Environment-friendly regenerated flame-retardant polyethylene sheath material and preparation method thereof

Abstract

The invention relates to a polyethylene sheath material, in particular to an environment-friendly regenerated flame-retardant polyethylene sheath material and a preparation method thereof. According to the preparation method of the environment-friendly regenerated flame-retardant polyethylene sheath material, through selection of the recycled polyethylene sheath, reasonable formula design, mutual combination of various auxiliary agents with different functions and a designed processing technology, the environment-friendly regenerated flame-retardant polyethylene sheath material is prepared; therefore, the low-smoke low-halogen flame-retardant cable material with good mechanical property, aging resistance, low-smoke low-halogen flame-retardant property and processability is prepared at lower cost.

Description

Technical Field

[0001] The present application relates to a polyethylene sheath material, and in particular to an environmentally friendly recycled flame-retardant polyethylene sheath material and a preparation method thereof. Background Art

[0002] Cables are wire products used to transmit electrical (magnetic) energy, information and realize electromagnetic energy conversion. They are composed of one or more conductor cores and their respective sheaths. With the continuous development of the electric power industry, the performance requirements for cable sheath materials are getting higher and higher. Polyethylene (PE) has gradually become one of the excellent raw materials for communication and power cable sheath materials due to its corrosion resistance, stable chemical properties, excellent dielectric properties and mechanical properties. However, there are few studies on the recycling and application of waste cable sheath materials in my country, which has caused waste of resources and environmental pollution. As the price of polyethylene raw materials gradually rises, it is particularly important to apply waste cable sheath materials to the preparation of sheath materials to obtain environmentally friendly recycled flame-retardant polyethylene sheath materials with low cost and guaranteed performance. Summary of the invention

[0003] In order to solve the problem of recycling of waste polyethylene sheath materials and the gradually increasing cost of polyethylene sheath materials, the present application provides an environmentally friendly recycled flame-retardant polyethylene sheath material and a preparation method thereof.

[0004] The first aspect of the present application provides a method for preparing an environmentally friendly recycled flame-retardant polyethylene sheath material, comprising at least the following steps: S1, obtaining a recycled halogen-containing polyethylene sheath, crushing, washing, and dehydrating to obtain recycled polyethylene sheath fragments, placing the recycled polyethylene sheath fragments in an internal mixer for a first internal mixer to obtain a first mixture, and feeding the first mixture into a screw extruder, extruding and granulating at 100° C.-130° C. to obtain recycled polyethylene sheath particles; S2, by weight percentage, 38wt%-40wt% of recycled polyethylene sheath particles, 8wt%-12wt% of linear low density polyethylene resin, 11wt%-14wt% of metallocene polyethylene resin, 2wt%-3wt% of polyethylene grafted maleic anhydride particles, 2wt%-3wt% of halogen flame retardant, 25wt%-27wt% of magnesium hydroxide flame retardant, 3wt%-4wt% of carbon black masterbatch, 1.2wt%-1.7wt% of zinc stearate, 0.4wt%-0.6wt% of antioxidant and 0.4wt%-0.6wt% of coupling agent are put into an internal mixer for second internal mixing to obtain a second mixture, and the second mixture is put into a screw extruder for extrusion and granulation at 100°C-130°C to obtain an environmentally friendly recycled flame-retardant polyethylene sheath material.

[0005] Halogen-containing polyethylene sheaths contain halogens and other substances, which have a great impact on the environment during the waste process. Therefore, the preparation method of this application selects halogen-containing polyethylene sheaths for recycling. Halogen-containing polyethylene sheaths have the mechanical, aging-resistant, flame-retardant and other properties required by cable sheaths. Its ingredients include a certain amount of antioxidants, carbon black, halogen flame retardants and other additives. The recycled halogen-containing polyethylene sheaths are processed and granulated, and then the environmentally friendly recycled flame-retardant polyethylene sheath material is obtained through reasonable formula design and processing and granulation, which is conducive to improving the uniformity and stability of the performance of environmentally friendly recycled flame-retardant polyethylene sheath materials.

[0006] The preparation method of the present application adds an appropriate amount of magnesium hydroxide halogen-free flame retardant and halogen flame retardant. Through the synergistic effect of the two flame retardants, the environmentally friendly recycled flame retardant polyethylene sheath material has the advantages of excellent flame retardant properties and low smoke while taking into account mechanical properties.

