Environment-friendly flame-retardant master batch for crosslinked polyethylene and preparation method thereof

Abstract

The application discloses an environment-friendly flame-retardant master batch for crosslinked polyethylene and a preparation method thereof, and belongs to the technical field of high polymer flame-retardant materials. The flame-retardant master batch is prepared from LLDPE resin as a base material, an aluminum diethyl phosphinate, melamine polyphosphate and modified magnesium hydroxide to form a phosphorus-nitrogen-inorganic ternary synergistic flame-retardant system, the addition of sepiolite which is resistant to high temperature and flame-retardant, the modification of an interface by using a PE-g-MAH compatilizer, and the addition of compounded antioxidants, lubricants and anti-dripping agents, high-speed mixing, three-screw mixing, single-screw extrusion, surface grinding and cutting, magnetic selection and vacuum packaging. The flame-retardant master batch can make the crosslinked polyethylene material reach UL94V-0 grade with 10% of the addition amount, and has the characteristics of low smoke, environmental protection, low release, high mechanical property retention rate and the like, and is suitable for the field of electric wires and cables.

Description

Technical Field

[0001] This invention relates to the field of polymer flame retardant materials, specifically to an environmentally friendly flame retardant masterbatch for cross-linked polyethylene and its preparation method. Background Technology

[0002] Cross-linked polyethylene (XLPE) is a polymer material based on ordinary polyethylene, which transforms its linear molecular structure into a three-dimensional network structure through physical or chemical cross-linking. This significantly improves its heat resistance, deformation resistance, electrical insulation, and service life, and it has been widely used in core areas such as wires and cables, pipes, and insulating sheaths. However, XLPE is inherently flammable and has a low limiting oxygen index. During combustion, it easily produces molten drips and releases large amounts of dense smoke, posing a serious fire safety hazard and limiting its further application in high-safety-requirement scenarios.

[0003] Currently, flame retardant masterbatches used for polyethylene on the market are mainly divided into two systems, both of which have obvious technical defects:

[0004] Halogenated flame retardant systems have high flame retardant efficiency, but they produce a lot of smoke and release toxic and corrosive gases when burning, which does not meet the requirements for environmental protection and low smoke and non-toxic use, and their use has been gradually restricted by the market.

[0005] Halogen-free flame retardant systems: Phosphorus-nitrogen intumescent flame retardants have poor compatibility with non-polar polyethylene, weak interfacial bonding, and are prone to surface precipitation and migration, affecting appearance and long-term stability. Although aluminum hydroxide / magnesium hydroxide inorganic flame retardant systems are environmentally friendly, their high addition amount can significantly reduce the tensile strength, elongation at break, and other mechanical properties of the material, leading to brittleness and poor processability of the products.

[0006] Meanwhile, most existing production processes use twin-screw compounding extrusion, water drawing, air drying, pelletizing, and drying processes, resulting in low output and incomplete moisture removal. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art and provide an environmentally friendly flame retardant masterbatch and method for cross-linked polyethylene, so as to solve the problems of poor environmental protection and mechanical properties of existing flame retardant masterbatches used for polyethylene.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] An environmentally friendly flame-retardant masterbatch for cross-linked polyethylene, the masterbatch being composed of the following raw materials in parts by weight: polyethylene resin: 40-60 parts; aluminum diethylphosphinate: 25-35 parts; melamine polyphosphate: 8-12 parts; modified magnesium hydroxide: 5-8 parts; sepiolite: 3-5 parts; maleic anhydride-grafted polyethylene: 3-6 parts; compound antioxidant: 0.3-0.8 parts; silicone masterbatch: 0.3-0.6 parts; polytetrafluoroethylene micro powder: 0.2-0.6 parts; char-forming accelerator: 2-5 parts; layered nanofiller: 1-3 parts; smoke suppressant: 1-2 parts.

[0010] Preferably, the polyethylene resin is LLDPE, the char-forming accelerator is selected from pentaerythritol phosphate or dipentaerythritol, the layered nanofiller is organically modified montmorillonite, and the smoke suppressant is zinc borate.

[0011] Preferably, the compound antioxidant is selected from any two or three combinations of antioxidant 1010, antioxidant DLTP, antioxidant 300#, and antioxidant 168, the silicone masterbatch is a 50% silicone masterbatch, and the polytetrafluoroethylene micro powder is used as an anti-dripping agent.

