Preparation method of high-temperature-resistant and radiation-resistant polypropylene-based cable insulating material

Abstract

The invention relates to a preparation method of a high-temperature-resistant and radiation-resistant polypropylene-based cable insulating material, which comprises the following steps: by taking a styrene thermoplastic elastomer and polypropylene as base materials, using a free radical initiator and taking an aromatic compound with a conjugated structure as an assistant cross-linking agent, carrying out dynamic cross-linking reaction through a torque rheometer to obtain the high-temperature-resistant and radiation-resistant polypropylene-based cable insulating material. The cable insulating material with high breakdown field strength and deep trap density is developed, and the cable insulating material has higher radiation resistance and can be used as a nuclear power cable insulating material.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable insulation, and particularly relates to a preparation method of a polypropylene-based cable insulation material with high temperature resistance and radiation resistance. Background Art

[0002] Nuclear power is one of the preferred clean energies and an important means for human society to cope with the energy crisis. The first priority of nuclear power development is safety. The reliability of various electrical equipment in the nuclear island is the foundation for the safe operation of nuclear power plants. A large number of cables laid in the nuclear island are called the "blood vessels" and "nerves" of nuclear power plants and are key electrical equipment for realizing functions such as power transmission, power supply, instrumentation control, and communication. A nuclear power unit with a capacity of one million kilowatts requires more than 100 types of cables, and the usage amount is about 3000 km. The high-temperature and high-radiation environment in the nuclear power plant will cause serious damage to the cable insulation material and accelerate the performance degradation of the polymer material. It is not easy to replace the cable insulation in the nuclear power plant, and once insulation failure occurs, it may threaten the use safety of the nuclear power system. At present, the nuclear cable insulation materials widely used in the third-generation nuclear power plants in China are mainly polyolefin materials such as polyethylene (PE). According to statistics, within the design life of the third-generation reactor and during normal operation, the total accumulated high-energy gamma-ray irradiation dose of the insulation material can reach 210 kGy, and the operating temperature can reach up to 57°C at the highest. At present, China has built the fourth-generation high-temperature gas-cooled reactor nuclear power plant. The fourth-generation nuclear power plant has higher safety, but its environmental temperature is higher, and the operating temperature that the cable insulation in it needs to withstand can reach 100°C. This has significantly exceeded the limit operating temperature of 90°C for polyolefin cable insulation materials specified in the national standard GB / T 9330-2020, which will cause accelerated degradation of the insulation material and threaten the operation safety of the nuclear power plant. Therefore, it is necessary to develop new radiation-resistant and high-temperature-resistant nuclear cable insulation materials.

[0003] Isotactic polypropylene (iPP) has the characteristics of high melting point and excellent electrical properties. It is regarded as a potential high-temperature resistant cable insulation material, but its flexibility and radiation resistance are poor. Dynamic vulcanization (also known as dynamic cross-linking) refers to the melt blending of elastomer and resin under a certain temperature field and a strong shear field. The elastomer undergoes an in-situ vulcanization and cross-linking reaction under the action of a cross-linking agent, and forms small particles under the action of shear, which are dispersed in the resin matrix to form a "sea-island" phase structure. The resulting product is called thermoplastic vulcanizate (TPV). After iPP and rubber are dynamically cross-linked, the cross-linked network structure has the ability to consume and control the development of silver streaks, which helps to improve the toughness of iPP. Studies have shown that aromatic structures can protect the polymer main chain under irradiation, disperse irradiation energy, and reduce irradiation damage. Therefore, introducing aromatic ring structures in the molecular chain or adding aromatic compounds to the matrix can improve the radiation resistance of the material. Styrene thermoplastic elastomer (TPES) has high radiation resistance and aging resistance, and is often used to blend with iPP to prepare cable insulation materials. It can improve the mechanical properties of the material while ensuring the electrical properties of the base material. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a high-temperature resistant and radiation resistant polypropylene-based cable insulation material. Styrene thermoplastic elastomer and polypropylene are used as matrix materials, free radical initiators are used, aromatic compounds with conjugated structures are used as auxiliary cross-linking agents, and dynamic cross-linking reactions are carried out through a torque rheometer to develop a cable insulation material with high breakdown field strength and deep trap density, which has higher radiation resistance and can be used for nuclear power cable insulation materials.

