**3. Results**

The amount of nanosilver suspension absorption after the impregnation process was measured to be 0.38 g/cm3. Results of the permeability tests showed that the lowest specific gas permeability was observed in specimens before NS-impregnation or heat treatment (NS-HT-165 treatment, 6.898 × 10−<sup>13</sup> m<sup>3</sup> m<sup>−</sup>1), and the highest was found in NS-HT-185 after NS-impregnation (15.576 × 10−<sup>13</sup> m<sup>3</sup> m<sup>−</sup>1).

In the un-impregnated specimens, heat treatment slightly increased the specific gas permeability values in all three temperatures of 145, 165, and 185 ◦C, but the increase was not statistically significant (Figure 2). The highest increase in the un-impregnated specimens was observed in HT-145 treatment (only 5.3%). As for the nanosilver-impregnated specimens (the right columns of Figure 2), impregnation with the nanosuspension significantly increased the permeability in all treatment (Figure 2). In some cases, the amount of increase was more than 107.5%. The highest specific gas permeability was found in the NS-HT-185 treatment after the NS-impregnation and before the heat treatment. The increasing effect of heat treatment on permeability was significantly intensified by the thermal conductivity of silver nanoparticles; the highest increase caused by heat treatment of NS-impregnated specimens was seen in NS-HT-145 treatment (20.8%). The only treatment showing a decreasing trend in permeability caused by heat treatment was NS-HT-185. This treatment showed a decrease of about 8.8%.

**Figure 2.** Specific longitudinal gas permeability in the beech specimens (×10−<sup>13</sup> m<sup>3</sup> m<sup>−</sup>1) (error bars indicate the standard deviation for each column).

The maximum pull-off adhesion strength was observed in the control specimens (un-impregnated and un-heated) painted with polyester (8.98 MPa), and the lowest pull-off strength was found in the un-painted and un-heated specimens that were NS-impregnated (3.10MPa) (Figure 3). NS-impregnation generally increased pull-off strength in the heat-treated painted specimens. In the unpainted specimens, however, a reverse trend was observed.

**Figure 3.** Pull-off adhesion strength (MPa) of different treatments of beech specimens (error bars indicate the standard deviation for each column).
