A kind of zinc hydroxystannate coated piperazine modified ammonium polyphosphate composite flame retardant and its preparation method and application

Abstract

The application discloses a kind of zinc hydroxystannate coated piperazine modified ammonium polyphosphate composite flame retardant and its preparation method and application.Utilize the electronegative oxygen atom of zinc hydroxystannate and the polar group-NH2 + Form hydrogen bond connection, to build molecular association structure.And by infrared spectrum characterization association-NH2 + Group of the infrared shift of association of the present application successfully prepared zinc hydroxystannate and piperazine modified ammonium polyphosphate mass ratio is 1: (5-20) molecular association flame retardant, the raw materials used have realized industrial production.The beneficial effects of the present application are as follows: preparation process is simple, easy to operate, the mass ratio of zinc hydroxystannate and piperazine modified ammonium polyphosphate of the molecular association flame retardant prepared is 1:20, and when the addition amount in nylon 6 is 10wt%, the limiting oxygen index reaches 30.3%, UL-94 reaches V-0 level, and the smoke suppression effect is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of composite flame retardant materials technology, specifically a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate, its preparation method and application. Background Technology

[0002] Nylon 6 (PA6) is a crystalline, thermoplastic engineering plastic with a melting point of 215℃-225℃. It possesses excellent dielectric properties, is resistant to alkalis, most salts, aliphatic hydrocarbons, and aromatic compounds, and exhibits good toughness. However, it has a low elastic modulus and can absorb water and acids, causing swelling. It also has a tendency to plasticize. Primarily used in injection molding, it serves as functional components in automotive, machinery, and electrical products. Besides injection molding, it is also widely used in extrusion molding of films and monofilaments. PA6 fibers are mainly used to weave socks, shirts, underwear, and gloves, and are also used in the manufacture of fishing nets, parachutes, insulation materials, and tire cords. However, PA6 has a limiting oxygen index of only 20%-22%, classifying it as a flammable polymer. During combustion, it produces a large amount of smoke, has a high peak heat release rate, and a rapid flame spread, seriously threatening human life and property. Yunnan Province is rich in phosphorus and tin resources, therefore, zinc hydroxystannate has been industrially produced. Under a nitrogen atmosphere, the initial decomposition temperature (T5%) of zinc hydroxystannate is only 187.6℃, while the processing temperature of PA6 is 240℃. Therefore, the flame retardant zinc hydroxystannate does not meet the processing requirements of PA6. Most domestic and international technologies for modifying zinc hydroxystannate use organic solvents, which pose significant safety and corrosion risks.

[0003] Piperazine-modified ammonium polyphosphate (PAPP) is a highly efficient phosphorus-nitrogen intumescent flame retardant with a T5% of 322.3℃ under a nitrogen atmosphere, and its thermal stability meets the processing requirements of PA6. However, when PAPP is used alone to retard PA6, at least 30wt% of PAPP is required to achieve UL-94 V1 rating. High addition amounts lead to a significant decrease in the mechanical properties of the material, and its compatibility with PA6 still needs improvement.

[0004] Chinese invention patent application CN 101772537 B discloses a polymer material comprising a halogen-free flame retardant incorporated within a polymer matrix. The flame retardant comprises at least ammonium polyphosphate and / or its derivatives and oligomeric or polymeric 1,3,5-triazine derivatives or a mixture of these substances, and at least one compound selected from: phosphates, pyrophosphates, polyphosphates, organic and inorganic phosphonates, organic and inorganic phosphonites, stannates, molybdates or borates of Group II, III or IV elements or transition elements Fe, Zn, Ti, Mn, Zr and Mo; precondensed melamine derivatives; melamine salts and other compounds; ethylenediamine phosphate; piperazine phosphate; piperazine pyrophosphate; 1,3,5-trihydroxyethyl isocyanurate; 1,3,5-triglycidyl isocyanurate; and triallyl isocyanurate. The weight ratio of component A to component B is 10:1 to 1:1. Based on the total weight of components A, B, C, and D, components A and B account for 60-99% by weight, and components C and D account for 1-40% by weight. The polymer material is a thermoplastic elastomer (TPE). This technical solution has a complex preparation process, is not easy to scale up for mass production, and cannot meet the processing requirements of high flame-retardant nylon.

