A flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs and preparation method thereof

Abstract

The invention discloses a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs and a preparation method thereof, the method comprising the following steps: S1, preparing a hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs: S1‑1, preparing graphene oxide GO; S1‑2, preparing reduced graphene oxide r‑GO; S1‑3, preparing a hydrotalcite-based filler by a one-pot method; S2, loading a flame retardant on a hydrotalcite-based filler by an impregnation method to obtain a flame retardant modified filler; S3, coating a polymer on the flame retardant modified filler to obtain a composite modified filler; S4, mixing the composite modified filler, a stabilizer, a plasticizer with PVC to obtain a flame retardant modified PVC composite material. The PVC composite material provided by the present invention has excellent mechanical strength and thermal stability, and has both excellent flame retardancy and smoke suppression effects.

Description

Technical Field

[0001] The invention relates to the field of PVC materials, and in particular to a flame-retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs and a preparation method thereof. Background Art

[0002] PVC (polyvinyl chloride) is a polymer formed by the polymerization of vinyl chloride monomers in the presence of initiators such as peroxides and azo compounds or under the action of light or heat according to the free radical polymerization mechanism; with the rapid development of the polymer industry, it has been used in all walks of life in human society, such as in aerospace, transportation, electronics, building materials and automobiles. However, PVC materials also have the following defects during application:

[0003] First, there are unstable structures (such as tertiary carbon atoms, allyl chloride, etc.) and residual free radicals in the PVC molecular chain. During the processing, when it is subjected to heat and shear force, it is easy to degrade and age, and remove small molecular hydrogen chloride (HCl). The generated HCl will further catalyze the degradation of the carbon chain. Therefore, improving the thermal stability of PVC is very important for extending the service life of the product and broadening its application.

[0004] Secondly, PVC is not a completely safe fireproof material. When burning, PVC produces a large amount of black smoke and toxic gases such as hydrogen chloride. Adding flame retardants is a common means to solve the flammability problem of PVC. For example, patent CN118388902B discloses a highly flame-retardant and heat-stable modified polyvinyl chloride material and its preparation method, patent CN117777615B discloses a high-temperature flame-retardant PVC material and its preparation method, and patent CN118344686B discloses a PVC material containing a flame retardant plasticizer and its preparation method. However, common flame retardants are difficult to disperse in polymers and have poor compatibility with polymers, resulting in reduced flame retardant efficiency; when the amount of flame retardant added is large, the mechanical properties of polymer composites will be significantly reduced; in addition, some flame retardants are prone to migration sites in organic systems, causing the flame retardants to gradually fail.

[0005] Therefore, it is necessary to improve the existing technology to provide a more reliable solution. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs and a preparation method thereof in view of the deficiencies in the above-mentioned prior art.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: in the first aspect of the present invention, a method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs is provided, comprising the following steps:

[0008] S1. Preparation of hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs:

[0009] S1-1, preparing graphene oxide GO;

[0010] S1-2, preparing reduced graphene oxide r-GO;

[0011] S1-3, one-pot preparation of hydrotalcite-based filler r-GO@-La-SiO2-LDHs:

[0012] S2, loading a flame retardant on a hydrotalcite-based filler by an impregnation method to obtain a flame retardant modified filler;

[0013] S3, coating the flame retardant modified filler with a polymer to obtain a composite modified filler;

[0014] S4, mixing the composite modified filler, stabilizer, plasticizer and PVC to obtain a flame retardant modified PVC composite material.

[0015] Preferably, step S1-1 is specifically:

[0016] Graphite and sodium nitrate are added to concentrated sulfuric acid with a concentration of 95-98wt%, and the reaction is stirred under ice bath conditions. Then KMnO4 is added, stirred at 10-20°C, the temperature is raised to 30-40°C, and the reaction is continued by stirring. Deionized water is added to the product, the temperature is raised to 90-100°C and maintained for 10-30 minutes, and deionized water and H2O2 solution are added in sequence. The product is allowed to stand, and the supernatant is removed after the system is separated. The product is washed with deionized water until it is neutral, and dried to obtain graphene oxide GO.

[0017] Preferably, step S1-2 is specifically:

[0018] S1-2-1. Add NaOH and Na2CO3 into deionized water and stir until completely dissolved to prepare an alkaline solution with a NaOH concentration of 0.5-2 mol / L and a Na2CO3 concentration of 0.25-1 mol / L;

[0019] S1-2-2. Take graphene oxide and add it to deionized water, disperse it by ultrasonic, then add alkaline solution dropwise until the pH of the system is 9-10.5. After the addition is complete, react under heating and centrifuge. Wash the solid product with deionized water until it is neutral, vacuum dry to constant weight, and grind to obtain reduced graphene oxide r-GO.

[0020] Preferably, step S1-3 is specifically:

[0021] S1-3-1, taking nano-mesoporous silica, reduced graphene oxide r-GO, and La(NO3)3, adding them to deionized water, and ultrasonically dispersing them to obtain dispersion 1;

[0022] S1-3-2, add Mg(NO3)2·6H2O, Al(NO3)2·9H2O and sodium citrate to deionized water, and perform sonication to obtain dispersion 2;

[0023] S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10±0.5 with alkaline solution, perform ultrasonic dispersion, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react under heating, filter after the reaction, wash the solid product with deionized water until it is neutral, vacuum dry, and grind to obtain a modified hydrotalcite filler: r-GO@-La-SiO2-LDHs.

[0024] Preferably, step S1 specifically comprises:

[0025] S1-1. Preparation of graphene oxide:

[0026] 10-40g of graphite and 5-20g of sodium nitrate are added to 200-1000mL of concentrated sulfuric acid with a concentration of 95-98wt%, and stirred for reaction for 5-30min under ice bath conditions, then 30-130g of KMnO4 is added, and the mixture is stirred for 20-60min at 10-20°C, and the mixture is heated to 30-40°C, and the mixture is stirred for reaction for 5-20h. 400-1600mL of deionized water is added to the product, and the mixture is heated to 90-100°C and maintained for 10-30min, and then 400-1500mL of deionized water and 5-20mL of H2O2 solution with a concentration of 20-25wt% are added in sequence, and the mixture is allowed to stand for 30-90min. After the system is separated into layers, the supernatant is removed, and the obtained product is washed with deionized water until neutralized, and dried at 60-80°C for 12-48h to obtain graphene oxide GO.

