Plasma-induced surface modification and adhesion enhancement of polypropylene surface

Unoriented (UPP) and biaxially oriented (BOPP) polypropylene films were treated under radio frequency plasma of air, nitrogen, oxygen, and ammonia. Surface modification of polypropylene films was investigated by using surface energy measurement and attenuated total reflection (ATR)-FTIR spectroscopy. Surface energy of air and nitrogen plasma-treated polypropylene film increased for shorter treatment time and then decreased and attained an equilibrium value. Such changes in surface energy were not observed for oxygen and ammonia plasma-treated polypropylene film, which increased to an equilibrium value. ATR-FTIR studies revealed characteristic differences in the absorption spectra for short-duration and long-duration treatments. From the relative intensity change in the C-H stretching vibration, the mechanism of surface chemical reaction could be inferred. Studies regarding the durability of surface modification due to plasma treatment were evaluated by investigating surface energy of samples aged for 2 months. Treated films subjected to peel strength measurement showed improvement in bondability for UPP and BOPP film by hydrophilic surface modification accompanied by surface crosslinking. (C) 2002 Wiley Periodicals, Inc.