Sofia Martinez
Ultraviolet (UV) radiation from the sun can be harmful to both people and objects, causing degradation, discolouration, and brittleness over time. While no plastic is entirely protected against UV rays, many plastics offer excellent levels of UV resistance, increasing lifespan and preventing elongation. Factors such as thickness, coatings, and additives like blockers, absorbers, and stabilizers can enhance a plastic's ability to block UV radiation. Polycarbonate, for instance, is a popular choice for UV protection due to its impact resistance and ability to withstand outdoor use.
| Characteristics | Values |
|---|---|
| Plastic protection from UV rays | Varies depending on the type of plastic and its thickness, coatings, and additives |
| Plastic degradation from UV rays | UV radiation can cause plastics to degrade, discolour, or become brittle over time |
| Factors influencing UV protection | - Type of plastic: Polycarbonate, acrylic, PVDF, PAI, and polyester are known for their UV resistance - Thickness: Thicker plastic sheets generally provide better UV protection - Coatings: Clear plastics with UV-resistant coatings can block UV radiation and extend the material's lifespan - Additives: Blockers, absorbers, and stabilizers can be added to plastics to protect against UV radiation |
| Examples of plastic with good UV resistance | - Polycarbonate: Used in protection shields and bullet-resistant applications - High-density polyethylene (HDPE): Used in children's outdoor playground equipment - FRP: A thermosetting plastic with glass fibre reinforcement and additives, used in outdoor structures and components - PVDF: Offers thermal stability, abrasion shielding, and protection against UV radiation |
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What You'll Learn
Thickness of plastic sheets
While plastic sheets can protect against UV rays, it is important to note that no plastic is entirely protected against UV rays and radiation. The sun's UV rays can break down chemical bonds in polymers, causing plastics to wear down and disintegrate over time, known as photodegradation. Photodegradation can cause discoloration, particularly yellowing or whitening ("chalking"), resulting in a loss of strength and increased brittleness.
Polycarbonate sheets, for example, are commonly used for roofing and provide protection from UV radiation. They block the entire relevant UV spectrum, including both UVA and UVB rays. Even a thin sheet of polycarbonate can absorb UV rays, offering better protection than sun protection cream. However, the absorption of UV radiation can lead to discolouration and a decrease in the sheet's performance over time.
To address this issue, manufacturers apply a protective layer to the polycarbonate sheets. This UV protection is intended to preserve the sheet's integrity and performance rather than shield those underneath it from UV rays. The protective layer is invisible and does not affect the sheet's physical or optical characteristics.
When selecting plastic sheets for UV protection, it is essential to consider the specific application and project requirements. Components for outdoor use or industrial applications typically demand higher UV resistance to maintain optimal quality and performance.
In addition to polycarbonate, other UV-resistant plastics are available on the market, such as PAI and PVDF. PAI offers strength, stiffness, wear resistance, and low friction qualities, but it is expensive and requires additional curing processes for full UV protection. PVDF, on the other hand, provides excellent thermal stability, abrasion shielding, and resistance to chemicals and UV radiation. It comes in two forms: homopolymer and copolymer, each offering unique advantages in terms of strength and impact resistance.
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UV-resistant coatings
The UV resistance of a coating determines its ability to withstand ultraviolet radiation, such as sunlight. Coatings used outdoors must be UV-resistant. Rilsan®, Halar®, and ETFE are examples of coatings that can withstand higher doses of sunlight.
Some companies, such as SyBridge Technologies, offer UV-resistant plastics that incorporate these additives. For example, PVDF is a UV light-resistant plastic with high thermal stability, abrasion resistance, and protection against chemicals and UV radiation. It is commonly used in chemical tank liners and semiconductor equipment. PAI is another UV-resistant plastic known for its strength, stiffness, and wear resistance. However, it tends to be more expensive and may require additional post-curing processes to maximize its potential.
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Plastic additives
While plastic is prone to UV damage, there are several plastic additives that can be used to improve UV resistance. These additives can be stabilizers, absorbers, or blockers.
Stabilizers are chemical agents that prevent the rupture of polymer bonds by dissipating UV radiation, yielding lower UV levels that won't harm the polymer. Hindered Amine Light Stabilizers (HALS) are common stabilizers that convert excited UV reactions into stable chemical reactions.
Absorbers are organic compounds that absorb UV light and emit it as less harmful wavelengths, such as heat. Benzophenones and benzotriazoles are commonly used absorbers. Benzotriazoles have a minimal impact on the colour of materials and can be used in low doses, often in conjunction with acrylic and polycarbonate to maintain transparency. Benzophenones, on the other hand, are combined with polyvinyl chloride (PVC) and polyolefins, as these plastics are not very UV-resistant.
