Effect of Pigment Dispersion on Durability of a TiO2 Pigmented Epoxy Coating During Outdoor Exposure

The effect of pigment dispersion on durability of a TiO2 pigmented epoxy coating during outdoor exposure has been investigated. Well-dispersed and poorly dispersed coating samples were prepared through the addition or absence of a dispersant in the coating formulation. Ultra small angle neutron scattering (USANS) and scanning electron microscopy (SEM) showed that pigment aggregation occurs in the absence of dispersant. A thin, clear layer of epoxy was observed at the air/exposed surface interface in both the dispersed and non-dispersed samples. Chemical degradation and physical changes during UV exposure were measured by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), and loser scanning confocal microscopy (LSCM). Results showed that the degree of pigment dispersion and the thickness of the clear layer contributed to weathering. Changes in surface topography and gloss loss during UV degradation were correlated with degree of pigment dispersion. Ripples and bumps on the top surface of the poorly dispersed coating greatly affected gloss. Bulk and surface mechanical properties were investigated using dynamic mechanical thermal analysis (DMTA) and instrumented indentation, respectively. Relative to the neat epoxy coatings, the addition of TiO2 particles into the epoxy coatings increased elastic modulus but decreased the glass transition temperatures (T-g) of both of the pigmented coatings. Relationships between surface and bulk mechanical property changes and chemical degradation are discussed.