Recyclable nuclear pore structure MOF nanoflame retardant and preparation method thereof

Abstract

The present application relates to a kind of recyclable nuclear pore structure MOF nano flame retardant and its preparation method, belong to the cross technical field of nano and flame retardant.The present application provides a kind of nuclear pore structure MOF nano flame retardant, polyurethane foam is soaked in high concentration nano flame retardant, and foam material no longer appears melt drop phenomenon and self-extinguishes from fire, cannot be secondarily ignited, and foam material shows good flame-retardant heat-insulating effect, and smoke suppression effect is outstanding.After being introduced into foam material, the elasticity of foam material itself is improved, in addition, the nuclear pore structure of it gives foam material itself higher sound insulation and noise reduction effect.

Description

TECHNICAL FIELD

[0001] The present application relates to a recyclable nuclear pore structure MOF nanometer flame retardant and a preparation method thereof, and belongs to the technical field of nanometer and flame retardant cross. BACKGROUND

[0002] Flexible polyurethane foam (FPUF) is widely used in transportation, furniture, car seats and construction industries due to its excellent thermal insulation effect and high resilience characteristics. Flexible polyurethane foam contains some block copolymers, and its toughness is based on the phase separation between soft segments and hard segments. Its internal structure has a large number of open pores, and has good flexibility and use comfort. However, the foam material is easily ignited and produces a large amount of melt droplets and smoke (such as CO, NOx and HCN), and due to the large specific surface area of the foam material, its burning speed is much faster than other polymer materials, which increases the difficulty of fire rescue and seriously threatens people's life and property safety. Adding flame retardant during the foaming process of the foam is an efficient and convenient solution, but this process often requires a large amount of flame retardant (more than 20wt%), which usually destroys the foam structure, resulting in high loss of elasticity of the foam material and the flame retardant is usually difficult to recycle. Therefore, it is necessary to construct an efficient and original performance retaining flame retardant system for flexible polyurethane foam.

[0003] With the research on foam materials, it is found that surface coating treatment of polyurethane foam is a way to ensure the mechanical properties of the material itself and improve the flame retardant properties of polyurethane foam. In addition, many studies have shown that introducing nanomaterials into polymer matrices can achieve the retention or enhancement of their original mechanical properties, which provides a way to retain the high resilience characteristics of polyurethane foam materials. Metal organic framework (MOF) as a new type of nanomaterial, has achieved certain application in the fields of sensors, gas adsorption, catalysis and drug delivery, etc. due to its flexibility in composition and structure. Studies have confirmed that surface modification of polymer matrices using MOF materials can endow the materials with many excellent properties, which provides a new direction for flame-retardant polyurethane foam. MOF nanomaterials can be dispersed in an aqueous solution for foam surface coating, and an alcohol-based dispersion liquid can be used in post-processing to separate the foam and the flame retardant, which can realize the recycling of foam materials and flame retardants and meet the theme of green environmental protection.

[0004] However, research has confirmed that the flame retardant contribution of existing MOF materials to polymers is negligible, and the appropriate combination of MOF with organic ligands with flame retardant effects is a new direction for the development of flame retardants. The composite use of MOF nanomaterials and traditional flame retardant ligands (ligands need to have a certain acidity and alkalinity) can combine the active metals in the MOF raw materials, the flame retardant elements in the ligand flame retardant, and the unique nanostructure of MOF to achieve excellent flame retardant and smoke suppression effects. However, the existing modified MOF material structures are mostly core-shell or hollow structures, which have certain disadvantages for the adsorption of toxic gases during the combustion process. It is necessary to prepare a new type of MOF material with a core-pore structure to achieve efficient adsorption of toxic gases and thus achieve the expected flame retardant and smoke suppression effects. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art described above and to propose a recyclable nuclear pore structure MOF nano flame retardant and a preparation method thereof. The method is a scheme for preparing MOF nanomaterials by slow etching in an ice-water bath, and a nuclear pore structure MOF nano flame retardant is synthesized and prepared. The present invention utilizes an in-situ acid etching scheme to generate HCl on the MOF surface for pore etching and introduces a phosphorus-nitrogen expansion flame retardant system, thereby optimizing the flame retardant effect and gas adsorption capacity of the MOF material itself. By using an immersion coating method, the MOF is ultrasonically dispersed in water and then coated on the surface of a polyurethane foam, thereby greatly ensuring the excellent performance of the foam material itself. In the subsequent flame retardant recovery process, the present invention adopts an alcohol immersion method to achieve efficient separation of the flame retardant and the polymer matrix, which is of great significance for green nano flame retardancy and broadening the scope of use of the material.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A recyclable nuclear pore structure MOF nano flame retardant has a nuclear pore structure with a core inside and pores outside. Due to the introduction of the acidic system, in-situ etching is achieved on the ZIF-67 surface, so that the pores on its surface are expanded into a mesoporous structure. The nano flame retardant retains the original metal frame structure of ZIF-67, with a solid organic-inorganic hybrid core inside, mainly composed of Co and N elements, and an acidic component mainly composed of P and N elements is loaded on the outside.

