Global weathering of aromatic engineering thermoplastics

The rates of gloss loss and color shift for 24 aromatic engineering thermoplastics at nine exposure sites world-wide have been compared relative to a commercial Miami exposure site. The scatter among individual samples was large, but on average, light dose alone was enough to account for almost all of the rate differences among the various sites for these materials. Temperature, humidity, rainfall, and acid rain seemed to play minor roles for most samples. Samples containing no particulate pigment had more erratic gloss loss and showed some dependency on the amount of rainfall. The overall “cleanliness” of the samples seemed to be an important factor in gloss retention, and washing protocols during the exposure period and before readings were important variables in cases of slow erosion and/or no particulate pigment. Microbial growth (fungus) was observed on Miami samples after 12–18 months of exposure, but none was seen at any other site.

Relative to Miami defined as 1.0, the average rates of color shift and gloss loss were approximately 0.67 in the northern U.S., 0.8 in the central U.S., and 1.15 in the U.S. desert southwest. Southern Europe was nearly as harsh as Miami, while Northern Europe was comparable to the northern U.S. Northern Europe was found to be somewhat harsher than expected while the northern U.S. was slightly less harsh than expected based on light dose or temperature-weighted light dose. These conclusions apply only to aromatic engineering plastics and should not be assumed to hold for other kinds of materials, such as polyolefins or coatings, without experimental verification.