Ethan Clarke
Plastic is a versatile material with a wide range of applications. However, its exposure to ultraviolet (UV) radiation can lead to degradation, causing aesthetic and structural issues such as yellowing, bleaching, and brittleness. This raises the question: How well does plastic block UV rays? The answer is that it depends on the type of plastic and the presence of additives. Some plastics, like polycarbonate, are highly effective UV blockers, while others, such as polypropylene, lose strength rapidly when exposed to UV. Acrylic, a popular choice for UV protection, can block up to 98% of UV rays but varies in effectiveness depending on additives and manufacturing processes. Overall, while some plastics offer substantial UV protection, the specific composition and treatment of the material play a crucial role in determining its UV-blocking capabilities.
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What You'll Learn
UV-resistant plastics
Plastics are highly susceptible to UV damage, which can cause discolouration, a loss of tensile strength, and make the plastic brittle and prone to cracking. However, some plastics are more resistant to UV damage than others.
Acrylic is one of the few manufacturing materials that is inherently UV-resistant. It is a transparent plastic that suffers as little as 3% degradation over a 10-year period when used outdoors. It is also a popular choice for outdoor signs and displays, light fixtures, decorative panels, and coloured lenses due to its good scratch resistance. However, it is not very strong and is rarely used for load-bearing parts.
Polycarbonate is another plastic that offers relative UV resistance, along with being incredibly impact-resistant and far stronger than acrylic. It is also comparable to acrylic in terms of transparency and is tolerant of major temperature fluctuations. These qualities make polycarbonate a good choice for heavy-duty products such as helmets, safety goggles, shields, and safety windows. However, it is more expensive than many other materials.
HDPE, or high-density polyethylene, is a thermoplastic that is often used in playground equipment due to its durability and soft qualities. It is also extremely resistant to acids, alcohols, and bases. However, untreated HDPE will become extremely weak after 6-24 months of sun exposure.
Other plastics that offer some degree of UV resistance include PAI, a high-performance thermoplastic with exceptional UV resistance and good malleability; PVDF; PTFE; and polyester, including PET.
The UV resistance of plastics can also be improved by adding UV stabilizers or blockers such as carbon black, titanium dioxide, benzophenones, benzotriazoles, and HALS (Hindered Amine Light Stabilizers).
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UV degradation in plastics
Ultraviolet (UV) radiation can cause degradation in plastics through physical and chemical changes. The degradation effects of UV are of great concern to manufacturers and users of materials that are intended for use and storage outdoors and are exposed to sunlight. UV degradation in plastics can be avoided by using stabilizers, absorbers, or blockers. For outdoor applications, carbon black can be added at around a 2% level to provide protection by the blocking process. Other pigments such as titanium dioxide can also be effective. Organic compounds such as benzophenones and benzotriazoles are typical absorbers that selectively absorb UV and re-emit at a less harmful wavelength, mainly as heat.
The photochemical effect of UV radiation within the polymer structure can lead to degradation of the material. This can cause a chalky appearance and a color shift on the surface of the material, and the component surface becomes brittle. Polypropylene (PP) and low-density polyethylene (LDPE) are two types of polymers at increased risk of degradation due to the interaction of ultraviolet rays with tertiary carbon bonds within their chain structure. This then reacts with oxygen in the atmosphere, producing carbonyl groups in the main chain, and the exposed areas become prone to cracking or discoloration.
The extent of plastic degradation depends on both the weathering mechanism and the material. Environmental factors such as exposure to UV irradiation and elevated temperatures affect the breakdown of plastics in aquatic environments. Studies have shown that weathering of plastics results in the release of micro- and nanoparticles.
UV filtering acrylic is a popular solution that can filter out up to 98% of harmful UV light, making it ideal for protecting artwork, paper, or other keepsakes that can turn yellow, fade, and become brittle. However, not all UV filtering plexiglass sheets are created equally, as some block more UV rays than others, and some even filter out harmful visible light rays.
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UV-resistant plastic applications
Plastics are widely used in a variety of applications, but they are prone to degradation from UV radiation. This degradation can cause discolouration, loss of strength, and brittleness. To mitigate this, UV-resistant plastics are developed, either inherently or through additives, to provide protection for the plastic and the underlying product.
One of the most commonly used UV-resistant plastics is acrylic. Acrylic is popular due to its inherent UV resistance, with only about 3% degradation over a decade. It is also optically clear, scratch-resistant, and can be used as a replacement for glass. These qualities make it ideal for signage, displays, light fixtures, decorative panels, and lenses. However, its rigidity and lack of strength limit its use in load-bearing applications.
High-Density Polyethylene (HDPE) is another commonly used UV-resistant plastic. It is durable yet easily meltable and mouldable, making it suitable for a wide range of applications. HDPE is resistant to acids, alcohols, and bases, and is often used in playground equipment, outdoor furniture, containers, and pipes.
