Cable sheath capable of improving shielding effect and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite materials, and discloses a cable sheath capable of improving a shielding effect and a preparation method thereof, the cable sheath capable of improving the shielding effect comprises the following components by weight: 70-110 parts of a polymer matrix precursor; 2 to 5 parts of an isocyanate group functionalized carbon nanotube; 1 to 3 parts of furfuryl functionalized graphene; 2 to 5 parts of nano manganese zinc ferrite; the polymer matrix precursor comprises polyether polyol and diisocyanate, and the cable sheath also comprises one or more of the following auxiliary additives: an antioxidant, a crosslinking agent, a crosslinking agent, a crosslinking agent, a crosslinking agent and a crosslinking agent. An ultraviolet absorber; a lubricant; and a foaming nucleating agent. According to the invention, by constructing a carbon nanotube / ferrite synergistic shielding network and a thermally reversible crosslinking network, the cable sheath has the functions of broadband efficient shielding and thermally induced self-repairing.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite materials, in particular to a cable sheath with improved shielding effect and a preparation method thereof. Background Art

[0002] With the rapid development of modern electronic communications, aerospace, and precision instrumentation technologies, the integration of electronic equipment is increasing, and electromagnetic interference (EMI) issues within their operating environments are becoming increasingly severe. As a key component connecting various devices and transmitting signals and energy, the cable sheath not only physically protects the internal cable core but also serves as the primary barrier against external electromagnetic interference and ensures signal transmission integrity. Therefore, developing cable sheath materials with excellent electromagnetic shielding performance and high reliability is crucial to ensuring the stable operation of the entire electronic system.

[0003] To achieve electromagnetic shielding, a commonly used technique is to blend conductive fillers, such as metal powder, carbon fiber, carbon nanotubes, or graphene, with a polymer matrix (such as polyvinyl chloride, polyethylene, or thermoplastic polyurethane). This creates a conductive network within the insulating polymer matrix, imparting electromagnetic shielding capabilities to the composite material. This approach can improve the material's electromagnetic shielding effectiveness to a certain extent and is currently the mainstream technology in this field.

[0004] Although adding conductive fillers to polymer matrices to prepare electromagnetic shielding composite materials is a common method in the existing technology, this technical route still has some shortcomings: First, the shielding mechanism of this type of material is highly dependent on the reflection loss of electromagnetic waves by the conductive network and lacks an effective absorption loss mechanism. This causes its shielding effectiveness to be highly selective to frequency, making it difficult to maintain high efficiency within a wide frequency band. At the same time, the reflected electromagnetic waves may also cause secondary interference to other surrounding electronic equipment.

[0005] Secondly, once traditional cable sheath materials are cracked and damaged by scratches, bending or impact, the damage is irreversible. This is because the chemical cross-linked network or physical entanglement structure inside is static and lacks the internal driving force for structural reorganization and bond repair after damage, resulting in reduced reliability and shortened service life under harsh service conditions.

[0006] In addition, during the preparation process, due to the extremely high specific surface area and surface energy of nano-conductive fillers, their wettability and compatibility with the polymer matrix are usually poor, which makes the fillers very easy to agglomerate in the matrix rather than being evenly dispersed. This not only seriously damages the integrity of the conductive network and causes a significant decrease in shielding performance, but these agglomerates also act as stress concentration points, deteriorating the mechanical properties of the material. Summary of the Invention

[0007] The purpose of the present invention is to provide a cable sheath with improved shielding effect and a preparation method thereof, which solves the problem that the existing cable sheath material has a narrow shielding band and low reliability due to irreversible damage during service.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: In a first aspect, the present invention provides a cable sheath with improved shielding effect: The cable sheath comprises the following components in parts by weight: Polymer matrix precursor: 70-110 parts; isocyanate functionalized carbon nanotubes: 2-5 parts; furfural functionalized graphene: 1-3 parts; nano manganese zinc ferrite: 2-5 parts; bismaleimide: 0.5-2 parts.

