Polypropylene is one of the most widely used plastic materials because of an excellent balance between properties, processability, and cost. Nevertheless, polypropylene is characterized by very low surface energy, and this has a negative effect on adhesion properties. The use of polypropylene in technological applications requires, in many cases, a surface pretreatment to modify surface activity, thus enhancing good adhesion levels. In this work, we have used photopolymerization of acrylic acid (AA) monomer on polypropylene surface by using UV radiation. This enables photografting of AA (highly polar) on polypropylene topmost layers, thus having a positive effect on overall surface activity of polypropylene surface and, consequently, adhesion properties can be remarkably improved. We have evaluated the influence of the exposure time to UV radiation on wettability changes and adhesion properties. Wettability changes have been studied by contact angle measurements and subsequent surface energy calculation. Chemical changes produced by photopolymerization of AA have been followed by Fourier transformed infrared spectroscopy. Mechanical characterization of adhesion joints has been carried out in two different ways: peel and shear. Fractured surface of adhesion joints has been characterized by scanning electron microscopy. The overall results show a remarkable increase in mechanical properties of adhesion joints for exposure times of about 180 s, which represents an interesting time from an industrial point of view. Therefore, photopolymerization process is highly useful to increase adhesion properties of polypropylene. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3256-3264, 2010