Causes of aging of wire and cable can be analyzed from internal and external causes.
1) Internal Cause
1 The chemical structure of polymer materials: The chemical composition of macromolecules, the degree of unsaturation of the chain, and the proportion of each component of the copolymer can affect the aging properties of the polymer. For example, C—F and Si—O bond energy is high and it is not easy to break, so PTFE and silicone resins have good aging resistance; polypropylene contains a large number of tertiary carbon atoms, and hydrogen on tertiary carbon atoms is easily oxidized. Polypropylene has poor aging properties. As another example, natural rubber contains a large number of double bonds, so its aging is not as good as saturated rubber.
2 The physical structure of polymer materials: molecular weight and molecular weight distribution, aggregation state (crystallization, orientation, glassy, ​​highly elastic, and amorphous state) also affect the aging of polymers. The polymer has a high degree of crystallinity or is in a glassy state because macromolecular segments are immobilized, cannot move autonomously, and active groups are immobilized, making them resistant to chemical solvents and acids and bases and slowing down the aging process. Thermoset plastics, for example, form a bulk structure after curing, and have better resistance to aging than they did before they were cured.
3 Compounding agents and impurities: Some low-molecular additives, such as plasticizers, may slowly volatilize to accelerate aging, and some of the initiator residues may also accelerate the aging process.
2) External factors
1Physical factors: including sunlight, heat, electricity, force and high-energy radiation, of which light and heat are the main ones. For example, different polymers can absorb different wavelengths of sunlight, and photochemical reactions occur, resulting in the breakdown of chemical bonds.
2 chemical factors: including oxygen, ozone, salt spray, acid, alkali, salt and other chemical reagents, corrosive gases. Among them, oxygen is the main one, and polymers are susceptible to oxidation and destruction. Ozone cannot be ignored in high-voltage insulation.
3 biological factors: microorganisms, molds, termites, insects and so on. Such as termites, etc. eat food materials.
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