A thermoplastic polyolefin insulating material, its preparation method and application

Abstract

This invention relates to the field of insulating materials, and more particularly to a thermoplastic polyolefin insulating material, its preparation method, and its applications. The raw materials for preparing the thermoplastic polyolefin insulating material mainly include functional modified monomers and polyolefins. The polyolefins include poly4-methylpentene, and the functional modified monomers are unsaturated acid anhydrides and their analogues, including at least one of citrate anhydride, maleimide, and maleic anhydride. The thermoplastic polyolefin insulating material prepared by this invention exhibits excellent high-temperature resistance and high-temperature DC volume resistivity, making it suitable for long-term use under high temperature and high electric field strength conditions. It can be used in the field of cable insulation materials and has thermoplastic recyclability.

Description

Technical Field

[0001] This invention relates to the field of insulating materials, and more particularly to a thermoplastic polyolefin insulating material, its preparation method, and its application. Background Technology

[0002] With the rapid development of the power industry, power grid systems are moving towards higher voltage levels and larger power transmission capacities, placing higher demands on the performance of insulation materials. Currently, the maximum long-term operating temperature of cross-linked polyethylene (XLPE) insulation materials in operation is 70-90℃, with a maximum voltage level of 500kV. Under this trend, traditional polyethylene insulation materials can no longer meet the higher long-term operating temperature requirements. Therefore, there is an urgent need to develop new insulation materials for power equipment to adapt to the requirements of higher operating temperatures and electric fields. Furthermore, because XLPE materials require chemical cross-linking during production, the material changes from its original thermoplastic to thermosetting nature. On the one hand, chemical cross-linking consumes a large amount of energy, and the degassing process generates waste gas emissions; on the other hand, thermosetting XLPE cannot be recycled after its lifespan as cable insulation and can only be disposed of through traditional methods such as incineration, resulting in huge carbon emissions and serious environmental pollution. Therefore, the inherent characteristics of XLPE can no longer meet the development needs of environmentally friendly power systems and energy systems under the "dual-carbon" strategy.

[0003] Thermoplastic polyolefins, represented by polypropylene, polybutene, and poly4-methylpentene, are a class of polymeric plastics with relatively simple chemical structures, possessing all the advantages of polyethylene. Moreover, compared to polyethylene, these polyolefins have higher melting temperatures and thermal stability, as well as stronger electrical insulation properties. As insulating materials, they hold promise for adapting to more demanding working environments and widespread application in energy systems with higher load capacities. Furthermore, due to their thermoplastic properties, the cross-linking and degassing process can be eliminated during processing, and material recycling can be achieved at the end of their lifespan at the engineering level, thus fully meeting the "dual-carbon" strategic development needs of my country's new energy system. Currently, the industry has experimented with using polypropylene as the main insulation material for cables to develop new high-capacity recyclable cable systems. Related research and engineering applications show that polypropylene insulation can operate safely and stably at temperatures up to 90℃. However, the melting temperature of polypropylene is approximately between 140-160℃. Related thermorheological performance tests show that polypropylene begins to exhibit significant melting endothermic phenomena at around 120℃, indicating a decrease in its thermal stability, accompanied by a significant decline in its electrical insulation properties, represented by its volume resistivity. Therefore, the low melting temperature and thermal stability of polypropylene, and the resulting significant decrease in volume resistivity, have become key bottlenecks restricting its application in cable systems with higher temperatures and larger capacities than 90°C.

[0004] Poly(4-methylpentene) is a novel thermoplastic polyolefin material developed in recent years. Its chemical structure is very similar to polyethylene and polypropylene, thus possessing all the advantages of these materials. More importantly, poly(4-methylpentene) has regular butene side groups, which significantly affect its crystal structure and molecular chain interactions, thereby greatly improving its melting temperature and thermal stability, and consequently enhancing its electrical insulation properties. The melting temperature of poly(4-methylpentene) can reach 200-240℃, and its long-term operating temperature is not lower than 100℃, exhibiting significantly stronger thermal stability than polypropylene. Therefore, it holds promise for replacing polypropylene cable insulation at higher operating temperatures. However, similar to polypropylene, poly(4-methylpentene) also suffers from poor electrical insulation performance at high temperatures, particularly a significant decrease in volume resistivity. Therefore, it is necessary to further improve its volume resistivity at high temperatures without compromising its heat resistance. Clearly, developing high-heat-resistant polyolefin cable insulation materials that can replace polypropylene cable insulation is of great significance for applications in high-capacity, high-voltage power transmission, offshore wind power transmission systems, low-carbon emission cable transmission systems, and for promoting the development of high-capacity power cables and their high-temperature-resistant materials. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a thermoplastic polyolefin insulating material with a melting temperature exceeding 200°C and high volume resistivity and strong electrical insulation properties at 100°C.

