High-melt-strength flame-retardant polypropylene composite material and preparation method thereof

Abstract

The invention discloses a flame-retardant polypropylene composite material with high melt strength and a preparation method thereof, and the polypropylene composite material with a thermally reversible branched structure is directly prepared by adding a composition of polypropylene, a branched component, a free radical initiator, a flame retardant and the like into an extruder. The polypropylene composite material not only has high melt strength, but also has excellent processability and flame retardant property, and the preparation method is simple and easy to implement.

Description

Technical Field

[0001] The invention relates to a method for preparing a high melt strength flame retardant polypropylene composite material, in particular to the preparation and application of a polypropylene composite material with low flame retardant effect and high melt strength. Background Art

[0002] Polypropylene (PP) is the fastest growing variety among thermoplastic resins, and its good performance-price ratio determines its broad application areas. High melt strength polypropylene (HMSPP) with excellent performance can overcome the defects of unstable processing performance in thermoforming, blow molding and foaming molding caused by poor anti-sag of ordinary polypropylene, and has excellent thermal stability and high temperature dimensional stability, high toughness and tensile strength, superior microwave adaptability, good environmental effects and easy recycling. It occupies an important position in high-end special polypropylene materials.

[0003] The improvement of the melt strength of polypropylene is mainly achieved by introducing long-chain branching structures into polypropylene molecules to increase chain entanglement, thereby enhancing the interaction between molecular chains in the molten state. At present, the mature HMSPP preparation technologies in the world mainly include radiation irradiation, catalytic polymerization and extrusion modification. Although there are many HMSPP preparation technologies at home and abroad, products with excellent performance are mainly obtained by radiation irradiation or metallocene catalytic polymerization. Both methods have problems such as high energy consumption, high cost, complex process, and difficulty in large-scale production, resulting in expensive products. The reactive extrusion method is a free radical reaction between polypropylene in a molten state and a free radical initiator and a multifunctional monomer in a screw extruder. Due to its simple operation, this method is currently the most widely used method for preparing HMSPP, but the main problem is that the multifunctional monomer is very easy to cause the product to produce gel, and strict process control is required to achieve stable product performance.

[0004] Another difficulty in the application of polypropylene is that the polypropylene oxygen index is low, only about 18%. Polypropylene is a flammable substance, which generates a lot of heat when burning, accompanied by molten droplets, and is very easy to spread flames. Therefore, polypropylene needs to be flame-retardant modified to meet application needs, especially for products exported to the European Union, where end users often require halogen-free flame retardancy. In addition, unlike general flame-retardant polypropylene products, whether the HMSPP resin after adding flame retardants still has sufficiently high melt strength and processing performance, and whether it has good flame retardant properties, are all issues that need to be paid attention to.

[0005] Inorganic flame retardants are non-toxic and harmless flame retardants with relatively ideal application and development effects at present. They mainly include aluminum hydroxide and magnesium hydroxide. Among them, magnesium hydroxide has more prominent advantages. It is significantly better than aluminum hydroxide in terms of smoke suppression performance and thermal stability. In addition, Mg(OH)2 has a higher thermal decomposition temperature. It needs to absorb a large amount of heat during the heating process, which can reduce the combustion temperature of the polymer material surface; thermal decomposition will release a large amount of water, which can dilute the air on the surface of the polymer material and slow down the combustion rate of the polymer; the decomposition to generate MgO covering the surface of the polymer material can also isolate the air and play a role in heat insulation, thereby preventing the combustion of polymer materials, and MgO itself is a good refractory material. In addition, MgO has a relatively large specific surface area, which can absorb a large amount of smoke and reduce smoke emissions, and water vapor can also dilute the smoke to play a role in smoke elimination. However, Mg(OH)2 has strong hydrophilicity, positive charge on the surface, and high surface energy of the crystals, which makes it easy for the particles to agglomerate and have poor dispersibility, affecting its bonding and adhesion in polymer materials. At the same time, Mg(OH)2 has strong hydrophilicity, poor compatibility with most hydrophobic polymer materials, and weak interface bonding, resulting in low flame retardant efficiency after compounding. How to achieve uniform dispersion of nanoscale Mg(OH)2 in polypropylene has always been a difficult problem that has troubled people. At the same time, how to generate strong interface interactions between the chemically inert polypropylene matrix and Mg(OH)2 is also the key to determining whether Mg(OH)2 can effectively enhance polypropylene. The present invention proposes to use thermally reversible dynamic covalent bonds to realize the long-chain branching structure design of polypropylene, and introduce the above-mentioned thermally reversible dynamic covalent bonds into polypropylene resin in combination with a simple reaction extrusion method, thereby directly realizing the preparation of HMSPP in the screw processing process of polypropylene resin. The addition of a grafting monomer containing a carboxyl group and capable of forming a thermally reversible dynamic covalent bond can form a coordination effect with the modified Mg(OH)2 to promote the dispersion of the flame retardant. The polypropylene composite material prepared by the method has the characteristics of high melt strength, good processing performance and excellent flame retardant performance. Summary of the invention

