A polyolefin composite material, its preparation method and application

Abstract

This invention relates to the field of polymer composite materials technology, and discloses a polyolefin composite material, its preparation method, and its applications. The polyolefin composite material comprises the following raw materials: recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame-retardant masterbatch, compatibilizer, synergistic flame retardant, and anti-hydrolysis agent; the toughening agent's monomers include ethylene and propylene; the halogen-free flame-retardant masterbatch has a particle size Dv50 ≥ 10 μm. The polyolefin composite material provided by this invention possesses good mechanical properties, good flame retardancy, is environmentally friendly and low-carbon, and is resistant to high-humidity environments. Compared with currently widely used injection-molded thermoplastics, this material is easy to extrude and can be vacuum-formed, offering advantages such as low molding and processing costs and high cost-effectiveness. It can be applied to the preparation of larger-sized plastic parts such as battery pack covers and energy storage battery pack covers, and has good safety performance.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a polyolefin composite material, its preparation method, and its application. Background Technology

[0002] In recent years, with the advancement of global energy transition and carbon neutrality strategies, the energy storage battery industry has ushered in unprecedented development opportunities. As a key component of new energy vehicles and energy storage systems, the safety and reliability of energy storage battery packs are paramount. The battery pack cover, as an important part of the battery pack, bears the crucial responsibility of protecting the battery modules from damage caused by external impacts, compression, and other factors.

[0003] Currently, commonly used materials for battery pack covers include metals, thermosetting plastics, and carbon fiber composites. Among them, metal materials such as steel plates and aluminum alloys have high strength and rigidity, but their high density and heavy weight do not conform to the development trend of lightweight automobiles; thermosetting plastics are relatively lightweight, but their flame retardancy and weather resistance still need improvement, and the products are difficult to recycle and reuse at a high value after being scrapped; carbon fiber composites have advantages such as high strength, corrosion resistance, fatigue resistance, and good flame retardancy, but their high cost limits their widespread application.

[0004] Polypropylene (PP) is a semi-crystalline material with advantages such as being non-toxic, odorless, and having low density. It boasts good overall performance and high cost-effectiveness, making it widely used in home appliances, automobiles, and other fields. However, the strength, toughness, and flame retardant properties of existing polypropylene materials are still insufficient to meet the stringent requirements for battery pack covers. Summary of the Invention

[0005] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a polyolefin composite material; a second objective is to provide a method for preparing such a polyolefin composite material; and a third objective is to provide applications of such a polyolefin composite material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A first aspect of the present invention provides a polyolefin composite material comprising the following raw materials: recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant and anti-hydrolysis agent;

[0008] The toughening agent comprises ethylene and propylene monomers; the halogen-free flame retardant masterbatch has a particle size Dv50 ≥ 10 μm.

[0009] In some embodiments of the present invention, the polyolefin composite material further includes the following raw materials: antioxidants and lubricants.

[0010] In some embodiments of the present invention, the polyolefin composite material comprises the following raw materials by weight percentage:

[0011]

[0012] In some specific embodiments of the present invention, the polyolefin composite material comprises the following raw materials by weight percentage:

[0013]

[0014] In some embodiments of the present invention, the density of the recycled polypropylene is 0.89-0.93 g / cm³. 3 .

[0015] In some embodiments of the present invention, the melt flow index of the recycled polypropylene at test conditions of 230°C / 2.16kg is 1g / 10min-8g / 10min.

[0016] In some specific embodiments of the present invention, the melt index of the recycled polypropylene under test conditions of 230℃ / 2.16kg is 1g / 10min-5g / 10min.

[0017] In this invention, recycled polypropylene is used as the resin matrix, which can endow the composite material with good processing characteristics and balanced physical and mechanical properties. Compared with virgin polypropylene, it can realize the recycling of waste resources, with low cost and is more green and environmentally friendly.

[0018] In some embodiments of the present invention, the density of the linear low-density polyethylene is 0.91-0.93 g / cm³. 3 .

