Toughened and Flame-Retardant Polypropylene Composite Based on Gradation Synergy and Preparation Method

Abstract

The present invention discloses a toughened and flame-retardant polypropylene composite material based on gradation coordination and a preparation method thereof. The polypropylene composite material comprises raw materials in parts by weight: 100 parts of polypropylene, 10 - 15 parts of composite inorganic rigid particles, 15 - 18 parts of composite flame retardant, 3 - 5 parts of elastic interface agent, 0 - 3 parts of toughening agent, 0.5 - 1 part of dispersant, and 0.3 - 0.5 part of nucleating agent; the elastic interface agent is used to disperse and coat the gradation inorganic rigid particles and the gradation flame retardant to form an elastic modified material with a core-shell structure for polypropylene, which can effectively change the propagation direction of microcracks during impact, prevent interface fracture caused by excessive local stress during impact yield, and greatly improve the impact resistance of the material. Through interface modification, the flame retardant is uniformly dispersed in polypropylene to achieve a good flame retardant effect, and the problem of the decline in the mechanical properties of the material caused by adding the flame retardant is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer material modification, and particularly relates to a toughened and flame-retardant polypropylene composite based on gradation coordination and a preparation method thereof. Background Art

[0002] As a widely used general-purpose plastic at present, polypropylene has gradually increased its usage in fields such as household appliances and automotive parts due to its good thermoforming processability, high strength, high stiffness, high hardness, and good chemical stability. Especially, the side methyl groups of isotactic polypropylene are on the same side of the main chain plane, with regular structure, high crystallinity, and outstanding dimensional stability, strength, and flexural fatigue resistance. By modifying polypropylene, its application fields can be broadened, making it the best material to replace engineering plastics. Especially currently, in the fields of robots, drones, and automobiles, there is an urgent need for thin-walled injection-molded parts. For example, the outer shells, frames, and internal structural parts of robots; the wing protectors of drones, and the interior sun visors of automobiles, etc., using polypropylene materials are becoming a trend.

[0003] However, there are still obvious deficiencies in the process of promoting the engineering application of polypropylene plastics, mainly manifested in poor impact resistance at low temperatures. When used for the wing protectors of drones, it cannot effectively absorb the impact energy during high-altitude drops, and there is a risk of cracking. In addition, polypropylene has deficiencies in flame retardancy. For example, when using modified polypropylene for the battery pack housing of new energy vehicles, it is required not only to have high strength, high rigidity, and high impact resistance, but also to have a V0-level flame retardancy to ensure safety. These defects have restricted the expansion of polypropylene applications.

[0004] In order to fully exert the application potential of polypropylene in fields such as the automotive industry, drones, and robots, it is necessary to toughen and flame-retard polypropylene. The existing toughening of polypropylene mainly involves blending with elastomeric toughening agents and nano-inorganic rigid particles. For example, the low-temperature toughness and rigid-tough polypropylene nanocomposite and its preparation method disclosed in Chinese Patent Publication No. CN113912948B achieve low-temperature toughening and rigid-tough balance by using elastomers and inorganic rigid particles to modify polypropylene. However, due to the relatively large distance between monomer molecules in polypropylene materials and the weak binding force between molecular chains, the molecular chains are prone to move under the action of external stress. Excessive use of elastomers for toughening will reduce its stiffness and strength while improving the toughness of polypropylene, making it difficult to meet the requirements of replacing engineering materials with polypropylene. When a single nano-inorganic rigid particle is used to toughen plastics, it mainly relies on the stress concentration effect of the inorganic rigid particle to cause microcracks in the material when it is impacted, absorbing a certain amount of deformation energy. However, if these microcracks cannot be contained, they may expand into destructive cracks, thereby reducing the toughness of the material.