[0006] The object of the present invention is to provide a high melt strength flame retardant polypropylene composite material and a preparation method thereof. In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] A method for preparing a low-shrinkage flame-retardant high-melt-strength polypropylene composite material in an extruder, the method comprising mixing the following components in an extruder: a polypropylene resin A, a component B represented by the following formula (I), a component C represented by the following formula (II), a component D represented by the following formula (III), a free radical initiator E, a free radical stabilizer F, and a flame retardant G, collecting the mixture from the extruder and cooling the mixture to obtain a polypropylene composite material;

[0008]

[0009] In formula (I), R 1 for R 2 is O or S; in formula (II), R 3 C1~C6 straight chain alkane or C6~C 14 An aromatic group; in formula (III), R 4 C1~C6 straight chain alkane or C6~C 14 Aromatic base.

[0010] Furthermore, the polypropylene resin A is isotactic polypropylene.

[0011] Furthermore, the component B is ethylene, styrene or methacrylate containing furanyl or thienyl; the added mass of the component B is 0.01% to 5% of the mass of the polypropylene resin A, preferably 0.1% to 2%.

[0012] Further, wherein the component C is a bismaleimide compound, R 3 It is an aliphatic group or an aromatic group, preferably p-phenyl, p-diphenylmethane, n-butyl, n-hexyl; the added mass of component C is 0.01% to 5% of the mass of the polypropylene resin A, preferably 0.05% to 2%.

[0013] Further, wherein the component D is a carboxylated 3-maleimide compound, R 4 It is an aliphatic group or an aromatic group, preferably p-phenyl, p-diphenylmethane, n-butyl, n-hexyl; the added mass of the component D is 0.01% to 5% of the mass of the polypropylene resin A, preferably 0.05% to 2%.

[0014] Furthermore, the free radical initiator E is a thermal decomposition free radical initiator, an organic peroxide or an azo initiator, preferably an alkyl peroxide, a hydroperoxide, an acyl peroxide, or a peroxycarbonate; the added mass of the free radical initiator E is 0.01% to 1% of the mass of the polypropylene resin A, preferably 0.05% to 0.5%.

[0015] Furthermore, the free radical stabilizer component F is selected from at least one of hindered phenol antioxidants, phosphite antioxidants, or alkyl ester antioxidants; the added mass of component F is 0.05% to 1% of the mass of the polypropylene resin A, preferably 0.1% to 0.5%.

[0016] Furthermore, the flame retardant component G is modified magnesium hydroxide; the added mass of the component G is 1 to 100% of the mass of the polypropylene resin A, preferably 1% to 50%.

[0017] Furthermore, the flame retardant component G is modified magnesium hydroxide, and its preparation method includes the following steps: (1) magnesium hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) are placed in a vacuum drying oven for drying at a temperature of 80°C for 8 hours. (2) DOPO (D) is modified by a vinyl silane coupling agent (Z), and the reaction conditions are bulk polymerization, temperature of 140°C, and time of 5 hours. The vinyl silane coupling agent is 0.01% to 80% of the molar mass of DOPO, preferably 10% to 50%. (3) DOPO (ZD) modified by the coupling agent is modified with Mg(OH)2, and the reaction medium is ethanol, the temperature is 80°C, and the time is 6 hours. ZD is 0.01% to 80% of the mass of Mg(OH)2, preferably 10% to 50%. (4) The final modified Mg(OH)2 is placed in a vacuum drying oven for drying at a temperature of 60°C for 8 hours.

