Polyethylene cable with flexibility and fire resistance and preparation method thereof

Abstract

The invention discloses a polyethylene cable with flexibility and fire resistance and a preparation method of the polyethylene cable, and relates to the technical field of polyethylene cables, the polyethylene cable comprises a cable core and a polyethylene protective sleeve, the polyethylene protective sleeve comprises the following components, the plastic is prepared from the following components in parts by mass: 50 to 70 parts of low-density polyethylene, 20 to 30 parts of modified polyolefin elastomer, 10 to 25 parts of lignin modified copolymer, 0.5 to 1 part of antioxidant, 0.6 to 1.2 parts of zinc oxide and 1 to 2 parts of talcum powder. The modified polyolefin elastomer is prepared from POE-g-MAH (Polyolefin Elastomer-g-MAH) and a DOPO Schiff base derivative; the lignin modified copolymer is prepared from lauryl methacrylate, isobornyl methacrylate and a lignin macroinitiator.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene cables, and specifically to a polyethylene cable with both flexibility and fire resistance and a preparation method thereof. Background Art

[0002] In the field of electrical engineering, cables play a crucial role in power transmission and signal conveyance. Traditional cables, especially those made of ordinary materials, often face challenges in terms of flexibility and fire resistance.

[0003] Flexibility is crucial in various applications of cables. In modern building wiring, industrial equipment connection, and even some portable electronic devices, cables need to be bent, twisted, or passed through complex spaces. Cables with insufficient flexibility may be difficult to install, and over time, repeated bending can cause internal damage such as conductor breakage or insulation layer cracking, thus affecting the normal operation of the electrical system.

[0004] On the other hand, fire safety is an inescapable issue. In the event of a fire, cables may become fuel for the fire, spreading the fire and releasing toxic gases, endangering lives and property. Therefore, the fire resistance of cables is crucial for ensuring the safety of buildings and industrial facilities.

[0005] Polyethylene is a widely used material in cable manufacturing. Among them, high-density polyethylene (HDPE) has certain mechanical strength and chemical resistance. However, it often shows limitations in terms of flexibility. The molecular structure of HDPE is relatively regular and closely packed, resulting in a relatively hard material, which limits its use in application scenarios with higher flexibility requirements.

[0006] In contrast, low-density polyethylene (LDPE) has a more branched molecular structure. This structure endows LDPE with excellent flexibility. It can be easily bent and shaped, suitable for application scenarios where cables need to be frequently bent. However, the inherent flammability of LDPE has always been a drawback. When exposed to fire, LDPE will burn rapidly, which poses a major threat to fire safety.

[0007] Therefore, it is of great significance to invent a polyethylene cable with both flexibility and fire resistance. Summary of the Invention

[0008] The purpose of the present invention is to provide a polyethylene cable with both flexibility and fire resistance and a preparation method thereof to solve the problems raised in the prior art.

[0009] To achieve the above purpose, the present invention provides the following technical solutions: A polyethylene cable with both flexibility and fire resistance, the polyethylene cable comprises a cable core and a polyethylene protective sheath, the polyethylene protective sheath comprises the following components: low-density polyethylene, modified polyolefin elastomer, lignin modified copolymer, antioxidant, zinc oxide, talcum powder; Furthermore, the modified polyolefin elastomer is prepared from POE-g-MAH and DOPO Schiff base derivatives; Furthermore, the lignin modified copolymer is prepared from lauryl methacrylate, isobornyl methacrylate and lignin macromolecular initiator.

[0010] Furthermore, the low-density polyethylene model is 2426H; Further, the antioxidant is any one of antioxidant 1010 or B225; Furthermore, the polyethylene protective sleeve comprises the following components, calculated by weight: 50-70 parts of low-density polyethylene, 20-30 parts of modified polyolefin elastomer, 10-25 parts of lignin modified copolymer, 0.5-1 parts of antioxidant, 0.6-1.2 parts of zinc oxide, and 1-2 parts of talc.