[0006] Specifically, the first aspect of this invention provides a thermoplastic polyolefin insulating material, which is a polyolefin modified with functional chemical groups. The raw materials for preparing the thermoplastic polyolefin insulating material include functional modified monomers and polyolefins, with a mass ratio of functional modified monomers to polyolefins of (0.01-0.3):1; the polyolefin includes poly4-methylpentene, the functional modified monomers include unsaturated acid anhydrides and their analogues, the degree of polymerization of the thermoplastic polyolefin insulating material is 1-1000, and the melting temperature T is... m The temperature range is 200-240℃; the DC volume resistivity of thermoplastic polyolefin insulating materials at 100℃ and a field strength of 10 kV / mm is greater than 1×10⁻⁶. 13 Ω•m.

[0007] As an implementable example, the unsaturated anhydrides and analogues mentioned include at least one of citralic anhydride, maleimide, and maleic anhydride.

[0008] Furthermore, the unsaturated anhydride and its analogues are maleic anhydride.

[0009] As an implementable example, the poly4-methylpentene includes homopolymer poly4-methylpentene and / or copolymer poly4-methylpentene.

[0010] The highly polar carbonyl group in maleic anhydride molecules is a key functional structure. After modification, these polar groups form numerous "charge traps" on the poly(4-methylpentene) molecular chain. When the material is in a high-temperature, high-electric-field environment, these charge traps effectively capture free charge carriers, such as electrons and ions, reducing the average mobility of charge carriers and thus reducing macroscopic leakage current. Ultimately, this significantly improves the high-temperature DC volume resistivity of the material. Simultaneously, maleic anhydride is an unsaturated anhydride monomer, and its double bond structure readily undergoes graft polymerization with poly(4-methylpentene) under the action of a free radical initiator. This allows for the stable branching of functional groups onto the poly(4-methylpentene) molecular chain, preventing the formation of functional groups during the modification process. The grafting process is less prone to incomplete reaction or detachment of functional groups. Compared with similar monomers such as maleimide and citrate anhydride, maleic anhydride has a higher branching content of functional chemical groups, resulting in higher grafting efficiency and more uniform group distribution, which is more conducive to improving insulation performance. In addition, maleic anhydride grafting modification is a branching modification at the molecular chain level, which does not change the main chemical structure and crystallization characteristics of poly4-methylpentene, thus retaining its high melting temperature of 200-240℃ and high heat resistance. At the same time, it does not change the thermoplasticity of poly4-methylpentene. After modification, it can still be processed by melt extrusion granulation and can be recycled and reused after the end of its life. The production process does not require a crosslinking degassing process, which can avoid the high carbon emissions of traditional crosslinked polyethylene.

[0011] As an example of implementation, the raw materials for preparing the thermoplastic polyolefin insulating material also include free radical initiators.

[0012] Furthermore, the mass ratio of the polyolefin to the free radical initiator is 1000:(1-3).

[0013] Furthermore, the free radical initiator includes peroxide free radical initiators and / or azo free radical initiators.

[0014] Furthermore, the peroxide-based free radical initiator includes one or more of the following: benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide (2-ethylhexanoate), and dicyclohexyl peroxide.

[0015] Furthermore, the azo radical initiators include azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0016] As an example of implementation, the raw materials for preparing the thermoplastic polyolefin insulating material also include solvents and interface agents.

[0017] Furthermore, the solvent includes at least one of xylene, toluene, decahydronaphthalene, chlorobenzene, dichlorobenzene, and dibutyl phthalate.

[0018] Furthermore, the interface agent includes at least one of anhydrous ethanol, N,N-dimethyldiamide, and chloroform.

[0019] As an implementable example, the method for preparing the thermoplastic polyolefin insulating material includes the following steps: S1. Add the free radical initiator and the functional modified monomer to the first reaction vessel, seal the reaction system, and stir and mix under nitrogen protection; S2. Add an interface agent to the first reactor, dissolve it, and raise the temperature to carry out a self-polymerization reaction; S3. Add the polyolefin to the second reactor and add solvent to allow it to swell; S4. Add the polyolefin swollen in step S3 to the first reactor and carry out the grafting modification reaction under nitrogen atmosphere. S5. After the reaction is complete, cool the mixture, add ethanol to precipitate the precipitate, filter, and dry to obtain the modified polyolefin. S6. Add the modified polyolefin to the screw extruder, melt extrude and granulate to obtain the thermoplastic polyolefin insulation material.