[0027] S1-2. Preparation of reduced graphene oxide r-GO:

[0028] S1-2-1. Add NaOH and Na2CO3 into deionized water and stir until completely dissolved to prepare an alkaline solution with a NaOH concentration of 0.5-2 mol / L and a Na2CO3 concentration of 0.25-1 mol / L;

[0029] S1-2-2, take 0.5-2g of graphene oxide and add it to 25-100mL of deionized water, ultrasonically disperse it for 5-30min, then add alkaline solution dropwise until the pH of the system is 9-10.5, react at 60-70°C for 10-40h after the addition is complete, centrifuge, wash the solid product with deionized water until it is neutral, vacuum dry it at 60-80°C to constant weight, grind it, and obtain reduced graphene oxide r-GO;

[0030] S1-3. One-pot preparation of modified hydrotalcite filler: r-GO@-La-SiO2-LDHs:

[0031] S1-3-1, take 0.5-2g of nano-mesoporous silica, 1-4g of r-GO, 0.172-0.686g of La(NO3)3, add them to 150-600mL of deionized water, and disperse them by ultrasonic for 15-60min to obtain dispersion 1;

[0032] S1-3-2, add 1.28-5.12 g of Mg(NO3)2·6H2O, 1.875-7.5 g of Al(NO3)2·9H2O, and 0.6-2.4 g of sodium citrate into 150-600 mL of deionized water, and ultrasonicate for 5-20 min to obtain dispersion 2;

[0033] S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10±0.5 with alkaline solution, ultrasonicate for 30-90 min, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 120-140°C for 8-24 h, filter after the reaction, wash the solid product with deionized water until neutral, vacuum dry at 60-90°C for 5-24 h, and grind to obtain the modified hydrotalcite filler: r-GO@-La-SiO2-LDHs.

[0034] Preferably, step S2 specifically comprises:

[0035] Take 0.5-2g of triphenyl phosphate and add it to 50-200mL of acetone, stir for 2-10min, then add 2.5-10g of modified hydrotalcite filler, shake on a shaker at 60-75°C for 6-24h, filter, wash with ethanol and deionized water in turn, and vacuum dry at 50-70°C for 4-12h to obtain a flame retardant modified filler.

[0036] Preferably, step S3 specifically comprises:

[0037] S3-1, adding flame retardant modified filler, fatty alcohol polyoxyethylene ether ammonium sulfate and ethanol into deionized water, stirring to obtain a mixed solution 1;

[0038] S3-2, adding acrylic acid, methacrylic acid, methyl methacrylate and butyl acrylate into a mixed solution of deionized water and ethanol, stirring to obtain a mixed solution 2;

[0039] S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring, then add potassium persulfate, and then heat to 65-70°C and react for 0.5-2h;

[0040] S3-4, add the remaining mixed solution 2 dropwise to the product of step 1 under stirring, add potassium persulfate after the addition is completed, raise the temperature to 72-78°C, react for 1.5-5h, and obtain a composite modified filler.

[0041] Preferably, step S3 specifically comprises:

[0042] S3-1, add 2.5-10g of flame retardant modified filler, 1-4g of fatty alcohol polyoxyethylene ether ammonium sulfate, and 75-300mL of ethanol into 150-500mL of deionized water, and stir at 500-2000rpm for 15-60min to obtain a mixed solution 1;

[0043] S3-2, add 3.5-14 g of acrylic acid, 1.5-6 g of methacrylic acid, 2.5-10 g of methyl methacrylate, and 2.5-10 g of butyl acrylate into 50-200 mL of a mixed solution consisting of deionized water and ethanol in a volume ratio of 1:1, and stir for 5-20 min to obtain a mixed solution 2;

[0044] S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring for 5-30 minutes, add 0.05-0.2g of potassium persulfate, and then heat to 65-70°C and react for 0.5-2h;

[0045] S3-4, add the remaining mixed solution 2 drops to the product of step 1 under stirring, and complete the addition within 0.3-3 hours. Then add 0.075-0.3g potassium persulfate, raise the temperature to 72-78°C, and react for 1.5-5 hours to obtain a composite modified filler.

[0046] Preferably, the stabilizer is a mixture of zinc stearate and calcium stearate, and the plasticizer is dioctyl phthalate;

[0047] Step S4 is specifically as follows:

[0048] Weigh 100 g of PVC powder, 0.5-2 g of zinc stearate, 0.6-3.6 g of calcium stearate, 1-4 g of dioctyl phthalate, and 9-36 g of a composite modified filler, add them into a mixer, stir and mix for 5-20 min, add the resulting mixture into an open mill, mix at 160-185° C. for 5-30 min, and obtain a flame retardant modified PVC composite material.

[0049] The second aspect of the present invention provides a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, characterized in that it is prepared by the method as described above.

[0050] The beneficial effects of the present invention are:

[0051] The PVC composite material provided by the present invention has excellent mechanical strength and thermal stability, and has excellent flame retardant performance and smoke suppression effect. The present invention uses a composite modified filler prepared based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs to modify PVC, which can significantly improve the comprehensive performance of the PVC material.

[0052] The present invention can further improve the flame retardant properties, mechanical strength and stability of PVC by compounding LDHs with rGO, and then can greatly improve the compatibility with the PVC organic system through the coating effect of the polyacrylate organic film, and achieve uniform dispersion; at the same time, the polyacrylate itself can play a role in toughening, improving processing performance and impact resistance of PVC. In the present invention, nano-mesoporous silica can play a role in strengthening and toughening on the one hand, and can load the flame retardant through its mesoporous structure on the other hand, which can play a slow release effect, and combined with the coating effect of the polyacrylate organic film, the flame retardant can be evenly dispersed in the PVC system while reducing its direct contact with the PVC organic system, and will not deteriorate the mechanical strength of the PVC system; the flame retardant can be slowly released into the system, and the release amount is small during normal use, and when a fire occurs, the release amount will rise rapidly, and the temperature rises to soften and rupture the polyacrylate organic film on the surface of the nano-mesoporous silica, and gradually melt, so that the flame retardant triphenyl phosphate in the mesopore is quickly released to play its flame retardant effect. In the present invention, the rare earth La plays the role of intermediate bridge in the preparation of r-GO@-La-SiO2-LDHs. On the other hand, La has many 4f and 5d empty orbitals, which can be used as a central ion to form a coordination bond with the unstable chlorine atom on the PVC main chain, so that the carbon-chlorine bond is in a stable state that is not easy to break, slowing down the thermal degradation of PVC, thereby improving the thermal stability of PVC. In the composite modified filler structure system of the present invention, the components play a role of mutual cooperation and synergistic enhancement in improving the mechanical properties, flame retardant properties and thermal stability of PVC. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The sustained release performance test results of the modified filler and the composite modified filler prepared in Example 1;