[0011] Furthermore, the preparation method of the modified polyolefin elastomer comprises the following steps: Under nitrogen atmosphere, add levodopa and sodium hydroxide to ethanol, heat to 80-85°C, stir evenly, add furfural ethanol solution, keep warm for 4-5h, and rotary evaporate to obtain Schiff base; Under a nitrogen atmosphere, add Schiff base and DOPO to ethanol, heat to 80-85°C for reaction for 8-9h, vacuum distill, adjust the pH of the product to 2.0-2.1, wash with deionized water, and vacuum dry at 80-85°C to obtain a DOPO Schiff base derivative; POE-g-MAH and 3-amino-1,2,4-triazole are added to an internal mixer, heated to 100-105° C. and stirred for 10-15 minutes, DOPO Schiff base derivative and zinc chloride are added, and the mixture is stirred at the same temperature for 15-20 minutes to obtain a modified polyolefin elastomer.

[0012] Further, the maleic anhydride grafting rate in the POE-g-MAH is 1.07 mol%; Furthermore, in the preparation process of the Schiff base, the molar ratio of levodopa: sodium hydroxide: furfural is 1:1:1; Furthermore, in the preparation process of the DOPO Schiff base derivative, the molar ratio of Schiff base:DOPO is 1:1; Furthermore, in the preparation process of the modified polyolefin elastomer, the mass ratio of POE-g-MAH:DOPO Schiff base derivative:3-amino-1,2,4-triazole:zinc chloride is (24-36):(4-16):1:1.

[0013] Furthermore, the preparation method of the lignin-modified copolymer comprises the following steps: Add lignin into tetrahydrofuran. Under a nitrogen atmosphere, add triethylamine and a tetrahydrofuran solution of 2-bromo-2-methylpropionyl bromide, and heat to 65-68 °C for reaction for 48-50 h. Add deionized water to terminate the reaction to obtain brominated lignin. Add the brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 2,2'-bipyridine, copper bromide, lauryl methacrylate, and isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycle operations, heat to 70-72 °C and stir for reaction for 24-26 h. Add the reaction product into anhydrous methanol for precipitation, filter, and dry under vacuum at 80-85 °C to obtain the lignin-modified copolymer.

[0014] Furthermore, in the three freeze-vacuum-thaw cycle operations, copper wire is added after the first freeze, and nitrogen is introduced after the third freeze. Furthermore, the content of phenolic hydroxyl groups in the lignin is 1.5-1.7 mmol / g, and Mn = 3000 g / mol. Furthermore, the bromine group content in the brominated lignin is 2.0 mmol / g, and Mn = 1800 g / mol. Furthermore, in the preparation process of the brominated lignin, the mass ratio of lignin:triethylamine:2-bromo-2-methylpropionyl bromide is 2:(2.8-3):(2.8-3). Furthermore, in the preparation process of the lignin-modified copolymer, the molar ratio of brominated lignin:2,2'-bipyridine:copper bromide:lauryl methacrylate:isobornyl methacrylate is (0.4-0.5):(0.12-0.3):(0.02-0.05):(240-300):(560-700).

[0015] A preparation method of a polyethylene cable with both flexibility and fire resistance comprises the following steps: Add low-density polyethylene, modified polyolefin elastomer, lignin-modified copolymer, antioxidant, zinc oxide, and talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, and cool and shape to form a protective sleeve coated on the surface of the cable core to obtain the polyethylene cable.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The present invention introduces zinc-based coordination bonds into the interface between DOPO Schiff base derivatives and POE-g-MAH to prepare a modified polyolefin elastomer. Maleic anhydride grafted POE (POE-g-MAH) reacts with triazole groups to form amide bonds, and then forms dynamic coordination bonds with Zn²⁺. This coordination network enhances the interfacial bonding between DOPO Schiff base derivatives and the matrix, promotes stress transfer, and at the same time, the dynamic bond breakage-recombination dissipates energy to avoid stress concentration. The coordination bonds significantly enhance the interfacial interaction between lignin and non-polar polyolefin elastomers, promote the dispersion of DOPO Schiff base derivatives in the polyolefin matrix, and greatly enhance the fire resistance of the cable while improving the mechanical properties of the cable.

[0017] 2. The present invention grafts lauryl methacrylate (flexible long chain) and isobornyl methacrylate (rigid bicyclic structure) onto lignin as a rigid backbone to form an elastomer network with "rigidity and flexibility combined" through atom transfer radical polymerization. The compatibility between traditional acrylate elastomers and polyolefin elastomers is generally poor. The present invention uses POE-g-MAH to make the molecular chains of polyolefin elastomers carry polar anhydride groups, thereby improving the compatibility with acrylate elastomers and further improving the flexibility and fire resistance of polyethylene cables.