[0009] Preferably, the polymer matrix precursor comprises polyether polyol and diisocyanate. These two components act as reactive monomers in the subsequent preparation process to form a polyurethane elastomer matrix through in-situ polymerization, providing the sheath with basic mechanical properties and insulation.

[0010] In order to further optimize the material properties, the cable sheath may also use one or more auxiliary additives, the types and weight proportions of which are as follows: 0.5-1.5 parts of antioxidant, used to improve the material's resistance to thermal oxidative aging; 0.2-0.8 parts of ultraviolet absorber, used to improve weather resistance; 0.1-0.5 parts of lubricant, used to improve processing fluidity; 0.1-0.5 parts of foaming nucleating agent, used to control the pore structure during the foaming process.

[0011] In the technical solution of the present invention: The isocyanate (-NCO) groups on the surface of the isocyanate-functionalized carbon nanotubes chemically bond with the hydroxyl (-OH) groups on the polyurethane matrix segments during in-situ polymerization, forming a stable grafted structure. This structure significantly enhances the interfacial compatibility between the carbon nanotubes and the matrix, ensuring uniform dispersion within the matrix without agglomeration, thereby safeguarding the integrity of the conductive network and the stability of the shielding properties.

[0012] Nano-manganese zinc ferrite absorbs electromagnetic waves through mechanisms such as hysteresis loss and eddy current loss. The nano-manganese zinc ferrite complements the conductive network of carbon nanotubes, expanding the shielding mechanism from single reflection loss to a combination of reflection and absorption, effectively broadening the effective frequency range of electromagnetic shielding.

[0013] The furfuryl groups on the surface of the furfuryl-functionalized graphene, along with bismaleimide molecules, together constitute the thermally repairable system of the present invention. The maleimide groups undergo a Diels-Alder addition reaction at 90-110°C, forming dynamic covalent bonds, thereby constructing a thermally reversible crosslinked network within the polymer matrix. When the sheath material is damaged and microcracks form, heating the damaged area breaks the already formed dynamic covalent bonds, increasing the local fluidity of the material. Subsequently, during cooling, the broken functional groups undergo a Diels-Alder reaction at the crack interface, re-forming covalent bonds, thereby healing the cracks and restoring the material's mechanical properties.

[0014] The second aspect of the present invention provides a method for preparing the cable sheath, which comprises the following steps: pre-dispersion, reactive extrusion and foaming molding.

[0015] Step 1: Pre-dispersion: The total amount of the polyether polyol is equally divided into a first part and a second part.

[0016] The isocyanate-functionalized carbon nanotubes, furfural-functionalized graphene, nano-manganese zinc ferrite, bismaleimide, and one or more auxiliary additives selected as needed are mixed with the first part of the polyether polyol.

[0017] The mixing process is carried out in an ultrasonic device with an ultrasonic treatment frequency of 20-40 kHz and a time of 30-60 minutes.

[0018] The purpose of this step is to utilize the ultrasonic cavitation effect to break up the agglomeration and achieve uniform dispersion of various nano-functional fillers in the liquid phase of polyol before entering the reaction system, thereby forming a high-dispersion premix required for subsequent reactions.

[0019] Step 2, reactive extrusion: This step is completed in a twin-screw extruder.

[0020] The second part of polyether polyol and the diisocyanate are fed into the main feed port of the twin-screw extruder.

[0021] At the same time, the premix prepared in step 1 is fed into the twin-screw extruder from a side feed port located downstream of the melting section.

[0022] Through this feeding method, the main components are first melted and mixed under the shearing action of the screw to form the mainstream melt; and the premix is ​​subsequently added from the side, mainly distributed in the outer layer of the melt flow, and finally a radial gradient distribution structure is formed in the extrudate with the concentration of functional fillers increasing from the inside to the outside.

[0023] This structure can more effectively concentrate the shielding and repair functional components on the surface of the sheath, thereby improving its utilization efficiency.

