Toughening flame-retardant polypropylene composite material based on grading synergy and preparation method thereof

Abstract

The invention discloses a toughened flame-retardant polypropylene composite material based on grading synergy and a preparation method thereof. The polypropylene composite material comprises the following raw materials in parts by weight: 100 parts of polypropylene, 10-15 parts of composite inorganic rigid particles, 15-18 parts of a composite flame retardant, 3-5 parts of an elastic interface agent, 0-3 parts of a toughening agent, 0.5-1 part of a dispersing agent and 0.3-0.5 part of a nucleating agent, the elastic interface agent is used for dispersing and coating the graded inorganic rigid particles and the graded flame retardant to form an elastic modified material with a core-shell structure, and the elastic modified material is used for polypropylene, so that the microcrack propagation direction during impact can be effectively changed, interface fracture caused by overlarge local stress during impact yield is prevented, and the impact resistance of the material is greatly improved. The flame retardant is uniformly dispersed in polypropylene through interface modification, so that a good flame retardant effect is achieved, and the problem that the mechanical property of the material is reduced due to addition of the flame retardant is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material modification, and in particular to a toughened flame-retardant polypropylene composite material based on grading synergy and a preparation method thereof. Background Art

[0002] Polypropylene is a widely used general-purpose plastic. Due to its good thermoforming processability, high strength, high stiffness, high hardness and good chemical stability, its use in home appliances and automotive parts is gradually increasing. In particular, the side methyl groups of isotactic polypropylene are on the same side of the main chain plane, with a regular structure, high crystallinity, outstanding dimensional stability, strength and bending fatigue resistance. By modifying polypropylene, its application field can be broadened and it can become the best material to replace engineering plastics. In particular, the current robots, drones, and automobiles are in urgent need of thin-walled injection molding parts, such as the robot's shell, frame, and internal structural parts; for example, the wings of drones and the interior sun visors of cars are made of polypropylene, which has become 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 guards of drones, they cannot effectively absorb the impact energy when falling from a high altitude, and there is a risk of cracking. In addition, polypropylene has deficiencies in flame retardancy. For example, the battery pack shell of new energy vehicles uses modified polypropylene, which requires not only high strength, high rigidity and high impact resistance, but also V0 level flame retardancy to ensure safety. These defects have limited the expansion of polypropylene applications.

[0004] In order to give full play to the application potential of polypropylene in the fields of automobile industry, drones, robots, etc., it is imperative to toughen and flame retardantly modify polypropylene. The existing toughening of polypropylene mainly uses elastomer toughening agents and nano inorganic rigid particles to blend. For example, the polypropylene nanocomposite material with low-temperature toughness and rigidity and its preparation method disclosed in China's invention patent publication number CN113912948B uses elastomers and inorganic rigid particles to modify polypropylene to achieve low-temperature toughening and rigidity balance. However, due to the large molecular spacing between monomers of polypropylene materials and the weak bonding force between molecular chains, the molecular chains are easy to move under the action of external stress. Excessive use of elastomer toughening will reduce the stiffness and strength of polypropylene while improving its toughness, making it difficult to meet the requirements of polypropylene to replace engineering materials. When a single nano inorganic rigid particle is used to toughen plastics, it mainly relies on the stress concentration effect of the inorganic rigid particles, causing the material to produce microcracks when impacted and absorb 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. On the other hand, in order to obtain flame-retardant polypropylene, more flame retardants are usually added. Flame retardants have greater adhesion, and particles adhere to each other and condense to become larger, making it difficult to disperse. Adding a large amount of flame retardants will destroy the continuous phase structure inside the material, thereby reducing the strength and toughness of the material. In particular, the addition of flame retardants is easy to precipitate and cause defects such as spots on the surface of the product. Summary of the invention

[0005] The present invention proposes 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 problem of low strength and toughness of flame-retardant polypropylene at present. The key technology used to solve this problem is to make polypropylene have both 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.

