Branched polyolefin material modified polypropylene composite material and preparation method thereof

Abstract

The invention discloses a polypropylene composite material modified by a branched polyolefin material. The polypropylene composite material comprises the following components in parts by weight: 10-40 parts of polypropylene with a high melt index, 30-50 parts of impact-resistant polypropylene with a low melt index, 10-35 parts of the branched polyolefin material and 15-25 parts of filler. The branched polyolefin material has a long and short branched chain structure, and the weight-average molecular weight of the branched polyolefin material is 2000-8000000 g / mol; the branching degree is 40-180 / 1000 DEG C, and the melt index is 0.01-20 g / 10 min under the conditions that the temperature is 190 DEG C and the load is 2.16 kg. The technical problem that the mechanical property of an ethylene-butylene copolymer as an elastomer is not better than that of an ethylene-octylene copolymer is solved by adopting the light olefin as a raw material and optimizing the molecular structure and combination of the material, and compared with the traditional POE ethylene-octylene copolymer, the light olefin is adopted as the raw material, so that the raw material cost is reduced, and the economic benefit is improved; the low-temperature toughness and the mechanical property of the polypropylene composite material are obviously improved, and the polypropylene composite material is especially suitable for the plastic modification field.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials and molding processing thereof, and in particular relates to a branched polyolefin material toughened and modified polypropylene composite material and a preparation method and application thereof. Background Art

[0002] Polypropylene (PP) materials have excellent mechanical properties and chemical stability, and they also have the advantages of strong heat resistance, low price, rich raw material sources and easy processing, which makes them widely used in the fields of automobiles, aerospace, home appliances, medicine and petrochemicals. Ordinary polypropylene materials often have the characteristics of poor impact toughness, especially the brittleness of the materials at low temperatures, which to a certain extent limits the large-scale application of polypropylene materials and requires toughening modification of polypropylene. At present, the most commonly used elastomers for toughening polypropylene are EPR (ethylene propylene rubber), EPDM (ethylene propylene diene monomer rubber), SBS (styrene-butadiene-styrene block copolymer), POE (polyolefin elastomer), etc. PP / POE is an elastomer toughened PP system developed in recent years. It has the best toughening effect, good weather resistance, good fluidity, good thermal stability and good processing performance. It is also the most commonly used elastomer toughened PP system. POE has very good compatibility with PP, and the toughening effect, especially the low-temperature toughening effect, is very obvious, which is better than EPDM and EPR. Currently in the field of plastic modification, POE has gradually replaced EPDM and become the mainstream toughening modifier.

[0003] POE is a copolymer synthesized by random copolymerization of ethylene and 1-butene or 1-octene, with a 1-butene or 1-octene content between 15% and 45% (generally >20%) and a crystallinity of less than 25%. The mechanical properties of POE (C8-POE) obtained by copolymerization of ethylene and 1-octene are generally better than those of POE (C4-POE) obtained by copolymerization of ethylene and 1-butene. However, since the difficulty of obtaining 1-octene raw materials is much higher than that of 1-butene, the production capacity of 1-octene is low and the price is much higher than that of 1-butene, which also leads to the price of C8-POE being much higher than that of C4-POE. The presence of short chain branches significantly improves the impact strength, but since POE is synthesized by metallocene catalysts, the molecular weight distribution is usually narrow, which leads to significant pseudoplasticity of POE materials and significant shear thinning at higher screw speeds, which leads to poor processing stability and a high defect rate of the product obtained by processing and molding. In addition, short chain branches do not have advantages in filler dispersion and upper limit of loading, which is not conducive to improving the overall performance of the product.

[0004] More than 80% of the materials for the front and rear bumpers of automobiles are modified polypropylene, which is required to have good impact resistance, good weather resistance, good formability, good toughness, and excellent paint adhesion. After PP is toughened with elastomer, the resulting polypropylene composite material usually has good toughness at room temperature, and the cantilever beam notch impact strength can reach 40-100KJ / m 2 However, the toughness decreases significantly at low temperature (-30℃), usually only reaching 3~10KJ / m 2 , down by an order of magnitude. In cold environments, bumper materials become brittle and their toughness decreases. They are prone to breakage when impacted, forming sharp sections that can cause secondary damage to pedestrians. Therefore, it is necessary to improve the toughness of POE and obtain modified polypropylene composite materials with excellent comprehensive performance while reducing costs. In particular, the low-temperature toughness can be further improved, and the impact resistance of vehicle bumpers in low-temperature environments can be improved. Summary of the invention