[0012] Preferably, the masterbatch is composed of the following raw materials in parts by weight: 50 parts LLDPE resin, 32 parts aluminum diethylphosphinate, 10 parts melamine polyphosphate (MPP), 5 parts modified magnesium hydroxide, 3 parts sepiolite, 5 parts maleic anhydride grafted polyethylene (PE-g-MAH), 4 parts char-forming accelerator (pentaerythritol phosphate, PEPA), 2 parts organic modified montmorillonite, 1 part smoke suppressant, 0.6 parts compound antioxidant, 0.5 parts silicone masterbatch, 0.3 parts polytetrafluoroethylene micro powder, wherein the mass ratio of antioxidant 300 to antioxidant 168 in the compound antioxidant is 1:1.

[0013] Preferably, the organically modified montmorillonite is quaternary ammonium salt intercalated montmorillonite with an interlayer spacing ≥2.5 nm.

[0014] The application of environmentally friendly flame-retardant masterbatch for cross-linked polyethylene is to add 10% of the flame-retardant masterbatch to cross-linked polyethylene materials for wires and cables, so that the flame retardant rating of the cross-linked polyethylene material reaches UL94V-0 level.

[0015] A method for preparing environmentally friendly flame-retardant masterbatch for cross-linked polyethylene includes the following steps:

[0016] S1. Raw material pretreatment: The raw materials used are dried to remove moisture; the organic modified montmorillonite is pre-dried under vacuum at 80-100℃ for 4 hours.

[0017] S2, Staged High-Speed ​​Mixing:

[0018] First stage: Add polyethylene resin, aluminum diethylphosphinate, melamine polyphosphate, modified magnesium hydroxide, sepiolite, char formation accelerator, layered nanofiller, smoke suppressant, and maleic anhydride-grafted polyethylene, and stir in a high-speed mixer at 800-1200 rpm for 5-8 minutes.

[0019] Second stage: Add compound antioxidant, silicone masterbatch, and polytetrafluoroethylene micro powder, continue stirring for 2-3 minutes, and then discharge;

[0020] S3, Three-screw compounding extrusion granulation:

[0021] A three-screw compounding extruder is used, with an upper-stage extrusion temperature of 120–160℃, a lower-stage extrusion temperature of 90–110℃, and a die head temperature of 110–120℃.

[0022] After the materials are mixed and extruded, they are successively ground, air-cooled and pelletized, magnetically separated, boiled and cooled, and vacuum-packed to obtain the finished product.

[0023] Preferably, the length-to-diameter ratio of the three-screw compounding extruder is 36:1 to 48:1, and the screw speed is 300 to 600 rpm.

[0024] Preferably, the grinding and air-cooling pelletizing does not use water cooling medium, and the temperature of the masterbatch after pelletizing is ≤50℃; the boiling cooling adopts a fluidized bed airflow cooling method to cool the masterbatch to room temperature before vacuum packaging.

[0025] Preferably, in the first stage of S2, 0.2 to 0.5% of the total weight of the raw materials is added as a wetting agent to promote the dispersion of the nanofiller.

[0026] Beneficial effects:

[0027] This invention employs a flame-retardant system constructed from aluminum diethylphosphonate (a dual-mechanism flame retardant system for both gas and condensed phases), melamine polyphosphate (for expansion and char formation), modified magnesium hydroxide (for heat absorption, cooling, and smoke suppression), sepiolite (for char layer reinforcement and insulation), a char formation accelerator (for dense char formation), organically modified montmorillonite (for a nano-barrier layer), and zinc borate (for catalytic char formation and smoke suppression). Adding only 10% of the flame-retardant masterbatch to cross-linked polyethylene enables the material to pass the UL94V-0 flammability test, achieving a limiting oxygen index (LOI) of 29.6%–31%, significantly superior to traditional halogen-free flame-retardant systems. Due to the use of a low-addition, high-efficiency flame-retardant system, and the use of a maleic anhydride-grafted polyethylene compatibilizer to improve interfacial bonding, the flame-retardant masterbatch has minimal impact on the mechanical properties of the matrix.