[0005] Meanwhile, existing technologies that use organic solvent systems to prepare zinc hydroxystannate-modified ammonium polyphosphate through ball milling suffer from problems such as high solvent toxicity, uneven dispersion, and high energy consumption. Furthermore, there are no reports in domestic or international literature on achieving excellent flame-retardant effects in PA6 through micron-level physical mixing of zinc hydroxystannate and piperazine-modified ammonium polyphosphate via hydrogen bonding.

[0006] Therefore, there is an urgent need for a flame retardant and its preparation method that has a simple synthesis process, significant thermal stability and flame retardant properties, can be applied to the field of nylon flame retardancy, and meets the processing requirements of high flame retardant nylon. Summary of the Invention

[0007] To address the shortcomings of the existing technology described above, this invention provides a zinc hydroxystannate-coated piperazine-modified ammonium polyphosphate composite flame retardant. This flame retardant utilizes the electronegative oxygen atoms in zinc hydroxystannate and the polar -NH2 groups in piperazine-modified ammonium polyphosphate. + Hydrogen bonds are formed, enabling zinc hydroxystannate to successfully coat piperazine-modified ammonium polyphosphate. This process has the advantages of high thermal stability, good compatibility with PA6, significant synergistic effect of flame retardancy and smoke suppression, and a green and environmentally friendly preparation process.

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned zinc hydroxystannate-coated piperazine-modified ammonium polyphosphate composite flame retardant, which uses deionized water as the sole solvent and achieves uniform coating of nano-sized zinc hydroxystannate on the surface of piperazine-modified ammonium polyphosphate through a low-temperature in-situ precipitation reaction, rather than physical mixing.

[0009] A third objective of this invention is to provide the application of the zinc hydroxystannate-coated piperazine-modified ammonium polyphosphate composite flame retardant in the field of nylon flame retardancy.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate, wherein zinc hydroxystannate is linked to piperazine-modified ammonium polyphosphate through hydrogen bonds, thereby coating the piperazine-modified ammonium polyphosphate to form an associative compound, wherein the hydrogen bonds cause the infrared characteristic peaks of the polar groups of piperazine-modified ammonium polyphosphate to shift to lower wavenumbers.

[0011] The electronegative oxygen atom of zinc hydroxystannate and the polar -NH2 group in piperazine-modified ammonium polyphosphate + Hydrogen bonds are formed, which lead to the formation of -NH2 groups in piperazine-modified ammonium polyphosphate. + The infrared characteristic peak shifts to lower wavenumbers by 150-200 cm. -1 Thus, a molecular association structure of zinc hydroxystannate and piperazine-modified ammonium polyphosphate was constructed.

[0012] The mass ratio of zinc hydroxystannate to piperazine-modified ammonium polyphosphate in the composite is 1:(5-20).

[0013] When the additive amount of the compound in the nylon 6 formulation is 10wt%, the limiting oxygen index is ≥30%, the UL-94 reaches V-0 level, the tensile strength retention rate is ≥80%, the peak heat release rate is reduced by ≥50%, and the smoke suppression effect is significant.

[0014] The complex was prepared by mixing zinc hydroxystannate and piperazine-modified ammonium polyphosphate in a mass ratio of 1:(10-48).

[0015] The preparation method of the composite flame retardant of zinc hydroxystannate coated piperazine-modified ammonium polyphosphate includes the following steps: (1) Dissolve piperazine-modified ammonium polyphosphate and zinc hydroxystannate in a solvent and stir mechanically; (2) Set the temperature at 0.33-1℃ and react for at least 19 hours. Centrifuge the mixture after reaction, collect the precipitate, wash it with deionized water, freeze dry it, and grind it.

[0016] The preparation method of the composite flame retardant of zinc hydroxystannate coated piperazine-modified ammonium polyphosphate includes the following steps: (1) Dissolve piperazine-modified ammonium polyphosphate, zinc sulfate and sodium stannate in a solvent and stir mechanically; (2) Set the temperature at 0.33-1℃ and react for at least 19 hours. Centrifuge the mixture after reaction, collect the precipitate, wash it with deionized water, freeze dry it, and grind it.

[0017] The preparation method of the composite flame retardant of zinc hydroxystannate coated piperazine-modified ammonium polyphosphate includes the following steps: (1) Prepare a solution by ultrasonically dissolving piperazine-modified ammonium polyphosphate in a solvent; (2) Add zinc sulfate solution to the above solution to prepare a mixed solution; (3) Add sodium stannate solution to the mixed solution prepared in step (2); (4) The temperature is set at 0.33-1℃ and the reaction time is at least 19h. The precipitate is collected, centrifuged, washed with deionized water, freeze-dried, and ground.

