Diethylphosphinic acid-piperazine phosphate flame retardant as well as preparation method and application thereof

Abstract

The invention discloses a diethylphosphinic acid-piperazine phosphate flame retardant as well as a preparation method and application thereof, and aims to solve the problems of low flame retardant efficiency and poor compatibility of the conventional phosphorus-nitrogen flame retardant. The preparation method of the diethylphosphinic acid-piperazine phosphate flame retardant comprises the following steps: 1, adding piperazine and sodium diethylhypophosphite into a reaction device, adding distilled water, stirring and heating; 2, placing hydrochloric acid in a constant-pressure dropping funnel, dropwise adding hydrochloric acid, and heating for reaction; 3, adding phosphoric acid, heating for reaction, and cooling for crystallization; and 4, carrying out suction filtration and washing on the reaction liquid, and drying to obtain the phosphorus-nitrogen flame retardant diethyl phosphinic acid-piperazine phosphate. The PDHP flame retardant disclosed by the invention has good compatibility with a TPS material matrix. The flame retardant contains P-O, P-C and piperazine groups at the same time, and shows an efficient flame retardant effect in TPS. The TPS flame retardant is applied to TPS flame retardant modification.

Description

Technical Field

[0001] The invention relates to the field of phosphorus-nitrogen flame retardants, and in particular to a diethylphosphinic acid-piperazine phosphate flame retardant and a preparation method and application thereof. Background Art

[0002] Styrene-based thermoplastic elastomers (TPS) have the excellent properties of high elasticity, aging resistance, and oil resistance of traditional cross-linked vulcanized rubber at room temperature. They are a type of elastomer that can be plasticized and molded at high temperatures. They are widely used in automobile manufacturing, rail transportation, construction engineering, electronic appliances, aerospace, and other fields. However, traditional TPS is composed of styrene-ethylene / butylene-styrene triblock copolymer (SEBS), cyclohexane oil / aromatic oil / paraffin oil, and polyolefins (mainly polypropylene). Like traditional polyolefin polymers, TPS is extremely flammable, and the combustion process is accompanied by a large amount of flaming droplets and thick smoke, which poses a serious threat to people's lives and property safety. Therefore, in most of the application fields of TPS, it is necessary to perform necessary flame retardant modification on TPS.

[0003] In the early days, halogen flame retardants occupied a major position in the flame retardant modification process of TPS due to their low addition amount in TPS and high flame retardant efficiency. However, halogen flame retardants release a large amount of corrosive gases and strong carcinogens such as dioxins when the polymer burns, causing serious harm to people's life, health and environmental protection. Therefore, Europe has introduced the RoHS Directive and REACH regulations to restrict the use of halogen flame retardants, making the current halogen-free flame retardant TPS materials the main research direction. At present, the halogen-free flame retardants commonly used in TPS mainly include metal hydroxides, nitrogen-based, phosphorus-based and phosphorus-nitrogen flame retardants. Among them, the metal hydroxide commonly used in TPS flame retardant is mainly magnesium hydroxide, which has the advantages of being cheap, easy to obtain and environmentally friendly, but in the process of TPS flame retardant modification, it is added in large amounts, which greatly reduces the mechanical properties of flame-retardant TPS. Nitrogen flame retardants, such as melamine cyanurate and melamine derivatives, have the advantages of low toxicity, smoke suppression, low corrosiveness, and excellent thermal stability. However, when this type of flame retardant is used alone to modify TPS flame retardant, the desired flame retardant effect is often not achieved, which requires the addition of other types of flame retardants for compound use. Compared with phosphorus flame retardants, phosphorus-nitrogen flame retardants show better flame retardant efficiency in TPS through the synergistic effect of the condensed phase and the gas phase. However, due to the flammable structure of TPS itself, the traditional phosphorus-nitrogen flame retardant, which is mainly based on catalytic carbonization and carbon layer shielding, needs to be added to TPS at more than 30wt% to obtain the corresponding UL-94V-0 grade. At the same time, the more polar groups in the structure of traditional phosphorus-nitrogen flame retardants make them poorly compatible with the material matrix. At a high addition amount, it is easy to cause the mechanical properties of flame-retardant TPS to be significantly reduced. Therefore, it is urgent to develop high-efficiency phosphorus-nitrogen flame retardants suitable for TPS materials to meet the current rapidly developing high-end manufacturing industry's demand for high-performance flame-retardant TPS. Summary of the invention

