Abstract— <p>We investigated the effect of the beam plasma parameters on the modification of the polypropylene surface properties in argon and air atmospheres. This beam plasma was generated by a ribbon electron beam at a pressure of 0.1–10 Pa. The results show a non-monotonic increase in plasma concentration (up to 3 × 10¹⁵ m^–3) at a pressure of 1 Pa for argon plasma. This increase might be associated with the ignition of a beam-plasma discharge. However, this dependence of plasma parameters on pressure is monotonous for air plasma. The study shows that air plasma treatment provides a more pronounced reduction in the wetting edge angle compared to argon plasma. This decrease might be explained by the combined physical and chemical effects of the air active components. The use of electric potential had made it possible to enhance surface modification, especially at low pressures. The highest processing efficiency was achieved in the 1–5 Pa range, where an optimal balance is maintained between plasma density and particle energy. In addition, the air plasma ensures a longer retention of hydrophilic properties compared to argon plasma treatment. The obtained results can be important for the processing polymer materials technologies development.</p>