[0019] In some embodiments of the present invention, the linear low-density polyethylene has a melt index of 0.1 g / 10 min to 10 g / 10 min under test conditions of 190 °C / 2.16 kg.

[0020] In some specific embodiments of the present invention, the melt index of the linear low-density polyethylene under test conditions of 190℃ / 2.16kg is 0.1g / 10min-3g / 10min.

[0021] In this invention, linear low-density polyethylene is used as a melt strength modifier. It makes full use of the fact that polyethylene has a lower melting point and a wider melting range than polypropylene. During vacuum forming, it can effectively improve the melt strength of polypropylene and avoid problems such as vacuum forming cracking and severe wall thinning caused by low melt strength. In addition, linear low-density polyethylene also has a lower glass transition temperature and good flexibility, which can effectively improve the impact toughness of composite materials.

[0022] In some embodiments of the present invention, the toughening agent contains ethylene monomer at a content greater than or equal to 10 wt%.

[0023] In some embodiments of the present invention, the toughening agent has a melt index of 1 g / 10 min to 10 g / 10 min under test conditions of 230 °C / 2.16 kg.

[0024] In some embodiments of the present invention, the toughening agent is selected from at least one of ethylene propylene diene monomer (EPDM) and ethylene propylene copolymer (EPR).

[0025] In some specific embodiments of the present invention, the toughening agent is an ethylene-propylene copolymer.

[0026] In this invention, a copolymer containing both ethylene and propylene segments is selected as a toughening agent. This not only increases the toughness and load-bearing strength of the composite material, but also improves the compatibility between recycled polypropylene and linear low-density polyethylene, overcomes the delamination defects caused by their thermodynamic incompatibility, and improves the appearance properties of the composite material.

[0027] In some embodiments of the present invention, the phosphorus content in the halogen-free flame retardant masterbatch is 15wt%-30wt%, and the nitrogen content is 15wt%-35wt%.

[0028] In some embodiments of the present invention, the halogen-free flame retardant masterbatch uses polypropylene resin or polyethylene resin as a carrier.

[0029] In some embodiments of the present invention, the particle size Dv50 of the halogen-free flame retardant active ingredient in the halogen-free flame retardant masterbatch is 5-15 μm.

[0030] In some embodiments of the present invention, the effective content of the halogen-free flame retardant masterbatch is 50wt%-80wt%.

[0031] In this invention, nitrogen-phosphorus halogen-free flame retardant masterbatch is used. Compared with flame retardant powder of the same series, halogen-free flame retardant masterbatch has a larger particle size, which can overcome the defects of poor flowability and easy bridging of small particle size powder, improve the dispersibility of flame retardant in the mixing process, improve the mixing effect, and improve production efficiency.

[0032] In some embodiments of the present invention, the synergistic flame retardant is selected from at least one of kaolin, diatomaceous earth, and wollastonite.

[0033] In some embodiments of the present invention, the average particle size of the synergistic flame retardant is 0.3-1.5 μm.

[0034] In some specific embodiments of the present invention, the synergistic flame retardant is kaolin.

[0035] In this invention, inorganic flame retardants are used to exert a synergistic flame retardant effect. They utilize their high heat capacity and low thermal conductivity to absorb heat and reduce the transfer of heat to combustible materials, providing a thermal shielding effect. The synergistic flame retardant decomposes and absorbs heat at high temperatures, which can reduce the temperature of the material surface. The water vapor and carbon dioxide produced by the decomposition can also inhibit the spread of flames, effectively improving the ablation resistance of the material.

[0036] In some embodiments of the present invention, the compatibilizer includes maleic anhydride grafted reactive compatibilizers.

[0037] In some embodiments of the present invention, the melt index of the compatibilizer at test conditions of 190°C / 2.16kg is 60g / 10min-400g / 10min.

[0038] In some embodiments of the present invention, the grafting rate of the compatibilizer is 0.3%-2%.

