Comparative Research Regarding the Hydrophilic Extractives Content in Turkey Oak and Sessile Oak Wood and Their Related Staining Susceptibility by Reaction with Iron

Abstract

The paper presents the experimental results concerning the amount of extractable substances and the color changes determined by the reaction of the tannins contained in wood with iron. Tests were performed comparatively with sapwood and heartwood samples of two Quercus species, namely Turkey oak (Quercus cerris L.) and sessile oak (Quercus petraea (Matt.) Liebl.). The findings show that Turkey oak sapwood has an unexpectedly high amount of extractable substances, higher than the heartwood of the same species. This result was obtained with three extraction methods (cold water, hot water, and NaOH 1% solution). The FTIR investigation of the extracts impregnated on quantitative filter paper seems to confirm these results. Visual assessment and color measurements after applying FeCl₃ highlight that both oak species are prone to staining in contact with iron due to their tannin content. The values of the total color difference between the state and after the reaction with FeCl₃, lower fer for Turkey oak compared to sessile oak, correlate with a lower extractive content of this wood species.