[0018] The preparation method of the composite flame retardant of zinc hydroxystannate coated piperazine-modified ammonium polyphosphate includes the following steps: (1) Dissolve zinc sulfate in a solvent to prepare a solution; (2) Dissolve piperazine-modified ammonium polyphosphate in deionized water by ultrasonication, and add it to the above solution to prepare a mixed solution; (3) Add sodium stannate solution to the above mixed solution; (4) Add sodium stannate solution to obtain a mixed solution; (5) The temperature is set between 0.33-1℃, the reaction is carried out for at least 19 hours, the precipitate is collected, centrifuged, washed with deionized water, freeze-dried, ground and the flame retardant is obtained.

[0019] The preparation method of the composite flame retardant of zinc hydroxystannate coated piperazine-modified ammonium polyphosphate includes the following steps: (1) Dissolve piperazine-modified ammonium polyphosphate in deionized water by ultrasonication and place it in a container; (2) Set the temperature of the above container to 0.33-1℃; (3) Add zinc sulfate solution to the container; (4) Add sodium stannate solution; (5) The reaction time is at least 19 hours. The precipitate is collected by centrifugation, washed with deionized water, freeze-dried, and ground to obtain the flame retardant.

[0020] Preferably, the temperature is 0.66-0.88℃.

[0021] Preferably, the association reaction time is 19-25 hours.

[0022] Preferably, the mechanical stirring speed is 100-210 r / min.

[0023] Preferably, the solvent is deionized water or a mixture of ethanol and water; most preferably, the solvent is deionized water.

[0024] When the mass ratio of zinc hydroxystannate to piperazine-modified ammonium polyphosphate in the composite is 1:(5-20), the mass ratio of zinc hydroxystannate to piperazine-modified ammonium polyphosphate in the raw materials is 1:(10-48).

[0025] The ultrasonic frequency for ultrasonic dispersion of the piperazine-modified ammonium polyphosphate is 20-60 kHz, preferably 40 kHz.

[0026] The composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate is used in the preparation of nylon flame retardant materials, and its addition amount is 10-24 wt% of the nylon flame retardant material. Preferably, the addition amount is 10 wt%. Preferably, the nylon flame retardant material is nylon 6.

[0027] This invention experimentally determined the key factors affecting the hydrogen bond formation between zinc hydroxystannate and piperazine-modified ammonium polyphosphate: these include solvent type and concentration, the mass ratio of the two components in the flame retardant, reaction time, and stirring speed. By optimizing these parameters, a uniformly coated and stably associated flame retardant can be obtained.

[0028] The zinc hydroxystannate-coated piperazine-modified ammonium polyphosphate composite of this invention can effectively retard PA6, is halogen-free and low in toxicity, and has good flame retardant and smoke suppression effects. Compared with commercially available melamine cyanuric acid (MCA), the amount added is smaller, the raw materials are already industrialized, the solvent used is deionized water, the production process is green and environmentally friendly, and it has commercial prospects.

[0029] This invention has achieved unexpected technical effects: (1) Under the same total addition amount (10wt%) and the same ratio of zinc hydroxystannate (ZHS): piperazine modified ammonium polyphosphate (PAPP) (1:20), the LOI of in-situ coating (30.3%) was 5.1 percentage points higher than that of physical blending (25.2%), and the UL-94 was upgraded from V-2 to V-0, an improvement of two levels.

[0030] (2) At lower addition amounts (10wt% vs 30wt%), the LOI (30.3%) of the nylon flame retardant material prepared by the present invention was significantly higher than that of 30% piperazine-modified ammonium polyphosphate (PAPP) (26.8%) and 30% zinc hydroxystannate (ZHS) (24.5%) alone, demonstrating that the synergistic effect far exceeds that of simple addition.

[0031] (3) The mechanical property retention rate (87% for tensile and 82% for impact) is significantly better than that of physical blending (77% for tensile and 69% for impact), proving that the core-shell structure improves the interfacial compatibility.

[0032] (4) The peak heat release rate is reduced by 51%-59%, and the smoke density is reduced by 66%-72%, with a smoke suppression effect that is significantly better than existing technologies.

