**5. Conclusions**

The wood of Norway spruce (*Picea abies*) was activated using DCSBD plasma, including heat-treated samples. Activation proceeded in atmospheric air and frequent working gases used in industry: N2, O2, Ar, all at atmospheric pressure. Two activation distances were considered: in the plasma zone and above it. Activation at a 0.15 mm gap from the electrode led in all cases to an increase in the SFE. That means the starting SFE difference of TMW made at different temperatures was lost.

At a distance of 1 mm from the electrode increase of SFE occurred only when O2 and Ar were used as working gas. However, it was observed that after treatment in air and N2 the values of SFE decrease due to polar part reduction. This effect is of importance in the case of industrial plasma application where it is hard to keep the working distance while treating timber. Understanding the reasons behind this effect could help us determine appropriate conditions for plasma treatment and maximize the desired effect.

Wood material was compared to PMMA, which does not show a similar effect. It is therefore a material matter of wood and its morphological and chemical composition. After the SEM analyses, it could be stated that no morphological changes take place during short plasma treatment. It was shown that heating of wood during the plasma treatment did not influence the SFE, either.

The hydrophobization effects that were shown are explained by the chemical reactions of long-lived plasma generated particles and hemicellulose on the wood surface.

A slight reduction of SFE on thermally modified spruce was achieved also by short term UV light exposure, generated by DCSBD at a 1 mm distance. From the comparison of spruce with beech wood, it could be stated that the effect of UV irradiation differs depending on wood type. To fully understand the effect of UV on wood, further thorough testing on multiple types of wood could be recommended and UV effects such as short exposure time, intensity, etc. to be assessed.

**Author Contributions:** Conceptualization, O.G., and J.R.; formal analysis, Z.K.; investigation, Z.K.; writing—original draft preparation, Z.K., and O.G.; writing—review and editing, O.G. and J.R.; supervision, O.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Education, Youth, and Sports of the Czech Republic, gran<sup>t</sup> number LM2018097.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable

**Data Availability Statement:** Data available in a publicly accessible repository. The data presented in this study are openly available in [repository name e.g., FigShare] at [doi], reference number [reference number].

**Acknowledgments:** We would like to thank the Department of Wood Science at the Mendel University in Brno for providing the thermally treated wood samples.

**Conflicts of Interest:** The authors declare no conflict of interest.