[0005] In view of this, the present invention aims to overcome the defects and shortcomings in the prior art, and proposes a polypropylene composite material modified by a branched polyolefin material and a preparation method thereof, as well as an application in the field of vehicle bumpers.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A branched polyolefin material modified polypropylene composite material comprises the following components in parts by weight:

[0008] High melt index polypropylene 10-40 parts

[0009] 30-50 parts of low melt index impact polypropylene

[0010] 10-35 parts of branched polyolefin material

[0011] Filler 15-25 parts

[0012] The low melt index impact polypropylene has a melt index of 10-20 g / 10 min under the test conditions of 230° C. and a load of 2.16 kg; the high melt index polypropylene has a melt index of 50-80 g / 10 min under the test conditions of 230° C. and a load of 2.16 kg;

[0013] The branched polyolefin material has a long and short branched chain structure, a weight average molecular weight of 2000-8000000 g / mol, a branching degree of 40-180 / 1000C, and a melt index of 0.01-20 g / 10 min at 190°C and a load of 2.16 kg.

[0014] The branched polyolefin material modified polypropylene composite material preferably comprises the following components in parts by weight:

[0015] High melt index polypropylene 26-30 parts

[0016] Low melt index impact polypropylene 45-50 parts

[0017] 16-35 parts of branched polyolefin material

[0018] 15 to 25 parts of filler.

[0019] Furthermore, the branched polyolefin material is one or more combinations of branched structural materials prepared by solution polymerization using ethylene or ethylene and C3-C5 olefins as raw materials, and the branched polyolefin material is preferably a single ethylene branched polymerization product. The appearance of the branched polyolefin material can be elastomer, rubber, oil or wax.

[0020] Furthermore, the weight average molecular weight of the branched polyolefin material is preferably 50,000 to 500,000 g / mol, the degree of branching is 55 to 120 / 1000C, and the melt index at 190°C and a load of 2.16 kg is 0.5 to 15 g / 10 min.

[0021] Furthermore, the main component of the branched polyolefin material has a melting point of -20°C to 90°C, preferably 20 to 80°C; and a crystallinity of 0 to 15%, preferably 0.1 to 15%.

[0022] In the present invention, the branched polyolefin material can be prepared by the following method:

[0023] Add an organic solvent, a catalyst and a co-catalyst into a reactor, control the temperature at 10-100° C., introduce ethylene into the reactor to carry out a polymerization reaction, the ethylene pressure is 0.1-5 MPa, the reaction time is 10-90 min, after the reaction is completed, add the reaction solution into acidified ethanol to terminate the reaction to obtain a solid precipitate, wash and dry the solid precipitate to obtain a branched polyolefin material;

[0024] The catalyst is a late transition metal catalyst;

[0025] The late transition metal catalyst is a metal complex olefin polymerization catalyst with a late transition metal atom such as nickel (II), palladium (II), iron (II), cobalt (II), ruthenium (II) as the active center, and the chelating ligand is selected from the types of N^N, P^N, N^O, P^O, etc. All kinds of late transition metal catalysts disclosed in the prior art that can catalyze ethylene polymerization to prepare branched polyolefins and can obtain the defined parameters of the branched polyolefin material of the present invention can be applied to the present invention.

[0026] Furthermore, the late transition metal catalyst is a Brookhart catalyst, such as a (a-diimine) nickel / palladium complex, and more preferably an α-diimine nickel catalyst.

[0027] The cocatalyst is one or more of diethylaluminum monochloride, ethylaluminum dichloride, methylaluminoxane, polymethylaluminoxane, ethylaluminum sesquichloride (EASC), preferably ethylaluminum sesquichloride.

[0028] The molar ratio of Al in the co-catalyst to Ni in the α-diimine nickel catalyst is 50 to 1000:1.

[0029] The polymerization reaction is carried out in an organic solvent, and the organic solvent is one or more of dichloromethane, toluene and n-hexane.

[0030] Preferably, the polymerization reaction temperature is 20 to 80° C. and the reaction pressure is 0.5 to 3 MPa.

[0031] In the present invention, a branched structure with adjustable length and short branched chain structures is obtained by long chain branching polymerization in a solution using a late transition metal catalyst. Since the present invention is an in-situ polymerization of ethylene, the branched chain contains long chains and short chains, has a high degree of branching, and the long branched chain increases the crosslinking point, has a low crystallinity, and improves the performance of the elastomer.

