Wavelength-Dependent Photodamage

An alternative representation of the wavelength sensitivity of a polymer is the activation spectrum (which is specific to the sonrce of light used). It is useful in assessing broad regions of the solar spectrum most effective in promoting degradation of the 

FIGURE 6.5 Action spectrum for the light-induced yellowing of mechanical pulp. Source Reproduced with permission from Heilddla and Karha (2014). 

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, AD, of a plastic material on exposure to solar radiation (or other radiation source) with a spectral irradiance distribution H X) is assumed to be an additive function depending on the wavelength sensitivity function of the degradation process E(X). 

The damage AD is the product of the quantum efficiency and the radiation absorbed by the sample (Martin et al., 2003) As the action spectrum E(X) is unitless, the activation spectrum has units (W/mVnm). Then, at any given wavelength 

---