COF nanosheet for enhancing flame retardant performance of PVC and PE pipes, and preparation method and application thereof

Abstract

The application discloses a COF nanosheet for enhancing the flame-retardant property of PVC and PE pipes and a preparation method and application thereof. The nanosheet contains a COF skeleton composed of elements such as N, P and Br; in the preparation, a hydrothermal synthesis method is used to react hexachlorotriphosphazene, 3-bromo-2,6-dimethylpyridine and 4-pyridine formaldehyde at high temperature to obtain a COF crystal nucleus, and the crystal nucleus is subjected to plane growth at a higher temperature to finally generate the COF nanosheet ZR-COF. The ZR-COF nanosheet obtained by the application is applied to PE and PVC pipes as a flame-retardant additive, the synergistic effect of various flame-retardant elements greatly enhances the flame-retardant property of the PE and PVC pipes, the sheet structure can be fully contacted with the PVC and PE, and the mechanical strength of the PVC and PE can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method and application of COF nanosheets for enhancing the flame retardant performance of PVC pipe materials. BACKGROUND

[0002] Polyvinyl chloride (PVC) pipe materials are widely used in building water supply and drainage, electrical cable sleeve (electrician sleeve), agricultural irrigation, communication sheath, chemical fluid transportation, mine ventilation and drainage, etc. due to their excellent corrosion resistance, electrical insulation, processing performance, cost-effectiveness and certain mechanical strength. In the above applications, especially in the scenarios of building interiors (electric wire sleeve, drainage pipe), power systems (cable sheath), mines, public transportation (subway, tunnel), etc., strict requirements are put forward for the flame retardant performance of the materials. Although the flame retardant performance of traditional PVC pipe materials is higher than that of many plastics, they are difficult to process and need to add a large amount of plasticizer, which reduces the limiting oxygen index of the PVC pipe materials. In some high-demand application scenarios (such as high-rise building core pipes and harsh power environments), the flame retardant grade of PVC pipe materials still needs to be further improved to meet the standards. PVC releases a large amount of smoke and toxic and harmful substances such as hydrogen chloride (HCl) gas and dioxin during combustion or high-temperature pyrolysis, which seriously threatens personnel safety and equipment facilities. Therefore, improving the flame retardant grade of PVC pipe materials is an inevitable requirement to meet safety regulations and market demand.

[0003] Polyethylene (PE) pipe materials are widely used in urban water supply systems, gas transportation, agricultural irrigation, industrial fluid pipelines and ground source heat pump engineering due to their excellent flexibility, low-temperature impact resistance, chemical stability, non-toxicity and long service life. In the scenarios of underground comprehensive pipe galleries, building interior interpenetration laying, chemical industry parks and tunnel engineering, PE pipe materials need to meet strict fire safety standards. Once a fire occurs, flammable PE pipe materials may become a carrier for the spread of fire, releasing a large amount of flammable gas and molten droplets, and exacerbating disaster risks. Therefore, improving the flame retardant performance of PE pipe materials is a core technical challenge to ensure public safety.

[0004] The flame-retardant polyethylene corrugated pipe material in patent CN 118359862 A introduces a modified antioxidant, and the generated phosphoric acid and boric acid can further combine to form high-stability boron phosphate, which covers the surface of the polyethylene resin matrix, thereby improving the flame retardant performance of the polyethylene corrugated pipe material through synergistic effect. The flame-retardant polyvinyl chloride prepared in patent CN 119912768 A adopts 4-carboxyphenylboronic acid in composite modified attapulgite to form a B-O-B crosslinked network structure at high temperature, which can synergistically act with composite metal oxides (zinc oxide, manganese oxide) to improve the thermal stability and density of the carbon layer, thereby improving the flame retardant performance of the PVC pipe material. Although the flame retardant performance of polyethylene and polyvinyl chloride pipe materials is improved, the technical effect is single. SUMMARY

[0005] The application aims at the shortcomings of current PE and PVC pipes that are easy to burn and decompose under high temperature conditions, and provides a COF nanosheet for enhancing the flame retardant performance of PVC pipes, a preparation method and application thereof. The nanosheet contains a COF skeleton composed of elements such as N, P and Br; in the preparation, a hydrothermal synthesis method is used to obtain a COF crystal nucleus by reacting hexachlorotriphosphazene, 3-bromo-2,6-dimethylpyridine and 4-pyridine formaldehyde at high temperature, and the crystal nucleus is subjected to plane growth at a higher temperature to finally generate the COF nanosheet ZR-COF.