[0054] Figure 2 The tensile strength test results of the PVC composite materials prepared in Examples 1-3 and Comparative Examples 1-3;

[0055] Figure 3 The bending strength test results of the PVC composite materials prepared in Examples 1-3 and Comparative Examples 1-3;

[0056] Figure 4 The limiting oxygen index test results of the PVC composite materials prepared in Examples 1-3 and Comparative Examples 1-3;

[0057] Figure 5 The smoke density test results of the PVC composite materials prepared in Examples 1-3 and Comparative Examples 1-3;

[0058] Figure 6 These are the test results of heat deformation temperature of PVC composite materials prepared in Examples 1-3 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0059] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0060] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0061] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0062] The present invention provides a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, and the preparation method thereof comprises the following steps:

[0063] S1. Preparation of hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs:

[0064] S1-1. Preparation of graphene oxide:

[0065] 10-40g of graphite and 5-20g of sodium nitrate are added to 200-1000mL of concentrated sulfuric acid with a concentration of 95-98wt%, and stirred for reaction for 5-30min under ice bath conditions, then 30-130g of KMnO4 is added, and the mixture is stirred for 20-60min at 10-20°C, and the mixture is heated to 30-40°C, and the mixture is stirred for reaction for 5-20h. 400-1600mL of deionized water is added to the product, and the mixture is heated to 90-100°C and maintained for 10-30min, and then 400-1500mL of deionized water and 5-20mL of H2O2 solution with a concentration of 20-25wt% are added in sequence, and the mixture is allowed to stand for 30-90min. After the system is separated into layers, the supernatant is removed, and the obtained product is washed with deionized water until neutralized, and dried at 60-80°C for 12-48h to obtain graphene oxide GO.

[0066] S1-2. Preparation of reduced graphene oxide r-GO:

[0067] S1-2-1. Add NaOH and Na2CO3 into deionized water and stir until completely dissolved to prepare an alkaline solution with a NaOH concentration of 0.5-2 mol / L and a Na2CO3 concentration of 0.25-1 mol / L;

[0068] S1-2-2, take 0.5-2g of graphene oxide and add it to 25-100mL of deionized water, ultrasonically disperse it for 5-30min, then add alkaline solution dropwise until the pH of the system is 9-10.5, react at 60-70°C for 10-40h after the addition is complete, centrifuge, wash the solid product with deionized water until it is neutral, vacuum dry it at 60-80°C to constant weight, grind it, and obtain reduced graphene oxide r-GO;

[0069] S1-3. One-pot preparation of modified hydrotalcite filler: r-GO@-La-SiO2-LDHs:

[0070] S1-3-1, take 0.5-2g of nano-mesoporous silica, 1-4g of r-GO, 0.172-0.686g of La(NO3)3, add them to 150-600mL of deionized water, and disperse them by ultrasonic for 15-60min to obtain dispersion 1;

[0071] S1-3-2, add 1.28-5.12 g of Mg(NO3)2·6H2O, 1.875-7.5 g of Al(NO3)2·9H2O, and 0.6-2.4 g of sodium citrate into 150-600 mL of deionized water, and ultrasonicate for 5-20 min to obtain dispersion 2;

[0072] S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10±0.5 with alkaline solution, ultrasonicate for 30-90 min, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 120-140°C for 8-24 h, filter after the reaction, wash the solid product with deionized water until neutral, vacuum dry at 60-90°C for 5-24 h, and grind to obtain the modified hydrotalcite filler: r-GO@-La-SiO2-LDHs.

[0073] S2. Loading a flame retardant on a hydrotalcite-based filler by an impregnation method to obtain a flame retardant modified filler:

[0074] Take 0.5-2g of triphenyl phosphate and add it to 50-200mL of acetone, stir for 2-10min, then add 2.5-10g of modified hydrotalcite filler, shake on a shaker at 60-75°C for 6-24h, filter, wash with ethanol and deionized water in turn, and vacuum dry at 50-70°C for 4-12h to obtain a flame retardant modified filler.

[0075] S3, coating the flame retardant modified filler with a polymer to obtain a composite modified filler:

[0076] S3-1, add 2.5-10g of flame retardant modified filler, 1-4g of fatty alcohol polyoxyethylene ether ammonium sulfate, and 75-300mL of ethanol into 150-500mL of deionized water, and stir at 500-2000rpm for 15-60min to obtain a mixed solution 1;

[0077] S3-2, add 3.5-14 g of acrylic acid, 1.5-6 g of methacrylic acid, 2.5-10 g of methyl methacrylate, and 2.5-10 g of butyl acrylate into 50-200 mL of a mixed solution consisting of deionized water and ethanol in a volume ratio of 1:1, and stir for 5-20 min to obtain a mixed solution 2;

[0078] S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring for 5-30 minutes, add 0.05-0.2g of potassium persulfate, and then heat to 65-70°C and react for 0.5-2h;

[0079] S3-4, add the remaining mixed solution 2 drops to the product of step 1 under stirring, and complete the addition within 0.3-3 hours. Then add 0.075-0.3g potassium persulfate, raise the temperature to 72-78°C, and react for 1.5-5 hours to obtain a composite modified filler.

[0080] S4. Preparation of flame retardant modified PVC composite material:

[0081] Weigh 100g PVC (polyvinyl chloride) powder, 0.5-2g zinc stearate, 0.6-3.6g calcium stearate, 1-4g dioctyl phthalate, and 9-36g composite modified filler, add them into a mixer, stir and mix for 5-20min, add the obtained mixture into an open mill, mix at 160-185°C for 5-30min, and obtain a flame retardant modified PVC composite material.

[0082] Among them, the stabilizer is a mixture of zinc stearate and calcium stearate, and the plasticizer is dioctyl phthalate.

[0083] The nano-mesoporous silica is a homemade or commercially available product. In a preferred embodiment, a product with a particle size of 50-500 nm is used.

[0084] The present invention uses a composite modified filler prepared based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs to modify PVC, which can significantly improve the flame retardant and mechanical properties of the PVC material. The main mechanism is described below in conjunction with a specific preparation method to facilitate understanding of the present invention.

