Graft modified polypropylene cable material and preparation method thereof

Abstract

The invention provides a grafted modified polypropylene cable material and a preparation method thereof, and belongs to the field of cable materials. The cable material comprises 50-70 parts of styrene grafted polypropylene, 20-40 parts of a thermoplastic elastomer, 0.5-2 parts of an antioxidant and 5-10 parts of a voltage stabilizer. The preparation method comprises the following steps: blending styrene grafted polypropylene, a thermoplastic elastomer, an oxidant and a voltage stabilizer through a torque rheometer, and carrying out twin-screw extrusion granulation. The grafted modified polypropylene, the thermoplastic elastomer, the oxidizing agent and the voltage stabilizer are blended, the defects that a traditional polypropylene insulating material is large in brittleness, prone to aging and the like are overcome, the prepared cable material has excellent insulating performance, mechanical toughness and electrical aging resistance, the strict requirements of high-voltage and ultrahigh-voltage cables for insulating materials are met, and the service life of the cable material is prolonged. Wide industrial application prospects are realized.

Description

Technical Field

[0001] This invention relates to the field of cable material technology, specifically to a grafted modified polypropylene cable material and its preparation method. Background Technology

[0002] Compared to traditional cross-linked polyethylene (XLPE) materials, polypropylene (PP) cable insulation materials exhibit superior performance in heat resistance, insulation, and mechanical strength. Furthermore, their production process is relatively simple, requiring no cross-linking and enabling recycling, making them widely recognized in the industry as a potential replacement for XLPE cable insulation. However, pure PP has significant performance limitations: high crystallinity, high rigidity, and poor toughness, making it difficult to meet the bending requirements of high-voltage DC cables for insulation materials. On the other hand, under high-voltage DC environments, it is prone to space charge accumulation, leading to localized electric field distortion and accelerating insulation aging.

[0003] To improve the mechanical toughness and electrical properties of polypropylene (PP), existing technologies typically involve copolymerizing PP with other olefin monomers to prepare copolymer polypropylene (IPC). However, in actual IPC production, ethylene, as a key comonomer, exhibits significant differences in its specific dosing amount regarding its impact on the final material properties. Currently, there is no consensus in the industry regarding the optimal range for ethylene dosing. Some studies have shown that nanoparticle modification of PP or the induction of β-crystal formation by organic nucleating agents can effectively improve the electrical properties and mechanical toughness of PP. However, nanoparticles are prone to agglomeration, causing interfacial defects and affecting batch stability. Furthermore, nucleating agents are prone to migrating and precipitating from the matrix during long-term high-temperature service, leading to a loosened crystalline structure, and their long-term reliability remains to be verified.

[0004] In recent years, grafting polar functional groups onto nonpolar polymers has been an effective way to regulate polymer charge transport properties and improve polymer electrical performance. Styrene, as an unsaturated vinyl compound, has a unique benzene ring structure that affects the injection and migration of space charge. Patent CN121086408A discloses a self-reinforced polypropylene cable insulation material. By grafting polar vinyl monomers (such as styrene) onto the PP backbone to form a polypropylene graft copolymer, β-crystal formation is induced. Deep-level charge traps are constructed using polar groups, effectively suppressing space charge accumulation and improving breakdown strength and heat distortion temperature. However, the elongation at break of this material is only about 224%, limiting its application in cable applications requiring repeated bending. Patent CN119119636A discloses a polypropylene cable insulation material with high dielectric properties that is resistant to long-term electrical aging. It uses a free radical-regulated voltage stabilizer containing xanthate groups, combined with functional fillers and polymer elastomers (such as SEBS and POE). The voltage stabilizer and fillers are stably dispersed in the PP phase through a two-step extrusion process, which significantly extends the breakdown life of the material under high voltage and solves the problems of electrical dendrite and free radical aging. Although it improves mechanical properties (tensile strength 21.4-22.8 MPa, elongation at break 400.8-429.3%), the dielectric properties are weakened due to insufficient interfacial compatibility. Moreover, it does not introduce deep traps on the PP main chain through molecular design, resulting in limited space charge suppression ability.

[0005] Furthermore, melt blending PP-g-St with thermoplastic elastomers improves toughness while retaining the excellent electrical properties of PP-g-St. However, due to the poor compatibility between the thermoplastic elastomer and the PP-g-St matrix, localized agglomeration regions of the elastomer occur. When the composite material is applied in a high-voltage environment, these agglomeration regions may induce electric field concentration, causing the local electric field to exceed the breakdown field strength of the composite material itself, thereby inducing the risk of insulation failure.

