the temperature reaction is 4 to 8h;

[0035] S2. Dissolve the flame retardant intermediate in S1 in an organic solvent, add hexachlorocyclotriphosphazene dissolved in the organic solvent dropwise, heat the reaction, then cool, distill under reduced pressure, wash with deionized water, filter, and dry to obtain a phenolic acid-based phosphorus-nitrogen flame retardant, the molar ratio of the flame retardant intermediate to hexachlorocyclotriphosphazene is in the range of 1:1 to 3:1, the organic solvent is any one of acetonitrile or tetrahydrofuran, the temperature range of the temperature reaction is 60 to 80°C, and the time range of the temperature reaction is 6 to 12 hours.

[0036] The invention also discloses a phenolic acid-based phosphorus-nitrogen flame retardant, which is prepared by the preparation method of the phenolic acid-based phosphorus-nitrogen flame retardant.

[0037] The present invention also discloses the application of the phenolic acid-based phosphorus-nitrogen flame retardant in flame-retardant polylactic acid, wherein the mass fraction of the phenolic acid-based phosphorus-nitrogen flame retardant in the flame-retardant polylactic acid is 1.5-2.5% by mass.

[0038] Specifically, in this embodiment, the phenolic acid-based phosphorus-nitrogen flame retardant and the flame-retardant polylactic acid containing the phenolic acid-based phosphorus-nitrogen flame retardant are specifically prepared by the above method;

[0039] (1) dissolving 0.5 mol of chlorogenic acid in anhydrous ethanol, adding 0.5 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), reacting at 70° C. for 8 h, cooling, distilling under reduced pressure, washing with deionized water, filtering, and drying to obtain a flame retardant intermediate;

[0040] (2) 0.1 mol of the flame retardant intermediate is dissolved in tetrahydrofuran, 0.1 mol of hexachlorocyclotriphosphazene (HCCP) dissolved in tetrahydrofuran is added dropwise, the mixture is reacted at 60° C. for 12 h, cooled, distilled under reduced pressure, washed with deionized water, filtered, and dried to obtain a phenolic acid-based phosphorus-nitrogen flame retardant.

[0041] The composite material containing 1.5% phenolic acid-based phosphorus nitrogen flame retardant and 98.5% polylactic acid, in terms of mass percentage, was placed at 80°C for vacuum drying for 4 h, melt blended in a micro extruder (temperature 185°C, speed 50 r / min, time 10 min), extruded into pellets, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain a flame-retardant polylactic acid material.

[0042] Example 2

[0043] In this embodiment, the method in Example 1 is also used to prepare a phenolic acid-based phosphorus-nitrogen flame retardant and a flame-retardant polylactic acid containing the phenolic acid-based phosphorus-nitrogen flame retardant, but the specific material ratio, reaction conditions, etc. are different;

[0044] (1) dissolving 0.5 mol of p-coumaric acid in anhydrous ethanol, adding 0.5 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), reacting at 75° C. for 6 h, cooling, distilling under reduced pressure, washing with deionized water, filtering, and drying to obtain a flame retardant intermediate;

[0045] (2) 0.3 mol of the flame retardant intermediate is dissolved in tetrahydrofuran, 0.1 mol of hexachlorocyclotriphosphazene (HCCP) dissolved in tetrahydrofuran is added dropwise, the mixture is reacted at 65° C. for 8 h, cooled, distilled under reduced pressure, washed with deionized water, filtered, and dried to obtain a phenolic acid-based phosphorus-nitrogen flame retardant.

[0046] The composite material containing 2.5% phenolic acid-based phosphorus nitrogen flame retardant and 97.5% polylactic acid, in terms of mass percentage, was placed at 80°C for vacuum drying for 4 h, melt blended in a micro extruder (temperature 185°C, speed 50 r / min, time 10 min), extruded into pellets, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain a flame-retardant polylactic acid material.

[0047] Example 3

[0048] In this embodiment, the method in Example 1 is also used to prepare a phenolic acid-based phosphorus-nitrogen flame retardant and a flame-retardant polylactic acid containing the phenolic acid-based phosphorus-nitrogen flame retardant, but the specific material ratio, reaction conditions, etc. are different;

[0049] (1) dissolving 0.5 mol of caffeic acid in anhydrous ethanol, adding 0.5 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), reacting at 80° C. for 4 h, cooling, vacuum distillation, washing with deionized water, filtering, and drying to obtain a flame retardant intermediate;

[0050] (2) 0.2 mol of the flame retardant intermediate is dissolved in acetonitrile, 0.1 mol of hexachlorocyclotriphosphazene (HCCP) dissolved in acetonitrile is added dropwise, the mixture is reacted at 80° C. for 6 h, cooled, distilled under reduced pressure, washed with deionized water, filtered, and dried to obtain a phenolic acid-based phosphorus-nitrogen flame retardant.

