DEGRADATION OF PLASTICS IN THE ENVIRONMENT - Plastics and Environmental Sustainability - page 229

a beam of near-monochromatic radiation at different wavelengths followed
by measuring the yellowness index with a colorimeter.
Figure 6.5 Action spectrum for the light-induced yellowing of mechanical
pulp.
Source: Reproduced with permission from Heikkilä and Kärhä (2014).
An alternative representation of the wavelength sensitivity of a polymer is
the activation spectrum (which is specific to the source of light used). It
is useful in assessing broad regions of the solar spectrum most effective in
promoting degradation of the plastic material. Unlike single-wavelength (or
monochromatic) sensitivity plots, these provide information on the effects
of broad spectral bands of the solar spectrum. They yield information on
synergistic and antagonistic effects encountered at different wavelengths.
The effects of different wavebands in the solar-simulated spectrum are
isolated using a series of cut-on filters. 10 Andrady (1997; Andrady et al.,
1992) gives a good description of the cut-on filter technique and how it is
usedtogenerateactivationspectra. Figure6.6 showsanactivationspectrum
for the change in yellowness index of unstabilized Lexan PC film (0.70 mm)
exposed to sunlight (Andrady et al., 1992). The 320-338 nm waveband