[0006] In summary, existing polypropylene composite materials struggle to achieve synergistic optimization of mechanical, electrical, and aging resistance properties. Therefore, there is an urgent need to develop a novel polypropylene cable insulation material that simultaneously achieves high breakdown strength, high elongation at break, low electric field distortion, and long-term service stability. Summary of the Invention

[0007] The main objective of this invention is to provide a grafted modified polypropylene cable material and its preparation method, thereby solving the problems mentioned in the background art. This invention constructs deep trap sites in the polypropylene chain segments by grafting styrene onto polypropylene, and works synergistically with thermoplastic elastomers, antioxidants, and voltage stabilizers to optimize interfacial compatibility and stress distribution, reduce electric field distortion, and achieve a synergistic improvement in electrical performance, mechanical performance, resistance to electrical aging, and electric field uniformity. This has significant practical value.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A grafted modified polypropylene cable material comprises the following components by weight: 50-70 parts of styrene-grafted polypropylene; 20-40 parts of thermoplastic elastomer; 0.5-2 parts of a first antioxidant; and 5-10 parts of a voltage stabilizer.

[0010] The sum of the mass parts of the above-mentioned styrene-grafted polypropylene, thermoplastic elastomer, and voltage stabilizer is 100.

[0011] Preferably, the styrene-grafted polypropylene is prepared by melt grafting polypropylene, dicumyl peroxide, styrene monomer, and a second antioxidant in a mass ratio of 100:(0.1-0.5):20:(1.5-2.5).

[0012] Preferably, the preparation method of the styrene-grafted polypropylene is as follows: polypropylene, dicumyl peroxide, styrene monomer and antioxidant are mixed and dispersed, then added to a torque rheometer, and the mixture is stirred and reacted at high temperature to obtain the grafted product. After purification, styrene-grafted polypropylene is obtained.

[0013] Preferably, the conditions for the high-temperature stirring reaction are: reaction temperature of 190-200℃ and rotation speed of 80-120 rpm.

[0014] Preferably, the purification process includes: first dissolving the grafted product in xylene, heating it under reflux at high temperature to fully dissolve the grafted product in xylene; then adding the xylene solution containing the grafted product to acetone, letting it stand for a period of time, filtering it, and finally placing the powdered filter cake in a drying oven to dry it, thereby obtaining purified styrene-grafted polypropylene.

[0015] Preferably, the second antioxidant is a semi-hindered phenolic compound 2908, and the polypropylene is isotactic polypropylene.

[0016] This invention uses isotactic polypropylene (iPP) because iPP has a higher degree of crystallinity than atactic polypropylene (sPP), resulting in stronger molecular chain activity, easier monomer diffusion, and easier control of the grafting rate. At the same time, the crystalline region can maintain the stability of the molecular chain backbone and avoid excessive degradation during the grafting process.

[0017] Preferably, the grafting rate of the styrene-grafted polypropylene is 8%-12%.

[0018] During the experiment, the inventors discovered that the grafting rate of styrene-grafted polypropylene not only affects the compatibility and dielectric properties between polypropylene and elastomers, but may also affect melt adhesion, shear heat generation, and processing dwell time, thereby affecting the thermal stability and mechanical properties of cable materials. However, when the amount of reactants or reaction conditions are adjusted, the grafting rate of styrene-grafted polypropylene can be controlled at 8%-12%, at which point the overall performance of the resulting cable material is better.

[0019] Preferably, the thermoplastic elastomer is one or more of EPDM, SEBS, POE, and PBE.

[0020] Preferably, the first antioxidant is one or more of antioxidants 1010, A0-1010, 1076, 1330, and 168.

[0021] Preferably, the voltage stabilizer is one or more of the aromatic ketone compounds AOHBP, RBBT, and RQCT.

[0022] A second aspect of the present invention provides a method for preparing the grafted modified polypropylene cable material, comprising the following steps: (1) According to the mass ratio, styrene-grafted polypropylene, thermoplastic elastomer and first antioxidant are added to the rheometer in sequence. After mixing evenly, voltage stabilizer is added and the mixture is continued to be mixed to obtain a mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature, main machine speed and feed screw speed, and extrude and granulate to obtain grafted modified polypropylene cable material.