[0004] The invention aims to solve the problems of low flame retardant efficiency and poor compatibility of existing phosphorus-nitrogen flame retardants, and provides a diethylphosphinic acid-piperazine phosphate flame retardant and a preparation method and application thereof.

[0005] The structural formula of the diethylphosphinic acid-piperazine phosphate flame retardant (PDHP) of the present invention is as follows:

[0006]

[0007] The preparation method of the above-mentioned diethylphosphinic acid-piperazine phosphate flame retardant comprises the following steps:

[0008] 1. Add piperazine and diethyl sodium hypophosphite into a reaction device, then add distilled water into the reaction device, stir thoroughly, and heat to dissolve piperazine and diethyl sodium hypophosphite;

[0009] 2. Place hydrochloric acid in a constant pressure dropping funnel and slowly drop hydrochloric acid into the reaction system of the reaction device. After the addition of hydrochloric acid is completed, heat it to 58-62°C to allow it to react fully;

[0010] 3. Then add phosphoric acid to the reaction system, raise the temperature to 78-82°C, react for 2-5 hours, and then cool the reaction solution for crystallization;

[0011] 4. The cooled reaction liquid is filtered and washed, and then placed in a forced air drying oven for drying at 105° C. for 3 to 6 hours to obtain a phosphorus-nitrogen flame retardant, diethylphosphinic acid-piperazine phosphate (PDHP).

[0012] Furthermore, the heating temperature in step 1 is 35-40°C.

[0013] Furthermore, in step 1, the molar ratio of piperazine, diethyl sodium hypophosphite and distilled water is 1:1:(5.5-6.5).

[0014] Furthermore, the dripping speed in step 2 is 1 to 3 drops per second.

[0015] Furthermore, the reaction time in step 2 is 0.5 to 1 h.

[0016] Furthermore, the molar ratio of the hydrochloric acid in step 2 to the piperazine in the reaction system is 1:1.

[0017] Furthermore, the molar ratio of phosphoric acid in step three to piperazine in the reaction system is 1:1.

[0018] The invention also provides application of diethylphosphinic acid-piperazine phosphate flame retardant in flame retardant styrene thermoplastic elastomer.

[0019] Furthermore, the specific method of using the diethylphosphinic acid-piperazine phosphate flame retardant to flame retard styrene-based thermoplastic elastomer is: the styrene-based thermoplastic elastomer and the flame retardant are mixed, heated and melted, hot pressed, and then cold pressed into shape.

[0020] Beneficial effects of the present invention:

[0021] The present invention uses diethylphosphinic acid and phosphate groups containing PC and PO structures and piperazine with excellent carbon-forming performance as starting raw materials through molecular structure design, introduces them into the same flame retardant molecular structure through ion exchange and complex salt reaction, and successfully prepares diethylphosphinic acid-piperazine phosphate flame retardant containing multiple flame retardant groups at the same time.