[0018] 3. On the one hand, utilize the synergistic flame retardant effect of DOPO Schiff base derivatives (DOPO inhibits the combustion chain reaction through free radical capture (PO· and PO2·), and its rigid benzene ring structure promotes the formation of a carbon layer to block heat and oxygen; the C=N bond in the Schiff base structure decomposes at high temperature to generate non-combustible gases such as NH3, diluting the concentration of combustible gases, forming a dual gas-phase-condensed-phase flame retardant mechanism). On the other hand, use levodopa in the DOPO Schiff base derivative structure and lignin in the lignin-modified copolymer as carbon sources for synergistic flame retardant effect to further improve the fire resistance of the cable. Detailed implementation mode

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] In the following examples, the preparation method of DOPO Schiff base derivatives includes the following steps: Under a nitrogen atmosphere, add 0.1 mol of levodopa and 0.1 mol of sodium hydroxide to ethanol, heat to 80 °C, stir evenly, add an ethanol solution containing 0.1 mol of furfural, keep the temperature for reaction for 4 h, and perform rotary evaporation to obtain Schiff base; Under a nitrogen atmosphere, 0.1 mol of Schiff base and 0.1 mol of DOPO were added to ethanol, heated to 80 °C and reacted for 8 h, then vacuum distilled, the pH of the product was adjusted to 2.0, washed with deionized water, and dried in vacuo at 80 °C to obtain the DOPO Schiff base derivative.

[0021] A preparation method of brominated lignin, comprising the following steps: 2 g of lignin was added to tetrahydrofuran. Under a nitrogen atmosphere, 3 g of triethylamine and a tetrahydrofuran solution of 3 g of 2-bromoisobutyryl bromide were added, heated to 65 °C and reacted for 48 h, and deionized water was added to terminate the reaction to obtain brominated lignin. Example 1

[0022] A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: 36 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole were added to a mixer, heated to 100 °C and stirred for 10 min, 4 g of DOPO Schiff base derivative and 1 g of zinc chloride were added, and stirred at a constant temperature for 15 min to obtain a modified polyolefin elastomer; S2: 0.4 g of brominated lignin was added to a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, and 560 g of isobornyl methacrylate were added, stirred evenly, and subjected to three freeze-vacuum-thaw cycles, heated to 70 °C and stirred for 24 h, the reaction product was added to anhydrous methanol for precipitation, filtered, and dried in vacuo at 80 °C to obtain a lignin-modified copolymer; S3: 70 parts of low-density polyethylene, 20 parts of modified polyolefin elastomer, 10 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talc were added to a mixer in sequence, mixed, transferred to a twin-screw extruder for extrusion and coated on the outer surface of the cable core, and cooled and shaped to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable. Example 2

[0023] A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: 24 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole were added to a mixer, heated to 100 °C and stirred for 10 min, 16 g of DOPO Schiff base derivative and 1 g of zinc chloride were added, and stirred at a constant temperature for 15 min to obtain a modified polyolefin elastomer; S2: Add 0.4 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, and 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir for reaction for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain the lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 20 parts of modified polyolefin elastomer, 10 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, and cool and shape to form a protective sleeve coated on the surface of the cable core to obtain the polyethylene cable. Example 3

[0024] A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 30 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a kneader, heat to 100 °C and stir for 10 min, add 10 g of DOPO Schiff base derivative and 1 g of zinc chloride, and keep stirring for 15 min to obtain the modified polyolefin elastomer; S2: Add 0.4 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, and 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir for reaction for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain the lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 20 parts of modified polyolefin elastomer, 10 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, and cool and shape to form a protective sleeve coated on the surface of the cable core to obtain the polyethylene cable. Example 4

[0025] A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 30 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a kneader, heat to 100 °C and stir for 10 min, add 10 g of DOPO Schiff base derivative and 1 g of zinc chloride, and keep stirring for 15 min to obtain the modified polyolefin elastomer; S2: Add 0.5 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, and 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir for reaction for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain the lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 20 parts of modified polyolefin elastomer, 10 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, cool and shape to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable.

[0026] The remaining steps are the same as those in Example 3. Example 5

[0027] A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 30 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a kneader, heat to 100 °C and stir for 10 min, add 10 g of DOPO Schiff base derivative and 1 g of zinc chloride, keep warm and stir for 15 min to obtain a modified polyolefin elastomer; S2: Add 0.5 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, and 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir for reaction for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain the lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 25 parts of modified polyolefin elastomer, 15 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, cool and shape to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable.

