Passing UV Light with Acrylic|
Article - March 6, 2016 By LarsonElectronics.com
Passing UV Light with Acrylic
Ultraviolet (UV) light has contrasting effects on plastics and glass, depending on the properties of the material. Acrylic is a widely used thermoplastic in mainstream and industrial sectors for lightweight covers, replacements for traditional glass and protective barriers.
Read on to learn about the robust properties of acrylic and its applications in marine environments, security and commercial lighting.
What is Acrylic?
Acrylic is a transparent sheet that is and composed of Methyl Methacrylate (MMA) and Poly Methyl Methacrylate (PMMA) resin. PMMA, also known as acrylic glass, can be broken down into the following types: extruded and cast. Extruded (or continuous cast) acrylic is manufactured by pushing the liquid plastic through rollers, where it is pressed and cooled down. This results in an impure acrylic variant that is softer and more prone to scratching, than cast acrylic. Cell cast acrylic is produced by pressing liquid plastic in a mold (usually made of glass). The final product is considered to be more expensive, compared to extruded acrylic, but is also more durable.
Compared to standard glass, the material is up to two times lighter; and at a thickness between 25 mm and 35 mm, it is bullet-resistant. Examples of this type of application can be seen in presidential escort vehicles, the pope mobile and armored transportation vessels. Acrylic does not degrade rapidly (turn yellow or brittle) and can last for several decades without showing signs of deterioration.
Perhaps the most advantageous property of the thermoplastic (for manufacturers) is its ability to be shaped. Cast acrylic can be machined to take on specific sizes and configurations. When customizing structures, manufacturers could create acrylic-based products without seams via chemical welding- resulting in one, solid piece. Mainstream applications of the material includes shower doors, windows and skylights.
Acrylic and UV Light
UV light has very little effects on acrylic, making it ideal for outdoor applications. The material can withstand persistent UV exposure for long periods of time. Acrylic glass is capable of transmitting UV bands, as low as 300 nm. This is relevant because irradiation by visible light between 400 nm and 500 nm has been proven to cause slight color fading and insignificant structural damage. UV bands between 300 nm and 400 nm can lead to similar, but more damaging effects. As wavelengths continue to get shorter, the damaging effects of UV light increases. Hence, UV irradiation at 300 nm is up to 200 times more dangerous, compared to blue-green light bands at 500 nm.
Acrylic boasts a refractive index standard of 1.49 to the sodium D line. This allows the panel to transmit up to 92 percent of light during application (with eight percent reflectance loss). The material absorbs short wavelengths of light in the UV range, while allowing longer wavelengths in the visible light spectrum to pass through.
Compared to plastics with thin, protective UV-resistant layers or coatings, acrylic-based sheets are thicker and more stable. Manufacturers may apply additives to the panel to promote UV absorption, when used for architectural or marine products. In the car manufacturing industry, acrylic is utilized during the production of rear tail-lights due to its ability to display colors accurately and resilient resistance to weathering, including UV light.
Acrylic versus Polycarbonate
In optical applications, acrylic is often paired against polycarbonate. When comparing light transmission rates, acrylic is more efficient (92 percent light transmission rate, as mentioned earlier) with polycarbonate only reaching up to 88 percent light transmission rate- and a refractive standard of 1.585. It is important to consider that manufacturers may increase light transmission levels of polycarbonate (in some cases, as high as 98.5 percent) by adding special coatings.
Polycarbonate is incredibly durable, but the material is prone to scratching at the surface. Acrylic offers better abrasion-resistant properties than polycarbonate, though coatings may also be applied to the latter material to reduce damage from scratching. Such coatings may improve the lifespan of polycarbonate sheets up to 25+ years for high-quality variants. Unlike glass, unsightly scratches on acrylic surfaces can be buffed out.
In high temperature environments, polycarbonate offers more resistance with a heat distortion temperature rating of 264 degrees Fahrenheit. Acrylic supports a heat distortion temperature rating of 200 degrees Fahrenheit under a load of 260 psi, but does not actually melt until 320 degrees Fahrenheit. Such properties suggest that polycarbonate is suitable for applications in structures that require stability. Furthermore, heat stability plays a salient role in the efficiency of various coatings. Hence, it is possible to incorporate more conductive layers or surfaces to polycarbonate.