[0020] As an example of implementation, the raw materials for preparing the thermoplastic polyolefin insulating material also include antioxidants.

[0021] Furthermore, the antioxidants include antioxidant 1010 and antioxidant 168, with a mass ratio of antioxidant 1010 to antioxidant 168 of (0.8-1.5):1.

[0022] Furthermore, the raw materials for preparing the thermoplastic polyolefin insulating material include functional modified monomers, polyolefins, free radical initiators, interface agents, and antioxidants.

[0023] A second aspect of the present invention provides a method for preparing a thermoplastic polyolefin insulating material, comprising the following steps: S1. Add the free radical initiator and the functional modified monomer to the first reaction vessel, seal the reaction system, and stir and mix under nitrogen protection; S2. Add an interface agent to the first reactor, dissolve it, and raise the temperature to carry out a self-polymerization reaction; S3. Add the polyolefin to the second reactor and add solvent to allow it to swell; S4. Add the polyolefin swollen in step S3 to the first reactor and carry out the grafting modification reaction under nitrogen atmosphere. S5. After the reaction is complete, cool the mixture, add ethanol to precipitate the precipitate, filter, and dry to obtain the modified polyolefin. S6. Mix the modified polyolefin and antioxidant, add them to a screw extruder, melt extrude and granulate to obtain thermoplastic polyolefin insulation material.

[0024] As an feasible example, the raw materials for step S6 may also include one of ethylene-propylene copolymer, ethylene-octene copolymer, ethylene-4-methylpentene copolymer, and propylene-4-methylpentene.

[0025] As an feasible example, in step S2, the temperature of the self-polymerization reaction is 45-65℃, and the time of the self-polymerization reaction is 5-30 min; in step S3, the swelling temperature is 110-130℃, and the swelling time is 0.5-2.5 h; in step S4, the temperature of the grafting modification reaction is 90-140℃, and the time of the grafting modification reaction is 3-6 h.

[0026] A third aspect of the present invention provides an application of a thermoplastic polyolefin insulating material in the preparation of cable insulation materials.

[0027] Beneficial effects (I) This invention introduces a large number of charge traps through the strongly polar carbonyl groups of unsaturated anhydrides and their analogues, maleic anhydride, effectively capturing charge carriers, reducing the average carrier mobility and macroscopic leakage current, and making the DC volume resistivity of the material greater than 1×10 at 100℃ and 10kV / mm field strength. 13 Ω•m, meeting the long-term use requirements under high temperature and high electric field strength.

[0028] (ii) The present invention uses poly-4-methylpentene with a melting temperature of 200-240℃ as the matrix. After being modified by branching of functional chemical groups, it still retains high heat resistance. The melting temperature is not lower than 200℃ and the long-term service temperature is not lower than 100℃, which is significantly better than traditional polyethylene, polypropylene and modified polypropylene materials, and is suitable for applications in higher temperature scenarios.

[0029] (iii) The material products obtained by the present invention retain thermoplasticity, and the production process does not require the chemical cross-linking and degassing process of traditional cross-linked polyethylene, thus reducing energy consumption and waste gas emissions. After the end of its service life, it can be recycled and reused by melt extrusion and other methods, avoiding the high carbon emissions caused by incineration, which meets the requirements of environmentally friendly power systems and the "dual carbon" strategy development.

[0030] (iv) In this invention, maleic anhydride is preferred as a functional modifying monomer and its graft polymerization reaction with poly(4-methylpentene) is stable. The grafting efficiency is higher than that of similar monomers such as maleimide and citrate anhydride. The branching content and degree of branching of functional chemical groups can be precisely controlled to ensure uniform micro-distribution of groups and further optimize insulation performance.