[0028] The remaining steps are the same as those in Example 4. Example 6

[0029] Preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 30 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a mixer, heat to 100 °C and stir for 10 min, add 10 g of DOPO Schiff base derivative and 1 g of zinc chloride, keep warm and stir for 15 min to obtain a modified polyolefin elastomer; S2: Add 0.5 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir to react for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain a lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 30 parts of modified polyolefin elastomer, 25 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, and cool and shape to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable.

[0030] The remaining steps are the same as those in Example 4.

[0031] Comparative Example 1: Preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 36 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a mixer, heat to 100 °C and stir for 10 min, add 4 g of DOPO Schiff base derivative and 1 g of zinc chloride, keep warm and stir for 15 min to obtain a modified polyolefin elastomer; S2: Add 0.4 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir to react for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain a lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 18 parts of polyolefin elastomer POE, 2 parts of DOPO, 10 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, and cool and shape to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable; The remaining steps are the same as those in Example 1.

[0032] Comparative Example 2: A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 36 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a kneader, heat to 100 °C and stir for 10 min, add 4 g of DOPO Schiff base derivative and 1 g of zinc chloride, keep warm and stir for 15 min to obtain a modified polyolefin elastomer; S2: Add 0.4 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir to react for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain a lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 18 parts of polyolefin elastomer POE-g-MAH, 2 parts of DOPO, 10 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, cool and shape to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable; The remaining steps are the same as those in Example 1.

[0033] Comparative Example 3: A preparation method of a polyethylene cable with both flexibility and fire resistance: S1: Add 36 g of POE-g-MAH and 1 g of 3-amino-1,2,4-triazole into a kneader, heat to 100 °C and stir for 10 min, add 4 g of DOPO Schiff base derivative and 1 g of zinc chloride, keep warm and stir for 15 min to obtain a modified polyolefin elastomer; S2: Add 0.4 g of brominated lignin into a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, add 0.12 g of 2,2'-bipyridine, 0.02 g of copper bromide, 240 g of lauryl methacrylate, 560 g of isobornyl methacrylate, stir evenly, perform three freeze-vacuum-thaw cycles, heat to 70 °C and stir to react for 24 h, add the reaction product into anhydrous methanol for precipitation, filter, and dry in vacuum at 80 °C to obtain a lignin-modified copolymer; S3: Add 70 parts of low-density polyethylene, 20 parts of modified polyolefin elastomer, 30 parts of lignin-modified copolymer, 0.5 part of antioxidant, 0.6 part of zinc oxide, and 1 part of talcum powder into a mixer in sequence, mix, transfer to a twin-screw extruder for extrusion and coat on the outer surface of the cable core, cool and shape to form a protective sleeve coated on the surface of the cable core to obtain a polyethylene cable; The remaining steps are the same as those in Example 1.

[0034] Experiment: Vicat softening temperature test: The test was carried out with reference to GB / T 1633-2000, and the heating rate was set at 2 °C / min.

[0035] Flame retardancy test: The LOI was tested according to the method of GB / T 2406.2-2009; the vertical burning rating was tested with reference to the method of GB / T 2408-2021; Mechanical property test: The test was carried out with reference to the method of GB / T 1040.3-2006. The specimen was a type 5 dumbbell sheet with a thickness of 1 mm and a tensile rate of 250 mm / min; The experimental results are shown in Table 1 below.

[0036]

[0037] Table 1 Data Sheet for Performance Test of Polyethylene Cable Conclusion: The polyethylene cable prepared by the present invention has excellent flexibility and fire resistance.

[0038] In Comparative Example 1, POE-g-MAH was not used, and the polyolefin elastomer lacked polar anhydride groups, resulting in reduced compatibility with low-density polyethylene and lignin-modified copolymer.

[0039] In Comparative Example 2, the DOPO flame retardant was added to the matrix alone, resulting in reduced compatibility. In Comparative Example 3, an excessive amount of lignin-modified copolymer was added, resulting in reduced compatibility.

[0040] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be embraced by the present invention.

Claims

1. A polyethylene cable having both flexibility and fire resistance, characterized in that: The polyethylene cable comprises a cable core and a polyethylene protective sheath, wherein the polyethylene protective sheath comprises the following components: low-density polyethylene, modified polyolefin elastomer, lignin modified copolymer, antioxidant, zinc oxide, and talcum powder; The modified polyolefin elastomer is prepared from POE-g-MAH and DOPO Schiff base derivatives; The lignin modified copolymer is prepared from lauryl methacrylate, isobornyl methacrylate and a lignin macromolecular initiator.