[0033] The aforementioned effects cannot be expected from existing technologies and are therefore unexpected technical effects.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: the raw materials are industrialized, the solvent is deionized water, there is no waste gas or solid waste generated, it is green and environmentally friendly, and easy to separate; the zinc hydroxystannate-coated piperazine-modified ammonium polyphosphate forming an associative compound can effectively retard PA6, is halogen-free and low in toxicity, and has flame retardant and smoke-suppressing effects; when the mass ratio of zinc hydroxystannate to piperazine-modified ammonium polyphosphate associative compound is 1:20, and the addition amount in nylon 6 (PA6) is 10%wt, the limiting oxygen index exceeds 30%, the UL-94 is V0 level, and the smoke-suppressing effect is significant. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope image of piperazine-modified ammonium polyphosphate. Figure 2 This is a scanning electron microscope image of zinc hydroxystannate; Figure 3 The X-ray diffraction pattern of zinc hydroxystannate is shown. Figure 4 These are scanning electron microscope images of the associative compound obtained in Example 1 of this invention at two magnifications; Figure 5 This is a comparison of the infrared spectra of the associative compounds obtained in Example 1 of the present invention; Figure 6 These are scanning electron microscope images of the associative compound obtained in Example 2 of this invention at two magnifications; Figure 7 These are scanning electron microscope images of the associative compound obtained in Example 3 of the present invention at two magnifications; Figure 8 The energy dispersive X-ray spectrum of the composite flame retardant (mass ratio 1:20) of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate prepared in Example 1 of this invention is shown below. Figure 9 The energy dispersive X-ray spectrum of the composite flame retardant (mass ratio 1:10) of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate prepared in Example 2 of this invention is shown below. Figure 10 The energy dispersive X-ray spectrum of the composite flame retardant (mass ratio 1:5) of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate prepared in Example 3 of this invention is shown. Detailed Implementation

[0036] To clearly illustrate the technical solution of the invention, specific embodiments are provided, but the scope of the invention is not limited to the following embodiments.

[0037] Preparation of piperazine-modified ammonium polyphosphate (PAPP) The preparation method of piperazine-modified ammonium polyphosphate is as follows: 800 mL of anhydrous ethanol and 60 mL of deionized water are mixed and poured into a three-necked flask, which is then fixed on a support with an oil bath. 60 g of anhydrous piperazine is added, and the mixture is mechanically stirred at 230 r / min for 10 minutes at room temperature. Then, 120 g of ammonium polyphosphate with a degree of polymerization of approximately 1500 is dissolved in 200 mL of anhydrous ethanol and poured into the three-necked flask. The oil bath temperature is set to 90°C, and nitrogen gas is introduced for protection. A condenser is inserted to prevent excessive evaporation of alcohol. Ammonia gas is continuously generated during the reaction. The reaction is completed after 7 hours. The reaction product is filtered through two layers of medium-speed filter paper, washed twice with anhydrous ethanol, placed in a forced-air drying oven, and dried at 60°C for 12 hours. After drying, micron-sized piperazine-modified ammonium polyphosphate (PAPP) powder can be obtained without grinding.

[0038] Verification test of the conversion rate of zinc hydroxystannate (ZHS) synthesis When zinc sulfate solution and sodium stannate solution are reacted to produce zinc hydroxystannate powder, it was found through actual preparation that the reaction is not 100% conversion. The actual yield of the target product is relatively small, and most of the reactants fail to form precipitates but exist in the solution as soluble substances. Therefore, the conversion rate of this reaction varies depending on the conditions.

[0039] The following two comparative examples of zinc hydroxystannate (ZHS) preparation show significantly different results obtained from two preparation reactions with reactant concentrations differing by a factor of four. The first example was prepared as follows: 400 mL of 0.1 mol / L zinc sulfate monohydrate solution and 400 mL of 0.1 mol / L sodium stannate solution were prepared. The reaction temperature was 0.66℃, and the reaction time was 5 hours. After centrifugation, the product was freeze-dried at -5℃ for 48 hours to obtain zinc hydroxystannate powder with a conversion rate of 50%. The preparation method of the second example is as follows: Prepare 400 mL of 0.5 mol / L zinc sulfate monohydrate solution and 400 mL of 0.5 mol / L sodium stannate solution. The reaction temperature is 0.66℃ and the reaction time is 5 hours. After centrifugation, freeze-dry at -5℃ for 48 hours to obtain zinc hydroxystannate powder with a conversion rate of 65%.

[0040] The experimental results from the above examples and other data show that the conversion rate increases linearly with concentration under the above conditions. The prepared zinc hydroxystannate powder, after grinding, becomes zinc hydroxystannate powder with a length of about 200 nanometers.

