Development of radiation resistant polymer materia

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Progress in radiation resistant polymer materials for wires and cables

I. Introduction

after high-energy radiation, polymer materials are easy to produce free radicals or react with atomic oxygen in the air, resulting in material cracking, cross-linking, branching, etc., affecting the properties of materials. With the large-scale demand of nuclear power plants, aerospace instruments, nuclear analysis and the production of nuclear materials, excellent radiation resistant polymer materials are needed for wires and cables, control cables and other packaging materials

the methods to improve the radiation resistance of polymer composites are mainly from the following two aspects: (1) capture free radicals, mainly by adding antioxidants, but it is effective in inert atmosphere, but the effect is poor in the presence of oxygen. (2) Adding materials can absorb radiant energy and convert it into heat energy through some intermediate state. Benzene ring usually has this effect. Therefore, in the past, polymer materials or additives containing benzene rings were often added to PVC, PE, EPDM and other materials. They have been widely used. Some inorganic materials also have this effect, but it cannot be explained from the mechanism. With the development of polymer materials and the improvement of nuclear industry standards, new methods and materials have been studied and applied []

II. Progress in radiation resistant polymer materials

1. Polyimide

polymers containing benzene rings can usually convert radiation energy into heat energy through internal conversion. The most important one is polyimide, which can remove H atoms because it contains a system with high content of multiple benzene rings. The most famous one is kapton@, but it is limited due to its strong absorption of other spectral segments, For this reason, other kinds of polyimides have been further developed and utilized. For example, it is only by increasing twisting to destroy their molecular chain sequencing, or by adding two independent polyphenyl ring groups to two imide rings, and further by adding trifluoromethyl and residual diimide groups to react to enhance the electron to reduce the complex ligand effect Although the wires and cables of polyimide materials have been applied, more extensive choices are still under further study.

2, si4n3 fiber

si4n3 fiber, as an excellent radiation and high temperature resistant electrical insulation material, is widely used in nuclear power plants and steel plants. It can be used in temperature resistance above 10000c and aerospace applications. It is synthesized from a kind of Polycarbosilane

3. Silicon carbide fiber reinforced silicon carbide composites

silicon carbide composites are also used because of their excellent thermal stability, radiation resistance and corrosion resistance, and silicon carbide fiber reinforced silicon carbide composites can be made into extremely important materials. It usually adopts the method of immersion pyrolysis, and faces many problems that need to be improved in the process flow and the selection of new materials

4. Plasma deposition

by coating a protective layer on the surface of polymer materials, it is also a frequently used method that it is not affected by rays. Plasma deposition is one of the most effective and concerned means, such as coating the surface of materials with a layer of diamond like coating.

5. Adding organometallic compounds

although other methods are very effective, the cost is high, Recently, the method of adding organometallic compounds has attracted much attention. After the metal is attacked by oxygen atoms, it produces an oxide film to protect the polymer substrate. After wear, it can repair itself and produce a new protective film. At present, it is mainly limited to organic aluminum and organic tin

6. Metal based polymer materials

are inspired by the addition of organometallic compounds. At present, this method is still under discussion

III. radiation crosslinked polymers and their industrial applications

after radiation crosslinking of polymer materials, a certain cross-linking point is formed between polymer macromolecules, which improves the molecular weight of the polymer and forms a three-dimensional structure molecule, which has an impact on the physical properties of the polymer with a history of 510 years:

(1) improve the thermal stability (including high-temperature characteristics and thermal oxygen aging)

(2) improve tensile strength and reduce elasticity; Especially to improve the tensile strength at high temperature

after radiation crosslinking, the tensile strength, wear resistance and other mechanical properties of the material can be improved. But it is worth noting that this is not absolute, especially for semi crystalline polymers, the tensile strength of cross-linked polymers will decrease after a certain degree of cross-linking

in addition, radiation can also improve the environmental stress tear resistance and low temperature brittleness of polyolefins, but the most important thing is to improve the mechanical properties at high temperature

(3) the crosslinked polymer cannot be dissolved by solvent, but can only be swelled by solvent

compared with chemical crosslinking, radiation crosslinking has the following advantages:

(1) there is no need to add heating initiator, which can avoid pre crosslinking in the mixing process