[0039] In some specific embodiments of the present invention, the compatibilizer is selected from at least one of maleic anhydride-grafted polypropylene (PP-g-MAH), maleic anhydride-grafted polyolefin elastomer (POE-g-MAH), and maleic anhydride-grafted ethylene propylene diene monomer (EPDM-g-MAH).

[0040] In this invention, the addition of a compatibilizer can improve the interfacial bonding force between the halogen-free flame retardant masterbatch and the recycled polypropylene matrix resin, thereby effectively improving the strength and flame retardant properties of the material.

[0041] In some embodiments of the present invention, the melting point of the anti-hydrolysis agent is 105-120°C.

[0042] In some embodiments of the present invention, the anti-hydrolysis agent includes a polycarbodiimide anti-hydrolysis agent.

[0043] In this invention, the addition of an anti-hydrolysis agent can effectively improve the defects of nitrogen-phosphorus halogen-free flame retardants, such as easy migration under high temperature and humidity, poor resistance to high temperature boiling water, and easy degradation of flame retardant performance, which is beneficial to ensuring the flame retardant performance of the material.

[0044] In some embodiments of the present invention, the antioxidant is selected from at least one of hindered phenolic antioxidants, thioester antioxidants, and phosphite antioxidants.

[0045] In some embodiments of the present invention, the antioxidant is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanuric acid (antioxidant 3114), 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)trimethylbenzene (antioxidant 330), tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate (antioxidant 1790), trinonylphenyl phosphite (antioxidant TNPP), tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168), and bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626).

[0046] In this invention, the addition of antioxidants can prevent the material from undergoing high-temperature oxidative degradation during processing, while also improving the material's resistance to oxidative degradation during use.

[0047] In some embodiments of the present invention, the lubricant is selected from at least one of zinc stearate, calcium stearate, magnesium stearate, polyethylene wax, polypropylene wax, and N,N'-ethylene bis-stearamide.

[0048] In this invention, the addition of lubricant can give the material good lubrication properties, improve the dispersion performance of flame retardants and synergistic flame retardants in the material, reduce the friction between the material and the equipment cylinder, and improve the material's demolding properties and appearance gloss.

[0049] A second aspect of the present invention provides a method for preparing the polyolefin composite material described in the first aspect of the present invention, comprising the following steps:

[0050] The raw materials are mixed and melt-blended using a twin-screw extruder, then extruded and granulated to obtain the polyolefin composite material.

[0051] In some embodiments of the present invention, the mixing speed is 1000-3000 r / min and the mixing time is 2-5 min.

[0052] In some embodiments of the present invention, the twin-screw extruder is a parallel twin-screw extruder with a length-to-diameter ratio of (35-45):1.

[0053] In some embodiments of the present invention, the temperatures of each feeding section of the twin-screw extruder from the hopper to the die are as follows: Zone 1: 120-180℃, Zone 2: 130-180℃, Zone 3: 170-190℃, Zone 4: 170-200℃, Zone 5: 170-200℃, Zone 6: 170-200℃, Zone 7: 170-200℃, Zone 8: 170-200℃, Zone 9: 190-210℃, and Zone 10: 190-220℃.

[0054] In some embodiments of the present invention, the screw speed of the twin-screw extruder is 300-700 r / min.

[0055] In some embodiments of the present invention, the frequency of the feed screw of the main hopper of the twin-screw extruder is 20-45Hz.

[0056] In some embodiments of the present invention, the vacuum degree of the twin-screw extruder is 400-600 mmHg.

[0057] A third aspect of the present invention provides the application of the polyolefin composite material described in the first aspect of the present invention in the preparation of a battery pack cover.

[0058] In some embodiments of the present invention, the battery pack includes an electric vehicle battery pack and an energy storage battery pack.