[0007] Furthermore, since the polyethylene resin matrix in the halogen-containing polyethylene sheath is mainly high-density polyethylene, it has the advantages of high strength, good mechanical properties and stable physical and chemical properties, but weak tensile properties, fluidity and processability. Therefore, the preparation method of the present application is blended and modified by adding an appropriate amount of low-density polyethylene and metallocene polyethylene, and the compounding of low-density polyethylene and high-density polyethylene is beneficial to improving the mechanical properties, fluidity and processing properties of environmentally friendly recycled flame-retardant polyethylene sheath materials; metallocene polyethylene resin refers to a linear low-density copolymer of ethylene and olefins with a narrow distribution molecular weight obtained by coordination polymerization using metallocene compounds as catalysts, which has high flexibility and high elongation, and is added to a polyethylene system containing a large amount of magnesium hydroxide flame retardant, which can improve the flexibility and elongation of the polyethylene sheath, prevent cable cracking, and improve the mechanical properties of environmentally friendly recycled flame-retardant polyethylene sheath materials. And because the compatibility between the magnesium hydroxide flame retardant and the resin matrix is ​​poor, the processing extrusion performance of the polyethylene sheath material is affected. The addition of metallocene polyethylene resin can achieve the coating of the magnesium hydroxide flame retardant, thereby improving the compatibility between the magnesium hydroxide flame retardant and the resin matrix, and further improving the processing performance of the environmentally friendly recycled flame-retardant polyethylene sheath material.

[0008] Furthermore, the preparation method of the present application adds an appropriate amount of polyethylene grafted maleic anhydride particles, carbon black masterbatch, zinc stearate, antioxidant and coupling agent. The synergistic effect of the above-mentioned additives is beneficial to further improve the mechanical properties, anti-aging properties, flame retardant properties, processing properties, and uniformity and stability of the environmentally friendly recycled flame-retardant polyethylene sheath material.

[0009] In summary, the preparation method of the environmentally friendly recycled flame-retardant polyethylene sheath material of the present application, through the selection of recycled polyethylene sheath, reasonable formula design, the combination of various functional additives and designed processing technology, enables the present application to prepare environmentally friendly recycled flame-retardant polyethylene sheath material with good mechanical properties, anti-aging properties, low smoke and low halogen flame retardant properties and processing performance at a lower cost.

[0010] In any embodiment, the step of placing the recycled polyethylene sheath fragments in a mixer for first mixing to obtain a first mixture specifically comprises: 100 parts of recycled polyethylene sheath fragments, 0.2-0.5 parts of aluminum acetylacetonate, and 0.5-2 parts of biomass fibers are placed in an internal mixer for first internal mixing to obtain a first mixture, wherein the first internal mixing time is more than 15 minutes, and the material temperature is ensured to be above 135°C.

[0011] The recycled polyethylene sheaths are often used for a long time, and studies have shown that the polyethylene sheaths may have undergone changes such as molecular chain breakage, molecular weight reduction, and carbon black agglomeration due to light aging during use. The breakage of polyethylene molecular chains and the reduction of molecular weight often increase the melt index and reduce the viscosity of polyethylene, which deteriorates the mechanical properties of polyethylene sheaths. The carbon black in the polyethylene sheath is an excellent anti-ultraviolet stabilizer, which can improve the anti-aging properties of polyethylene by absorbing ultraviolet rays. When carbon black agglomerates and has poor dispersion, the absorption coefficient of carbon black to ultraviolet rays will be reduced, which is not conducive to the anti-aging properties of the polyethylene sheath. Therefore, the preparation method of the present application adds aluminum acetylacetonate during the refining of recycled polyethylene sheath fragments, which can catalyze the cross-linking reaction of broken polyethylene molecular chains in the molten state. When the amount of aluminum acetylacetonate added is controlled within the above range, it can avoid the effect of promoting cross-linking effectively due to too little dosage, and avoid excessive cross-linking due to excessive dosage, thereby affecting the thermoplasticity of polyethylene, thereby maintaining the processing performance of the recycled polyethylene sheath while improving the mechanical properties of the recycled polyethylene sheath and the environmentally friendly recycled flame-retardant polyethylene sheath material. Furthermore, the preparation method of the present application adds an appropriate amount of biomass fiber during the refining process of the recycled polyethylene sheath fragments. As a natural polymer material, the biomass fiber has abundant hydroxyl groups, which can interact with the functional groups (such as hydroxyl groups, carboxyl groups, etc.) on the surface of carbon black, thereby improving the dispersion of carbon black in the matrix material. The biomass fiber has a certain rigidity and length, which can further prevent the agglomeration of carbon black particles. When the amount of biomass fiber added is controlled within the above range, it can avoid that too little amount cannot effectively promote the dispersion of carbon black, and too much amount can avoid reducing the fluidity, thereby maintaining the processing performance of the recycled polyethylene sheath while improving the anti-aging performance of the recycled polyethylene sheath and the environmentally friendly recycled flame-retardant polyethylene sheath material.