[0018] Furthermore, the vinyl silane coupling agent includes but is not limited to 3-(methacryloyloxy)propyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltrimethoxyethoxysilane, vinyltri-tert-butoxysilane and the like.

[0019] Further, the extruder is a twin-screw extruder having at least six zones, wherein the temperature of the first zone is higher than 90°C, the temperature of the second zone is higher than 150°C, the temperature of the third zone is higher than 180°C, the temperature of any subsequent zone is higher than 190°C, wherein the temperature of any zone is lower than 230°C, and wherein the residence time of the polypropylene resin A in the twin-screw extruder is 30 seconds to 300 seconds.

[0020] Furthermore, the components A to G are continuously fed into the extruder; preferably, the components A, E and F are mixed and continuously fed into the extruder, and the components B, C and G are mixed and continuously fed into the third zone or the fourth zone of the extruder.

[0021] Furthermore, the high melt strength flame-retardant polypropylene composite material is used for polypropylene molded products.

[0022] The present invention has the following beneficial effects:

[0023] (1) The above-mentioned thermally reversible dynamic covalent bonds are introduced into the polypropylene resin, thereby realizing the preparation of HMSPP during the screw processing process. Since the covalent bonds formed by the DA reaction can be dissociated after heating, it will not affect the melt processing properties of the polypropylene itself, so that the composite material can be molded under the conventional processing conditions of polypropylene.

[0024] (2) Compared with pure magnesium hydroxide, the modified magnesium hydroxide flame retardant designed by the present invention exhibits excellent flame retardant properties at a low filling amount.

[0025] (3) The modified magnesium hydroxide flame retardant in the present invention can coordinate with the carboxyl-containing graft monomer with dynamic covalent bond function to form a cross-linked network and construct a stable composite material structure. It can improve the compatibility between the flame retardant and polypropylene and solve the problem of weak interfacial force between PP and the flame retardant. It helps to improve the melt strength of polypropylene, strengthen the dispersion of the flame retardant, improve the flame retardant performance, and also improve the mechanical properties of the polypropylene material.

[0026] (4) The components of the present invention are carefully designed and compounded in a specific ratio. The obtained polypropylene composite material not only has a good flame retardant effect, but also has a melt strength greater than 10 cN, and has more superior comprehensive performance. DETAILED DESCRIPTION

[0027] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0028] Component B:

[0029] Component B having a structure shown in formula (I) includes but is not limited to the following structure:

[0030]

[0031] Component C:

[0032] Component C having a structure shown in formula (II) includes but is not limited to the following structures:

[0033]

[0034] Component D:

[0035] Component D having a structure shown in formula (III) includes but is not limited to the following structures:

[0036]

[0037] Component G:

[0038] The preparation method of modified magnesium hydroxide comprises the following steps: (1) placing magnesium hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO in a vacuum drying oven for drying at a temperature of 80°C for 8 hours; (2) modifying DOPO with 3-(methacryloyloxy)propyltrimethoxysilane, the reaction conditions being bulk polymerization, a temperature of 140°C, and a time of 5 hours; the amount of vinyl silane coupling agent used is 10% of the molar amount of DOPO; (3) modifying DOPO modified by the coupling agent with Mg(OH)2, the reaction medium being ethanol, a temperature of 80°C, and a time of 6 hours; the amount of DOPO modified by the coupling agent used is 50% of the mass of Mg(OH)2; and (4) drying the final modified Mg(OH)2 in a vacuum drying oven at a temperature of 60°C for 8 hours.

[0039] Example 1

[0040] In parts by mass, 100 parts of polypropylene (melt index MFR=3g / 10min, 230°C), 0.2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), 0.2 parts of antioxidant 168 (radical stabilizer), 0.8 parts of component B1 of the present invention, 0.2 parts of component C1 of the present invention, 0.2 parts of component D1 of the present invention, and 30 parts of component G of the present invention are mixed, and then the mixture is added to a twin-screw extruder for melting. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 90s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0041] Example 2

