Flame-retardant foamed polypropylene composite material and preparation method thereof

Abstract

The present invention belongs to the technical field of polypropylene composite materials and relates to a flame-retardant foamed polypropylene composite material and a preparation method thereof. The composite material comprises: polypropylene, polystyrene, ethylene-octene copolymer, tris(2,3-dibromopropyl)isocyanurate, a flame retardant synergist, a cross-linking agent, a compatibilizer, a lubricant, an antioxidant, an anti-ultraviolet absorber, expanded microspheres, and a nucleating agent; the flame retardant synergist is a mixture of polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, and melamine polyphosphate. The present invention adds polystyrene and ethylene-octene copolymer to improve the foaming effect and mechanical properties of the material, adds a flame retardant synergist to synergize with the main flame retardant to improve the flame retardant properties of the material, adds expanded microspheres for physical foaming, and adds a nucleating agent to improve foaming efficiency and quality, thereby obtaining a foamed polypropylene composite material with high flame retardancy and excellent foaming and mechanical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of polypropylene composite materials and relates to a flame retardant foamed polypropylene composite material and a preparation method thereof. Background Art

[0002] Since the 1990s, China's foam plastics industry has experienced rapid growth, with three major product categories emerging in the market: polyurethane soft and rigid foams, polystyrene foam, and polyethylene foam. While these materials play an important role in their respective fields, they also have significant drawbacks. For example, polyurethane foam can leave harmful isocyanate residues during the foaming process, making the foamed material non-recyclable. The production of polystyrene foam typically requires the use of chlorofluorocarbons (CFCs) or butane as a blowing agent, which not only pollutes the environment but also results in an extremely long degradation cycle, posing a threat to the natural ecosystem. While polyethylene foam offers good flexibility and cushioning properties, it suffers from poor rigidity and a maximum operating temperature of only 80°C, limiting its application in high-temperature environments.

[0003] In contrast, polyolefins, especially polypropylene foam materials, have received widespread attention due to their unique advantages. Polypropylene foam materials not only have good thermal stability and chemical corrosion resistance, but also show high toughness and strength, while the processing cost is relatively low. More importantly, this material has little impact on the environment during production and post-waste treatment, which meets the requirements of sustainable development. Therefore, polypropylene foam materials are considered to be an important direction for the future development of the foam plastics industry and have gradually become a hot topic of concern. For example, Chinese patent CN114015186A discloses a foamed polypropylene material and a preparation method thereof, comprising the following components in parts by weight: 100 parts of polypropylene, 0.5 to 1 part of a foaming agent, 1 to 5 parts of an elastomer, and 1 to 5 parts of a cross-linking agent. A foamed polypropylene material is prepared by mixing and extrusion granulation, and has excellent mechanical and dielectric properties and high temperature resistance. For example, Chinese patent CN116041855A discloses a high-melt-strength micro-foamed polypropylene composite material and its preparation method. The composite material is prepared by grafting hydrogenated polybutadiene (not fully hydrogenated) onto the polypropylene backbone to produce polypropylene with long chain branches. This gives the polypropylene high melt strength and facilitates foaming control. However, none of these patents address flame retardancy modification of polypropylene. Polypropylene is inherently flammable, posing a safety hazard in everyday life. Therefore, research on effective flame retardant modification of polypropylene is particularly necessary.

[0004] For example, Chinese patent CN118271747A discloses a halogen-free, fluorine-free flame-retardant polypropylene composite material, its preparation method, and application. By adding phosphate, melamine, and piperazine flame retardants, a halogen-free, fluorine-free flame-retardant polypropylene composite material with excellent flowability and flame retardancy is obtained. Another example is Chinese patent CN118240298A, which discloses a low-smoke, halogen-free, highly flame-retardant polypropylene composite material and its preparation method. The composite material comprises the following components, calculated by mass percentage: 5-30 wt% polypropylene resin, 50-80 wt% magnesium hydroxide, 5-20 wt% toughening agent, 0-5 wt% wollastonite, 0-5 wt% montmorillonite, 0.1-1 wt% antioxidant, and 0.1-1 wt% lubricant. The composite material is produced by high-speed mixing and extrusion granulation. However, none of these patents involve foaming the polypropylene, resulting in the material lacking lightweight, high strength, and good resilience, limiting its application in certain fields.

[0005] Although some achievements have been made in polypropylene foam materials and flame retardant modification, how to effectively combine these two properties to make polypropylene foam materials have excellent mechanical properties and flame retardancy remains the focus of future research. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a flame retardant foamed polypropylene composite material and a preparation method thereof.

[0007] One object of the present invention is achieved by the following technical solutions:

[0008] A flame-retardant foamed polypropylene composite material comprises the following components in parts by weight:

[0009] 100 parts of polypropylene resin, 10-15 parts of polystyrene resin, 10-15 parts of ethylene-octene copolymer, 20-25 parts of tris(2,3-dibromopropyl)isocyanurate, 10-20 parts of flame retardant synergist, 0.2-0.8 parts of crosslinking agent, 2-4 parts of compatibilizer, 2-5 parts of lubricant, 0.4-0.8 parts of antioxidant, 0.4-0.8 parts of anti-ultraviolet absorber, 1-3 parts of expanded microspheres, and 5-10 parts of nucleating agent.

