Fading Some Introductory Definitions

In this chapter, by the term weathering we mean fading because other aspects of weathering, first of all resulting from oxidative degradation of plastics and WPCs, were considered in the preceding chapter. 

When subjected to UV light, composite materials fade. This happens because high-energy UV light (whether we consider it as waves in an electromagnetic field, or as a stream of massless particles called photons) breaks polymer chains and other organic compounds at the surface. They are often broken in such a manner that free radicals are formed and propagated, until the free radicals are terminated by themselves (e.g., due to recombination), or by added antioxidants. 

The protective effect of colorants against fading depends on the type of pigments and antioxidants, their sources, amounts, and, of course, climatic and other 

TABLE 16.1 Shift in 6 vaiue on the Hunter iab scaie in the course of weathering of some WPC deck boards 

Only the 12 row shows natural, outdoors weathering (35,000h) all other figures are related to accelerated weathering, in Q-Sun 3000 (0.35 W/m at 340 nm, 102 18 cycle, 63°C black panel temperature). The data are arranged in the order of decreasing of the yellow component (b) compared to the initial value. 

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