[0022] The flame retardant of the present invention contains PO, PC and piperazine groups at the same time, and is applied to the flame retardant modification of TPS, and exhibits an efficient flame retardant effect in TPS. Compared with the existing phosphorus-nitrogen flame retardant, the PDHP flame retardant of the present invention exhibits better flame retardant efficiency in TPS. When the addition amount of PDHP in TPS reaches 25wt%, the TPS / PDHP composite material successfully passes the UL-94V-0 level, and the limiting oxygen index is increased from 17.5% of pure TPS to 27.8%. At the same time, due to the presence of the PDHP terminal ethyl structure, the flame retardant PDHP has good compatibility with TPS, and TPS / 25wt% PDHP still maintains 81.2% of its tensile strength compared with pure TPS. Compared with the traditional phosphorus-nitrogen flame retardant, PDHP exhibits excellent flame retardant efficiency in TPS, while maintaining good mechanical properties of the material, thereby preparing a flame retardant TPS composite material with excellent comprehensive performance. At the same time, it overcomes the problem that the addition amount of traditional phosphorus-nitrogen flame retardants is large, which leads to the destruction of the mechanical properties of the flame retardant TPS composite material.

[0023] The presence of the terminal ethyl group in the PDHP flame retardant of the present invention makes it have good compatibility with the TPS material matrix. The initial thermal degradation temperature Tinitial of the flame retardant PDHP under nitrogen conditions is 232.3°C, and the residual carbon content reaches 18.6wt% at 800°C, which shows that the flame retardant PDHP has good thermal stability and excellent carbon-forming performance. And the DSC test found that the melting point of the product is 147.1°C. Unlike traditional liquid phosphate flame retardants, this product is easier to add because it has a fixed melting point and has excellent processing performance.

[0024] Compared with the existing phosphorus-nitrogen flame retardant synthesis technology, the phosphorus-nitrogen flame retardant PDHP prepared by the method of the present invention has mild reaction conditions during the synthesis process, uses water as the reaction solvent, has a simple preparation method, does not require the use of high-pressure reaction, has high safety and synthesis efficiency, is easy to industrialize, and has good application prospects.

[0025] The present invention is of great significance for expanding the application of TPS in high-end fields such as new energy, rail transit, and 5G communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 FTIR spectra of raw materials PA, SDHP and product PDHP;

[0027] Figure 2 For flame retardant PDHP 13 C NMR;

[0028] Figure 3 For flame retardant PDHP 31 P NMR;

[0029] Figure 4 is the thermogravimetric analysis curve of the product PDHP;

[0030] Figure 5 This is the DSC curve of the product PDHP. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0032] Specific implementation method 1: The structural formula of the diethylphosphinic acid-piperazine phosphate flame retardant (PDHP) in this implementation method is as follows:

[0033]

[0034] The existing flame retardants for TPS are mainly based on hypophosphite phosphorus-nitrogen compound systems. In TPS, the multi-component phosphorus-nitrogen system constructed with hypophosphite has a strong polarity in its molecular structure and poor dispersibility in the material matrix. It is often necessary to add more than 30wt% to make TPS reach UL-94V-0 level. At the same time, its compatibility with the TPS matrix is ​​poor, and defects are easily formed inside the material, thereby significantly reducing the mechanical strength and durability of its composite material. The single-molecule PDHP phosphorus-nitrogen flame retardant prepared by the present invention has a terminal ethyl group in its structure, which increases its compatibility with the TPS material. Compared with the traditional phosphorus-nitrogen compound system, the flame retardant (PDHP) of the present invention can keep TPS with excellent mechanical properties. In addition, the PDHP molecular structure contains piperazine and a variety of phosphorus-containing groups at the same time, wherein the presence of PO bonds and piperazine groups enables the TPS composite material to obtain excellent carbonization performance, while the PC bonds in the PDHP molecular structure give the material more efficient gas-phase flame retardant properties through the effect of free radical capture. Therefore, compared with the traditional phosphorus-nitrogen compound flame retardant system, the flame retardant PDHP of the present invention can enable TPS to achieve better flame retardant and mechanical properties at a lower addition amount.

