A lightweight reinforced flame-retardant polypropylene composite material and preparation method thereof

Abstract

The present application proposes a lightweight reinforced flame-retardant polypropylene composite material and a preparation method thereof, and relates to the technical field of flame-retardant polymer materials. A lightweight reinforced flame-retardant polypropylene composite material is prepared by the following method: 3‑5 parts of polypropylene are dissolved in an appropriate amount of decalin to prepare a polyethylene solution; 3‑4 parts of flame retardant monomers and 0.5‑1.5 parts of multilayer graphene are added to the polypropylene solution; a chemically inert gas is passed into the solution and ultrasonic irradiation is applied to the above solution for 15‑20 minutes. Then the solvent is removed and recovered, and dried. The dried product is mixed with 95‑97 parts of polypropylene and extruded and granulated to obtain a lightweight reinforced flame-retardant polypropylene composite material. The lightweight reinforced flame-retardant polypropylene composite material provided in the present application has a tensile strength of ≥35.4MPa and an impact strength of ≥4.8kJ·m ‑2 , density 0.90g.cm ‑3 , the flame retardant performance reaches V0 level, and it has good mechanical properties and flame retardant properties.

Description

Technical Field

[0001] The present application relates to the technical field of flame retardant polymer materials, and in particular to a lightweight reinforced flame retardant polypropylene composite material and a preparation method thereof. Background Art

[0002] Polypropylene (PP) is one of the five major general-purpose plastics. It is non-absorbent, highly heat-resistant, and has good processability. It has a wide range of applications and is also the general-purpose plastic with the lowest density. However, polypropylene has a simple chemical structure, contains only two elements, C and H, has a decomposition temperature of around 370°C, and a limiting oxygen index of 18%, making it an extremely flammable polymer. In addition, polypropylene has a low tensile strength. These shortcomings limit its scope of application. It needs to be modified.

[0003] In the prior art, flame retardants are usually used to improve the flame retardant properties of polypropylene. Flame retardants are generally low molecular weight substances, and the addition of flame retardants will reduce the strength of the material.

[0004] In order to improve the strength of flame-retardant PP, the performance of the composite material can be effectively improved by adding a large amount of reinforcing fibers, but there will be a "wick effect" when PP burns, resulting in a decrease in flame retardancy. Therefore, the amount of flame retardant needs to be further increased, but in turn, the strength of the material is reduced. The reasons for this phenomenon are: first, flame retardants are generally polar, and polypropylene is non-polar. The compatibility of the two is poor, which affects the dispersion of flame retardants in PP; second, reinforcing agents such as (fibers, whiskers, etc.) are polar, and it is difficult to disperse in non-polar PP; third, flame retardants and reinforcing agents are both polar, and flame retardants are more likely to be adsorbed on polar reinforcing agents; fourth, flame retardants are low molecular weight and easy to migrate, especially during processing, they are easy to migrate and aggregate, further affecting the flame retardant effect.

[0005] In order to solve the above problems, ZL201711340969.3 grafted halogen flame retardants to polypropylene molecular chains through solid phase grafting, and then melt blended with magnesium salt whiskers to obtain flame retardant and reinforced polypropylene composite materials. However, since this technology uses initiators during solid phase grafting, it is inevitable that there will be initiator residues; the low conversion rate of solid phase grafting leads to residual flame retardant monomers, and the residual initiators will affect the processing and performance of subsequent materials, and the residual flame retardants are easy to migrate. In addition, the amount of reinforcing agent used in this technology is relatively high, which will cause negative effects such as reduced processing fluidity, increased density and insufficient material lightweight.

[0006] Among the reinforcing materials, graphene is gaining more and more attention. The thickness of graphene is about 0.335nm, which is equivalent to the thickness of a carbon atom layer. It is the thinnest material known in the world. Its strength is 100 times that of the best steel in the world, up to 130GPa, and its elastic modulus is 1.1TPa. It is the material with the highest strength and hardness known so far. Adding a small amount of graphene can greatly improve the material performance, and has little effect on the density of the material. At present, the addition of graphene is basically done by simple blending, but simple melt blending cannot fully exert the advantages of graphene, such as dispersion and peeling problems. Summary of the invention

[0007] In view of the shortcomings of the prior art, the present invention aims to provide a flame-retardant polypropylene composite material and a preparation method thereof which can achieve enhanced flame retardant without substantially affecting the material density. The method combines polymer mechanochemical synthesis technology and multilayer graphene dispersion and exfoliation technology.

