Microcellular polypropylene composite material and method for preparing the same

Abstract

The application discloses a kind of micro-foamed polypropylene composite material and its preparation method, specifically including polypropylene resin, glycidyl methacrylate (GMA), flame-retardant reinforcing agent, initiator, coupling agent and antioxidant.The composite material is grafted by glycidyl methacrylate (GMA) in polypropylene, and flame-retardant reinforcing agent is added as the reinforcing phase, and the interface bonding degree of flame-retardant reinforcing agent and polypropylene matrix is enhanced by coupling agent, so as to significantly improve the melt strength and mechanical properties of polypropylene, and the polypropylene composite material with light weight, high strength, heat insulation, sound insulation characteristics is obtained by flame-retardant high-performance micro-foaming injection molding process, which can be widely used in automobile, building, packaging and other fields.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite material preparation, specifically relating to a method for preparing a high-strength, flame-retardant, high-performance micro-foamed polypropylene composite material. Background Technology

[0002] Polypropylene (PP) is a common plastic with excellent heat resistance, corrosion resistance, and low cost, making it widely used in industry and daily life. However, PP has low melt strength and poor mechanical properties, limiting its application in some high-performance fields. To improve the performance of PP, researchers have tried various reinforcement methods, such as adding inorganic fillers, organic fibers, and nanoparticles. Among these, basalt fiber, as a new reinforcing material, has advantages such as high strength, high modulus, corrosion resistance, and low cost, and has been widely used in composite materials and other fields.

[0003] Zinc hexahydroxystannate (ZHS) is a novel green flame retardant with advantages such as non-toxicity, stability, high efficiency, and excellent flame retardant properties, and is receiving increasing attention. Studies have shown that ZHS exhibits good flame retardant properties in most polymer materials, such as polyvinyl chloride (PVC), flexible PVC, polyester, and epoxy resin. However, inorganic flame retardants often require large addition amounts to achieve good flame retardant effects and have poor compatibility with polymers. By compounding different flame retardants to produce a synergistic flame retardant effect, not only can costs be reduced, but also superior flame retardant performance can be obtained. Therefore, it is necessary to provide a new high-strength, flame-retardant, high-performance microfoamed composite material and its preparation method to solve the above problems.

[0004] Flame-retardant high-performance microfoamed materials have a distinct skin-core-skin sandwich structure with micron-sized pores inside, which can significantly enhance the material's toughness, energy absorption properties, and sound absorption properties. However, there are several problems with using fiber-reinforced composite materials for flame-retardant high-performance microfoaming. First, the melt strength of polypropylene is insufficient, and it cannot completely encapsulate the foaming agent during pore growth. Second, the interfacial bonding between the fiber and the matrix in fiber-reinforced composite materials is low, causing pores to grow at the fiber-matrix interface, which is difficult to control. This further reduces the interfacial bonding and affects the fiber's reinforcing performance. Summary of the Invention

[0005] The purpose of this invention is to provide a micro-foamed polypropylene composite material and its preparation method. This addresses the problems of low melt strength, poor interfacial bonding after adding reinforcing phases, significant loss of mechanical properties after foaming, and decreased flame retardant properties in existing polypropylene technologies.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] Firstly, the high-strength, flame-retardant, high-performance micro-foamed polypropylene composite material is prepared by reacting raw materials comprising the following components:

[0008] 70-100 parts by weight of polypropylene resin, 1-5 parts by weight of grafting agent, 1-10 parts by weight of flame retardant reinforcing agent, 0.1-1 parts by weight of initiator, 1-5 parts by weight of coupling agent, and 0.0001-0.001 parts by weight of antioxidant.

[0009] Preferably, in the above-mentioned high-strength, flame-retardant, high-performance microfoamed polypropylene, the polypropylene resin is a copolymer polypropylene resin with a molecular weight of 50 × 10⁻⁶. 4 ~55×10 4 The melt index is 1-5 g / 10 min under the conditions of g / mol, molecular weight distribution index of 10-15, and 2.16 kg.

[0010] Preferably, the grafting agent is glycidyl methacrylate (GMA).

[0011] Preferably, the initiator is 2,2,6,6-tetramethylpiperidine oxide (TEMPO).

[0012] The coupling agent described in this invention is an acylhydrazine coupling agent, preferably at least one selected from benzoylhydrazine, methacrylhydrazine, and allylhydrazine. More preferably, the coupling agent is methacrylhydrazine.