[0008] A method for preparing a core pore structure MOF nano flame retardant, the specific steps are as follows:

[0009] Step 1: First, a certain amount of 2-methylimidazole is dissolved in methanol, which is referred to as solution A;

[0010] Dissolve cobalt nitrate hexahydrate in the same volume of methanol and record it as solution B;

[0011] Solution A is slowly added to solution B, and nucleated at room temperature. The supernatant is removed by centrifugation, and dried in a vacuum oven to obtain purple ZIF-67 powder;

[0012] In step two, a certain amount of purple ZIF-67 powder is dispersed in methanol or ethanol by ultrasonic treatment until no obvious particles are observed, and a purple liquid is obtained, which is recorded as solution C. Solution C is placed in a refrigerator (4-10℃) for cooling and standby;

[0013] In step three, a certain amount of gel-state hydroxyethyl s-triazine is dispersed in methanol and ultrasonically treated for 30-50 min until completely dissolved. Spirocyclic phosphorus oxychloride (SPDPC) is added as a phosphorus source and ultrasonically dispersed for 1-1.5 h, and recorded as solution D (pH is between 1 and 5).

[0014] In step four, solution D is added to solution C through a constant pressure dropping funnel. Solution C is controlled at a temperature of 5-10℃ by an ice-water bath. The dropping speed of solution D is controlled to simulate the wind erosion phenomenon in real life. After the slow addition is completed, the ice-water bath reaction is continued until the end. The supernatant is removed by centrifugation, washed with ethanol for several times, and then dried in a vacuum oven to obtain a blue-purple powder, which is a nuclear pore structure MOF nanometer flame retardant.

[0015] In step one, 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. The vacuum drying pressure is 0.08-0.1MPa, and the temperature is 60-70℃.

[0016] In step two, the ultrasonic dispersion time is 10-30 min. The ratio of purple ZIF-67 powder to methanol or ethanol is 1g:150-200mL.

[0017] In step three, the molar ratio of hydroxyethyl s-triazine to spirocyclic phosphorus oxychloride (SPDPC) is 2-2.2:3. The ratio of hydroxyethyl s-triazine to methanol is 1g:60-120mL.

[0018] In step four, the ice-water bath temperature needs to be controlled at 5-10℃. If the temperature exceeds this range, ZIF-67 will be etched excessively and will not have a core-shell structure. The mass ratio of hydroxyethyl s-triazine to ZIF-67 is 1:0.5-0.8.

[0019] The dropping time of solution D is 1-4h. After the dropping is completed, the ice-water bath reaction is continued for 3-6h.

[0020] Beneficial effects

[0021] 1. The present invention provides a nuclear pore structure MOF nano flame retardant, which is different from the existing preparation method. It proposes a new structural nano ZIF material prepared by imitating the wind erosion phenomenon in nature. It has good mass transfer and thermal conductivity and a high decomposition temperature. The present invention provides a nuclear pore structure MOF nano flame retardant, which is a new green and environmentally friendly flame retardant and can be recycled. It can achieve the separation of flame retardant and foam material under ethanol immersion, which is in line with the current theme of green environmental protection.