[0008] In order to solve the above technical problems, the technical solution adopted in this application is:

[0009] In one aspect, the present application provides a lightweight reinforced flame-retardant polypropylene composite material, comprising the following raw materials in parts by weight:

[0010] 100 parts of polypropylene, 3-4 parts of halogen flame retardant monomer and 0.5-1.5 parts of multilayer graphene.

[0011] On the other hand, the present application provides a method for preparing a lightweight reinforced flame-retardant polypropylene composite material, comprising the following steps:

[0012] S1. Take 3-5 parts of polypropylene and dissolve it in a solvent to prepare a polypropylene solution with a mass fraction of 3-5%;

[0013] S2, adding halogen flame retardant monomer and multilayer graphene to the polypropylene solution and mixing evenly;

[0014] S3, introducing an inert gas into the mixed solution of step S2, and irradiating it with ultrasound;

[0015] S4, removing the solvent from the recovered mixed solution after irradiation treatment and drying;

[0016] S5. The dried product is mixed with the remaining polypropylene raw material, and then extruded and granulated to obtain the lightweight reinforced flame-retardant polypropylene composite material.

[0017] The principles of this application include:

[0018] 1) Ultrasonic mechanochemical copolymerization

[0019] Ultrasonic copolymerization is based on the generation of large free radicals by macromolecular chains under ultrasonic irradiation. Such free radicals can trigger monomers, or two different macromolecular free radicals can combine alternately, or one macromolecular free radical can transfer with another macromolecular chain activated by ultrasonic energy to generate copolymers. The mechanical work done by polymers under external forces is concentrated in the form of elastic energy at the defects of the polymer structure, and local high temperature, high pressure, and strong ionization are generated inside the polymer under the action of ultrasonic cavitation. Since the area with the most concentrated energy is very small (10 -3 -10 -7 cm) and lasts for a very short time (about 10 -3 -10 -6 s), so when this highly concentrated energy exceeds the bond energy of the macromolecular chain, it can quickly break the macromolecular chain and generate long-chain free radicals. This long-chain free radical can initiate the copolymerization of monomers to form copolymers, such as Figure 1 shown.

[0020] Ultrasonic copolymerization is generally carried out in a polymer dilute solution mechanochemical system. At this time, the polymer chains in the system are in a free chain state without mutual interference, and the interaction between the chain segments is weak. The transmission and diffusion of ultrasound are more favorable to the movement of chains or chain segments. On the other hand, when the concentration of the polymer solution is high, the viscosity is high, which is not conducive to ultrasonic cavitation.

[0021] In the ultrasonic copolymerization reaction, in order to replace the oxygen in the solution that has an inhibitory effect and to produce "steady-state cavitation bubbles" under ultrasonic irradiation, it is necessary to pass chemically inert gas into the solution to facilitate the generation of active large free radicals.

[0022] As a mechanochemical reaction, ultrasonic polymerization does not follow the Arrhenius equation. The higher the temperature, the faster the reaction. Instead, the lower the reaction temperature, the faster the reaction speed. This can be seen as the lower the temperature, the higher the cavitation rupture strength, which can promote the polymerization reaction.

[0023] 2) Multilayer graphene is easier to disperse than single-layer graphene

[0024] The thickness of multilayer graphene with 5-10 layers is still at the nanoscale. Compared with the single-layer graphene in the usual sense, its specific surface area is much smaller. It is relatively difficult to agglomerate in the polymer matrix and can achieve better uniform dispersion.

[0025] 3) Ultrasonic peeling of multilayer graphene

[0026] Ultrasonic waves radiate in the multi-layer graphite suspension in a sparse and dense manner, causing the liquid to flow and generate a large number of tiny bubbles. These bubbles form and grow in the negative pressure area of ​​the longitudinal propagation of ultrasonic waves, and quickly close in the positive pressure area. In this process called the "cavitation" effect, the bubble closure can form more than 1.0×10 8 The instantaneous high pressure of Pa atmospheres and the continuous high pressure are like a series of small "explosions" that continuously impact multi-layer graphene, causing the graphene sheets to quickly peel off and form a few layers or a single layer.

[0027] 4) Ultrasonication promotes the dispersion of multilayer graphene in polymers

[0028] Ultrasonic waves may produce "cavitation" effects in liquids, forming local high temperatures, high pressures or strong shock waves and microjets. These effects combined lead to the destruction of the agglomeration structure of particles in the system, the enlargement of the gaps between particles until they break, forming a dispersed system and improving the dispersion of powders.