Polycarbonate is a strong and impact-resistant UV-resistant plastic. It is more expensive than other options but offers excellent resistance to UV radiation. Polycarbonate is used in applications such as goggles, face shields, windows, and containers, where its strength and clarity are advantageous.
Other UV-resistant plastics include PTFE, a fluoropolymer used in bearings, non-stick surfaces, and gaskets, and Polyetherimide (PEI), a flexible and rigid plastic used in industrial and automotive applications.
In addition to these inherent UV-resistant plastics, additives can be used to enhance the UV resistance of other plastics. Carbon black, titanium dioxide, benzophenones, and benzotriazoles are common additives that act as blockers or absorbers of UV radiation. These additives are combined with plastics that have poor UV resistance, such as PVC and polyolefins, to improve their performance in outdoor applications.
UV-resistant plastics are essential in a wide range of industries, including transportation, agriculture, construction, and recreation. By selecting the appropriate plastic and considering factors such as impact resistance, strength, transparency, and weather resistance, products can be designed to withstand the degrading effects of UV radiation.
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UV-transmitting acrylic
There are two types of clear acrylic: UVA (ultraviolet absorbing) and UVT (ultraviolet transmitting). While the former is more popular and widely used, the latter is important in applications where UV-A and UV-B light transmission is required. UVT acrylic is transparent to UV light and offers superior quality and clarity. It has excellent light transmission and weatherability, and is unaffected by sunlight. UVT acrylic resists ageing and maintains stability under variable conditions of heat, cold, moisture and other exposures. It will not warp, crack, craze or corrode.
UVT acrylic is half the weight of comparable glass and has good shatter resistance and excellent durability. Acrylic polymers are among the most light-stable transparent plastics due to their exceptionally low absorption of light. They are almost totally transparent to all visible light and to long-wavelength ultraviolet light (UV light with a wavelength greater than 290 nanometres).
UVT acrylic has no ultraviolet filtering chemicals, so it transmits ultraviolet light as low as 290 nm. In contrast, UVA acrylic has additives incorporated within the polymer that block out most ultraviolet light.
UVT acrylic is available in various specifications, including ASTM D-4802, ASM-L-P-391, MIL-P-8184, and MIL-P-25690.
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UV protection
The effectiveness of plastic as a UV blocker depends on several factors, including the type of plastic, the presence of additives, and the wavelength of UV radiation.
Not all plastics are created equal when it comes to UV protection. Some plastics, such as polycarbonate, are known for their superior UV-blocking abilities, while others, like polypropylene, are more susceptible to degradation when exposed to UV rays. Polyester, which is a family of plastics with varying characteristics, generally exhibits good UV resistance compared to polypropylene.
The presence of additives can significantly enhance the UV-blocking properties of plastic. Carbon black, for instance, can provide protection by blocking UV rays when added at around a 2% level. Other pigments, such as titanium dioxide, and organic compounds like benzophenones and benzotriazoles, act as absorbers by selectively absorbing UV radiation and re-emitting it at less harmful wavelengths. Additionally, stabilizers like Hindered Amine Light Stabilizers (HALS) prevent the chemical reaction of free radicals, thereby inhibiting degradation.
The transmission edge for different plastics is typically around the 365-400 nm zone. UV filtering acrylic sheets are popular and can block up to 98% of UV rays with wavelengths shorter than 400 nanometers. However, it's important to note that not all UV filtering plexiglass sheets are the same, and some block more UV rays than others. Certain types of UV filtering sheeting, like UF3 acrylic and museum-grade acrylic, can even filter out harmful visible light rays in the lower violet range from 400 to 500 nanometers.
UV radiation can cause aesthetic and structural changes in plastics. Non-UV-resistant plastics may exhibit yellowing, leaching of dyed materials, surface bleaching, and cracking. These alterations can lead to increased project costs and downtime for component replacement. Therefore, it is essential to select the appropriate UV-resistant materials for specific applications.
In summary, while plastic can provide varying levels of UV protection depending on its composition and additives, it is not a complete blocker of UV radiation. The effectiveness of UV protection also depends on the specific type of plastic and the additives used.
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Frequently asked questions
It depends on the type of plastic. Some plastics can block up to 98% of UV light, while others are designed to transmit UV light.
Polyester is a good candidate for UV exposure. Acrylic is another plastic that blocks UV light.
UV transmitting acrylic allows up to 92% UV ray transmission.
UV energy absorbed by plastics can cause degradation, resulting in a chalky appearance, colour shift, and a brittle structure.
By using stabilizers, absorbers, or blockers. Carbon black, titanium dioxide, benzophenones, and benzotriazoles are commonly used to protect plastics from UV degradation.
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