What factors involves UV Light affect a plastic material ?
The UV Light Resistance of plastics involves a number of factors that can affect your material choice; there are three that figure most prominently: thickness, opacity, and the use of stabilizers. These three factors are combined to defend plastics against Ultraviolet (UV) light.
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What is Ultraviolet (UV) Light ?
Ultraviolet (UV) light is the light at shorter wavelengths than visible light. Among 3 types of UV lights, UVB usually does the most damage to plastics and is the type of light we need to test when checking plastic’s UV resistance.
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How UV Light degrades Plastics ?
Light degrades plastics by transferring its energy into the plastic. This energy can cause damage by creating heat, or this energy can actually break molecular bonds in a plastic’s structure. Both the heat and the breaking of bonds can create a loss of physical properties in the plastic. The higher energy of the UVB rays causes almost all UV damage in plastics. Regular visible light causes almost no degradation even over many years of exposure.
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Ways to improve UV Resistance:
Opacity
Plastics in opaque color are plastics that “light” do not pass through. In an opaque plastic the light has to break down the outer layer before it can break down the inner section of the plastic. The inner layer of plastic can retain its strength much longer the more opaque the plastic. If a plastic is completely black (or some other opaque color) then the light only acts on the surface and much less damage will occur over time. Most GeoSynthetic materials used for exposed sunlight are heavily loaded with carbon black or other pigments to make them opaque.
Thickness
Thicker materials allow the surface to suffer some UV degradation while still retaining the strength in the inner core material. In exposed lining materials a thickness over 40 mil (1.0 mm) is usually recommended for long term UV resistance. In materials where the strength is provided by a fabric (supported materials) an opaque coating of typically 0.4 mm (15 mils) on each side is required to prevent UV degradation of the fabric’s strength.
UV Stabillizer
The UVB light that attacks plastics creates reactive degradation byproducts that can cause a reaction of molecule damage that can accelerate the breakdown of the material. UV stabilizers are added to plastics to prevent these degradation byproducts from causing additional damage. UV stabilizers act as “sponges” to soak up these reactive byproducts and to stop the chain reaction before additional damage occurs.
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How long it last?
Each material is tested for UV Resistance; however each location where a industrial or agriculture is installed has a different UV exposure level. No two locations will get exactly the same amount of sunshine, and most locations do not get the same amount of sunshine from year-to-year. A test performed in Arizona or Florida may not be typical of the service life in your area. This makes it difficult to make general statements about UV resistance of materials.
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How UV Resistance tested ?
Typical UV tests quote ASTM G53, and state 500 hours or 2000 hours with 70% or 90% strength retained. Some tests will also state that a Xenon arc was used. Unfortunately this is not enough information to make a reasonable correlation to exposed life. There are a number of variations on the UV test methods, and there are many sources of UV light used in the test (Xenon light uses a number of different filters that can change the results). The best source of information is to look at actual exposure data collected from outdoor exposure tests.
There are two main outdoor exposure facilities in North America, one in Florida, and one in Arizona. At each of these facilities they expose plastic materials to the sun for extended periods of time, often with a series of mirrors of magnifying glasses to concentrate the sun onto the sample. The sun’s intensity is measured (in Langley’s) and a rating is given to the plastic material based on the number of Langleys it receives. Laboratory UV tests, such as ASTM G53 allows us to perform quality control checks on materials without having to perform 5 and 10 years tests outdoors.
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AmeriPacific Industrial Fabrics and Netting Products:
Each material contains UV Stabilizer abd has been carefully formulated for the maximum exposed lifetime for its intended usage. Please note that the values given are only approximate. The actual UV resistance rating of the material may vary considerably an is heavily dependant on the amount of sunshine received at the installation location.
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