Effect of TiO2 pigment type on the UV degradation of filled coatings

Abstract

The objective of this study was to investigate the effect of the photoreactivity of titanium dioxide (TiO 2 ) 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 TiO 2 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.

Consideration of roles of commercial TiO2 pigments in aromatic polyurethane coating via the photodegradation of dimethyl toluene-2,4-dicarbamate in non-aqueous solution

“…In order to suppress the photoreactivity of titanium dioxide while maintaining its UV-shielding performance, inert oxides such as SiO 2 , Al 2 O 3 , ZrO 2 and CeO 2 have usually been applied as coatings on titanium dioxide surfaces [13][14][15]. Unfortunately, the photoreactivity of titanium dioxide pigment is still one of the most important influential factors in degradation of coatings [16,17]. It is therfore necessary to understand the role of TiO 2 pigments in the process of PU degradation.…”

Surface degradation process affected by heterogeneity in nano-titanium dioxide filled acrylic urethane coatings under accelerated UV exposure

“…In this way, morphology evolution at the same location can be monitored as a function of exposure time. The root mean square (RMS) [14] surface roughness, R q , was calculated to quantify the morphology changes in surface and subsurface of coatings during the UV exposure. Eq.…”

“…Thereby, the remainder of the paper will focus on the effect of nanoparticle dispersion on morphological changes in AU coatings under wet and dry conditions with UV exposure. accelerate degradation of polymeric materials [10,14]. It is shown in Table 1 that the photoreactivity of the three nanoparticles is ranked as P A >> P C > P B .…”

“…Some studies have been carried out to investigate the effect of TiO 2 on the photodegradation of polymeric composites [13][14][15][16][17]. Clerici et al [13] investigated the effect of pigmentary TiO 2 dispersion on the durability of epoxy coatings.…”

“…They found that difference in dispersion state played a significant role in polymer degradation. Wang et al [14] investigated the effect of TiO 2 pigment type in terms of surface treatment, particle size and dispersion on the photodegradation of filled coatings. In their study, nanosize TiO 2 with high photoreactivity and micron size TiO 2 with low photoreactivity were used.…”