Loading effect at etching of polypropylene films in oxygen-nitrogen plasma

The results of the studies of the loading effect under the action of a low temperature plasma of an oxygen-nitrogen mixture on the surface of a polypropylene (PP) film are presented. A gravimetric method was used to study the kinetics of the material’s etching. The composition of the functional groups on the PP surface was characterized by the method of Fourier Transform Infrared by Attenuated Total Reflectance (FT-IR ATR). The loading effect was observed in the entire range of the gas compositions. It is accompanied by the increasing of the content of the functional groups in the modified layer; namely, of the double bonds for any gas composition and oxygen- or nitrogen-containing species dependent on the mixture composition. In the general case, the loading effect is more pronounced when the initial gas contains less oxygen. The degree of this dependence differs strongly for various O2: N2 ratios. This is probably associated with the extreme character of the changes in the fluxes of the active particles from the plasma to the sample. The influence of the gas composition on the loading effect is relatively small when the O2 fraction in the mixture constitutes 100–10%. The increasing of the load degree results in the increasing of the concentration of the oxygen-containing groups on the surface; the nitrogen-containing groups were not registered. When the O2 fraction in the mixture is lower than 10%, the reciprocal influence of the volumetric and heterogeneous processes is enhanced considerably. The water vapors enter into the reactions of etching owing to the oxygen deficit. The nitriding of the surface occurs simultaneously with its oxidation. The competition of these processes is more pronounced for larger loads of the reactor.