**4. Discussion**

The quantitative change described above is consistent regarding the change of the measured contact angle values. The measured contact angle, TPC and TSCC values in case of di fferent wood species show similar trend under the entire artificial ageing period.

Despite the fact that the total phenol content increases almost 15-times during 240 h of artificial xenon radiation and the total soluble carbohydrate content increases only 6–8 times, the substantially higher presence of carbohydrate has a greater influence on the contact angle of the liquid drops. Based on the decrease of contact angles an improved wood surface wettability can be concluded.

The most reactive wood components during photodegradation are the lignin and the extractives [39,41,42]. The reason for contact angle changes in the first 15–20 h of artificial radiation is that the decomposition of lignin and extractives begins, and the total phenolic content increases. In the subsequent radiation interval begins the decay of cellulose and hemicelluloses, which are less sensitive to photodegradation. The total soluble carbohydrate content increases compensate the e ffect of hydrophobic phenolic compounds and this is manifest in the diminution of strong variation in the contact angle values. As cellulose and hemicelluloses are present on the wood surface (and in the whole wood material) in essentially larger quantities, their hydrophilic nature is strongly manifested in the next radiation interval proved, also by decreasing contact angle values. The observed chemical

changes were further investigated with Fourier-transform infrared spectroscopy and these results will be published in the near future.

Overall, the performed t-test statistical analysis resulted in values close to 0 in each combination, which indicate that similarity exists between the measured data sets, and supports the observation that the contact angle value, for example, is susceptible to follow surface chemical changes. The ANOVA test also indicates that there is a real difference between the tested, measured data groups in each combination, as the value was close to zero.
