Dynamic cross-linked polypropylene cable insulating material with thermal mechanical stability and preparation method of dynamic cross-linked polypropylene cable insulating material

Abstract

The invention discloses a dynamic cross-linked polypropylene cable insulating material with thermal mechanical stability and a preparation method thereof, and belongs to the technical field of high-voltage cable insulating materials. Polypropylene is used as a matrix, reactive sites are introduced through maleic anhydride grafted polypropylene, then a polysulfhydryl compound and isocyanate react under the catalysis of organic base to generate thiocarbamate dynamic covalent bonds, and the material is endowed with reprocessing performance. Meanwhile, small organic molecules or low polymers containing strong polar groups are introduced into the system to serve as deep trap regulation and control units, the small organic molecules or low polymers are uniformly dispersed in a matrix to form deep-energy-level electron trapping centers, electrons injected under the action of an electric field can be effectively trapped by the traps, the concentration and mobility of free carriers are greatly reduced, and the photoelectric conversion efficiency is improved. And finally, the polypropylene cable insulating material with relatively high thermal mechanical property, deep trap regulation and control capability and reprocessing property is obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of high-voltage cable insulation materials, and particularly relates to a dynamic cross-linked polypropylene cable insulation material with thermomechanical stability and its preparation method. Background Technology

[0002] With rapid socio-economic development and continuous improvement in electrification levels, global electricity demand continues to grow. The integration of new energy sources into the grid, long-distance power transmission, and increased urban load density have made high-voltage transmission systems increasingly important in power infrastructure. To reduce line losses, improve transmission efficiency, and achieve large-capacity, long-distance power transmission, high-voltage direct current (HVDC) transmission technology has been widely adopted. Compared to alternating current (AC) transmission, DC transmission offers advantages such as lower line losses, longer transmission distances, and stronger controllability. Therefore, the use of high-voltage DC cables has been increasing year by year, particularly in submarine cables, urban underground power grids, and new energy transmission projects.

[0003] In high-voltage direct current (HVDC) cable systems, insulation materials are the core factors determining cable reliability and service life. Currently, cross-linked polyethylene (XLPE) is widely used as the mainstream cable insulation material in the HVDC cable field. XLPE forms a three-dimensional network structure through chemical cross-linking, exhibiting excellent thermal stability and mechanical strength under high-temperature conditions. However, with the increasing emphasis on green manufacturing and the circular economy, the non-recyclability of XLPE materials has become increasingly prominent. The cross-linking structure of XLPE materials consists of irreversible chemical bonds, making it difficult to remelt and process once cross-linking is complete, and waste materials are difficult to recycle. Furthermore, the cross-linking process of XLPE typically requires the use of peroxide initiators, which generates small-molecule byproducts such as methane and acetophenone, necessitating lengthy degassing treatment. This not only increases the production cycle but may also affect the material's electrical properties and environmental safety. Therefore, developing recyclable and environmentally friendly cable insulation materials has become an important direction for industry development.

[0004] Against this backdrop, polypropylene (PP) has gradually become a potential candidate material to replace XLPE due to its excellent electrical insulation properties, low dielectric loss, high volume resistivity, and melt-processable characteristics. As a thermoplastic material, polypropylene has advantages such as recyclability, short processing cycles, and no cross-linking byproducts, aligning with the development trend of green manufacturing. Therefore, research on polypropylene insulation materials for high-voltage DC cables has been increasing in recent years.

[0005] However, traditional isotactic polypropylene is a typical thermoplastic semi-crystalline material with insufficient thermomechanical stability under high-temperature conditions. When cables operate for extended periods at temperatures of 90–105°C or even higher, polypropylene is prone to morphological relaxation, decreased crystal structure stability, and a significant reduction in storage modulus, thus affecting the dimensional stability and mechanical support capacity of the insulation layer. Furthermore, under the long-term influence of a high-voltage DC electric field, space charge accumulation easily occurs within polypropylene. Due to the unevenness of carrier injection, migration, and capture processes, charge accumulation regions form within the material, leading to distorted electric field distribution, increased local electric field strength, and ultimately, localized breakdown, severely impacting the safe operation of the cable. These problems become increasingly prominent with higher voltage levels and longer operating times.

