Microbial growth on outdoor-weathered plastics

Microbial growth, presumably fungus or mildew, has been found growing on samples of aromatic engineering thermoplastics after 6–24 months of outdoor exposure at Miami, Florida test sites. Similar growth has been reported on automotive coatings, and although the phenomenon on plastics is known among practitioners, it has not been documented in the literature. Images of microbial growth by various techniques show the morphology, often exhibited as star-shaped features 2–3 mm in diameter. Infrared techniques show the presence of protein, and profilometry shows that the features are growing on the surface and are not cracks or pits into the surface. Washing studies show that some of the growth is easily washed away but some clings strongly.