[0023] Preferably, in step (1), the temperature for uniform mixing is 180-200℃ and the time is 5-15 min; the mixing time is 8-12 min and the rotation speed is 280-320 rpm.

[0024] Preferably, in step (2), the barrel temperature is 180-220℃, the main machine speed is 80-120rpm, and the feed screw speed is 20-40rpm.

[0025] A third aspect of the present invention provides the application of the grafted modified polypropylene cable material in power cables.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The styrene-grafted polypropylene cable material prepared by this invention has a significantly lower internal space charge density than that of pure polypropylene and elastomer blended cable material, while its volume resistivity is much higher than that of pure polypropylene blended elastomer cable material. This indicates that the grafted styrene can provide a large number of deep trap sites for polypropylene, effectively capturing and binding charge carriers, effectively suppressing the injection and accumulation of space charge in polypropylene, reducing local electric field distortion, and making the electric field distribution more uniform. This provides a guarantee for improving the long-term operational stability of cable insulation materials under high electric fields.

[0027] 2. This invention effectively improves the polarity of the polypropylene matrix and its interfacial compatibility with other components by introducing PP-g-St with a grafting rate of 8-12%. Simultaneously, the use of aromatic ketone compounds as voltage stabilizers significantly enhances the electrical properties of the material, resulting in an AC breakdown field strength of 120-230 kV / mm and a DC breakdown field strength of 400-450 kV / mm for the cable material. This voltage stabilizer can be inserted into the polypropylene chain segments and synergistically regulates the crystal structure of polypropylene with thermoplastic elastomers and antioxidants, improving the mechanical properties of the cable material. Tensile strength reaches 25.3-41.3 MPa, and elongation at break reaches 580.3-750.8%. Furthermore, the maximum electric field distortion rate of the cable material is only 19.3%-27.8%, effectively suppressing the accumulation of space charge and partial discharge, significantly improving the reliability and service life of the cable insulation layer during long-term operation.

[0028] 3. Through the synergistic effect of its components, this invention solves the defects of insufficient toughness and poor resistance to electrical aging of polypropylene materials alone. The resulting material has excellent insulation, mechanical toughness and resistance to electrical aging, meeting the stringent requirements of high-voltage and ultra-high-voltage cables for insulation materials, and has broad prospects for industrial application. Detailed Implementation

[0029] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. The following embodiments are only for illustrating the technical solution of this invention and are not intended to limit the invention.

[0030] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in the field; and unless otherwise specified, the raw materials used in parallel experiments are from the same batch.

[0031] The sources of some of the raw materials used in this invention are as follows: iPP: T28F, melt flow index 3.4 g / 10 min, Sinopec; EPDM: Nordel 4570, ethylene content 55wt%, ENB content 4.5wt%, Dow Chemical; POE: DF710, melt flow index 0.825 g / 10 min, Mitsui Chemicals; SEBS: YH-502T, styrene content 30wt%, density 0.91g / cm³ 3 Baling Petrochemical; Antioxidants 1010, 1076, and 1130, from Sinopec; Voltage stabilizers AOHBP, RBBT, and RQCT, Shanghai Titan Technology Co., Ltd. Dicumyl peroxide (DCP), xylene, Shanghai Aladdin Biochemical Technology Co., Ltd. Styrene-grafted polypropylene, with a grafting rate of 8-12%, is prepared in-house using the following method: S1. After physically mixing polypropylene, dicumyl peroxide, styrene monomer, and the second antioxidant, the mixture is placed in a torque rheometer at a temperature of 195℃. A Cam Rotors type rotor is used, and the rotor speed is controlled at 100 rpm. The reaction time is 6-8 min. After the reaction is completed, the grafted product is obtained. The mass ratio of polypropylene, dicumyl peroxide, styrene monomer, and the second antioxidant is 100:(0.1-0.5):20:(1.5-2.5).

[0032] S2. Take 5g of graft product and place it in 200mL of xylene. Heat and reflux at 130℃ for 2h to fully dissolve the graft product in xylene. Then pour the xylene solution containing the graft product into 200mL of acetone. After standing for a period of time, an emulsion mixture is obtained and filtered. Finally, put the filtered powdery filter cake into a drying oven and dry it to constant weight to obtain purified styrene-grafted polypropylene (PP-g-St).

[0033] Example 1: A grafted modified polypropylene cable material comprises the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer EPDM, 2 parts of antioxidant 1010, and 10 parts of voltage stabilizer AOHBP.

