Polycarbonate is a strong, lightweight, and transparent thermoplastic material often chosen for outdoor applications like roofing, greenhouses, and protective glazing due to its high impact resistance. Although it offers advantages over traditional glass, it is susceptible to the sun’s ultraviolet (UV) radiation, which initiates material breakdown. Understanding how long polycarbonate lasts requires examining this degradation process and the factors that determine its longevity.
The Process of UV Degradation in Polycarbonate
The core limitation of polycarbonate in sunlight is its sensitivity to specific UV radiation wavelengths, triggering photodegradation. High-energy UV photons break the polymer chains, causing the material’s molecular weight to decrease over time. This chain scission reaction reduces the plastic’s strength.
This chemical breakdown first manifests visually as yellowing and hazing, caused by the formation of degradation products like quinones. UV radiation primarily affects the surface layer, penetrating only about 25 micrometers deep. The decrease in molecular weight makes the surface brittle and prone to cracking or chalking. Photo-oxidation, occurring in the presence of oxygen, further accelerates this breakdown, reducing impact strength.
Factors Determining Polycarbonate Lifespan Outdoors
The outdoor lifespan of polycarbonate ranges from a few years to more than two decades, depending on environmental and material factors. The most important factor is the presence and quality of a factory-applied UV protective layer. Untreated or low-quality polycarbonate can show yellowing and embrittlement in as little as five to seven years.
High-quality sheets with co-extruded UV protection are engineered for long-term resistance, often lasting 10 to 20 years, with some products warranted up to 25 years. This layer absorbs damaging UV rays before they reach the core material. Geographical location also plays a significant role, as areas closer to the equator or at higher altitudes accelerate the rate of degradation.
The specific climate contributes to endurance, as high heat and moisture accelerate damage. Thermal cycling, the repeated expansion and contraction from temperature swings, physically stresses the material.
Strategies for Maximizing Longevity
The most immediate action during installation is confirming that the UV-protected side of the sheet is oriented outward, directly facing the sun. Manufacturers clearly label this side, and improper installation drastically reduces the lifespan to that of an uncoated sheet.
Regular, gentle cleaning prevents the accumulation of dirt, debris, and pollutants that can compromise the UV coating. Cleaning should involve mild soap and water, using a soft cloth or sponge. Avoid abrasive cleaners, scrapers, or high-pressure washers. Harsh chemicals, especially those containing ammonia, should never be used as they can chemically damage the material.
If a sheet lacks factory protection or the existing coating is compromised, aftermarket solutions can be applied. These include specialized UV-blocking liquid coatings or adhesive protective films against solar radiation. Incorporating physical shading elements, such as awnings or placement under tree cover, can significantly reduce daily UV exposure.