[0006] To improve the thermomechanical stability of polypropylene, existing technologies typically employ chemical crosslinking methods, such as peroxide crosslinking or radiation crosslinking, to form a three-dimensional crosslinked network structure, thereby enhancing its high-temperature mechanical properties. However, chemically crosslinked polypropylene, similar to XLPE, loses its melt-processing capability, making material reuse impossible and contradicting the principles of green and sustainable development. Furthermore, the degree of crosslinking is difficult to precisely control; excessive crosslinking can lead to increased brittleness and decreased electrical properties.

[0007] Another common modification method is to introduce inorganic nanofillers, such as nano-alumina and nano-silica, to improve electrical performance through interfacial polarization and carrier trapping effects. However, in practical applications, nanoparticles are prone to aggregation, making it difficult to ensure uniform dispersion. Interfacial defects may even become areas of concentrated electric field, affecting long-term electrical reliability. Furthermore, the introduction of nanofillers typically increases the difficulty of material processing and may affect material transparency and mechanical ductility.

[0008] In recent years, dynamic covalent network (CAN) materials have gradually attracted attention. Dynamic covalent bonds can undergo reversible breakage and recombination under certain temperature conditions, enabling materials to maintain their cross-linked structure while possessing topological rearrangement capabilities. These materials exhibit thermomechanical stability similar to thermoset materials at high temperatures, and can be reprocessed and molded at even higher temperatures or under specific conditions, thus combining thermal stability and recyclability. However, existing CAN materials are mostly concentrated in epoxy or rubber systems, with limited research on polypropylene insulation materials for high-voltage DC cables. Furthermore, simply introducing dynamic bonds may not effectively suppress space charge accumulation, resulting in limited improvement in electric field stability.

[0009] Therefore, developing a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, space charge suppression capability, and reprocessability has significant engineering application value and industrial significance. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention proposes a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability and its preparation method. This invention constructs a network system within the polypropylene system that combines dynamic cross-linking structure and deep trap control capabilities. By introducing reversible dynamic bonds and polar electron trapping units at the molecular level, it achieves a synergistic improvement in thermomechanical stability and space charge suppression capability. Furthermore, the dynamically cross-linked polypropylene cable insulation material provided by this invention possesses melt-processable properties, meeting the environmental protection and sustainability requirements of high-voltage DC cable insulation materials.

[0011] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following raw materials in parts by weight: 100 parts polypropylene (PP), 5-20 parts maleic anhydride-grafted polypropylene (PP-g-MAH), 0.5-5 parts polythiol compound, 0.2-3 parts isocyanate, 0.1-1.5 parts deep trap control unit, and 0.01-0.2 parts organic base catalyst; The deep trap control unit is a polar compound containing triazine, imide, fluoroaromatic ring or nitrile group.

[0012] Furthermore, the polypropylene is selected from isotactic polypropylene, syndiotactic polypropylene, or atactic polypropylene.

[0013] Furthermore, the amount of maleic anhydride grafted into the maleic anhydride-grafted polypropylene is 0.3 to 1.5 wt%.

[0014] Further, the multi-thiol compound is selected from dithiol compounds or polythiol compounds; the dithiol compound is selected from 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,10-decanedithiol, 1,4-benzenedithiol, 4,4'-thiobisbenzenethiophenol or 3,6-dioxa-1,8-octanedithiol; the polythiol compound is selected from trimethylolpropanetri(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetra(3-mercaptobutyrate) or trimethylolpropanetri(3-mercaptopropionate).

[0015] Further, the isocyanate is selected from aliphatic isocyanates, aromatic isocyanates, or polyfunctional isocyanates; the aliphatic isocyanate is selected from hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, or 1,4-butanediisocyanate; the aromatic isocyanate is selected from toluene diisocyanate, diphenylmethane diisocyanate, terephthalic diisocyanate, or 1,3-phenyl diisocyanate; the polyfunctional isocyanate is selected from hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, diphenylmethane diisocyanate trimer, or polyisocyanate prepolymer.

[0016] Furthermore, the deep trap control unit is selected from melamine, cyanuric acid, pyromellitic dianhydride derivatives, bisphenol A type polyimide oligomers, p-cyanobenzoic acid, dicyanobiphenyl, or 4,4′-(hexafluoroisopropyl)phthalic anhydride.

[0017] Furthermore, the organic base catalyst is selected from tertiary amines, imidazoles, or strong base organic catalysts.