[0042] In parts by mass, 100 parts of polypropylene (melt index MFR=3g / 10min, 230°C), 0.3 parts of diisopropylbenzene peroxide (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), and 0.2 parts of antioxidant 168 (radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 0.8 parts of component B2 of the present invention, 0.2 parts of component C1 of the present invention, 0.2 parts of component D1 of the present invention, and 30 parts of component G of the present invention are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0043] Example 3

[0044] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), and 0.2 parts of antioxidant 168 (radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 0.8 parts of component B3 of the present invention, 0.13 parts of component C2 of the present invention, 0.2 parts of component D1 of the present invention, and 30 parts of component G of the present invention are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0045] Example 4

[0046] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.3 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), and 0.2 parts of antioxidant 168 (radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 1 part of component B3 of the present invention, 0.25 parts of component C2 of the present invention, 0.2 parts of component D1 of the present invention, and 30 parts of component G of the present invention are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0047] Example 5

[0048] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.3 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), and 0.2 parts of antioxidant 168 (radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 2 parts of component B3 of the present invention, 0.5 parts of component C2 of the present invention, 0.5 parts of component D1 of the present invention, and 30 parts of component G of the present invention are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0049] Example 6

[0050] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.3 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), and 0.2 parts of antioxidant 168 (radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 4 parts of component B3 of the present invention, 1 part of component C2 of the present invention, 0.2 parts of component D1 of the present invention, and 30 parts of component G of the present invention are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0051] Comparative Example 1

[0052] In parts by mass, 100 parts of polypropylene (melt index MFR=3g / 10min, 230°C), 0.1 parts of antioxidant 1010 (free radical stabilizer), and 0.2 parts of antioxidant 168 (free radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled in a circulating water bath and pelletized to obtain the final product.

[0053] Comparative Example 2

[0054] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (free radical initiator), 0.1 parts of antioxidant 1010 (free radical stabilizer), and 0.2 parts of antioxidant 168 (free radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 1 part of component B3 of the present invention is added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0055] Comparative Example 3

[0056] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.15 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (free radical initiator), 0.1 parts of antioxidant 1010 (free radical stabilizer), 0.2 parts of antioxidant 168 (free radical stabilizer), and 1 part of divinylbenzene are mixed, and then the mixture is added to a twin-screw extruder for melting. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled in a circulating water bath and pelletized to obtain the final product.

[0057] Comparative Example 4

[0058] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.3 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (radical initiator), 0.1 parts of antioxidant 1010 (radical stabilizer), and 0.2 parts of antioxidant 168 (radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 4 parts of component B3 of the present invention, 1 part of component C2 of the present invention, 0.2 parts of component D1 of the present invention, and 30 parts of magnesium hydroxide are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0059] Comparative Example 5

[0060] In parts by mass, 100 parts of polypropylene (melt index MFR = 3g / 10min, 230°C), 0.2 parts of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (free radical initiator), 0.1 parts of antioxidant 1010 (free radical stabilizer), and 0.2 parts of antioxidant 168 (free radical stabilizer) are mixed, and then the mixture is added to a twin-screw extruder for melting; 2 parts of component B3 of the present invention, 1 part of component C2 of the present invention, and 30 parts of component G of the present invention are mixed and added to the third zone of the extruder from the side feed port. The temperature of the first zone of the extruder is 100°C, the temperature of the second zone is 160°C, the temperature of the third zone is 190°C, the temperature of the fourth and fifth zones is 200°C, the temperature of the sixth zone is 190°C, the residence time is 180s, and the extruded product is cooled and pelletized in a circulating water bath to obtain the final product.

[0061] The performance tests of the polypropylene composite materials prepared in the above examples and the polypropylene composite materials prepared in the comparative examples are listed in the following Table 1.

[0062] Table 1 Properties of polypropylene composite materials

[0063]

[0064]

[0065] The high melt strength polypropylene prepared by the present invention can generate a long chain branching structure in the polypropylene because the component C therein can undergo a [4+2] cycloaddition reaction (i.e., Diels-Alder reaction) with the component B connected to the polypropylene molecular chain, thereby improving the melt strength of the polypropylene. In addition, the component D can undergo a [4+2] cycloaddition reaction (i.e., Diels-Alder reaction) with the component B connected to the polypropylene molecular chain, and Mg 2+ -The coordination between the carboxyl groups forms a cross-linked network structure, which further improves the melt strength of the composite material.