[0029] 5) Synergistic flame retardant effect of graphene and halogen flame retardants

[0030] Halogen flame retardants can work together with graphene to form a complex flame retardant system, inhibit flame propagation and combustion process, reduce combustion temperature and oxygen index, and thus achieve flame retardant effect.

[0031] In addition, the halogen flame retardant grafted polypropylene generated by the present invention has a volume-increasing effect on multilayer graphene, which can improve the compatibility of multilayer graphene and polypropylene, and make the multilayer graphene fully and evenly dispersed in the polypropylene composite material, giving full play to the synergistic flame retardant effect of the two, while also effectively exerting the reinforcing effect of the multilayer graphene. Therefore, the lightweight reinforced flame-retardant polypropylene composite material provided by the present invention significantly improves the flame retardant properties of the composite material while improving higher mechanical properties and maintaining lightweight. It can be seen from the results of the embodiment that the tensile strength of the lightweight reinforced flame-retardant polypropylene composite material is ≥35.4MPa, and the impact strength is ≥7.3kJ·m -2 , density is 0.9g.cm -3 , the flame retardant performance reaches V0 level.

[0032] The present invention also provides a method for preparing the lightweight reinforced flame-retardant polypropylene composite material. The method comprises the following steps: firstly grafting a halogen-based flame retardant as a monomer onto a polypropylene macromolecular chain, thereby solving the dispersion and migration problems of the flame-retardant monomer; and then mixing the polypropylene grafted with the halogen-based flame retardant with multilayer graphene. By exerting different flame-retardant effects of the two, a flame-retardant synergistic effect can be better achieved. By utilizing the reinforcing effect of the multilayer graphene, the enhanced modification of the polypropylene is achieved.

[0033] Compared with the prior art, the embodiments of the present application have at least the following advantages or beneficial effects:

[0034] 1) When nitrogen is introduced into the polypropylene solution and then ultrasonically irradiated, the polypropylene macromolecular chain will break to generate active free radicals, which can trigger the monomer to react in an environment with monomers; pentachlorophenyl acrylate and / or 2,4,6-tribromophenyl acrylate are monomers that can undergo free radical polymerization. Thus, polypropylene-pentachlorophenyl acrylate copolymer or polypropylene-2,4,6-tribromophenyl acrylate copolymer can be generated through this operation.

[0035] 2) The free radicals synthesized by chemical synthesis are generated by the breakage of polypropylene molecular chains, and no initiator needs to be added. The monomer conversion rate is high and there is basically no residue.

[0036] 3) Ultrasonic irradiation helps to disperse multilayer graphene in PP; it also helps to peel off multilayer graphene, thereby making the number of multilayer graphene layers smaller.

[0037] 4) Polypropylene-pentachlorophenyl acrylate copolymer or polypropylene-2,4,6-tribromophenyl acrylate copolymer has a surface active effect, which helps to improve the interface between graphene and PP, thereby facilitating the dispersion of graphene in PP. In addition, the amount of multilayer graphene added is small, so the density of the composite material is basically not affected while improving its mechanical properties and flame retardant properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 Schematic diagram of macromolecular chain breakage and copolymerization in ultrasonic copolymerization for this application. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to specific embodiments.

[0042] A lightweight reinforced flame-retardant polypropylene composite material, comprising the following raw materials in parts by weight:

[0043] 100 parts of polypropylene, 3-4 parts of halogen flame retardant monomer and 0.5-1.5 parts of multilayer graphene.

[0044] The raw material for preparing the lightweight reinforced flame-retardant polypropylene composite material in the present application comprises 100 parts of polypropylene. The present application has no special limitation on the degree of polymerization of the polypropylene, and any degree of polymerization well known to those skilled in the art can be selected.

[0045] Based on the mass of polypropylene, the raw materials for preparing the enhanced flame-retardant polypropylene composite material in the present application contain 3-4 parts of halogen flame retardant monomers. In the present application, the halogen flame retardant monomers are preferably one or a mixture of pentachlorophenyl acrylate and 2,4,6-tribromophenyl acrylate; in the present application, when the halogen flame retardant monomers are two of the above specific options, there is no special limitation on the proportion of each substance, and they can be mixed in any proportion.

[0046] In the present application, the halogen flame retardant monomer can not only play a flame retardant role, but also improve the compatibility of multilayer graphene and polypropylene.