[0051] The composite material containing 2.0% phenolic acid-based phosphorus nitrogen flame retardant and 98.0% polylactic acid, in terms of mass percentage, was placed at 80°C for vacuum drying for 4 h, melt blended in a micro extruder (temperature 185°C, rotation speed 50 r / min, time 10 min), extruded into pellets, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain a flame-retardant polylactic acid material.

[0052] Example 4

[0053] In this embodiment, the method in Example 1 is also used to prepare a phenolic acid-based phosphorus-nitrogen flame retardant and a flame-retardant polylactic acid containing the phenolic acid-based phosphorus-nitrogen flame retardant, but the specific material ratio, reaction conditions, etc. are different;

[0054] (1) dissolving 0.5 mol of caffeic acid in anhydrous ethanol, adding 0.5 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), reacting at 80° C. for 4 h, cooling, vacuum distillation, washing with deionized water, filtering, and drying to obtain a flame retardant intermediate;

[0055] (2) 0.3 mol of the flame retardant intermediate is dissolved in tetrahydrofuran, 0.1 mol of hexachlorocyclotriphosphazene (HCCP) dissolved in tetrahydrofuran is added dropwise, the mixture is reacted at 75° C. for 10 h, cooled, distilled under reduced pressure, washed with deionized water, filtered, and dried to obtain a phenolic acid-based phosphorus-nitrogen flame retardant.

[0056] The composite material containing 2.0% phenolic acid-based phosphorus nitrogen flame retardant and 98.0% polylactic acid, in terms of mass percentage, was placed at 80°C for vacuum drying for 4 h, melt blended in a micro extruder (temperature 185°C, rotation speed 50 r / min, time 10 min), extruded into pellets, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain a flame-retardant polylactic acid material.

[0057] Comparative Example 1

[0058] This embodiment provides a method for preparing a phenolic acid-based flame retardant and a flame-retardant polylactic acid containing the phenolic acid-based flame retardant

[0059] 0.5 mol of caffeic acid was dissolved in anhydrous ethanol, 0.5 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was added, the mixture was reacted at 70° C. for 6 h, cooled, distilled under reduced pressure, washed with deionized water, filtered, and dried to obtain a phenolic acid-based flame retardant.

[0060] The composite material containing 2.0% phenolic acid-based phosphorus nitrogen flame retardant and 98.0% polylactic acid, in terms of mass percentage, was placed at 80°C for vacuum drying for 4 h, melt blended in a micro extruder (temperature 185°C, rotation speed 50 r / min, time 10 min), extruded into pellets, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain a flame-retardant polylactic acid material.

[0061] Comparative Example 2

[0062] This embodiment provides a method for preparing a phenolic acid-based flame retardant and a flame-retardant polylactic acid containing the phenolic acid-based flame retardant

[0063] 0.3 mol of caffeic acid was dissolved in tetrahydrofuran, and 0.1 mol of hexachlorocyclotriphosphazene (HCCP) dissolved in tetrahydrofuran was added dropwise, reacted at 75° C. for 10 h, cooled, distilled under reduced pressure, washed with deionized water, filtered, and dried to obtain a phenolic acid-based flame retardant.

[0064] The composite material containing 2.0% phenolic acid-based phosphorus nitrogen flame retardant and 98.0% polylactic acid, in terms of mass percentage, was placed at 80°C for vacuum drying for 4 h, melt blended in a micro extruder (temperature 185°C, rotation speed 50 r / min, time 10 min), extruded into pellets, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain a flame-retardant polylactic acid material.

[0065] Comparative Example 3

[0066] This embodiment provides a polylactic acid without flame retardant

[0067] The polylactic acid was placed in a vacuum dryer at 80°C for 4 hours, melt-blended in a micro extruder (temperature 185°C, rotation speed 50r / min, time 10min), extruded into granules, and then compression molded on a micro injection molding machine (temperature 190°C) to obtain the polylactic acid material.

