Long-term use of PVC wire in humid environments can cause a series of physical changes due to a combination of moisture penetration, chemical reactions, and environmental factors. These changes directly impact its electrical performance, mechanical strength, and service life.
Moisture in humid environments can penetrate the PVC wire insulation through micropores or surface defects. PVC is inherently hygroscopic, and its rate of moisture absorption accelerates significantly under high temperature and humidity conditions. After moisture penetration, the gaps between the PVC molecular chains are filled with water molecules, causing the insulation layer to expand and microscopic cracks or blisters to appear on the surface. Long-term moisture absorption can also cause hydrolysis in the PVC material, breaking the molecular chains and making the insulation layer hard and brittle, losing its original flexibility and elasticity. These physical changes significantly reduce the insulation performance of the PVC wire and increase the risk of electrical leakage.
When PVC wire comes into contact with water in a humid environment, certain components in the material may undergo hydrolysis. For example, the plasticizer in the PVC insulation layer gradually precipitates under the action of moisture, causing the insulation layer to harden. At the same time, the ester or ether bonds in the PVC molecular chain may hydrolyze, producing small molecules such as carboxylic acids or alcohols. These products further degrade the material's chemical structure and accelerate the aging of the insulation. Furthermore, humid environments can trigger oxidation reactions in PVC wire, especially at high temperatures or in the presence of oxygen. Oxidative degradation occurs at the junctions between chlorine atoms and carbon atoms in the PVC molecular chain, causing discoloration and brittleness.
Microorganisms thrive in humid environments, and microbial activity on or within PVC wire can significantly impact its physical properties. The acidic metabolites secreted by microorganisms corrode the PVC material, destroying its molecular structure and causing mottling and corrosion marks on the insulation surface. Over time, microbial attack can also loosen the internal structure of the PVC wire, reducing its mechanical strength. This physical change not only affects the appearance of the PVC wire but also shortens its service life.
Moisture in humid environments can cause electrochemical corrosion on the surface of PVC wire conductors. This is particularly true for copper or aluminum conductors. The presence of salt or impurities can create a galvanic effect, accelerating the oxidation process. The formation of an oxide layer or corrosion products on the conductor surface increases contact resistance and localized overheating. Long-term corrosion can also reduce the conductor's cross-sectional area, increase resistance, and even cause short circuit failure. This physical change can severely affect the conductivity of PVC wire and increase the risk of electrical fires.
Temperature fluctuations in humid environments can exacerbate the thermal expansion and contraction of PVC wire. When PVC absorbs moisture, its coefficient of thermal expansion changes, resulting in greater internal stress during temperature fluctuations. Long-term, repeated thermal expansion and contraction can cause fatigue cracks in the PVC wire insulation and even separation from the conductor. This physical change can damage the PVC wire's structural integrity and reduce its resistance to environmental stress cracking.
Moisture and salt in humid environments can also corrode the PVC wire sheathing material. The sheathing material is susceptible to hydrolysis and aging in humid conditions, resulting in surface cracking, peeling, or discoloration. Physical damage to the sheathing reduces its protective effect on the internal conductor, making the PVC wire more susceptible to mechanical damage and chemical corrosion. This physical change shortens the overall service life of the PVC wire and increases maintenance costs. To mitigate the physical changes of PVC wire in humid environments, a series of protective measures are necessary. For example, choose PVC materials with better hydrolysis resistance or add a waterproofing agent; apply a waterproof coating or use a double-layer insulation structure on the PVC wire surface; keep the environment dry during storage and use, and avoid long-term exposure to moisture; regularly test the insulation performance and conductor condition of PVC wire, and replace aging wires promptly.