[0012] In any embodiment, the density of the linear low-density polyethylene resin is 0.920±0.05 g / cm 3 , melt flow rate is 0.1g / 10min-0.4g / 10min, tensile strength is 30MPa-33MPa, elongation at break is 650%-750%; the density of the metallocene polyethylene resin is 0.920±0.1g / cm 3 , melt flow rate is 3.4g / 10min-3.6g / 10min, tensile strength is 35MPa-37MPa, and elongation at break is 650%-730%.

[0013] Mixing the linear low-density polyethylene resin within the above parameter range with the recycled halogen-containing polyethylene sheath particles is conducive to further improving the mechanical properties, fluidity and processing properties of the environmentally friendly recycled flame-retardant polyethylene sheath material. Adding the metallocene polyethylene resin within the above parameter range is conducive to further improving the mechanical properties and processing properties of the polyethylene sheath material.

[0014] In any embodiment, the density of the polyethylene grafted maleic anhydride particles is 0.920±0.01 g / cm 3 , melt flow rate is 0.5g / 10min-1.2g / 10min, tensile strength is 20MPa-24MPa, and elongation at break is 700%-800%.

[0015] Polyethylene grafted maleic anhydride is a polymer interface coupling agent, compatibilizer, and dispersion promoter. It is grafted with polar groups and can greatly improve the compatibility between polymers and the dispersibility of functional additives. By adding the above polyethylene grafted maleic anhydride particles in the preparation process of environmentally friendly recycled flame-retardant polyethylene sheathing materials, it is beneficial to further improve the mechanical properties of polyethylene sheathing materials.

[0016] In any embodiment, the density of the recycled polyethylene sheathed particles is ≤0.94 g / cm 3 , tensile strength is 13.5MPa-15.5MPa, elongation at break is 400%-600%, and oxygen index is 26%-28%.

[0017] The various indicators of the recycled polyethylene sheathing material particles are within the above ranges, and when used to prepare environmentally friendly recycled flame-retardant polyethylene sheathing materials, the environmentally friendly recycled flame-retardant polyethylene sheathing materials have good mechanical properties and anti-aging properties.

[0018] In any embodiment, the halogen flame retardant is chlorinated polyethylene powder with a volatile matter of ≤0.4%; the magnesium hydroxide flame retardant is physical magnesium hydroxide, and the D50 of the magnesium hydroxide flame retardant is ≤3.5 μm.

[0019] The above-mentioned halogen flame retardant and magnesium hydroxide flame retardant are added in the preparation process of the environmentally friendly recycled flame retardant polyethylene sheath material. Through the synergistic effect of the two, the environmentally friendly recycled flame retardant polyethylene sheath material has excellent flame retardant effect. Compared with the traditional halogen-containing polyethylene sheath material, the halogen content is greatly reduced, and the smoke emission is at a low smoke level, so that low-smoke and low-halogen environmentally friendly recycled flame retardant polyethylene sheath material is prepared.

[0020] In any embodiment, the carbon black masterbatch is a masterbatch with LLDPE as a carrier, a carbon black content of 44.5%-45.5%, and an ash content of ≦1%.

[0021] Adding the above-mentioned carbon black masterbatch during the preparation process of the environmentally friendly recycled flame-retardant polyethylene sheath material is beneficial to further improve the anti-aging performance of the environmentally friendly recycled flame-retardant polyethylene sheath material.

[0022] In any embodiment, the antioxidant includes antioxidant 1010 and antioxidant DLTP, and the mass ratio of the antioxidant 1010 to the antioxidant DLTP is 1:1.

[0023] Antioxidant 1010 is a high molecular weight hindered phenol antioxidant with low volatility and low migration. It can effectively prevent the thermal oxidation degradation of polyethylene sheath during long-term aging. Antioxidant DLTP is a sulfur-containing antioxidant with excellent performance. It can achieve a good synergistic effect when used in combination with the main antioxidant 1010. It can better ensure that the performance of polyethylene sheath does not drop significantly in harsh environments and improve the ability of long-term aging. By adding the above two antioxidants in the preparation process of environmentally friendly recycled flame-retardant polyethylene sheath material, the synergistic effect of the two is conducive to further improving the anti-aging performance of environmentally friendly recycled flame-retardant polyethylene sheath material.