[0041] Example 1 A method for preparing a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate, comprising the following steps: (1) Dissolve 6.28g of zinc sulfate monohydrate in 150mL of deionized water to make a solution, and pour it into a three-necked flask with a capacity of 1000mL; (2) Place the three-necked flask in a low-temperature constant temperature bath with the temperature set at 0.33℃, and apply mechanical stirring at a stirring speed of 210r / min. (3) Dissolve 120g of piperazine-modified ammonium polyphosphate in 700mL of deionized water and sonicate it at a frequency of 40kHz for 30min to obtain a dispersion of piperazine-modified ammonium polyphosphate. Add the dispersion of piperazine-modified ammonium polyphosphate to the three-necked flask mentioned above. (4) Dissolve 7.44g of sodium stannate in 150mL of deionized water to make a solution, and add it to the three-necked flask mentioned above; (5) After mixing and reacting for 19 hours, the mixed solution after reaction is centrifuged, the resulting precipitate is washed three times with deionized water, freeze-dried at -5℃ for 48 hours, and then ground to obtain a molecular association flame retardant with a mass ratio of zinc hydroxystannate and piperazine-modified ammonium polyphosphate of 1:20.

[0042] The above-mentioned component feed amounts were determined based on the experimentally verified conversion rate data of zinc hydroxystannate (ZHS). In this embodiment, the ZHS:PAPP mass ratio of the prepared composite flame retardant is 1:20, with a total associative mass of 52.5g, of which the mass of pure ZHS sample is approximately 2.5g. Under the above reaction conditions, combined with the previous conversion rate verification experiment results, the corresponding reaction conversion rate of 6.28g zinc sulfate monohydrate and 7.44g anhydrous sodium stannate is 25%, therefore the target ZHS yield is 2.5g.

[0043] Example 2 A method for preparing a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate, comprising the following steps: (1) Dissolve 120g piperazine-modified ammonium polyphosphate in 700mL of deionized water and sonicate it with ultrasonic waves at a frequency of 40kHz for 30min to obtain a dispersion of piperazine-modified ammonium polyphosphate. Pour the dispersion of piperazine-modified ammonium polyphosphate into a three-necked flask with a capacity of 1000mL and place the three-necked flask in a low-temperature constant temperature bath at a temperature of 0.33℃. At the same time, apply mechanical stirring with a stirring speed of 210r / min. (2) Dissolve 11.2g of zinc sulfate monohydrate in 150mL of deionized water to make a solution, and add it to the three-necked flask mentioned above; (3) Dissolve 13.3g of sodium stannate in 150mL of deionized water to make a solution, and add it to the three-necked flask mentioned above; (4) After mixing and reacting for 19 hours, the mixed solution after reaction was centrifuged, the precipitate was washed three times with deionized water, and then freeze-dried at -5℃ for 48 hours. Then, the precipitate was ground to obtain a molecular association flame retardant with a mass ratio of zinc hydroxystannate and piperazine-modified ammonium polyphosphate of 1:10.

[0044] Example 3 A method for preparing a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate, comprising the following steps: (1) Dissolve 24.01g of sodium stannate in 150mL of deionized water, place it in a three-necked flask with a capacity of 1000mL, and place the three-necked flask in a low temperature constant temperature bath at 0.33℃. At the same time, apply mechanical stirring with a stirring speed of 210r / min. (2) Dissolve 120g of piperazine-modified ammonium polyphosphate in 700mL of deionized water and sonicate at 40kHz for 30min to obtain a dispersion of piperazine-modified ammonium polyphosphate. Add the dispersion of piperazine-modified ammonium polyphosphate to the three-necked flask mentioned above. (3) Dissolve 20.26g of zinc sulfate monohydrate in 150mL of deionized water to make a solution, and add it to the three-necked flask mentioned above; (4) After mixing and reacting for 19 hours, the mixed solution was centrifuged, the precipitate was washed three times with deionized water, and then freeze-dried at -5°C for 48 hours. After grinding, a molecular association flame retardant with a mass ratio of zinc hydroxystannate and piperazine-modified ammonium polyphosphate of 1:5 was obtained.

[0045] After scaling up 10 times, the product performance was consistent with the small-scale test: adding 10wt% to PA6 resulted in an LOI of 30.1%, a UL-94 V-0 rating, and a tensile strength retention rate of 86%, proving that the process can be scaled up.