[0059] Compared with the prior art, the beneficial effects of the present invention are:

[0060] 1) The polyolefin composite material provided by this invention uses recycled polypropylene as the main matrix. Compared with virgin polypropylene, it can realize the recycling of waste resources and has the characteristics of being economical, green, environmentally friendly, low-carbon, and environmentally friendly. The addition of linear low-density polyethylene effectively improves the impact toughness and processing performance of the composite material. The addition of halogen-free flame retardant masterbatch ensures the flame retardancy of the material while overcoming the defects of poor flowability and easy powder bridging of halogen-free flame retardant powder, thus improving production efficiency. The addition of a polymeric toughening agent containing ethylene and propylene monomers improves the compatibility between matrix resins, gives the material good appearance characteristics, and improves impact toughness. The addition of an anti-hydrolysis agent overcomes the defects of nitrogen-phosphorus halogen-free flame retardants, such as easy migration under high temperature and humidity and poor resistance to high-temperature boiling water, thus improving the flame retardant performance of the material. Through the synergistic effect of multiple raw materials, a tensile strength greater than 22 MPa and a cantilever beam notched impact strength greater than 4.2 KJ / m are obtained. 2 A polyolefin composite material with a flexural strength greater than 34MPa, a flexural modulus greater than 1500MPa, a flame retardant rating of up to V-0, resistance to high temperature ablation, and good processing performance.

[0061] 2) The preparation method of the polyolefin composite material provided by the present invention has simple steps, mild process conditions, and is suitable for industrial application;

[0062] 3) The polyolefin composite material provided by this invention has the characteristics of good mechanical properties, good flame retardancy, green and low carbon, and resistance to high humidity environment. Compared with the thermoplastic plastics that are currently commonly used for injection molding, this material is easy to extrude and can be vacuum formed, which has the advantages of low molding and processing cost and high cost performance. It can be applied to the preparation of plastic parts such as battery pack covers and energy storage battery pack covers of larger size, and has good safety performance. Detailed Implementation

[0063] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0064] The raw material information used in the following examples and comparative examples is shown in Table 1 below:

[0065] Table 1. Information on raw materials used in the examples and comparative examples.

[0066]

[0067] Among them, the recycled polypropylene has a content of 0.89-0.93 g / cm³. 3 The melt flow index of linear low-density polyethylene (LLDPE) under test conditions of 230℃ / 2.16kg was 2g / 10min-4g / 10min; the density of LLDPE was 0.91-0.93g / cm³. 3 The melt index of the ethylene-propylene copolymer is 0.7 g / 10 min to 2.3 g / 10 min under test conditions of 190℃ / 2.16 kg; the ethylene monomer content in the copolymer is greater than or equal to 10 wt%, and the melt index is 1 g / 10 min to 10 g / 10 min under test conditions of 230℃ / 2.16 kg; the grafting rate of the compatibilizer is 0.3% to 2%, and the melt index is 60 g / 10 min to 400 g / 10 min under test conditions of 190℃ / 2.16 kg; the phosphorus content in the halogen-free flame retardant masterbatch is ≥18 wt%, the nitrogen content is ≥19 wt%, the effective content is 50 wt% to 80 wt%, and the particle size Dv50 is 10 μm; the average particle size of the kaolin is 0.3 to 1.5 μm; the melting point of the polycarbodiimide hydrolysate is 105 to 120℃; and the particle size Dv50 of the halogen-free flame retardant powder is 7.2 μm.

[0068] Example 1

[0069] This embodiment prepares a polyolefin composite material, and the raw materials are shown in Table 2:

[0070] Table 2. Composition of polyolefin composite materials in Example 1

[0071]

[0072] The preparation method of polyolefin composite materials includes the following steps:

[0073] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 1500 r / min for 5 min.

[0074] The well-mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 450 r / min, the frequency of the main hopper feed screw is 28 Hz, and the vacuum degree is 500 mmHg. The material is then blended, melted and extruded.

[0075] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0076] Example 2

[0077] This embodiment prepares a polyolefin composite material, and the raw materials are shown in Table 3:

[0078] Table 3. Composition of polyolefin composite materials in Example 2

[0079]

[0080] The preparation method of polyolefin composite materials includes the following steps:

[0081] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 1500 r / min for 3 min.