[0006] The specific solution to the problem is: A toughened flame-retardant polypropylene composite material based on graded synergy, characterized in that it comprises the following raw materials measured 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 parts of dispersant, and 0.3-0.5 parts of nucleating agent; wherein: The composite inorganic rigid particles are composed of grade I particles, grade II particles, and grade III particles in a mass ratio of (2-3):1:(1-2); wherein the grade I particles are zero-dimensional inorganic powders with a particle size of less than 50 nm; the grade II particles are two-dimensional inorganic powders with a thickness of 50-100 nm; and the grade III particles are one-dimensional inorganic powders with a diameter of 0.1-1 µm. The composite flame retardant is composed of zinc borate with a particle size of less than 10 nm, diethyl aluminum hypophosphite 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:(2-4):(4-6).

[0007] Preferably, the polypropylene is copolymer polypropylene, and the melt flow index under 230°C and 2.16kg load is 10-60g / 10min. Copolymer polypropylene has good rigidity and basic impact resistance, and suitable fluidity is conducive to uniform dispersion of grade ingredients.

[0008] Preferably, the zero-dimensional inorganic powder is selected from at least one of talc, kaolin, barium sulfate, montmorillonite, zinc oxide, aluminum oxide, glass beads, 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 a diameter-to-thickness 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 a length-to-diameter ratio of 30-50.

[0009] The existing technology usually uses a single nano inorganic powder as a rigid particle to toughen polypropylene. When subjected to external impact, the inorganic rigid particles induce the surrounding polypropylene to yield and deform, resulting in micro cracks that expand and absorb the impact energy, thus achieving the toughening effect. However, as the impact force increases further, the micro cracks absorb the impact energy and continue to expand, eventually leading to fracture of the material interface, and the toughening ability is limited.

[0010] In order to improve the toughening effect of inorganic rigid particles on polypropylene, the present invention improves the strength and impact resistance of polypropylene, especially the low-temperature impact resistance, by grading and coordination of grade I particles, grade II particles, and grade III particles of different shapes and particle sizes. Among them, zero-dimensional inorganic powder can produce more force dispersion points when the material is impacted, prevent stress concentration, and disperse the impact energy of the material; two-dimensional inorganic powder has a micro-flaky structure, which can effectively change the direction of micro-crack expansion during impact, prevent the material from cracking and increase the rigidity and strength of the material; one-dimensional inorganic powder has a fibrous structure, which prevents interface fracture caused by excessive local stress during impact yielding, so that the impact resistance and anti-cracking performance of the material are improved as a whole.

[0011] Preferably, the composite flame retardant is composed of zinc borate with a particle size of less than 10nm, diethyl aluminum hypophosphite with a particle size of 0.1-1µm, and cyanuric acid melamine with a particle size of 10-20µm, in a mass ratio of 1:3:4. When the temperature is higher than 280°C, zinc borate releases crystal water, which plays an endothermic cooling role. Nano-scale zinc borate will increase the contact area with the polypropylene material. When burning, zinc borate can absorb a large amount of heat and decompose, thereby reducing the temperature of the combustion area and slowing down the combustion rate; at the same time, nano-scale zinc borate decomposes to form a large area of ​​glassy layer to isolate oxygen, suppress smoke and prevent the formation of molten droplets. Diethyl aluminum hypophosphite is used as the main flame retardant, with a decomposition temperature of 380°C. When the temperature rises, diethyl aluminum hypophosphite will emit phosphorus-containing substances. When further heated by open flames, phosphorus-containing free radical quenchers are formed to effectively retard. Melamine cyanurate has a decomposition temperature of 350°C. It can dehydrate and release nitrogen at high temperature to form a dense carbonized layer, which isolates oxygen, reduces the flame spread rate, and significantly reduces the smoke density and toxic gas emissions produced by combustion.