[0005] The present invention solves the technical problem by the following technical solutions:

[0006] A method for preparing a high temperature resistant and radiation resistant polypropylene-based cable insulation material, the method comprising the following steps:

[0007] S1. Select styrene thermoplastic elastomer TPES with elongation at break>1200%, high molecular weight, low unsaturation and high compatibility with isotactic polypropylene iPP and isotactic polypropylene iPP pellets and vacuum dry them in a vacuum drying oven at 70°C for 24h;

[0008] S2, adding the dried styrene thermoplastic elastomer TPES into the torque rheometer, and adding a crosslinking agent to mix thoroughly;

[0009] S3. Add the dried isotactic polypropylene iPP and the co-crosslinking agent into a torque rheometer for dynamic crosslinking reaction to obtain a polypropylene-based cable insulation material iPP / TPES TPV with high flexibility and radiation resistance.

[0010] Moreover, the weight parts of the styrenic thermoplastic elastomer TPES are 30 - 60 parts, the weight parts of the crosslinking agent are 0.1 - 1 part, the weight parts of the isotactic polypropylene iPP are 40 - 70 parts, and the weight parts of the co-crosslinking agent are 0.1 - 3 parts.

[0011] Moreover, the crosslinking agent is any one or more of dicumyl peroxide (DCP), 2,5 - dimethyl - 2,5 - di - tert - butylperoxyhexane (bis - 25), vinyltrimethoxysilane (VTMS), and vinyltriethoxysilane (VTEOS).

[0012] Moreover, the co - crosslinking agent is 4,4′ - stilbenedicarboxylic acid (SDA).

[0013] The advantages and beneficial effects of the present invention are as follows:

[0014] 1. In the present invention, TPES and iPP are mixed by dynamic crosslinking, and the aromatic voltage stabilizer 4,4′ - stilbenedicarboxylic acid is added to improve the crosslinking effect, while enhancing the electrical and radiation resistance of the composite material, and enhancing the radiation resistance of iPP, which is beneficial to the application of iPP - based cable insulation materials under nuclear power conditions.

[0015] 2. In the present invention, the aromatic voltage stabilizer 4,4′ - stilbenedicarboxylic acid is used as a co - crosslinking agent, which can simultaneously improve the electrical properties and radiation resistance of the iPP / TPES composite material, and the preparation process is simple, and the improvement effect on the electrical properties and radiation resistance of the material is significant; at the same time, the electrical and radiation resistance properties of the system can be adjusted by adjusting the contents of TPES, the crosslinking agent and the co - crosslinking agent, and the problem of poor radiation resistance of polypropylene can be solved, laying a foundation for the application of polypropylene - based cable insulation materials in the nuclear power system. Brief Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the AC breakdown field strength of the polypropylene - based cable insulation material of the present invention;

[0017] Figure 2 It is a schematic diagram of the preparation mechanism of the present invention. Detailed Embodiments

[0018] The present invention will be further described in detail below through specific embodiments. The following embodiments are only descriptive and not restrictive, and the protection scope of the present invention cannot be limited thereby.

[0019] As Figure 2 shown, a preparation method of a high - temperature - resistant and radiation - resistant polypropylene - based cable insulation material, the innovation of which lies in: the steps of the method are as follows:

[0020] (1) Select SEBS with an elongation at break > 1200%, a relatively high molecular weight, a relatively low degree of unsaturation, and a relatively high compatibility with iPP. Together with iPP pellets, dry them in a vacuum drying oven at 70°C under a vacuum atmosphere for 24 h;

[0021] (2) Weigh 9 g of SEBS and 0.01 g of DCP and add them together to a torque rheometer. React for 1 min. Set the temperature of the torque rheometer to 170°C and the rotor speed to 60 r / min;

[0022] (3) Weigh 21 g of iPP and 0.1 g - 0.3 g of SDA and add them together to the torque rheometer for a dynamic crosslinking reaction for 5 min 30 s;

[0023] (4) Finally, obtain an iPP / SEBS TPV composite material with relatively high flexibility and radiation resistance. After irradiation with 250 kGy, for the sample without adding DCP and SDA, the AC breakdown field strength decreased by 8.2%. For the TPV material added with DCP and 0.1 g of SDA, the AC breakdown field strength decreased by 3.5%. For the material added with DCP and 0.3 g of SDA, the AC breakdown field strength decreased by 0.7%.