[0047] Based on the mass of polypropylene, the raw material for preparing the lightweight reinforced flame-retardant polypropylene composite material in the present application contains 0.5 to 15 parts of multilayer graphene, preferably 0.7 to 1.3 parts, and more preferably 0.9 to 1.2 parts.

[0048] In some embodiments of the present application, the multilayer graphene has 5 to 10 layers. In the present application, the multilayer graphene can cooperate with the halogen flame retardant to improve the flame retardant properties of the polypropylene composite material, and can also improve the mechanical properties of the polypropylene composite material.

[0049] A method for preparing a lightweight reinforced flame-retardant polypropylene composite material comprises the following steps:

[0050] S1. Take 3-5 parts of polypropylene and dissolve it in a solvent to prepare a polypropylene solution with a mass fraction of 3-5%;

[0051] S2, adding halogen flame retardant monomer and multilayer graphene to the polypropylene solution and mixing evenly;

[0052] S3, introducing an inert gas into the above solution and irradiating it with ultrasound;

[0053] S4, removing the solvent from the recovered solution after irradiation treatment and drying;

[0054] S5. The dried product is mixed with the remaining polypropylene raw material, and then extruded and granulated to obtain the lightweight reinforced flame-retardant polypropylene composite material.

[0055] In some embodiments of the present application, the solvent is decalin.

[0056] In some embodiments of the present application, the inert gas in the above step S3 is a mixture of one or more of nitrogen, helium and argon.

[0057] In some embodiments of the present application, the ultrasonic irradiation temperature in the above step S3 is 20-30°C and the time is 15-20 minutes.

[0058] In some embodiments of the present application, the extrusion granulation temperature in the above step S5 is 165-220°C.

[0059] In some embodiments of the present application, the extrusion granulation is divided into six zones for temperature control, and the temperatures of the six zones are 165-175°C, 188-192°C, 193-198°C, 199-203°C, 205-215°C, and 205-215°C respectively.

[0060] In a specific embodiment of the present application, the temperatures of the six zones may be 170°C, 190°C, 195°C, 200°C, 210°C, and 205°C; 170°C, 190°C, 195°C, 200°C, 210°C, and 210°C; 175°C, 195°C, 195°C, 200°C, 210°C, and 215°C.

[0061] In the present application, the aspect ratio in the extrusion granulation process is 32, and the screw speed is 150-300 r / min, preferably 160-190 r / min, and most preferably 170-180 r / min.

[0062] In the present application, the pelletizing speed in the extrusion granulation process is 300-600 r / min, preferably 350-550 r / min, and most preferably 400-500 r / min.

[0063] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0064] Example 1

[0065] 3 parts by weight of polypropylene are dissolved in an appropriate amount of decalin to prepare a polypropylene solution with a mass fraction of 3%, and then 3 parts by weight of pentachlorophenyl acrylate and 1.2 parts by weight of multilayer graphene are added to the polypropylene solution; the solution is irradiated with ultrasound for 15 minutes under the condition of passing nitrogen gas into the solution, and the reaction temperature is 25°C; then the decalin solvent is removed and recovered and dried.

[0066] The dried product was mixed with 97 parts by weight of polypropylene and extruded into pellets in a twin-screw extruder with a length-to-diameter ratio of 32 and six-zone temperature control. The processing temperatures of zones 1 to 6 were 170° C., 190° C., 195° C., 200° C., 210° C., and 205° C., and the die head temperature was 210° C. The screw speed was 180 r / min and the pelletizing speed was 400 r / min to prepare the lightweight reinforced flame-retardant polypropylene composite material of this embodiment.

[0067] Example 2

[0068] 3 parts by weight of polypropylene are dissolved in an appropriate amount of decalin to prepare a 3% polypropylene solution, and then 3 parts by weight of 2,4,6-tribromophenyl acrylate and 1.2 parts by weight of multilayer graphene are added to the polypropylene solution; the solution is irradiated with ultrasound for 18 minutes under the condition of passing nitrogen gas through the solution, and the reaction temperature is 28° C.; then the decalin solvent is removed and recovered and dried.

[0069] The dried product was mixed with 97 parts by weight of polypropylene and extruded into pellets in a twin-screw extruder with a length-to-diameter ratio of 32 and six-zone temperature control. The processing temperatures of zones 1 to 6 were 170°C, 190°C, 195°C, 200°C, 210°C, 210°C, and the die head temperature was 210°C. The screw speed was 250 r / min and the pelletizing speed was 450 r / min to prepare the lightweight reinforced flame-retardant polypropylene composite material of this embodiment.