[0046] The component feed amounts in Examples 2 and 3 were based on the conversion rate verification results described in Example 1. Under the specific reaction conditions described above, zinc sulfate monohydrate and anhydrous sodium stannate were used to prepare composite flame retardants with ZHS:PAPP mass ratios of 1:10 and 1:5, respectively. These examples demonstrate that the order of component addition has no effect on the final reaction product.

[0047] For ease of description, the data in the above embodiments are all small-scale laboratory data. According to the reaction mechanism and process characteristics of the present invention, the same effect can still be obtained by scaling up production according to the proportions of the above embodiments in actual industrial production.

[0048] The flame retardant sample prepared in Example 1 was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Figure 1The image shows a scanning electron microscope (SEM) image of piperazine-modified ammonium polyphosphate (PAPP). As can be seen from the image, PAPP consists of columnar particles with uneven sizes ranging from 5 to 20 micrometers and smooth surfaces, making them prone to aggregation. Figure 2 The image shows a scanning electron microscope (SEM) image of zinc hydroxystannate (ZHS). As can be seen from the image, ZHS has a near-spherical shape with a diameter of approximately 200 nanometers, and the particles are relatively uniform in size and tend to aggregate. Figure 4 The image shows a scanning electron microscope (SEM) image of the flame retardant prepared in Example 1 of this invention. The particles are not uniform, but each micron-sized PAPP particle contains nano-sized ZHS particles. Some particles show significant ZHS aggregation. Compared to direct physical mixing, the associative mixture is more uniform, ensuring that each PAPP particle is associated with ZHS through hydrogen bonds. Furthermore, the PAPP particles are not tightly bound together but rather exhibit a relatively dispersed state. Through comparison... Figure 1 , 2 As can be seen from Figures 4 and 5, nanoscale zinc hydroxystannate successfully coated micron-sized piperazine-modified ammonium polyphosphate.

[0049] from Figure 3 The X-ray diffraction pattern of zinc hydroxystannate shows that its characteristic peaks are in perfect agreement with the crystal form of JCPDS:59-0543ZHS in the standard library, proving the successful synthesis of zinc hydroxystannate and its corresponding crystal form. The absence of obvious impurity peaks in the spectrum indicates that the synthesized product is pure-phase zinc hydroxystannate, with no byproducts generated, and will not introduce additional impurities that would affect the flame-retardant properties of the flame retardant.

[0050] Figure 5 The image shows a comparison of the infrared spectra of ZHS, PAPP, APP, and the flame retardant prepared in Example 1 of this invention. As can be seen from the image, the P-OH stretching vibration peak of the flame retardant prepared in Example 1 is at 3225 cm⁻¹. -1 The peak of the P-OH stretching vibration in PAPP is at 3244 cm⁻¹. -1 At the location, the NH2 of the flame retardant prepared in Example 1 + The characteristic peak is at 2135 cm⁻¹ -1 2314cm -1 At that point, and in PAPP, NH2 + Characteristic peak at 2140 cm⁻¹ -1 2483cm -1 In other words, the NH2 content of the flame retardant prepared in Example 1. + The characteristic peaks and the P-OH stretching vibration peak showed infrared spectral shifts relative to PAPP, with NH2 showing an increase. + The characteristic peak shifts to lower wavenumbers by 5-169 cm. -1 The P-OH stretching vibration peak shifted to a lower wavenumber by 19 cm. -1 The polar groups P-OH and NH2 in PAPP +PAPP forms molecular associations with the polar -OH groups in ZHS through hydrogen bonds, significantly enhancing the intermolecular forces between PAPP and ZHS, without changing the structure of their respective individual molecules.

[0051] Figure 4 , Figure 6 and Figure 7 The images shown are scanning electron microscope (SEM) images of the flame retardants prepared in Examples 1-3 of this invention. Figure 1 This is a scanning electron microscope image of piperazine-modified ammonium polyphosphate without zinc hydroxystannate coating, compared with... Figure 1 The comparison shows that the flame retardant prepared in Example 1 has a regular crystal structure, a smooth and flat surface, and no obvious adhering substances. Each micron-sized PAPP particle has nano-sized ZHS particles. The flame retardant prepared in Example 2 has a rough surface, with ZHS particles on each PAPP particle, and some particles are completely coated with ZHS. In contrast, the flame retardant prepared in Example 3 has almost completely lost its crystal structure, exhibiting a loose, flocculent structure. Almost every PAPP particle is coated with ZHS, with only a few PAPP particles uncoated and bearing a small amount of ZHS particles. In conclusion, Example 1 is the preferred embodiment of the present invention.