[0085] In the present invention, graphene oxide GO is firstly synthesized by using the improved Hummers method, and then r-GO is prepared by reducing GO by strong alkali, which is conducive to the interlacing of polyvinyl chloride molecular chains between graphite sheets;

[0086] Then, a one-pot method was used to prepare r-GO-coated, nano-mesoporous silica and rare earth lanthanum-doped modified hydrotalcite filler: r-GO@-La-SiO2-LDHs. In this process, La 3+ On the one hand, it is added into the magnesium-aluminum hydrotalcite system, and on the other hand, La 3+ It can coordinate with the silanol groups on the surface of nano-mesoporous silica and the hydroxyl groups on the surface of r-GO, thus playing the role of an intermediate bridge, so that nano-mesoporous silica is grafted onto the surface of r-GO, thus forming a composite structure system of r-GO coated LDHs, La doped in LDHs, and nano-mesoporous silica grafted on r-GO;

[0087] Then, the flame retardant triphenyl phosphate is loaded by the pore structure of nano-mesoporous silica through an impregnation method to obtain a flame retardant modified filler;

[0088] Finally, acrylic acid, methacrylic acid, methyl methacrylate and butyl acrylate are used as mixed monomers to polymerize on the surface of the flame retardant modified filler to form an organic coating layer of polyacrylate to obtain a composite modified filler.

[0089] Magnesium aluminum hydrotalcite LDHs have a special layered structure and chemical composition, which makes them a non-toxic, cheap and efficient PVC thermal stabilizer. The unique layered structure and porous structure of hydrotalcite can effectively absorb HCl produced by the thermal decomposition of PVC, thereby improving the thermal stability of PVC (Liu Zhaonian, Wang Zhen, Gu Zhaohui, et al. Progress in hydrotalcite and its application in polyvinyl chloride [J]. Plastics, 2021(005):050.). On the other hand, LDHs also have excellent flame retardant and smoke suppression properties. The flame retardant mechanism of LDHs can be attributed to the combination of the following three functions: heat absorption, gas dilution and carbonization (Qiao Peng. Preparation of rare earth hydrotalcite / graphene oxide hybrid materials and research on flame retardant TPU [D]. Qingdao University of Science and Technology, 2020.).

[0090] Reduced Graphene Oxide (rGO) is a material that reduces graphene oxide (GO) to graphene through a reduction reaction. GO is a graphene derivative with oxygen-containing functional groups and is chemically active. The rGO obtained after reduction has fewer oxidized functional groups, increased reduction degree, and more stable chemical properties than GO. rGO has excellent mechanical strength, thermal conductivity and thermal conductivity, can improve the mechanical properties of PVC, and can play a role in carbonization and physical barrier in the system, thereby improving flame retardancy.

[0091] However, magnesium aluminum hydrotalcite and reduced graphene oxide both have the defects of agglomeration and difficulty in uniform dispersion in organic systems when used in PVC organic materials. In addition, in order to further improve the flame retardant properties of PVC, the traditional solution usually adopts the method of adding additional flame retardants, but this method has the following steps: flame retardants are difficult to disperse in polymers and have poor compatibility with polymers, resulting in reduced flame retardant efficiency; when the amount of flame retardant added is large, it will significantly reduce the mechanical properties of polymer composites; in addition, some flame retardants are prone to migration in organic systems, causing the flame retardants to gradually become ineffective.

[0092] The present invention can overcome the above-mentioned defects by constructing a special composite modified filler structure system: (1) By compounding LDHs with rGO, the flame retardant properties, mechanical strength and stability of PVC can be further improved, and then the coating effect of the polyacrylate organic film can greatly improve the compatibility with the PVC organic system and achieve uniform dispersion; at the same time, the polyacrylate itself can play a role in toughening PVC, improving processing performance and impact resistance. (2) On the one hand, nano-mesoporous silica can play a reinforcing and toughening role. On the other hand, it can load flame retardants through its mesoporous structure, which can have a slow-release effect. Combined with the coating effect of the polyacrylate organic film, the flame retardant can be evenly dispersed in the PVC system while reducing its direct contact with the PVC organic system, and will not deteriorate the mechanical strength of the PVC system. The flame retardant therein can be slowly released into the system, and the release amount is small during normal use. However, when a fire occurs, the release amount will increase rapidly. The temperature rise causes the polyacrylate organic film on the surface of the nano-mesoporous silica to soften and rupture, and gradually melt, so that the flame retardant triphenyl phosphate in the mesopores is quickly released to exert its flame retardant effect. (3) The rare earth La plays an intermediate bridging role in the preparation of modified hydrotalcite filler: r-GO@-La-SiO2-LDHs. On the other hand, La has many 4f and 5d empty orbitals, which can be used as a central ion to form a coordination bond with the unstable chlorine atoms on the PVC main chain, making the carbon-chlorine bond stable and not easy to break, slowing down the thermal degradation of PVC, thereby improving the thermal stability of PVC. Therefore, in the composite modified filler structure system of the present invention, the components play a role of mutual cooperation and synergistic enhancement in improving the mechanical properties, flame retardant properties and thermal stability of PVC.

[0093] The above is the overall concept of the present invention, and detailed embodiments and comparative examples are provided below on the basis of the overall concept of the present invention to further illustrate the present invention.

[0094] The sources of some of the raw materials involved in the following examples and comparative examples are as follows:

[0095] PVC powder, brand: German vinnolit, purchased from Shanghai Honglei Plastic Chemical Co., Ltd.;

[0096] Triphenyl phosphate, Shandong Jibei New Materials Co., Ltd.;

[0097] Dioctyl phthalate, Shandong Jibei New Materials Co., Ltd.;

[0098] Fatty alcohol polyoxyethylene ether ammonium sulfate, Jiangsu Runfeng Synthetic Technology Co., Ltd.;

[0099] Nano-mesoporous silica, particle size 200-300 nm, Jiangsu Xianfeng Nanomaterial Technology Co., Ltd., catalog number: 104014;

[0100] Example 1

[0101] A flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, and a preparation method thereof comprises the following steps:

[0102] S1. Preparation of hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs:

[0103] S1-1. Preparation of graphene oxide:

[0104] 20g of graphite and 10g of sodium nitrate were added to 450mL of 98wt% concentrated sulfuric acid, stirred for 15min under ice bath conditions, then 65g of KMnO4 was added, stirred at 20°C for 40min, heated to 35°C, and continued to stir for 10h, 800mL of deionized water was added to the product, the temperature was raised to 98°C and maintained for 20min, and then 800mL of deionized water and 10mL of 25wt% H2O2 solution were added in sequence, and the mixture was allowed to stand for 60min. After the system was separated into layers, the supernatant was removed, and the product was washed with deionized water until neutral, and dried at 65°C for 24h to obtain graphene oxide GO.

