Environmental Engineering Reference
In-Depth Information
yields the most degradation. Note that activation spectra depend on both
wavelength sensitivity and the fraction of radiation in the wavelength
interval of interest in the solar spectrum. As the fractional UVA in solar
radiation is much higher than that of UVB, the most damaging region for
plastics tend to be located at the UVA wavelengths.
Figure 6.6
Effect of different solar radiation wavebands on the yellowness
index of unstabilized Lexan polycarbonate film (0.70 mm) exposed to
natural sunlight facing 26° South in Miami, FL.
Source: Reproduced with permission from Andrady et al. (1992).
As a first approximation, the change in a property
D
, Δ
D
, of a plastic
material on exposure to solar radiation (or other radiation source) with a
spectral irradiance distribution
H
(
λ
) is assumed to be an additive function
depending onthewavelength sensitivity functionofthedegradation process
E
(
λ
).
The damage Δ
D
is the product of the quantum efficiency and the radiation
absorbed by the sample (Martin et al., 2003) As the action spectrum
E
(
λ
) is
unitless, the activation spectrum has units (W/m
2
/nm). Then, at any given
wavelength
