Extended UV exposure causes fading or color changes in thermoplastics, but the effects are not limited to appearance. Prolonged exposure typically leads to plastic degradation, making it brittle, prone to cracking, and reducing its mechanical strength.
Let's start by examining what happens when your product is exposed to sunlight:
UV degradation in thermoplastics occurs when UV radiation breaks chemical bonds in the polymer chains. This bond scission weakens the material and allows oxygen to react with the fragmented molecules. The phenomenon, known as photo-oxidation, accelerates the degradation process.
The initial effects are seen at the surface, where UV light and oxygen concentrations are highest. As the surface breaks down, the effects penetrate deeper into the material.
Additionally, many plastics contain stabilizers, pigments, and other additives, which can also degrade due to UV exposure, causing color changes (fading) and making the material more susceptible to various environmental factors.
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When designing a plastic product exposed to UV light, consider these factors and tips to ensure durability, functionality, and long-term aesthetic appeal.:
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Please keep in mind that all thermoplastics are sensitive to UV light, though some are more affected than others. This is an important consideration in every design project.
Consider the amount of UV light your product will be exposed to, as well as the duration of exposure. Take into account different market regions. For instance, is your product used in high-UV areas like Australia or California.
Test the material candidates in a UV chamber. Changes in color and surface are easy to detect, but it’s also essential to examine how UV exposure affects ductility and mechanical strength. The first sign of degradation is often crazing (small cracks), followed by chalking or surface erosion.
Opt for materials with inherently good UV resistance, such as PA6, PBT, PMMA, or ASA.
Avoid general-purpose grades of UV-sensitive materials, such as PC, ABS, or HD-PE.
Leverage the expertise of your material supplier. Almost all polymers are available in UV-modified versions. While blockers, stabilizers, and absorbers do not eliminate UV effects, they significantly extend the product's lifetime by delaying degradation.
UV-modified grades of colorants are also available. Opt for darker colors, as they block UV light more effectively than lighter tones. A visual shift from black to grey is often more acceptable than changes from white to yellow or red to pink. Carbon black is an efficient UV blocker.
Look for a reference product that has survived under similar conditions for an extended period and learn from its material selection and robustness.
Indoor lighting (especially halogen lights) emits some UV light, which may not be enough to degrade your product but can cause color changes. This is particularly important in medical products, where you don't want white components to turn yellow.
Coating may be an option. For example, motorcycle visors are silicate lacquer coated polycarbonate.
Wishing you success with your project!
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