Development of dirt resistant polymer coatings
In the construction industry, prepainted metal strip is a widely used material for fagade and roofs of building intended for commercial used. The physical properties of modem coatings are outstanding, however one big problem that remains and which affects the overall coatings performance is dirt pick up. Firstly the effect of weathering induced chemical composition change was evaluated using photo-acoustic infrared spectroscopy (PA-FTIR), and X-ray photoelectron spectroscopy (XPS). The results shown that photo-oxidation processes occurs via Norrish type I and type 11 reaction at several sites on the polymer backbone, with the ester linkage and the melamine crosslinkage being the more reactive. Secondly aluminosilicates have been found to be the main source of soiling with organic pollutants also responsible but to a minor extent, the presence of such dirt was confirmed by XPS analyses. Unusual peak shape was observed on the carbon narrow scans with low binding photoelectron emitted. Finally Polymer/organically modified layered silicates (PLS) nanocomposites are a new class of filled polymer with ultrafine phase dimension. They improve considerably the physical properties of the coating while reducing dirt pick up. The best results were obtained when the insitu intercalative method was used. However the implication of the onium salts is obscure and the relation between the nanocomposite structure and its properties is not well understood.