[0035] Specific implementation method 2: The preparation method of the diethylphosphinic acid-piperazine phosphate flame retardant in this implementation method comprises the following steps:

[0036] 1. Add piperazine and diethyl sodium hypophosphite into a reaction device, then add distilled water into the reaction device, stir thoroughly, and heat to dissolve piperazine and diethyl sodium hypophosphite;

[0037] 2. Place hydrochloric acid in a constant pressure dropping funnel and slowly drop hydrochloric acid into the reaction system of the reaction device. After the addition of hydrochloric acid is completed, heat it to 58-62°C to allow it to react fully;

[0038] 3. Then add phosphoric acid to the reaction system, raise the temperature to 78-82°C, react for 2-5 hours, and then cool the reaction solution for crystallization;

[0039] 4. The cooled reaction liquid is filtered and washed, and then placed in a forced air drying oven for drying at 105° C. for 3 to 6 hours to obtain a phosphorus-nitrogen flame retardant, diethylphosphinic acid-piperazine phosphate (PDHP).

[0040] Specific implementation method 3: The heating temperature in step 1 of this implementation method is 35-40° C. Other steps and parameters are the same as those in specific implementation method 2.

[0041] Specific embodiment 4: In step 1 of this embodiment, the molar ratio of piperazine, diethyl sodium hypophosphite and distilled water is 1:1:(5.5-6.5). Other steps and parameters are the same as those of specific embodiment 2 or 3.

[0042] Specific implementation method 5: The dripping speed in step 2 of this implementation method is 1 to 3 drops per second. The other steps and parameters are the same as those in specific implementation methods 2 to 4.

[0043] Specific implementation method 6: The reaction time in step 2 of this implementation method is 0.5 to 1 hour. The other steps and parameters are the same as those in specific implementation methods 2 to 5.

[0044] Specific embodiment 7: The molar ratio of hydrochloric acid in step 2 of this embodiment to piperazine in the reaction system is 1: 1. Other steps and parameters are the same as those in specific embodiments 2 to 6.

[0045] Specific embodiment 8: The molar ratio of phosphoric acid in step 3 of this embodiment to piperazine in the reaction system is 1: 1. Other steps and parameters are the same as those in specific embodiments 2 to 7.

[0046] Specific implementation method 9: This implementation method is to use the diethylphosphinic acid-piperazine phosphate flame retardant in flame retardant styrene-based thermoplastic elastomer.

[0047] Specific embodiment 10: The specific method of flame retardant styrene thermoplastic elastomer with diethylphosphinic acid-piperazine phosphate flame retardant in this embodiment is: mix styrene thermoplastic elastomer and flame retardant, heat and melt, hot press, and then cold press to form. Other steps and parameters are the same as those of specific embodiment 9.

[0048] The embodiments of the present invention are described in detail below. The following embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation schemes and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0049] Embodiment 1:

[0050] The preparation method of the diethylphosphinic acid-piperazine phosphate flame retardant of this embodiment comprises the following steps:

[0051] Step 1: Synthesis of intermediate 1 diethylphosphinic acid-piperazine

[0052] Install a thermometer, a mechanical stirrer and a constant pressure dropping funnel on a 500mL fully dried four-necked flask. Add 8.6g (0.1mol) of anhydrous piperazine and 14.4g (0.1mol) of diethyl sodium hypophosphite into the four-necked flask. Use water as the solvent, add 100g of distilled water into the four-necked flask, stir thoroughly, heat to 35°C to fully dissolve piperazine and diethyl sodium hypophosphite, and keep the temperature constant at this temperature. At this time, the solution is colorless and transparent. Then weigh 9.85g (0.1mol) of hydrochloric acid and add it to the constant pressure dropping funnel. Slowly add hydrochloric acid to the solution. After the hydrochloric acid is added, heat to 60°C to allow it to react fully to obtain a transparent solution intermediate 1. The synthetic route of intermediate 1 is as follows:

[0053]

[0054] Step 2: Synthesis of diethylphosphinic acid-piperazine phosphate (PDHP)