[0024] In this example, iPP and hydrogenated styrene-butadiene thermoplastic elastomer (SEBS) are mixed in a ratio of 70:30. Using dicumyl peroxide (DCP) as a crosslinking agent and 4,4′-diphenylstilbene dicarboxylic acid (SDA) as a co-crosslinking agent, the obtained composite material is named SDA, and the composite material without adding SDA and DCP is named A. After hot-pressing the A and SDA composite materials into thin sheet samples, perform gamma-ray irradiation treatment of 250 kGy in air, and compare the AC breakdown field strength before and after irradiation; before and after 250 kGy gamma-ray irradiation, the AC breakdown field strength of the composite material is as Figure 1 shown. The improvement effect of the radiation resistance after adding SDA is that the AC breakdown field strength of the samples in the SDA group is higher than that in the A group, and the decrease in the AC breakdown field strength after irradiation is less.

[0025] In the present invention, TPES and iPP are subjected to a dynamic crosslinking reaction in a torque rheometer, and then aromatic voltage stabilizer 4,4′-diphenylstilbene dicarboxylic acid (SDA) is added as a co-crosslinking agent. There are a large number of aromatic ring structures in TPES. After dynamic crosslinking, the formed three-dimensional network structure is more stable, and at the same time, it is dispersed in the iPP matrix in the form of small particles, which is more conducive to reducing radiation damage. Using SDA as a co-crosslinking agent, on the one hand, it can play the role of a voltage stabilizer to capture free radicals and disperse the damage caused by the initiator and radiation-induced free radicals to the iPP molecular chain. On the other hand, it can improve the breakdown field strength of the matrix material. Moreover, the aromatic structure of SDA can play the role of dispersing radiation energy and reducing the damage of radiation energy to the matrix material.

[0026] Therefore, the TPV material prepared by this method has high electrical properties, heat resistance and radiation resistance, which is beneficial to the long-term use of cable insulation under nuclear power conditions and has great application potential as a nuclear power cable insulation material.

[0027] The present invention improves the performance of iPP, which originally has poor radiation resistance, and prepares a cable insulation material with high temperature resistance, radiation resistance and higher insulation. It has certain guiding significance for the material selection and design of future nuclear power cable insulation materials.

[0028] The present invention can prepare a radiation-resistant polypropylene-based cable insulation material for use in the high-temperature environment inside the nuclear island of a nuclear power plant. By using an aromatic voltage stabilizer as a co-crosslinking agent, a certain styrene thermoplastic elastomer and isotactic polypropylene are selected, and a polypropylene / styrene thermoplastic vulcanizate with excellent electrical properties and radiation resistance is prepared through dynamic crosslinking. This method can improve the radiation resistance of the polypropylene-based composite material, so that after a radiation dose of 250 kGy, the electrical properties decrease less, which is beneficial to long-term use in a radiation environment. The present invention can be applied to the fourth-generation nuclear power plants with high-temperature and high-radiation environments, laying a foundation for the selection of future nuclear power cable insulation materials.

[0029] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments and drawings.

Claims

1. A method for preparing a high temperature resistant and radiation resistant polypropylene-based cable insulation material, characterized in that: The steps of the method are: S1. Select styrene thermoplastic elastomer TPES with elongation at break>1200%, high molecular weight, low unsaturation and high compatibility with isotactic polypropylene iPP and isotactic polypropylene iPP pellets and vacuum dry them in a vacuum drying oven at 70°C for 24h; S2, adding the dried styrene thermoplastic elastomer TPES into the torque rheometer, and adding a crosslinking agent to mix thoroughly; S3. Add the dried isotactic polypropylene iPP and the co-crosslinking agent into a torque rheometer for dynamic crosslinking reaction to obtain a polypropylene-based cable insulation material iPP / TPES TPV with high flexibility and radiation resistance.

2. The method for preparing a high temperature resistant and radiation resistant polypropylene-based cable insulation material according to claim 1, characterized in that: The weight proportion of the styrene-based thermoplastic elastomer TPES is 30 to 60 parts, the weight proportion of the crosslinking agent is 0.1 to 1 part, the weight proportion of the isotactic polypropylene iPP is 40 to 70 parts, and the weight proportion of the auxiliary crosslinking agent is 0.1 to 3 parts.

3. The method for preparing a high temperature resistant and radiation resistant polypropylene-based cable insulation material according to claim 1, characterized in that: The crosslinking agent is any one or more of dicumyl peroxide (DCP), 2,5-dimethyl-2,5-di-tert-butyl peroxide hexane (bis-25), vinyl trimethoxy silane (VTMS), and vinyl triethoxy silane (VTEOS).

4. The method for preparing a high temperature resistant and radiation resistant polypropylene-based cable insulation material according to claim 1, characterized in that: The auxiliary cross-linking agent is 4,4′-stilbene dicarboxylic acid (SDA).

Images