Effects of UV degradation on surface hydrophobicity, crack, and thickness of MWCNT-based nanocomposite coatings

Surface degradation is a common problem in polymeric coatings when they are exposed to sunlight, moisture, and oxygen. In order to reduce their surface degradation, thus keeping the coatings' original properties, multi-wall carbon nanotubes (MWCNTs) were added, and the coatings were exposed to UV light and salt fog for various lengths of time. At 0 days of UV exposure, contact angle values of 0%, 0.25%, 0.5%, 1%, and 2% MWCNT-based nanocomposite coatings of 75 mu m (similar to 3 mil) thickness were between 85 degrees and 89 degrees. However, after 16 days of UV exposure, contact angle values of the same samples were reduced to 11 degrees, 13 degrees, 34 degrees, 50 degrees, and 54 degrees respectively. Longer UV exposures resulted in several microcracks on the surface of the coated samples in the absence of nanoscale inclusions, while very minimal cracks or degradation appeared on the MWCNT-loaded samples. Test results also showed that UV exposure along with salt fogging reduced the coating thickness up to 24% at 0% CNTs; in contrast, this reduction was only 7% with a 2% MWCNT coating. These results clearly indicate that MWCNTs added to polymeric coatings reduce UV degradation, lessen surface cracks, protect the film thickness, and hence increase the lifetime of the polymeric coatings. (C) 2011 Elsevier B.V. All rights reserved.