Effect of TiO2 pigment type on the UV degradation of filled coatings |
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Authors: | Deborah L Wang Stephanie S Watson Li-Piin Sung I-Hsiang Tseng Craig J Bouis Raymond Fernando |
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Affiliation: | (1) Building and Fire Research Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Stop 8615, Gaithersburg, MD 20899, USA;(2) Department of Chemistry and Biochemistry, California Polytechnic State University, San Luis Obispo, CA 93407, USA;(3) School of Chemical Engineering, Purdue University, West Lafayette, IN 47906, USA |
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Abstract: | The objective of this study was to investigate the effect of the photoreactivity of titanium dioxide (TiO2) pigments on the photodegradation of polymeric coatings used in exterior applications. Two polymer matrices, an amine-cured
epoxy (EP) and an acrylic urethane (AU), containing three types of TiO2 pigments, classified by different levels of photoreactivity, were studied. Specimens were exposed on an ultraviolet (UV)
weathering chamber, the Simulated Photodegradation by High Energy Radiant Exposure device at the National Institute of Standards
and Technology. Two exposure conditions were used: ambient, dry condition 25°C and 0% relative humidity (RH)] and high temperature,
wet condition (55°C and 75% RH), which is similar to more severe outdoor exposures. The physical and chemical degradations
of the filled coatings were monitored at periodic intervals using a combination of laser scanning confocal microscopy (LSCM)
and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Progression of degradation on the coating
surfaces was characterized by LSCM in terms of changes in surface roughness and morphology, pigment agglomerate size, and
the occurrence of pits or holes in the coatings. The observed physical changes were correlated to the chemical changes measured
by ATR-FTIR as a function of UV exposure time. Both EP and AU systems showed less degradation in terms of surface roughness
and morphological changes under the dry conditions compared to the wet exposure conditions. It was observed that both the
pigment type (and hence photoreactivity) and particle dispersion strongly affected the degradation of both EP and AU systems. |
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