[0018] Furthermore, the dynamic crosslinking bonds of the dynamically crosslinked polypropylene cable insulation material are thiocarbamate bonds, and the density of the dynamic crosslinking bonds is 0.05–0.15 mmol / g; the gel content of the dynamically crosslinked polypropylene cable insulation material is 50–75%.

[0019] This invention provides a method for preparing a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability as described above, comprising the following steps: Polypropylene and maleic anhydride-grafted polypropylene are melt-mixed, and then a multi-thiol compound, isocyanate and deep trap control unit are added. The melt reaction continues, followed by extrusion granulation and cooling drying to obtain the dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0020] Furthermore, the temperature of the melt mixing is 190°C, and the equipment for melt mixing is a twin-screw extruder.

[0021] The present invention also provides a method for reprocessing dynamically cross-linked polypropylene cable insulation material with thermomechanical stability as described in the above technical solution, comprising: crushing the dynamically cross-linked polypropylene cable insulation material and hot-pressing it at 200°C and 5-15MPa pressure for 1-2 hours to obtain reprocessed dynamically cross-linked polypropylene cable insulation material.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects: This invention achieves simultaneous improvement in the high-temperature morphological stability and DC electric field stability of polypropylene cable insulation materials through the synergistic design of dynamic cross-linking networks and polar electron-trapping structural units. Specifically, this invention uses polypropylene as a matrix, introduces reactive sites by grafting maleic anhydride onto polypropylene, and then utilizes the addition reaction between polythiol compounds and isocyanates under the catalysis of an organic base to generate dynamic covalent bonds of thiocarbamate, forming a three-dimensional reversible cross-linking network. This network maintains structural integrity at high temperatures and undergoes topological rearrangement under the promotion of an organic base, endowing the material with reprocessing properties. Simultaneously, small organic molecules or oligomers containing strongly polar groups are introduced into the system as deep trapping control units, which are uniformly dispersed in the matrix to form deep-level electron-trapping centers. These traps can effectively trap electrons injected under the action of an electric field, significantly reducing the concentration and mobility of free carriers, ultimately resulting in a polypropylene cable insulation material with high thermomechanical properties, deep trapping control capabilities, and reprocessing properties.

[0023] The thermomechanically stable dynamic cross-linked polypropylene cable insulation material provided by this invention exhibits the following characteristics during use: When the temperature rises, the dynamic bonds of the thiocarbamate in the material undergo a reversible exchange reaction, maintaining the stress release capability of the network structure and preventing the morphological relaxation and modulus decrease of traditional thermoplastic polypropylene under high-temperature conditions. When the material is subjected to an electric field, deep trap modulation units form a deep trap energy level structure within the material. Electrons entering the deep traps from the conduction band are difficult to escape, thereby suppressing space charge accumulation and improving the uniformity of the electric field distribution. This invention achieves a balance between the thermomechanical properties, electric field stability, and reprocessability of the material without introducing inorganic nanofillers. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The process flow diagrams for the preparation method and reprocessing method of the thermomechanically stable dynamic cross-linked polypropylene cable insulation material provided by the present invention are shown below. Figure 2 This is a schematic diagram illustrating the mechanism of the present invention in regulating the deep traps in the dynamic cross-linked polypropylene cable insulation material using a deep trap regulation unit; Figure 3 The image shows the Weibull distribution of DC breakdown strength of the dynamically cross-linked polypropylene cable insulation material with thermomechanical stability prepared in Example 1 of this invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] This invention provides a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following raw materials in parts by weight: 100 parts polypropylene, 5-20 parts maleic anhydride-grafted polypropylene, 0.5-5 parts polythiol compound, 0.2-3 parts isocyanate, 0.1-1.5 parts deep trap control unit, and 0.01-0.2 parts organic base catalyst; more preferably: 100 parts polypropylene, 10-20 parts maleic anhydride-grafted polypropylene, 1.5-3.5 parts polythiol compound, 0.8-1.5 parts isocyanate, 0.3-1.2 parts deep trap control unit, and 0.05-0.08 parts organic base catalyst.

[0028] In a preferred embodiment, the polypropylene is selected from isotactic polypropylene, syndiotactic polypropylene, or atactic polypropylene; the amount of maleic anhydride grafted in the maleic anhydride-grafted polypropylene is 0.3–1.5 wt%, more preferably 0.6–1.0 wt%. In this invention, polypropylene and maleic anhydride-grafted polypropylene constitute the polypropylene matrix unit, and the maleic anhydride-grafted polypropylene is used to provide reactive sites, enabling the system to have a basis for crosslinking reactions.

