Activation Spectra: Techniques and Applications to Stabilization and Stability Testing of Materials

Abstract

The activation spectrum of a material represents the relative amount of damage caused by individual spectral regions of the source to which the material is exposed. Experimental techniques used to determine activation spectra include (1) narrow-band radiation utilizing interference filters or a grating or prism spectrograph and (2) polychromatic radiation with sharp cut-on UV/visible transmitting glass filters to define the relative effects of radiation by individual spectral regions during exposure to all wavelengths longer than the cut-on of the filter. The spectral effects of radiation on a material are determined by measurement of spectral changes, i.e., by UV, visible or infrared spectroscopy, and, if sample size permits, by changes in physical properties. Applications of activation spectra include the development of light stable materials, the design of meaningful light stability tests, timing of exposures based on actinic radiation and prediction of service life by providing a means of determining effective dosage. Examples are given to demonstrate many of the applications of activation spectra and comparison is made with action spectra which represent the wavelength sensitivity of a material independent of the spectral emission properties of the radiation source.

The Missing Link – Light-Induced (280–1,600 nm) Free Radical Formation in Human Skin

“…Acquisition of the experimental data is based on the method used by Searle [30,31] , specified in the ASTM Standard Practice G178-0331 and adapted to our specific application to take into account the action spectrum calculation.…”

Accelerated weathering of unsaturated polyester resins. Aspects of appearance change

“…For this goal, sharp cut-on filters with much steeper transition slopes compared with the glass filters traditionally used were applied [19]. Transmission characteristics of the filters have been determined using UV-Vis spectroscopy and are shown in Fig.…”

“…Because the activation and action spectrum give information on the damage due to the effect of different wavelengths, both are generally more useful than the absorption spectrum giving the absorbed amount of radiation energy as a function of wavelength. The fraction of the absorbed energy effective in creating chemical changes is not necessarily independent of wavelength due to the quantum efficiency which may be wavelength dependent [19,21].…”

Influence of temperature, UV-light wavelength and intensity on polypropylene photothermal oxidation

“…4a and b) and the activation spectrum of the polymer on the other side. Indeed, the action and activation spectra represent the wavelength dependence of a photoprocess effectiveness and of the extent of degradation (damages) respectively (for further details, refer to the following reviews [17,18]). Therefore, they only differ from the spectral distributions of the molar extinction coefficient and absorbed quanta by the spectral distribution of the quantum yield for the involved photoprocess.…”

“…Nonetheless, not only the light intensity but also its wavelength and, in particular, the light source spectral distribution must be considered since specific spectral sensitivities were evidenced for various polymers (see reviews [17,18]), including polypropylene [19e21]. This notion of polymer light sensitivity can be correlated with the first law of photochemistry attesting that only absorbed quanta can initiate reactions, if they have a sufficient energy to dissociate a chemical bond [22,23].…”