Surface energy of wood treated with water-borne wood preservatives

In this study, the contact angles of four different reference liquids (distilled water, diiodomethane, formadide and glycerol) formed on the surfaces of wood treated with chromated copper arsenate (CCA) and other two new-emerging copper-based water-borne systems (commercial name: NW and NS) were measured with a sessile drop method. Based on the contact angle data, the surface energy was obtained using a acid-base approach. The total surface energy consisted of a Lifshiz-van der Waals (LW) parameter and an acid-base (AB) parameter.Resultsshowed that NW and CCA treatments made the wood surface more hydrophobic while an NS treatment had the reverse effect on the wood surface mainly due to the increased penetration of earlywood. By using three liquids, diiodomethane, formamide and distilled water, the total surface energy obtained for untreated earlywood, untreated latewood, CCA-treated earlywood, CCA-treated latewood, NW-treated earlywood, NW-treated latewood, NS-treated earlywood and NS-treated latewood were 43.1, 44.5, 43.4, 45.1, 49.4, 40.6, 46.0, and 40.9 mJ/m², respectively. The surface energy of CCA-treated wood was almost the same as that of untreated wood. After NW and NS treatments, the surface energy of both earlywood and latewood both changed little. But for an entire piece of wood, the average surface energy of wood after NW and NS treatments remained the same.