Surface treatment of polymer films is
usually necessary to improve surface wetting and adhesion characteristics.
Traditional liquid chemical processes have several disadvantages in contrast
to dry finishing processes, like plasma technology. Dielectric barrier
discharges at atmospheric pressure are extensively studied for surface
treatment, however, almost no research has been done on surface treatment
with a dielectric barrier discharge at medium pressure. Therefore, in this
paper, a polypropylene (PP) film is plasma-treated with a dielectric barrier
discharge (DBD) in nitrogen at medium pressure (5.0 kPa). The surface
properties of the plasma-treated samples are examined using contact angle
measurements, X-ray photoelectron spectroscopy (XPS) and atomic force
microscopy (AFM). Results show that the surface wettability is significantly
enhanced after plasma treatment. The incorporation of nitrogen on the
surface is significant (10 at%), demonstrating the ability of the used
DBD set-up to generate nitrogen-containing functional groups on the PP
surface. Nevertheless, a considerable amount of oxygen (10 at%) is
incorporated onto the PP surface underlining the extreme reactivity of
oxygen active species and the difficulty in overcoming the air contamination
problem. Moreover, AFM analysis reveals that the nitrogen plasma creates
large changes in the surface morphology of the PP film due to the selective
etching of the amorphous regions of the polymer film.