[0024] While the material is being transported along the screw, the extruder temperature is set at 160-195°C and the screw speed is set at 150-300 rpm. Under these conditions, the polyether polyol and diisocyanate undergo in-situ polymerization to form a polyurethane matrix.

[0025] Step 3: Foaming molding: In the middle and rear sections of the twin-screw extruder, supercritical carbon dioxide fluid at a pressure of 15-25 MPa is injected into the formed polymer melt.

[0026] The high-pressure fluid acts as a physical foaming agent, dissolving and evenly dispersing in the melt. When the melt carrying the high-pressure gas passes through the extruder die, the sudden drop in pressure causes the carbon dioxide dissolved in the melt to separate and rapidly expand, forming a large number of tiny cells, thus obtaining a sheath with a microporous structure.

[0027] Step 4: Cooling, shaping and thermal annealing: The extruded microporous sheath is first water-cooled or air-cooled to rapidly cool and set, and then passes through an infrared heating channel for an online thermal annealing treatment at 90-110°C for 30-60 seconds.

[0028] This thermal annealing step provides the necessary activation energy for the aforementioned Diels-Alder reaction, prompting the furfuryl-functionalized graphene distributed in the material to react with bismaleimide, ultimately forming a thermally reversible cross-linked network that gives the material self-healing capabilities.

[0029] In summary, the present invention includes at least one of the following beneficial technical effects: 1. This invention combines conductive isocyanate-functionalized carbon nanotubes with magnetic nano-manganese-zinc ferrite to create both a conductive loss network and magnetic loss centers within the polymer matrix. These two shielding fillers, operating with different mechanisms, work synergistically, enabling the cable sheath to not only efficiently reflect but also effectively absorb electromagnetic waves, resulting in excellent electromagnetic shielding performance across a wide frequency band.

[0030] 2. By introducing furfuryl-functionalized graphene and bismaleimide, this invention constructs a thermoreversible dynamic covalent network within the material based on the Diels-Alder reaction. When the sheath is damaged by external forces and microcracks develop, simply heating the damaged area triggers the breaking and reforming of the dynamic covalent bonds in the network, thereby healing the cracks and restoring the material's integrity and mechanical properties, extending the cable's service life in harsh environments.

[0031] 3. The carbon nanotubes in this invention are functionalized with isocyanate groups, allowing the -NCO groups on their surfaces to chemically graft onto polyurethane matrix segments during the reactive extrusion process. This in-situ chemical bonding enhances interfacial compatibility between the filler and the matrix, effectively preventing nanofiller aggregation due to interfacial incompatibility and ensuring uniform dispersion within the matrix, providing a structural foundation for stable shielding and mechanical properties.

[0032] 4. The preparation method of the present invention utilizes a primary and lateral gradient feed method, which allows the functional filler to be concentrated more in the outer layer of the sheath. This improves the utilization efficiency of the functional components while maintaining core shielding and repair performance. Furthermore, by introducing a supercritical carbon dioxide physical foaming process, a microporous structure is formed within the sheath, effectively reducing the overall density and dielectric constant of the material, achieving lightweighting and further optimizing impedance matching, which helps to enhance shielding effectiveness. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below with reference to preparation examples, embodiments, comparative examples and test examples.

[0034] Preparation Example 1: Preparation of isocyanate functionalized carbon nanotubes includes the following steps: 1.0 g of commercially available multi-walled carbon nanotubes was added to 100 mL of a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid in a 3:1 volume ratio. The mixture was stirred magnetically in a 60°C water bath for 4 hours to introduce carboxyl functional groups onto the carbon nanotube surfaces.

[0035] After the reaction is complete, the mixture is centrifuged to collect the lower layer of product. The product is repeatedly washed by centrifugation with deionized water until the pH value of the supernatant is close to 7. The washed product is dried in a vacuum oven at 80°C for 12 hours to obtain carboxylated carbon nanotube powder.

[0036] Under nitrogen protection, 1.0 g of the obtained carboxylated carbon nanotubes was dispersed in 200 mL of anhydrous N,N-dimethylformamide (DMF) and ultrasonicated for 30 minutes to achieve uniform dispersion. 10.0 g of toluene-2,4-diisocyanate (TDI) was added to the dispersion.