[0082] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 460 r / min, the frequency of the main hopper feed screw is 26 Hz, and the vacuum degree is 550 mmHg. The material is then blended, melted and extruded.

[0083] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0084] Example 3

[0085] This embodiment prepares a polyolefin composite material, and the raw materials are shown in Table 4:

[0086] Table 4. Composition of polyolefin composite materials in Example 3

[0087]

[0088]

[0089] The preparation method of polyolefin composite materials includes the following steps:

[0090] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 1800 r / min for 3 min.

[0091] The well-mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 600 r / min, the frequency of the main hopper feed screw is 30 Hz, and the vacuum degree is 550 mmHg. The material is then blended, melted and extruded.

[0092] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0093] Example 4

[0094] This embodiment prepares a polyolefin composite material, and the raw materials are shown in Table 5:

[0095] Table 5. Composition of polyolefin composite materials in Example 4

[0096]

[0097]

[0098] The preparation method of polyolefin composite materials includes the following steps:

[0099] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 2000 r / min for 4 min.

[0100] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 650 r / min, the frequency of the main hopper feed screw is 32 Hz, and the vacuum degree is 580 mmHg. The material is then blended, melted and extruded.

[0101] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0102] Comparative Example 1

[0103] This comparative example prepares a polyolefin composite material, and the raw materials are shown in Table 6:

[0104] Table 6. Raw material composition of polyolefin composite materials in Comparative Example 1

[0105]

[0106] The preparation method of polyolefin composite materials includes the following steps:

[0107] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 2000 r / min for 4 min.

[0108] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 650 r / min, the frequency of the main hopper feed screw is 32 Hz, and the vacuum degree is 580 mmHg. The material is then blended, melted and extruded.

[0109] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0110] Comparative Example 2

[0111] This comparative example prepares a polyolefin composite material, and the raw materials are shown in Table 7:

[0112] Table 7. Raw material composition of polyolefin composite materials in Comparative Example 2

[0113]

[0114] The preparation method of polyolefin composite materials includes the following steps:

[0115] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 2000 r / min for 4 min.

[0116] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 650 r / min, the frequency of the main hopper feed screw is 32 Hz, and the vacuum degree is 580 mmHg. The material is then blended, melted and extruded.

[0117] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0118] Comparative Example 3

[0119] This comparative example prepares a polyolefin composite material, and the raw materials are shown in Table 8:

[0120] Table 8. Raw material composition of polyolefin composite materials in Comparative Example 3

[0121]

[0122]

[0123] The preparation method of polyolefin composite materials includes the following steps:

[0124] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant powder, compatibilizer, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 2000 r / min for 4 min.

[0125] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 650 r / min, the frequency of the main hopper feed screw is 32 Hz, and the vacuum degree is 580 mmHg. The material is then blended, melted and extruded.

[0126] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0127] Comparative Example 4

[0128] This comparative example prepares a polyolefin composite material, and the raw materials are shown in Table 9:

[0129] Table 9. Raw material composition of polyolefin composite materials in Comparative Example 4

[0130]

[0131]

[0132] The preparation method of polyolefin composite materials includes the following steps:

[0133] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, synergistic flame retardant, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 1500 r / min for 3 min.

[0134] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 460 r / min, the frequency of the main hopper feed screw is 26 Hz, and the vacuum degree is 550 mmHg. The material is then blended, melted and extruded.

[0135] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0136] Comparative Example 5

[0137] This comparative example prepares a polyolefin composite material, and the raw materials are shown in Table 10:

[0138] Table 10. Raw material composition of polyolefin composite materials in Comparative Example 5

[0139]

[0140] The preparation method of polyolefin composite materials includes the following steps:

[0141] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, anti-hydrolysis agent, antioxidant and lubricant to a high-speed mixer and stir at 1500 r / min for 5 min.

[0142] The well-mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 450 r / min, the frequency of the main hopper feed screw is 28 Hz, and the vacuum degree is 500 mmHg. The material is then blended, melted and extruded.