[0032] Furthermore, the filler is talcum powder with a particle size of 0.01 to 0.1 μm or glass fiber with a particle size of 0.1 to 10 mm.

[0033] Furthermore, the branched polyolefin material modified polypropylene composite material may further include an antioxidant and a lubricant. The branched polyolefin material modified polypropylene composite material includes the following components in parts by weight:

[0034] High melt index polypropylene 10-40 parts

[0035] 30-50 parts of low melt index polypropylene

[0036] 10-35 parts of branched polyolefin material

[0037] Filler 15-25 parts

[0038] Antioxidant 0.1~0.5 parts

[0039] Lubricant 0.1-0.5 parts.

[0040] Preferably, the antioxidant is any one of phenolic and phosphite antioxidants or a mixture of both.

[0041] Preferably, the lubricant is a mixture of any one or more of silicone, ester, amide, polyethylene, and fatty acid lubricants.

[0042] The present invention also provides a method for preparing the branched polyolefin material modified polypropylene composite material, the method comprising:

[0043] The raw materials are mixed evenly according to the formula ratio and then added to the feeding port of a twin-screw extruder, or a twin-screw extruder with a separate metering system is used to continuously feed the components into the extruder feeding port according to the formula ratio, and melt granulated at a temperature of 180-250° C. to obtain the branched polyolefin material modified polypropylene composite material.

[0044] Furthermore, the aspect ratio of the twin-screw extruder is (30-50):1, the processing temperature is 180-250°C, the screw speed is 300-600rpm, and the feed rate is 300-900kg / h.

[0045] The typical extrusion process for melt granulation is as follows: conveying section temperature 90-140°C, melting section temperature 180-250°C (preferably 180-230°C), homogenizing section temperature 180-250°C (preferably 200-220°C), die temperature 180-250°C (preferably 200-220°C), and screw speed 100-200rpm.

[0046] In the present invention, the branching degree of the branched polyolefin material is improved, and different branch types and lengths are matched. The material has a special molecular chain entanglement structure and rheological properties and a lower glass transition temperature. Its toughening effect is significantly improved compared with conventional elastomers or rubbers, and the room temperature and low temperature notched impact strength of the polypropylene composite material is greatly improved.

[0047] The present invention also provides application of the branched polyolefin material modified polypropylene composite material in preparing automobile bumpers.

[0048] The present invention also provides a polypropylene composite material for an automobile bumper, wherein the polypropylene composite material for an automobile bumper is a polypropylene composite material modified by a branched polyolefin material.

[0049] Compared with the prior art, the present invention has the following advantages:

[0050] The present invention adds a branched polyolefin material with a long and short branched chain structure as a toughening agent, which can effectively improve the toughening efficiency of the matrix and the filler loading effect, while allowing the composite material to maintain good processing stability and reduce the defect rate.

[0051] The present invention adopts light olefin raw materials and solves the technical problem that the mechanical properties of ethylene-butene copolymer as an elastomer are not as good as those of ethylene-octene copolymer by optimizing the molecular structure and combination of materials. Compared with traditional POE ethylene-octene copolymer, the use of light olefin as raw material reduces the raw material cost and improves the economic benefit.

[0052] The invention significantly improves the low-temperature toughness of the polypropylene composite material, significantly improves the impact resistance at a temperature of -30°C, and when used as a bumper material, it is not easy to break in a low-temperature environment, thereby improving the impact safety of the vehicle at low temperatures.

[0053] The invention adopts low melt index impact-resistant polypropylene and high melt index polypropylene for compounding. The high melt index polypropylene raw material has good fluidity, is conducive to injection molding production, and is the optimization direction of polypropylene composite materials. However, the high melt index also means that the molecular weight of polypropylene is low, and its modulus and notched impact strength are difficult to improve. The invention adopts low melt index impact-resistant polypropylene and high melt index polypropylene for compounding, improves the impact resistance through the low melt index impact-resistant polypropylene, maintains the fluidity through the high melt index polypropylene, and adds talcum powder or (and) glass fiber of a specific size to cooperate with the branched polyolefin material. The branched polyolefin material of the invention has a large melt index and good fluidity, is conducive to improving the compatibility with polypropylene, and the filler is also easier to be evenly dispersed in the polypropylene, which is conducive to exerting the reinforcing effect of the filler. Therefore, the mechanical properties of the polypropylene composite material of the invention are significantly improved, and it is particularly suitable for the field of plastic modification. DETAILED DESCRIPTION

[0054] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0055] The present invention is described in detail below in conjunction with embodiments.