[0013] The antioxidants of this invention include primary antioxidants and secondary antioxidants; the primary antioxidant is a hindered primary antioxidant, preferably one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenylmethyl)benzene; the secondary antioxidant is a phosphite secondary antioxidant, preferably one or more of tris[2,4-di-tert-butylphenyl] phosphite, tris(nonylphenyl) phosphite, and tetrakis(2,4-di-tert-butylphenyl-4-4'-biphenyl)-bisphosphate.

[0014] Preferably, the primary antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (1010), and the secondary antioxidant is tris[2,4-di-tert-butylphenyl] phosphite (168).

[0015] The preparation method of the flame retardant reinforcing agent of the present invention includes the following steps:

[0016] 1) Basalt fiber pretreatment: Take 50g-80g of basalt fiber in a beaker, add 150ml-230ml of anhydrous ethanol, ball mill for 8-15 hours, sonicate, filter, and dry for later use;

[0017] 2) Preparation of modified basalt: Take 80ml to 180ml of anhydrous ethanol and deionized water in a volume ratio of 9:1 and mix them evenly in a three-necked flask. Add 0.5ml to 3.5ml of titanate coupling agent HY-201 and ultrasonically disperse for 60 to 90 minutes. Add the pretreated basalt fiber to the flask and stir the reaction at 80℃ for 4 to 6 hours. After washing and drying, the modified basalt fiber is obtained.

[0018] 3) Preparation of zinc hexahydroxystannate modified basalt fiber composite material: Take 50g-80g of the modified basalt fiber prepared in step 2) and dissolve it in 200ml-300ml of 50%-70% ethanol aqueous solution. Add 3g-8g of zinc hexahydroxystannate and stir vigorously at 85℃ for 4h-6h. Filter, wash and dry to obtain zinc hexahydroxystannate modified basalt fiber composite material.

[0019] Secondly, this invention provides a method for preparing high-strength, flame-retardant, high-performance micro-foamed polypropylene composite materials, comprising the following steps: according to a ratio,

[0020] a) Polypropylene resin, GMA and initiator are heated and melted in a twin-screw extruder at a temperature controlled at 200℃~240℃ to carry out in-situ grafting reaction.

[0021] b) The product obtained in step a), coupling agent, antioxidant, and flame retardant reinforcing agent are mixed evenly in a high-speed mixer and then added to the hopper of a twin-screw extruder. Extrusion granulation is completed in the twin-screw extruder to obtain a polypropylene composite material with high melt strength.

[0022] c) Add the product from step b) into the injection molding machine barrel and use supercritical nitrogen to perform flame-retardant high-performance micro-foaming injection molding to obtain flame-retardant high-performance micro-foamed products.

[0023] Preferably, the basalt fiber is a short fiber with a diameter of 10μm to 12.7μm and an average length of 4mm to 6mm.

[0024] The beneficial effects of this invention are as follows:

[0025] 1) This invention introduces zinc hexahydroxystannate-modified basalt fiber composite material into micro-foamed polypropylene products, a simple and convenient method. Basalt fiber, as an inorganic material, has poor compatibility with polymers such as polypropylene. Modifying basalt fiber with the titanate coupling agent HY-201 effectively improves the fiber's surface structure. The modified basalt surface is attached with lipophilic groups, enhancing its compatibility with polymers and thus providing better reinforcement.

[0026] 2) Zinc hexahydroxystannate (HHSS) can not only form a coupling reaction with the titanate coupling agent HY-201 on modified basalt fibers through its active hydroxyl groups, but also combine with the phosphate ester groups generated after the hydrolysis of the pyrophosphate groups of HY-201. This allows HHSS to be chemically coated onto the modified basalt fibers, forming a novel composite material. When HHSS decomposes thermally, it releases water molecules to absorb heat and dilute the oxygen concentration. Simultaneously, the Zn²⁺ and Sn⁴⁺ in HHSS promote the cross-linking of the polyene structure in polypropylene during combustion, thus forming a char layer. This, together with the basalt fibers, forms a dense heat-insulating layer, significantly improving the flame-retardant effect compared to adding HHSS alone. Furthermore, HY-201 contains numerous long chains, improving compatibility with polymer foams, refining processing technology, and enhancing the mechanical properties of the composite material.

[0027] 3) Glycidyl methacrylate (GMA) is a vinyl monomer with three active reactive sites that can chemically react with the PP matrix, thereby improving the interfacial bonding between PP and the reinforcing phase. This invention involves grafting GMA onto the polypropylene backbone to prepare polypropylene with long branches, resulting in polypropylene with higher melt strength and easier foaming control. Compared to methods involving adjusting the catalyst at the synthesis end, this method for preparing long-branched polypropylene is simpler, lower in cost, and allows for continuous production.

