A PU Tube, also known as a polyurethane hose, undergoes progressive physical and chemical changes when placed outdoors without shelter under long-term solar irradiation. The primary destructive factor is ultraviolet light in sunlight, which, together with outdoor high temperatures, rain, wind and sand, accelerates aging and failure of the tube. The entire aging process can be divided into three phases: early, middle and late, each with distinct observable characteristics.
Early-stage aging mainly brings subtle visual changes without functional failures. A brand-new PU Tube features a smooth, transparent surface and sufficient toughness. After 1 to 3 months of continuous sun exposure, surface gloss gradually fades, accompanied by whitening, hazing and slight yellowing. Transparent tubes turn cloudy, while colored ones fade and darken. At this point, molecular structures inside the polyurethane material have just started to suffer damage. Flexibility, pressure resistance and sealing performance remain largely intact. Only the surface material undergoes mild oxidation, which will not interfere with normal operation.
Mid-stage aging centers on attenuation of physical properties and gradual loss of functionality. After half a year to one year of continuous sunlight exposure, ultraviolet rays keep breaking polyurethane molecular chains and reducing crosslinking density. The PU Tube becomes noticeably harder, less flexible and harder to bend, with slower rebound and loss of its original softness. Fine microcracks and slight peeling emerge on the surface, and wear resistance decreases greatly. Debris easily flakes off upon friction. At this stage, tensile and pressure-bearing capacity declines. Deformation may occur under slight compression or bending, sealing stability of the pipeline weakens, and minor air or liquid leakage can occasionally happen.
Late-stage aging marks complete failure where the tube loses all usable value. More than one year of outdoor exposure, especially under intense summer sunlight and heat, doubles the aging speed. Tiny cracks expand into deep fissures, the outer layer peels off extensively and turns powdery, and the whole tube becomes brittle. Bending or light impact will lead to cracking or fracture. The material nearly loses all toughness, with compressive and impact resistance completely invalidated. Air leakage, liquid seepage and tube bursting frequently occur. Meanwhile, rainwater and temperature differences between day and night create extra damage. Water permeates molecular gaps and speeds up hydrolytic aging, and brittle cracking becomes even more severe in low-temperature environments.
It should be noted that ordinary unmodified PU Tube has poor weather resistance and ages rapidly under outdoor sunlight. UV-resistant and anti-aging modified outdoor-grade PU Tube can slow down aging, yet it cannot eliminate aging completely. It will still degrade gradually after long-term outdoor use, only with a much longer service life. Therefore, standard PU Tube is not recommended for long-term open-air application. For outdoor scenarios, protective sleeves or weather-resistant modified products should be selected.