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Weathering report: long-lasting synthetics

August 1st, 2013 / By: / Awnings & Shades, Markets

New technology can create more resilient,
longer-lasting synthetic fibers.

Synthetic turf has evolved dramatically since garnering mainstream attention for its use in the Houston Astrodome in the 1960s. Once used almost exclusively on playing fields, turf is truly changing the game in all types of applications ranging from golf courses and playgrounds to the house down the street.

Advancements in turf technology are to thank for an increased global interest; it now holds its color and characteristics longer and presents many cost-saving and environmental benefits. In water conservation alone, the owner of a full-sized synthetic turf playing field can expect to save anywhere from 500,000–1,000,000 gallons of water compared to a grass field. Add gas and labor savings into the equation, and the value only increases.

The synthetic fibers industry can learn much about weathering from the synthetic turf market because many of the technologies and methods developed in this area can be applied across all outdoor synthetic fiber applications, from umbrellas and awnings to geotextiles and truck or boat coverings. End product manufacturers (EPMs) can look to these advances when determining what is best for the fabrics in their products and how they will serve customers in various climate regions.

This article focuses on the nature of polymers, weathering test methods and predicting synthetic fiber performance in various climates—and how all of this can be applied to finding the right mix of additives and colorants to ensure the best long-term results for customers and protect against costly warranty claims

The nature of polymers

To ensure long-term performance, it is important for end product manufacturers to look at the factors that impact durability of synthetic fibers that outdoor fabric producers consider, including: radiant energy from sunlight, a broad range of fluctuating temperatures, humidity, oxygen (oxidation), rainfall and condensed moisture in the form of dew, particulate and gaseous contaminants, and stress (wear).

Levels of these parameters differ greatly among regions around the globe, so the climate in which the fiber will be used should be considered during the product design phase. For example, synthetic fibers outdoors in Arizona will weather at a faster rate than in the Netherlands because of significantly lower rainfall and humidity and higher ambient temperatures and total solar radiation.

and the polymer’s makeup have a profound effect on the long-term performance of synthetic fiber products. According to the Grotthus-Draper law of photophysics and photochemistry, absorption of radiation by any component in the synthetic fiber system can cause that component to degrade over time. Preventing the cause (absorption of radiation) will prevent the effect (degradation of the system).

By nature, all polymers absorb radiation and can be divided into two groups:

Polymers that absorb radiation through impurities. Impurities can occur when the colorant and the polymer are melted together during the extrusion process. For example, processing temperatures that are too high will increase impurities, degrading components and opening the door for radiation absorption when exposed to sunlight. Consequently, temperatures must be closely monitored lot-to-lot to ensure the consistency and performance/weatherability of the product.

Polymers that are built from monomers having chromophoric properties. Chromophores, such as aromatic rings, are chemical structures that absorb light to produce an “effect,” such as a color. The presence of chromophores in polymers will cause intensive absorption of UV light and will have negative effects on the performance of the product.

In either case, EPMs should not only look at their own processes, but also their suppliers. How colors are corrected and compounded—and at what temperatures—can have an effect on performance. Material and process quality should be monitored the entire way through the supply chain to achieve the best results.

If all polymers inherently absorb radiation, then it stands to reason that all polymers will need to be modified to withstand weathering—including polypropylene and linear low-density polyethylene (LLDPE).

Design testing

After examining the climate in which the fiber will be used and the methods in which it will be processed, product designs need to be tested and adjustments made to ensure the best performance.

There are two ways of testing how synthetic fiber will endure the test of time in outdoor applications: outdoor testing and accelerated testing in a lab. Outdoor weathering involves subjecting test samples to prolonged, real-world exposure to light, moisture and fluctuating temperatures. For the most comprehensive results, two or more test locations should be selected with extreme variances in weather conditions. Outdoor testing gives a real sense for how the fiber will weather in an actual application. The primary drawback is the time it takes to achieve actionable data—eight or more years, which is equal to the average warranty coverage for color fading and physical property retention. For this reason, fiber producers should conduct both outdoor and accelerated testing on products.

Accelerated testing answers the question: how many hours of lab-simulated weathering will it take to expose the fiber product to enough UV light to equate to one year outdoors in a certain global area? This depends on regional climate variances. The ultimate goal remains the same, however: determining how these environmental conditions impact the color, appearance and physical properties of the synthetic fiber product.

There are two accepted accelerated weathering test methods for synthetic turf: ISO 4892-3 using a QUV weathering tester or ISO 4892-2 using a xenon arc weatherometer. For the most accurate test results, the German DIN 18035-7 test standard with the ISO 4892-2 (xenon arc) test method is recommended. This approach is more comprehensive with the inclusion of total solar radiance, which encompasses near IR, UV light and visible light, as well as 18 minutes of water spray every two hours to simulate rainfall and the subsequent dry-off period.

Simulated rainfall is an important element of the test because it is more akin to real-life rain than the condensation method used in ISO 4892-3 (QUV), which can cause low-molecular weight components of the polymer, such as UV stabilizers and antioxidants, to migrate and wash away, causing flawed results. Using the xenon arc weatherometer, technicians can more tightly control relative humidity.

Warranty and predicted performance

Kilo-Langley (kL) is a unit of measure for penetrating radiation that, when used in combination with accelerated and outdoor testing, can be a useful tool in determining how synthetic fibers will perform in different climates. The earth is exposed to a minimum of 60 kL (arctic regions) to a maximum of 220 kL (Sahara Desert) of solar irradiation each year. Rainfall and elevation affect the amount of solar irradiation in a given area. The higher the elevation, the greater the total solar irradiation will be.

Looking at an example from the synthetic turf market, which can be applied to other types of outdoor fabrics, geographic areas in which most sports fields are built (U.S., Europe and Asia) will fall between 100 and 160 kL. By knowing the kL exposure of the geographic area, the lamp being used (340 nm or 420 nm in Figure 2), filter and the lamp calibration, which is dictated by the chosen standard procedure, one can easily calculate the total number of hours the sample should be tested using either a xenon arc weatherometer or QUV chamber to simulate one year of solar irradiation.

Based on kL calculations and subsequent accelerated testing, some companies are so confident in the weatherability and fade resistance of their products that they are providing a written UV-guarantee on filament yarn spun with the custom-color master batches made specifically for the demands of synthetic turf applications—up to 10 years lifetime for polyethylene and up to eight years lifetime for polyamide

Talk to your suppliers

Achieving the most useful, actionable data on the durability performance of synthetic fiber comes from using a combination of xenon arc accelerated testing, real-life outdoor weathering and kL calculations. Look to suppliers for support with product design, lab testing and outdoor testing facilities for a broad range of analyses to help achieve durability goals.

Finding the right mix of these additives for the region and application can ensure the long-term durability of synthetic fibers, while helping to reduce costly warranty claims:

  • Color master batches that are proven to provide superior colorfastness and lot-to-lot consistency
  • UV stabilizers that offer outstanding resistance to sunlight proven through rigorous quality control standards
  • Antioxidants that effectively prevent the degrading effects of oxidation on the polymer

When EPMs understand the ins and outs of technologies used throughout the supply chain, they know their products are designed with the highest quality materials from start to finish.

Larry Campbell is the technical development director for fibers, engineered materials and turf at Americhem Inc. For more information, visit www.americhem.com.

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