[0055] Weigh 11.5g (0.1mol) of phosphoric acid and add it to the transparent intermediate 1. After the phosphoric acid is added, heat it to 80°C and react for 3h. After the reaction is completed, cool the reaction system to cool and crystallize. Then, filter and wash the reaction solution, put it into a blast drying oven and dry it at 105°C for 3 hours to prepare the flame retardant diethylphosphinic acid-piperazine phosphate (PDHP), which is a white powder. The synthesis route of PDHP is as follows:

[0056]

[0057] (I) Characterization of the product diethylphosphinic acid-piperazine phosphate (PDHP)

[0058] Figure 1 The infrared spectra of the raw material piperazine (PA), sodium diethyl hypophosphite (SDHP) and the product PDHP are shown in Figure 1. The infrared spectra of the raw material SDHP show that: 1476 cm -1 The absorption peak at 2940 cm is the stretching vibration of PC. -1 and 2889cm -1 The absorption peak at 1028 cm -1 and 1104cm -1 The absorption peak at 3208cm -1 The absorption peak corresponds to the stretching vibration of NH in the piperazine molecule. As the reaction of PA and SDHP proceeds, the NH in the product (3208cm -1 )、P=O(1104cm -1) and PO(1028cm -1 ) is clearly retained. In addition, at 952cm -1 and 2584cm -1 P-OH and -NH 2 + The new absorption peak indicates that the flame retardant diethylphosphinic acid-piperazine phosphate (PDHP) was successfully prepared in the experiment.

[0059] Synthetic product PDHP 13 C NMR spectrum Figure 2 As shown in the PDHP carbon NMR spectrum, the peaks at δ6.3ppm and δ21.1ppm correspond to the -CH 3 and -CH 2 -carbon atom peak; the peaks at δ21.8ppm and δ41.7ppm are attributed to the peaks of 4 carbon atoms and 3 carbon atoms on the piperazine ring, respectively. 13 C NMR analysis data confirmed that the reaction between diethyl sodium hypophosphite and piperazine was successful.

[0060] Synthetic product PDHP 31 P NMR spectrum Figure 3 As shown in the figure, the characteristic peaks of PDHP at δ1.3ppm and δ50.4ppm indicate that the synthetic product has two phosphorus chemical environments, corresponding to the peaks of 2 phosphorus atoms in the phosphate group and 1 phosphorus atom in the diethylphosphite group. 13 C and 31 The analysis results of the P NMR spectrum show that the structure of the synthesized product is consistent with that of the target product, proving that the phosphorus-nitrogen flame retardant PDHP was successfully synthesized.

[0061] (II) Performance test of product diethylphosphinic acid-piperazine phosphate (PDHP)

[0062] like Figure 4 As shown, PDHP was tested by thermogravimetric analysis (TGA), and the results showed that the initial thermal decomposition temperature of the flame retardant PDHP was 232.3°C, and the residual carbon amount at 800°C was 18.6wt%, indicating that the PDHP prepared in this embodiment has good thermal stability and excellent carbon-forming performance, and can meet the processing temperature requirements of most elastomer materials.

[0063] Figure 5This is the DSC curve of the flame retardant DPEP. Pure PDHP is a white solid powder at room temperature. Through the DSC test, it can be seen that the melting point of the flame retardant DPEP is 147.1°C, which shows that the flame retardant is easy to add during the processing, and because it has a corresponding melting point, it has good dispersion in the material matrix during the TPE material processing.

