Light degradation protection

UV absorbers may be used for two reasons to protect the plastic from UV degradation, and to prevent product degradation due to UV rays passing through the plastic. Chemically UV absorbers may be based on substituted phenols or benzophenones. Examples include 2-hydroxy-4-n-octoxybenzophenone, other hydroxy-benzophenones and compounds of oxalic anilide. These are usually added at a 0.1-0.2% level. Prevention of light penetration and protection of the plastic from light degradation can also be achieved by the addition of iron oxides and carbon. 

ABS will be degraded by UV light unless protective additives are incorporated into the formulation. 

To avoid the problem with light degradation the fabrics must be properly selected (i.e., polyester) and UV stabilized. As the period in which the fabric is exposed is short (in terms of months), no serious problems are to be expected. In case of more or less permanent applications under exposed conditions the fabric must be protected against direct sunlight. There are a number of methods of surface protection for geosystems. To provide additional UV and abrasion protection to the exposed sections of tubes, a coating of elastomeric polyurethane is often used. This coating, however, has a tendency to peel after about a number of months and therefore, has to be re-applied. 

Stabilizers. Antioxidants provide protection against UV light and thermal oxidative degradation. Hindered phenols are the most common nonstaining antioxidants. For SBR latices, two additional type of stabilizers must be used. 

Certain fillers are commonly added to protect the urethane backbone from oxidative degradation. Carbon black and titanium dioxide are commonly used in conjunction with antioxidants to protect polyether polyurethanes in exterior adhesive applications that may be exposed to oxygen and light (Fig. 12). 

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