[0143] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0144] Comparative Example 6

[0145] This comparative example prepares a polyolefin composite material, and the raw materials are shown in Table 11:

[0146] Table 11. Raw material composition of polyolefin composite materials in Comparative Example 6

[0147]

[0148] The preparation method of polyolefin composite materials includes the following steps:

[0149] Add recycled polypropylene, linear low-density polyethylene, toughening agent, halogen-free flame retardant masterbatch, compatibilizer, synergistic flame retardant, antioxidant and lubricant to a high-speed mixer and stir at 2000 r / min for 4 min.

[0150] The uniformly mixed material is added to the main feed hopper of a parallel twin-screw extruder with a length-to-diameter ratio of 40:1. The temperatures of each section (zones 1-10) of the extruder from the hopper to the die are set to 150℃, 160℃, 170℃, 180℃, 180℃, 190℃, 180℃, 190℃, 190℃ and 200℃ respectively. The screw speed of the main extruder is 650 r / min, the frequency of the main hopper feed screw is 32 Hz, and the vacuum degree is 580 mmHg. The material is then blended, melted and extruded.

[0151] The pellets that come out of the extruder die are cooled in a water tank and dried by a fan, and then enter a pelletizer for pelletizing to obtain polyolefin composite materials with a length of 3-5 mm and a diameter of 2-4 mm.

[0152] Performance testing

[0153] The performance of the polyolefin composites prepared in Examples 1-4 and Comparative Examples 1-6 was tested. The test items and reference standards are as follows:

[0154] 1. Tensile strength: Tested according to GB / T 1040-2018 "Determination of tensile properties of plastics";

[0155] 2. Notched impact strength of cantilever beam: Tested according to GB / T 1843-2008 "Standard for Determination of Impact Strength of Plastic Cantilever Beams";

[0156] 3. Bending strength and bending modulus: Tested in accordance with GB / T 9341-2008 "Determination of bending properties of plastics";

[0157] 4. Flame retardancy: Tested according to UL 94 fire rating;

[0158] 5. Ablation resistance time: Plastic square plates with a side length of 150 mm and a thickness of 3.0 mm were prepared from the polyolefin composite materials in Examples 1-4 and Comparative Examples 1-6. They were placed above the blue inner flame of a Bunsen burner with a flame height of 125 mm and a blue inner flame height of 40 mm, 40 mm away from the Bunsen burner. The plane of the sample was kept perpendicular to the flame. The time from when the flame burned the center of the sample to when it just began to burn through was recorded as the ablation resistance time. Three plates were taken for each test and the average value was taken.

[0159] 6. Molding and processability: The evaluation criteria are as follows:

[0160] ①Advantages: During extrusion granulation, the raw and auxiliary materials are fed stably and smoothly, the extruder current is stable, and the strip drawing and pelletizing are normal; the vacuum forming is smooth, the surface of the parts is flat, and it fits tightly with the mold;

[0161] ② In the middle: the feeding of raw materials and auxiliary materials is unstable and not smooth during extrusion granulation, the extruder current fluctuates, and the strip drawing and pelletizing are normal; the vacuum forming is smooth, the surface of the parts is basically flat, and it fits tightly with the mold;

[0162] ③ Poor: The feeding of raw materials and auxiliary materials is unstable and not smooth during extrusion granulation, the extruder current fluctuates significantly, and the strip drawing and pelletizing are normal; the vacuum forming process is difficult, the surface of the parts is uneven, and the parts do not fit tightly with the mold.

[0163] Table 12 Performance test results of polyolefin composite materials in Examples 1-4 and Comparative Examples 1-6

[0164]

[0165]

[0166] Table 12 shows the performance test results of the polyolefin composites in Examples 1-4 and Comparative Examples 1-6. As can be seen from Table 12, the polyolefin composites prepared in Examples 1-4 have a tensile strength greater than 22 MPa and a cantilever beam notched impact strength greater than 4.2 KJ / m². 2 The flexural strength is greater than 34MPa, the flexural modulus is greater than 1500MPa, the mechanical properties are balanced and all are at a superior level; the flame retardancy rating of the polyolefin composite material can reach V-0, with excellent flame retardancy, good ablation resistance and good processing performance, which can meet the requirements of battery pack cover for the physical properties, flame retardancy and processing performance of the prepared material.