[0010] The polypropylene resin of the present invention is preferably a high melt strength polypropylene, and the melt strength of the polypropylene resin is 5 to 50 cN. The test conditions are: using a melt strength meter, extrusion temperature 200 ° C, tensile acceleration 20 mm / S 2The temperature difference between the melting point and the onset of micropore rupture of ordinary polypropylene is small. Furthermore, its low viscosity and poor solubility make it unable to retain the gas produced by the decomposition of the foaming agent, making it unsuitable for direct foaming. However, high-melt-strength polypropylene has a higher melt strength, which enables it to maintain gas stability during the melt foaming process, thereby forming a uniform and controllable pore structure. Furthermore, high-melt-strength polypropylene can also improve the mechanical properties and processability of composite materials.

[0011] More preferably, the melt strength of the polypropylene resin is 10-20 cN.

[0012] Preferably, the weight average molecular weight of the polystyrene resin is 1*10 4 ~9*10 6 , Mw / Mn is 1-1.4. The addition of polystyrene to polypropylene resin in the present invention significantly improves the overall foaming performance of the material. The molecular weight and distribution of polystyrene affect its melt viscosity and foaming performance. An appropriate molecular weight can provide sufficient melt strength to support the bubbles formed during the foaming process, while a uniform molecular weight distribution helps to achieve a uniform cell structure.

[0013] Preferably, the ethylene-octene copolymer has a melt index of 15-30 g / 10 min, tested under the following conditions: temperature 190°C, die 2.095 mm, and load 2.16 kg. Ethylene-octene copolymers with high melt indexes exhibit good compatibility with PP. The addition of this material not only imparts excellent toughness and resilience to the composite, but also improves the dispersion between the filler and the matrix resin, further enhancing the composite's overall properties, such as flame retardancy. Furthermore, it improves the material's processing fluidity and increases the composite's foaming efficiency.

[0014] More preferably, the melt index of the ethylene-octene copolymer is 20-25 g / 10 min.

[0015] Preferably, the flame retardant synergist is a mixture of polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, and melamine polyphosphate.

[0016] More preferably, the flame retardant synergist is a mixture of polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, and polyphosphate melamine in a mass ratio of 1:(1-1.5):(2-2.5):(2-2.5).

[0017] The flame retardant in this invention is a composite flame retardant composed primarily of tris(2,3-dibromopropyl) isocyanurate (CAS NO: 52434-90-9), with a mixture of polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, and melamine polyphosphate as synergists. Tris(2,3-dibromopropyl) isocyanurate is a highly effective bromine-nitrogen intumescent flame retardant. In this system, combined with other flame retardants, tris(2,3-dibromopropyl) isocyanurate not only exhibits excellent flame retardancy but also exhibits low volatility, good compatibility, durability, water resistance, and non-toxicity. Tris(2,3-dibromopropyl)isocyanurate decomposes into hydrogen bromide upon exposure to high temperatures. This hydrogen bromide captures the reactive free radicals (such as OH·, O·, and H·) that propagate the combustion chain reaction, generating less reactive bromine radicals, which slows or even terminates combustion. The resulting hydrogen bromide gas is dense and difficult to ignite. It not only dilutes oxygen in the air but also coats the surface of the material, isolating it from the air and slowing its combustion rate or causing it to self-extinguish, achieving flame retardancy. Polymethylsiloxane forms a dense, non-combustible silicon-carbon layer during combustion, effectively isolating it from oxygen and heat, thereby achieving flame retardancy. Furthermore, polymethylsiloxane promotes char formation and increases the yield. Furthermore, the addition of polymethylsiloxane improves the material's processing fluidity and mold release properties, enhancing its overall processability. The phosphorus in tris(2,2,2-trifluoroethyl) phosphate (TPP) produces non-combustible compounds at high temperatures that coat the surface of the material, blocking combustion. Furthermore, its high-temperature decomposition produces hydrogen fluoride gas, which reacts with free radicals in the flame to replace hydrogen atoms or form hydrofluoric acid, disrupting the flame chain reaction and slowing or inhibiting flame spread. Furthermore, TPP forms a non-combustible protective film on the surface of the material when it decomposes at high temperatures, preventing flames from burning and providing a significant anti-drip effect. Melamine cyanurate and melamine polyphosphate are intumescent nitrogen-based flame retardants. When they decompose at high temperatures, they form a dense carbon foam layer that coats the polymer surface, providing thermal insulation and oxygen isolation. Furthermore, their decomposition produces non-combustible gases, such as nitrogen and carbon dioxide, which dilute oxygen and absorb heat, thereby lowering the surface temperature and achieving flame retardancy. In summary, the present invention utilizes the synergistic effect between multiple flame retardants to improve the flame retardant efficiency of the polymer, reduce the content of certain components in the flame retardant system, ensure the processability and flowability of the material while meeting high flame retardancy requirements, and effectively control costs, thereby achieving low-amount and high-efficiency flame retardants.

[0018] Preferably, the crosslinking agent is one or more of an aromatic divinyl compound, a diacrylate compound, a multifunctional crosslinking agent, and a diol compound. Aromatic divinyl compounds may be listed as divinylbenzene and / or divinylnaphthalene; diacrylate compounds may be listed as one or more of ethylene glycol diacrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, and tetraethylene glycol diacrylate; multifunctional crosslinking agents may be listed as one or more of pentaerythritol triacrylate, trimethylolethane triacrylate, trimethylolpropane triacrylate, pentaerythritol trimethacrylate, trimethylolethane trimethacrylate, trimethylolpropane trimethacrylate, and tetramethylolmethane tetramethacrylate; and glycol compounds may be listed as one or more of butanediol, ethylene glycol, and 1,5-pentanediol.

[0019] The addition of a crosslinker changes the molecular connection and structure of the material, increasing the number of intermolecular connection points and forming a tighter spatial network structure, thereby improving the material's mechanical strength, wear resistance, and other mechanical properties. Furthermore, in this system, mild crosslinking can also improve the material's foaming stability.