[0105] S1-2. Preparation of reduced graphene oxide r-GO:

[0106] S1-2-1. Add NaOH and Na2CO3 into deionized water and stir until completely dissolved to prepare an alkaline solution with a concentration of 1 mol / L NaOH and a concentration of 0.5 mol / L Na2CO3;

[0107] S1-2-2. Take 1 g of graphene oxide and add it to 50 mL of deionized water. Ultrasonic dispersion is performed for 15 minutes. Then, alkaline solution is added dropwise until the pH of the system is 10. After the addition is completed, the reaction is carried out at 65°C for 20 hours. Centrifugation is performed, and the solid product is washed with deionized water until it is neutral. It is vacuum dried at 70°C to constant weight and ground to obtain reduced graphene oxide r-GO.

[0108] S1-3, one-pot preparation of hydrotalcite-based filler r-GO@-La-SiO2-LDHs:

[0109] S1-3-1. Take 1g of nano-mesoporous silica, 2g of r-GO, and 0.343g of La(NO3)3, add them into 300mL of deionized water, and disperse them by ultrasonic for 30min to obtain dispersion 1.

[0110] S1-3-2, add 2.56 g of Mg(NO3)2·6H2O, 3.75 g of Al(NO3)2·9H2O, and 1.2 g of sodium citrate into 300 mL of deionized water, and ultrasonicate for 10 min to obtain dispersion 2;

[0111] S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10 with an alkaline solution (the same as in step S1-2), ultrasonicate for 45 minutes, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 135°C for 12 hours, filter after the reaction, wash the solid product with deionized water until it is neutral, vacuum dry at 70°C for 10 hours, and grind to obtain a modified hydrotalcite filler: r-GO@-La-SiO2-LDHs.

[0112] S2, impregnation method loading flame retardant to obtain flame retardant modified filler:

[0113] Take 1 g of triphenyl phosphate and add it to 100 mL of acetone, stir for 5 min, then add 5 g of modified hydrotalcite filler, shake on a shaker at 70 ° C for 12 h, filter, wash with ethanol and deionized water in turn, and vacuum dry at 60 ° C for 8 h to obtain a flame retardant modified filler.

[0114] S3, coating the flame retardant modified filler with a polymer to obtain a composite modified filler:

[0115] S3-1, add 5 g of flame retardant modified filler, 2 g of fatty alcohol polyoxyethylene ether ammonium sulfate, and 150 mL of ethanol into 250 mL of deionized water, and stir at 1000 rpm for 30 min to obtain a mixed solution 1;

[0116] S3-2, add 7 g of acrylic acid, 3 g of methacrylic acid, 5 g of methyl methacrylate, and 5 g of butyl acrylate into 100 mL of a mixed solution consisting of deionized water and ethanol in a volume ratio of 1:1, and stir for 10 min to obtain a mixed solution 2;

[0117] S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring for 15 minutes, add 0.1g of potassium persulfate, and then heat to 68°C and react for 1 hour;

[0118] S3-4, add the remaining mixed solution 2 drops to the product of step 1 under stirring, and complete the dropwise addition within 1.5 hours. Then add 0.15 g of potassium persulfate, raise the temperature to 75° C., and react for 3 hours to obtain a composite modified filler.

[0119] S4. Preparation of flame retardant modified PVC composite material:

[0120] 100 g of PVC powder, 1 g of zinc stearate, 1.8 g of calcium stearate, 2 g of dioctyl phthalate and 18 g of a composite modified filler were weighed and added into a mixer and stirred for 10 min. The resulting mixture was added into an open mill and mixed at 170° C. for 15 min to obtain a flame-retardant modified PVC composite material.

[0121] Example 2

[0122] A flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, and a preparation method thereof comprises the following steps:

[0123] S1. Preparation of hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs:

[0124] S1-1. Preparation of graphene oxide:

[0125] 20g of graphite and 10g of sodium nitrate were added to 450mL of 98wt% concentrated sulfuric acid, stirred for 15min under ice bath conditions, then 65g of KMnO4 was added, stirred at 20°C for 40min, heated to 35°C, and continued to stir for 10h, 800mL of deionized water was added to the product, the temperature was raised to 98°C and maintained for 20min, and then 800mL of deionized water and 10mL of 25wt% H2O2 solution were added in sequence, and the mixture was allowed to stand for 60min. After the system was separated into layers, the supernatant was removed, and the product was washed with deionized water until neutral, and dried at 65°C for 24h to obtain graphene oxide GO.

[0126] S1-2. Preparation of reduced graphene oxide r-GO:

[0127] S1-2-1. Add NaOH and Na2CO3 into deionized water and stir until completely dissolved to prepare an alkaline solution with a concentration of 1 mol / L NaOH and a concentration of 0.5 mol / L Na2CO3;

[0128] S1-2-2. Take 1 g of graphene oxide and add it to 50 mL of deionized water. Ultrasonic dispersion is performed for 15 minutes. Then, alkaline solution is added dropwise until the pH of the system is 10. After the addition is completed, the reaction is carried out at 65°C for 20 hours. Centrifugation is performed, and the solid product is washed with deionized water until it is neutral. It is vacuum dried at 70°C to constant weight and ground to obtain reduced graphene oxide r-GO.

[0129] S1-3, one-pot preparation of hydrotalcite-based filler r-GO@-La-SiO2-LDHs:

[0130] S1-3-1, take 1.2g nano-mesoporous silica, 1.8g r-GO, 0.343g La(NO3)3, add to 300mL deionized water, ultrasonically disperse for 30min, and obtain dispersion 1;

[0131] S1-3-2, add 2.56 g of Mg(NO3)2·6H2O, 3.75 g of Al(NO3)2·9H2O, and 1.2 g of sodium citrate into 300 mL of deionized water, and ultrasonicate for 10 min to obtain dispersion 2;

[0132] S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10 with alkaline solution, ultrasonicate for 45 minutes, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 135°C for 12 hours, filter after the reaction, wash the solid product with deionized water until it is neutral, vacuum dry at 70°C for 10 hours, and grind to obtain the modified hydrotalcite filler: r-GO@-La-SiO2-LDHs.

