Surface Composition and Interaction of Thermally Treated White Oak with White Sprits

The surface composition and energy of two thermally treated white oak stave sources and the acidic composition of their white spirit extracts were studied to determine whether composition of the maturing extract could be attributed to variability in surface composition due to degradation of lignin, cellulose, and extractives with thermal treatment and extraction. The sources were from the Ozarks and Appalachia. Surface composition was determined by X-Ray photoelectron spectroscopy (XPS). Surface energy was obtained from the wicking method of contact angle determination with probe liquids and application of the van Oss geometric mean equation. Acid-base properties and composition of the white spirit extract were identified from titration plots and gas chromatographic analysis of the extract using a column for separating volatile and free fatty acids, esters, and aromatic aldehydes.

XPS results showed a minimum oxygen-to-carbon (O/C) ratio and acid-to-base ratio at 150 ^οC for the Appalachian oak and 200 ^οC for the Ozark oak. The minimum O/C ratios were compared to theoretical O/C ratios of cellulose (0.83), lignin (0.34), and extractives (0.12). A decrease in O/C ratio was interpreted as an increase in high carbon content extractives and lignin at the surface, whereas an increase was interpreted as either increased oxidation due to thermal treatment or a decrease of these materials at the surface due to extraction. Greater increases were observed in the O/C ratio for the Ozark than for the Appalachian oak upon extraction at higher thermal treatment. The acidic-to- basic composition was defined as the ratio of alcohol (R-OH) and acid (R-COOH) groups to carbonyl (C=O) and aliphatic and aromatic carbon (C-C) groups. At lower thermal treatments the Ozark oak showed little change in acid-to-base ratio. Higher acid-to-base ratios and greater increases in this ratio were observed with the Ozark samples upon extraction at the higher thermal treatments. Surface energy analysis for acidic and basic functional groups present using the wicking method of contact angle analysis and van Oss geometric mean equation showed that the minimum acid-base ratio was obtained at 150 ^οC for both oaks. Gas chromatographic analysis showed greater activity upon extraction in the Ozark extract as evidenced by more peaks with greater signal strength.