[0029] In a preferred embodiment, the multi-thiol compound is selected from dithiol compounds or polythiol compounds; the dithiol compound is selected from 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,10-decanedithiol, 1,4-benzenedithiol, 4,4'-thiobisbenzenethiophenol, or 3,6-dioxa-1,8-octanedithiol; the polythiol compound is selected from trimethylolpropanetrios(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetra(3-mercaptobutyrate), or trimethylolpropanetrios(3-mercaptopropionate); the multi-thiol compound is further preferably trimethylolpropanetrios(3-mercaptopropionate) or pentaerythritol tetra(3-mercaptopropionate). In this invention, the polythiol compound and isocyanate form a reactive crosslinking unit. Under the action of an organic base catalyst, the two undergo an addition reaction to form a dynamic covalent bond structure of thiocarbamate. The thiocarbamate structure constitutes the dynamic crosslinking network nodes of the material, enabling the polypropylene backbone to form a three-dimensional reversible crosslinking structure, thereby maintaining the integrity of the network under high temperature conditions.

[0030] In a preferred embodiment, the isocyanate is selected from aliphatic isocyanates, aromatic isocyanates, or polyfunctional isocyanates; the aliphatic isocyanate is selected from hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, or 1,4-butanediisocyanate; the aromatic isocyanate is selected from toluene diisocyanate, diphenylmethane diisocyanate, terephthalic diisocyanate, or 1,3-phenyl diisocyanate; the polyfunctional isocyanate is selected from hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, diphenylmethane diisocyanate trimer, or polyisocyanate prepolymer; the isocyanate is further preferably hexamethylene diisocyanate, isophorone diisocyanate, or dicyclohexylmethane diisocyanate.

[0031] In a preferred embodiment, the deep trap control unit is a polar compound containing triazine, imide, fluoroaromatic ring, or nitrile group, more preferably melamine, cyanuric acid, pyromellitic dianhydride derivative, bisphenol A type polyimide oligomer, p-cyanobenzoic acid, dicyanobiphenyl, or 4,4′-(hexafluoroisopropyl)phthalic anhydride, and even more preferably melamine, pyromellitic dianhydride derivative, bisphenol A type polyimide oligomer, or 4,4′-(hexafluoroisopropyl)phthalic anhydride. The deep trap control unit in this invention is an organic small molecule or oligomer containing a strongly polar group, dispersed within a polypropylene matrix, forming electron trapping centers within the material. These electron trapping centers are used to control the trap energy level distribution within the material, increasing the trap energy level depth and trap density, so that electrons injected under the action of an electric field are trapped by deep traps, thereby reducing the free carrier concentration.

[0032] In a preferred embodiment, the deep trap control unit can form a deep trap structure with an energy level greater than 0.8 eV inside the material to improve the DC electric field stability of the material.

[0033] A schematic diagram illustrating the mechanism by which this invention utilizes a deep trap control unit to regulate deep traps in dynamically cross-linked polypropylene cable insulation material is shown below. Figure 2 As can be seen, after introducing the deep trap control unit, the polar structure contained in the deep trap control unit forms a stable electron trapping center in the polypropylene matrix. When electrons are injected into the material by the electrode under the action of an electric field, some electrons migrate from the conduction band and are trapped by the deep level traps formed by the aforementioned polar structure, thereby forming a stable deep trap energy level structure inside the material. Since the deep traps have high trap energy levels, once electrons are trapped, they are difficult to escape and re-enter the conduction band to participate in the conduction process, thus effectively reducing the concentration and mobility of free carriers inside the material. Through this deep trap control mechanism, the accumulation of space charge inside the material can be significantly suppressed, electric field distortion can be reduced, and the electric field stability and insulation reliability of the material under the action of a DC electric field can be improved.

[0034] In a preferred embodiment, the organic base catalyst is selected from tertiary amines, imidazoles, or strong base organic catalysts, more preferably triethylamine, N,N-diisopropylethylamine, N,N-dimethylbenzylamine, 1-methyl-1H-imidazolium, 2-methylimidazolium, or 1,5,7-triazabicyclodecene, and even more preferably triethylamine, N,N-diisopropylethylamine, or 1-methyl-1H-imidazolium. The organic base catalyst in this invention serves as a dynamic control unit, used to promote the reaction rate between thiol groups and isocyanates, and to promote the reversible exchange reaction of thiocarbamate bonds under heating conditions, enabling network topological rearrangement of the material at high temperatures, thus achieving material reprocessing.