[0133] S2, impregnation method loading flame retardant to obtain flame retardant modified filler:

[0134] Take 1 g of triphenyl phosphate and add it to 100 mL of acetone, stir for 5 min, then add 5 g of modified hydrotalcite filler, shake on a shaker at 60 ° C for 14 h, filter, wash with ethanol and deionized water in turn, and vacuum dry at 60 ° C for 8 h to obtain a flame retardant modified filler.

[0135] S3, coating the flame retardant modified filler with a polymer to obtain a composite modified filler:

[0136] S3-1, add 5 g of flame retardant modified filler, 2 g of fatty alcohol polyoxyethylene ether ammonium sulfate, and 150 mL of ethanol into 250 mL of deionized water, and stir at 1000 rpm for 30 min to obtain a mixed solution 1;

[0137] S3-2, add 7 g of acrylic acid, 3 g of methacrylic acid, 5 g of methyl methacrylate, and 5 g of butyl acrylate into 100 mL of a mixed solution consisting of deionized water and ethanol in a volume ratio of 1:1, and stir for 10 min to obtain a mixed solution 2;

[0138] S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring for 15 minutes, add 0.1g of potassium persulfate, and then heat to 68°C and react for 1 hour;

[0139] S3-4, add the remaining mixed solution 2 drops to the product of step 1 under stirring, and complete the dropwise addition within 1.5 hours. Then add 0.15 g of potassium persulfate, raise the temperature to 75° C., and react for 3 hours to obtain a composite modified filler.

[0140] S4. Preparation of flame retardant modified PVC composite material:

[0141] 100 g of PVC powder, 1.2 g of zinc stearate, 1.6 g of calcium stearate, 2 g of dioctyl phthalate and 17 g of a composite modified filler were weighed and added to a mixer and stirred for 10 min. The resulting mixture was added to an open mill and mixed at 170° C. for 15 min to obtain a flame-retardant modified PVC composite material.

[0142] Example 3

[0143] A flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, and a preparation method thereof comprises the following steps:

[0144] S1. Preparation of hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs:

[0145] S1-1. Preparation of graphene oxide:

[0146] 20g of graphite and 10g of sodium nitrate were added to 450mL of 98wt% concentrated sulfuric acid, stirred for 15min under ice bath conditions, then 65g of KMnO4 was added, stirred at 20°C for 40min, heated to 35°C, and continued to stir for 10h, 800mL of deionized water was added to the product, the temperature was raised to 98°C and maintained for 20min, and then 800mL of deionized water and 10mL of 25wt% H2O2 solution were added in sequence, and the mixture was allowed to stand for 60min. After the system was separated into layers, the supernatant was removed, and the product was washed with deionized water until neutral, and dried at 65°C for 24h to obtain graphene oxide GO.

[0147] S1-2. Preparation of reduced graphene oxide r-GO:

[0148] S1-2-1. Add NaOH and Na2CO3 into deionized water and stir until completely dissolved to prepare an alkaline solution with a concentration of 1 mol / L NaOH and a concentration of 0.5 mol / L Na2CO3;

[0149] S1-2-2. Take 1 g of graphene oxide and add it to 50 mL of deionized water. Ultrasonic dispersion is performed for 15 minutes. Then, alkaline solution is added dropwise until the pH of the system is 10. After the addition is completed, the reaction is carried out at 65°C for 20 hours. Centrifugation is performed, and the solid product is washed with deionized water until it is neutral. It is vacuum dried at 70°C to constant weight and ground to obtain reduced graphene oxide r-GO.

[0150] S1-3, one-pot preparation of hydrotalcite-based filler r-GO@-La-SiO2-LDHs:

[0151] S1-3-1, take 0.8g nano-mesoporous silica, 2.2g r-GO, 0.343g La(NO3)3, add to 300mL deionized water, ultrasonically disperse for 30min, and obtain dispersion 1;

[0152] S1-3-2, add 2.56 g of Mg(NO3)2·6H2O, 3.75 g of Al(NO3)2·9H2O, and 1.4 g of sodium citrate into 300 mL of deionized water, and ultrasonicate for 10 min to obtain dispersion 2;

[0153] S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10 with alkaline solution, ultrasonicate for 45 minutes, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 135°C for 12 hours, filter after the reaction, wash the solid product with deionized water until it is neutral, vacuum dry at 70°C for 10 hours, and grind to obtain the modified hydrotalcite filler: r-GO@-La-SiO2-LDHs.

[0154] S2, impregnation method loading flame retardant to obtain flame retardant modified filler:

[0155] Take 1 g of triphenyl phosphate and add it to 100 mL of acetone, stir for 5 min, then add 5 g of modified hydrotalcite filler, shake on a shaker at 70 ° C for 12 h, filter, wash with ethanol and deionized water in turn, and vacuum dry at 60 ° C for 8 h to obtain a flame retardant modified filler.

[0156] S3, coating the flame retardant modified filler with a polymer to obtain a composite modified filler:

[0157] S3-1, add 4.5 g of flame retardant modified filler, 2 g of fatty alcohol polyoxyethylene ether ammonium sulfate, and 150 mL of ethanol into 250 mL of deionized water, and stir at 1000 rpm for 30 min to obtain a mixed solution 1;

[0158] S3-2, add 7 g of acrylic acid, 3 g of methacrylic acid, 5 g of methyl methacrylate, and 5 g of butyl acrylate into 100 mL of a mixed solution consisting of deionized water and ethanol in a volume ratio of 1:1, and stir for 10 min to obtain a mixed solution 2;

[0159] S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring for 15 minutes, add 0.1g of potassium persulfate, and then heat to 68°C and react for 1 hour;

[0160] S3-4, add the remaining mixed solution 2 drops to the product of step 1 under stirring, and complete the dropwise addition within 1.5 hours. Then add 0.15 g of potassium persulfate, raise the temperature to 75° C., and react for 3 hours to obtain a composite modified filler.

[0161] S4. Preparation of flame retardant modified PVC composite material:

[0162] 100 g of PVC powder, 1 g of zinc stearate, 1.8 g of calcium stearate, 2 g of dioctyl phthalate and 18.5 g of a composite modified filler were weighed and added into a mixer and stirred for 10 min. The resulting mixture was added into an open mill and mixed at 170° C. for 15 min to obtain a flame-retardant modified PVC composite material.

