The basic reseach on the surface sulfonation of polypropylene (PP) is very important for design of surfaces for higher functionalization. For this purpose, liquid-phase sulfonation of polypropylene surfaces at various temperatures and different time periods was performed using concentrated sulphuric acid. The physical and chemical changes produced by the sulfonation on the polypropylene surfaces were determined by contact angle measurements, mechanical analysis, UV-Vis spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Both surface polarity and wettability of PP films were improved by sulfonation at low temperatures for short time periods; however, sulfonation at longer times, or higher temperatures, caused degradation of PP films. All sulfonated film samples had lower yield stress and stress at break. (c) Koninklijke Brill NV, Leiden, 2008