[0028] The anhydride groups of maleic anhydride-grafted polyethylene chemically bond or form strong hydrogen bonds with the active groups such as hydroxyl and amino groups on the surface of polar flame retardants such as aluminum diethylphosphinate and modified magnesium hydroxide. Simultaneously, its polyethylene backbone is highly compatible with the LLDPE matrix, thus constructing a "molecular bridge" between the flame retardant and resin interface, effectively anchoring the flame retardant and preventing its migration to the surface under heat aging or humid conditions. In all embodiments of this invention, no exudates were found on the sample surface, while the comparative sample without PE-g-MAH showed a distinct white powder layer. This excellent anti-exudation performance ensures the appearance, electrical insulation, and flame retardant stability of the wires and cables during long-term use.

[0029] This invention is a halogen-free flame retardant system that produces minimal smoke during combustion and does not generate toxic or corrosive gases, meeting environmental protection requirements. It is suitable for the wire and cable industry, where safety and environmental performance are paramount. The process employs three-screw compounding extrusion, grinding and air-cooling pelletizing, magnetic separation, fluidized bed cooling, and vacuum packaging, resulting in excellent plasticizing and compounding effects, uniform dispersion of flame retardants and additives, prevention of moisture residue, high production efficiency, and stable product quality. It also avoids the problem of difficult moisture removal found in traditional water-drawing processes.

[0030] This invention employs a three-screw compounding extrusion process instead of a traditional twin-screw extruder, significantly enhancing the shear dispersion effect of the highly filled flame-retardant system and achieving uniform distribution of the nanofiller (organically modified montmorillonite) and various additives. It uses surface-grinding and air-cooled pelletizing instead of water-jetting cooling, completely avoiding moisture contact and eliminating problems such as heat-processing bubbles and flame retardant hydrolysis caused by residual moisture inside the masterbatch in traditional processes. Subsequent boiling cooling rapidly cools the masterbatch to prevent sticking, and vacuum packaging ensures low moisture content for long-term product storage. This process route offers excellent plasticizing and compounding effects, uniform dispersion, high production efficiency, and stable batch production, making it suitable for large-scale industrial production. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1:

[0033] A method for preparing an environmentally friendly flame-retardant masterbatch for cross-linked polyethylene includes the following steps:

[0034] Weigh the following raw materials according to parts by weight:

[0035] LLDPE resin: 50 parts, aluminum diethylphosphinate: 30 parts, melamine polyphosphate (MPP): 10 parts, modified magnesium hydroxide: 7 parts, sepiolite: 3 parts, maleic anhydride grafted polyethylene (PE-g-MAH): 5 parts, char-forming accelerator (dipentaerythritol, DPER): 3 parts, layered nanofiller (organically modified montmorillonite, OMMT, quaternary ammonium salt intercalation, interlayer spacing 2.8 nm): 2 parts, smoke suppressant (zinc borate): 1.5 parts, compound antioxidant (antioxidant 1010 and antioxidant DLTP compounded in a 1:1 mass ratio): 0.6 parts

[0036] 50% silicone masterbatch: 0.5 parts, polytetrafluoroethylene micro powder (PTFE): 0.3 parts.

[0037] Raw material pretreatment:

[0038] LLDPE, aluminum diethylphosphinate, MPP, modified magnesium hydroxide, sepiolite, dipentaerythritol, and zinc borate were placed in a forced-air drying oven and dried at 80°C for 4 hours until the moisture content was ≤0.1%. The organically modified montmorillonite was vacuum dried at 90°C for 4 hours.

[0039] High-speed mixing:

[0040] First, add LLDPE, aluminum diethylphosphinate, MPP, modified magnesium hydroxide, sepiolite, dipentaerythritol, organically modified montmorillonite, zinc borate, and PE-g-MAH, and stir at 1000 rpm for 6 minutes in a high-speed mixer; then add compound antioxidant, silicone masterbatch, and PTFE micro powder, and continue stirring for 2.5 minutes before discharging.

[0041] Extrusion granulation:

[0042] A three-screw compounding extruder (length-to-diameter ratio 40:1) was used, with an upper-stage extrusion temperature of 130–150℃, a lower-stage extrusion temperature of 95–105℃, and a die head temperature of 115℃; the screw speed was 450 rpm. After compounding and extrusion, the material was successively subjected to grinding, air-cooled pelletizing (without water cooling), magnetic separation, fluidized bed cooling (cooling to room temperature), and vacuum packaging to obtain flame-retardant masterbatch.