[0022] 2. The present invention provides a core pore structure MOF nano flame retardant. After the polyurethane foam is soaked in a high concentration of the nano flame retardant, the foam material no longer has the melting drop phenomenon and is self-extinguishing when away from the fire, and cannot be re-ignited. The foam material exhibits good flame retardant and heat insulation effects and outstanding smoke suppression effects.

[0023] 3. The present invention provides a MOF nano flame retardant with a nuclear pore structure. Thanks to its novel nuclear pore morphology, after being introduced into the foam material, the elasticity of the foam material itself is improved. In addition, its nuclear pore structure gives the foam material itself a higher sound insulation and noise reduction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Transmission electron microscope image and element content of the ZIF@PST nano flame retardant synthesized by the present invention;

[0025] Figure 2 The X-ray diffraction pattern of the ZIF@PST nano flame retardant synthesized by the present invention;

[0026] Figure 3 Compression cycle test of FPUF blank foam;

[0027] Figure 4 The load-displacement diagram of ten compression cycles of FPUF-ZIF@PST prepared in the present invention. DETAILED DESCRIPTION

[0028] The following examples are given in combination with the experimental results of the present invention to further illustrate the present invention.

[0029] Example 1

[0030] A method for preparing a core pore structure MOF nano flame retardant, the specific steps are as follows:

[0031] Step 1: Use methanol to dissolve the reaction raw materials, and let them stand at room temperature for 24 hours to prepare ZIF-67 with a typical dodecahedral structure. First, dissolve 95.36g (0.48mol) of 2-methylimidazole in 500mL of methanol solution, which is recorded as solution A, and dissolve 17.46g (0.06mol) of cobalt nitrate hexahydrate in the same volume of methanol solution, which is recorded as solution B. Solution A is slowly added dropwise to B, and the solution is precipitated and nucleated at room temperature for 24 hours. The supernatant is centrifuged and removed, and dried in a vacuum oven at 70°C (vacuum degree 0.1MPa) to obtain purple ZIF-67 powder with a yield of 22.3%. The ZIF-67 prepared under this condition is more uniform, and the subsequent etched nanomaterials prepared are more uniform.

[0032] Step 2: Take 3g of ZIF-67 powder in ethanol solvent and ultrasonically disperse it until there are no obvious particles. The purple liquid is recorded as solution C and placed in a refrigerator (4℃~10℃ refrigerated) to cool for later use. Weigh 6g of gel-state hydroxyethyl-s-triazine and disperse it in ethanol. Ultrasonicate for 30min until completely dissolved. Add 8.13g of SPDPC as a phosphorus source and ultrasonically disperse for 1h. Record it as solution D (acidic, pH between 1-3) and transfer it to a constant pressure dropping funnel. Use an ice-water bath to control the reaction temperature to 5-10℃, simulate the wind erosion phenomenon in real life, control the solution D drop rate, slowly add it for 3h, and continue the ice-water bath reaction for 6h until the end. Centrifuge to remove the supernatant, wash with ethanol several times, and vacuum dry at 70℃ (vacuum degree 0.1MPa) to obtain a blue-purple powder, which is the core pore structure MOF nano flame retardant ZIF@PST, with a yield of 85.3%.

[0033] Example 2

[0034] A method for preparing a core pore structure MOF nano flame retardant, the specific steps are as follows:

[0035] Step one, this step is similar to Example 1, and an amplification experiment was carried out under the same conditions. The reaction raw materials were dissolved in methanol, and ZIF-67 with a typical dodecahedral structure was prepared by standing molding at room temperature for 24 hours. First, 190.72g (0.96mol) of 2-methylimidazole was dissolved in 1000mL of methanol solution and recorded as solution A. 34.92g (0.12mol) of cobalt nitrate hexahydrate was dissolved in the same volume of methanol solution and recorded as solution B. Solution A was slowly added dropwise to B, and the nucleation was precipitated at room temperature for 24 hours. The supernatant was centrifuged and removed. Purple ZIF-67 powder was obtained by drying in a vacuum oven at 70°C (vacuum degree 0.1MPa) with a yield of 25%. The ZIF-67 yield prepared under these conditions was higher and the particle size was more uniform, and the etching nanomaterial prepared by subsequent use was more uniform.

