Porous hollow structure MOF nano flame retardant and preparation method thereof

Abstract

The present application relates to a kind of porous hollow structure MOF nano flame retardant and its preparation method, belong to the cross field of nanotechnology and flame retardant technology.The porous hollow structure MOF nano flame retardant provided by the present application is different from the existing flame retardant etching preparation method, using in-situ generated hydrochloric acid, nitrogen slowly blows out excess acid gas to ensure that no over-etching occurs, in-situ acid etching reaming is prepared to obtain a kind of porous hollow structure MOF nano flame retardant.The porous hollow structure MOF nano flame retardant provided by the present application is different from the existing MOF structure, by reaming increase mass transfer effect, mass transfer and heat conduction effect are good, and decomposition temperature is high.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of porous hollow structure MOF nano flame retardant and its preparation method, belong to the cross field of nanotechnology and flame retardant technology. BACKGROUND

[0002] As a kind of thermosetting resin material, due to its excellent mechanical properties, thermal stability, electrical insulation and corrosion resistance, epoxy resin has a wide range of applications in structure, machinery, electronics and aerospace fields. However, like most polymer materials, EP has two obvious shortcomings: flammability and toxicity of smoke, a large amount of black smoke produced when epoxy resin burns, which makes the visibility of the environment poor, which makes it difficult for people to escape and survive when they are at risk of fire. In addition, the high crosslinking density of EP leads to poor toughness and low fracture energy, limiting its development in advanced materials. Therefore, it is of great significance to improve the flame retardancy, smoke suppression and mechanical properties of EP.

[0003] The combination of phosphorus-based flame retardants and nitrogen-based flame retardants shows great potential in thermal insulation, smoke suppression and low toxicity enhanced flame retardant performance. Spirocyclic phosphorus oxychloride derivatives are intumescent flame retardants with unique nitrogen-phosphorus structural units. Due to the synergistic effect of phosphorus and nitrogen, they have good thermal stability and catalytic carbonization effect, which is also the key to their research as flame retardants. Based on the excellent ability of phosphorus-nitrogen intumescent flame retardants in fire extinguishing and smoke suppression, in order to improve the ability of composite materials to prevent fire hazards and retain the original performance of the material, the flame retardant not only needs to have flame-retardant elements, but also needs to be designed through clever structure to obtain a new type of flame retardant with excellent flame-retardant performance without damaging the mechanical properties of the matrix.

[0004] It should be noted that in order to achieve the flame-retardant effect, a high amount of flame retardant is often required, and the problem of the aggregation of flame retardant, which leads to the decrease of the overall mechanical properties of the matrix, still needs to be solved. Traditional phosphorus-nitrogen intumescent flame retardants have one-dimensional (0D) structure and cannot be effectively dispersed in the polymer system, but it has been reported that the dispersion of flame retardants in the matrix can be improved by forming various sizes of mismatched structures. ZIF-67 is a kind of 3D nanomaterial, due to its rich micro / intermediate pore nanochannels and its ability to encapsulate / adsorb particles, it has significant advantages in suppressing smoke production. By adding 0D phosphorus-nitrogen flame retardant for surface modification, the pores of ZIF-67 are opened by etching treatment using the acidity of phosphorus-nitrogen intumescent flame retardant, which is beneficial to optimize the dispersion of flame retardant in EP and improve its smoke suppression effect, realize high-efficiency flame-retardant and smoke-suppression, and improve the mechanical properties of epoxy resin material itself. SUMMARY

[0005] The purpose of the present application is to solve the problems of low flame retardant efficiency, poor smoke suppression effect, easy agglomeration of flame retardant, and damage to the mechanical properties of epoxy resin composite material of the existing flame retardant.

[0006] The purpose of the present application is realized by the following technical scheme.

[0007] A porous hollow structure MOF nano flame retardant, due to the in-situ etching effect of the acidic component, the internal structure collapses, showing a hollow structure, and the surface benefits from the inward etching effect of the acid, and the surface structure is opened to form many pores. That is, the nano flame retardant is hollow inside due to the in-situ etching effect of HCl; the outside has a porous structure with good mass transfer and heat insulation effect; the original organic-inorganic hybrid structure is retained, and the elements are mainly P, Co and N.

[0008] A porous hollow structure MOF nano flame retardant preparation method, the specific steps are as follows:

[0009] Step one, using alcohol solution to dissolve the raw materials, room temperature 24h static molding preparation with typical dodecahedron structure ZIF-67. First, a certain amount of 2-methylimidazole is dissolved in alcohol solution, which is denoted as solution A, and cobalt nitrate hexahydrate is dissolved in the same volume of alcohol solution, which is denoted as solution B. Slowly add solution A to B, nucleate at room temperature, centrifuge to remove the supernatant, and vacuum oven dry to obtain purple ZIF-67 powder.

