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SynopsisT h e wavelength sensitivity of a compounded extruded rigid poly(viny1 chloride) formulation t o yellowing under exposure t o filtered xenon radiation is determined using a cut-on filter technique. Spectral sensitivity of the formulation in the absence and the presence of 2.5 phr of rutile titanium dioxide was examined, and the results were compared t o those previously reported for the yellowing of an identical vinyl formulation exposed to monochromatic light. Maximum in the activated spectrum for yellowing under exposure to filtered xenon radiation was found t o be in the wavelength region 300-320 nm for both types of samples. The results agreed qualitatively with those previously obtained in the study of the same material exposed to monochromatic light.

The irreversible changes in chemical and physical properties of polymeric materials exposed to the environment are caused by the combined action of all weather factors, including solar radiation, heat, moisture, oxygen, and atmospheric pollutants. However, the actinic radiation of the sun absorbed by materials is the critical factor. It initiates the chemical reactions that lead to degradation through its bond breaking capabilities. The wavelength specificity of degradation, and its material dependency are illustrated by the activation spectra of various types of polymers. The contributions of the other major environmental factors to weathering and various types of outdoor weathering tests are described. The significant advances in development of weatherable polymeric materials have increased the need for more rapid evaluations by both outdoor and laboratory accelerated tests. Their validity depends on how well they simulate the effects of exposure to end‐use environments in terms of failure modes, mechanism of degradation, and stability rankings of materials. The most important factor in good correlations between laboratory accelerated and outdoor weathering tests is adequate simulation of the spectral power distribution of the natural source over the full range of actinic wavelengths. The types commonly used in laboratory accelerated devices are compared with solar radiation and the effects of their deviations in the uv and visible regions are discussed. The effect of increased stress levels of irradiance, temperature, and moisture on acceleration factors and on correlation with natural weathering tests are described. Techniques for predicting lifetimes under natural weathering based on laboratory accelerated tests are reviewed.

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