[0037] The mixture was heated to 80°C and stirred mechanically for 24 hours. During this reaction, the carboxyl functional group reacted with an isocyanate group in the TDI molecule, causing the TDI molecule to be grafted onto the surface of the carbon nanotubes.

[0038] After the reaction, the product was collected by centrifugation and washed three times with excess anhydrous toluene to completely remove unreacted TDI. Finally, the product was dried in a vacuum oven at 60°C for 24 hours to obtain isocyanate-functionalized carbon nanotubes.

[0039] Preparation Example 2: The preparation method of furfuryl-functionalized graphene comprises the following steps: Graphene oxide (GO) was prepared by the improved Hummers method: 5.0 g of natural flake graphite was added to 120 mL of concentrated sulfuric acid. 15.0 g of potassium permanganate was slowly added under ice, and the mixture was stirred for 2 hours. The reaction was then transferred to a 35°C water bath and allowed to react for 12 hours. After the reaction, the mixture was poured into 500 mL of deionized water containing hydrogen peroxide. After the solution turned golden yellow, it was centrifuged, washed until neutral, and finally freeze-dried to obtain graphene oxide powder.

[0040] 1.0 g of the prepared graphene oxide powder was dispersed in 200 mL of deionized water and ultrasonicated for 1 h to form a uniform GO dispersion.

[0041] 5.0 g of furfurylamine was added to the GO dispersion, and the mixture was refluxed in a 95°C oil bath for 24 hours. During this reaction, the amino groups in the furfurylamine molecules reacted with the epoxy groups on the graphene oxide surface, introducing furfuryl functional groups onto the graphene sheets.

[0042] After the reaction is completed, the product is centrifuged and washed multiple times with deionized water and ethanol in sequence to remove unreacted furfurylamine.

[0043] The washed product is freeze-dried to obtain furfuryl-functionalized graphene.

[0044] Example 1: The present embodiment provides a cable sheath with improved shielding effect. The cable sheath includes the following components in parts by weight: 60 parts of polyether polyol, 30 parts of diisocyanate, 3.5 parts of isocyanate-functionalized carbon nanotubes prepared in Preparation Example 1, 2 parts of furfuryl-functionalized graphene prepared in Preparation Example 2, 3.5 parts of nano-manganese zinc ferrite, 1.2 parts of bismaleimide, 1 part of antioxidant, 0.5 part of ultraviolet absorber, 0.3 part of lubricant, and 0.3 part of foaming nucleating agent.

[0045] The preparation method of the cable sheath is as follows: S1. Pre-dispersion: Divide 60 parts of polyether polyol into 30 parts of a first part and 30 parts of a second part. Mix 3.5 parts of isocyanate-functionalized carbon nanotubes, 2 parts of furfuryl-functionalized graphene, 3.5 parts of nano-manganese zinc ferrite, 1.2 parts of bismaleimide, 1 part of an antioxidant, 0.5 parts of a UV absorber, 0.3 parts of a lubricant, and 0.3 parts of a foaming nucleating agent with the 30 parts of polyether polyol in the first part, place the mixture in an ultrasonic apparatus, and treat at a frequency of 30 kHz for 45 minutes to obtain a premix.

[0046] S2. Reactive Extrusion: 30 parts of the second portion of polyether polyol and 30 parts of diisocyanate were fed into the main feed port of a twin-screw extruder. Simultaneously, the premix prepared in step S1 was fed into the extruder through a side feed port located downstream of the melting section. The temperature of each extruder zone was set at 180°C, and the screw speed was set at 200 rpm for reactive extrusion.

[0047] S3. Foaming molding: In the middle and rear section of the twin-screw extruder, supercritical carbon dioxide fluid with a pressure of 20 MPa is injected into the melt, and the melt is extruded through the die head to form a microporous sheath due to pressure drop.