[0020] More preferably, the crosslinking agent is one or more of divinylbenzene, 1,5-pentanediol, and pentaerythritol triacrylate.

[0021] Preferably, the compatibilizer is one or more of hydrogenated styrene-butadiene-styrene terblock copolymer, styrene-isoprene-styrene terblock copolymer, and styrene-butadiene-styrene terblock copolymer.

[0022] The compatibilizer used in the present invention can, on the one hand, improve the interfacial compatibility of different matrix resins when melted at high temperature, and on the other hand, increase the compatibility between the inorganic filler and the polymer resin, so that the inorganic phase can be evenly distributed in the polymer phase, effectively avoiding the separation and mutual repulsion between different materials, thereby perfectly reflecting the various properties of the material.

[0023] Preferably, the expanded microspheres are expanded microspheres formed by using a thermoplastic polymer as the shell and carbon dioxide and nitrogen as the core material in a volume ratio of 1:0.5-2.

[0024] More preferably, the particle size of the expanded microspheres is 10-50 μm, and even more preferably 30-40 μm.

[0025] Unlike traditional chemical foaming agents, expandable microspheres have a core-shell structure, consisting of a thermoplastic polymer shell and an enclosed low-boiling-point gas. This core-shell structure allows the microspheres to expand when heated. When heated to a certain temperature, the shell of the expandable microspheres softens and becomes plastic. Simultaneously, the low-boiling-point core material within the microspheres vaporizes, generating internal pressure that causes the shell to expand, thus achieving the foaming effect. The use of expandable microspheres eliminates the risk of residual foaming agent during the foaming process of traditional chemical foaming agents, which can lead to reduced overall material performance and environmental concerns.

[0026] Preferably, the nucleating agent is a mixture of nano calcium silicate and nano basic zinc carbonate.

[0027] The present invention uses a mixture of nano calcium silicate and nano basic zinc carbonate as a nucleating agent. On the one hand, it can improve the polypropylene crystallization rate, accelerate the crystallization process, increase the number of crystal nuclei, make the polymer resin phase crystallization in the system more perfect, be stressed more evenly, thereby improving the impact strength and surface strength of the final composite material and improving its overall mechanical properties. On the other hand, the nucleating agent can provide enough tiny cores in the system of the present invention, accelerate the generation of bubbles in the foaming process, thereby improving the foaming effect. The tiny core provided by the nucleating agent can also optimize the cell structure, make the cells evenly distributed, and avoid the situation of insufficient or too high local density. In addition, the nucleating agent can also reduce the foaming temperature and pressure, shorten the foaming time, and improve the foaming efficiency.

[0028] More preferably, the nucleating agent is a mixture of nano calcium silicate and nano basic zinc carbonate in a mass ratio of (1-2): (2-3).

[0029] Preferably, the particle size of the nucleating agent is 1 to 50 nm, more preferably 10 to 20 nm.

[0030] Lubricants can improve the processing properties of materials during processing, reduce the internal and external friction of materials during high-temperature extrusion, and thus improve the processing flow properties of materials. The types of lubricants of the present invention are not particularly limited, but any substance that can improve the processing properties of materials is within the protection scope of the present invention. Preferably, the lubricant is one or more of fatty acid lubricants, fatty acid salt lubricants, hydrocarbon lubricants, fatty amide lubricants, and silicone lubricants. Fatty acid lubricants can be listed as one or more of saturated fatty acids, unsaturated fatty acids, and hydroxy fatty acids; fatty acid salt lubricants can be listed as one or more of fatty acid potassium, fatty acid sodium, and fatty acid ethanolamine; hydrocarbon lubricants can be listed as one or more of paraffin wax, polyethylene wax, and halogenated hydrocarbons; fatty amide lubricants can be listed as one or more of ethylene bisstearamide, fatty acid amide, and alkylene bisfatty acid amide; and silicone lubricants can be listed as polysiloxane.

[0031] The invention adds an antioxidant and an anti-ultraviolet absorber into the polypropylene composite material to improve the light resistance and weather resistance of the polypropylene composite material.

[0032] Polypropylene molecules are very sensitive to photooxidation, primarily due to the presence of tertiary carbon atoms in their molecular unit structure. The hydrogen on these tertiary carbon atoms is very unstable and easily oxidized, causing accelerated degradation of polypropylene. Adding antioxidants can utilize their active groups to capture free radicals, preventing oxidation of polypropylene and extending its service life.

[0033] Preferably, the antioxidant may be one or more of phenolic antioxidants, thiol antioxidants, phosphites, and pentaerythritol ester antioxidants. The present invention does not impose any particular requirements on the specific selection of the antioxidant; any phenolic antioxidant, thiol antioxidant, amide antioxidant, or pentaerythritol ester antioxidant that can exert an antioxidant effect falls within the scope of the present invention. For example, phenolic antioxidants include one or more of butylated hydroxytoluene, butylated hydroxyanisole, tert-butylhydroquinone, and antioxidant 1076; thiol antioxidants include one or more of tetrapropionic acid disulfide, lipoic acid, acetylcysteine, cysteine, and glutathione; phosphite antioxidants include one or more of tris(2,4-di-tert-butylphenol)phosphite, dioctadecyl pentaerythritol diphosphite, and bis(3,5-di-tert-butylphenol)pentaerythritol diphosphite; pentaerythritol ester antioxidants include one or more of pentaerythritol diphosphate distearyl, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and pentaerythritol tetrakis(3-laurylthiopropionate).

[0034] Polypropylene is less resistant to UV rays and is susceptible to oxidation, discoloration, and degradation, which can lead to a decrease in material performance. Adding a UV absorber can absorb UV rays and prevent them from corroding polypropylene, thereby extending its service life.