[0005] On the other hand, in order to obtain flame-retardant polypropylene, a relatively large amount of flame retardant is usually added. The flame retardant has a large adhesiveness, and the particles adhere to each other and aggregate to become larger, making it difficult to disperse. The addition of a large amount of flame retardant will damage the continuous phase structure inside the material, resulting in a decrease in material strength and toughness. In particular, the addition of the flame retardant is likely to precipitate, causing defects such as surface spots on the product. Summary of the Invention

[0006] The present invention provides a toughened flame-retardant polypropylene composite material based on gradation synergy and a preparation method thereof. The purpose is to promote the engineering application of polypropylene materials and overcome the problems of low strength and toughness of current flame-retardant polypropylene. The key technology adopted to solve this problem is to make polypropylene have excellent flame retardant properties and mechanical properties through the gradation of inorganic rigid particles and the gradation of flame retardants, so as to broaden the application of polypropylene materials.

[0007] The specific solution to the problem is as follows:

[0008] A toughened flame-retardant polypropylene composite material based on gradation synergy, characterized in that it comprises the following raw materials by weight: 100 parts of polypropylene, 10-15 parts of composite inorganic rigid particles, 15-18 parts of composite flame retardant, 3-5 parts of elastic interface agent, 0-3 parts of toughening agent, 0.5-1 part of dispersant, 0.3-0.5 part of nucleating agent; wherein:

[0009] The composite inorganic rigid particles are composed of grade I particles, grade II particles, and grade III particles according to a mass ratio of (2-3):1:(1-2); wherein, the grade I particles are zero-dimensional inorganic powders with a particle size less than 50 nm; the grade II particles are two-dimensional inorganic powders with a thickness of 50-100 nm; the grade III particles are one-dimensional inorganic powders with a diameter of 0.1-1 µm;

[0010] The composite flame retardant is composed of zinc borate with a particle size less than 10 nm, aluminum diethylphosphinate with a particle size of 0.1-1 µm, and melamine cyanurate with a particle size of 10-20 µm according to a mass ratio of 1:(2-4):(4-6).

[0011] Preferably, the polypropylene is copolymer polypropylene, and the melt flow index at 230 °C and a load of 2.16 kg is 10-60 g / 10 min. Copolymer polypropylene has good rigidity and basic impact resistance, and suitable fluidity is conducive to the uniform dispersion of the graded materials.

[0012] Preferably, the zero-dimensional inorganic powder is selected from at least one of talc powder, kaolin, barium sulfate, montmorillonite, zinc oxide, aluminum oxide, glass microspheres, calcium carbonate, and silicon dioxide; the two-dimensional inorganic powder is selected from at least one of flaky mica powder, graphite, and molybdenum disulfide with an aspect ratio of 10-50; the one-dimensional inorganic powder is selected from at least one of fibrous calcium sulfate whiskers, aluminum borate whiskers, calcium carbonate whiskers, glass fibers, and carbon fibers with an aspect ratio of 30-50.

[0013] In the prior art, a single nano-inorganic powder is usually used as a rigid particle to toughen polypropylene. When subjected to an external force impact, the inorganic rigid particles cause the surrounding polypropylene to undergo yield deformation, generating microcrack propagation to absorb the impact energy and achieve the toughening effect. However, as the impact force further increases, the microcracks absorb the impact energy and continuously expand, eventually leading to interface fracture of the material, and the toughening ability is limited.

[0014] In order to improve the toughening effect of inorganic rigid particles on polypropylene, the present invention synergistically combines grade I particles, grade II particles, and grade III particles with different morphologies and different particle sizes to improve the strength and impact resistance of polypropylene, especially the low-temperature impact resistance. Among them, the zero-dimensional inorganic powder can generate more stress dispersion points when the material is impacted, preventing stress concentration and dispersing the impact energy of the material; the two-dimensional inorganic powder has a micro-flaky structure, which can effectively change the propagation direction of microcracks during impact, prevent the material from cracking, and increase the rigidity and strength of the material; the one-dimensional inorganic powder has a fibrous structure, preventing interface fracture caused by excessive local stress during impact yield, and overall improving the impact resistance and anti-cracking performance of the material.