[0056] Example 1

[0057] In 100 mL of n-hexane solvent, α-diimine nickel catalyst (2 μmol) and sesquiethylaluminum chloride (2 mmol, Al:Ni molar ratio=1000) were added, the temperature was controlled at 20-80° C., ethylene was introduced to carry out polymerization reaction, timing was started after the ethylene pressure was stable, the ethylene pressure was 0.1-5 MPa, the reaction time was 10-70 min, after the reaction was completed, the reaction solution was added to 200 mL of acidified ethanol, stirred for 10 h, filtered, washed with ethanol, and vacuum dried to obtain a branched polyolefin material;

[0058] The α-diimine nickel catalyst used in this embodiment is prepared according to the following reaction formula:

[0059]

[0060] In the formula I, R 1 is phenyl or substituted phenyl, wherein the substituted phenyl is p-aminophenyl, p-methylphenyl, p-methoxyphenyl or p-tert-butylphenyl;

[0061] R2 is phenyl or substituted phenyl, wherein the substituted phenyl is p-methylphenyl, p-methoxyphenyl, p-fluorophenyl or p-tert-butylphenyl;

[0062] R 3 is phenyl or substituted phenyl, wherein the substituted phenyl is p-methoxyphenyl, p-fluorophenyl or p-tert-butylphenyl;

[0063] In a toluene solvent, the aniline compound represented by formula II and diacetyl are mixed in a molar ratio of 2 to 2.2:1, and heated to 60 to 90°C for reaction for 20 to 24 hours under the action of a catalytic amount of p-toluenesulfonic acid. Then, the mixture is separated by water using a water separator and refluxed for 2 to 3 days to obtain a diimine ligand compound represented by formula III;

[0064] The diimine ligand compound shown in formula III and (DME)NiBr 2 The mixture is mixed in a molar ratio of 1:0.5-2, dissolved in a dichloroethane solvent, and stirred for reaction for 10-24 hours under nitrogen protection to obtain an α-diimine nickel catalyst as shown in formula I.

[0065] In this example, R 1 , R 2 , R 3 All of them are α-diimine nickel catalysts of tert-butylphenyl, and the specific method is as follows:

[0066] 2,4-di(p-tert-butylphenyl)-6-di-p-tert-butylphenyl methylaniline (4mmol) and diacetyl (2mmol) were dissolved in 100mL toluene, and 10mg of p-toluenesulfonic acid (PTSA) was added, and the mixture was stirred and refluxed at 80°C for 24h. Then, the mixture was refluxed for 3 days using a Dean-Stark water separator. After the reaction solution was cooled to room temperature, part of the solvent was evaporated under reduced pressure to precipitate a solid. 400mL of methanol was added to precipitate a solid product, which was filtered, and the filter cake was washed with methanol and dried to obtain a diimine ligand compound with a yield of 81%.

[0067] Under nitrogen protection, diimine ligand compound and (DME)NiBr 2 (0.2 mmol) and diimine ligand compound (0.20 mmol) were mixed and dissolved in 5 mL of dichloromethane, stirred and reacted at room temperature for 20 h, and dichloromethane was removed under reduced pressure and ether was added to precipitate a red solid, which was filtered, washed with ether, and dried to obtain α-diimine nickel catalyst. The yield was about 85%.

[0068] With ethylene as raw material, n-hexane as solvent, α-diimine nickel catalyst as catalyst, sesquiethylaluminum chloride as co-catalyst, by adjusting the ratio of main catalyst and co-catalyst, process and product compound combination, branched structure material B1 (reaction temperature 30°C, pressure 0.4MPa, melt index 1.2g / 10min, molecular weight 130,000, branching degree 45 / 1000C, crystallinity 15%, melting point 75°C), branched structure material B2 (reaction temperature 45°C, pressure 0.5MPa, melt index 10g / 10min) and branched structure material B3 (reaction temperature 45°C, pressure 0.5MPa, melt index 10g / 10min) were prepared respectively. n, molecular weight 180,000, branching degree 65 / 1000C, melting point 63°C, crystallinity 8%), branched structure material B3 (melt index 5g / 10min, molecular weight 250,000, branching degree 80 / 1000C, melting point 60°C, crystallinity 4%, reaction temperature 50°C, pressure 0.6MPa), branched structure material B4 (reaction temperature 70°C, pressure 2.5MPa, melt index 1g / 10min, molecular weight 450,000, melting point 20°C, branching degree 120 / 1000C, crystallinity 0.2%).