[0035] Preferably, the anti-ultraviolet absorber can be selected from one or more of benzotriazole anti-ultraviolet absorbers, hindered amine anti-ultraviolet absorbers, and benzophenone anti-ultraviolet absorbers.

[0036] The present invention does not impose any special requirements on the selection of anti-ultraviolet absorbers. Any benzotriazole anti-ultraviolet absorbers, hindered amine anti-ultraviolet absorbers, and benzophenone anti-ultraviolet absorbers that can play an anti-ultraviolet role are within the protection scope of the present invention. Benzotriazole anti-ultraviolet absorbers can include one or more of 2-(2-hydroxy 3,5-di-tert-butyl)-5-chloro-benzotriazole, 2-(2-hydroxy 5-methyl-benzotriazole, and 2-(2-hydroxy-3-tert-butyl-5-methyl)-5-chloro-benzotriazole; hindered amine anti-ultraviolet absorbers can be selected from bis-1,2,2,6,6-pentamethylpiperidinol sebacate, bis-1-octyloxy-, 2,2,6,6-tetramethylpiperidinol sebacate, and bis-1-octyloxy-, 2,2,6,6-tetramethylpiperidinol sebacate. One or more of methyl piperidinol ester, poly (1-octyloxy)-, 2,2,6,6-tetramethyl piperidinol sebacate, and poly (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinethanol) succinate; benzophenone-based anti-UV absorbers may include one or more of 2-hydroxy-4-n-octyloxy benzophenone (UV absorber UV-531), UV absorber UV-9, and UV absorber UV-284.

[0037] Another object of the present invention is achieved through the following technical solutions:

[0038] A method for preparing a flame-retardant foamed polypropylene composite material comprises the following steps:

[0039] (1) Weighing polypropylene resin, polystyrene resin, ethylene-octene copolymer, tris(2,3-dibromopropyl)isocyanurate, flame retardant synergist, crosslinking agent, compatibilizer, lubricant, antioxidant, and anti-ultraviolet absorber in parts by weight and mixing to obtain component A; weighing expanded microspheres and nucleating agent in parts by weight and mixing to obtain component B;

[0040] (2) Component A is added through the front feeding device of the extruder, and component B is added through the side feeding device of the extruder, and the flame retardant foamed polypropylene composite material is obtained by extrusion granulation.

[0041] Preferably, the mixing in step (1) is carried out at 5-40° C. for 5-30 min.

[0042] Preferably, the front feeding device is located in the feeding section of the extruder, and the side feeding device is located in the melting section of the extruder.

[0043] Preferably, the temperature of each section of the extruder is: 155-180°C in the feeding section, 170-190°C in the conveying section, 180-215°C in the melting section, and 180-210°C in the die.

[0044] Preferably, the main engine speed of the extruder is 10-50 rpm, the unloading speed of the front feeding device is 10-20 rpm, and the unloading speed of the side feeding device is 2-5 rpm.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention adds a certain amount of polystyrene resin and ethylene-octene copolymer to polypropylene with high melt strength. The addition of polystyrene resin within a certain range is beneficial to improving the foaming efficiency and mechanical properties of the material and improving the processing flow performance; and the addition of ethylene-octene copolymer can also improve the mechanical properties, flame retardancy, foaming effect and flow processing performance of the composite material.

[0047] 2. The present invention adds a mixture of polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, and polyphosphate melamine in a mass ratio of 1:(1-1.5):(2-2.5):(2-2.5) as a flame retardant synergist and compounds it with the main flame retardant tris(2,3-dibromopropyl) isocyanurate, utilizing the synergistic flame retardant effect between the flame retardants to achieve low-amount and high-efficiency flame retardants.

[0048] 3. The present invention adopts a multi-system physical foaming method to prepare a low-density flame-retardant polypropylene composite material. The obtained composite material has excellent foaming effect and avoids the problem of high chemical foaming agent residue in traditional foaming materials.

[0049] 4. The present invention uses a mixture of nano calcium silicate and basic zinc carbonate as a nucleating agent. The synergistic effect of the two is not only conducive to the foaming of the material, but also can improve the mechanical properties of the material.

[0050] 5. The flame retardant foamed polypropylene composite material provided by the present invention has the following properties: elongation at break is 18~30%, tensile strength is 20~30MPa (test standard GB / T16421-1996); oxygen index is 31~34% (test standard GB / T5454-1997); impact strength is 10~15kj / m 2 (Test standard GB / T1843-2008); color fastness grade reaches level 5 and above (test standard GB / T8427-2008); density is 0.6~0.8g / cm 3 (Test standard GB / T 6343-2009); melt index 5-7 g / min (test temperature 190°C, die 2.095 mm, load 2.16 kg). The polypropylene composite material prepared by the present invention not only has good flame retardancy, but also has good foaming effect, low density, and excellent mechanical properties, processing properties, and weather resistance.

