Long-term light resistance

Figure 3.9. SN curves diagrammatic examples based on PA, PMMA and PTPE 3.1.6 Long-term light and UV resistance...

Another fundamental interaction issue is halogenated FRs negative effert on UV stability. This especially affects POs formulated for outdoor use, which rely on light-stabilizing (HALS) additives for long-term UV resistance. Here, a nonhalogenated FR is the obvious solution, or, if possible a more innovative approach described in Case 5. 1. 

Poly(butyl methacrylate) (PBMA) began to be used as a picture varnish in the early 1930s. It encountered a considerable success because of its resistance to yellowing, adequate flexibility, no dirt pick-up and good solubility in nonpolar hydrocarbon solvents. Products based on PBMA, such as Elvacite 2044 and Elvacite 2045 by Du Pont, were abandoned when it was discovered that under light exposure they cross-link to an unexpected extent becoming insoluble [64]. From this point of view acrylic copolymers based on methyl and ethyl acrylates/methacrylates show a much better long-term stability. 

As noted earlier, poly(methyl methacrylate) plastic has excellent resistance to ultraviolet radiation. Nevertheless, in long-term outdoor applications or in lighting fixtures, small amounts of ultraviolet absorbers are employed to retard the yellowing and degradation in physical properties which would otherwise occur. 

---