[0006] The technical scheme of the application is as follows:

[0007] A COF nanosheet for enhancing the flame retardant performance of PVC and PE pipes, the COF nanosheet being the following compound:

[0008]

[0009] The wavy line in the formula represents a repeating unit (-N-P- chemical bond); the thickness of the nanosheet is 2-20 nm.

[0010] The preparation method of the COF nanosheet for enhancing the flame retardant performance of PVC and PE pipes comprises the following steps:

[0011] Hexachlorotriphosphazene and 3-bromo-2,6-dimethylpyridine are added into a reaction tube, then toluene is added into the tube under anhydrous and oxygen-free environment, 4-pyridine formaldehyde is dropped into the solution after dissolution, and the reaction is carried out at a high temperature section for 1-2 h and at a low temperature section for 65-75 h; then filtration, washing and drying are carried out, the nanosheet is put into anhydrous methanol for ultrasonic treatment and drying to obtain the ZR-COF nanosheet;

[0012] 8-12 g of hexachlorotriphosphazene, 10-20 g of 3-bromo-2,6-dimethylpyridine and 15-25 g of 4-pyridine formaldehyde are dissolved in 1 liter of toluene;

[0013] The high temperature section is 110-130 DEG C in a microwave reactor or 180-220 DEG C in a conventional reactor;

[0014] The low temperature section is 80-90 DEG C in a microwave reactor or 130-180 DEG C in a conventional reactor.

[0015] The anhydrous and oxygen-free environment is a nitrogen atmosphere.

[0016] The ultrasonic time is 10-60 min.

[0017] The application of the COF nanosheet for enhancing the flame retardant performance of PVC and PE pipes is used as a flame retardant additive in the pipes.

[0018] The method comprises the following steps:

[0019] The ZR-COF nanosheet, antioxidant 1010, heat stabilizer and base material are poured into a high-speed dispersion machine at a rotating speed of 500-2000 r / min -1 After mixing at room temperature for 5-15 min, the mixture is discharged to obtain a mixed material; the mixed material is added into a double-screw extruder at a speed of 5-12 kg / h -1 After the pipe is extruded through a die, it is cooled to room temperature to obtain a pre-crosslinked PE pipe or PVC pipe.

[0020] The mass ratio is ZR-COF nanosheet: antioxidant: heat stabilizer 1010: base material = 1-5: 0.01-0.05: 0.01-0.05: 15-20.

[0021] The antioxidant 1010 is (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester); and the heat stabilizer is dibutyltin dilaurate.

[0022] The base material is polyethylene resin or polyvinyl chloride resin.

[0023] The substantial features of the present application are:

[0024] The present application uses a heating method to polymerize hexachlorotriphosphazene, 3-bromo-2,6-dimethylpyridine and 4-pyridine formaldehyde monomers through chemical reaction, and constructs a nanosheet structure with special ionization modification by adjusting the polymerization temperature and ultrasonic separation. At high temperature, the monomers rapidly polymerize to form a ZR-COF core, and then the ZR-COF nanosheet grows into a layered structure in a two-dimensional plane at a higher temperature, and then the nanosheet is further layered by ultrasonic separation. Due to the ultra-thin thickness of the COF nanosheet, more contact area can be provided with less addition amount, and the unique structure of the COF also has more cavities.