2. A polyethylene cable having both flexibility and fire resistance according to claim 1, characterized in that: The polyethylene protective sleeve comprises the following components, calculated by mass: 50-70 parts of low-density polyethylene, 20-30 parts of modified polyolefin elastomer, 10-25 parts of lignin modified copolymer, 0.5-1 parts of antioxidant, 0.6-1.2 parts of zinc oxide and 1-2 parts of talc.

3. The polyethylene cable having both flexibility and fire resistance according to claim 1, characterized in that: The preparation method of the modified polyolefin elastomer comprises the following steps: POE-g-MAH and 3-amino-1,2,4-triazole are added to an internal mixer, heated to 100-105° C. and stirred for 10-15 minutes, DOPO Schiff base derivative and zinc chloride are added, and the mixture is stirred at the same temperature for 15-20 minutes to obtain a modified polyolefin elastomer.

4. A polyethylene cable having both flexibility and fire resistance according to claim 3, characterized in that: In the preparation process of the modified polyolefin elastomer, the mass ratio of POE-g-MAH:DOPO Schiff base derivative:3-amino-1,2,4-triazole:zinc chloride is (24-36):(4-16):1:

1.

5. The polyethylene cable having both flexibility and fire resistance according to claim 3, characterized in that: The preparation method of the DOPO Schiff base derivative comprises the following steps: Under nitrogen atmosphere, add levodopa and sodium hydroxide to ethanol, heat to 80-85°C, stir evenly, add furfural ethanol solution, keep warm for 4-5h, and rotary evaporate to obtain Schiff base; Under nitrogen atmosphere, Schiff base and DOPO were added to ethanol, heated to 80-85°C for reaction for 8-9h, vacuum distilled, the pH of the product was adjusted to 2.0-2.1, washed with deionized water, and vacuum dried at 80-85°C to obtain a DOPO Schiff base derivative.

6. A polyethylene cable having both flexibility and fire resistance according to claim 5, characterized in that: In the preparation process of Schiff base, the molar ratio of L-DOPA: sodium hydroxide: furfural is 1:1:1; in the preparation process of DOPO Schiff base derivative, the molar ratio of Schiff base: DOPO is 1:

1.

7. The polyethylene cable having both flexibility and fire resistance according to claim 1, characterized in that: The preparation method of the lignin modified copolymer comprises the following steps: Add lignin to tetrahydrofuran, add triethylamine and 2-bromoisobutyryl bromide in tetrahydrofuran solution under nitrogen atmosphere, heat to 65-68°C for 48-50h, add deionized water to terminate the reaction, and obtain brominated lignin; The brominated lignin is added to a mixed solvent of tetrahydrofuran and N,N-dimethylformamide, and 2,2'-bipyridine, copper bromide, lauryl methacrylate and isobornyl methacrylate are added, stirred evenly, and three freeze-vacuum-thaw cycles are performed, and the mixture is heated to 70-72°C and stirred for reaction for 24-26 hours. The reaction product is added to anhydrous methanol for precipitation, filtered, and vacuum dried at 80-85°C to obtain a lignin modified copolymer.

8. The polyethylene cable having both flexibility and fire resistance according to claim 7, characterized in that: In the preparation process of brominated lignin, the mass ratio of lignin: triethylamine: 2-bromoisobutyryl bromide is 2: (2.8-3): (2.8-3).

9. The polyethylene cable having both flexibility and fire resistance according to claim 7, characterized in that: In the preparation process of the lignin modified copolymer, the molar ratio of brominated lignin: 2,2'-bipyridine: copper bromide: lauryl methacrylate: isobornyl methacrylate is (0.4-0.5): (0.12-0.3): (0.02-0.05): (240-300): (560-700).

10. A method for preparing a polyethylene cable having both flexibility and fire resistance according to any one of claims 1 to 9, characterized in that: The following steps are involved: Low-density polyethylene, modified polyolefin elastomer, lignin modified copolymer, antioxidant, zinc oxide and talcum powder are added to a mixer in sequence, mixed, transferred to a twin-screw extruder for extrusion and coated on the outer surface of the cable core, cooled and shaped to form a protective sheath coated on the surface of the cable core, and a polyethylene cable is obtained.

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