## 4 Conclusions  
The study determined the effect of the type of material, or more precisely, the effect of the manufacturing process and the additives used to produce PLA-based films, on the plasma activation efficiency of the film assessed by improved wettability, and on selected properties of the film that may indicate its aging and susceptibility to hydrophobic recovery as a result of storage.  
The type of material was found to have a significant effect on the water contact angle of unmodified films, while it did not significantly affect the WCA value after plasma modification. For all polylactide films, a significant reduction in WCA was observed following plasma activation with both oxygen and argon plasma.  
Activation for all films resulted in the conversion of weakly polar surfaces into polar surfaces, with changes in the values of the polar and dispersion components of SFE depending on the type of film. For oxygen activation, similar total SFE values were obtained for all films, while they were slightly different from film to film when using argon plasma activation.  
Aging effects due to plasma activation were presented for all films tested, and no negative impact of the activation on film properties was observed. Plasma activation--by either oxygen nor argon--did not lead to significant changes in color or gloss that lowered the quality of the films, nor to a significant reduction in tensile strength that further affected refining or printing processes. Conversely, the observed changes in sample weight and roughness are closely related to the type of film and the type of gas used for activation, and are consistent with the specific nature of a given plasma.  
Based on the results, the type of film was found to affect the course of hydrophilic recovery, which was confirmed by the analysis of contact angle, as well as SFE results and those of its components. The aging course of modified films depends on the type of gas used for activation. The changes--an increase in the water contact angle, as well as a decrease in the SFE and its polar component--for films modified with argon plasma typically have a monotonic course, while those for films modified with oxygen plasma are non-monotonic with a sudden peak or decline, respectively, observed at 14 days of storage. Such a course of hydrophobic recovery of PLA films modified by oxygen plasma can be a subject of further detailed studies in this area to explain the processes occurring during this phenomenon. However, from an application perspective, it is important to note that storage shorter than or equal to 7 days does not cause significant hydrophobic recovery, regardless of the type of plasma activation. Although the trend of changes depends on the type of gas used for activation, the magnitude of changes depends on the film.  
Conceptualization and methodology, J.I.-P.; investigation, J.I.-P. and P.T.; writing--original draft preparation, J.I.-P.; writing--review and editing, J.I.-P. and E.D.; supervision, E.D.; project administration, E.D.; funding acquisition, J.I.-P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the European Union within the European Social Fund from WUT Development Program and by the Dean of the Faculty of Mechanical and Industrial Engineering WUT within the RnD Grant.