[0025] The structure design enables the nanosheet to produce multidimensional interaction with the polymer matrix of the PE and PVC pipe material, promotes uniform dispersion and stable existence of the nanosheet in the resin matrix. The obtained ZR-COF as an additive of the PE and PVC pipe material contains elements such as N, P, Br and a carbon layer difficult to burn, and the synergistic effect of various flame-retardant elements in the flame-retardant aspect can make it have better flame-retardant effect, the synergistic effect of N, Br elements and N-P bonds on the skeleton can greatly enhance the flame-retardant performance, and the cavity structure can store and absorb toxic gas. The flame-retardant strength of the PE and PVC pipe material is significantly improved. The unique sheet structure of the nanosheet can fully contact with the PVC and PE matrix to form a crosslinked structure, and greatly improve the mechanical properties of the pipe material.

[0026] The beneficial effects of the present application are:

[0027] The present application is dedicated to making up for the defects of the current PE and PVC pipe material in single performance improvement, and further provides a preparation method and application approach of the COF nanosheet for enhancing the flame-retardant performance of the PVC and PE pipe material. The ZR-COF nanosheet is generated by heating, and the monomers of hexachlorotriphosphazene, 3-bromo-2, 6-dimethylpyridine and 4-pyridine formaldehyde are polymerized to generate ZR-COF, and the nanosheet structure is constructed by adjusting the polymerization temperature. The structure design enables the nanosheet to produce multidimensional interaction with the polymer matrix of the PE and PVC pipe material, promotes uniform dispersion and stable existence of the nanosheet in the resin matrix. Since the cavity structure can adsorb the overflowed HCl gas, the generation of harmful gas can be greatly reduced; the skeleton contains a carbon layer difficult to burn, which can prevent the contact of oxygen with the matrix; the synergistic effect of various flame-retardant elements in the flame-retardant aspect can make it have better flame-retardant effect, and the synergistic effect of N, Br elements and N-P bonds on the skeleton can greatly enhance the flame-retardant performance. The unique sheet structure of the nanosheet can fully contact with the PVC and PE matrix to form a crosslinked structure, and greatly improve the mechanical properties of the pipe material.

[0028] The application takes hexachlorotriphosphazene, 3-bromo-2,6-dimethylpyridine and 4-pyridine formaldehyde monomer as raw materials, constructs COF nanosheets with special ionization modification nanosheet structure by adjusting the polymerization temperature in the hydrothermal synthesis of COF, and prepares PE and PVC plastic pipes by taking the COF nanosheets as additives in different proportions. Compared with the PE and PVC pipes without the addition, the COF nanosheets are uniformly dispersed in the PE and PVC matrix, and due to the high strength and rigidity of the COF nanosheets and the strong interaction between the COF nanosheets and the polymer molecular chains, the COF nanosheets can effectively bear and transfer the stress when the pipe is subjected to tensile force, thereby significantly improving the tensile strength of the pipe, and the PE and PVC pipes are increased by 20% and 29% respectively. The COF nanosheets contain a carbon layer with flame retardant in the skeleton, which can prevent oxygen from contacting the base material; the synergistic effect of various flame-retardant elements can make the COF nanosheets have better flame-retardant effect, the synergistic effect of N, Br elements and N-P bonds on the skeleton of the COF nanosheets can greatly enhance the flame-retardant performance, and the cavity structure of the COF nanosheets can also absorb harmful gases; the flame-retardant rate of the PE and PVC pipes containing the COF nanosheets is increased by more than 70% and 25% compared with the pure pipes. Therefore, the COF nanosheet additive of the application can significantly improve the overall performance of the PE and PVC pipes. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a scanning electron microscope image of the ZR-COF nanosheets obtained in Example 1. 13 C is a solid nuclear magnetic spectrum.

[0030] Figure 2 is a scanning electron microscope image of the ZR-COF nanosheets obtained in Example 1. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the application more clear, the application is further described in detail below in combination with the drawings and examples. It should be understood that the specific implementation described herein is only used to explain the application, and is not used to limit the application.