(2) crosslinking is carried out at room temperature, which can save energy and avoid environmental pollution

(3) the crosslinking process is simple and easy to control. The degree of crosslinking can be controlled by adjusting the radiation dose

(4) a wide range of applications, such as PP, chlorinated polyethylene (CPE), fluorine materials, etc

(5) high efficiency and low cost

(6) improve electrical properties: under high-pressure steam, the steam of steam crosslinked PE cable will inevitably penetrate into the PE layer, causing many micropores. If the concentration of dirt is high, the cable is prone to "electrical tree phenomenon" in use, and the introduction of crosslinking agent will damage the high-frequency characteristics of the material. Radiation crosslinking can avoid or eliminate these micropores, dirt or bulges, and eliminate the phenomenon of "water tree" and "electric tree", so as to ensure the uniformity and high purity of the insulation layer, so that it has better high-frequency characteristics and long-term performance. Therefore, people regard radiation processing as another industrial revolution after machining, thermal processing and electrical processing

(7) radiation crosslinking is especially suitable for the production of small lines. It can be crosslinked after high-speed extrusion, which is higher than the production speed of chemical crosslinked small lines

the most widely used product in radiation crosslinking processing is crosslinked polyethylene (XPE). After radiation crosslinking of PE, its maximum working temperature in wire and cable materials can be increased from 140 ℃ to 250 ℃ [23]. Another feature is the "memory effect", which has been made into heat shrinkable materials for large-scale use [24]. In organic PTC (positive temperature coefficient of electricity) materials, when the temperature exceeds the melting point of polymer materials, NTC (negative temperature coefficient) effect will appear, while radiation crosslinked pe/cb materials can not only reduce or even eliminate NTC effect, but also maintain the stability of organic PTC materials after multiple electrothermal cycles

radiation processing technology in China is a high-tech developed in recent 20 years, especially the wide application of high-power electron accelerators with a power of more than 50KW and 60Co sources with a power of more than 100000 Curies, which has promoted the continuous development of radiation processing industry. Radiation crosslinked wire and cable is the pillar industry of radiation processing. After irradiation, polyolefin has significantly improved its various properties as cable material and widened its application scope, especially in the fields of computer control, household appliances, offshore oil drilling platforms, high-rise buildings, electronic and electrical products. With the development of petroleum exploration, aerospace, computer, communication, transportation and household appliance industries, it is also urgent to develop high-quality cables that can withstand harsh environmental conditions. Many research institutes, chemical plants and colleges and universities have successively carried out theoretical research on radiation chemistry, applied basic research on radiation crosslinked polyolefins and material formulation research

nevertheless, the wires and cables currently developed in China have poor thermal stability, short service life and few varieties, which are far from meeting the market demand. In particular, radiation crosslinked polyolefin wires and cables with heat resistance of 150 ℃ and radiation resistant cables have not yet passed the test, so that the consumption of such products in China can only be replaced or imported with expensive fluoroplastic insulated wires, which costs tens of millions of dollars of foreign exchange every year

when LDPE is in contact with some surface active substances, it is easy to produce cracks under the action of external forces, so its application range is limited. In many cases, LDPE can no longer meet the requirements of materials, and HDPE must be used, such as medium temperature self limiting heating wire and cable and wire and cable materials with higher temperature levels. Therefore, the research of crosslinking materials based on HDPE is also very important. Moreover, the degradation mechanism of HDPE and LDPE after irradiation may also be different

with the development of society and the needs of mankind, the requirements for materials are higher and higher. On the one hand, people develop new polymer materials, and on the other hand, they use existing polymer materials for blending and modification. The research shows that when the blended polymer material is irradiated by high-energy rays, the components affect each other, which mainly depends on the compatibility in addition to its own factors [6]. Radiation modification of polyolefin blends has been studied for a long time and has been applied in many aspects. It can not only improve its properties, but also control the morphology in the processing process


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author unit: School of chemistry and chemical engineering, Shanghai Jiaotong University, Shanghai Key Laboratory of electrical insulation and thermal aging; Postal Code: 200240

* Shanghai major scientific and technological research project project No.:

* * communication contact: Jiang Pingkai, Professor, doctoral advisor; Email: pkjiang@(end)

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