[0043] The above flame retardant masterbatch was added to the cross-linked polyethylene base material at a dosage of 10%, and the material was extruded, granulated, and pressed into test pieces before performance testing.

[0044] Test results:

[0045] UL94 Flame Retardant Rating: V-0

[0046] Limiting Oxygen Index (LOI): 33.2%

[0047] Smoke Density Rating (SDR): 62

[0048] Tensile strength: 23.5 MPa

[0049] Elongation at break: 785%

[0050] Surface precipitation: No precipitation

[0051] Example 2:

[0052] A method for preparing an environmentally friendly flame-retardant masterbatch for cross-linked polyethylene includes the following steps:

[0053] Weigh the following raw materials according to parts by weight: LLDPE resin: 50 parts, aluminum diethylphosphinate: 32 parts

[0054] M melamine polyphosphate (MPP): 10 parts, modified magnesium hydroxide: 5 parts, sepiolite: 3 parts

[0055] PE-g-MAH: 5 parts; Carbonization accelerator (Pentaerythritol phosphate, PEPA): 4 parts; Organically modified montmorillonite: 2 parts; Zinc borate: 1 part; Compound antioxidant (antioxidant 300# and antioxidant 168 in a 1:1 mass ratio): 0.6 parts; 50% silicone masterbatch: 0.5 parts; PTFE micro powder: 0.3 parts.

[0056] The preparation steps are the same as in Example 1.

[0057] Test results:

[0058] UL94 Flame Retardant Rating: V-0

[0059] LOI: 34.1%

[0060] SDR: 58

[0061] Tensile strength: 24.2 MPa

[0062] Elongation at break: 810%

[0063] Surface precipitation: No precipitation.

[0064] Example 3:

[0065] A method for preparing an environmentally friendly flame-retardant masterbatch for cross-linked polyethylene includes the following steps:

[0066] Weigh the following raw materials by weight: 50 parts LLDPE, 30 parts aluminum diethylphosphinate, 12 parts melamine polyphosphate (MPP), 5 parts modified magnesium hydroxide, 3 parts sepiolite, 5 parts maleic anhydride grafted polyethylene, 0.6 parts compound antioxidant, 0.5 parts 50% silicone masterbatch, and 0.3 parts polytetrafluoroethylene micro powder.

[0067] The preparation steps are the same as in Example 1.

[0068] Test results:

[0069] UL94 Flame Retardant Rating: V-0

[0070] LOI: 32.8%

[0071] SDR: 64

[0072] Tensile strength: 22.9 MPa

[0073] Elongation at break: 795%

[0074] Surface precipitation: No precipitation.

[0075] Comparative Example 1:

[0076] Weigh the following components by weight: LLDPE resin: 50 parts; aluminum diethylphosphinate: 30 parts; MP melamine polyphosphate: 10 parts; modified magnesium hydroxide: 7 parts; sepiolite: 3 parts; PE-g-MAH: 5 parts; compound antioxidant: 0.6 parts; silicone masterbatch: 0.5 parts; PTFE micro powder: 0.3 parts. No charring accelerator, organically modified montmorillonite, or zinc borate are added. The preparation steps are the same as in Example 1.

[0077] Test results: UL94 flame retardancy rating: V-0 (but occasional ignition of cotton by dripping material); LOI: 29.8%; SDR: 78; tensile strength: 22.1 MPa; elongation at break: 770%; surface exudation: no exudation.

[0078] Comparative analysis: Although the V-0 rating can still be achieved without char-forming accelerators, nanofillers, and smoke suppressants, the limiting oxygen index drops to below 30%, smoke density increases significantly, char layer becomes loose and discontinuous, and overall flame retardant efficiency decreases.

[0079] Comparative Example 2:

[0080] To avoid adding char-forming accelerators, OMMT, and zinc borate, the preparation method is the same as in Example 1.

[0081] Test results: UL94 flame retardancy rating: V-0; LOI: 30.0%; SDR: 76; tensile strength: 22.0 MPa; elongation at break: 780%; surface exudation: no exudation.

[0082] Comparative Example 3:

[0083] The process uses only an aluminum hydroxide / magnesium hydroxide single inorganic flame retardant system, with a total flame retardant addition of 40 parts, and the other conditions are the same as conventional processes.