[0015] Preferably, the composite flame retardant is composed of a grade I ratio of zinc borate with a particle size less than 10 nm, aluminum diethylphosphinate with a particle size of 0.1-1 µm, and melamine cyanurate with a particle size of 10-20 µm in a mass ratio of 1:3:4. When the temperature of zinc borate is higher than 280 °C, it releases crystal water, playing an endothermic cooling role. The nano-scale zinc borate will increase the contact area with the polypropylene material. During combustion, zinc borate can absorb a large amount of heat and decompose, thereby reducing the temperature in the combustion area and slowing down the combustion rate; at the same time, the nano-scale zinc borate decomposes to form a large-area glassy layer to isolate oxygen, suppress smoke, and prevent the formation of molten droplets. Aluminum diethylphosphinate, as the main flame retardant, has a decomposition temperature of 380 °C. When the temperature rises, aluminum diethylphosphinate emits phosphorus-containing substances. When further encountering an open flame and rising in temperature, it forms a phosphorus-containing free radical quencher for efficient flame retardancy. Melamine cyanurate has a decomposition temperature of 350 °C, which can dehydrate and release nitrogen at high temperatures, generating a dense carbonized layer to isolate oxygen, reduce the flame spread rate, and significantly reduce the smoke density and toxic gas emissions generated during combustion.

[0016] The addition of flame retardants usually leads to an increase in interfacial defects in polypropylene due to poor dispersion, resulting in a decrease in strength, toughness, and flexural modulus. In the present invention, the types of flame retardants are coordinated, the grading of different particle sizes, and the combination of different decomposition temperatures are adopted. Through elastic interface modification, the flame retardants are uniformly dispersed in polypropylene to achieve good flame retardant effects and certain toughening effects.

[0017] Preferably, the elastic interface agent is at least one of hydroxyl-terminated polybutadiene liquid rubber, amino-terminated liquid nitrile rubber, and carboxyl-terminated liquid nitrile rubber. Hydroxyl-terminated, amino-terminated, and carboxyl-terminated groups have good polarity, and their polar groups have good bonding effects with the interfaces of inorganic rigid particles, zinc borate, and aluminum diethylphosphinate, enabling the elastic interface agent to coat the inorganic rigid particles, zinc borate, and aluminum diethylphosphinate to form an elastic modified material with a dispersed core-shell structure. Firstly, it solves the dispersibility and compatibility of powder materials in polypropylene; secondly, it increases the interfacial adhesion between the powder and polypropylene. The inorganic rigid particles and the flame retardant are approximately finely divided elastic microparticles dispersed in polypropylene to prevent the material interface from breaking during impact.

[0018] Preferably, the toughening agent is an acrylate thermoplastic elastomer containing a glycidyl methacrylate functional group. For example, the toughening agents with the Arkema grades AX8900 and AX8700 can not only increase the low-temperature toughness of polypropylene but also act as a compatibilizer to increase the compatibilizing and dispersing properties of the flame retardant and inorganic rigid particles with polypropylene.

[0019] Preferably, the dispersant is at least one of ethylene bisoleamide, ethylene bisstearamide, and stearic acid; through mechanical pre-dispersion, the dispersant is effectively adsorbed on the surfaces of inorganic rigid particles, zinc borate, and aluminum diethylphosphinate powder to form a protective film to prevent agglomeration between particles.

[0020] Preferably, the nucleating agent is a sorbitol-based nucleating agent or / and a carboxylate metal salt-based nucleating agent; when the polypropylene material is injection-molded into a product, the higher the crystallinity, the closer the molecular chain arrangement, the stronger the intermolecular force, and the higher the tensile strength. However, the product becomes brittle, and the impact strength decreases with the increase in crystallinity. The addition of the nucleating agent changes the crystallization characteristics and crystallization morphology of polypropylene, forming fine and uniformly distributed crystal nuclei, which significantly improve its toughness while ensuring the tensile strength.