[0028] 4) The high strength of the above-mentioned high-strength, flame-retardant, high-performance micro-foamed polypropylene composite material is obtained through the synergistic effect of zinc hexahydroxystannate modified basalt fiber composite material and in-situ grafting modification. Its cantilever beam notched impact strength at room temperature is 40-50 kJ / m. 2 Compared to unmodified polypropylene, this process can improve performance by up to 200%. The high melt strength, flame-retardant, high-performance microcellular polypropylene composite material prepared by this process can be produced continuously, with low cost and excellent performance. Detailed Implementation

[0029] The present invention will be further illustrated by the following embodiments, but it should be understood that these embodiments should not be used to limit the present invention.

[0030] Example 1

[0031] The raw materials for the high-strength, flame-retardant, high-performance microfoamed polypropylene composite material of this embodiment include the following parts by weight: 90 parts polypropylene resin (EP300H, Wanhua Chemical), 1 part 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 1 part glycidyl methacrylate (GMA), 3 parts methacryloyl hydrazide, 5 parts flame retardant reinforcing agent, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0032] Its preparation method includes the following steps:

[0033] 1) Basalt fiber pretreatment: Take 50g of basalt fiber in a beaker, add 150ml of anhydrous ethanol and ball mill for 12h, sonicate, filter and dry for later use;

[0034] 2) Preparation of modified basalt: Take 100 ml of anhydrous ethanol and deionized water in a volume ratio of 9:1 and mix them evenly in a three-necked flask. Add 1 ml of titanate coupling agent HY-201 and ultrasonically disperse for 60 min. Take the pretreated basalt fiber and add it to the flask. Stir and react at 80℃ for 4 h. After washing and drying, the modified basalt fiber is obtained.

[0035] 3) Preparation of zinc hexahydroxystannate modified basalt fiber composite material: Take 50g of the modified basalt fiber prepared in step 2) and dissolve it in 200ml of 50% ethanol aqueous solution. Add 5g of zinc hexahydroxystannate and stir vigorously at 85℃ for 4h. Filter, wash and dry to obtain zinc hexahydroxystannate modified basalt fiber composite material.

[0036] 4) Mix polypropylene particles, GMA, and initiator (TEMPO), and heat and melt the mixed raw materials in a twin-screw extruder at a temperature controlled at 220°C to carry out in-situ grafting reaction.

[0037] 5) After the grafted modified polypropylene, coupling agent, antioxidant, and flame retardant reinforcing agent are mixed evenly in a high-speed mixer, they are added to the hopper of a twin-screw extruder and extruded and granulated in the twin-screw extruder to obtain a polypropylene composite material with high melt strength.

[0038] 6) The high melt strength polypropylene composite material prepared above is added into the injection molding machine barrel. By controlling the supercritical nitrogen gas intake, flame-retardant high-performance micro-foaming injection molding is carried out to finally obtain flame-retardant high-performance micro-foamed products.

[0039] Example 2

[0040] The raw materials for the high-strength, flame-retardant, high-performance microfoamed polypropylene composite material of this embodiment include the following parts by weight: 91 parts polypropylene resin (EP300H, Wanhua Chemical), 0.5 parts 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 3 parts glycidyl methacrylate (GMA), 2.5 parts methacryloyl hydrazide, 3 parts flame retardant reinforcing agent, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0041] The preparation method is the same as in Example 1.

[0042] Example 3

[0043] The raw materials for the high-strength, flame-retardant, high-performance microfoamed polypropylene composite material of this embodiment include the following parts by weight: 87 parts polypropylene resin (EP300H, Wanhua Chemical), 0.5 parts 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 5 parts glycidyl methacrylate (GMA), 2.5 parts methacryloyl hydrazide, 5 parts flame retardant reinforcing agent, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0044] The preparation method is the same as in Example 1.

[0045] Comparative Example 1

[0046] The raw materials for this comparative example of high-strength, flame-retardant, high-performance microfoamed polypropylene composite material include the following parts by weight: 85 parts polypropylene resin (EP300H, Wanhua Chemical), 0.5 parts 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 5 parts glycidyl methacrylate (GMA), 2.5 parts methacryloyl hydrazide, 10 parts basalt fiber, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0047] Its preparation method includes the following steps:

[0048] (1) Mix polypropylene particles, grafting agent and initiator (TEMPO), and heat and melt the mixed raw materials in a twin-screw extruder at a temperature of 220°C to carry out in-situ grafting reaction.