[0024] In any embodiment, the coupling agent includes a silane coupling agent, and the zinc oxide content of the zinc stearate is 12%.

[0025] Silane coupling agent can be used to improve the interfacial compatibility between resin and additives, making it easier for environmentally friendly recycled flame-retardant polyethylene sheathing materials to be plasticized and formed into a whole. By adding silane coupling agent during the preparation of environmentally friendly recycled flame-retardant polyethylene sheathing materials, it is beneficial to further improve the uniformity and stability of the performance of environmentally friendly recycled flame-retardant polyethylene sheathing materials. By adding zinc stearate with a zinc oxide content of 12% during the preparation of environmentally friendly recycled flame-retardant polyethylene sheathing materials, it can be used as a lubricant and stabilizer to further improve the processing performance and stability of environmentally friendly recycled flame-retardant polyethylene sheathing materials.

[0026] A second aspect of the present application provides an environmentally friendly recycled flame-retardant polyethylene sheath material, which is prepared according to the preparation method described in any embodiment.

[0027] The environmentally friendly recycled flame-retardant polyethylene sheath material prepared by the preparation method of the present application has lower manufacturing cost and good mechanical properties, anti-aging properties, low-smoke and low-halogen flame-retardant properties and processing properties.

[0028] In summary, this application has the following beneficial effects: (1) The preparation method of the environmentally friendly recycled flame-retardant polyethylene sheath material of the present application is to obtain the environmentally friendly recycled flame-retardant polyethylene sheath material by processing and granulating the recycled halogen-containing polyethylene sheath through reasonable formula design and processing and granulation, which is beneficial to improving the uniformity and stability of the performance of the environmentally friendly recycled flame-retardant polyethylene sheath material; by adding an appropriate amount of magnesium hydroxide halogen-free flame retardant and halogen flame retardant, through the synergistic effect of the two flame retardants, the environmentally friendly recycled flame-retardant polyethylene sheath material has the advantages of excellent flame retardant properties and low smoke while taking into account the mechanical properties; by adding low-density polyethylene and metallocene polyethylene for blending modification, the compounding of low-density polyethylene and high-density polyethylene is beneficial to improving the environmentally friendly recycled flame-retardant polyethylene The mechanical properties, fluidity and processing properties of the sheath material; adding metallocene polyethylene resin to the polyethylene system containing magnesium hydroxide halogen-free flame retardant can improve the flexibility and elongation of the polyethylene sheath, and can achieve the coating of the magnesium hydroxide flame retardant, improve the compatibility between the magnesium hydroxide flame retardant and the resin matrix, thereby further improving the mechanical properties and processing properties of the environmentally friendly recycled flame-retardant polyethylene sheath material; adding an appropriate amount of polyethylene grafted maleic anhydride particles, carbon black masterbatch, zinc stearate, antioxidant and coupling agent, the synergistic effect of the above additives is conducive to further improving the mechanical properties, anti-aging properties, flame retardancy, processing properties and performance uniformity and stability of the environmentally friendly recycled flame-retardant polyethylene sheath material.

[0029] (2) On the basis of the above-mentioned method for improving the preparation of environmentally friendly recycled flame-retardant polyethylene sheath material, by adding an appropriate amount of aluminum acetylacetonate during the refining process of the recycled polyethylene sheath fragments, it can catalyze the cross-linking reaction of the broken polyethylene molecular chains in the molten state, thereby maintaining the processing performance of the recycled polyethylene sheath while improving the mechanical properties of the recycled polyethylene sheath and the environmentally friendly recycled flame-retardant polyethylene sheath material. Furthermore, by adding an appropriate amount of biomass fiber during the refining process of the recycled polyethylene sheath fragments, the processing performance of the recycled polyethylene sheath is maintained while improving the anti-aging performance of the recycled polyethylene sheath and the environmentally friendly recycled flame-retardant polyethylene sheath material.

[0030] (3) The preparation method of the environmentally friendly recycled flame-retardant polyethylene sheath material of the present application, through the selection of recycled polyethylene sheath, reasonable formula design, the combination of various additives with different functions and processing technology, can prepare environmentally friendly recycled flame-retardant polyethylene sheath material with good mechanical properties, anti-aging properties, low smoke and low halogen flame retardant properties and processing performance at a lower cost. DETAILED DESCRIPTION

[0031] The raw materials in this application include the following parts: The present application is further described in detail below with reference to examples and comparative examples.

