Solar radiation, polymeric materials

External factors that will influence polymer mechanical properties are temperature or thermal treatment, temperature history, large differences in pressure, and environmental factors such as humidity, solar radiation, or other types of radiation. The mechanical properties of polymer are also sensitive to the methods and variables used for testing, such as strain deformation as well as the rate at which the strain is performed. Finally, the mechanical behavior of polymeric materials and the values of their mechanical properties will be sensitive to the kind of strain that is imposed by the applied force, namely, tension, compression, biaxial, or shear. 

General Effects of Solar Radiation of Polymeric Materials... 

The effects of temperature on the aging behavior of polymeric materials became especially clear when materials for the interior equipment of motor vehicles were tested. Since these are often exposed to solar radiation at high temperatures, the test conditions for artificial weathering must be selected accordingly. A specific black panel temperature is set in the weathering devices. 

A nonconcentrating solar heat collector consists of a transparent cover, an absorber, tubes or ducts for the heat transport fluid, and an insulated case that limits the thermal losses to the environment. The collector cover serves several important functions it permits the passage of the solar radiation, prevents loss of heat, and protects the absorber from mechanical and weathering damage. The cover is selected for the highest transmittance of solar radiation and the lowest transmittance of the infi ared reradiated from the absorber. Polymeric materials have a low absorptivity for solar radiation and the absorptance can be decreased, compared to glass, by using thinner sheets or films. 

The photon energy in solar radiation is the most damaging component of the outdoor environment, serving to initiate a wide variety of chemical changes in polymeric materials [Trozzolo, 1976]. 

The shift in activation spectrum with thickness of an aromatic polymer exposed to solar radiation demonstrates the importance of testing these materials in the form in which they will be used in practice. The type of ultraviolet absorber required to screen the harmful wavelengths and its effectiveness will differ with the thickness of the aromatic-type polymeric tested. Due to differences among different types of polymeric materials in the effect of thickness on their wavelength sensitivities, the form in which they are tested can change their stability ranking. 

Effect of SPD of the Radiation Source on Weathering. The wavelengths responsible for degradation of a specific polymeric material vary with the SPD of the radiation source. Differences between the laboratory accelerated test source and the natural source in the wavelengths that degrade a material, which are identified by the activation spectra (see section on Spectral Effects of Solar Radiation Activation Spectra), can have the following consequences (53) ... 

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