**5. Conclusions**

Chemical changes of the wood surface layer, which can be well monitored by using total phenolic and soluble carbohydrate content examinations, are influenced by the photodegradation of the main wood components: cellulose, hemicelluloses, and lignin. According to test results of TPC and TSCC experiments, by using the 75-μm thin layer of wood specimens, both phenolic and carbohydrate content alter to a grea<sup>t</sup> extent due to photodegradation. The quantity increases of total soluble carbohydrates, which gives information about the degradation of cellulose and hemicelluloses, and their basically greater presence in wood material, influences the contact angle of liquid drops more than the total phenolic compounds.

To our best knowledge, there is no article that reports on TPC and TSCC evaluation considering the surface detached wood particles observed under artificial ageing. The present study shows that the preparation method and evaluation of TPC and TSCC can be significant. This could be a grea<sup>t</sup> advantage and novel technique, thus representing a good contribution to the surface science of wood. In that sense, our attempt to draw attention to the method used might also be useful to researchers from the other fields of the wood science, like surface treatment and the gluing of wood.

**Author Contributions:** Conceptualization, E.A.P. and L.C.; methodology, T.H. and L.C.; software, E.A.P. and A.N.M; validation, E.A.P., A.N.M. and T.H.; formal analysis, C.C.; investigation, E.A.P. and A.N.M.; resources, C.C.; data curation, L.C.; writing—original draft preparation, E.A.P.; writing—review and editing, E.A.P. and L.C.; visualization, E.A.P. and A.N.M.; supervision, C.C.; project administration, C.C.; funding acquisition, L.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the European Union and the State of Hungary, co-financed by the European Social Fund in the framework of TAMOP 4.2.4. A/2-11-1-2012-0001 National Excellence Program.

**Acknowledgments:** This article was made in frame of "the EFOP-3.6.1-16-2016-00018—Improving the role of research + development + innovation in the higher education through institutional developments assisting intelligent specialization in Sopron and Szombathely". IKEA Industry Sopron Ltd. for wood material supply and the carpenter workshop team of US-SKF for their skillful work are gratefully acknowledged.

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