[0069] With ethylene and octene as raw materials, alkane as solvent and transition metal complex as catalyst, a branched structure elastomer B5 (melting index 1.1 g / 10min, molecular weight 200,000, branching degree 40 / 1000C, crystallinity 18%, melting point 60°C) was prepared.

[0070] The branched structure materials B1, B2, B3, B4 and the branched structure elastomer B5 are respectively used to prepare polypropylene composite materials, and the specific steps are as follows:

[0071] 45 kg of low melt index polypropylene (MFR = 18 g / 10 min), 26 kg of high melt index polypropylene (MFR = 53 g / 10 min), 16 kg of branched polyolefin (experiment 1 uses branched structural material B1, experiment 2 uses branched structural material B2, experiment 3 uses branched structural material B3, experiment 4 uses branched structural material B4, and experiment 5 uses branched structural elastomer B5), 15 kg of talc CX3000 (particle size 0.03 μm), 0.3 kg of antioxidant 1010, 0.2 kg of antioxidant 168, 0.2 kg of zinc stearate, and 0.1 kg of lubricant TR451 were melt-extruded using a twin-screw extruder with an aspect ratio of 40:1. The extrusion conditions were: conveying section temperature 100°C, melting section temperature 210°C, homogenizing section temperature 210°C, die temperature 210°C, and screw speed 120 rpm.

[0072] The physical and mechanical properties of polypropylene composites made from five different elastomers are shown in Table 1:

[0073] Table 1

[0074]

[0075]

[0076] The experimental results show that the branching degree of the branched structural material B1 of Experiment 1 is only 45 / 1000C, its melt index is low, and its molecular weight is also low. Although its strength, modulus and impact strength are good, its low-temperature impact resistance is poor.

[0077] The elastomer of Experiment 5 is ethylene-octene copolymer, which has the lowest degree of branching among the four elastomers. However, its mechanical properties are better than those of Experiment 1. The impact strength is significantly improved compared with that of Experiment 1. This may be because octene has long chains, and the long chain branches form a curled structure, which improves the toughness and impact resistance of polypropylene. However, the long chain branches will also cause the melt index to decrease, which is not conducive to industrial applications.

[0078] Although the elastomer of Experiment 5 has a lower degree of branching, its overall performance is better than that of the ethylene-branched material of Experiment 1.

[0079] However, in experiments 2, 3, and 4, the branching degree of ethylene copolymers was increased without using octene raw materials, and branched structural materials with a branching degree of 55 to 120 / 1000C were used. The low-temperature impact resistance was significantly improved, and the mechanical properties at room temperature were also significantly improved compared with experiments 1 and 5, meeting the standard requirements of polypropylene for bumpers. The melt index of the polypropylene composite material prepared by the present invention is greater than 15g / 10min, meeting the injection molding requirements. In addition, the raw materials of experiments 2, 3, and 4 are light olefin ethylene, which is cheap and more cost-effective than the octene raw materials of experiment 5.

[0080] Example 2

[0081] The branched structural materials B1, B2, B3, B4 and B5 are respectively used to prepare polypropylene composite materials, and the specific steps are as follows:

[0082] 50kg of low melt index polypropylene (MFR=15g / 10min), 30kg of high melt index polypropylene (MFR=65g / 10min), 20kg of branched polyolefin (branched structural material B1 was used in experiment 6, branched structural material B2 was used in experiment 7, branched structural material B3 was used in experiment 8, branched structural material B4 was used in experiment 9, and branched structural elastomer B5 was used in experiment 10), 20kg of glass fiber (length 1-5mm, aspect ratio 150), 0.3kg of antioxidant 1010, 0.2kg of antioxidant 168, 0.2kg of zinc stearate, and 0.1kg of lubricant TR451 were melt-extruded using a twin-screw extruder with an aspect ratio of 40:1. The extrusion conditions were: conveying section temperature 100°C, melting section temperature 210°C, homogenizing section temperature 210°C, die temperature 210°C, and screw speed 120rpm.

[0083] The physical and mechanical properties of polypropylene composites made from five different elastomers are shown in Table 2:

[0084] Table 2

[0085]

[0086] The filler used in experiments 6 to 10 is glass fiber, which can further improve the strength and slightly reduce the melt index compared to talc. From the comparison between experiments 6 to 10, it can be seen that the increase in branching degree can improve the low-temperature toughness and significantly improve the impact resistance.

[0087] Example 3

[0088] The materials were added according to the formula in Table 3. The raw materials and preparation process were the same as those in Example 1.