[0052] The composite flame retardants prepared in Examples 1-3 (with mass ratios of zinc hydroxystannate to piperazine-modified ammonium polyphosphate of 1:20, 1:10, and 1:5, respectively) were characterized by EDS elemental distribution. Figures 8-10 As shown, the results indicate that as the proportion of zinc hydroxystannate decreases, the elemental distribution of the composite particles exhibits a regular change. In the EDS diagram of the composite flame retardant prepared in Example 3, the Sn and Zn element signals are strong and uniformly cover the particle outline, while the P element signal is weak, indicating that the ammonium polyphosphate is coated with zinc hydroxystannate, and the zinc hydroxystannate coating layer has a large thickness and high coverage. In the EDS diagram of the composite flame retardant prepared in Example 2, the Sn and Zn elements are still uniformly distributed, while the P element signal is significantly enhanced and corresponds to the particle outline, indicating the formation of a thin and continuous coating structure. In the EDS diagram of the composite flame retardant prepared in Example 1, the Sn and Zn element signals are significantly weakened, while the P element signal is extremely strong and completely overlaps with the particle outline, indicating that zinc hydroxystannate forms a uniform thin coating layer on the surface of piperazine-modified ammonium polyphosphate, which not only provides a structural basis for synergistic flame retardancy but also maximizes the retention of the effective flame retardant components of ammonium polyphosphate, avoiding the influence of excessively thick coating layers on its char formation catalysis process.

[0053] SEM morphology and EDS elemental surface distribution characterization results show that Example 1 is the preferred embodiment of the present invention, providing an ideal microstructure basis for achieving efficient synergistic flame retardancy.

[0054] When the molecular association flame retardant prepared in Example 1 was applied to flame-retardant nylon 6 (PA6), the limiting oxygen index of the composite increased from 21.4% of pure PA6 to 30.3% when 10% by mass was added, and the UL-94 rating was improved from no rating to V-0 flame retardant rating of pure PA6.

[0055] Comparative Example Comparative Example 1: Pure Nylon 6

[0056] Standard samples were prepared by melt extrusion and injection molding of nylon 6 resin at 240℃. Test performance: LOI=21.4%, UL-94 grade not specified, tensile strength 75MPa, impact strength 5.5kJ / m². Comparative Example 2: Zinc hydroxystannate added alone

[0057] 30 wt% uncoated zinc hydroxystannate (commercially available, average particle size 500 nm) was melt-blended with nylon 6. Due to partial decomposition of zinc hydroxystannate at a processing temperature of 240°C, bubbles were generated, resulting in a rough surface on the injection-molded sample. Test performance: LOI=24.5%, UL-94 V2 grade, tensile strength 52 MPa (retention rate 69%), impact strength 3.2 kJ / m² (retention rate 58%). Comparative Example 3: Piperazine-modified ammonium polyphosphate added alone

[0058] 30 wt% piperazine-modified ammonium polyphosphate was melt-blended with nylon 6. Test performance: LOI=26.8%, UL-94 V1 grade, tensile strength 48 MPa (retention rate 64%), impact strength 2.8 kJ / m² (retention rate 51%). Comparative Example 4: Physical blending of zinc hydroxystannate and PAPP (1:20)

[0059] 6g of zinc hydroxystannate and 120g of piperazine-modified ammonium polyphosphate were physically mixed in a high-speed mixer for 10 min, and then melt-blended with nylon 6 at a total addition rate of 10wt%. Test performance: LOI=25.2%, UL-94 V2 rating, tensile strength 58MPa (77% retention), impact strength 3.8kJ / m² (69% retention). Physical mixing showed no synergistic effect, and the flame retardant performance was significantly lower than in Example 1.

[0060] Application example: Preparation and performance testing of flame-retardant nylon 6 composite materials PA6 was dried in a forced-air drying oven at 80℃ for 10 hours. PA6 was then added to a Banbury mixer and mixed to 240℃. The composite flame retardants obtained in Examples 1-3 were mixed with nylon 6 resin at 10wt% each, and then added to the Banbury mixer for melt blending at 240℃. The Banbury mixer speed was 50 r / min, and the mixing time was 13-16 minutes. After mixing, samples were taken, the composite material was shaped, and dried for about 1 hour. It was then hot-pressed in a flat vulcanizing machine at 240℃. The hot-pressing temperature was first preheated in the flat vulcanizing machine for 13-20 minutes, and then the hot-pressing time was adjusted to 400 seconds. The corresponding test samples were obtained after the hot-pressing time was completed. The performance test results are shown in Table 1.