[0032]

[0033] As shown in the above structural formula: the ZR-COF nanosheets are generated by high-temperature reaction of hexachlorotriphosphazene, 3-bromo-2,6-dimethylpyridine and 4-pyridine formaldehyde, and the ZR-COF nanosheets are taken as additives of PE and PVC pipes.

[0034] The obtained ZR-COF nanosheets are honeycomb-like topological structure polymers, and the whole molecule circulates in this structure, and the wavy line in the formula represents the -P-N- chemical bond connected next.

[0035] The application discloses a COF nanosheet additive with enhanced mechanical strength and flame retardation effect, which is applied to PE and PVC pipes. Embodiments 1-3 are applied to the preparation of reinforced PE pipes, and embodiments 4-6 are applied to the preparation of reinforced PVC pipes.

[0036] Embodiment 1:

[0037] The application discloses a method for preparing a flame-retardant pipe and application thereof, and has the characteristics that the method comprises the following steps:

[0038] Synthesis of ZR-COF: 9.5 g of hexachlorotriphosphazene and 15 g of 3-bromo-2,6-dimethylpyridine were added into a reaction tube, and then the tube was vacuumized and filled with nitrogen, and the operation was repeated three times. 1L of toluene was added into the tube under anhydrous and oxygen-free environment, 20.5 g of 4-pyridine formaldehyde was added dropwise into the solution after the substance was fully dissolved, and then the solution was subjected to rapid nucleation at 120 DEG C in a microwave reactor for 1.5 hours, and then the solution was transferred into a low-temperature reactor at 85 DEG C for 70 hours. After the reaction was completed, the reaction product was obtained by filtration, and then the reaction product was washed with a large amount of anhydrous methanol and dichloromethane in sequence, and then the reaction product was dried, ultrasonically separated in anhydrous methanol and dried again, and then a gray-green powder was obtained, which was ZR-COF nanosheet. The yield is about 88%.

[0039] The chemical structure of ZR-COF was further tested and analyzed by solid-state nuclear magnetic resonance (SSNMR), and the test result is shown in the following table. Figure 1 The SSNMR spectrum shows that the signal resonance peaks of 119.6, 129.4, 135.7 and 145.7 ppm correspond to carbon atoms on a benzene ring, the signal resonance peaks of 124.3, 143.3 and 148.0 ppm correspond to carbon atoms on a pyridine ring, and the signal resonance peak of 190.0 ppm does not appear at a carbon atom in a C=O bond, which indicates that the reaction is completely performed, and the appearance of the signal resonance peak of 155.5 ppm belonging to a carbon atom in a C=C bond further proves that ZR-COF is successfully prepared.

[0040] As shown in the scanning electron microscope (SEM) image of Figure 2 ZR-COF is a multi-layer stacked nanosheet structure, which indicates that ZR-COF is successfully synthesized as a nanosheet through high-temperature nucleation and low-temperature crystallization. The thickness of the multi-layer nanosheet can be roughly estimated to be about 15 nm from the gap of the multi-layer nanosheet shown in the picture.

[0041] Preparation of PE pipe: the ZR-COF, dibutyltin dilaurate, antioxidant 1010 and polyethylene were poured into a high-speed dispersion machine at a mass ratio of 2:0.01:0.01:15, and then the mixture was kneaded at a rotation speed of 600 r / min -1 and a room temperature for 10 min, and then the mixture was discharged to obtain a mixed material. The mixed material was discharged at a speed of 6 kg / h -1ZR-COF, dibutyltin dilaurate, antioxidant 1010, polyethylene were added into the twin-screw extruder at a speed of 2 r / min, the temperature of the six sections of the twin-screw was controlled, the first section was 110℃, the second section was 150℃, the third section was 160℃, the fourth section was 180℃, the fifth section was 200℃, the temperature of the die was 225℃, and the screw rotation speed was 130 r / min -1 After the pipe was extruded from the die, it was cooled to room temperature to obtain the pre-crosslinked polyethylene pipe.