[0167] Compared to Example 4, replacing linear low-density polyethylene with an equal amount of polyolefin elastomer (POE) drastically reduced the strength and rigidity of the material. Furthermore, the material was prone to surface wrinkling defects during vacuum forming, leading to decreased molding stability. Compared to Example 4, replacing ethylene-propylene copolymer with an equal amount of polyolefin elastomer (POE) somewhat reduced the strength and rigidity of the material. Compared to Example 4, replacing halogen-free flame retardant masterbatch with equivalent halogen-free flame retardant powder resulted in powder bridging during production, deteriorating the material's processing performance and reducing production efficiency. Compared to Example 2, Comparative Example 4 showed a significant decrease in strength without compatibilizer, but little change in rigidity. Compared to Example 1, Comparative Example 5 showed a shortened high-temperature flame erosion resistance time and deteriorated performance without kaolin. Compared to Example 4, Comparative Example 6 showed little change in mechanical properties without anti-hydrolysis agent, but a significant decrease in flame retardant performance under warm water boiling conditions. The polyolefin composite material provided by this invention exhibits synergistic effects among its components, resulting in excellent mechanical properties, flame retardancy, and moldability. However, altering the formulation of the composite material can lead to a decline in its overall performance, hindering its application.

Claims

1. A polyolefin composite material, characterized in that, It is prepared from the following raw materials by mass percentage: Recycled polypropylene 20%-45%; Linear low-density polyethylene 10%-25%; Toughening agent 1%-8%; Halogen-free flame retardant masterbatch 30%-45%; Compatibilizer 1%-8%; Synergistic flame retardant 2%-10%; Anti-hydrolysis agent 1%-5%; Antioxidant 0.1%-1%; Lubricant 0.1%-1%; The toughening agent comprises ethylene and propylene monomers; the halogen-free flame retardant masterbatch has a particle size Dv50 ≥ 10 μm. The synergistic flame retardant is selected from at least one of kaolin, diatomite, and wollastonite. The anti-hydrolysis agent includes a polycarbodiimide anti-hydrolysis agent.

2. The polyolefin composite material according to claim 1, characterized in that, The melt flow index of the recycled polypropylene at test conditions of 230℃ / 2.16kg is 1g / 10min-8g / 10min.

3. The polyolefin composite material according to claim 1, characterized in that, The linear low-density polyethylene has a melt index of 0.1 g / 10 min to 10 g / 10 min under test conditions of 190 °C / 2.16 kg.

4. The polyolefin composite material according to claim 1, characterized in that, The toughening agent contains ethylene monomer at a content greater than or equal to 10 wt%.

5. The polyolefin composite material according to claim 4, characterized in that, The toughening agent has a melt flow index of 1 g / 10 min to 10 g / 10 min under the test conditions of 230℃ / 2.16 kg.

6. The polyolefin composite material according to claim 1, characterized in that, The halogen-free flame retardant masterbatch contains 15wt%-30wt% phosphorus and 15wt%-35wt% nitrogen.

7. The polyolefin composite material according to claim 1, characterized in that, The compatibilizer includes maleic anhydride-grafted reactive compatibilizers.

8. The polyolefin composite material according to any one of claims 1-7, characterized in that, The polyolefin composite material has a diameter of 2-4 mm and a length of 3-5 mm.

9. A method for preparing the polyolefin composite material according to any one of claims 1-8, characterized in that, Includes the following steps: The raw materials are mixed and melt-blended using a twin-screw extruder, then extruded and granulated to obtain the polyolefin composite material.

10. The use of the polyolefin composite material according to any one of claims 1-8 in the preparation of a battery pack cover.

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