[0035] In a preferred embodiment, the dynamic crosslinking bonds of the dynamically crosslinked polypropylene cable insulation material are thiocarbamate bonds, and the density of the dynamic crosslinking bonds is 0.05–0.15 mmol / g; the gel content of the dynamically crosslinked polypropylene cable insulation material is 50–75%. This invention controls the gel content and the density of the dynamic crosslinking bonds within the above ranges to ensure a balance between the material's thermomechanical stability and processing performance.

[0036] This invention provides a method for preparing a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability as described above, comprising the following steps: Polypropylene and maleic anhydride-grafted polypropylene are melt-mixed, and then a multi-thiol compound, isocyanate and deep trap control unit are added. The melt reaction continues, followed by extrusion granulation and cooling drying to obtain the dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0037] In a preferred embodiment, the temperature of the melt mixing is 190°C, and the equipment for melt mixing is a twin-screw extruder.

[0038] In a preferred embodiment, the continued melting reaction time is 3 to 7 minutes.

[0039] This invention also provides a method for reprocessing dynamically cross-linked polypropylene cable insulation material with thermomechanical stability as described above, comprising: pulverizing the dynamically cross-linked polypropylene cable insulation material and hot-pressing it at 200°C and 5–15 MPa for 1–2 hours to obtain a reprocessed dynamically cross-linked polypropylene cable insulation material. After pulverizing the dynamically cross-linked polypropylene cable insulation material provided by this invention, under specific temperature and pressure conditions, the dynamic cross-linking network in the material undergoes topological rearrangement, allowing the material to be reformed without permanent performance loss, thus achieving recyclable reprocessing of the material.

[0040] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0041] Figure 1 The present invention provides a process flow diagram of the preparation method of dynamically cross-linked polypropylene cable insulation material with thermomechanical stability and the reprocessing method of dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0042] Example 1 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts isotactic polypropylene, 15 parts maleic anhydride-grafted polypropylene (maleic anhydride grafting amount is 0.8 wt%), 2.5 parts trimethylolpropane tris(3-mercaptopropionate), 1.2 parts hexamethylene diisocyanate, 0.5 parts melamine, and 0.05 parts triethylamine; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.11 mmol / g, and the gel content is 60%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability includes the following specific steps: 100g of isotactic polypropylene and 15g of maleic anhydride-grafted polypropylene were sequentially added to a twin-screw extruder and melt-mixed at 190℃. Subsequently, 2.5g of trimethylolpropane tris(3-mercaptopropionate), 1.2g of hexamethylene diisocyanate, 0.5g of melamine, and 0.05g of triethylamine were added, and the reaction was continued at 60rpm for 3min. After the reaction was completed, the mixture was extruded, granulated, cooled, and dried to obtain a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0043] The dynamically cross-linked polypropylene cable insulation material prepared in Example 1 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 0.92 MPa at 160°C, a DC breakdown strength of 368 kV / mm at 30°C, and a β value of 17.

[0044] DMA storage modulus testing process: The test was conducted on a Q800 dynamic thermomechanical analyzer manufactured by TA Instruments in the United States. The sample specifications were strip-shaped samples with a thickness of 1.0±0.1mm, a length of 40.0±1.0mm, and a width of 8.0±0.5mm. The deformation mode was tensile mode, the periodic stress frequency was 1Hz, the test temperature range was 20-200℃, and the heating rate was 3℃ / min.

[0045] DC breakdown strength test procedure: A 25mm diameter brass ball-to-ball electrode is used. During the test, the electrode and the sample are immersed in transformer oil to ensure that the entire electrode is completely submerged in the oil to avoid unnecessary discharge during the experiment. The voltage rise rate is selected as 1kV / mm. After obtaining 10 valid data points for each sample, a two-parameter Weibull distribution is fitted using the following formula. The breakdown strength with a cumulative breakdown probability of 63.2% is extracted as the intrinsic breakdown strength, and the standard deviation is calculated. ; In the formula, E is the DC breakdown strength test value; E0 is the characteristic AC breakdown strength, which corresponds to the AC breakdown strength when the cumulative breakdown probability is 63.2%; β is the shape parameter, which can reflect the dispersion of breakdown data. The smaller β is, the greater the dispersion of breakdown data. Generally, the shape parameter needs to be greater than 10 to ensure high data consistency.