[0012] The addition of flame retardants usually leads to increased interface defects of polypropylene due to poor dispersion, and decreased strength, toughness and bending modulus. The present invention adopts the coordination of flame retardant types, gradation of different particle sizes, and coordination of different decomposition temperatures, and uniformly disperses the flame retardant in polypropylene through elastic interface modification to achieve good flame retardant effect and certain toughening effect.

[0013] 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. The terminal hydroxyl group, amino-terminated, and carboxyl-terminated groups have good polarity, and their polar groups have good bonding effects with the inorganic rigid particles, zinc borate, and diethyl aluminum hypophosphite interface, so that the elastic interface agent covers the inorganic rigid particles, zinc borate, and diethyl aluminum hypophosphite to form a dispersed shell-core structure elastic modified material, which first solves the dispersibility and compatibility of the powder material in polypropylene; secondly, it increases the interfacial adhesion between the powder and polypropylene, and the inorganic rigid example and the flame retardant are dispersed in the polypropylene as fine elastic particles to prevent the material interface from breaking during impact.

[0014] Preferably, the toughening agent is an acrylic thermoplastic elastomer containing a glycidyl methacrylate functional group, such as Arkema's toughening agents AX8900 and AX8700, which can not only increase the low-temperature toughness of polypropylene, but also act as a compatibilizer to increase the compatibility and dispersion of flame retardants, inorganic rigid particles and polypropylene.

[0015] Preferably, the dispersant is at least one of ethylenebisoleamide, ethylenebisstearamide and stearic acid; through mechanical pre-dispersion, the dispersant is effectively adsorbed on the surface of inorganic rigid particles, zinc borate and diethylaluminum hypophosphite powder to form a protective film to prevent agglomeration between particles.

[0016] Preferably, the nucleating agent is a sorbitol nucleating agent or / and a carboxylic acid metal salt nucleating agent; when the polypropylene material is processed into products by injection molding, the higher the crystallinity, the tighter the molecular chain arrangement, the stronger the intermolecular force, and the higher the tensile strength. However, the product is brittle, and the impact strength decreases with the increase of crystallinity. The addition of the nucleating agent changes the crystallization characteristics and crystal morphology of polypropylene, and the crystal forms small and evenly distributed nuclei, which significantly improves its toughness while ensuring tensile strength.

[0017] Further preferably, the nucleating agent is a sorbitol nucleating agent and a carboxylic acid metal salt nucleating agent in a mass ratio of 2:1; the significant advantage is that the sorbitol nucleating agent can provide nucleation sites, promote the regular arrangement and crystallization of polypropylene segments at the nucleation sites, and the polyhydroxy structure of the sorbitol nucleating agent forms a stable interaction with the polypropylene chain, reduces the activation energy required for crystallization, and accelerates the formation of grains. Carboxylic acid metal salts are easily dispersed in polypropylene, which can effectively accelerate the crystallization rate and promote the refinement of grain size, thereby improving the toughness of the material.

[0018] The preparation method of the toughened flame-retardant polypropylene composite material based on gradation synergy is characterized in that the specific preparation method is as follows: S1. The composite inorganic rigid particles, composite flame retardant, dispersant, nucleating agent are premixed in a high mixer, and then sent to a jet mill for depolymerization and dispersion, and a pre-dispersed material is obtained by a classifier; S2. The pre-dispersed material and the elastic interface agent are added to a three-roll mill for grinding and dispersion, and the roller temperature of the three-roll mill is controlled to be below 60 ° C. Grind 3-4 times to obtain an elastic modified material with a core-shell structure; S3. The elastic modified material of the core-shell structure is uniformly mixed with polypropylene and a toughening agent, added into a twin-screw extruder for melt extrusion, and granulated by hot cutting on the die face through air cooling of the die head to obtain a toughened flame-retardant polypropylene composite material based on grading synergy; wherein the screw aspect ratio of the twin-screw extruder is ≥48 / 1, and the temperature control range of each heating section is: 90-100°C in the first section; 100-110°C in the second section; 100-110°C in the third section; 150-160°C in the fourth section; 170-180°C in the fifth section; 190-200°C in the sixth section; 190-200°C in the seventh section; 180-190°C in the eighth section; 180-190°C in the ninth section; 160-170°C in the tenth section; the fifth section and the eighth section of the twin-screw extruder are provided with vacuum exhaust ports.

