X-ray photoelectron spectroscopy of wood treated with hydroxymethylated resorcinol

This paper attempted to use X-ray photoelectron spectroscopy (XPS) to determine the surface chemistry of wood treated with hydroxymethylated resorcinol (HMR), a coupling agent that enhances the durability of wood adhesive bonding. Wood veneers of hard maple were soaked in HMR solution for either 1, 15, or 30 min. XPS analyses showed that the treated surfaces exhibited an increase in the non-oxidized carbons (C1), a decrease in C-O bonds (C2), and an unaltered or decreased C{double bond, short}O or O-C-O bonds (C3), when compared to the control (unsoaked) samples. Despite these findings, the oxygen-to-carbon (O/C) ratios increased with HMR treatments, and the attributes of carbonate species ( CO₃^{2 -} and HCO₃^-) were identified. Further analyses revealed that these species were of sodium salts, which also formed in sodium hydroxide (0.08 N) treatment of wood. Overall, this study paves the way for relating the surface oxidation states of the treated wood to the adhesive bond strength, with an ultimate attempt to identify the possible roles of surface chemistry in adhesion durability of wood products.