[0034] The preparation method of the grafted modified polypropylene cable material includes the following steps: (1) According to the mass ratio, PP-gS, EPDM and 1010 are added to the torque rheometer in sequence. After high-speed mixing at 190℃ for 10 min, AOHBP is added, the feed port is sealed, and the mixture is continued to be mixed in the mixing chamber at 300 rpm for 10 min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0035] Example 2: A grafted modified polypropylene cable material comprises the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer SEBS, 2 parts of antioxidant 1076, and 10 parts of voltage stabilizer RBBT.

[0036] The preparation method of the grafted modified polypropylene cable material includes the following steps: (1) According to the mass ratio, PP-gS, SEBS and 1076 were added to the torque rheometer in sequence. After high-speed mixing at 190℃ for 10 min, RBBT was added, the feeding port was sealed, and the mixture was continued to be mixed in the mixing chamber at 300 rpm for 10 min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0037] Example 3: A grafted modified polypropylene cable material comprises the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer POE, 2 parts of antioxidant 168, and 10 parts of voltage stabilizer RQCT.

[0038] The preparation method of the grafted modified polypropylene cable material includes the following steps: (1) According to the mass ratio, PP-gS, POE and 168 were added to the torque rheometer in sequence. After high-speed mixing at 190℃ for 10 min, RQCT was added, the feeding port was sealed, and the mixture was continued to be mixed in the mixing chamber at 300 rpm for 10 min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0039] Example 4: A grafted modified polypropylene cable material comprises the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 15 parts of thermoplastic elastomer SEBS and 15 parts of POE, 2 parts of antioxidant 1010, and 10 parts of voltage stabilizer AOHBP.

[0040] The preparation method of the grafted modified polypropylene cable material includes the following steps: (1) According to the mass ratio, PP-gS, SEBS, POE and 1010 were added to the torque rheometer in sequence. After high-speed mixing at 190℃ for 10 min, AOHBP was added, the feeding port was sealed, and the mixture was continued to be mixed in the mixing chamber at 300 rpm for 10 min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0041] Example 5: A grafted modified polypropylene cable material comprises the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer SEBS, 1 part of antioxidants 1010 and 1 part of antioxidant 1076, and 10 parts of voltage stabilizer AOHBP.

[0042] The preparation method of the grafted modified polypropylene cable material includes the following steps: (1) According to the mass ratio, PP-gS, SEBS and 1010 and 1076 were added to the torque rheometer in sequence. After high-speed mixing at 190℃ for 10 min, AOHBP was added, the feeding port was sealed, and the mixture was continued to be mixed in the mixing chamber at 300 rpm for 10 min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0043] Example 6: A grafted modified polypropylene cable material comprises the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer SEBS, 2 parts of antioxidant 1010, 5 parts of voltage stabilizer AOHBP, and 5 parts of RBBT.

[0044] The preparation method of the grafted modified polypropylene cable material includes the following steps: (1) According to the mass ratio, PP-gS, SEBS and 1010 were added to the torque rheometer in sequence. After high-speed mixing at 190℃ for 10 min, AOHBP and RBBT were added. The feed port was sealed and the mixture was continued to be mixed in the mixing chamber at 300 rpm for 10 min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0045] Comparative Example 1: This comparative example provides a grafted modified polypropylene cable material comprising the following components by weight: 70 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer SEBS, and 2 parts of antioxidant 1010.

[0046] The preparation method of the grafted modified polypropylene cable material is as follows: (1) PP-gS, SEBS and 1010 were added to the torque rheometer in sequence according to the mass ratio, and the mixture was mixed at 190℃ and 300rpm for 10min to obtain the mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature to 210°C, the main machine speed to 100 rpm, and the feed screw speed to 30 rpm. After the material is extruded and cooled, the grafted modified polypropylene cable material is obtained.

[0047] Comparative Example 2: This comparative example provides a grafted modified polypropylene cable material comprising the following components by weight: 60 parts of styrene-grafted polypropylene PP-g-St, 30 parts of thermoplastic elastomer SEBS, and 10 parts of voltage stabilizer AOHBP.

[0048] The preparation method of the grafted modified polypropylene cable material is the same as in Example 1.

