## 3 Results and Discussion
### Changes in Selected Film Properties as a Result of Plasma Modification  
Surface roughness and the degree of surface development have a significant impact on surface wettability and printability. An increase in roughness indicates that the surface of the substrate has developed, which should translate into better wettability and adhesion of ink or adhesive to the material [61]. However, significant changes in roughness can also indicate material degradation. Significant roughness changes (exceeding 100 nm) were observed only for films modified with argon plasma (Figure 3), which can be explained by slightly higher water contact angle values for such activated materials. The increase in roughness can be explained by the peculiarities of the argon plasma mechanism leading to significant etching of the surface during plasma interaction with the material [62]. Particular changes in this regard were observed for NTSS film (Figure 4), for which the mass loss is the highest (Figure 5). However, the results may also be influenced by the much smaller thickness of the material compared to the other two films. The effect of oxygen activation on roughness was negligible, which is consistent with the results obtained by [PERSON] et al. [22] and [PERSON] et al. [63]. This is due to the fact that during both oxygen and ambient air activation, the improvement in material wettability is due to the resulting polar functional groups containing oxygen, which interact strongly with water molecules, and not due to physical etching of the material surface as is the case during argon activation (Figure 4). Another parameter to determine material degradation that is easy to measure, besides roughness, is the change in sample weight. A change in the mass of a sample can indicate the removal of contaminants from the surface of the material, oxidation of the material, and etching of the material [64]. In general, the mass is reduced as a result of defragmentation of the polymer and removal of degradation products to the environment. For all films, greater weight loss was observed as a result of oxygen activation than argon activation (Figure 5). This may be related to the fact that during oxygen plasma activation, products weakly bound to the sample surface are formed on the surface of the modified PLA [3,19]. Moreover, the largest weight changes were observed for NTSS film. This may be due to its much smaller thickness compared to the other films. For BCP and TCL films, the changes were at a similar level. Another parameter indicative of material aging and degradation is the strength of plastics, most often determined by measuring tensile strength. The reduction in strength is a consequence of the tearing of polymer chains. It is known that chain crosslinking and chain rupture can occur simultaneously during plasma activation. Strong chain-break reactions cause etching of the polymer surface, while crosslinking inhibits this process [13]. Plasma activation caused a reduction in the tensile strength of all the oxygen-plasma-activated films (Figure 6). Considering the weight loss of the activated samples, it can be concluded that material degradation has occurred, translating into lower tensile strength values. However, it should be emphasized that the observed changes are not significant enough to affect the application of the materials. Moreover, it is worth noting that argon plasma has no significant effect on the tensile strength of the material. This is due to the fact that during argon activation there is crosslinking of polymer chains, while with oxygen activation the main mechanisms are surface oxidation accompanied by chain scission rather than crosslinking.