[0042] The polyethylene was a powder material with a powder diameter of 45 µm.

[0043] Example 2:

[0044] The other steps were the same as in Example 1, and the mass ratio of ZR-COF, dibutyltin dilaurate, antioxidant 1010, and polyethylene was changed from 2:0.01:0.01:15 to 2:0.01:0.01:18.

[0045] The polyethylene was a powder material with a powder diameter of 45 µm.

[0046] Example 3:

[0047] The other steps were the same as in Example 1, and the mass ratio of ZR-COF, dibutyltin dilaurate, antioxidant 1010, and polyethylene was changed from 2:0.01:0.01:15 to 2:0.01:0.01:20.

[0048] The polyethylene was a powder material with a powder diameter of 45 µm.

[0049] Example 4:

[0050] The other steps were the same as in Example 1, and the mass ratio of ZR-COF, dibutyltin dilaurate, antioxidant 1010, and polyethylene was changed from 2:0.01:0.01:15 to 2:0.01:0.01:15.

[0051] The polyvinyl chloride was a powder material with a powder diameter of 20 µm.

[0052] Example 5:

[0053] The other steps were the same as in Example 1, and the mass ratio of ZR-COF, dibutyltin dilaurate, antioxidant 1010, and polyethylene was changed from 2:0.01:0.01:15 to 2:0.01:0.01:18.

[0054] The polyvinyl chloride is a powder material, and the powder has a diameter of 20 µm.

[0055] Example 6:

[0056] The other steps are the same as those in Example 1, and the mass ratio of ZR-COF, dibutyltin dilaurate, antioxidant 1010 and polyethylene is changed to 2:0.01:0.01:20, instead of 2:0.01:0.01:15.

[0057] The polyvinyl chloride is a powder material, and the powder has a diameter of 20 µm.

[0058] Comparative Example 1:

[0059] Preparation of PE pipe: the dibutyltin dilaurate, antioxidant 1010 and polyethylene are poured into a high-speed disperser at a mass ratio of 0.01:0.01:15, and then kneaded at a speed of 600 r min -1 at room temperature for 10 min, and then discharged to obtain a mixture. The mixture is added into a double-screw extruder at a speed of 6 kg h -1 , and the double screw is controlled at six stages, i.e., the first stage is controlled at 110℃, the second stage is controlled at 150℃, the third stage is controlled at 160℃, the fourth stage is controlled at 180℃, the fifth stage is controlled at 200℃, the temperature of the die is controlled at 225℃, and the screw rotation speed is controlled at 130 r min -1 . After the pipe is extruded from the die, it is cooled to room temperature to obtain a pre-crosslinked polyethylene pipe.

[0060] The polyethylene is a powder material, and the powder has a diameter of 45 µm.

[0061] Comparative Example 2:

[0062] The other steps are the same as those in Comparative Example 1, and the mass ratio of dibutyltin dilaurate, antioxidant 1010 and polyethylene is changed to 1:0.01:0.01:15, instead of 0.01:0.01:15.

[0063] The polyvinyl chloride is a powder material, and the powder has a diameter of 20 µm.

[0064] In order to verify the properties of the materials obtained in Examples 1 to 6 and Comparative Examples 1 to 2, the following related characterization and performance test are carried out.

[0065] (1) 13C solid nuclear magnetic resonance

[0066] The prepared HUT4 is tested by using an Agilent 600 M nuclear magnetic resonance spectrometer of Agilent Company. Figure 1The 13C solid nuclear magnetic spectrum of ZR-COF is shown in Figure 1, which shows that ZR-COF is successfully synthesized.

[0067] (II) Scanning electron microscope

[0068] The prepared ZR-COF nanosheets were respectively subjected to scanning electron microscope test. Figure 2 It can be obviously observed that the two materials prepared by metal salt exfoliation exhibit nanosheet structure.