[0019] Preferably, the roller spacing of the three-roll mill is adjusted to: the gap between the middle and rear rollers is 30-50µm; the gap between the middle and front rollers is 20-30µm; 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 grinds and disperses the high-viscosity material by mutual extrusion of the surfaces of the three horizontal rollers and friction dispersion of the speed difference of different rollers.

[0020] Preferably, the twin-screw extruder has a screw length-diameter ratio of 52 / 1; the screw with a large length-diameter ratio ensures that the material is fully mixed and sheared and dispersed. A lower temperature is set in the first to third sections to prevent the rubber body in the shell-core elastic modified material from solidifying prematurely, so that it is fully dispersed in the polypropylene; in the fourth to tenth sections, the shell-core elastic modified material is sheared and dispersed with the polypropylene, and at the same time, the rubber body in the shell-core elastic modified material is gradually solidified, the elasticity is increased, and it is completely compatible and dispersed with the polypropylene.

[0021] Compared with the prior art, the beneficial effects of the present invention are: (1) The present invention uses graded inorganic rigid particles of different shapes (zero-dimensional, two-dimensional, one-dimensional) and different particle sizes to toughen polypropylene. When the polypropylene material is impacted by external force, the direction of microcrack propagation during impact can be effectively changed to prevent interface fracture caused by excessive local stress during impact yielding, thereby ensuring that the material has excellent impact resistance while increasing rigidity and strength. By grading inorganic rigid particles, toughening agents can be omitted or used less, and toughness can be increased without losing tensile strength and rigidity.

[0022] (2) The present invention utilizes a dispersant and an elastic interface agent containing polar groups to disperse and coat inorganic rigid particles and flame retardants to form an elastic modified material 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 bonding force between the powder and polypropylene, and prevent the interface of the material from breaking during impact.

[0023] (3) The present invention adopts the coordination of flame retardant types, different particle size grading, and different decomposition temperatures. The flame retardant is evenly dispersed in polypropylene through interface modification. A good flame retardant effect can be achieved by using less flame retardant, avoiding the problem of reducing the mechanical properties of the material due to adding too much flame retardant. DETAILED DESCRIPTION

[0024] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0025] The raw material specifications and equipment parameters used in the examples and comparative examples are as follows. Other raw materials not specified are conventional commercially available materials or raw materials conventionally selected in the art.

[0026] Polypropylene: Grade K7760, MI 56g / 10min, tensile yield stress 23.5MPa, room temperature impact strength 5.0KJ / m 2 , flexural modulus 1100MPa, load heat deformation temperature 100℃, Yanshan Petrochemical Company.

[0027] Grade I particle zinc oxide: particle size is less than 50nm.

[0028] Grade I particle silica: particle size is less than 50nm.

[0029] Grade II particle mica powder: thickness 50-100nm, diameter-to-thickness ratio 10-50.

[0030] Grade III particles: calcium sulfate whiskers; diameter 0.5-1µm, aspect ratio 30-50.

[0031] Grade III calcium carbonate whiskers: diameter 0.5-1µm, aspect ratio 30-50.

[0032] Zinc borate: particle size less than 10nm (pre-grinded).

[0033] Diethylaluminum hypophosphite: particle size 0.1-1µm (pre-grinded).

[0034] Melamine cyanurate: particle size 10-20µm, Shouguang Weidong Chemical Co., Ltd.

[0035] Toughening agent: Brand AX8900, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, Arkema, France.