[0051] 6. The preparation process of the flame-retardant foamed polypropylene composite material of the present invention is simple and suitable for mass production. DETAILED DESCRIPTION

[0052] The technical scheme of the present invention is further described below by specific examples. It should be understood that the specific examples described herein are only used to help understand the present invention and are not intended to be limiting of the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0053] Example 1

[0054] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0055] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0056] The melt strength of polypropylene resin is 15 cN, and the weight average molecular weight of polystyrene resin is 6.5*10 5 , Mw / Mn is 1.2, the melt index of ethylene-octene copolymer is 22g / 10min, the flame retardant synergist is 2.08 parts of polymethylsiloxane, 2.5 parts of tris(2,2,2-trifluoroethyl) phosphate, 5.21 parts of melamine cyanurate, 5.21 parts of polyphosphate melamine (mass ratio is about 1:1.2:2.5:2.5), the crosslinker is pentaerythritol triacrylate, the compatibilizer is hydrogenated styrene-butadiene-styrene ternary block copolymer, the lubricant is ethylene bisstearamide, and the antioxidant The anti-ultraviolet agent is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], the anti-ultraviolet agent is 2-hydroxy-4-n-octyloxybenzophenone, the expanded microspheres are expanded microspheres formed by thermoplastic acrylate polymer as the shell and carbon dioxide and nitrogen in a volume ratio of 1:1 as the core material, and the particle size is 30-40μm; the nucleating agent is 3 parts of nano-calcium silicate and 5 parts of nano-basic zinc carbonate (mass ratio is 1.5:2.5), and the particle size range of nano-calcium silicate and nano-basic zinc carbonate is 10-20nm.

[0057] The flame retardant foamed polypropylene composite material of this embodiment is prepared by the following method:

[0058] Weigh polypropylene resin, polystyrene resin, ethylene-octene copolymer, tris(2,3-dibromopropyl)isocyanurate, flame retardant synergist, crosslinking agent, compatibilizer, lubricant, antioxidant, and anti-ultraviolet absorber in parts by weight, mix them in a low-pressure mixer at a temperature of 25°C for 13 minutes, and obtain component A. Weigh expanded microspheres and nucleating agent in parts by weight, mix them in a low-pressure mixer at a temperature of 20°C for 10 minutes, and obtain component B.

[0059] The component A mixture was added to the front feeder of a parallel, co-rotating twin-screw extruder equipped with a side feeder for melt extrusion. Component B was simultaneously added through the side feeder for melt extrusion. The screw section temperatures were: 170°C for the feeding section, 180°C for the conveying section, 200°C for the melting section, and 195°C for the die head. The main engine speed was 24 rpm, the front feeder discharge speed was 17 rpm, and the side feeder discharge speed was 3 rpm. After melt extrusion, the mixture was air-cooled and pelletized to obtain composite pellets.

[0060] Example 2

[0061] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0062] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 25 parts, flame retardant synergist: 18 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0063] The flame retardant synergist is 2.5 parts of polymethylsiloxane, 3 parts of tris(2,2,2-trifluoroethyl) phosphate, 6.25 parts of melamine cyanurate, and 6.25 parts of polyphosphate melamine (mass ratio is 1:1.2:2.5:2.5). The specific ingredients and proportions of the other components are the same as in Example 1. The preparation method of the polypropylene composite material is the same as in Example 1.

[0064] Example 3

[0065] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0066] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 20 parts, flame retardant synergist: 10 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0067] The flame retardant synergist is 1.39 parts of polymethylsiloxane, 1.67 parts of tris(2,2,2-trifluoroethyl) phosphate, 3.47 parts of melamine cyanurate, and 3.47 parts of polyphosphate melamine (mass ratio is approximately 1:1.2:2.5:2.5). The specific ingredients and proportions of the other components are the same as in Example 1. The preparation method of the polypropylene composite material is the same as in Example 1.

[0068] Example 4

[0069] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0070] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 10 parts;

[0071] The flame retardant synergist is 2.3 parts of polymethylsiloxane, 2.3 parts of tris(2,2,2-trifluoroethyl) phosphate, 4.6 parts of melamine cyanurate, and 5.8 parts of polyphosphate melamine (mass ratio is 1:1:2:2.5); the nucleating agent is 3.75 parts of nano calcium silicate and 6.25 parts of nano basic zinc carbonate (mass ratio is 1.5:2.5); the specific ingredients and proportions of the other components are the same as those in Example 1, and the preparation method of the polypropylene composite material is the same as that in Example 1.

[0072] Example 5

[0073] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0074] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2.8 parts, nucleating agent: 8 parts;

[0075] The compatibilizer is a styrene-isoprene-styrene ternary block copolymer, and the specific ingredients and proportions of the other components are the same as those in Example 1. The preparation method of the polypropylene composite material is the same as that in Example 1.

[0076] Example 6

[0077] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0078] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 1.2 parts, nucleating agent: 8 parts;

[0079] The specific ingredients and their proportions of the components in Example 6 are the same as those in Example 1, and the preparation method of the polypropylene composite material is the same as that in Example 1.

[0080] Example 7

[0081] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0082] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.8 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0083] The specific ingredients and their proportions of the components in Example 7 are the same as those in Example 1, and the preparation method of the polypropylene composite material is the same as that in Example 1.

[0084] Example 8

[0085] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0086] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 2.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0087] The specific ingredients and their proportions of the components in Example 8 are the same as those in Example 1, and the preparation method of the polypropylene composite material is the same as that in Example 1.

[0088] Example 9

[0089] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0090] Polypropylene resin: 100 parts, polystyrene resin: 10 parts, ethylene-octene copolymer: 12 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0091] The specific ingredients and their proportions of the components in Example 9 are the same as those in Example 1, and the preparation method of the polypropylene composite material is the same as that in Example 1.

[0092] Example 10

[0093] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0094] Polypropylene resin: 100 parts, polystyrene resin: 12 parts, ethylene-octene copolymer: 10 parts, tris(2,3-dibromopropyl)isocyanurate: 23 parts, flame retardant synergist: 15 parts, crosslinking agent: 0.5 parts, compatibilizer: 3.5 parts, lubricant: 3.5 parts, antioxidant: 0.5 parts, anti-ultraviolet absorber: 0.5 parts, expanded microspheres: 2 parts, nucleating agent: 8 parts;

[0095] The specific ingredients and their proportions of the components in Example 10 are the same as those in Example 1, and the preparation method of the polypropylene composite material is the same as that in Example 1.

