How does the performance of vitrified polyolefin cable material deteriorate when exposed to ultraviolet radiation for a long time?
Release Time : 2025-12-15
The performance degradation of vitrified polyolefin cable material under long-term ultraviolet (UV) irradiation is a complex process involving molecular structure, chemical bond breakage, additive failure, and physical morphological changes. UV light, as a high-energy light wave, can penetrate the material surface and directly act on the chemical bonds in the polyolefin molecular chain, initiating a photo-oxidation reaction and leading to performance degradation from the microscopic to the macroscopic level.
The core function of UV irradiation is to trigger the photo-oxidative degradation of the polyolefin molecular chain. The main chain of polyolefin materials consists of carbon-carbon single bonds and carbon-hydrogen bonds. These chemical bonds have low bond energies and are easily excited by high-energy photons (wavelength 200-400 nm) in UV light, causing bond breakage and the generation of free radicals. These free radicals, as reactive intermediates, further react with oxygen in the air to generate polar substances such as peroxides, aldehydes, and ketones. These degradation products destroy the chemical structure of the material, gradually transforming it from its original insulating state to a conductive or semi-conductive state, significantly reducing its insulation performance. For example, cross-linked polyethylene (XLPE), which originally had high insulation resistance, may experience a decrease in insulation resistance by several orders of magnitude under long-term UV irradiation, losing its electrical isolation function.
Ultraviolet (UV) radiation also accelerates the degradation of additives in materials. Polyolefin cable materials typically contain antioxidants, plasticizers, and other additives to improve their heat resistance, flexibility, and processability. However, these additives can volatilize or decompose under UV exposure. For example, antioxidants are gradually consumed during the absorption of free radicals; when their concentration drops below a critical value, the material loses its antioxidant protection, accelerating the thermal aging process. The volatilization of plasticizers causes the material to harden and become brittle, losing its original flexibility and becoming prone to cracking under bending or vibration, further weakening its insulation performance.
The synergistic effect of UV radiation and high temperature exacerbates the thermal aging of materials. Outdoor cables exposed to direct sunlight may have surface temperatures significantly higher than ambient temperatures, especially in summer, when the surface temperature of black cables can reach high levels. High temperatures accelerate the movement of polyolefin molecular chains, increasing free volume and ionic conductivity, leading to a further decrease in insulation resistance. Simultaneously, high temperatures promote the formation of photo-oxidation products, creating a vicious cycle that causes significant performance degradation of the material in a short period. For example, cables exposed to high temperatures and ultraviolet radiation for extended periods may experience a significant decrease in tensile strength and a marked reduction in elongation at break, failing to meet mechanical performance requirements.
UV radiation also alters the surface morphology of materials. During photo-oxidative degradation, polyolefin materials exhibit surface cracking and powdering. Cracking, caused by uneven surface shrinkage, creates microcracks that act as channels for moisture and chemical substances, accelerating the deterioration of the internal insulation layer. Powdering results from the shedding of degradation products from the material's surface, manifesting as a white powdery substance. This powder reduces the material's surface resistivity, increasing the risk of leakage. Furthermore, UV radiation causes color changes, gradually shifting the material from its initial black or gray to yellow or brown, a direct manifestation of the accumulation of photo-oxidative products.
The degradative effect of UV radiation on vitrified polyolefin cable material is also evident in its long-term cumulative effect. Even at low UV intensities, prolonged exposure will gradually degrade material performance. This cumulative effect is particularly pronounced in outdoor cables, which typically withstand decades of environmental erosion. Over time, the insulation, mechanical properties, and weather resistance of materials will decline, eventually leading to an increase in cable failure rate and a shortened service life.