[0070] Example 3

[0071] 3 parts by weight of polypropylene are dissolved in an appropriate amount of decalin to prepare a 3% polypropylene solution, and then 4 parts by weight of 2,4,6-tribromophenyl acrylate and 1.2 parts by weight of multilayer graphene are added to the polypropylene solution; the solution is irradiated with ultrasound for 20 minutes under the condition of passing nitrogen gas through the solution, and the reaction temperature is 22° C.; then the decalin solvent is removed and recovered and dried.

[0072] The dried product was mixed with 97 parts by weight of polypropylene and extruded into pellets in a twin-screw extruder with a length-to-diameter ratio of 32 and six-zone temperature control. The processing temperatures of zones 1 to 6 were 175°C, 195°C, 195°C, 200°C, 210°C, 215°C, and the die head temperature was 210°C. The screw speed was 270 r / min and the pelletizing speed was 500 r / min. The lightweight reinforced flame-retardant polypropylene composite material of this embodiment was prepared.

[0073] Example 4

[0074] 4 parts by weight of polypropylene are dissolved in an appropriate amount of decalin to prepare a polypropylene solution with a mass fraction of 4%, and then 3 parts by weight of pentachlorophenyl acrylate and 1.2 parts by weight of multilayer graphene are added to the polypropylene solution; the solution is irradiated with ultrasound for 15 minutes under the condition of passing nitrogen gas into the solution, and the reaction temperature is 25°C; then the decalin solvent is removed and recovered and dried.

[0075] The dried product was mixed with 96 parts by weight of polypropylene and extruded into pellets in a twin-screw extruder with a length-to-diameter ratio of 32 and six-zone temperature control. The processing temperatures of zones 1 to 6 were 170° C., 190° C., 195° C., 200° C., 210° C., and 205° C., and the die head temperature was 210° C. The screw speed was 180 r / min, and the pelletizing speed was 400 r / min, to prepare the lightweight reinforced flame-retardant polypropylene composite material of this embodiment.

[0076] Comparative Example 1

[0077] 100 parts by weight of polypropylene, 3 parts by weight of pentachlorophenyl acrylate and 2 parts by weight of multilayer graphene were premixed, and the premix was subjected to reactive extrusion granulation in a twin-screw extruder with an aspect ratio of 32 and temperature control in six zones, and the processing temperatures of zones 1 to 6 were 170° C., 190° C., 195° C., 200° C., 210° C., 205° C., and the die head temperature was 210° C. The screw speed was 180 r / min and the pelletizing speed was 350 r / min, to prepare the polypropylene composite material of this comparative example.

[0078] Comparative Example 2

[0079] 8 parts by weight of polypropylene are dissolved in an appropriate amount of decalin to prepare a polypropylene solution with a mass fraction of 8%, and then 3 parts by weight of pentachlorophenyl acrylate and 1.2 parts by weight of multilayer graphene are added to the polypropylene solution; the solution is irradiated with ultrasound for 15 minutes under the condition of passing nitrogen gas into the solution, and the reaction temperature is 25°C; then the decalin solvent is removed and recovered and dried.

[0080] The dried product was mixed with 92 parts by weight of polypropylene and extruded into pellets in a twin-screw extruder with a length-to-diameter ratio of 32 and six-zone temperature control. The processing temperatures of zones 1 to 6 were 170° C., 190° C., 195° C., 200° C., 210° C., and 205° C., and the die head temperature was 210° C. The screw speed was 180 r / min, and the pelletizing speed was 400 r / min, to prepare the lightweight reinforced flame-retardant polypropylene composite material of this comparative example.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is that the ultrasonic irradiation reaction temperature in this comparative example is 55°C.

[0083] Comparative Example 4

[0084] The difference between this comparative example and Example 1 is that in the ultrasonic irradiation process in this comparative example, no inert gas is introduced into the solution.

[0085] Experimental example

[0086] The composite material products prepared in Examples 1-4 and Comparative Examples 1-4 of the present application were made into standard strips for testing. The specific testing method is as follows:

[0087] 1. Tensile strength: Tested in accordance with GB / T1040.1.

[0088] 2. Impact strength: Tested in accordance with GB / T1843.

[0089] 3. Flame retardant performance: tested according to UL-94.

[0090] The test results are shown in Table 1.