[0021] Further preferably, the nucleating agent is a sorbitol-based nucleating agent and a metal carboxylate-based nucleating agent used in a mass ratio of 2:1; the significant advantage is that the sorbitol-based nucleating agent can provide nucleation sites, promote the regular arrangement and crystallization of polypropylene chain segments at the nucleation sites, and the polyhydroxy structure of the sorbitol-based nucleating agent forms a stable interaction with the polypropylene chain, reducing the activation energy required for crystallization and accelerating the formation of crystal grains. The metal carboxylate is easily dispersed in polypropylene, can effectively accelerate the crystallization rate, and make the crystal grain size finer, thereby enhancing the toughness of the material.

[0022] For the preparation method of the above-mentioned toughened and flame-retarded polypropylene composite material based on gradation synergy, the characteristics are as follows:

[0023] S1. Premix the composite inorganic rigid particles, composite flame retardant, dispersant, and nucleating agent in a high-speed mixer, then send them into a jet mill for depolymerization and dispersion, and obtain a pre-dispersed material through a classifier.

[0024] S2. Add the pre-dispersed material and the elastic interface agent to a three-roll mill for grinding and dispersion, control the roller temperature of the three-roll mill to be lower than 60 °C, and grind 3-4 times to obtain an elastic modified material with a core-shell structure.

[0025] S3. Mix the elastic modified material with a core-shell structure, polypropylene, and toughening agent evenly, add them to a twin-screw extruder for melt extrusion, and granulate by air-cooled die face hot cutting through a die head to obtain a toughened and flame-retarded polypropylene composite material based on gradation synergy; wherein, the length-diameter ratio of the screw of the twin-screw extruder is ≥ 48 / 1, and the temperature control range of each heating section is: the first section area is 90-100 °C; the second section area is 100-110 °C; the third section area is 100-110 °C; the fourth section area is 150-160 °C; the fifth section area is 170-180 °C; the sixth section area is 190-200 °C; the seventh section area is 190-200 °C; the eighth section area is 180-190 °C; the ninth section area is 180-190 °C; the tenth section area is 160-170 °C; the fifth section area and the eighth section area of the twin-screw extruder are provided with vacuum exhaust ports.

[0026] Preferably, the roller gap of the three-roll mill is adjusted as follows: the gap between the middle and rear rollers is 30-50 µm; the gap between the middle and front rollers is 20-30 µm; the speed ratio of the rear, middle, and front rollers of the three-roll mill is 1:2.5:(5.5-6.5); the three-roll mill performs friction dispersion through the mutual extrusion of the surfaces of the three horizontal rollers and the speed difference of different rollers, and grinds and disperses the high-viscosity material.

[0027] Preferably, the screw of the twin-screw extruder is a large L / D ratio screw with an L / D ratio of 52 / 1; the large L / D ratio screw ensures that the material is fully kneaded, sheared and dispersed. A lower temperature is set in the first to third zones to prevent premature curing of the rubber in the elastic modifier of the core-shell structure, so that it is fully dispersed in the polypropylene; in the fourth to tenth zones, the elastic modifier of the core-shell structure is sheared and dispersed with the polypropylene, and at the same time, the rubber in the elastic modifier of the core-shell structure is gradually cured, the elasticity increases, and it is completely compatible and dispersed with the polypropylene.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) The present invention uses inorganic rigid particles with different morphologies (zero-dimensional, two-dimensional, one-dimensional) and different particle sizes for graded toughening of polypropylene. When the polypropylene material is impacted by an external force, it can effectively change the propagation direction of microcracks during impact, prevent interfacial fracture caused by excessive local stress during impact yield, and ensure that the material has excellent impact resistance while increasing rigidity and strength. By grading inorganic rigid particles, less or no toughening agent is required, and toughness is increased while tensile strength and rigidity are not lost.

