Effects of temperature on the weathering of engineering thermoplastics

We have determined the activation energies (E_a) of yellowing and gloss loss for a large number of engineering thermoplastics and blends under accelerated weathering conditions. The E_a often depend on the property measured and exposure conditions, although they vary over a fairly small range. Under the CIRA/sodalime-filtered xenon arc conditions most likely to be representative of outdoor exposure, the E_a for gloss loss was ≤5 kcal/mol for all samples tested. The E_a for yellowing was also ≤5 kcal/mol except for SAN and ABS. Evidently the color bodies formed from photo-oxidation of SAN are more sensitive to temperature. A reaction with an E_a of 5 kcal/mol will increase its rate by about 33% for each 10 °C increase in temperature near room temperature. Temperature is an important, but not overwhelming, variable in the weathering of most engineering thermoplastics.