[0064] (III) Performance analysis of phosphorus-nitrogen flame-retardant TPS materials

[0065] The phosphorus-nitrogen flame-retardant TPS composite material was prepared by using diethylphosphinic acid-piperazine phosphate (PDHP), and its flame retardant properties were tested as follows:

[0066] 1. Preparation of phosphorus-nitrogen flame-retardant TPS composite material samples

[0067] Place polypropylene (PP) and styrene-ethylene / butylene-styrene triblock copolymer (SEBS) in a blast drying oven at 80°C for 3 hours and then take them out for use. Add SEBS and cyclopentane oil (Oil) to a high-speed mixer in a ratio of 2:1 for oil filling. After fully mixing, take them out and place them in a container for 48 hours to prepare O-SEBS. PP, O-SEBS and flame retardant are heated and melt-blended for 15 minutes using a torque rheometer. The temperatures of each heating zone are 180°C, 180°C and 180°C, respectively, and the speed is 60r / min. Then, after hot pressing under a press at 180°C, cold pressing is performed. TPS is composed of PP and O-SEBS. TPS and flame retardant (PDHP) are made into phosphorus-nitrogen flame-retardant TPS composite materials, wherein the mass of PDHP in composite material TPS1 accounts for 23% of the phosphorus-nitrogen flame-retardant TPS composite material, the mass of PDHP in composite material TPS2 accounts for 24% of the phosphorus-nitrogen flame-retardant TPS composite material, the mass of PDHP in composite material TPS3 accounts for 25% of the phosphorus-nitrogen flame-retardant TPS composite material, and the mass of PDHP in composite material TPS4 accounts for 26% of the phosphorus-nitrogen flame-retardant TPS composite material.

[0068] The samples obtained above were cut into standard specimens for performance testing.

[0069] 2. Flame retardant performance test of TPS material

[0070] The flame retardant TPS material samples prepared above were cut into standard specimens and tested for performance. Table 1 shows the characterization of TPS materials by vertical combustion (UL-94) and limiting oxygen index (LOI) tests. The relevant data are shown in Table 1. The pure TPS material is extremely flammable. After ignition, it burns violently until it burns out. The limiting oxygen index is only 17.5%, and a large amount of thick smoke and molten droplets with fire will be produced, which is very likely to cause secondary fire hazards. With the introduction of phosphorus-nitrogen flame retardant PDHP, the flame retardant properties of TPS composite materials are significantly improved. When the addition amount of PDHP reaches 23wt%, the TPS1 flame retardant composite material successfully passes the UL-94V-2 level, and the LOI value is 26.8%. With the further increase in the amount of PHDP introduced, when the addition amount of PDHP reaches 25wt%, the TPS3 composite material successfully passes the UL-94V-0 level, and the limiting oxygen index reaches 27.6%, which is 58.0% higher than that of pure TPS. This is because the introduction of PDHP improves the carbonization performance of TPS composites and plays an inhibitory role in the gas phase, thus giving TPS / PDHP excellent flame retardant properties. In addition, when TPS / PDHP composites obtain UL-94V-0 grade, they can still maintain good mechanical properties, which provides a good solution for the preparation of flame-retardant TPU composites with excellent comprehensive performance.

[0071] Table 1 Vertical combustion and limiting oxygen index test data of flame retardant TPS composite materials

[0072]

[0073] 3. Mechanical properties test of TPS materials

[0074] The flame retardant TPS material samples prepared above were cut into standard specimens and subjected to an elastomer tensile test at a tensile speed of 200 mm / min. The test data are shown in Table 2.

[0075] Table 2 Test data of tensile strength and elongation at break of flame retardant TPS composite materials

[0076]

[0077] The tensile strength of pure TPS is 22.3MPa, and the elongation at break is 905.2%. With the introduction of PDHP flame retardant, the tensile strength and elongation at break of TPS / PDHP flame retardant composite material decrease slightly. Compared with pure TPS, the tensile strength and elongation at break of TPS 3 flame retardant composite material only decrease by 18.8% and 13%, because PDHP is a single molecule flame retardant, and the terminal ethyl group in the structure increases the compatibility between PDPH and the material matrix, so that the TPS / PDHP flame retardant composite material maintains relatively excellent mechanical properties. At present, it has been reported that the TPS flame retardant composite material with UL-94V-0 grade has been obtained. Due to the large amount of flame retardant introduced, the tensile strength and elongation at break of TPS composite material often decrease greatly, while the mechanical properties of the TPS / PDHPH composite material of the present invention are significantly maintained, which is of great significance for expanding the application of flame retardant TPS composite material.

