Weathering of Polymeric Materials

Abstract

Abstract The useful service life of polymeric materials depends on their ability to resist the effects of critical weather factors responsible for the deterioration of either or both the appearance and physical properties necessary in their applications. The effects of weather result from complex interactions of the environmental elements, primarily solar radiation, heat/cold, moisture, oxygen, and pollutants, with the materials. By far, the most destructive environmental factor is the ultraviolet (UV) portion of terrestrial solar radiation absorbed by a material because it is capable of breaking some of the chemical bonds and thus initiating the degradation reactions. Because photodegradation is wavelength specific, close simulation of the spectral power distribution (SPD)of the natural source by the radiation source used for laboratory accelerated weathering is essential for simulating the natural weathering processes. The presence of short wavelengths below the solar UV cut‐on, the absence of long wavelength UV and short wavelength visible radiation, and relative intensities that do not simulate those of solar radiation can produce differences in degradation mechanisms, types of failure, and weatherability rankings of products compared with natural weathering. Sample temperatures and type and amount of moisture have a significant influence on the rate of degradation through their effects on the secondary reactions following bond breakage. Unrealistic levels of all stress factors have to be used with caution to obtain good correlation of degradation processes between accelerated and natural weathering. Because acceleration of weathering by increase in the critical stress factors differs for each material and formulation, the acceleration factor must be determined experimentally for each product. The effects of critical weather factors on polymeric materials and the various types of outdoor and laboratory‐accelerated weathering tests and their test parameters are described. The critical weather factors in natural and artificial weathering are compared and potential methodologies for predicting long‐term performance of polymeric materials are reviewed.