Formation of hydrophobic wood surface by means of thermal treatment and surface modification with alkyl ketene dimer (AKD)

One of the major shortcomings of wood-based materials compared to technical materials is attributed to their poor dimensional stability in changing climates and in contact with liquid water. Heat treatment induces chemical change with a consequent decreasing of reactivity of the material showing unwanted surface inactivation. Alkyl ketene dimer (AKD) is a widely used sizing agent in papermaking, which serves to reduce the uptake of water into paper and thus ensures e.g. printability. AKD molecules can directly react with hydroxyl group of cellulose forming β-ketoester linkages by esterification. In the present study, AKD has been studied as a potential hydrophobic reagent for thermo-treated and untreated wood. To understand how thermo treatment and AKD influences the wood surface of two native species, (Alnus cordata Loisel and Cedrus deodara Roxb.), the samples were treated in Termovuoto® plant technology at 200 °C for 3 hours and then surface were sprayed with AKD, at 5% of solution. 0.5g/m2 and 1 g/m2 quantity of AKD for each treatment were used. The contact angle measurements and ATR-FTIR analysis on Alder and Cedar of treated and untreated wood were investigated. The main results indicated that the contact angle of aqueous solution against wood was changed during time. Treated alder showed an increase of wettability compared to untreated wood. No effect on cedar wood was depicted. When AKD was used the effect of heat treatment on wettability was negligible. A different chemical behaviour was observed on Cedar wood compared to Alder on both heating and AKD treatment effect.