[0048] S4. Cooling and shaping and thermal annealing: The extruded sheath is cooled and shaped in a water tank, and then passed through an infrared heating channel for online thermal annealing at 100° C. for 45 seconds to obtain the final cable sheath.

[0049] Example 2: This embodiment provides a cable sheath with improved shielding effect. The cable sheath comprises the following components in parts by weight: 48 parts of a polyether polyol, 22 parts of a diisocyanate, 2 parts of the isocyanate-functionalized carbon nanotubes prepared in Preparation Example 1, 1 part of the furfuryl-functionalized graphene prepared in Preparation Example 2, 2 parts of nano-manganese zinc ferrite, 0.5 parts of bismaleimide, and auxiliary additives of the same types and amounts as in Example 1. The preparation method is exactly the same as in Example 1.

[0050] Example 3: This embodiment provides a cable sheath with improved shielding effectiveness. The cable sheath comprises the following components in parts by weight: 75 parts of a polyether polyol, 35 parts of a diisocyanate, 5 parts of the isocyanate-functionalized carbon nanotubes prepared in Preparation Example 1, 3 parts of the furfuryl-functionalized graphene prepared in Preparation Example 2, 5 parts of nano-manganese zinc ferrite, 2 parts of bismaleimide, and auxiliary additives of the same types and amounts as in Example 1. The preparation method is exactly the same as in Example 1.

[0051] Comparative Example 1: The difference between this comparative example and Example 1 is that nano manganese zinc ferrite is not added in this comparative example. The preparation method is exactly the same as that of Example 1.

[0052] Comparative Example 2: This comparative example differs from Example 1 in that furfuryl-functionalized graphene and bismaleimide are not added in this comparative example. The preparation method is exactly the same as that of Example 1.

[0053] Comparative Example 3: This comparative example differs from Example 1 in that an equal weight of commercially available pristine multi-walled carbon nanotubes is used in place of the isocyanate-functionalized carbon nanotubes prepared in Preparation Example 1, and an equal weight of commercially available pristine graphene is used in place of the furfuryl-functionalized graphene prepared in Preparation Example 2. The preparation method is identical to that of Example 1.

[0054] Comparative Example 4: The raw material components and amounts used in this comparative example were identical to those in Example 1. The primary difference between the preparation method and that in Example 1 lies in the reactive extrusion step: the premix prepared in Step S1, 30 parts of the second portion of polyether polyol, and 30 parts of diisocyanate were all fed simultaneously through the main feed port of a twin-screw extruder for conventional co-extrusion. All other preparation conditions were identical to those in Example 1.

[0055] Test Example 1: Experimental steps: The test equipment used is a vector network analyzer. The test method is based on GJB6190-2008 and adopts the coaxial transmission line method.

[0056] The sheath samples prepared in Examples 1-3 and Comparative Examples 1-4 were cut into coaxial ring-shaped samples with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm. The sample thickness was 2.0 mm, and the sample surface was ensured to be flat.

[0057] The annular specimen was clamped in a coaxial test fixture and connected to the two ports of a vector network analyzer. A frequency sweep test was performed in the frequency range of 8.2-12.4 GHz. The scattering parameters of each sample were recorded, and the total electromagnetic shielding effectiveness of the material was calculated based on the scattering parameters. The test results are shown in Table 1.

[0058] Table 1: Electromagnetic shielding effectiveness test data of various examples and comparative examples sample 8.5GHz 10.3GHz 12.1GHz Example 1 48.2 51.5 53.6 Example 2 43.7 46.1 47.9 Example 3 52.4 54.8 56.1 Comparative Example 1 35.8 34.5 33.7 Comparative Example 2 47.9 51.2 53.1 Comparative Example 3 25.1 24.3 23.8 Comparative Example 4 42.6 45.9 47.2 From Table 1, we can get: The combination of isocyanate-functionalized carbon nanotubes and nano-manganese zinc ferrite effectively improves the shielding performance of the material. This is because the conductive network constructed by carbon nanotubes primarily affects electromagnetic waves through conductivity loss and interfacial polarization loss, while nano-manganese zinc ferrite, as a magnetic medium, introduces additional hysteresis loss and natural resonance loss mechanisms. The synergistic effect of these two loss mechanisms expands the shielding frequency band and improves the overall shielding effectiveness.