[0049] Comparative Example 3: This comparative example provides a grafted modified polypropylene cable material comprising the following components by weight: 90 parts of styrene-grafted polypropylene PP-g-St, 2 parts of antioxidant 1010, and 10 parts of voltage stabilizer AOHBP.

[0050] The preparation method of the grafted modified polypropylene cable material is the same as in Example 1.

[0051] Comparative Example 4: This comparative example provides a cable material of styrene-free grafted polypropylene, comprising the following components by weight: 60 parts isotactic polypropylene (iPP), 30 parts thermoplastic elastomer (SEBS), 2 parts antioxidant 1010, and 10 parts voltage stabilizer (AOHBP).

[0052] The preparation method of the polypropylene cable material is the same as in Example 1.

[0053] The grafted modified polypropylene cable materials prepared in the above embodiments and comparative examples were subjected to performance tests, and the test standards are as follows: (1) Breakdown field strength: The AC and DC breakdown field strength of the sample were tested according to GB / T1408.1-2016 and GB / T1408.2-2016 standards. The sample was placed in a spherical electrode filled with insulating oil, the test temperature was 25℃, the sample thickness was 0.2mm, the voltage rise rate was 1kV / s, the breakdown voltage at 12 points was measured and the breakdown field strength was calculated. The formula is as follows: , In the formula, E is the breakdown field strength, in kV / mm; U is the applied voltage, in kV; and d is the sample thickness, in mm.

[0054] (2) Tensile property test: conducted in accordance with GB 13022-1991 standard, with a sample thickness of 1 mm.

[0055] (3) Volume resistivity test: The sample was tested using a three-electrode device and a high-resistivity meter. The electric field strength was 10 kV / mm.

[0056] (4) Space charge test: The surface potential decay method was used for testing. The test temperature was 40℃, the applied DC electric field strength was 20kV / mm, and the polarization time was 60min. The maximum electric field distortion rate after sample polarization was used as the evaluation index parameter of space charge, which can quantitatively assess the degree of distortion of electric field amplitude. The formula is as follows:

[0057] In the formula, ΔE max E is the maximum electric field distortion rate. max E is the electric field amplitude at 1800 s polarization. av This represents the average field strength.

[0058] The test results are shown in Table 1.

[0059] Table 1. Performance test results of the examples and comparative examples.

[0060] As shown in Table 1, the AC breakdown field strength of Example 3 is 223.5 kV·mm.-1 DC breakdown field strength (447.8 kV·mm) -1 ) and volume resistivity (18.2×10 16 The highest Ω·m value indicates the best electrical insulation performance; simultaneously, its elongation at break is as high as 750.8%, significantly better than other embodiments; indicating that the material has excellent flexibility and crack resistance, making it suitable for high-voltage cable insulation applications. Embodiments 4-6 were optimized by compounding elastomers, dual antioxidants, or dual voltage stabilizers, but none surpassed Embodiment 3 in terms of electrical performance or toughness; this indicates that the combination of elastomer POE, antioxidant 168, and voltage stabilizer RQCT achieves the best synergistic effect.

[0061] Compared with Examples 1-6: Comparative Example 1, due to the absence of voltage stabilizer, exhibited significantly deteriorated electrical performance: the AC breakdown field strength decreased substantially to 131.8 kV·mm. -1 The electric field distortion rate is as high as 40.1%, and the volume resistivity is as low as 12.4 × 10⁻⁶. 16 The results (Ω·m) indicate that the voltage stabilizer effectively suppresses the injection and accumulation of space charge under high electric fields, alleviates local electric field concentration, and thus improves the uniformity of electric field distribution, significantly enhancing the breakdown strength and volume resistivity of the material. This further verifies that the voltage stabilizer can effectively improve the electrical properties of the modified polypropylene cable material, providing crucial support for the long-term and stable insulation performance of the material under complex electric field environments. Comparative Example 2, lacking an antioxidant, exhibits inferior overall performance (electrical, mechanical, and processing stability) compared to the examples. This is because the antioxidant, during the preparation of the modified polypropylene cable material, reduces molecular chain breakage and cross-linking by blocking the thermo-oxidative degradation reaction of polypropylene molecules, protecting the integrity of the polypropylene molecular structure, and maintaining the material's mechanical toughness and dielectric stability. This lays the molecular structural foundation for the stable performance required for the cable insulation material's long-term service life. The above results demonstrate that the synergistic effect of the voltage stabilizer and antioxidant can effectively reduce the risk of aging and distortion of the material under electric fields, thereby improving its reliability and service life under complex operating conditions.