[0078] Compared with the traditional phosphorus-nitrogen flame retardant, the advantages of the diethylphosphinic acid-piperazine phosphate flame retardant synthesized by the present invention in the flame-retardant TPS composite material are as follows: 1) During the synthesis process of PDHP, no catalyst and organic solvent are required, and it is a pure water system synthesis, and the preparation method is simple and easy, which solves the problems of high energy consumption and safe production in the synthesis process of traditional flame retardants; 2) The piperazine group with excellent carbonization performance is introduced into the molecular structure of PDHP, thereby giving the TPS composite material excellent carbonization performance; 3) The presence of the diethylphosphinic acid group in the molecular structure of PDPH makes it 1) P· and PO· are produced during the combustion process, which have excellent quenching effect on the H·, O·, and HO· high-energy free radicals produced during the combustion of the polymer, thereby achieving a gas phase inhibition effect; 2) PDHP introduces PC and PO groups into the same molecular structure, and through the synergistic effect of the gas phase and the condensed phase, it exhibits efficient flame retardant properties in TPS materials; 3) PDHP has high flame retardant efficiency in TPS materials and a small amount of addition. At the same time, the presence of the terminal ethyl structure in the structure makes it have good compatibility with TPS materials, so that the flame retardant TPS maintains certain mechanical properties. In summary, the structural design of the phosphorus-nitrogen flame retardant PDHP provides a new idea for the preparation of flame retardant TPS materials with excellent comprehensive performance.

Claims

1. A diethylphosphinic acid-piperazine phosphate flame retardant, characterized in that: The structural formula of the flame retardant is as follows:

2. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 1, characterized in that: The method comprises the following steps:

1. Add piperazine and diethyl sodium hypophosphite into a reaction device, then add distilled water into the reaction device, stir thoroughly, and heat to dissolve piperazine and diethyl sodium hypophosphite; 2. Place hydrochloric acid in a constant pressure dropping funnel and slowly drop hydrochloric acid into the reaction system of the reaction device. After the addition of hydrochloric acid is completed, heat it to 58-62°C to allow it to react fully; 3. Then add phosphoric acid to the reaction system, raise the temperature to 78-82°C, react for 2-5 hours, and then cool the reaction solution for crystallization; 4. After the cooled reaction liquid is filtered and washed, it is placed in a forced air drying oven and dried at 105° C. for 3 to 6 hours to obtain the phosphorus-nitrogen flame retardant diethylphosphinic acid-piperazine phosphate.

3. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 2, characterized in that: The heating temperature in step 1 is 35-40°C.

4. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 2 or 3, characterized in that: In step 1, the molar ratio of piperazine, diethyl sodium hypophosphite and distilled water is 1:1:(5.5-6.5).

5. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 4, characterized in that: The dripping speed in step 2 is 1 to 3 drops per second.

6. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 5, characterized in that: The reaction time in step 2 is 0.5 to 1 h.

7. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 6, characterized in that: The molar ratio of hydrochloric acid in step 2 to piperazine in the reaction system is 1:

1.

8. The method for preparing the diethylphosphinic acid-piperazine phosphate flame retardant according to claim 7, characterized in that: The molar ratio of phosphoric acid in step 3 to piperazine in the reaction system is 1:

1.

9. Use of the diethylphosphinic acid-piperazine phosphate flame retardant as claimed in claim 1 in flame retardant styrene thermoplastic elastomer.

10. The use according to claim 9, characterized in that: The specific method of using diethylphosphinic acid-piperazine phosphate flame retardant to flame retard styrene thermoplastic elastomer is as follows: the styrene thermoplastic elastomer and the flame retardant are mixed, heated and melted, hot pressed, and then cold pressed to form.

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