[0010] Step two, take a certain amount of ZIF-67 powder in the solvent, ultrasonic dispersion to no obvious particles, get purple liquid denoted as solution C, placed in a three-necked flask for standby. Add spirocyclic phosphorus oxychloride (SPDPC) as phosphorus source to the three-necked flask, stir and disperse, then add 4,6-dihydroxy pyrimidine by constant pressure dropping funnel. Using oil bath nitrogen protection (control nitrogen rate) method, pre-react for a certain time (1-3h), then heat to 60-80℃, the heating rate is 5-10℃ / min, fully react for 12-24h, centrifuge to remove the supernatant, solvent is washed for many times, vacuum drying to get purple powder, which is porous hollow structure MOF nano flame retardant.

[0011] In the step one, the alcohol solution is one of anhydrous ethanol, anhydrous methanol or a mixed solvent; the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 4-8:1; the ratio of 2-methylimidazole to methanol is 1g:60-120mL, and the ratio of cobalt nitrate hexahydrate to methanol is 1g:60-120mL; solution A is a 2-methylimidazole solution, which needs to be heated or ultrasonically treated until completely dissolved if not completely dissolved, otherwise the morphology of ZIF-67 will be affected; solution B is a cobalt nitrate hexahydrate solution, and during the mixing process, the above-mentioned 2-methylimidazole solution A needs to be added dropwise into B for slow deposition, otherwise the uniformity and morphology of the product will be affected; the vacuum drying pressure is 0.08-0.1MPa, and the temperature is 70-80℃.

[0012] In the step two, ZIF-67 needs to be ultrasonically treated for 10-50min according to the solubility of the solvent; the ratio of ZIF-67 to the solvent is 1g:100-350mL; the solvent is one of methanol, ethanol, tetrahydrofuran, acetonitrile and acetone; the molar ratio of 4,6-dihydroxypyrimidine to SPDPC is 1.05:1.15-1.15; the dispersion time of the phosphorus source is 10-30min, which can be ultrasonically treated in a centrifuge tube; the mass ratio of SPDPC to ZIF-67 is 1:1-2:1; the nitrogen gas rate is 2mL / min-5mL / min, and the time should not be too fast, otherwise the solvent will be blown dry; the pre-reaction temperature and time are 30-50℃ and 1-3h respectively; the sufficient reaction time is 12-24h, and the morphology is more uniform if the time is longer, but the structure will be broken if the time is too long; the alternating solvent is dichloromethane and ethanol, and the washing is 2-4 times; the vacuum drying pressure is 0.08-0.1MPa, and the temperature is 70-80℃.

[0013] Beneficial effects

[0014] 1. The porous hollow structure MOF nano flame retardant provided by the application is different from the existing flame retardant etching preparation method, adopts the mode of in-situ generation of hydrochloric acid and slow blowing of excess acidic gas by nitrogen to ensure that excessive etching does not occur, and is prepared by in-situ acid etching and hole expansion to obtain a porous hollow structure MOF nano flame retardant.

[0015] 2. The porous hollow structure MOF nano flame retardant provided by the application is different from the existing MOF structure, the mass transfer effect is increased by hole expansion, the mass transfer and heat conduction effects are good, and the decomposition temperature is high.

[0016] 3. The porous hollow structure MOF nano flame retardant provided by the application does not appear to melt and drip in the flame-retardant epoxy resin and has outstanding flame-retardant and smoke-suppressing effects.

[0017] 4、The porous hollow structure MOF nano flame retardant provided by the application belongs to a novel green environmental protection flame retardant and benefits from the size mismatching of the 0D phosphorus-nitrogen flame retardant and the 3D ZIF-67 material, exhibits excellent dispersibility in the epoxy resin and improves the mechanical property of the epoxy resin, and the bending strength of the material itself is obviously improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The scanning electron microscope pictures of the ZIF-67 and ZIF@DHP nano flame retardants synthesized according to the application;

[0019] Figure 2 The transmission electron microscope picture of the ZIF@DHP nano flame retardant synthesized according to the application. DETAILED DESCRIPTION

[0020] The following gives examples in combination with the experimental results of the application to further illustrate the application.