[0062] Compared to Examples 1-6, Comparative Example 3, lacking thermoplastic elastomers and with excessively high PP-g-St content, exhibited embrittlement (elongation at break only 205.1%) and an electric field distortion rate as high as 48.3%. This indicates that thermoplastic elastomers can form a "soft and hard phase" structure within the polypropylene matrix, effectively dispersing internal stress, inhibiting microcrack propagation, and improving interfacial polarization behavior. This not only significantly improves elongation at break and tensile toughness but also helps reduce electric field distortion. This demonstrates that thermoplastic elastomers not only significantly enhance the elongation at break and tensile toughness but also help homogenize the internal electric field distribution and reduce the degree of electric field distortion. Comparative Example 4, using unmodified polypropylene, showed slightly weaker overall mechanical and electrical properties than the examples. This is because graft modification not only forms small spherulitic structures within the material, introducing deep traps, but also helps suppress carrier concentration and mobility, thereby improving various electrical properties. Furthermore, the grafted styrene increases the entanglement of polypropylene molecular chains, reduces micro-stress concentration points, and improves the material's mechanical toughness. The above results demonstrate that styrene grafting modification and blending with thermoplastic elastomers can improve the overall performance of polypropylene base materials to effectively address the challenges of safe operation of high-voltage cables.

[0063] In summary, this invention, through the compounding and synergistic design of styrene-grafted polypropylene, thermoplastic elastomer, antioxidant, and voltage stabilizer, achieves a synergistic improvement in electrical insulation (high breakdown field strength, high volume resistivity), mechanical toughness (high elongation at break, good tensile strength), and resistance to electrical aging (low electric field distortion) of cable materials. It can meet the stringent requirements of high-voltage and ultra-high-voltage cables for insulation materials and has broad prospects for industrial application.

[0064] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A grafted modified polypropylene cable material, characterized in that: It includes the following components by weight: 50-70 parts of styrene-grafted polypropylene; 20-40 parts of thermoplastic elastomer; 0.5-2 parts of primary antioxidant; and 5-10 parts of voltage stabilizer.

2. The grafted modified polypropylene cable material according to claim 1, characterized in that: The styrene-grafted polypropylene is prepared by melt grafting polypropylene, dicumyl peroxide, styrene monomer, and a second antioxidant in a mass ratio of 100:(0.1-0.5):20:(1.5-2.5).

3. The grafted modified polypropylene cable material according to claim 2, characterized in that: The preparation method of the styrene-grafted polypropylene is as follows: polypropylene, dicumyl peroxide, styrene monomer and antioxidant are mixed and dispersed, and then added into a torque rheometer. After high-temperature reaction, the grafted product is obtained, and after purification treatment, styrene-grafted polypropylene is obtained.

4. The grafted modified polypropylene cable material according to claim 2, characterized in that: The second antioxidant is a semi-hindered phenolic compound 2908, and the polypropylene is isotactic polypropylene.

5. The grafted modified polypropylene cable material according to claim 2, characterized in that: The grafting rate of the styrene-grafted polypropylene is 8%-12%.

6. The grafted modified polypropylene cable material according to claim 1, characterized in that: The thermoplastic elastomer is one or more of EPDM, SEBS, POE, and PBE.

7. The grafted modified polypropylene cable material according to claim 1, characterized in that: The first antioxidant is one or more of antioxidants 1010, A0-1010, 1076, 1330, and 168.

8. The grafted modified polypropylene cable material according to claim 1, characterized in that: The voltage stabilizer is one or more of the aromatic ketone compounds AOHBP, RBBT, and RQCT.

9. A method for preparing the grafted modified polypropylene cable material according to any one of claims 1 to 8, characterized in that: Includes the following steps: (1) According to the mass ratio, styrene-grafted polypropylene, thermoplastic elastomer and first antioxidant are added to the rheometer in sequence. After mixing evenly, voltage stabilizer is added and the mixture is continued to be mixed to obtain a mixture. (2) Add the mixture obtained in step (1) into a co-rotating twin-screw extruder, control the barrel temperature, main machine speed and feed screw speed, and extrude and granulate to obtain grafted modified polypropylene cable material.

10. The preparation method according to claim 9, characterized in that: In step (2), the barrel temperature is 180-220℃, the main machine speed is 80-120rpm, and the feed screw speed is 20-40rpm.

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