[0032] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available. Example 1

[0033] S1, Preparation of recycled polyethylene sheath particles: a. Require suppliers to select halogen-containing polyethylene sheaths and distinguish them from general low-smoke halogen-free polyethylene sheaths, and then crush, clean and dehydrate them to obtain recycled polyethylene sheath fragments; b. The recycled polyethylene sheath fragments were placed in a mixer for mixing. The mixing time was 15 min. When the time was satisfied and the material temperature reached 125 ° C, the mixing was terminated to obtain a first mixture. c. After the first mixture is put into a double cone twister, it is extruded and granulated by a double-stage extruder with a twin screw + single screw. The granulation temperature is 100-130°C, and a 20+120+40 mesh filter is used for filtration to remove impurities. After air cooling, sieving and homogenization, the recycled polyethylene sheath particles are obtained. The density of the recycled polyethylene sheath particles is 0.927g / cm 3 , tensile strength is 14.5MPa, elongation at break is 500%, and oxygen index is 27%.

[0034] S2, Preparation of environmentally friendly recycled flame-retardant polyethylene sheath material a. Ingredients: Weigh each component by weight, and weigh 39.5wt% of recycled polyethylene sheath particles, 11.5wt% of linear low-density polyethylene resin, 13wt% of metallocene polyethylene resin, 2.5wt% of polyethylene grafted maleic anhydride particles, 2.5wt% of chlorinated polyethylene, 26wt% of magnesium hydroxide flame retardant, 2.6wt% of carbon black masterbatch, 1.6wt% of zinc stearate, 0.2wt% of antioxidant 1010, 0.2wt% of antioxidant DLTP and 0.4wt% of silane coupling agent; Among them, the weighing accuracy of polyethylene base material and flame retardant is ±0.1kg, and the weighing accuracy of carbon black masterbatch and additives is ±0.01kg; the density of linear low-density polyethylene resin is 0.920g / cm 3 , melt flow rate is 0.1g / 10min, tensile strength is 33MPa, elongation at break is 750%; density of metallocene polyethylene resin is 0.930g / cm 3 , melt flow rate is 3.4g / 10min, tensile strength is 37MPa, elongation at break is 730%; density of polyethylene grafted maleic anhydride particles is 0.920g / cm3 , melt flow rate is 0.5g / 10min, tensile strength is 24MPa, and elongation at break is 800%; b. Internal mixing: The weighed materials are put into the internal mixer for internal mixing for 15 minutes. The powder needs to be swept once when the material temperature reaches 110°C, 130°C, and 145°C to ensure that the powder is completely incorporated into the material. When the time is satisfied and the material temperature reaches 155°C, the internal mixing is terminated to obtain the second mixture. c. Extrusion: The second mixture is put into a double cone through a conveyor for shearing, and then transported to a twin-screw + single-screw double-stage extruder of model SDJ-75 / 180 for plasticization, extrusion and granulation, wherein the speed is set to: 35.0Hz for twin screws, 20.0Hz for single screws. The temperature of the extruder is set to: 130℃-125℃-120℃-120℃-110℃-110℃-105℃-100℃-100℃-100℃ for the upper machine; 105℃-115℃-130℃-135℃ for the lower machine.

[0035] d. Filtration, pelletizing, cooling, and homogenization: A 20+120+40 mesh filter should be installed at the end of the double stage to ensure that impurities in the product are filtered out and to prevent unclean processing in the front stage of the recycled polyethylene sheathed particles; pelletizing requires uniform particle size without long strips or connected particles; air cooling is used, and after pelletizing, the particles are blown to the next stage by a fan while cooling; particles that do not meet the requirements in shape and size are removed; products are mixed in large silos to improve the uniformity of the materials; aluminum foil bags are used as inner bags and kraft paper packaging is used as outer bags for packaging.

[0036] Examples 2-4 and Comparative Examples 1-2 are basically similar to Example 1, except that the composition of the environmentally friendly recycled flame-retardant polyethylene sheath material is different, as shown in Table 1 for details.