[0021] Example 1

[0022] A porous hollow structure MOF nano flame retardant preparation method, the specific steps are as follows:

[0023] Step one, methanol is used to dissolve the reaction raw materials, and ZIF-67 with a typical dodecahedron structure is prepared by standing for molding at room temperature for 24 hours. First, 11.92g (0.18mol) of 2-methylimidazole is dissolved in 300mL of methanol solution, which is denoted as solution A, and 8.73g (0.03mol) of cobalt nitrate hexahydrate is dissolved in the same volume of methanol solution, which is denoted as solution B. Solution A is slowly added to solution B, and nucleation is settled at room temperature for 24 hours. The supernatant is removed by centrifugation, and the ZIF-67 powder is obtained by drying in a vacuum oven at 70℃ (vacuum degree 760mm Hg), with a yield of 10.3%.

[0024] Step two, place in a three-necked flask for standby. Connect a condenser tube, a nitrogen protection device and a constant pressure dropping funnel, weigh 2g of SPDPC and disperse in 30mL of methanol, ultrasonic treat for 30min until completely dissolved, add 0.8g of 4,6-dihydroxy pyrimidine through the constant pressure dropping funnel, and pre-react for 2h at 40℃. Gradually heat to 70℃, react for 12h to end the reaction, centrifuge at 3500rmp to pour off the supernatant, and then transfer to a filtration device. After washing with dichloromethane and ethanol alternately for 3 times, the purple powder obtained by drying in a vacuum oven at 75℃ (vacuum degree 760mm Hg) is the porous hollow structure MOF nano flame retardant ZIF@DHP, with a yield of 72.3%.

[0025] Example 2

[0026] A porous hollow structure MOF nano flame retardant preparation method, the specific steps are as follows:

[0027] Step one, using methanol to dissolve the reaction raw materials, room temperature 24h static molding preparation of typical ZIF-67 dodecahedron structure. First in 500mL methanol solution dissolved 95.36g (0.48mol) of 2-methylimidazole, it is recorded as solution A, 17.46g (0.06mol) of cobalt nitrate hexahydrate is dissolved in the same volume of methanol solution, it is recorded as solution B. Solution A is slowly added to B, room temperature 24h settlement nucleation, the supernatant is removed by centrifugation, vacuum oven 70℃ drying (vacuum degree 760mm Hg) to get purple ZIF-67 powder, yield 22.3%, the ZIF-67 prepared under this condition is more uniform, the subsequent use of the preparation of etching nanomaterials is more uniform.

[0028] Step two, take 3g of ZIF-67 powder dispersed in 500mL acetonitrile solvent, ultrasonic dispersion to no obvious particles, get purple liquid recorded as solution C, placed in a three necked flask for standby. Connect the condenser tube, nitrogen protection device and constant pressure dropping funnel, take SPDPC 5g dispersed in 200mL acetonitrile, ultrasonic treatment for 30min to completely dissolve, add 4,6-dihydroxy pyrimidine 1.02g through constant pressure dropping funnel, 50℃ pre reaction 3h. Gradient heating to 80℃, reaction 16h end reaction, 8000rmp centrifugation three times after pouring the supernatant to transfer to the filtration device, using dichloromethane and ethanol alternately 3 times, 80℃ vacuum drying (vacuum degree 760mm Hg) to get purple powder, that is, porous hollow structure MOF nanometer flame retardant ZIF@DHP, yield 83.3%.

[0029] Example 3

[0030] A porous hollow structure MOF nanometer flame retardant preparation method, the specific steps are as follows:

[0031] Step one, this step is similar to example 2, under the same conditions, using methanol to dissolve the reaction raw materials, room temperature 24h static molding preparation of typical ZIF-67 dodecahedron structure. First in 1000mL methanol solution dissolved 190.72g (0.96mol) of 2-methylimidazole, it is recorded as solution A, 34.92g (0.12mol) of cobalt nitrate hexahydrate is dissolved in the same volume of methanol solution, it is recorded as solution B. Solution A is slowly added to B, room temperature 24h settlement nucleation, the supernatant is removed by centrifugation, vacuum oven 70℃ drying (vacuum degree 760mm Hg) to get purple ZIF-67 powder, yield 25%, the ZIF-67 prepared under this condition has higher yield and more uniform particle size, the subsequent use of the preparation of etching nanomaterials is more uniform.

[0032] Step two, 5g of ZIF-67 powder was dispersed in 800mL of tetrahydrofuran solvent, ultrasonic dispersion until no obvious particles, get purple liquid recorded as solution C, placed in a three-necked flask for standby. Connect the condenser, nitrogen protection device and constant pressure dropping funnel, take SPDPC 8g dispersed in 200mL of tetrahydrofuran, ultrasonic treatment for 30min until completely dissolved, add 4, 6-dihydroxy pyrimidine 3.5g through constant pressure dropping funnel, pre-reaction at 45℃ for 3h. Gradient heating to 75℃, reaction for 24h, centrifugal at 8000rpm for three times, then transfer to the filtration device, washed with dichloromethane and ethanol alternately for 3 times, vacuum drying at 80℃ (vacuum degree 760mm Hg) to get purple powder, which is porous hollow structure MOF nano flame retardant ZIF@DHP, yield 89.3%.