[0059] The isocyanate-functionalized carbon nanotubes used in Example 1 have surface isocyanate groups that chemically bond with the polyurethane matrix during the reactive extrusion process. This interfacial chemical bond enhances the compatibility of the filler with the matrix, inhibits nanofiller aggregation, and promotes the formation of a more uniform and complete conductive network within the matrix. The unfunctionalized filler in Comparative Example 3, due to its high surface energy and poor compatibility with the matrix, is prone to agglomeration, disrupting the continuity of the conductive pathway and resulting in lower shielding effectiveness.

[0060] Example 1 employs a primary and lateral gradient feed method, resulting in a gradient distribution of shielding filler across the radial cross-section of the sheath, with the outer layer concentration being higher than the inner layer. This structure more effectively concentrates the shielding components in the primary area of ​​interaction between the material and electromagnetic waves—the sheath surface. This improves shielding resource utilization and achieves higher shielding effectiveness while maintaining the same total filler content.

[0061] Test Example 2: According to GB / T1040.2-2006 standard, the sheath materials prepared in Examples 1-3 and Comparative Examples 1-4 were molded into standard dumbbell-shaped splines.

[0062] The specimens were tensile tested using an electronic universal material testing machine at a temperature of 23±2°C and a tensile rate of 50 mm / min, and their tensile strength and elongation at break were recorded.

[0063] Five samples were tested for each group of samples, and the results were averaged. The test results are shown in Table 2.

[0064] Table 2: Mechanical properties test data of various examples and comparative examples sample Tensile strength (MPa) Elongation at break (%) Example 1 25.4 488 Example 2 24.1 510 Example 3 26.2 465 Comparative Example 1 25.9 495 Comparative Example 2 26.5 490 Comparative Example 3 14.8 215 Comparative Example 4 25.1 480 From Table 2, we can get: The samples of Examples 1-3 all have good tensile strength and elongation at break. Comparing the data of Example 1 with that of Comparative Example 3, the tensile strength and elongation at break of the former are higher than those of the latter.

[0065] In Example 1, the isocyanate-functionalized carbon nanotubes form chemical bonds with the polyurethane matrix through their surface functional groups, forming a stable filler-matrix interface. This strong interfacial interaction effectively transfers external stress from the relatively soft polymer matrix to the high-strength nanofillers, thereby improving the overall load-bearing capacity and toughness of the composite material.

[0066] In contrast, in Comparative Example 3, the filler without functionalization treatment has poor compatibility with the matrix and is easy to agglomerate, forming stress concentration points inside the material, like defects, causing the material to be destroyed under relatively low stress.

[0067] Test Example 3: Take the standard dumbbell-shaped specimen before testing in Test Example 2, and use a sharp blade to cut a prefabricated crack with a depth of about half the thickness of the specimen at the geometric center of the specimen perpendicular to the tensile direction.

[0068] The specimens with prefabricated cracks were placed in a constant temperature oven at 110°C for heat treatment for 60 minutes.

[0069] After the heat treatment, the specimens were taken out and cooled to room temperature.

[0070] The repaired specimen was subjected to a tensile test again according to the method of Test Example 2, and its tensile strength after repair was recorded.

[0071] The self-repair efficiency was calculated using the following formula: Repair efficiency (%) = (tensile strength after repair / original tensile strength) × 100%. The test results are shown in Table 3.

[0072] Table 3: Repair efficiency test data of various examples and comparative examples From Table 3 we can get: After cutting damage and heat treatment, the tensile strength of the samples in Examples 1-3 recovered to over 89% of their original strength, demonstrating high self-repair efficiency. This is in stark contrast to Comparative Example 2, which achieved a repair efficiency of only 10.6%. This data directly demonstrates the effectiveness of the repair system introduced in this invention.