[0036] Step two, 6g of ZIF-67 powder was dispersed in ethanol solvent by ultrasonic dispersion until no obvious particles were observed, obtaining a purple liquid recorded as solution C, which was placed in the refrigerator (4-10℃ refrigeration) for cooling. Gelatinous hydroxyethyl triazine 12g was dispersed in ethanol and ultrasonically treated for 1h until completely dissolved. 16.26g of SPDPC was added as a phosphorus source and ultrasonically dispersed for 1h, recorded as solution D (acidic, PH between 1-3), and transferred to a constant pressure dropping funnel. Using an ice water bath, the reaction temperature was controlled at 5-10℃, simulating the wind erosion phenomenon in real life, and the solution D was slowly added at a controlled rate for 4h. After completion, the ice water bath was continued for 6h until the end. The supernatant was removed by centrifugation, washed with ethanol several times, and vacuum dried at 70℃ (vacuum degree 0.1MPa) to obtain a blue-purple powder, which was the nuclear pore structure MOF nanoflame ZIF@PST, with a yield of 92.3%.

[0037] To characterize the structure of the nuclear pore structure MOF nanoflame ZIF@PST obtained above, transmission electron microscopy and X-ray diffraction spectrum tests were performed. The transmission electron microscopy results are shown in Figure 1 The MOF nanoflame ZIF@PST nanoflame showed a clear nuclear pore structure, and P element appeared in the elemental spectrum and the original Co element was retained. The XRD results are shown in Figure 2 The nuclear pore structure MOF nanoflame ZIF@PST retained the characteristic crystal surface structure of ZIF-67 and had a good crystal structure. The nuclear pore structure MOF nanoflame ZIF@PST obtained above was tested by thermogravimetric analysis, and the test results showed that its decomposition temperature was between 500-650℃, showing excellent thermal stability.

[0038] Preparation method of polyurethane foam coated with MOF nano flame retardant: The ZIF@PST nano flame retardant prepared in Example 2 is applied to the surface of polyurethane foam and soaked multiple times to obtain surface-modified flame-retardant polyurethane foam. First, the polyurethane foam is washed twice and then cut to the corresponding size for use. The ZIF@PST flame retardant prepared above (1g, 3g, 5g) is dispersed in 100mL of water and ultrasonically treated for 10min. The foam is soaked in the above solution and pressed multiple times after soaking for 10min to re-adsorb. The above steps are repeated three times, and the foam is dried in a 70℃ forced air oven for 12h to obtain polyurethane foam coated with ZIF@PST flame retardant. The mass of the polyurethane foam increases by 0.038g, 0.067g, and 0.15g, respectively. The foam materials FPUF-ZIF@PST-1, FPUF-ZIF@PST-3, and FPUF-ZIF@PST-5 are prepared. After conducting combustion tests, it was found that after being soaked in a 5% concentration of nano flame retardant, the foam material no longer showed dripping and self-extinguished when away from the fire, making it impossible to ignite again. Its limiting oxygen index can reach 30.1%. After adding this flame retardant, the peak heat release rate of polyurethane foam can be reduced by 52.3%, carbon dioxide production by 42.5%, and carbon monoxide production by 39.3%, with outstanding smoke suppression effect. In addition, its compression cycle picture is as follows Figure 3 and Figure 4 As shown, the polyurethane foam material after soaking maintains its original volume and its elastic modulus is increased to 1.6523MPa compared with the original foam material; its nuclear pore structure gives the foam material itself a higher sound insulation and noise reduction effect, and the sound insulation for sound waves above 2000HZ is increased to more than twice that of the original foam material (original foam 2.12~3.38dB / 1, new foam 4.99~8.00dB / 1).