[0030] (2) The present invention uses a dispersant and an elastic interfacial agent containing polar groups to disperse and coat inorganic rigid particles and flame retardants to form an elastic modifier with a core-shell structure, which can not only increase the dispersibility of the powder material in polypropylene, but also improve the compatibility with polypropylene, increase the binding force between the powder and polypropylene, and prevent interfacial fracture of the material during impact.

[0031] (3) The present invention uses the synergy of flame retardant types, grading of different particle sizes, and matching of different decomposition temperatures to uniformly disperse the flame retardant in polypropylene through interfacial modification. Good flame retardant effects can be achieved with less flame retardant, avoiding the problem of deterioration of the mechanical properties of the material caused by adding too much flame retardant. Specific Embodiments

[0032] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0033] The raw material specifications and equipment parameters used in the examples and comparative examples are as follows. Other raw materials not specified are commercially available conventional materials or raw materials conventionally selected in the art.

[0034] Polypropylene: grade K7760, MI is 56 g / 10 min, tensile yield stress is 23.5 MPa, room temperature impact strength is 5.0 KJ / m 2 , flexural modulus is 1100 MPa, heat distortion temperature under load is 100 °C, Yanshan Petrochemical Corporation.

[0035] Grade I zinc oxide particles: particle size less than 50 nm.

[0036] Grade I silica particles: particle size less than 50 nm.

[0037] Grade II mica powder particles: thickness 50 - 100 nm, diameter - thickness ratio 10 - 50.

[0038] Grade III calcium sulfate whisker particles; diameter 0.5 - 1 µm, length - diameter ratio 30 - 50.

[0039] Grade III calcium carbonate whisker particles: diameter 0.5 - 1 µm, length - diameter ratio 30 - 50.

[0040] Zinc borate: particle size less than 10 nm (pre - ground).

[0041] Aluminum diethylphosphinate: particle size 0.1 - 1 µm (pre - ground).

[0042] Melamine cyanurate: particle size 10 - 20 µm, Shouguang Weidong Chemical Co., Ltd.

[0043] Toughening agent: grade AX8900, ethylene - methyl acrylate - glycidyl methacrylate terpolymer, Arkema France.

[0044] Toughening agent: grade AX8700, ethylene - butyl acrylate - glycidyl methacrylate terpolymer, Arkema France.

[0045] Sorbitol nucleating agent: grade NX8000i, Milliken USA.

[0046] Carboxylic acid metal salt nucleating agent: grade NaV101, long - chain linear saturated sodium carboxylate with main component of carbon chain length C28 - C32, Clariant Chemicals.

[0047] Three - roll mill: model S260, slow, medium, and fast roll speed ratio: 1∶2.5∶6.25,

[0048] Twin - screw extruder: parallel co - rotating twin - screw extruder, model Φ53, length - diameter ratio L / D = 52, torque coefficient 13.5. Example 1

[0049] S1. Weigh the raw materials according to the raw material formula table in Table 1. Add Grade I zinc oxide particles, Grade II mica powder particles, Grade III calcium carbonate whisker particles, zinc borate, aluminum diethylphosphinate, melamine cyanurate, ethylene bisoleamide, nucleating agent NX8000i, and nucleating agent NaV101 into a high - speed mixer and premix for 5 min, then send them into a jet mill for depolymerization and dispersion by air impact. The classification speed is controlled at 1200 rpm. The agglomerated large particles are recycled and crushed by the classifier, and the completely depolymerized materials are collected to obtain pre - dispersed materials;

[0050] S2. Add the pre-dispersed material and the elastic interfacial agent, hydroxyl-terminated polybutadiene liquid rubber, to a three-roll mill for grinding and dispersion. Control the temperature of the three-roll mill's rollers below 60 °C, and adjust the gap between the middle and rear rollers to 30 µm; the gap between the middle and front rollers to 20 µm; Grind repeatedly 4 times to obtain an elastic modified material with a core-shell structure;