[0037] Table 1 Composition of environmentally friendly recycled flame-retardant polyethylene sheath materials of Examples 1-4 and Comparative Examples 1-2 composition Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Recycled polyethylene sheathing particles 39.5% 38% 39.5% 39.0% 45% 35% Linear low density polyethylene resin 11.5% 12% 10.7% 10.9% 5% 15% Metallocene polyethylene resin 13% 13% 13.3% 13.0% 13% 13% Polyethylene grafted with maleic anhydride 2.5% 3% 2.6% 2.6% 2.6% 3% Magnesium hydroxide 26% 26% 26.4% 27% 26.5% 26% Chlorinated Polyethylene 2.5% 2.5% 2.5% 2.5% 2.5% 2.5% Carbon Black Masterbatch 2.6% 2.6% 2.6% 2.6% 2.6% 2.6% Zinc stearate 1.6% 1.6% 1.6% 1.6% 1.6% 1.6% Antioxidant 1010 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% Antioxidant DLTP 0.2% 0.2% 0.2% 0.2% 0.2% 0.2% Silane coupling agent 0.4% 0.4% 0.4% 0.4% 0.4% 0.4% The relevant properties of Examples 1-4 and Comparative Examples 1-2 were tested according to the test standards of each property selected in GB / T15065-2009, and the results are shown in Table 2.

[0038] Table 2 Performance test of environmentally friendly recycled flame-retardant polyethylene sheath materials of Examples 1-4 and Comparative Examples 1-2

[0039] It can be seen from Examples 1-4 that when the content of recycled polyethylene sheath particles in the environmentally friendly recycled flame-retardant polyethylene sheath material is 38wt%-40wt%, the content of linear low-density polyethylene resin is 8wt%-12wt%, the content of metallocene polyethylene resin is 11wt%-14wt%, the content of polyethylene grafted maleic anhydride particles is 2wt%-3wt%, the content of halogen flame retardant is 2wt%-3wt%, the content of magnesium hydroxide flame retardant is 25wt%-27wt%, the content of carbon black masterbatch is 3wt%-4wt%, the content of zinc stearate is 1.2wt%-1.7wt%, the content of antioxidant is 0.4wt%-0.6wt%, and the content of coupling agent is 0.4wt%-0.6wt%, the environmentally friendly recycled flame-retardant polyethylene sheath material prepared by the preparation method of the present application has excellent mechanical properties and anti-aging properties.

[0040] From the comparison between Examples 1-4 and Comparative Examples 1-2, it can be seen that when the content of the recycled polyethylene sheath particles is controlled to 38wt%-40wt% and the content of the linear low-density polyethylene resin is controlled to 8wt%-12wt%, it is beneficial to further improve the mechanical properties and anti-aging properties of the environmentally friendly recycled flame-retardant polyethylene sheath material, so that it meets the requirements of the low-density polyethylene sheath material for physical and mechanical properties (tensile strength ≥13MPa, elongation at break ≥500%). Example 5

[0041] 1) Preparation of recycled polyethylene sheath material particles a. Require suppliers to select halogen-containing polyethylene sheaths and distinguish them from general low-smoke halogen-free polyethylene sheaths, and then crush, clean and dehydrate them to obtain recycled polyethylene sheath fragments; b. 100 parts by weight of recycled polyethylene sheath fragments, 0.3 parts by weight of aluminum acetylacetonate, and 1 part by weight of cellulose fiber were placed in an internal mixer for internal mixing. The powder was swept once when the material temperature reached 110°C, 135°C, and 145°C to ensure that the powder completely entered the material. When the material temperature was 145°C, internal mixing was performed for 25 minutes to obtain a first mixture; c. After the first mixture is put into a double cone twister, it is extruded and granulated by a double-stage extruder with a twin screw + single screw. The granulation temperature is 120°C, and a 20+120+40 mesh filter is used to filter to remove impurities. After air cooling, sieving and homogenization, the recycled polyethylene sheath particles are obtained; after testing, the density of the recycled polyethylene sheath particles is 0.93g / cm 3 , tensile strength is 15MPa, elongation at break is 550%, and oxygen index is 28%.