[0068] The flame retardant polylactic acid prepared in Examples 1-4 and the polylactic acid prepared in Comparative Examples 1-3 were tested for flame retardancy and mechanical properties, and the results are as follows:

[0069] Specifically, the vertical combustion grade is obtained by testing with a CZF-2 vertical combustion instrument in accordance with GB / T 2408-2008;

[0070] The limiting oxygen index is obtained by testing with an HC-2C oxygen index tester in accordance with GB / T 2406.1-2008;

[0071] The mechanical properties were obtained by using an Instron 3366 uniaxial tensile testing machine according to GB / T 1040.2-2006;

[0072] Table 1 Performance test results of polylactic acid composite materials provided in the embodiments of the present invention and comparative examples

[0073]

[0074] The flame retardant and mechanical properties test results of the flame retardant polylactic acid provided by Examples 1-4 and the polylactic acid provided by Comparative Examples 1-3 shown in Table 1 and the reference Figure 1 and Figure 2 It can be seen that the addition of the phenolic acid-based phosphorus-nitrogen flame retardant of the present invention effectively improves the flame retardant properties of polylactic acid. When the addition amount is greater than 1.5%, the limiting oxygen index of the polylactic acid composite material exceeds 28%, and at the same time passes the UL-94 vertical combustion test V-0 grade. In addition, compared with the flame retardant synthesized by modifying phenolic acid compounds using DOPO or HCCP alone, the phenolic acid-based phosphorus-nitrogen flame retardant contains phosphorus atoms of different valence states in its chemical structure, which can simultaneously exert condensed phase and gas phase flame retardant mechanisms, making up for the low flame retardant efficiency of a single flame retardant mechanism, and has a higher flame retardant efficiency for polylactic acid materials. The mechanical property test results show that the addition of the phenolic acid-based phosphorus-nitrogen flame retardant will not destroy the mechanical properties of polylactic acid, and its tensile strength and elongation at break remain basically unchanged. This is because the phenolic acid-based phosphorus-nitrogen flame retardant has good compatibility with the polylactic acid matrix. It can be seen that the phenolic acid-based phosphorus-nitrogen flame retardant provided by the present invention has high flame retardant efficiency for polylactic acid materials, does not affect the mechanical properties of the material, and is suitable for large-scale promotion and application.

[0075] This embodiment does not impose any formal limitation on the shape, material, structure, etc. of the present invention. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a phenolic acid-based phosphorus-nitrogen flame retardant, characterized in that: The following steps are involved: S1. dissolving a phenolic acid compound in anhydrous ethanol, adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, heating to react, then cooling, distilling under reduced pressure, washing with deionized water, filtering, and drying to obtain a flame retardant intermediate; S2, dissolving the flame retardant intermediate in S1 in an organic solvent, adding hexachlorocyclotriphosphazene dissolved in the organic solvent dropwise, heating to react, then cooling, distilling under reduced pressure, washing with deionized water, filtering, and drying to obtain a phenolic acid-based phosphorus-nitrogen flame retardant.

2. The method for preparing the phenolic acid-based phosphorus-nitrogen flame retardant according to claim 1, characterized in that: The phenolic acid compound in S1 is any one of chlorogenic acid, caffeic acid and p-coumaric acid.

3. The method for preparing a phenolic acid-based phosphorus-nitrogen flame retardant according to claim 1, characterized in that: The molar ratio of the phenolic acid compound to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide in S1 is 1:

1.

4. The method for preparing the phenolic acid-based phosphorus-nitrogen flame retardant according to claim 1, characterized in that: The temperature range of the temperature-raising reaction in S1 is 70-80° C., and the time range of the temperature-raising reaction is 4-8 hours.

5. The method for preparing a phenolic acid-based phosphorus-nitrogen flame retardant according to claim 1, characterized in that: The molar ratio of the flame retardant intermediate to hexachlorocyclotriphosphazene in S2 is in the range of 1:1 to 3:

1.

6. The method for preparing a phenolic acid-based phosphorus-nitrogen flame retardant according to claim 1, characterized in that: The organic solvent in S2 is any one of acetonitrile or tetrahydrofuran.

7. The method for preparing a phenolic acid-based phosphorus-nitrogen flame retardant according to claim 1, characterized in that: The temperature range of the temperature-raising reaction in S2 is 60-80° C., and the time range of the temperature-raising reaction is 6-12 hours.

8. Phenolic acid-based phosphorus-nitrogen flame retardant, characterized in that: The flame retardant is prepared by the method for preparing the phenolic acid-based phosphorus-nitrogen flame retardant according to any one of claims 1 to 7.

9. Use of the phenolic acid-based phosphorus-nitrogen flame retardant as claimed in claim 8 in flame-retardant polylactic acid.

10. The use of the phenolic acid-based phosphorus-nitrogen flame retardant in flame-retardant polylactic acid according to claim 9, characterized in that: Calculated by mass percentage, the mass fraction of the phenolic acid-based phosphorus-nitrogen flame retardant is 1.5-2.5%.

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