[0036] Toughening agent: Brand AX8700, ethylene-butyl acrylate-glycidyl methacrylate terpolymer, Arkema, France.

[0037] Sorbitol nucleating agent: Brand NX8000i, Milliken, USA.

[0038] Carboxylic acid metal salt nucleating agent: Brand NaV101, long-chain linear saturated carboxylic acid sodium salt with carbon chain length C28-C32 as the main component, Clariant Chemicals.

[0039] Three-roller grinding machine: Model S260, slow, medium and fast roller speed ratio: 1:2.5:6.25, Twin-screw extruder: Parallel co-rotating twin-screw extruder, model Φ53, aspect ratio L / D=52, torque coefficient 13.5. Example 1

[0040] S1. According to the raw material formula table in Table 1, the raw materials were weighed, and the grade I particles of zinc oxide, grade II particles of mica powder, grade III particles of calcium carbonate whiskers, zinc borate, diethyl aluminum hypophosphite, melamine cyanurate, ethylene bisoleamide, nucleating agent NX8000i, and nucleating agent NaV101 were added to the high mixer for premixing for 5 minutes, and then sent to the air flow mill for depolymerization and dispersion by air flow impact. The classification speed was controlled at 1200rpm, and the agglomerated large particles were refluxed and crushed by the classifier, and the completely depolymerized material was collected to obtain a pre-dispersed material; S2. Add the pre-dispersed material and the elastic interface agent hydroxyl-terminated polybutadiene liquid rubber to a three-roll mill for grinding and dispersion, control the roller temperature of the three-roll mill to be lower than 60°C, adjust the gap between the middle and rear rollers to 30µm; and the gap between the middle and front rollers to 20µm; repeat the grinding 4 times to obtain an elastic modified material with a core-shell structure; S3. The core-shell elastic modified material is mixed evenly with polypropylene, and the mixture is added into a twin-screw extruder for melt extrusion. The temperature of each heating section of the twin-screw extruder is controlled as follows: 90°C in the first section; 100°C in the second section; 110°C in the third section; 150°C in the fourth section; 170°C in the fifth section; 190°C in the sixth section; 190°C in the seventh section; 190°C in the eighth section; 180°C in the ninth section; and 170°C in the tenth section. Vacuum exhaust ports are provided in the fifth and eighth sections of the twin-screw extruder, and a vacuum pump is connected to discharge volatiles. The molten material is hot-cut and granulated through the air-cooled die surface of the die head, and then air-conveyed to a storage tank through a pipeline to obtain a toughened and flame-retardant polypropylene composite material based on grading synergy. Example 2

[0041] S1. According to the raw material formula table in Table 1, the raw materials were weighed, and the grade I particles of silica, grade II particles of mica powder, grade III particles of calcium sulfate whiskers, zinc borate, diethyl aluminum hypophosphite, melamine cyanurate, ethylene bisstearamide, and nucleating agent NX8000i were added to the high mixer for premixing for 5 minutes, and then sent to the air flow mill for depolymerization and dispersion by air flow impact. The classification speed was controlled at 1000 rpm, and the agglomerated large particles were refluxed and crushed by the classifier, and the completely depolymerized material was collected to obtain a pre-dispersed material; S2. Add the pre-dispersed material and the elastic interface agent amino-terminated liquid nitrile rubber to a three-roll mill for grinding and dispersion, control the roller temperature of the three-roll mill to be lower than 60°C, adjust the gap between the middle and rear rollers to 30µm; the gap between the middle and front rollers to 20µm; repeat the grinding 3 times to obtain an elastic modified material with a core-shell structure; S3. The core-shell elastic modified material is uniformly mixed with polypropylene and toughening agent AX8700, and the mixture is added into a twin-screw extruder for melt extrusion. The temperature of each heating section of the twin-screw extruder is controlled as follows: 90°C in the first section; 100°C in the second section; 110°C in the third section; 150°C in the fourth section; 170°C in the fifth section; 190°C in the sixth section; 190°C in the seventh section; 190°C in the eighth section; 180°C in the ninth section; and 170°C in the tenth section. Vacuum exhaust ports are provided in the fifth and eighth sections of the twin-screw extruder, and a vacuum pump is connected to discharge volatiles. The molten material is hot-cut and granulated through the air-cooled die surface of the die head, and then air-conveyed to a storage tank through a pipeline to obtain a toughened flame-retardant polypropylene composite material based on grading synergy.