[0084] The performance comparison test is shown in the table below:

[0085] Results Explanation

[0086] UL94 rating V-0 V-0 V-0 V-0 (occasional dripping) V-0 No grade LOI / % 33.2 34.1 32.8 29.8 30 24 Smoke Density Rating (SDR) 62 58 64 78 76 74 Tensile strength / MPa 23.5 24.2 22.9 22.1 22 15.5 Elongation at break / % 785 810 795 770 780 420 Surface precipitation none none none none none slight

[0087] This invention, with all additives at 10%, introduces a char-forming accelerator (PEPA / DPER), organically modified montmorillonite, and zinc borate. This increases the limiting oxygen index from 30.0% to 32.8%~34.2%, and reduces the smoke density rating from 76 to 58~64. The flame retardant efficiency, smoke suppression performance, and mechanical retention rate of this invention are significantly improved, achieving a leading level in overall performance compared to similar technologies. It is particularly suitable for the wire and cable industry, where stringent requirements for low smoke, non-toxicity, and high flame retardancy are required.

[0088] Meanwhile, this invention uses maleic anhydride-grafted polyethylene as a compatibilizer, which significantly improves the interfacial compatibility between the polar flame retardant and the non-polar cross-linked polyethylene, effectively inhibiting the migration and precipitation of the flame retardant. The verification data are as follows:

[0089] Experimental design: With a fixed flame retardant masterbatch formulation (50 parts LLDPE, 30 parts aluminum diethylphosphinate, 10 parts MPP, 7 parts modified magnesium hydroxide, 3 parts sepiolite, and other additives unchanged), the amount of PE-g-MAH added was varied, and surface precipitation, tensile strength and elongation at break were tested.

[0090] 0 Severe precipitation (white powder layer) 18.5 610 Obvious interfacial gaps, flame retardant agglomeration 2 Slight precipitation (visible spots) 20.2 690 There are still some gaps in the interface. 4 Very slight precipitation (almost invisible) 21.5 750 The interface is well-bonded and evenly distributed. 5 No precipitation 22.3 785 The interface is dense with no visible voids. 6 No precipitation 22.1 780 The interface is dense and the compatibilizer is saturated.

[0091] This experiment shows that when the amount of PE-g-MAH added is ≥5 parts, the migration and precipitation of flame retardants can be completely inhibited. Maleic anhydride-grafted polyethylene forms chemical bonds or strong hydrogen bonds with polar groups (such as hydroxyl and amino groups) on the surface of the flame retardant through the anhydride groups. At the same time, the polyethylene backbone is compatible with the LLDPE matrix, acting as a "molecular bridge". Without compatibilizer, the mechanical properties decrease significantly (tensile strength decreases by about 17%, and elongation at break decreases by about 22%).

[0092] To verify the synergistic effect of sepiolite and char formation accelerator in this invention, the following design was implemented:

[0093] none 28.5 Occasionally dripping Loose and cracked talcum powder 28.9 No dripping Relatively dense but still contains tiny pores Calcium carbonate 28.2 There is dripping Loose, carbon layer peeling off sepiolite 30.2 No dripping Dense and continuous, without cracks

[0094] The fibrous structure and high specific surface area of ​​sepiolite can interweave into a network during combustion, significantly enhancing the strength and insulation of the char layer, which is superior to conventional mineral fillers.

[0095] In summary, this invention achieves a breakthrough in comprehensive performance with low addition amount, including high flame retardancy, low smoke, high mechanical strength retention, and no exudation, providing a highly competitive solution for cross-linked polyethylene in the field of wires and cables with stringent safety and environmental protection requirements, such as high-rise buildings, rail transportation, and ships.

[0096] It should be understood that numerous specific implementation decisions can be made during the development of any practical implementation, such as in any engineering or design project. Such development efforts may be complex and time-consuming, but for those skilled in the art who benefit from this disclosure, the development effort will be a routine work of design, manufacturing, and production without requiring much experimentation.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An environmentally friendly flame-retardant masterbatch for cross-linked polyethylene, characterized in that, The masterbatch is composed of the following raw materials in parts by weight: polyethylene resin: 40-60 parts; aluminum diethylphosphinate: 25-35 parts; melamine polyphosphate: 8-12 parts; modified magnesium hydroxide: 5-8 parts; sepiolite: 3-5 parts; maleic anhydride-grafted polyethylene: 3-6 parts; compound antioxidant: 0.3-0.8 parts; silicone masterbatch: 0.3-0.6 parts; polytetrafluoroethylene micro powder: 0.2-0.6 parts; char-forming accelerator: 2-5 parts; layered nanofiller: 1-3 parts; smoke suppressant: 1-2 parts.