[0031] (v) The thermoplastic polyolefin insulation material prepared by this invention has the core advantages of high heat resistance, high insulation and recyclability. It can replace traditional cross-linked polyethylene, polypropylene and other insulation materials. It is suitable for large-capacity high-voltage power transmission, offshore wind power transmission system, low carbon emission cable transmission system and other fields, and promotes the development of ultra-large capacity power cables and high temperature resistant materials. Detailed Implementation

[0032] Example 1 The first aspect of this example provides a method for preparing a thermoplastic polyolefin insulating material, including the following steps: S1. Add 1.65g of peroxide free radical initiator 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (purchased from Jiangsu Qiangsheng Functional Chemical Co., Ltd.) and functional modified monomer maleic anhydride (purchased from Beijing Bailingwei Technology Co., Ltd.) to a 10L first reaction vessel, seal the reaction system, and stir and mix under nitrogen protection. S2. Add anhydrous ethanol as an interface agent (the mass-volume ratio of interface agent to functional modified monomer is 50:1) to the first reaction vessel, dissolve it, and heat it to 60°C to carry out the self-polymerization reaction for 10 min. S3. Add 1 kg of poly-4-methylpentene (model MX002, purchased from Mitsui Chemicals) to a 10 L second reactor, add the solvent p-dichlorobenzene (the mass-volume ratio of solvent to functional modified monomer is 1:50), and swell at 120 °C for 2 h. S4. Add the poly-4-methylpentene swollen in step S3 to the first reactor and carry out the grafting modification reaction at 130°C for 6 hours under nitrogen atmosphere. S5. After the reaction is complete, cool to room temperature (25°C), add excess anhydrous ethanol to precipitate the product, filter, and vacuum dry at 70°C for 10 hours to obtain modified poly(4-methylpentene). S6. Mix 0.5 kg of modified poly-4-methylpentene and 3000 ppm of antioxidant (antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio) evenly, add it to a twin-screw extruder, melt extrude and granulate to obtain thermoplastic polyolefin insulation material.

[0033] The second aspect of this example provides a thermoplastic polyolefin insulating material prepared according to the above-described method for preparing thermoplastic polyolefin insulating materials.

[0034] This example provides an application of a thermoplastic polyolefin insulating material in the preparation of cable insulation materials.

[0035] Comparative Example 1 The specific implementation method in this example is the same as in Example 1, except that the functional modified monomer is maleimide (purchased from Beijing Bailingwei Technology Co., Ltd.).

[0036] Comparative Example 2 The specific implementation method in this example is the same as in Example 1, except that the functional modified monomer is citrate anhydride (purchased from Beijing Bailingwei Technology Co., Ltd.).

[0037] Comparative Example 3 The specific implementation method in this example is the same as in Example 1, except that the poly-4-methylpentene is model DX045 and was purchased from Mitsui Chemicals.

[0038] Comparative Example 4 The specific implementation method in this example is the same as in Example 1, except that the contents of the functional modified monomer and the free radical initiator are different in step S1. Specifically, the free radical initiator 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is 7.20g, and the functional modified monomer maleic anhydride is 300g.

[0039] Comparative Example 5 This example provides a method for preparing polypropylene material: 1 kg of polypropylene (model T30s, purchased from Maoming Petrochemical) and 3000 ppm of antioxidant (antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio) are mixed and added to a twin-screw extruder, and then melt-extruded and granulated to obtain polypropylene material.

[0040] Comparative Example 6 This example provides a method for preparing poly-4-methylpentene material: 1 kg of poly-4-methylpentene (model MX002) and 3000 ppm of antioxidant (antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio) are mixed and added to a twin-screw extruder, and then melt-extruded and granulated to obtain poly-4-methylpentene material.

[0041] Comparative Example 7 This example provides a method for preparing poly-4-methylpentene material: 1 kg of poly-4-methylpentene (model DX045) and 3000 ppm of antioxidant (antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio) are mixed and added to a twin-screw extruder, and then melt-extruded and granulated to obtain poly-4-methylpentene material.

[0042] Comparative Example 8 The first aspect of this example provides a method for preparing a thermoplastic polyolefin insulating material, including the following steps: S1. Add 1.65g of free radical initiator 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and functional modified monomer maleic anhydride to a 10L first reaction vessel, seal the reaction system, and stir and mix under nitrogen protection. S2. Add anhydrous ethanol (the mass-volume ratio of the interface agent and the functional modified monomer is 1:50) to the first reaction vessel, dissolve it, and heat it to 60°C to carry out the self-polymerization reaction for 5 minutes. S3. Add 1 kg of polypropylene (model T30s, purchased from Maoming Petrochemical) to a 10 L second reactor, add solvent p-dichlorobenzene (the mass-volume ratio of solvent to functional modified monomer is 1:50), and swell at 120℃ for 2 h. S4. Add the polypropylene swollen in step S3 to the first reactor and carry out the grafting modification reaction at 130°C for 6 hours under nitrogen atmosphere. S5. After the reaction is complete, cool to room temperature (25°C), add excess anhydrous ethanol to precipitate the product, filter, and vacuum dry at 70°C for 10 hours to obtain modified polypropylene powder. S6. Mix 0.5 kg of modified polypropylene powder with 3000 ppm of antioxidant (antioxidant 1010 and antioxidant 168 are compounded in equal mass ratio), add to a twin-screw extruder, melt extrude and granulate to obtain thermoplastic polyolefin insulation material.