[0042] 2) Preparation of environmentally friendly recycled flame-retardant polyethylene sheath material a. Ingredients: weigh each component by weight, weigh 39.5% of recycled polyethylene sheath particles, 11.5% of linear low-density polyethylene resin, 13% of metallocene polyethylene resin, 2.5% of polyethylene grafted maleic anhydride particles, 2.5% of chlorinated polyethylene, 26% of magnesium hydroxide flame retardant, 2.6% of carbon black masterbatch, 1.6% of zinc stearate, 0.2% of antioxidant 1010, 0.20% of antioxidant DLTP and 0.4% of silane coupling agent, the weighing accuracy of polyethylene base material and flame retardant is ±0.1kg, and the weighing accuracy of carbon black masterbatch and additives is ±0.01kg; The density of linear low-density polyethylene resin is 0.920 g / cm 3 , melt flow rate is 0.1g / 10min, tensile strength is 33MPa, elongation at break is 750%; density of metallocene polyethylene resin is 0.930g / cm 3 , melt flow rate is 3.4g / 10min, tensile strength is 37MPa, elongation at break is 730%; density of polyethylene grafted maleic anhydride particles is 0.920g / cm 3 , melt flow rate is 0.5g / 10min, tensile strength is 24MPa, elongation at break is 800%; b. Internal mixing: The weighed materials are put into the internal mixer for internal mixing for 15 minutes. The powder needs to be swept once when the material temperature reaches 110, 130, and 145°C to ensure that the powder is completely incorporated into the material. When the time is satisfied and the material temperature reaches 155°C, the internal mixing is terminated to obtain the second mixture. c. Extrusion: The second mixture is put into the double cone through a conveyor for shearing, and then transported to a twin-screw + single-screw double-stage extruder of model SDJ-75 / 180 for plasticization, extrusion and granulation to obtain environmentally friendly recycled flame-retardant polyethylene sheath material, wherein the speed is set to: 35.0Hz for twin screws and 20.0Hz for single screws. The temperature of the extruder is set to: 130℃-125℃-120℃-120℃-110℃-110℃-105℃-100℃-100℃-100℃ for the upper machine; 105℃-115℃-130℃-135℃ for the lower machine.

[0043] d. Filtration, pelletizing, cooling, and homogenization: A 20+120+40 mesh filter should be installed at the end of the double stage to ensure that impurities in the product are filtered out and to prevent unclean processing in the front stage of the recycled polyethylene sheath particles. When pelletizing, the particles must be uniform in size without long strips or connected particles. Air cooling is used, and after pelletizing, the particles are blown to the next stage through a fan while cooling the particles. Particles that do not meet the requirements in shape and size are removed. Products are mixed in large silos to improve the uniformity of the materials.

[0044] e. Packaging: Use aluminum foil bag as inner bag and kraft paper bag as outer bag.

[0045] Embodiment 6-7 Examples 6-7 are substantially the same as Example 5, except that only aluminum acetylacetonate is added to Example 6, and only biomass fiber is added to Example 7.

[0046] The relevant properties of Examples 5-7 were tested according to the test standards of each property selected in GB / T15065-2009, and the results are shown in Table 3.

[0047] Table 3 Performance test of environmentally friendly recycled flame retardant polyethylene sheath materials of Examples 1, 5-7

[0048] From the comparison between Example 5 and Example 1, it can be seen that the addition of aluminum acetylacetonate and biomass fiber during the recycle of polyethylene sheath fragments is beneficial to further improve the mechanical properties and anti-aging properties of the environmentally friendly regenerated flame-retardant polyethylene sheath material. From the comparison between Example 6 and Example 5, it can be seen that only aluminum acetylacetonate is added during the recycle of polyethylene sheath fragments without adding biomass fiber, and the anti-aging properties of the environmentally friendly regenerated flame-retardant polyethylene sheath material are poor; from the comparison between Example 7, Example 1 and Examples 5 and 6, it can be seen that aluminum acetylacetonate is not added during the recycle of polyethylene sheath fragments, and the mechanical properties of the environmentally friendly regenerated flame-retardant polyethylene sheath material are poor.

[0049] Product extrusion process performance verification According to the evaluation of experimental data, Example 5 has the best comprehensive performance and is relatively stable, so Example 5 is selected for cable extrusion comparison. The extruder model is SJ90×25 (screw diameter 90mm, aspect ratio 25:1), the equipment manufacturer is Anhui Prius Electrical Machinery Co., Ltd., and the cable model selected for the tube extrusion die test machine is ZC-YJY23 2*6. The cable outer diameter is 14.0mm-16.0mm, and the production speed is 30m / min. The environmentally friendly recycled flame-retardant polyethylene sheath material of this application is extruded at an extrusion temperature of 120℃-130℃-140℃-145℃-150℃-150℃-150℃-150℃-150℃-150℃-150℃-150℃, and the extruded surface is relatively smooth and delicate, and the extruded appearance meets the process requirements. Compared with other polyethylene sheath materials, this application adopts recycled polyethylene sheath as the main body of the sheath material formula system. Through reasonable formula design, the combination of various functional additives and designed processing technology, this application can prepare environmentally friendly recycled flame-retardant polyethylene sheath materials with good mechanical properties, anti-aging properties, low smoke and low halogen flame retardant properties and processing performance at a lower cost, which has broad market application prospects.