[0042] Comparative Examples 1-1 to Comparative Examples 1-5 were subjected to comparative tests based on Example 1. Comparative Example 1-1 did not use an elastic interface agent, but used a toughening agent AX8900, and did not perform three-roll grinding. The rest of the preparation method was the same as that of Example 1, and the formula is shown in Table 1.

[0043] Comparative Examples 2-1 to Comparative Examples 2-5 were compared based on Example 2. Comparative Example 2-1 used diethyl aluminum hypophosphite (particle size 20-30 µm) without pre-grinding. The preparation method was the same as that of Example 2, and the formula was shown in Table 2.

[0044] Table 1: Raw material weight formula table of Example 1, Comparative Example 1-1 to Comparative Example 1-5

[0045] Table 2: Raw material weight formula of Example 2, Comparative Example 2-1 to Comparative Example 2-5

[0046] Mechanical properties testing: The polypropylene composite materials of the embodiment and the comparative example were injection molded into 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 tester was 50 mm / min; the bending strength and bending 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 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.

[0047] Flame retardant performance test: The polypropylene composite materials of the embodiment and the comparative example are injection molded into test specimens by an injection molding machine. According to the UL94 vertical combustion test standard, the material sample specimens are placed vertically, the sample thickness is 1.6mm, and the three levels of V-0, V-1, and V-2 are determined according to the combustion performance. Among them, the V-0 level represents the best flame retardant performance. After the sample has been subjected to two 10-second combustion tests, the flame goes out within 10 seconds, and no burning objects can fall. The V-1 level represents that after the sample has been subjected to two 10-second combustion tests, the flame goes out within 30 seconds, but the cotton wool located 30 cm below the sample cannot be ignited. The V-2 level represents that after the sample has been subjected to two 10-second combustion tests, the flame goes out within 30 seconds, but the cotton wool located 30 cm below the sample can be ignited.

[0048] According to GB / T 2406.2-2009 (Determination of combustion behavior of plastics by oxygen index method Part 2: Room temperature test), the test sample thickness is 4mm, oxygen and 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) of the material, the better the flame retardant performance of the material. The test results are shown in Table 3 and Table 4.

[0049] Table 3: Mechanical properties and flame retardant properties test data of Example 1, Comparative Examples 1-1 to Comparative Examples 1-5

[0050] Table 4: Mechanical properties and flame retardant properties test data of Example 2, Comparative Examples 2-1 to Comparative Examples 2-5

[0051] Through the experimental comparison of Example 1 and Comparative Examples 1-1 to Comparative Examples 1-5, the technical solution of the present invention adopts the grading coordination of inorganic rigid particles of different shapes and different particle sizes, which can effectively change the direction of microcrack expansion during impact, prevent interface fracture caused by excessive local stress during impact yield, and increase the rigidity and strength of the material while having excellent low-temperature impact resistance. The coating and dispersion of the elastic interface agent on the inorganic rigid example and the flame retardant are significant in improving the toughness and flame retardant properties of the material. Comparative Example 1-1 does not use an interface modified flame retardant, and the flame retardant is difficult to effectively disperse, affecting the impact performance and flame retardant effect of the material.

[0052] Through the experimental comparison of Example 2 and Comparative Examples 2-1 to Comparative Examples 2-5, the technical solution of the present invention adopts the coordination of different types of flame retardants, different particle size grading, and different decomposition temperatures to achieve a good flame retardant effect in polypropylene without affecting the mechanical properties of the material.