[0033] In order to characterize the structure of the porous hollow structure MOF nano flame retardant ZIF@DHP obtained above, scanning electron microscopy and transmission electron microscopy were used to characterize it. The scanning electron microscopy results are shown in Figure 1 Compared with the regular surface structure of ZIF-67, the nano flame retardant ZIF@DHP has obvious pore structure, but still has a rhombohedral dodecahedron structure. The transmission electron microscopy results are shown in Figure 2 The P element is loaded on the surface of the nano material, and the organic-inorganic hybrid Co-N structure is still retained in the metal framework. The thermal gravimetric test of the porous hollow structure MOF nano flame retardant ZIF@DHP obtained above shows that its decomposition temperature is between 600-650℃, which shows excellent thermal stability.

[0034] The porous hollow structure MOF nano flame retardant ZIF@DHP prepared in the application has excellent flame retardant effect and belongs to a new type of green and environmentally friendly flame retardant. In the flame-retardant epoxy resin, at an addition amount of 2%, the material does not appear to melt and drip, and the oxygen index (LOI) reaches 31.2%; after adding this flame retardant, the peak value of heat release rate can be reduced by 44.3%, and due to the mass transfer effect of the pore structure, the smoke suppression effect is outstanding, the amount of carbon dioxide produced during the combustion of the epoxy resin is reduced by 65.5%, and the amount of carbon monoxide produced is reduced by 49.3%. And due to the size mismatch between the 0D phosphorus-nitrogen flame retardant and the 3D ZIF-67 material, it shows excellent dispersibility in the epoxy resin and improves the mechanical properties of the epoxy resin, the bending strength of the material itself is increased from 100MPa to 144MPa, and the tensile strength is increased from 93Mpa to 110MPa.

[0035] The above detailed description of the specific description, the purpose, technical scheme and beneficial effects of the application are further described in detail, it should be understood that the above description is only a specific embodiment of the application, and is not used to limit the protection scope of the application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a porous hollow structure MOF nano flame retardant, the inside of the porous hollow structure MOF nano flame retardant being a hollow structure, and the outside being provided with a pore structure; the method comprising the following steps: Step 1: mixing 2-methyl imidazole and alcohol to obtain solution A, mixing a cobalt nitrate hexahydrate and alcohol solution to obtain solution B, adding solution A to solution B, settling at room temperature to form nuclei, centrifuging to remove supernatant, and vacuum drying to obtain ZIF-67 powder; Step 2: mixing the ZIF-67 powder with a solvent to obtain solution C; Step 3: adding spirocyclic phosphorus oxychloride to solution C obtained in Step 2, then adding 4, 6-dihydroxy pyrimidine, pre-reacting by introducing nitrogen, and then reacting by increasing the temperature, centrifuging to remove supernatant after the reaction is completed, washing, and vacuum drying to obtain the porous hollow structure MOF nano flame retardant. characterized in that In Step 3, the nitrogen flow rate is 2-5 mL / min, the pre-reaction temperature is 30-50℃, the pre-reaction time is 1-3 h, the temperature for the reaction by increasing the temperature is 60-80℃, the reaction time is 12-24 h, the vacuum drying pressure is 0.08-0.1 MPa, and the temperature is 70-80℃. 2.The method of claim 1, wherein in Step 1, the alcohol is ethanol or methanol. 3.The method of claim 2, wherein in Step 1, the molar ratio of 2-methyl imidazole to cobalt nitrate hexahydrate is 4-8:

1. 4.The method of claim 1, wherein in Step 1, the ratio of 2-methyl imidazole to alcohol is 1 g:60-120 mL, and the ratio of cobalt nitrate hexahydrate to alcohol is 1 g:60-120 mL. 5.The method of claim 1, wherein in Step 1, the vacuum drying pressure is 0.08-0.1 MPa, and the temperature is 70-80℃. 6.The method of claim 1, wherein in Step 2, the ratio of ZIF-67 powder to solvent is 1 g:100-350 mL. 7.The method of claim 6, wherein in Step 2, the solvent is one of methanol, ethanol, tetrahydrofuran, acetonitrile, and acetone. 8.The method of claim 1, wherein in Step 3, the molar ratio of 4, 6-dihydroxy pyrimidine to spirocyclic phosphorus oxychloride is 1.05:1.15-1, and the mass ratio of spirocyclic phosphorus oxychloride to ZIF-67 is 1:1-2:

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