[0089] Table 3 Comparative Examples and Examples Composition Formula (kg)

[0090]

[0091]

[0092] The physical and mechanical properties of the polypropylene composite materials of Experiments 11 to 14 are shown in Table 4:

[0093] Table 4

[0094]

[0095] In the present invention, low melt index impact polypropylene and high melt index polypropylene are compounded in a certain ratio, the impact resistance is improved by low melt index impact polypropylene, the fluidity is maintained by high melt index polypropylene, and the filler load dispersion and mechanical properties are improved by regulating the combination of the molecular structure of the toughening agent. In Experiment 12, the amount of high melt index PP is too low, resulting in a significant decrease in the melt index, and the amount of high melt index PP is small, the fluidity of the overall mixture is poor, which will lead to uneven dispersion of talc and elastomer, and reduced strength and impact resistance.

[0096] In Experiment 13, the amount of low melt index PP was too low, the melt index increased, but the impact resistance decreased significantly, and the toughness of the composite material was poor.

[0097] In Experiment 14, the amount of elastomer used was only 10 kg. Generally speaking, too little elastomer will lead to a significant decrease in low-temperature toughness. However, from the data of Experiment 14, the low-temperature toughness has decreased, but it still reaches 10 KJ / m 2 It can be seen that the toughening efficiency of the branched elastomer of the present invention is very high, and a good toughening effect can be achieved even with a relatively small amount.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A branched polyolefin modified polypropylene composite material, characterized in that The polypropylene composite material comprises the following components in parts by weight: High melt index polypropylene 10-40 parts 30-50 parts of low melt index impact polypropylene 10-35 parts of branched polyolefin material Filler 15-25 parts The low melt index impact polypropylene has a melt index of 10-20 g / 10 min under the test conditions of 230° C. and a load of 2.16 kg; the high melt index polypropylene has a melt index of 50-80 g / 10 min under the test conditions of 230° C. and a load of 2.16 kg; The branched polyolefin material has a long and short branched chain structure, a weight average molecular weight of 2000-8000000 g / mol, a branching degree of 40-180 / 1000C, and a melt index of 0.01-20 g / 10 min at 190°C and a load of 2.16 kg.

2. The polypropylene composite material according to claim 1, characterized in that The branched polyolefin material is one or more combinations of branched structural materials prepared by solution polymerization using ethylene or ethylene and C3-C5 olefins as raw materials.

3. The polypropylene composite material according to claim 2, characterized in that The branched polyolefin material is a single ethylene branched polymerization product.

4. The polypropylene composite material according to claim 1, characterized in that The branched polyolefin material has a weight average molecular weight of 50,000 to 500,000 g / mol, a branching degree of 55 to 120 / 1000C, and a melt index of 0.5 to 15 g / 10 min at 190°C and a load of 2.16 kg.

5. The polypropylene composite material according to claim 1, characterized in that The main component of the branched polyolefin material has a melting point of -20°C to 90°C and a crystallinity of 0 to 15%.

6. The polypropylene composite material according to claim 1, characterized in that The filler is talcum powder with a particle size of 0.01 to 0.1 μm or glass fiber with a particle size of 0.1 to 10 mm.

7. The polypropylene composite material according to claim 1, characterized in that The branched polyolefin material modified polypropylene composite material further comprises an antioxidant and a lubricant. The branched polyolefin material modified polypropylene composite material comprises the following components in parts by weight: High melt index polypropylene 10-40 parts 30-50 parts of low melt index polypropylene 10-35 parts of branched polyolefin material Filler 15-25 parts Antioxidant 0.1~0.5 parts Lubricant 0.1-0.5 parts.

8. The polypropylene composite material according to claim 7, characterized in that The antioxidant is any one of phenolic and phosphite antioxidants or a mixture of two thereof; the lubricant is any one or more of silicone, ester, amide, polyethylene and fatty acid lubricants.

9. The method for preparing a branched polyolefin material modified polypropylene composite material according to any one of claims 1 to 7, characterized in that The method is: The raw materials are mixed evenly according to the formula ratio and then added to the feeding port of a twin-screw extruder, or a twin-screw extruder with a separate metering system is used to continuously feed the components into the extruder feeding port according to the formula ratio, and melt granulated at a temperature of 180-250° C. to obtain the branched polyolefin material modified polypropylene composite material.

10. Use of the branched polyolefin material modified polypropylene composite material according to any one of claims 1 to 7 in the preparation of automobile bumpers.

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