[0051] S3. Mix the elastic modified material with a core-shell structure and polypropylene evenly, and add them to a twin-screw extruder for melt extrusion. The temperature of each heating section of the twin-screw extruder is controlled as follows: the first section is 90 °C; the second section is 100 °C; the third section is 110 °C; the fourth section is 150 °C; the fifth section is 170 °C; the sixth section is 190 °C; the seventh section is 190 °C; the eighth section is 190 °C; the ninth section is 180 °C; the tenth section is 170 °C; There are vacuum exhaust ports in the fifth section and the eighth section of the twin-screw extruder, connected to a vacuum pump to discharge volatile components. The molten material is granulated by air-cooled die-face hot cutting through a die head, and is sent to a storage tank through a pipeline by air to obtain a toughened and flame-retardant polypropylene composite material based on gradation coordination. Example 2

[0052] S1. Weigh the raw materials according to the raw material formula table in Table 1. Add grade I silica particles, grade II mica powder, grade III calcium sulfate whiskers, zinc borate, aluminum diethyl phosphinate, melamine cyanurate, ethylene bis-stearamide, and nucleating agent NX8000i to a high-speed mixer for pre-mixing for 5 minutes, and then send them to a jet mill for depolymerization and dispersion by air impact. The classification speed is controlled at 1000 rpm. The agglomerated large particles are recycled and crushed by a classifier, and the completely depolymerized material is collected to obtain a pre-dispersed material;

[0053] S2. Add the pre-dispersed material and the elastic interfacial agent, amino-terminated liquid nitrile rubber, to a three-roll mill for grinding and dispersion. Control the temperature of the three-roll mill's rollers below 60 °C, and adjust the gap between the middle and rear rollers to 30 µm; the gap between the middle and front rollers to 20 µm; Grind repeatedly 3 times to obtain an elastic modified material with a core-shell structure;

[0054] S3. Mix the elastic modified material with a core-shell structure, polypropylene, and toughening agent AX8700 evenly, and add them to a twin-screw extruder for melt extrusion. The temperature of each heating section of the twin-screw extruder is controlled as follows: the first section is 90 °C; the second section is 100 °C; the third section is 110 °C; the fourth section is 150 °C; the fifth section is 170 °C; the sixth section is 190 °C; the seventh section is 190 °C; the eighth section is 190 °C; the ninth section is 180 °C; the tenth section is 170 °C; There are vacuum exhaust ports in the fifth section and the eighth section of the twin-screw extruder, connected to a vacuum pump to discharge volatile components. The molten material is granulated by air-cooled die-face hot cutting through a die head, and is sent to a storage tank through a pipeline by air to obtain a toughened and flame-retardant polypropylene composite material based on gradation coordination.

[0055] Comparative Examples 1-1 to 1-5 were based on Example 1 for comparative tests. In Comparative Example 1-1, no elastic interface agent was used, toughening agent AX8900 was used, and three-roll grinding was not performed. The remaining preparation methods were the same as those in Example 1, and the formula is shown in Table 1.

[0056] Comparative Examples 2-1 to 2-5 were based on Example 2 for comparative tests. In Comparative Example 2-1, aluminum diethylphosphinate without pre-grinding (particle size 20 - 30 µm) was used, and its preparation method was the same as that in Example 2, and the formula is shown in Table 2.

[0057] Table 1: Raw material weight part formula table of Example 1, Comparative Examples 1-1 to 1-5

[0058]

[0059] Table 2: Raw material weight part formula table of Example 2, Comparative Examples 2-1 to 2-5

[0060]

[0061] Mechanical property testing:

[0062] The polypropylene composites of the examples and comparative examples were injection molded into test specimens by an injection molding machine. The tensile strength was tested according to the standard GB / T 1040, and the tensile rate of the tensile testing machine was 50 mm / min; the flexural strength and flexural modulus were tested according to the reference GB / T 9341, and the bending speed was 2 mm / min; the notched impact strength at room temperature of 23 °C and -30 °C was tested according to GB / T 1843, and the nominal energy was 2.75 J; the test results are shown in Tables 3 and 4.