[0043] 1. Branching content of functional chemical groups (GD) （n） Measurement: 3g of the material from Example 1 and Comparative Examples 1-8 was placed in a Soxhlet extractor and extracted with ethyl acetate for 24 hours to remove unbranched functional modified monomers. The extracts were then dried, weighed, and the branched content (GD) of the functional chemical groups was calculated. （n） GD （n） This represents the degree of branching of the functional chemical groups in the branched polyolefin of the material. In this invention, GD... （n） The calculation formula is as follows: ; In the formula, w0 is the mass of the polyolefin; w1 is the mass of the modified thermoplastic polyolefin insulating material before extraction; and w2 is the mass of the modified thermoplastic polyolefin insulating material after extraction.

[0044] 2. Determination of the average degree of polymerization (N) of branched chains of functional chemical groups: The weight-average molecular weight of the materials before and after branching treatment was measured using high-temperature gel permeation chromatography (high-temperature GPC), thereby calculating the average degree of polymerization (N) of the branched chains of the grafted functional chemical groups. The test method was performed according to the method specified in GB / T 27810-2011. The average degree of polymerization (N) of the branched chains of the functional chemical groups is calculated as follows: (weight-average molecular weight of the thermoplastic polyolefin insulating material after branching reaction - weight-average molecular weight of the polyolefin raw material) / molecular weight of the functional modified monomer.

[0045] 3. Determination of melting temperature: The procedure shall be carried out in accordance with the method specified in GB / T 19466-3-2004.

[0046] 4. Measurement of volume resistivity: The determination was performed according to the method specified in GB / T 31838.2-2019. The average thickness of the sample was 0.1 mm, and a 20 mm diameter gold plating layer was sputtered onto the surface using a vacuum gold sputtering device. The applied electric field strength was 10 kV / mm, and the test temperature was 100 °C.

[0047] The experimental results of the above tests are detailed in Table 1.

[0048] Table 1

[0049] Comparing the data from Example 1 and Comparative Examples 1-3, it can be seen that compared to pure poly-4-methylpentene materials without functional chemical grafting, the poly-4-methylpentene materials of Example 1 and Comparative Examples 1-2 grafted with unsaturated anhydride exhibit higher volume resistivity, meaning they have stronger electrical insulation properties and lower leakage current losses when used as cable insulation materials, which is beneficial to improving the transmission efficiency and operational reliability of cables. Example 1, and Comparative Examples 1-2, show the highest volume resistivity, indicating the best electrical insulation performance. This is partly due to the introduction of a large number of charge traps within the material by maleic anhydride grafting, effectively capturing microscopic charge carriers and suppressing leakage current. On the other hand, the GD of Example 1... （n） Compared to Comparative Examples 1-2, the degree of polymerization is higher, while the average degree of polymerization of the branched chains is lower. This means that maleic anhydride grafting has a higher grafting efficiency than the other two types of unsaturated anhydride grafting, and the microscopic distribution of the grafted functional chemical groups is more uniform, which is beneficial to improving electrical insulation performance.

[0050] Comparing the data from Examples 1, 3, 6, and 7, it can be seen that the volume resistivity of poly(4-methylpentene-1) in Comparative Example 6 is lower than that of poly(4-methylpentene-2) in Comparative Example 7. However, after grafting maleic anhydride, the volume resistivity of poly(4-methylpentene-1) modified in Example 1 is higher than that of poly(4-methylpentene-2) modified in Comparative Example 3. This indicates that grafting maleic anhydride onto poly(4-methylpentene-1) has a stronger effect on improving electrical insulation performance than grafting maleic anhydride onto poly(4-methylpentene-2). Therefore, it is more suitable as a cable insulation material.