[0061] Table 1 Flame retardant and mechanical properties of each embodiment and comparative example Comparative Example 1 21.4 No grade 75.0 100 5.5 100 850 - - Comparative Example 2 24.5 V2 52.0 69 3.2 58 720 15 28 Comparative Example 3 26.8 V1 48.0 64 2.8 51 650 24 34 Comparative Example 4 25.2 V2 58.0 77 3.8 69 680 20 31 Example 1 30.3 V0 65.0 87 4.5 82 420 51 66 Example 2 30.0 V0 63.0 84 4.2 76 380 55 69 Example 3 30.1 V0 60.0 80 4.0 73 350 59 72 As can be seen from the data in Table 1: (1) The LOI of Examples 1-3 is all >30%, and the UL-94 all reach V0 level, which is significantly better than the comparative examples; (2) Compared with Comparative Example 4, Example 1 increased the LOI by 5.1 percentage points and the UL-94 by two levels under the same total addition amount and the same proportion, proving that the core-shell structure formed by in-situ hydrogen bonding produced a significant synergistic effect, rather than a simple physical mixing; (3) The mechanical property retention rate of Examples 1-3 is all >73%, which is significantly better than that of Comparative Examples 2-4; (4) The peak heat release rate is reduced by 51-59%, and the smoke density is reduced by 66-72%, resulting in a significant smoke suppression effect.

[0062] In summary, the present invention provides a molecularly associated composite flame retardant prepared by coating piperazine-modified ammonium polyphosphate with zinc hydroxystannate, exhibiting significant flame retardant effects. Applying this composite flame retardant to the preparation of flame-retardant nylon 6 composite materials effectively retards nylon 6 and significantly suppresses smoke.

[0063] When the composite flame retardant prepared in Example 1 was applied to flame-retardant nylon 6, the limiting oxygen index of the prepared flame-retardant nylon 6 composite material increased from 21.4% of pure PA6 to 30.3% when 10% by mass was added. The UL-94 rating also improved from no rating for pure PA6 to V-0 flame retardant rating, proving that the composite flame retardant prepared in Example 1 had the most significant flame retardant effect and the best flame retardant performance.

[0064] The above description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. Simple changes and modifications made within the scope of the claims of the present invention are still within the scope of the present invention.

Claims

1. A composite flame retardant with zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate, characterized in that, Zinc hydroxystannate is linked to piperazine-modified ammonium polyphosphate via hydrogen bonds, thereby encapsulating the piperazine-modified ammonium polyphosphate to form an associative compound.

2. The composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 1, characterized in that, The mass ratio of zinc hydroxystannate to piperazine-modified ammonium polyphosphate in the composite is 1:(5-20).

3. The preparation method of a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 2, characterized in that, Includes the following steps: (1) Dissolve piperazine-modified ammonium polyphosphate and zinc hydroxystannate in a solvent and stir mechanically; (2) Set the temperature at 0.33-1℃ and react for at least 19 hours. Centrifuge the mixture after reaction, collect the precipitate, wash it with deionized water, freeze dry it, and grind it.

4. The preparation method of the composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 2, characterized in that, Includes the following steps: (1) Dissolve piperazine-modified ammonium polyphosphate, zinc sulfate and sodium stannate in a solvent and stir mechanically; (2) Set the temperature at 0.33-1℃ and react for at least 19 hours. Centrifuge the mixture after reaction, collect the precipitate, wash it with deionized water, freeze dry it, and grind it.

5. The method for preparing the composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 3 or 4, characterized in that, The temperature is 0.66-0.88℃.

6. A method for preparing a composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 3 or 4, characterized in that, The reaction time is 19-25 hours.

7. The method for preparing the composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 3 or 4, characterized in that, The mechanical stirring speed is 100-210 r / min.

8. The method for preparing the composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 3 or 4, characterized in that, The solvent is deionized water or a mixture of ethanol and water.

9. The method for preparing the composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 3 or 4, characterized in that, The piperazine-modified ammonium polyphosphate is ultrasonically dispersed at a frequency of 20-60 kHz.

10. The application of the composite flame retardant of zinc hydroxystannate coated with piperazine-modified ammonium polyphosphate according to claim 2 in the preparation of nylon flame retardant materials, wherein the amount added is 10-24 wt% of the nylon flame retardant material.

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