[0063] Flame retardant property testing:

[0064] The polypropylene composites of the examples and comparative examples were injection molded into test specimens by an injection molding machine. According to the UL94 vertical burning test standard, the material sample specimens were placed vertically, the sample thickness was 1.6 mm, and the combustion performance was judged according to three levels: V-0, V-1, and V-2. Among them, the V-0 level represents the best flame retardant performance. After two 10-second combustion tests, the flame goes out within 10 seconds, and no combustibles can fall off. The V-1 level represents that after two 10-second combustion tests, the flame goes out within 30 seconds, but it cannot ignite the absorbent cotton located 30 cm below the sample. V-2 represents that after two 10-second combustion tests, the flame goes out within 30 seconds, but it can ignite the absorbent cotton located 30 cm below the sample.

[0065] According to GB / T 2406.2-2009 (Plastics - Determination of burning behaviour by oxygen index - Part 2: Ambient-temperature test), the thickness of the test sample is 4 mm. An oxygen-nitrogen mixed gas is introduced, and the minimum oxygen volume concentration required to maintain the combustion of the sample is the oxygen index (OI). The higher the oxygen index (OI) value of the material, the better the flame retardant performance of the material. The test results are shown in Table 3 and Table 4.

[0066] Table 3: Data sheet for the detection of mechanical properties and flame retardant properties of Example 1, Comparative Examples 1-1 to 1-5

[0067]

[0068] Table 4: Data sheet for the detection of mechanical properties and flame retardant properties of Example 2, Comparative Examples 2-1 to 2-5

[0069]

[0070] Through the experimental comparison of Example 1 and Comparative Examples 1-1 to 1-5, the technical solution of the present invention adopts the grading coordination of inorganic rigid particles with different forms and different particle sizes, which can effectively change the propagation direction of microcracks during impact, prevent interfacial fracture caused by excessive local stress during impact yield, and the material has excellent low-temperature impact resistance while increasing rigidity and strength. The elastic interface agent's coating and dispersion of inorganic rigid particles and flame retardants are significant for improving the toughness and flame retardant performance of the material. In Comparative Example 1-1, the interfacial modified flame retardant was not used, and the flame retardant was difficult to be effectively dispersed, affecting the impact performance and flame retardant effect of the material.

[0071] Through the experimental comparison of Example 2 and Comparative Examples 2-1 to 2-5, the technical solution of the present invention adopts the coordination of different types of flame retardants, the grading of different particle sizes, and the cooperation of different decomposition temperatures to achieve good flame retardant effects in polypropylene without affecting the mechanical properties of the material.

[0072] The above are only the listed preferred embodiments and comparative analyses, and do not impose any form of limitation on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, can make equivalent embodiments with equivalent changes using the disclosed technical ideas. However, as long as it does not depart from the content of the technical solution of the present invention, it still belongs to the scope of the technical solution of the present invention.

Claims

1. A toughened and flame-retardant polypropylene composite material based on gradation coordination, characterized in that It includes the following raw materials measured by weight parts: 100 parts of polypropylene, 10 - 15 parts of composite inorganic rigid particles, 15 - 18 parts of composite flame retardant, 3 - 5 parts of elastic interface agent, 0 - 3 parts of toughening agent, 0.5 - 1 part of dispersant, 0.3 - 0.5 part of nucleating agent; wherein: The composite inorganic rigid particles are composed of grade-I particles, grade-II particles and grade-III particles according to the mass ratio of (2 - 3):1:(1 - 2); wherein, the grade-I particles are zero-dimensional inorganic powders with a particle size less than 50nm; the grade-II particles are two-dimensional inorganic powders with a thickness of 50 - 100nm; the grade-III particles are one-dimensional inorganic powders with a diameter of 0.1 - 1μm; The composite flame retardant is composed of zinc borate with a particle size less than 10nm, aluminum diethylphosphinate with a particle size of 0.1 - 1μm, and melamine cyanurate with a particle size of 10 - 20μm according to the mass ratio of 1:(2 - 4):(4 - 6); The elastic interface agent is at least one of hydroxyl-terminated polybutadiene liquid rubber, amino-terminated liquid nitrile rubber, and carboxyl-terminated liquid nitrile rubber.

