Enhanced surface wetting of pigment coated paper by UVC irradiation

The effect of UVC (lambda(max) = 254 nm) treatment on wettability of pigment-coated papers was examined. The paper samples were coated with conventional pigments including ground calcium carbonate (GCC), precipitated calcium carbonate aragonite (PCC), and Kaolin. The coating formulation also included poly(styrene-butadiene) (SB) latex binder and a dispersing agent, sodium polyacrylate (NaPA), for formation of a colloidally stable pigment slurry at a relatively high solids content. A significant decrease of contact angle of water on the studied pigment-coated papers was observed as a result of UVC treatment. The effect was most pronounced for carbonate-based coatings. In addition, the UVC treatment showed long-term stability. A detailed analysis of the surface chemical composition of the PCC-based coatings indicated that the UVC treatment leads to photooxidation and photodegradation, and eventual desorption of a thin NaPA overlayer from the pigment surface. This in turn increases the polarity of the surface and enhances its wettability.