Blockers provide a protective layer that blocks UV light from reaching the plastic. Carbon black is a commonly used blocker that can block UV rays at a rate of about 2%. Titanium dioxide is another effective blocker that is often used as a pigment.
Additionally, some plastics have inherent UV resistance. Acrylic, also known as Polymethyl methacrylate (PMMA) or plexiglass, is a transparent plastic that exhibits only 3% degradation over a decade when used outdoors. It is scratch-resistant and durable, making it a popular choice for long-term outdoor applications like signs, displays, and light fixtures. Nylon, a thermoplastic, is another UV-resistant plastic that is highly resistant to wear, heat, and chemicals.
Furthermore, specific forms of plastics like PVDF offer excellent UV resistance along with thermal stability and abrasion shielding. Homopolymer PVDF has higher strength and stiffness, while copolymer PVDF offers superior impact and stress crack resistance.
By using these plastic additives and choosing inherently UV-resistant plastics, manufacturers can improve the longevity and performance of their products, especially for outdoor applications.
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Plastic types
While no plastic is entirely protected against UV rays and radiation, many plastics offer excellent levels of UV resistance. These plastics increase lifespan, prevent elongation, and fight the effects of photodegradation such as discolouration, loss of strength, and increased brittleness.
- Polyvinyl Chloride (PVC): This plastic is not very resistant to UV light on its own. However, when combined with benzophenones, a UV-resistant additive, it can become more resistant.
- Polyolefins: Similar to PVC, polyolefins are not inherently UV-resistant. They are often combined with benzophenones to increase their resistance to UV rays.
- Polycarbonate: Also known by the trade name Lexan®, polycarbonate is a thermoplastic with impressive impact resistance—250 times greater than glass. It can be used outdoors when UV-stabilized.
- High-Density Polyethylene (HDPE): HDPE is a plastic that offers a good combination of stiffness, durability, and impact resistance. Since it cannot be damaged by UV rays, it is frequently used in the design of children's outdoor playground equipment.
- Polyetherimide (PEI): PEI is a common choice for industrial and automotive applications. It is highly UV-resistant, flexible, rigid, and has a high deflection temperature. It can be made to be either transparent or translucent.
- Polyamide-Imide (PAI): PAI has excellent strength, stiffness, wear resistance, and low friction qualities. It is often used for magnet wires, surgical instruments, and other parts that require tight tolerances and dimensional stability over time. However, it is expensive and often requires pricey post-curing processes to achieve its full potential against UV rays.
- Polyvinylidene Fluoride (PVDF): PVDF is a UV light-resistant plastic that offers incredible thermal stability, abrasion shielding, and protection against chemicals and UV radiation. It is easy to weld thanks to its high heat resistance. It comes in two forms: homopolymer PVDF, which has higher strength and stiffness, and copolymer PVDF, which offers superior impact and stress crack resistance.
- Fibre-Reinforced Plastic (FRP): FRP is a thermosetting plastic with glass fibre reinforcement. It has excellent UV resistance and is often used in the manufacturing of structures and structural components for outdoor use.
- Acrylic: Acrylic is one of the top options for UV resistance. Over ten years, it can have as little as 3% degradation, depending on the application.
Caring for Your Plastics
To ensure your plastic products maintain their UV resistance for as long as possible, it is important to care for them properly. Here are some tips:
- Avoid using products that could dull the plastic finish, such as alcohol or solvents, when cleaning.
- Protect the plastics from heat damage, such as setting hot items on outdoor furniture.
- Routinely hose off the items to remove surface dirt.
- Use cleaners designed for the specific type of plastic you have.
- Avoid activities that could scratch the surface of the plastic.
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Environmental factors
To mitigate the effects of UV radiation, various types of plastics with UV resistance are available. Polycarbonate is a popular choice for UV protection due to its impressive impact resistance and ability to block UV rays effectively. High-density polyethylene (HDPE), a plastic commonly used in children's outdoor playground equipment, is another option that is not susceptible to damage from UV rays. Additionally, additives such as blockers, absorbers, and stabilizers can enhance UV resistance in plastics. Blockers like carbon black and titanium dioxide provide protective coatings, while absorbers like benzophenones and benzotriazoles emit less harmful wavelengths of energy. Stabilizers, including hindered amine light stabilizers (HALS), prevent polymer bonds from rupturing due to UV radiation.
The thickness of plastic sheets also influences their UV protection capabilities, with thicker sheets generally providing better UV protection. Clear plastics with UV-resistant coatings can enhance their ability to block UV radiation and extend their lifespan. However, it's important to consider the specific needs of a project, as some applications may require higher UV resistance than others. For instance, polyester is suggested as a suitable candidate for UV exposure due to its chemical structure. Conversely, polypropylene is not recommended for projects exposed to UV rays because of its high degradation rate.
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