[0046] Figure 3 The image shows the Weibull distribution of the DC breakdown strength of the dynamically cross-linked polypropylene cable insulation material with thermomechanical stability prepared in Example 1. Figure 3 It can be seen that the dynamically cross-linked polypropylene cable insulation material prepared in Example 1 exhibits high DC breakdown strength at 30℃, with a characteristic breakdown strength reaching 368 kV / mm. Simultaneously, the Weibull shape parameter β value of this material is 17, indicating low dispersion in breakdown data, good internal structural uniformity, and stable and reliable electrical performance. These results demonstrate that by constructing a dynamic cross-linked thiocarbamate network and introducing deep trap control units in the polypropylene system, carrier migration and space charge accumulation can be effectively suppressed, thereby improving the DC breakdown performance and electric field stability of the material.

[0047] Example 2 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 1 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0048] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 2 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 92%.

[0049] Example 3 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts isotactic polypropylene, 20 parts maleic anhydride-grafted polypropylene (maleic anhydride grafting amount is 1.0 wt%), 3.5 parts pentaerythritol tetra(3-mercaptopropionate), 1.5 parts isophorone diisocyanate, 0.8 parts pyromellitic dianhydride derivative, and 0.08 parts N,N-diisopropylethylamine; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.11 mmol / g, and the gel content is 69%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability includes the following specific steps: 100g of isotactic polypropylene and 20g of maleic anhydride-grafted polypropylene were sequentially added to a twin-screw extruder and melt-mixed at 190℃. Subsequently, 3.5g of pentaerythritol tetra(3-mercaptopropionate), 1.5g of isophorone diisocyanate, and 0.8g of pyromellitic dianhydride derivative were added, along with 0.08g of N,N-diisopropylethylamine. The reaction was continued at 60rpm for 4min. After the reaction was completed, the mixture was extruded, granulated, cooled, and dried to obtain a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0050] The dynamically cross-linked polypropylene cable insulation material prepared in Example 3 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 1.05 MPa at 160°C, a DC breakdown strength of 375 kV / mm at 30°C, and a β value of 25.

[0051] Example 4 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 3 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0052] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 4 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 94%.

[0053] Example 5 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts isotactic polypropylene, 10 parts maleic anhydride-grafted polypropylene (maleic anhydride grafting amount is 0.6 wt%), 1.5 parts trimethylolpropane tris(3-mercaptopropionate), 0.8 parts hexamethylene diisocyanate, 0.3 parts dicyanbiphenyl, and 0.05 parts 1-methyl-1H-imidazolium; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.08 mmol / g, and the gel content is 64%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability includes the following specific steps: 100g of isotactic polypropylene and 10g of maleic anhydride-grafted polypropylene were sequentially added to a twin-screw extruder and melt-mixed at 190℃. Subsequently, 1.5g of trimethylolpropane tris(3-mercaptopropionate), 0.8g of hexamethylene diisocyanate, 0.3g of dicyanbiphenyl, and 0.05g of 1-methyl-1H-imidazolium were added, and the reaction was continued at 60rpm for 3min. After the reaction was completed, the mixture was extruded, granulated, cooled, and dried to obtain a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0054] The dynamically cross-linked polypropylene cable insulation material prepared in Example 5 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 0.75 MPa at 160°C, a DC breakdown strength of 350 kV / mm at 30°C, and a β value of 18.

[0055] Example 6 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 5 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0056] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 6 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 93%.

[0057] Example 7 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts isotactic polypropylene, 18 parts maleic anhydride-grafted polypropylene (maleic anhydride grafting amount is 0.9 wt%), 2.8 parts pentaerythritol tetra(3-mercaptopropionate), 1.3 parts dicyclohexylmethane diisocyanate, 0.6 parts 4,4′-(hexafluoroisopropyl)phthalic anhydride, and 0.05 parts triethylamine; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.08 mmol / g, and the gel content is 67%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability includes the following specific steps: 100g of isotactic polypropylene and 18g of maleic anhydride-grafted polypropylene were sequentially added to a twin-screw extruder and melt-mixed at 190℃. Subsequently, 2.8g of pentaerythritol tetra(3-mercaptopropionate), 1.3g of dicyclohexylmethane diisocyanate, 0.6g of 4,4′-(hexafluoroisopropyl)phthalic anhydride, and 0.05g of triethylamine were added, and the reaction was continued at 60rpm for 5min. After the reaction was completed, the mixture was extruded, granulated, cooled, and dried to obtain a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0058] The dynamically cross-linked polypropylene cable insulation material prepared in Example 7 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 0.98 MPa at 160°C, a DC breakdown strength of 370 kV / mm at 30°C, and a β value of 19.