[0096] Example 11

[0097] The flame retardant foamed polypropylene composite material of this embodiment is composed of the following components in parts by weight:

[0098] Polypropylene resin: 100 parts, polystyrene resin: 13 parts, ethylene-octene copolymer: 13 parts, tris(2,3-dibromopropyl)isocyanurate: 22 parts, flame retardant synergist: 18 parts, crosslinking agent: 0.3 parts, compatibilizer: 2 parts, lubricant: 3 parts, antioxidant: 0.4 parts, anti-ultraviolet absorber: 0.6 parts, expanded microspheres: 2 parts, nucleating agent: 6 parts;

[0099] The melt strength of polypropylene resin is 18 cN, and the weight average molecular weight of polystyrene resin is 6.5*10 5, Mw / Mn is 1.2, the melt index of ethylene-octene copolymer is 25g / 10min, the flame retardant synergist is 3 parts of polymethylsiloxane, 3 parts of tris(2,2,2-trifluoroethyl) phosphate, 6 parts of melamine cyanurate, and 6 parts of polyphosphate melamine (mass ratio is 1:1:2:2), the crosslinking agent is divinylbenzene, the compatibilizer is styrene-isoprene-styrene ternary block copolymer, the lubricant is polyethylene wax, the antioxidant is antioxidant 1076, the anti-ultraviolet agent is ultraviolet absorber UV-9, the expanded microspheres are expanded microspheres formed by thermoplastic acrylate polymer as the shell and carbon dioxide and nitrogen in a volume ratio of 1:1 as the core material, the particle size of which is 30~40μm; the nucleating agent is 2 parts of nano-calcium silicate and 4 parts of nano-basic zinc carbonate (mass ratio is 1:2), and the particle size range of nano-calcium silicate and nano-basic zinc carbonate is 10~20nm.

[0100] Comparative Example 1

[0101] The only difference between the components of the polypropylene composite material of Comparative Example 1 and Example 1 is that the flame retardant synergist of Comparative Example 1 is 15 parts of polymethylsiloxane, and the specific ingredients, contents and proportions of other components are the same as those of Example 1.

[0102] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0103] Comparative Example 2

[0104] The only difference between the components of the polypropylene composite material of Comparative Example 2 and Example 1 is that the flame retardant synergist in Comparative Example 2 is 15 parts of tris(2,2,2-trifluoroethyl) phosphate, and the specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0105] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0106] Comparative Example 3

[0107] The only difference between the components of the polypropylene composite material of Comparative Example 3 and Example 1 is that the flame retardant synergist in Comparative Example 3 is 15 parts of melamine cyanurate, and the specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0108] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0109] Comparative Example 4

[0110] The only difference between the components of the polypropylene composite material of Comparative Example 4 and Example 1 is that the flame retardant synergist of Comparative Example 4 is 15 parts of polyphosphate melamine, and the specific ingredients, contents and proportions of other components are the same as those of Example 1.

[0111] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0112] Comparative Example 5

[0113] The only difference between the components of the polypropylene composite material of Comparative Example 5 and Example 1 is that the flame retardant synergist in Comparative Example 5 is a mixture of 2.9 parts of tris(2,2,2-trifluoroethyl) phosphate, 6.05 parts of melamine cyanurate, and 6.05 parts of polyphosphate melamine (mass ratio is approximately 1.2:2.5:2.5), and the specific ingredients, contents, and component ratios of the other components are the same as those in Example 1.

[0114] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0115] Comparative Example 6

[0116] The only difference between the components of the polypropylene composite material of Comparative Example 6 and Example 1 is that the flame retardant synergist in Comparative Example 6 is 0 parts, and the specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0117] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0118] Comparative Example 7

[0119] The only difference between the components of the polypropylene composite material of Comparative Example 7 and Example 1 is that the flame retardant synergist in Comparative Example 7 is 2.5 parts of polymethylsiloxane, 6.25 parts of melamine cyanurate, and 6.25 parts of polyphosphate melamine (mass ratio is 1:2.5:2.5), and the specific ingredients, contents and proportions of the other components are the same as in Example 1.

[0120] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0121] Comparative Example 8

[0122] The only difference between the components of the polypropylene composite material of Comparative Example 8 and Example 1 is that the nucleating agent in Comparative Example 8 is 0 parts, and the specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0123] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0124] Comparative Example 9

[0125] The only difference between the components of the polypropylene composite material of Comparative Example 9 and Example 1 is that 2 parts of AC foaming agent azodicarbonamide are added in Comparative Example 9 instead of expanded microspheres. The specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0126] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0127] Comparative Example 10

[0128] The only difference between the components of the polypropylene composite material of Comparative Example 10 and Example 1 is that: 0 parts of expanded microspheres are added in Comparative Example 10, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0129] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0130] Comparative Example 11

[0131] The only difference between the components of the polypropylene composite material of Comparative Example 11 and Example 1 is that the nucleating agent in Comparative Example 11 is 5.25 parts of nano-calcium silicate and 8.75 parts of nano-basic zinc carbonate (mass ratio is 1.5:2.5) 14 parts, and the specific ingredients, contents and component ratios of other components are the same as in Example 1.