[0163] Comparative Example 1

[0164] The only difference between this example and Example 1 is that there is no step S2 in the preparation method of the hydrotalcite-based filler, that is, in step S3, the polymer is directly coated on the modified hydrotalcite filler to obtain a composite modified filler.

[0165] Comparative Example 2

[0166] The difference between this example and embodiment 1 is only step S1-3. In this example, step S1-3 is specifically as follows:

[0167] S1-3-21, add 2.56g of Mg(NO3)2·6H2O, 3.75g of Al(NO3)2·9H2O, and 1.2g of sodium citrate into 300mL of deionized water, and ultrasonicate for 10min to obtain a dispersion;

[0168] S1-3-3, add NaOH and Na2CO3 into deionized water, stir until completely dissolved, and prepare an alkaline solution with a concentration of NaOH of 1 mol / L and a concentration of Na2CO3 of 0.5 mol / L;

[0169] The pH value of the system was adjusted to 10 with alkaline solution, and ultrasonic treatment was performed for 45 minutes. The resulting mixture was transferred to a polytetrafluoroethylene-lined reactor and reacted at 135°C for 12 hours. After the reaction was completed, the solid product was filtered and washed with deionized water until neutral, and vacuum dried at 70°C for 10 hours. The modified hydrotalcite filler: r-GO@LDHs was obtained.

[0170] Comparative Example 3

[0171] The only difference between this example and Example 1 is that there is no step S3 in this example, that is, the flame retardant modified filler prepared in step S2 of the example is used as the composite modified filler to prepare the flame retardant modified PVC composite material.

[0172] 1. Test the sustained release performance of flame retardant modified fillers and composite modified fillers:

[0173] The modified filler and the composite modified filler prepared in Example 1 were tested for sustained release performance according to the following methods:

[0174] Take 5g of sample, wrap it in a filter bag and place it in a glass dish. Perform the following operations every 12 hours:

[0175] Add 20 mL of acetone and soak for 30 min, then rinse with acetone three times, take out, collect the rinse liquid and soaking liquid, combine them, measure the total volume of the liquid, and detect the concentration of triphenyl phosphate (detected by gas chromatography) therein to obtain the release amount;

[0176] The test was continued for 168 h, and the release curve was drawn with the cumulative value of the release percentage as the ordinate and the treatment time as the abscissa.

[0177] Release percentage cumulative value =, Q t represents the cumulative release amount within time t, and Q0 represents the total loading amount of triphenyl phosphate (the calculation method is: the total amount of triphenyl phosphate added in step S2 of Example 1-the amount of triphenyl phosphate remaining in the impregnation solution after impregnation).

[0178] Test results such as Figure 1 As shown, it can be seen that both the modified filler and the composite modified filler can achieve sustained release of triphenyl phosphate, and the release rate of the composite modified filler coated with the polyacrylate organic film is lower.

[0179] 2. The PVC composite materials prepared in the examples and comparative examples were hot pressed into samples of a certain thickness at 170°C ± 5°C on an electric tablet press (BP-8170-A, Dongguan Baopin Precision Instrument Co., Ltd.), and cut into specified sizes for the following tests:

[0180] (1) Tensile strength: Tested in accordance with standard GB / T1040.1-2018;

[0181] (2) Bending strength: Tested in accordance with GB / T 9341-2008;

[0182] (3) Limiting oxygen index (LOI): Tested in accordance with standard GB / T 2406-80;

[0183] (4) Smoke density test: Tested in accordance with standard GB / T 8627-2007;

[0184] (5) Heat deformation temperature test: Test in accordance with standard GB / T 1634.3-2004.

[0185] The test results are shown in Table 1 and Figure 2-6 As shown:

[0186] Table 1

[0187]

[0188] According to Table 1 and Figure 2-6 The test results show that the PVC composite materials prepared in Examples 1-3 have excellent mechanical strength and thermal stability, and have excellent flame retardant properties and smoke suppression effects. In Comparative Example 1, the nano-mesoporous silica is not loaded with flame retardant, so the flame retardant properties are reduced; in Comparative Example 2, no doped lanthanum and nano-mesoporous silica are added, and the flame retardant properties and thermal stability are significantly reduced; in Comparative Example 3, since the polyacrylate organic film is not coated, the dispersion of the flame retardant modified filler in the PVC system is affected, resulting in a reduction in the overall performance.

[0189] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, characterized in that: The following steps are involved: S1. Preparation of hydrotalcite-based filler based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs: S1-1, preparing graphene oxide GO; S1-2, preparing reduced graphene oxide r-GO; S1-3, one-pot preparation of hydrotalcite-based filler r-GO@-La-SiO2-LDHs; S2, loading a flame retardant on a hydrotalcite-based filler by an impregnation method to obtain a flame retardant modified filler; S3, coating the flame retardant modified filler with a polymer to obtain a composite modified filler; S4, mixing the composite modified filler, stabilizer, plasticizer and PVC to obtain a flame retardant modified PVC composite material; Step S1-3 is specifically as follows: S1-3-1, adding nano-mesoporous silica, reduced graphene oxide r-GO, and La(NO3)3 into deionized water, and performing ultrasonic dispersion to obtain dispersion 1; S1-3-2, add Mg(NO3)2·6H2O, Al(NO3)2·9H2O and sodium citrate to deionized water, and perform sonication to obtain dispersion 2; S1-3-3, add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10±0.5 with an alkaline solution, perform ultrasonic dispersion, transfer the obtained mixture to a polytetrafluoroethylene-lined reactor, react under heating, filter after the reaction, wash the solid product with deionized water until neutral, vacuum dry, and grind to obtain a hydrotalcite-based filler: r-GO@-La-SiO2-LDHs; Step S3 is specifically as follows: S3-1, adding flame retardant modified filler, fatty alcohol polyoxyethylene ether ammonium sulfate and ethanol into deionized water, stirring to obtain a mixed solution 1; S3-2, adding acrylic acid, methacrylic acid, methyl methacrylate and butyl acrylate into a mixed solution of deionized water and ethanol, stirring to obtain a mixed solution 2; S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring, then add potassium persulfate, and then heat to 65-70°C and react for 0.5-2h; S3-4, add the remaining mixed solution 2 dropwise to the product of step 1 under stirring, add potassium persulfate after the addition is completed, raise the temperature to 72-78°C, react for 1.5-5h, and obtain a composite modified filler.