[0073] In the sample presented in the examples, furfuryl-functionalized graphene and bismaleimide together form a thermoreversible chemical system based on the Diels-Alder reaction. When the material is heated to 110°C, the formed Diels-Alder addition bonds undergo reversible chemical cleavage, allowing the polymer segments to gain localized mobility at the crack interface. Subsequent cooling promotes the reintroduction of addition reactions between the furfuryl groups and the maleimide groups on either side of the crack, forming new covalent bonds and chemically repairing the crack.

[0074] Since Comparative Example 2 lacks this specific chemical reaction pair and does not have the above-mentioned repair mechanism, its mechanical properties cannot be restored after being damaged.

[0075] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A cable sheath for improving shielding effect, characterized in that: The cable sheath comprises the following components in parts by weight: Polymer matrix precursor: 70-110 parts; Isocyanate functionalized carbon nanotubes: 2-5 parts; Furfuryl functionalized graphene: 1-3 parts; Nano manganese zinc ferrite: 2-5 parts; Bismaleimide: 0.5-2 parts.

2. A cable sheath for improving shielding effect according to claim 1, characterized in that: The polymer matrix precursor includes polyether polyol and diisocyanate.

3. A cable sheath for improving shielding effect according to claim 1, characterized in that: The cable sheath further comprises one or more of the following auxiliary additives: Antioxidant: 0.5-1.5 parts; Ultraviolet absorber: 0.2-0.8 parts; Lubricant: 0.1-0.5 parts; Foaming nucleating agent: 0.1-0.5 parts.

4. A method for preparing a cable sheath with improved shielding effect, characterized in that: A method for preparing a cable sheath with improved shielding effect according to any one of claims 1 to 3, comprising the following steps: Pre-dispersion: mixing the isocyanate-functionalized carbon nanotubes, furfural-functionalized graphene, nano-manganese zinc ferrite and bismaleimide with half of the polyether polyol to obtain a premix; Reactive extrusion: the functional premix, the other half of the polyether polyol and the diisocyanate are reactively extruded, and an in-situ polymerization reaction occurs during the extrusion process; Foaming molding: foaming treatment is performed during the reactive extrusion process to obtain a sheath with a microporous structure.

5. The method for preparing a cable sheath with improved shielding effect according to claim 4, characterized in that: In step S1, the step of obtaining the functional premix comprises: Dividing the polyether polyol equally into a first part and a second part; The isocyanate-functionalized carbon nanotubes, the furfuryl-functionalized graphene, the nano-manganese zinc ferrite, the bismaleimide, the first part of the polyether polyol and the one or more auxiliary additives are mixed and treated at a frequency of 20-40 kHz for 30-60 minutes using an ultrasonic device to obtain the premix.

6. The method for preparing a cable sheath with improved shielding effect according to claim 4, characterized in that: In step S2, the reactive extrusion step includes: feeding the second part of polyether polyol and the diisocyanate into the main feed port of the twin-screw extruder; Synchronously feeding the premix into the twin-screw extruder from a side feed port located downstream of the melting section; Reactive extrusion is carried out in the twin-screw extruder, the temperature of the reactive extrusion is 160-195° C., and the screw speed is 150-300 rpm.

7. The method for preparing a cable sheath with improved shielding effect according to claim 4, characterized in that: In step S3, the foaming step includes: In the middle and rear section of the twin-screw extruder, supercritical carbon dioxide fluid with a pressure of 15-25 MPa is injected into the melt as a foaming agent, so that the foaming agent and the melt are uniformly mixed and then foamed by the pressure drop of the die head.

8. The method for preparing a cable sheath with improved shielding effect according to claim 4, characterized in that: The method further comprises cooling and shaping and thermal annealing: The microporous structure sheath is water-cooled or air-cooled for shaping, and then subjected to online thermal annealing treatment at a temperature of 90-110° C. for 30-60 seconds through an infrared heating channel to promote the reaction of the furfuryl-functionalized graphene with the bismaleimide to form a thermally reversible cross-linked network.

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