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Structural Water Content in Pigment-Grade TiO2 Particles Coated with Al2O3 and SiO2, and Their Effect on Polypropylene Photodegradation
Summary
This study investigates the structural water content present in polymer-coated titanium dioxide pigment particles, which are widely used in paints and coatings. Using spectroscopic and thermal analysis techniques, the researchers characterize how polymer coatings influence the retention and distribution of water within the TiO2 particle matrix. The findings have practical relevance for understanding the stability and performance of pigment dispersions.
The influence of structural water in alumina (Al2O3) and silica (SiO2) coated titanium dioxide (TiO2) pigments on the photodegradation behavior of polypropylene (PP) composites was investigated. Four commercial rutile TiO2 pigments with varying surface inorganic coatings were incorporated into PP plaques and subjected to accelerated UV weathering to simulate outdoor exposure. Photodegradation was assessed through gloss retention measurements, the carbonyl index (CI), and stress at break retention, while pigment morphology and composition were analyzed using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Surface charge and water content were determined through the zeta potential (ζ), Karl Fischer titration, thermogravimetric analysis (TGA), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results showed that low-alumina coating alone led to the lowest photodegradation resistance, the highest CI, and the lowest stress at break retention. In contrast, increasing alumina content enhanced photostability, reaching its maximum for combined alumina–silica coatings, which mitigated electron–hole pair migration. PP composites with high alumina–silica-coated TiO2 exhibited higher gloss retention (36%) compared to low-alumina samples (21%). Furthermore, statistical analysis using ANOVA revealed significant differences in coating content and ζ potential among the pigment grades. These findings provide novel insights into oxide-water interactions and the impact of structural water on the photodegradation of polymer composites.