[0049] (2) The grafted modified polypropylene particles, coupling agent, basalt fiber and antioxidant are mixed evenly in a high-speed mixer and then added to the hopper of a twin-screw extruder. The extrusion granulation is completed in the twin-screw extruder to obtain a polypropylene composite material with high melt strength.

[0050] (3) The high melt strength polypropylene composite material prepared above is added into the injection molding machine barrel, and micro-foaming injection molding is carried out by controlling the supercritical nitrogen gas intake, and finally micro-foamed products are obtained.

[0051] Comparative Example 2

[0052] The raw materials for this comparative example of high-strength, flame-retardant, high-performance microfoamed polypropylene composite material include the following parts by weight: 91 parts polypropylene resin (EP300H, Wanhua Chemical), 1 part 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 3 parts methacryloylhydrazine, 5 parts flame-retardant reinforcing agent, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl]phosphite.

[0053] Its preparation method includes the following steps:

[0054] (1) Polypropylene particles, flame retardant reinforcing agent, initiator, coupling agent and antioxidant are mixed evenly in a high-speed mixer and then added to the hopper of a twin-screw extruder. Extrusion granulation is completed in the twin-screw extruder to obtain a polypropylene composite material with high melt strength.

[0055] (2) The high melt strength polypropylene composite material prepared above is added into the injection molding machine barrel. By controlling the supercritical nitrogen gas intake, flame-retardant high performance micro-foaming injection molding is carried out to finally obtain micro-foamed products.

[0056] Comparative Example 3

[0057] The raw materials for this comparative example of high-strength, flame-retardant, high-performance microfoamed polypropylene composite material include the following parts by weight: 90 parts polypropylene resin (EP300H, Wanhua Chemical), 1 part 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 1 part glycidyl methacrylate (GMA), 3 parts methacryloyl hydrazide, 5 parts zinc hexahydroxystannate, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0058] Its preparation method includes the following steps:

[0059] (1) Mix polypropylene particles, grafting agent (GMA), initiator (TEMPO), flame retardant, coupling agent and antioxidant. Heat and melt the mixed raw materials in a twin-screw extruder at a temperature of 220°C to carry out in-situ grafting reaction.

[0060] (2) The high melt strength polypropylene composite material prepared above is added into the injection molding machine barrel. By controlling the supercritical nitrogen gas intake, flame-retardant high performance micro-foaming injection molding is carried out to finally obtain micro-foamed products.

[0061] Comparative Example 4

[0062] The raw materials for this comparative example of high-strength, flame-retardant, high-performance microfoamed polypropylene composite material include the following parts by weight: 91 parts polypropylene resin (EP300H, Wanhua Chemical), 0.5 parts 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 3 parts glycidyl methacrylate (GMA), 2.5 parts methacryloyl hydrazide, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0063] Its preparation method includes the following steps:

[0064] (1) Mix polypropylene particles, grafting agent (GMA), initiator (TEMPO), coupling agent and antioxidant. Heat and melt the mixed raw materials in a twin-screw extruder at a temperature of 220°C to carry out in-situ grafting reaction.

[0065] (2) The high melt strength polypropylene composite material prepared above is added into the injection molding machine barrel. By controlling the supercritical nitrogen gas intake, flame-retardant high performance micro-foaming injection molding is carried out to finally obtain micro-foamed products.

[0066] Comparative Example 5

[0067] The raw materials for this comparative example of high-strength, flame-retardant, high-performance microfoamed polypropylene composite material include the following parts by weight: 90 parts polypropylene resin (EP300H, Wanhua Chemical), 1 part 2,2,6,6-tetramethylpiperidine oxide (TEMPO), 1 part glycidyl methacrylate (GMA), 5 parts flame retardant reinforcing agent, 0.0005 parts pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and 0.0005 parts tris[2,4-di-tert-butylphenyl] phosphite.

[0068] Its preparation method includes the following steps:

[0069] (1) Mix polypropylene particles, grafting agent (GMA), initiator (TEMPO), flame retardant reinforcing agent and antioxidant. Heat and melt the mixed raw materials in a twin-screw extruder at a temperature of 220°C to carry out in-situ grafting reaction.

[0070] (2) The high melt strength polypropylene composite material prepared above is added into the injection molding machine barrel. By controlling the supercritical nitrogen gas intake, flame-retardant high performance micro-foaming injection molding is carried out to finally obtain micro-foamed products.

[0071] The specific test results are shown in Table 1.

