Fabrication of low surface free energy automotive clear coats: Mechanical and surface chemistry studies

This work aims at improving the surface chemistry and the mechanical properties of a commercial acrylicmelamine clear coat using a functional siliconized additive. The resistance of films against biological degradation was then investigated using pancreatin (simulated bird droppings) and Arabic gum (simulated tree gum). Variations in the surface and bulk chemical structures, as well as the thermomechanical characteristics of the clear coats at different concentrations of the additive, were investigated by a wide range of techniques inclusive of contact angle measurement, gonio-spectrophotometery, dynamic mechanical thermal analysis (DMTA), energy-dispersive spectroscopy, atomic force microscope, optical microscope, and attenuated totalreflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Negligible effect of additive on color change was revealed. It was shown that even at low loadings of additive it could migrate to the surface, producing hydrophobic films with very low surface free energies with water contact angle exceeding 100 degrees. In addition, it was found by DMTA and ATR-FTIR studies that the functional additive was covalently attached to the acrylicmelamine chains through its hydroxyl groups. However, phase separation was observed at high concentrations of additive, leading to reduced crosslinking density. The clear coat resistance against pancreatin and Arabic gum was improved using optimum concentrations of the additive. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013