[0053] The above are only preferred embodiments and comparative analysis, and are not intended to limit the present invention in any form. Any technician familiar with the profession can use the technical ideas disclosed above to make equivalent embodiments with equivalent changes without departing from the scope of the technical solution of the present invention. However, all equivalent embodiments that do not depart from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A toughened flame-retardant polypropylene composite material based on gradation synergy, characterized in that: The invention comprises the following raw materials measured 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 parts of dispersant, and 0.3-0.5 parts of nucleating agent; wherein: The composite inorganic rigid particles are composed of grade I particles, grade II particles, and grade III particles in a mass ratio of (2-3):1:(1-2); wherein the grade I particles are zero-dimensional inorganic powders with a particle size of less than 50 nm; the grade II particles are two-dimensional inorganic powders with a thickness of 50-100 nm; and the grade III particles are one-dimensional inorganic powders with a diameter of 0.1-1 µm. The composite flame retardant is composed of zinc borate with a particle size of less than 10 nm, diethyl aluminum hypophosphite 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:(2-4):(4-6).

2. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: The polypropylene is selected from copolymerized polypropylene having a melt flow index of 10-60 g / 10 min at 230° C. and a load of 2.16 kg.

3. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: The zero-dimensional inorganic powder is selected from at least one of talc, kaolin, barium sulfate, montmorillonite, zinc oxide, aluminum oxide, glass beads, 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 a diameter-to-thickness 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 a length-to-diameter ratio of 30-50.

4. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: The composite flame retardant is composed of zinc borate with a particle size of less than 10 nm, diethyl aluminum hypophosphite 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.

5. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: 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.

6. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: The toughening agent is an acrylic thermoplastic elastomer containing a glycidyl methacrylate functional group.

7. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: The dispersant is at least one of ethylene bisoleamide, ethylene bisstearamide and stearic acid.

8. The toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 1, characterized in that: The nucleating agent is a sorbitol nucleating agent and / or a carboxylic acid metal salt nucleating agent.

9. The method for preparing a toughened flame-retardant polypropylene composite material based on gradation synergy according to any one of claims 1 to 8, characterized in that: The specific preparation method is as follows: S1. The composite inorganic rigid particles, composite flame retardant, dispersant, nucleating agent are premixed in a high mixer, and then sent to a jet mill for depolymerization and dispersion, and a pre-dispersed material is obtained by a classifier; S2. The pre-dispersed material and the elastic interface agent are added to a three-roll mill for grinding and dispersion, and the roller temperature of the three-roll mill is controlled to be below 60 ° C. Grind 3-4 times to obtain an elastic modified material with a core-shell structure; S3. The elastic modified material of the core-shell structure is uniformly mixed with polypropylene and a toughening agent, added into a twin-screw extruder for melt extrusion, and granulated by hot cutting on the die face through air cooling of the die head to obtain a toughened flame-retardant polypropylene composite material based on grading synergy; wherein the screw aspect ratio of the twin-screw extruder is ≥48 / 1, and the temperature control range of each heating section is: 90-100°C in the first section; 100-110°C in the second section; 100-110°C in the third section; 150-160°C in the fourth section; 170-180°C in the fifth section; 190-200°C in the sixth section; 190-200°C in the seventh section; 180-190°C in the eighth section; 180-190°C in the ninth section; 160-170°C in the tenth section; the fifth section and the eighth section of the twin-screw extruder are provided with vacuum exhaust ports.

10. The method for preparing a toughened flame-retardant polypropylene composite material based on gradation synergy according to claim 9, characterized in that: The roller spacing of the three-roll mill is adjusted to: the gap between the middle and rear rollers is 30-50µm; the gap between the middle and front rollers is 20-30µm; the speed ratio of the rear, middle and front rollers of the three-roll mill is 1:2.5:(5.5-6.5).

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