[0066] The polypropylene prepared by the present invention has a melt strength of more than 10 cN at 180°C, and the melt strength increases with the increase of the degree of branching, which is significantly higher than that of ordinary polypropylene (Comparative Example 1) and polypropylene with only component B added but not component C (Comparative Example 2). This shows that the Diels-Alder reaction between component C and component B is the key to generating a long-chain branched structure and thus improving the melt strength of polypropylene. The melt strength of polypropylene with only components B and C added but not component D (Comparative Example 5) is significantly lower than that of Example 6, indicating that the double cross-linked network plays a key role. And the effect of the modified flame retardant (Examples 1-6) is significantly better than that of magnesium hydroxide (Comparative Example 4).

[0067] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a high melt strength flame-retardant polypropylene composite material, characterized in that: The method comprises mixing the following components in an extruder: a polypropylene resin A, a component B represented by the following formula (I), a component C represented by the following formula (II), a component D represented by the following formula (III), a free radical initiator E, a free radical stabilizer F, and a flame retardant G, and collecting and cooling the mixture from the extruder to obtain a polypropylene composite material; In formula (I), R 1 for or or , R 2 is O or S; in formula (II), R 3 It is a C1~C6 straight chain alkane or C6~C 14 An aromatic group; in formula (III), R 4 It is a C1~C6 straight chain alkane or C6~C 14 Aromatic base.

2. The method according to claim 1, characterized in that The polypropylene resin A is isotactic polypropylene.

3. The method according to claim 1, characterized in that The component B is ethylene, styrene or methacrylate containing furanyl or thienyl; the added mass of the component B is 0.01% to 5% of the mass of the polypropylene resin A.

4. The method according to claim 1, characterized in that: The component C is a bismaleimide compound, R 3 It is p-phenyl, p-diphenylmethane, n-butyl, and n-hexyl; the added mass of component C is 0.01% to 5% of the mass of the polypropylene resin A.

5. The method according to claim 1, characterized in that The component D is a carboxylated 3-maleimide compound, R 4 It is p-phenyl, p-diphenylmethane, n-butyl, and n-hexyl; the added mass of component D is 0.01% to 5% of the mass of the polypropylene resin A.

6. The method according to claim 1, characterized in that The free radical initiator E is a thermal decomposition free radical initiator, an organic peroxide or an azo initiator; the added mass of the free radical initiator E is 0.01% to 1% of the mass of the polypropylene resin A.

7. The method according to claim 1, characterized in that The free radical stabilizer F is selected from at least one of hindered phenol antioxidants, phosphite antioxidants, and alkyl ester antioxidants; the added mass of the free radical stabilizer F is 0.05% to 1% of the mass of the polypropylene resin A.

8. The method according to claim 1, characterized in that The flame retardant G is modified magnesium hydroxide; the added mass of the flame retardant G is 1 to 100% of the mass of the polypropylene resin A; The preparation method of the modified magnesium hydroxide comprises the following steps: (1) placing magnesium hydroxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO in a vacuum drying oven for drying at a temperature of 80 o C, time 8 hours; (2) DOPO was modified by using vinyl silane coupling agent, the reaction conditions were bulk polymerization, temperature 140 o C, time 5 hours; the amount of vinyl silane coupling agent is 0.01% to 80% of the molar amount of DOPO; (3) the coupling agent-modified DOPO is modified with Mg(OH)2, the reaction medium is ethanol, the temperature is 80 o C, time 6 hours; the amount of coupling agent modified DOPO is 0.01% to 80% of the mass of Mg(OH)2; (4) the final modified Mg(OH)2 is placed in a vacuum drying oven for drying at a temperature of 60 o C, time 8 hours.

9. The method according to claim 1, characterized in that: The extruder is a twin-screw extruder having at least six zones, wherein the temperature of the first zone is higher than 90°C, the temperature of the second zone is higher than 150°C, the temperature of the third zone is higher than 180°C, the temperature of any subsequent zone is higher than 190°C, wherein the temperature of any zone is lower than 230°C, and wherein the residence time of the polypropylene resin A in the twin-screw extruder is 30 seconds to 300 seconds.

10. A high melt strength flame retardant polypropylene composite material prepared according to the method according to any one of claims 1 to 9.

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