Background ultraviolet light deterioration is the process in which the strength of a geotextile is damaged or reduced due to exposure to sunlight. When considering the cosmic ultraviolet background, each of these bands samples many different regions.

The type of geotextile and the location of exposure will affect the time it will take to degrade the geotextile. The deterioration is the same for all polymer materials. Deterioration from ultraviolet light happens when energy from the sun breaks the bonds inside the polymer structure. The energy from sunlight can be divided into three categories by wavelength (ultraviolet, visible and infrared).

Wavelengths above 400 nm form visible, infrared light but do not cause deterioration of the polymers used in geotextiles. For popular polymers used in geotextiles, the deterioration is usually caused by wavelengths in the UV range which is less than 400 nm.

Photons with longer wavelengths than the needed wavelength for any bond making up the molecular chains will not have an effect on the chemical structure and will not cause deterioration. Wavelengths that are less than 280 nm can be very damaging to polymer materials but are filtered by the earth’s atmosphere so they are not considered a factor.

There are several variables or fluctuations that affect the UV stability of geotextiles regarding the exposure of fabric and the environment. The local environment will have a significant impact on the rate of UV deterioration in respect to the intensity of sunlight and the temperature. Even the exposure of a slope’s orientation toward the sunlight can make a difference.

Through tests that were performed on Propex, geotextiles were exposed in three different locations in the U.S. Across the board, the southwestern area of the U.S is more severe than the southeastern area and the level of deterioration is a great deal less in the north. Manufacturers add a variety of stabilizers to geotextile fibers and yarns to increase stability. The level and nature of these stabilizers have an impact on the overall stability of the fabric. UV penetrates into the yarn or fiber from the surface toward the core.

Therefore, a larger diameter of fiber or yarn will degrade more slowly than a smaller diameter of the same composition. Woven geotextiles have a much coarser yarn which will degrade at a much slower pace than non-woven geotextiles. Since UV deterioration starts at the surface of geotextiles, a thicker fabric will also deteriorate at a much slower pace than thinner fabrics. Therefore, Propex non-woven Geotex® 801 (around 8 oz/sq. yd) will deteriorate a lot slower under the same conditions as Geotex® 351 (4 oz/sq. yd). Also, the difference in the deterioration rate is less obvious for non-woven geotextiles that are around 9 oz per square yard.

The standard process for analyzing the stability of UV in geotextile is provided in ASTM D-4355. For this process, the xenon-arc light source is used and specimens are exposed to the light under controlled conditions of temperature and humidity. This light source is very much like natural sunlight in the UV range. There are also exposure methods that use fluorescent light sources but are not approved for use on geotextiles. The xenon-arc exposure test is only considered an index test and the results cannot be used directly for the end use.

Although there seems to be a correlation between xenon-arc exposure and outdoor exposure, the results cannot be used directly. The test uses a combination of high light intensity and elevated temperatures to degrade the specimens at a quicker pace than would actually take place in a natural environment during the same period of time.

Samples are exposed for 500 hours and after exposure, a two-inch strip tensile strength (ASTM D-4632) is tested. This fabric is then compared to the properties of the unexposed fabric to determine the percentage of the original strength retained over a set period of time. Nationally recognized AASHTO M 288 specifications for geotextiles used in highway applications require minimum strength retention of 50% after 500 hours of exposure, vs the exposure of silt fence which should be 70% after 500 hours. All Propex geotextiles are stabilized to offer at least 70% strength retention after 500 hours exposure according to ASTM D-4355.

The best way to prevent UV light from deteriorating the geotextile is to prevent sunlight from reaching the fabric. Once the fabric is covered in soil, asphalt, or other material, the possibility for degradation will be removed. That said, the geotextile should be covered as soon as possible once the protective wrapper has been removed. Manufacturers of geotextile add stabilizers to the resin used to make geotextiles. These stabilizers make the polymers a great deal more stable to prevent UV light deterioration.

Stabilizers will limit the amount of deterioration for standard times but will not provide protection for extended periods of time. Project specifications should be in writing to limit the exposure to a maximum of 14 days in order to minimize UV degradation. If there will be longer required exposure times, samples of the exposed fabric should be tested from time to time to verify that a destructive amount of strength has not taken place. When shipped, the protective wrapper on rolls of geotextile should remain in place until the material has been installed.

To help prevent erosion on a slope as well as let vegetation grow on that slope.

All orders ship for free. Curlex ships from TX and Wisconsin; Landlok 450 and Pyramat ship from TN.

It depends on how temporary or permanent a solution you want, and how steep the slope is. Use the Erosion Control Product Finder above to match a mat to your project, or call us at Eastgate Supply to talk it through.

Each of the TRM product lines above has installation instructions on its individual page. Please click on the product to find the installation guides.