[0072] Table 1 Performance test results of Examples 1-3 and Comparative Examples 1-5

[0073]

[0074]

[0075] As shown in Table 1, comparing the test data of Examples 1-3 and Comparative Examples 1-5, it can be seen that the comprehensive performance of the micro-foamed polypropylene composite material with added flame retardant reinforcing agent is significantly improved, especially the notched impact strength of simply supported beams, flexural modulus, and cell density. This is because the cells uniformly dispersed in the flame retardant high-performance micro-foamed polypropylene resin act as stress concentration points in the matrix, absorbing a large amount of energy, thereby hindering crack development and improving the impact resistance of the material, while also enhancing the flame retardant performance of the foam material. Furthermore, the in-situ grafting extends the branched structure and enhances the interfacial strength between the material and the fiber, increasing the material's ability to encapsulate bubbles during the foaming process and reducing the cell size. At the same time, the fiber, as a reinforcing phase, provides a large number of nucleation sites for bubbles, increasing the cell density.

[0076] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A microfoamed polypropylene composite material, prepared by reaction from raw materials comprising the following components: 70-100 parts by weight of polypropylene resin, 1-5 parts by weight of glycidyl methacrylate, 1-10 parts by weight of flame retardant reinforcing agent, 0.1-1 parts by weight of initiator, 1-5 parts by weight of coupling agent, and 0.0001-0.001 parts by weight of antioxidant. The preparation method of the flame retardant reinforcing agent includes the following steps: 1) Basalt fiber pretreatment: Take 50g~80g of basalt fiber in a beaker, add 150ml~230ml of anhydrous ethanol, ball mill for 8~15h, sonicate, filter, and dry for later use; 2) Preparation of modified basalt: Take 80ml~180ml of anhydrous ethanol and deionized water in a volume ratio of 9:1 and mix them evenly in a three-necked flask. Add 0.5ml~3.5ml of titanate coupling agent HY-201 and ultrasonically disperse for 60~90min. Add the pretreated basalt fiber to the flask and stir the reaction at 80℃ for 4h~6h. After washing and drying, the modified basalt fiber is obtained. 3) Preparation of zinc hexahydroxystannate modified basalt fiber composite material: Take 50g~80g of the modified basalt fiber prepared in step 2) and dissolve it in 200ml~300ml of 50%~70% ethanol aqueous solution, add 3g~8g of zinc hexahydroxystannate, stir vigorously at 85℃ for 4h~6h, filter, wash and dry to obtain zinc hexahydroxystannate modified basalt fiber composite material.

2. The composite material according to claim 1, characterized in that, The polypropylene resin is a copolymer polypropylene resin with a molecular weight of 50 × 10⁻⁶. 4 ~55×10 4 The melt index is 1-5 g / 10 min under the conditions of g / mol, molecular weight distribution index of 10-15, and 2.16 kg.

3. The composite material according to claim 1, characterized in that, The basalt fibers are short fibers with a diameter of 10μm to 12.7μm and an average length of 4mm to 6mm.

4. The composite material according to claim 1, characterized in that, The initiator is 2,2,6,6-tetramethylpiperidine oxide.

5. The composite material according to claim 1, characterized in that, The coupling agent is an acylhydrazine coupling agent.

6. The composite material according to claim 1, characterized in that, The coupling agent is at least one of benzoyl hydrazine, methacryl hydrazine, and allyl hydrazine.

7. The composite material according to claim 1, characterized in that, The antioxidants include primary antioxidants and secondary antioxidants; the primary antioxidants are hindered primary antioxidants, and the secondary antioxidants are phosphite secondary antioxidants.

8. The composite material according to claim 7, characterized in that, The primary antioxidant is one or more of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenylmethyl)benzene; the secondary antioxidant is one or more of tris[2,4-di-tert-butylphenyl] phosphite, tris(nonylphenyl) phosphite, and tetrakis(2,4-di-tert-butylphenyl-4-4'-biphenyl)-bisphosphate.

9. A method for preparing the microfoamed polypropylene composite material of claim 1, comprising the following steps: According to proportion, a) Polypropylene resin, GMA and initiator are heated and melted in a twin-screw extruder at a temperature controlled at 200℃~240℃ to carry out in-situ grafting reaction; b) The product obtained in step a), coupling agent, antioxidant, and flame retardant reinforcing agent are mixed evenly in a high-speed mixer and then added to the hopper of a twin-screw extruder. Extrusion granulation is completed in the twin-screw extruder to obtain a polypropylene composite material with high melt strength. c) Add the product from step b) into the injection molding machine barrel and use supercritical nitrogen to perform flame-retardant high-performance micro-foaming injection molding to obtain flame-retardant high-performance micro-foamed products.

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