[0091] Table 1

[0092]

[0093]

[0094] It can be seen from the data in Table 1 that the low solution concentration, low reaction temperature and the presence of chemically inert gas in the ultrasonic mechanical chemical system are all conducive to the reaction; the tensile strength of the reinforced flame-retardant polypropylene composite material is ≥35.4MPa and the impact strength is ≥4.8kJ·m -2 , flame retardant performance reaches V0 level, density is 0.90g.cm -3 . It can be seen that the lightweight reinforced flame-retardant polypropylene composite material prepared in this application significantly improves the flame retardant properties of the composite material while ensuring high mechanical properties, and the density of the material is basically equivalent to that of pure polypropylene. The process method of this application can make the halogen flame retardant and multilayer graphene play a synergistic role, improving the mechanical properties of the composite material and maintaining lightweight while improving the flame retardant properties of the material.

[0095] In summary, the lightweight reinforced flame-retardant polypropylene composite material and the preparation method thereof according to the embodiment of the present application have the following advantages:

[0096] 1) When nitrogen is introduced into the polypropylene solution and then ultrasonically irradiated, the polypropylene macromolecular chain will break to generate active free radicals, which can trigger the monomer to react in an environment with monomers; pentachlorophenyl acrylate and / or 2,4,6-tribromophenyl acrylate are monomers that can undergo free radical polymerization. Thus, polypropylene-pentachlorophenyl acrylate copolymer or polypropylene-2,4,6-tribromophenyl acrylate copolymer can be generated through this operation.

[0097] 2) The free radicals synthesized by chemical synthesis are generated by the breakage of polypropylene molecular chains, and no initiator needs to be added. The monomer conversion rate is high and there is basically no residue.

[0098] 3) Ultrasonic irradiation helps to disperse multilayer graphene in PP; it also helps to peel off multilayer graphene, thereby making the number of multilayer graphene layers smaller.

[0099] 4) Polypropylene-pentachlorophenyl acrylate copolymer or polypropylene-2,4,6-tribromophenyl acrylate copolymer has a surface active effect, which helps to improve the interface between graphene and PP, thereby facilitating the dispersion of graphene in PP. In addition, the amount of multilayer graphene added is small, so the density of the composite material is basically not affected while improving its mechanical properties and flame retardant properties.

[0100] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present application.

Claims

1. A lightweight reinforced flame-retardant polypropylene composite material, characterized in that: The invention is made of the following raw materials in parts by weight: 100 parts of polypropylene, 3-4 parts of halogen flame retardant monomer and 0.5-1.5 parts of multilayer graphene; The preparation method comprises the following steps: S1. Take 3-5 parts of polypropylene and dissolve it in a solvent to prepare a polypropylene solution with a mass fraction of 3-5%; S2, adding halogen flame retardant monomer and multilayer graphene to the polypropylene solution and mixing evenly; S3, introducing an inert gas into the mixed solution of step S2, and irradiating it with ultrasound, wherein the ultrasonic irradiation temperature is 20-30°C; S4, removing the solvent from the recovered mixed solution after irradiation treatment and drying; S5. The dried product is mixed with the remaining polypropylene raw material, and then extruded and granulated to obtain the lightweight reinforced flame-retardant polypropylene composite material.

2. The lightweight reinforced flame-retardant polypropylene composite material according to claim 1, characterized in that: The halogen flame retardant monomer is one of pentachlorophenyl acrylate and 2,4,6-tribromophenyl acrylate or a mixture of the two.

3. The lightweight reinforced flame-retardant polypropylene composite material according to claim 1, characterized in that: The multi-layer graphene has 5 to 10 layers.

4. The lightweight reinforced flame-retardant polypropylene composite material according to claim 1, characterized in that: The solvent is decalin.

5. The lightweight reinforced flame-retardant polypropylene composite material according to claim 1, characterized in that: The inert gas in step S3 is a mixture of one or more of nitrogen, helium and argon.

6. The lightweight reinforced flame-retardant polypropylene composite material according to claim 1, characterized in that: The ultrasonic irradiation time in step S3 is 15-20 minutes.

7. The lightweight reinforced flame-retardant polypropylene composite material according to claim 1, characterized in that: The extrusion granulation temperature in the step S5 is 165-220°C.

8. The lightweight reinforced flame-retardant polypropylene composite material according to claim 7, characterized in that: The extrusion granulation is divided into six zones for temperature control, and the temperatures of the six zones are 165-175°C, 188-192°C, 193-198°C, 199-203°C, 205-215°C and 205-215°C respectively.

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