[0132] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0133] Comparative Example 12

[0134] The only difference between the components of the polypropylene composite material of Comparative Example 12 and Example 1 is that the nucleating agent of Comparative Example 12 is 8 parts of nano-calcium silicate and does not contain basic zinc carbonate. The specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0135] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0136] Comparative Example 13

[0137] The only difference between the components of the polypropylene composite material of Comparative Example 13 and Example 1 is that the nucleating agent of Comparative Example 13 is 8 parts of nano basic zinc carbonate and does not contain nano calcium silicate. The specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0138] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0139] Comparative Example 14

[0140] The only difference between the components of the polypropylene composite material of Comparative Example 14 and Example 1 is that the polystyrene resin in Comparative Example 14 is 0 parts, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0141] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0142] Comparative Example 15

[0143] The only difference between the components of the polypropylene composite material of Comparative Example 15 and Example 1 is that the ethylene-octene copolymer in Comparative Example 15 is 0 parts, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0144] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0145] Comparative Example 16

[0146] The only difference between the components of the polypropylene composite material of Comparative Example 16 and Example 1 is that the ethylene-octene copolymer in Comparative Example 16 is 5 parts, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0147] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0148] Comparative Example 17

[0149] The only difference between the components of the polypropylene composite material of Comparative Example 17 and Example 1 is that the cross-linking agent in Comparative Example 17 is 0 parts, and the specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0150] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0151] Comparative Example 18

[0152] The only difference between the components of the polypropylene composite material of Comparative Example 18 and Example 1 is that the cross-linking agent in Comparative Example 18 is 1 part, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0153] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0154] Comparative Example 19

[0155] The only difference between the components of the polypropylene composite material of Comparative Example 19 and Example 1 is that the compatibilizer in Comparative Example 19 is 0 parts, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0156] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0157] Comparative Example 20

[0158] The only difference between the components of the polypropylene composite material of Comparative Example 20 and Example 1 is that the polystyrene resin in Comparative Example 20 is 20 parts, and the specific ingredients, contents and proportions of the other components are the same as those in Example 1.

[0159] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0160] Comparative Example 21

[0161] The only difference between the components of the polypropylene composite material of Comparative Example 21 and Example 1 is that the melt strength of the polypropylene resin in Comparative Example 21 is 3 cN, and the specific ingredients, contents and proportions of other components are the same as those in Example 1.

[0162] The preparation method of the polypropylene composite material is the same as that in Example 1.

[0163] The polypropylene composite materials of Examples 1-11 and Comparative Examples 1-21 were subjected to physical and chemical property tests. The test specifications are as follows: oxygen index test standard GB / T5454-1997; light fastness test standard GB / T8427-2008; impact strength test standard GB / T1843-2008; elongation at break and tensile strength test standard GB / T16421-1996; density test standard GB / T6343-2009; melt index test temperature 190°C, die 2.095mm, load 2.16kg. The test results are shown in Table 1:

[0164] Table 1 Physical and chemical properties of polypropylene composite materials of Examples 1-11 and Comparative Examples 1-21

[0165]

[0166] As can be seen from Table 1, the polypropylene composite material prepared by the present invention not only has good flame retardant properties, but also has good foaming effect, low density, and excellent mechanical properties, processing properties and weather resistance.

[0167] The polypropylene composite material formulation system of the present invention utilizes multi-system composite flame-retardant technology, fully utilizing the multi-mechanism synergistic effects between flame retardants. With the aid of a compatibilizer, the flame retardant effect is effectively exerted. Within a certain range, the flame retardant properties of the composite material improve with increasing amounts of flame-retardant components in the system, as shown in Examples 1, 2, and 3. The flame retardant synergist significantly enhances the flame retardant properties of the composite material of the present invention. The absence of a flame retardant synergist, the addition of only polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, or melamine polyphosphate, or the absence of polymethylsiloxane or tris(2,2,2-trifluoroethyl) phosphate in the flame retardant synergist, all affect the flame retardant properties of the material, as shown in Example 1 and Comparative Examples 1-7.

[0168] The present invention adopts a physical foaming method, and the resulting composite material has good foaming effect and low density. The coordinated use of nucleating agent and expanded microspheres makes the composite material have high foaming efficiency and small and uniformly distributed foaming cells. Within a certain range, as the expanded microspheres or nucleating agent components in the system increase, the foaming efficiency of the composite material is higher and the density is lower, see Examples 1, 4, 5, and 6. Not adding nucleating agent or expanded microspheres to the system or using other foaming agents instead of expanded microspheres, or not adding basic zinc carbonate or nano calcium silicate to the nucleating agent, will significantly affect the foaming performance and other comprehensive properties of the material, see Example 1 and Comparative Examples 8, 9, 10, 12, and 13. The nucleating agent in the system of the present invention not only affects the foaming performance, but also has a certain effect on improving the mechanical properties of the material, see Example 1 and Comparative Example 8. The addition of too much nucleating agent will lead to inappropriate compatibility of the material system, resulting in a decrease in various comprehensive properties such as mechanical properties, see Example 1 and Comparative Example 11.

[0169] In the present invention, polystyrene resin plays a positive role in improving foaming efficiency and enhancing the overall performance of the material. Increasing its dosage within a certain range improves the foaming efficiency and mechanical properties of the material, as shown in Examples 1 and 9. Without polystyrene resin, the resulting composite material exhibits significantly reduced mechanical properties and foaming efficiency, as shown in Example 1 and Comparative Example 14. However, excessive addition of polystyrene resin can lead to disharmony among the various component systems, affecting not only the mechanical properties and foaming efficiency of the composite material but also its melt index and impaired processing flowability, as shown in Example 1 and Comparative Example 20.

[0170] The use of high melt strength polypropylene in the present invention is a guarantee for preparing flame-retardant foamed polypropylene composite materials. If low melt strength polypropylene is used, the mechanical properties, foaming and flame retardant effects of the obtained composite materials will be reduced, see Example 1 and Comparative Example 21.