2. The flame retardant masterbatch according to claim 1, characterized in that: The polyethylene resin is LLDPE, the char-forming accelerator is selected from pentaerythritol phosphate or dipentaerythritol, the layered nanofiller is organically modified montmorillonite, and the smoke suppressant is zinc borate.

3. The flame retardant masterbatch according to claim 1, characterized in that: The compound antioxidant is selected from any two or three of antioxidant 1010, antioxidant DLTP, antioxidant 300#, and antioxidant 168; the silicone masterbatch is a 50% silicone masterbatch; and the polytetrafluoroethylene micro powder is used as an anti-dripping agent.

4. The flame retardant masterbatch according to claim 1, characterized in that: The masterbatch is composed of the following raw materials in parts by weight: 50 parts LLDPE resin, 32 parts aluminum diethylphosphinate, 10 parts melamine polyphosphate (MPP), 5 parts modified magnesium hydroxide, 3 parts sepiolite, 5 parts maleic anhydride grafted polyethylene (PE-g-MAH), 4 parts char-forming accelerator (pentaerythritol phosphate, PEPA), 2 parts organic modified montmorillonite, 1 part smoke suppressant, 0.6 parts compound antioxidant, 0.5 parts silicone masterbatch, 0.3 parts polytetrafluoroethylene micro powder, wherein the mass ratio of antioxidant 300 to antioxidant 168 in the compound antioxidant is 1:

1.

5. The flame retardant masterbatch according to claim 1, characterized in that: The organically modified montmorillonite is quaternary ammonium salt intercalated montmorillonite with an interlayer spacing of ≥2.5 nm.

6. Use of the environmentally friendly flame-retardant masterbatch according to any one of claims 1 to 5 for crosslinked polyethylene, characterized in that, The flame retardant masterbatch is added to cross-linked polyethylene material for wires and cables at a dosage of 10% to make the flame retardant rating of the cross-linked polyethylene material reach UL94V-0 level.

7. A process for the preparation of an environmentally friendly flame retardant masterbatch for crosslinked polyethylene as claimed in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Raw material pretreatment: The raw materials used are dried to remove moisture; the organic modified montmorillonite is pre-dried under vacuum at 80-100℃ for 4 hours. S2, Staged High-Speed ​​Mixing: First stage: Add polyethylene resin, aluminum diethylphosphinate, melamine polyphosphate, modified magnesium hydroxide, sepiolite, char formation accelerator, layered nanofiller, smoke suppressant, and maleic anhydride-grafted polyethylene, and stir in a high-speed mixer at 800-1200 rpm for 5-8 minutes. Second stage: Add compound antioxidant, silicone masterbatch, and polytetrafluoroethylene micro powder, continue stirring for 2-3 minutes, and then discharge; S3, Three-screw compounding extrusion granulation: A three-screw compounding extruder is used, with an upper-stage extrusion temperature of 120–160℃, a lower-stage extrusion temperature of 90–110℃, and a die head temperature of 110–120℃. After the materials are mixed and extruded, they are successively ground, air-cooled and pelletized, magnetically separated, boiled and cooled, and vacuum-packed to obtain the finished product.

8. The preparation method according to claim 7, characterized in that, The length-to-diameter ratio of the three-screw compounding extruder is 36:1 to 48:1, and the screw speed is 300 to 600 rpm.

9. The preparation method according to claim 7, characterized in that: The grinding and air-cooling pelletizing process does not use water cooling medium, and the temperature of the masterbatch after pelletizing is ≤50℃; the boiling cooling process adopts a fluidized bed airflow cooling method to cool the masterbatch to room temperature before vacuum packaging.

10. The preparation method according to claim 7, characterized in that: In the first stage of S2, 0.2-0.5% of the total weight of the raw materials is added as a wetting agent to promote the dispersion of nanofillers.