[0059] Example 8 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 7 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0060] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 8 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 91%.

[0061] Example 9 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability differs from Example 1 only in that the amount of melamine used is 1.2g (i.e., 1.2 parts), while the rest is the same as in Example 1; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of the dynamic cross-linking bonds is 0.12mmol / g, and the gel content is 71%.

[0062] The dynamic cross-linked polypropylene cable insulation material prepared in Example 9 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DC breakdown strength of 372 kV / mm at 30°C, a β value of 17, and a DMA storage modulus of 0.95 MPa at 160°C.

[0063] Example 10 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 9 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0064] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 10 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 94%.

[0065] Example 11 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts isotactic polypropylene, 15 parts maleic anhydride-grafted polypropylene (maleic anhydride grafting amount of 0.8 wt%), 2.0 parts 1,6-hexanedithiol, 1.1 parts hexamethylene diisocyanate, 0.5 parts melamine, and 0.05 parts triethylamine; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.07 mmol / g, and the gel content is 52%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability includes the following specific steps: 100g of isotactic polypropylene and 15g of maleic anhydride-grafted polypropylene were sequentially added to a twin-screw extruder and melt-mixed at 190℃. Subsequently, 2.0g of 1,6-hexanedithiol, 1.1g of hexamethylene diisocyanate, 0.5g of melamine, and 0.05g of triethylamine were added, and the reaction was continued at 60rpm for 4min. After the reaction was completed, the mixture was extruded, granulated, cooled, and dried to obtain a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

[0066] The dynamically cross-linked polypropylene cable insulation material prepared in Example 11 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 0.82 MPa at 160°C, a DC breakdown strength of 360 kV / mm at 30°C, and a β value of 16.

[0067] Example 12 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 11 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0068] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 12 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 90%.

[0069] Example 13 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts of syndiotactic polypropylene, 15 parts of maleic anhydride-grafted polypropylene (maleic anhydride grafting amount is 0.8 wt%), 2.5 parts of trimethylolpropane tris(3-mercaptopropionate), 1.2 parts of diphenylmethane diisocyanate (MDI), 0.6 parts of pyromellitic dianhydride derivative, and 0.05 parts of triethylamine; the dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.10 mmol / g, and the gel content is 65%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is the same as that in Example 1.

[0070] The dynamically cross-linked polypropylene cable insulation material prepared in Example 13 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 1.02 MPa at 160°C, a DC breakdown strength of 372 kV / mm at 30°C, and a β value of 21.

[0071] Example 14 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 13 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0072] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 14 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 91%.

[0073] Example 15 A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is composed of the following raw materials in parts by weight: 100 parts of atactic polypropylene, 18 parts of maleic anhydride-grafted polypropylene (maleic anhydride grafting amount is 0.9 wt%), 3.0 parts of pentaerythritol tetra(3-mercaptopropionate), 1.0 part of hexamethylene diisocyanate trimer, 0.5 parts of dicyanbiphenyl, and 0.05 parts of 1-methyl-1H-imidazolium. The dynamic cross-linking bonds of the dynamically cross-linked polypropylene cable insulation material are thiocarbamate bonds, the density of dynamic cross-linking bonds is 0.12 mmol / g, and the gel content is 72%. The preparation method of the above-mentioned dynamically cross-linked polypropylene cable insulation material with thermomechanical stability is the same as that in Example 1.

[0074] The dynamically cross-linked polypropylene cable insulation material prepared in Example 15 was molded at 200°C to obtain a sample with a thickness of about 200 μm. The sample was tested and found to have a DMA storage modulus of 1.08 MPa at 160°C, a DC breakdown strength of 378 kV / mm at 30°C, and a β value of 23.

[0075] Example 16 A reprocessing method for dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, comprising the following steps: The thermomechanically stable dynamic cross-linked polypropylene cable insulation material prepared in Example 15 was pulverized and then hot-pressed at 200°C and 10MPa for 1.5 hours to obtain reprocessed dynamic cross-linked polypropylene cable insulation material.