[0039] Recovery and separation of polyurethane foam and flame retardant: The resulting FPUF-ZIF@PST-5 foam was immersed in an ethanol solution. Due to its higher density, the modified foam sank in the ethanol solvent. After 30 minutes of immersion, the ethanol solvent turned blue, and the foam returned to white. The foam was transferred to a new ethanol solvent and soaked repeatedly until the blue color disappeared (this was achieved after three times). The blue ethanol was rotary evaporated to recover 0.136g of the original flame retardant ZIF@PST, achieving a recovery rate of 91%. The foam remained unchanged in quality and could be reused, achieving a recycling and environmentally friendly approach.

[0040] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A recyclable nuclear pore structure MOF nano flame retardant, characterized by: The nano flame retardant has a core-pore structure, with a core inside and holes outside. The interior is a solid organic-inorganic hybrid core, mainly composed of Co and N elements; The acidic components mainly composed of P and N elements are loaded externally; The steps of the flame retardant preparation method include: Step 1: Mix 2-methylimidazole and methanol to obtain solution A, and mix cobalt nitrate hexahydrate and methanol to obtain solution B; Solution A was added dropwise to solution B, and the solution was allowed to settle at room temperature to form nuclei. The supernatant was removed by centrifugation and vacuum dried to obtain ZIF-67 powder. Step 2: adding the ZIF-67 powder obtained in step 1 to methanol or ethanol and performing ultrasonic dispersion to obtain solution C; Step 3, mixing hydroxyethyl-s-triazine, spirocyclic phosphoryl chloride and methanol to obtain solution D; Step 4: adding the solution D obtained in step 3 dropwise to the solution C obtained in step 2 to react, and after the reaction is completed, centrifuging to remove the supernatant, washing, and vacuum drying to obtain a core pore structure MOF nano flame retardant; In the step 4, the temperature is controlled by an ice-water bath during the reaction, and the temperature of the ice-water bath is 5-10°C; The time for adding solution D dropwise is 1~4 hours; after the addition is completed, the reaction time in the ice-water bath is continued for 3~6 hours.

2. A method for preparing a nuclear pore structure MOF nano flame retardant, characterized in that The steps of the method include: Step 1: 2-methylimidazole and methanol are mixed to obtain solution A, and cobalt nitrate hexahydrate and methanol are mixed to obtain solution B; solution A is added dropwise to solution B, and the mixture is allowed to settle at room temperature to form nuclei, the supernatant is removed by centrifugation, and the mixture is vacuum dried to obtain ZIF-67 powder; Step 2: adding the ZIF-67 powder obtained in step 1 to methanol or ethanol and performing ultrasonic dispersion to obtain solution C; Step 3, mixing hydroxyethyl-s-triazine, spirocyclic phosphoryl chloride and methanol to obtain solution D; Step 4: adding the solution D obtained in step 3 dropwise to the solution C obtained in step 2 to react, and after the reaction is completed, centrifuging to remove the supernatant, washing, and vacuum drying to obtain a core pore structure MOF nano flame retardant; In the step 4, the temperature is controlled by an ice-water bath during the reaction, the ice-water bath temperature is 5-10° C., and the mass ratio of hydroxyethyl s-triazine to ZIF-67 is 1:0.5-0.8; The time for adding solution D dropwise is 1~4 hours; after the addition is completed, the reaction time in the ice-water bath is continued for 3~6 hours.

3. The method for preparing a nuclear pore structure MOF nano flame retardant according to claim 2, characterized in that: In the step 1, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 4-8:1; the ratio of 2-methylimidazole to methanol is 1 g:60-120 mL, and the ratio of cobalt nitrate hexahydrate to methanol is 1 g:60-120 mL; the vacuum drying pressure is 0.08-0.1 MPa, and the temperature is 60-70°C.

4. The method for preparing a nuclear pore structure MOF nano flame retardant according to claim 2, characterized in that: In the step 2, the ultrasonic dispersion time is 10-30 min; the ratio of purple ZIF-67 powder to methanol or ethanol is 1 g: 150-200 mL.

5. The method for preparing a nuclear pore structure MOF nano flame retardant according to claim 2, characterized in that: In the step 3, the molar ratio of hydroxyethyl s-triazine to spirocyclic phosphoryl chloride is 2-2.2:3; and the ratio of hydroxyethyl s-triazine to methanol is 1 g: 60-120 mL.

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