2. The toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 1, wherein The polypropylene is a copolymer polypropylene with a melt flow index of 10 - 60g / 10min at 230℃ under a load of 2.16kg.

3. The toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 1, wherein The zero-dimensional inorganic powder is selected from at least one of talc powder, kaolin, barium sulfate, montmorillonite, zinc oxide, alumina, glass beads, calcium carbonate, and silicon dioxide; the two-dimensional inorganic powder is selected from at least one of flaky mica powder with an aspect ratio of 10 - 50, graphite, and molybdenum disulfide; the one-dimensional inorganic powder is selected from at least one of fibrous calcium sulfate whiskers, aluminum borate whiskers, calcium carbonate whiskers, glass fibers, and carbon fibers with a length-to-diameter ratio of 30 - 50.

4. The toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 1, wherein, The composite flame retardant is composed of zinc borate with a particle size less than 10nm, aluminum diethylphosphinate with a particle size of 0.1 - 1μm, and melamine cyanurate with a particle size of 10 - 20μm according to the mass ratio of 1:3:

4.

5. The toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 1, characterized in that, The toughening agent is an acrylate thermoplastic elastomer containing glycidyl methacrylate functional groups.

6. The toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 1, wherein, The dispersant is at least one of ethylene bisoleamide, ethylene bisstearamide, and stearic acid.

7. The toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 1, wherein The nucleating agent is a sorbitol-based nucleating agent or / and a carboxylate metal salt-based nucleating agent.

8. The preparation method of a toughened and flame-retardant polypropylene composite material based on gradation coordination according to any one of claims 1-7, characterized in that, The specific preparation method is as follows: S1. Premix the composite inorganic rigid particles, composite flame retardant, dispersant, and nucleating agent in a high-speed mixer, then send them into a jet mill for depolymerization and dispersion, and obtain a pre-dispersed material through a classifier; S2. Add the pre-dispersed material and the elastic interface agent into a three-roll mill for grinding and dispersion, control the temperature of the three-roll mill roller below 60℃, and grind 3 - 4 times to obtain an elastic modified material with a core-shell structure; S3. Mix the elastic modifier of the core-shell structure evenly with polypropylene and the toughening agent, add them into a twin-screw extruder for melt extrusion, and granulate by die-face air-cooled hot cutting through a die head to obtain a toughened and flame-retardant polypropylene composite material based on gradation synergy; wherein, the length-diameter ratio of the screw of the twin-screw extruder is ≥48 / 1, and the temperature control range of each heating section is: the first section area is 90-100°C; the second section area is 100-110°C; the third section area is 100-110°C; the fourth section area is 150-160°C; the fifth section area is 170-180°C; the sixth section area is 190-200°C; the seventh section area is 190-200°C; the eighth section area is 180-190°C; the ninth section area is 180-190°C; the tenth section area is 160-170°C; the fifth section area and the eighth section area of the twin-screw extruder are provided with vacuum exhaust ports.

9. The preparation method of a toughened and flame-retardant polypropylene composite material based on gradation coordination according to claim 8, characterized in that, The roll gap of the three-roll grinder is adjusted to: the gap between the middle and rear rolls is 30-50 μm; the gap between the middle and front rolls is 20-30 μm; the speed ratio of the rear, middle and front rolls of the three-roll grinder is 1:2.5:(5.5-6.5).

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