[0069] (III) Tensile strength

[0070] The tensile strength of the plastic pipe prepared in Examples 1-6 and Comparative Examples 1-2 was tested according to the method specified in GB / T1040.2-2006.

[0071] (IV) Flame retardant test

[0072] The limiting oxygen index (LOI) standard test vertical combustion (UL-94) of the plastic pipe prepared in Examples 1-6 and Comparative Examples 1-2 was determined according to the national standard GB / T2408-2008 "Determination of the combustion performance of plastics by horizontal and vertical methods", and the vertical combustion grade of the composite material was determined by using CZF-2 type vertical combustion tester of Nanjing Jiangning County Analytical Instrument Factory.

[0073]

[0074] Compared with the PE pipe without ZR-COF nanosheet doping, the tensile strength of the PE pipe can be effectively improved after adding the nanosheet prepared in the application, and the tensile strength can be improved with the increase of the addition amount at low content, and the tensile strength can be reduced with the increase of the concentration at high addition amount. But with the increase of the amount, the flame retardant performance will be greatly improved.

[0075]

[0076] Compared with the PE pipe without ZR-COF nanosheet doping, the tensile strength of the PE pipe can be effectively improved after adding the nanosheet prepared in the application, and the tensile strength can be improved with the increase of the addition amount at low content, and the tensile strength can be reduced with the increase of the concentration at high addition amount. But with the increase of the amount, the flame retardant performance will be greatly improved.

[0077] The above only describes several preferred embodiments of the present application, but the present application is not limited to the above several specific embodiments. The above specific embodiments are illustrative and not restrictive, and researchers in the field can make improvements and refinements under the inspiration of the present application, while complying with the spirit and principles of the present application, which are all within the protection scope of the present application.

[0078] The remaining matters of the present application are known technologies.

Claims

1. A COF nanosheet for enhancing the flame retardant properties of PVC, PE pipes, characterized by, The COF nanosheet is the following compound: ； The thickness of the nanosheet is 2-20 nm; The preparation method of the COF nanosheet for enhancing the flame retardant performance of PVC and PE pipes comprises the following steps: In the reaction tube, add hexachlorotriphosphazene and 3-bromo-2,6-dimethylpyridine, then add toluene into the tube under anhydrous and anaerobic environment, after dissolution, drop 4-pyridine formaldehyde into the solution, and react at high temperature for 1-2 h, and then react at low temperature for 65-75 h; then filter, wash, dry, put into anhydrous methanol for ultrasonic, and dry to obtain ZR-COF nanosheet; 8-12 g of hexachlorotriphosphazene, 10-20 g of 3-bromo-2,6-dimethylpyridine, and 15-25 g of 4-pyridine formaldehyde are dissolved in 1 liter of toluene; The high temperature section is 110-130 DEG C in the microwave reactor, or 180-220 DEG C in the conventional reactor; The low temperature section is 80-90 DEG C in the microwave reactor, or 130-180 DEG C in the conventional reactor; The anhydrous and anaerobic environment is a nitrogen atmosphere; the ultrasonic time in anhydrous methanol is 10-60 min; The COF nanosheet for enhancing the flame retardant performance of PVC and PE pipes is used as a flame retardant additive in pipes; comprising the following steps: The ZR-COF nanosheet, antioxidant 1010, heat stabilizer and the base material are poured into a high-speed dispersion machine, mixed at a rotation speed of 500-2000 r / min -1 , and discharged after mixing at room temperature for 5-15 min to obtain a mixture; the mixture is added into a double-screw extruder at a speed of 5-12 kg / h -1 , and the PE pipe or PVC pipe is obtained after being extruded through a die head and cooled to room temperature. The mass ratio of ZR-COF nanosheet: antioxidant: heat stabilizer 1010: base material is 1-5: 0.01-0.05: 0.01-0.05: 15-20; The antioxidant 1010 is (tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid] pentaerythritol ester); the heat stabilizer is dibutyltin dilaurate; The base material is polyethylene resin or polyvinyl chloride resin.

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