2. The method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs according to claim 1, characterized in that: Step S1-1 is specifically as follows: Graphite and sodium nitrate are added to concentrated sulfuric acid with a concentration of 95-98wt%, and the reaction is stirred under ice bath conditions. Then KMnO4 is added, stirred at 10-20°C, the temperature is raised to 30-40°C, and the reaction is continued by stirring. Deionized water is added to the product, the temperature is raised to 90-100°C and maintained for 10-30 minutes, and deionized water and H2O2 solution are added in sequence. The product is allowed to stand, and the supernatant is removed after the system is separated. The product is washed with deionized water until it is neutral and dried to obtain graphene oxide GO.

3. The method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs according to claim 2, characterized in that: Step S1-2 is specifically as follows: S1-2-1. Add NaOH and Na2CO3 to deionized water and stir until completely dissolved to prepare an alkaline solution with a NaOH concentration of 0.5-2 mol / L and a Na2CO3 concentration of 0.25-1 mol / L; S1-2-2. Take graphene oxide and add it to deionized water, disperse it by ultrasonic, then add alkaline solution dropwise until the pH of the system is 9-10.

5. After the addition is complete, react under heating and centrifuge. Wash the solid product with deionized water until it is neutral, vacuum dry to constant weight, and grind to obtain reduced graphene oxide r-GO.

4. The method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs according to claim 3, characterized in that: Step S1 is specifically as follows: S1-1. Preparation of graphene oxide: 10-40g of graphite and 5-20g of sodium nitrate are added to 200-1000mL of concentrated sulfuric acid with a concentration of 95-98wt%, and stirred for reaction for 5-30min under ice bath conditions, then 30-130g of KMnO4 is added, and the mixture is stirred for 20-60min at 10-20°C, and the mixture is heated to 30-40°C, and the mixture is stirred for reaction for 5-20h. 400-1600mL of deionized water is added to the product, and the mixture is heated to 90-100°C and maintained for 10-30min, and then 400-1500mL of deionized water and 5-20mL of H2O2 solution with a concentration of 20-25wt% are added in sequence, and the mixture is allowed to stand for 30-90min. After the system is separated into layers, the supernatant is removed, and the obtained product is washed with deionized water until neutralized, and dried at 60-80°C for 12-48h to obtain graphene oxide GO. S1-2. Preparation of reduced graphene oxide r-GO: S1-2-1. Add NaOH and Na2CO3 to deionized water and stir until completely dissolved to prepare an alkaline solution with a NaOH concentration of 0.5-2 mol / L and a Na2CO3 concentration of 0.25-1 mol / L; S1-2-2, take 0.5-2g of graphene oxide and add it to 25-100mL of deionized water, ultrasonically disperse it for 5-30min, then add alkaline solution dropwise until the pH of the system is 9-10.5, react at 60-70°C for 10-40h after the addition is complete, centrifuge, wash the solid product with deionized water until it is neutral, vacuum dry it at 60-80°C to constant weight, grind it, and obtain reduced graphene oxide r-GO; S1-3, one-pot preparation of hydrotalcite-based filler: r-GO@-La-SiO2-LDHs: S1-3-1, add 0.5-2g of nano-mesoporous silica, 1-4g of r-GO, and 0.172-0.686g of La(NO3)3 into 150-600mL of deionized water, and disperse by ultrasonic for 15-60min to obtain dispersion 1; S1-3-2, add 1.28-5.12 g of Mg(NO3)2·6H2O, 1.875-7.5 g of Al(NO3)2·9H2O, and 0.6-2.4 g of sodium citrate into 150-600 mL of deionized water, and ultrasonicate for 5-20 min to obtain dispersion 2; S1-3-3. Add dispersion 2 to dispersion 1 under stirring, adjust the pH value of the system to 10±0.5 with alkaline solution, perform ultrasonication for 30-90 min, transfer the resulting mixture to a polytetrafluoroethylene-lined reactor, react at 120-140°C for 8-24 h, filter after the reaction, wash the solid product with deionized water until neutral, vacuum dry at 60-90°C for 5-24 h, and grind to obtain a hydrotalcite-based filler: r-GO@-La-SiO2-LDHs.

5. The method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs according to claim 1, characterized in that: Step S2 is specifically as follows: Take 0.5-2g of triphenyl phosphate and add it to 50-200mL of acetone, stir for 2-10min, then add 2.5-10g of hydrotalcite-based filler, shake on a shaker at 60-75°C for 6-24h, filter, wash with ethanol and deionized water in turn, and vacuum dry at 50-70°C for 4-12h to obtain a flame retardant modified filler.

6. The method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs according to claim 1, characterized in that: Step S3 is specifically as follows: S3-1, add 2.5-10g of flame retardant modified filler, 1-4g of fatty alcohol polyoxyethylene ether ammonium sulfate, and 75-300mL of ethanol into 150-500mL of deionized water, and stir at 500-2000rpm for 15-60min to obtain a mixed solution 1; S3-2, add 3.5-14 g of acrylic acid, 1.5-6 g of methacrylic acid, 2.5-10 g of methyl methacrylate, and 2.5-10 g of butyl acrylate into 50-200 mL of a mixed solution consisting of deionized water and ethanol in a volume ratio of 1:1, and stir for 5-20 min to obtain a mixed solution 2; S3-3, add 1 / 3 of the mass of mixed solution 2 to mixed solution 1 under stirring, continue stirring for 5-30 minutes, add 0.05-0.2g of potassium persulfate, and then heat to 65-70°C and react for 0.5-2h; S3-4, add the remaining mixed solution 2 drops to the product of step 1 under stirring, and complete the addition within 0.3-3 hours. Then add 0.075-0.3g potassium persulfate, raise the temperature to 72-78°C, and react for 1.5-5 hours to obtain a composite modified filler.

7. The method for preparing a flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs according to claim 1, characterized in that: in, The stabilizer is a mixture of zinc stearate and calcium stearate, and the plasticizer is dioctyl phthalate; Step S4 is specifically as follows: Weigh 100 g of PVC powder, 0.5-2 g of zinc stearate, 0.6-3.6 g of calcium stearate, 1-4 g of dioctyl phthalate, and 9-36 g of a composite modified filler, add them into a mixer, stir and mix for 5-20 min, add the resulting mixture into an open mill, mix at 160-185° C. for 5-30 min, and obtain a flame retardant modified PVC composite material.

8. A flame retardant modified PVC composite material based on graphene-coated hydroxy magnesium aluminum hydrotalcite LDHs, characterized in that: It is prepared by the method according to any one of claims 1 to 7.

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