[0076] The reprocessed dynamic cross-linked polypropylene cable insulation material prepared in Example 16 was tested according to the test method in Example 1. The results showed that the performance retention rate of the reprocessed dynamic cross-linked polypropylene cable insulation material was about 93%.

[0077] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A dynamically cross-linked polypropylene cable insulation material with thermomechanical stability, characterized in that, The raw materials include the following parts by weight: 100 parts polypropylene, 5-20 parts maleic anhydride-grafted polypropylene, 0.5-5 parts polythiol compound, 0.2-3 parts isocyanate, 0.1-1.5 parts deep trap control unit, and 0.01-0.2 parts organic base catalyst; The deep trap control unit is a polar compound containing triazine, imide, fluoroaromatic ring or nitrile group.

2. The dynamically cross-linked polypropylene cable insulation material with thermomechanical stability according to claim 1, characterized in that, The polypropylene is selected from isotactic polypropylene, syndiotactic polypropylene, or atactic polypropylene; The amount of maleic anhydride grafted into the maleic anhydride-grafted polypropylene is 0.3 to 1.5 wt%.

3. The dynamically cross-linked polypropylene cable insulation material with thermomechanical stability according to claim 1, characterized in that, The multi-thiol compound is selected from dithiol compounds or polythiol compounds; the dithiol compound is selected from 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,10-decanedithiol, 1,4-benzenedithiol, 4,4'-thiobisbenzenethiophenol, or 3,6-dioxa-1,8-octanedithiol; the polythiol compound is selected from trimethylolpropanetri(3-mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate), pentaerythritol tetra(3-mercaptobutyrate), or trimethylolpropanetri(3-mercaptopropionate).

4. The dynamically cross-linked polypropylene cable insulation material with thermomechanical stability according to claim 1, characterized in that, The isocyanate is selected from aliphatic isocyanates, aromatic isocyanates, or polyfunctional isocyanates; the aliphatic isocyanate is selected from hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, or 1,4-butanediisocyanate; the aromatic isocyanate is selected from toluene diisocyanate, diphenylmethane diisocyanate, terephthalic diisocyanate, or 1,3-phenyl diisocyanate; the polyfunctional isocyanate is selected from hexamethylene diisocyanate trimer, isophorone diisocyanate trimer, diphenylmethane diisocyanate trimer, or polyisocyanate prepolymer.

5. The dynamically cross-linked polypropylene cable insulation material with thermomechanical stability according to claim 1, characterized in that, The deep trap control unit is selected from melamine, cyanuric acid, pyromellitic dianhydride derivatives, bisphenol A type polyimide oligomers, p-cyanobenzoic acid, dicyanobiphenyl, or 4,4′-(hexafluoroisopropyl)phthalic anhydride.

6. The dynamically cross-linked polypropylene cable insulation material with thermomechanical stability according to claim 1, characterized in that, The organic base catalyst is selected from tertiary amines, imidazoles, or strong base organic catalysts.

7. The dynamically cross-linked polypropylene cable insulation material with thermomechanical stability according to claim 1, characterized in that, The dynamic crosslinking bonds of the dynamically crosslinked polypropylene cable insulation material are thiocarbamate bonds, and the density of the dynamic crosslinking bonds is 0.05–0.15 mmol / g; the gel content of the dynamically crosslinked polypropylene cable insulation material is 50–75%.

8. A method for preparing a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Polypropylene and maleic anhydride-grafted polypropylene are melt-mixed, and then a multi-thiol compound, isocyanate and deep trap control unit are added. The melt reaction continues, followed by extrusion granulation and cooling drying to obtain the dynamically cross-linked polypropylene cable insulation material with thermomechanical stability.

9. The preparation method according to claim 8, characterized in that, The melting and mixing temperature is 190°C, and the melting and mixing equipment is a twin-screw extruder.

10. A method for reprocessing a dynamically cross-linked polypropylene cable insulation material with thermomechanical stability as described in any one of claims 1 to 7, characterized in that, include: After pulverizing the dynamic cross-linked polypropylene cable insulation material, it is hot-pressed at 200℃ and 5-15MPa pressure for 1-2 hours to obtain the reprocessed dynamic cross-linked polypropylene cable insulation material.

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