[0050] Cable performance verification The cabling performance test was carried out, and the test results are shown in Table 4.

[0051] Table 4

[0052] According to the above experimental data, the environmentally friendly recycled flame-retardant polyethylene sheath material prepared in Example 5 has excellent product extrusion process performance, and the cable sheath prepared therefrom has excellent mechanical properties, anti-aging properties, carbon black content and carbon black dispersion.

[0053] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A method for preparing an environmentally friendly recycled flame-retardant polyethylene sheath material, characterized in that: At least the following steps are included: S1, obtaining a recycled halogen-containing polyethylene sheath, crushing, washing, and dehydrating to obtain recycled polyethylene sheath fragments, placing the recycled polyethylene sheath fragments in an internal mixer for a first internal mixer to obtain a first mixture, and feeding the first mixture into a screw extruder, extruding and granulating at 100° C.-130° C. to obtain recycled polyethylene sheath particles; S2, by weight percentage, 38wt%-40wt% of recycled polyethylene sheath particles, 8wt%-12wt% of linear low density polyethylene resin, 11wt%-14wt% of metallocene polyethylene resin, 2wt%-3wt% of polyethylene grafted maleic anhydride particles, 2wt%-3wt% of halogen flame retardant, 25wt%-27wt% of magnesium hydroxide flame retardant, 3wt%-4wt% of carbon black masterbatch, 1.2wt%-1.7wt% of zinc stearate, 0.4wt%-0.6wt% of antioxidant and 0.4wt%-0.6wt% of coupling agent are put into an internal mixer for second internal mixing to obtain a second mixture, and the second mixture is put into a screw extruder for extrusion and granulation at 100°C-130°C to obtain an environmentally friendly recycled flame-retardant polyethylene sheath material.

2. The preparation method according to claim 1, characterized in that: The step of placing the recycled polyethylene sheath fragments in a mixer for first mixing to obtain a first mixture specifically comprises: 100 parts by weight of recycled polyethylene sheath fragments, 0.2-0.5 parts by weight of aluminum acetylacetonate, and 0.5-2 parts by weight of biomass fibers are placed in an internal mixer for first internal mixing to obtain a first mixture, wherein the first internal mixing time is more than 15 minutes, and the material temperature is ensured to be ≥135°C.

3. The preparation method according to claim 1, characterized in that: The density of the linear low-density polyethylene resin is 0.920±0.05 g / cm 3 , melt flow rate is 0.1g / 10min-0.4g / 10min, tensile strength is 30MPa-33MPa, elongation at break is 650%-750%; the density of the metallocene polyethylene resin is 0.920±0.1g / cm 3 , melt flow rate is 3.4g / 10min-3.6g / 10min, tensile strength is 35MPa-37MPa, and elongation at break is 650%-730%.

4. The preparation method according to claim 1, characterized in that: The density of the polyethylene grafted maleic anhydride particles is 0.920±0.01 g / cm 3 , melt flow rate is 0.5g / 10min-1.2g / 10min, tensile strength is 20MPa-24MPa, and elongation at break is 700%-800%.

5. The preparation method according to claim 1, characterized in that: The density of the recycled polyethylene sheath particles is ≤0.94 g / cm 3 , tensile strength is 13.5MPa-15.5MPa, elongation at break is 400%-600%, and oxygen index is 26%-28%.

6. The preparation method according to claim 1, characterized in that: The halogen flame retardant is chlorinated polyethylene powder with a volatile matter of ≤0.4%; the magnesium hydroxide flame retardant is physical magnesium hydroxide, and the D50 of the magnesium hydroxide flame retardant is ≤3.5 μm.

7. The preparation method according to claim 1, characterized in that: The carbon black masterbatch is a masterbatch with LLDPE as a carrier, a carbon black content of 44.5%-45.5%, and an ash content of ≤1%.

8. The preparation method according to claim 1, characterized in that: The antioxidant includes antioxidant 1010 and antioxidant DLTP, and the mass ratio of the antioxidant 1010 to the antioxidant DLTP is 1:

1.

9. The preparation method according to claim 1, characterized in that: The coupling agent includes a silane coupling agent, and the zinc oxide content of the zinc stearate is 12%.

10. An environmentally friendly recycled flame-retardant polyethylene sheath material, characterized in that: The environmentally friendly recycled flame-retardant polyethylene sheath material is prepared according to the preparation method described in any one of claims 1 to 9.

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