Effect of low-pressure O 2 and Ar plasma treatments on the wettability and morphology of biaxial-oriented polypropylene (BOPP) film

Abstract

Low-pressure plasma treatments in an rf discharge of O 2 and Ar were employed to introduce polar functional groups onto the biaxial-oriented polypropylene (BOPP) surfaces to enhance the wettability and activation. The effects of plasma treatment on the morphology and wettability of the BOPP films were characterized using static contact angle measurements, attenuated total reflection (ATR)–FTIR spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). A clear increase in the surface energy of BOPP films due to O 2 and Ar plasma treatments was observed. The surfaces became highly hydrophilic when exposed for 20 s or longer to the plasma discharge. The wettability of polymer surface can be improved when oxygen functionalities are generated, which can be achieved directly in O-containing plasmas or via post plasma reactions. Small reduction in surface energy of plasma treated BOPP films, after 30 days aging showed that the plasma-induced cross-linking in BOPP film was not the dominant phenomena. With increasing the treatment power and time, rate of the decrease in surface energy after aging is reduced. AFM and SEM images revealed distinct changes in the topography of BOPP due to O 2 and Ar plasma treatments. Nodular structure is formed on the BOPP film during the treatment and the size of the nodules increases with the treatment time.