[0051] Comparing the data from Example 1 and Comparative Example 4, it can be seen that GD （n） The volume resistivity of Example 1, which is approximately 5%, is significantly higher than that of GD. （n）The average degree of polymerization of the branched chains in Example 1 is approximately 20%, compared to Comparative Example 4. There is also a significant difference in the average degree of polymerization of the branched chains, with Example 1 showing a lower degree than Comparative Example 4. This indicates that the material of Example 1 has stronger electrical insulation properties than Comparative Example 4, and is therefore more suitable as cable insulation. Its lower average degree of polymerization of the branched chains means that the grafted maleic anhydride chemical groups are more uniformly distributed microscopically, which is beneficial to improving electrical insulation performance.

[0052] Comparing the data from Example 1, Comparative Example 5, and Comparative Example 8, it can be seen that the melting temperature and volume resistivity of the maleic anhydride-grafted poly(4-methylpentene) material of Example 1 are significantly improved compared to the pure polypropylene of Comparative Example 5 and the maleic anhydride-grafted polypropylene material of Comparative Example 8. The maleic anhydride-grafted poly(4-methylpentene) material retains the advantage of the strong heat resistance of the polymer matrix, and its melting temperature is nearly 50°C higher than that of polypropylene and grafted polypropylene. Therefore, at the same temperature, the volume resistivity of Example 1 is also significantly higher than the latter two. This indicates that the material in Example 1 is suitable for use at operating temperatures higher than those of polypropylene cable insulation.

Claims

1. A thermoplastic polyolefin insulating material, characterized in that, The raw materials for preparation include functional modified monomers and polyolefins, with a mass ratio of functional modified monomers to polyolefins of (0.01-0.3):1; The polyolefin includes poly4-methylpentene, and the functional modifying monomers include unsaturated acid anhydrides and their analogues. The degree of polymerization of the thermoplastic polyolefin insulating material is 1-1000, and the melting temperature is 200-240℃. The thermoplastic polyolefin insulating material has a DC volume resistivity greater than 1×10⁻⁶ at 100℃ and a field strength of 10 kV / mm. 13 Ω•m.

2. The thermoplastic polyolefin insulating material according to claim 1, characterized in that, The unsaturated anhydrides and their analogues include at least one of citrate anhydride, maleimide, and maleic anhydride.

3. The thermoplastic polyolefin insulating material according to claim 2, characterized in that, The raw materials for preparing the thermoplastic polyolefin insulating material also include free radical initiators.

4. The thermoplastic polyolefin insulating material according to claim 3, characterized in that, The mass ratio of the polyolefin to the free radical initiator is 1000:(1-3).

5. The thermoplastic polyolefin insulating material according to claim 4, characterized in that, The free radical initiators include peroxide free radical initiators and / or azo free radical initiators.

6. The thermoplastic polyolefin insulating material according to claim 5, characterized in that, The peroxide-based free radical initiators include one or more of the following: benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, lauroyl peroxide, dodecyl peroxide, tert-butyl peroxide, diisopropyl peroxide, tert-butyl peroxide (2-ethylhexanoate), and dicyclohexyl peroxide. The azo radical initiators mentioned include azobisisobutyronitrile and / or azobisisoheptanenitrile.

7. The thermoplastic polyolefin insulating material according to claim 6, characterized in that, The raw materials for preparing the thermoplastic polyolefin insulating material also include solvents and interface agents.

8. The thermoplastic polyolefin insulating material according to claim 7, characterized in that, The solvent includes at least one of xylene, toluene, decahydronaphthalene, chlorobenzene, dichlorobenzene, and dibutyl phthalate; The interface agent includes at least one of anhydrous ethanol, N,N-dimethyldiamide, and chloroform.

9. A method for preparing a thermoplastic polyolefin insulating material according to claim 8, characterized in that, Includes the following steps: S1. Add the free radical initiator and the functional modified monomer to the first reactor and stir and mix under nitrogen protection; S2. Add an interface agent to the first reactor, dissolve it, and raise the temperature to carry out a self-polymerization reaction; S3. Add the polyolefin to the second reactor and add solvent to allow it to swell; S4. Add the polyolefin swollen in step S3 to the first reactor and carry out the grafting modification reaction under nitrogen atmosphere. S5. After the reaction is complete, cool the mixture, add ethanol to precipitate the precipitate, filter, and dry to obtain the modified polyolefin. S6. Add the modified polyolefin to the screw extruder, melt extrude and granulate to obtain the thermoplastic polyolefin insulation material.

10. An application of the thermoplastic polyolefin insulating material according to claim 8, characterized in that, It is used in the preparation of cable insulation materials.

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