[0171] Ethylene-octene copolymer has a great influence on the tensile fracture properties and fluidity of the material. When ethylene-octene copolymer is not added or its addition amount is reduced, the mechanical properties, flame retardancy, foaming effect and flow processing performance of the material will be reduced, see Examples 1, 10 and Comparative Examples 15, 16.

[0172] The compatibilizer used in the present invention can ensure perfect coordination between the materials, so that their various properties can be fully exerted. When the compatibilizer is reduced or not added, the comprehensive properties of the material are reduced because the components of the composite material cannot be perfectly integrated, as shown in Examples 1, 8 and Comparative Example 19.

[0173] The table above also shows that the mild crosslinking of the composite material of the present invention imparts a three-dimensional network structure to the composite material, significantly improving its mechanical properties and stabilizing its foaming effect. Without the addition of a crosslinking agent, the mechanical properties and foaming effect of the material are significantly reduced, as shown in Examples 1 and 7 and Comparative Example 17. Excessive addition of a crosslinking agent can degrade various material properties, as shown in Example 1 and Comparative Example 18.

[0174] The various aspects, embodiments, and features of the present invention should be considered in all respects as illustrative and not limiting, the scope of which is defined solely by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0175] In the preparation method of the present invention, the order of the steps is not limited to the order listed. Persons skilled in the art will appreciate that variations in the order of the steps are within the scope of the present invention without inventive effort. Furthermore, two or more steps or actions may be performed simultaneously.

[0176] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit its implementation. Persons skilled in the art may make various modifications, additions, or substitute similar methods for the described specific embodiments. It is not necessary and impossible to provide comprehensive examples of all implementations here. However, obvious variations or modifications arising from the essential spirit of the present invention remain within the scope of protection of the present invention, and interpreting them as any additional limitations would be contrary to the spirit of the present invention.

Claims

1. A flame retardant foamed polypropylene composite material, characterized in that: It comprises the following components in parts by weight: 100 parts of polypropylene resin, 10-15 parts of polystyrene resin, 10-15 parts of ethylene-octene copolymer, 20-25 parts of tris(2,3-dibromopropyl)isocyanurate, 10-20 parts of flame retardant synergist, 0.2-0.8 parts of crosslinking agent, 2-4 parts of compatibilizer, 2-5 parts of lubricant, 0.4-0.8 parts of antioxidant, 0.4-0.8 parts of anti-ultraviolet absorber, 1-3 parts of expanded microspheres, and 5-10 parts of nucleating agent; The flame retardant synergist is a mixture of polymethylsiloxane, tris(2,2,2-trifluoroethyl) phosphate, melamine cyanurate, and polyphosphate melamine in a mass ratio of 1:(1-1.5):(2-2.5):(2-2.5); The expanded microspheres are formed by using a thermoplastic polymer as the shell and carbon dioxide and nitrogen as the core material in a volume ratio of 1:0.5 to 2; The particle size of the expanded microspheres is 10-50 μm; The nucleating agent is a mixture of nano calcium silicate and nano basic zinc carbonate in a mass ratio of (1-2): (2-3); The particle size of the nucleating agent is 1-50 nm.

2. The flame retardant foamed polypropylene composite material according to claim 1, characterized in that: The melt strength of the polypropylene resin is 5-50 cN. The test conditions are: using a melt strength meter, extrusion temperature 200°C, tensile acceleration 20 mm / s 2 .

3. The flame retardant foamed polypropylene composite material according to claim 1, characterized in that: The weight average molecular weight of the polystyrene resin is 1*10 4 ~9*10 6 , Mw / Mn is 1~1.

4.

4. The flame retardant foamed polypropylene composite material according to claim 1, characterized in that: The melt index of the ethylene-octene copolymer is 15-30 g / 10 min, and the test conditions are: temperature 190° C., die 2.095 mm, and load 2.16 kg.

5. The flame retardant foamed polypropylene composite material according to claim 1, characterized in that: The crosslinking agent is one or more of an aromatic divinyl compound, a diacrylate compound, a multifunctional crosslinking agent, and a diol compound.

6. The flame retardant foamed polypropylene composite material according to claim 1, characterized in that: The compatibilizer is one or more of hydrogenated styrene-butadiene-styrene ternary block copolymer, styrene-isoprene-styrene ternary block copolymer, and styrene-butadiene-styrene ternary block copolymer.

7. The method for preparing a flame retardant foamed polypropylene composite material according to claim 1, wherein: The following steps are involved: (1) Weighing polypropylene resin, polystyrene resin, ethylene-octene copolymer, tris(2,3-dibromopropyl)isocyanurate, flame retardant synergist, crosslinking agent, compatibilizer, lubricant, antioxidant, and anti-ultraviolet absorber in parts by weight and mixing to obtain component A; weighing expanded microspheres and nucleating agent in parts by weight and mixing to obtain component B; (2) Component A is added through the front feeding device of the extruder, and component B is added through the side feeding device of the extruder, and the flame retardant foamed polypropylene composite material is obtained by extrusion granulation.

8. The preparation method according to claim 7, characterized in that The front feeding device is located in the feeding section of the extruder, and the side feeding device is located in the melting section of the extruder.

9. The preparation method according to claim 7, characterized in that The temperature of each section of the extruder is: feeding section 155~180℃, conveying section 170~190℃, melting section 180~215℃, and die head 180~210℃.

10. The preparation method according to claim 7, characterized in that The main engine speed of the extruder is 10~50rpm, the unloading speed of the front feeding device is 10~20rpm; the unloading speed of the side feeding device is 2~5rpm.

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