Forming textured hydrophobic surface coatings via mixed wax emulsion impregnation and drying of poplar wood

Hydrophilicity of fast-growing plantation wood is the major restriction for its outdoor applications. Herein, a novel method is reported for improving the hydrophobicity of Cathay poplar ( Populus cathayana Rehd.) by using a paraffin/carnauba (5:5 and 7:3)-mixed wax emulsion system. The poplar samples were impregnated in the single or mixed wax O / W emulsions of 4% solid content with subsequent drying treatment at 70 °C, which was higher than the paraffin wax melting point but lower than that of carnauba wax. The images obtained by field emission scanning electron microscopy confirmed that the mixed wax emulsion treatment developed textured surfaces in the inner lumen surface of wood cells and on the external surfaces of the samples comprising a continuous paraffin wax film with carnauba wax micropillars embedded in it. Contact angle analysis and water absorption tests show that the textured surface imparted the mixed wax emulsion-treated wood good hydrophobicity, rendering the initial contact angle greater than 140° and improving not only the surface property but also the long-term (120 or 192 h immersion) water repellency. In addition, free and bound water fractions in the treated wood were measured quantitatively using low-field nuclear magnetic resonance. The results show that the mixed wax emulsion treatment significantly decreased the free water content and delayed the bound water adsorption. In conclusion, this mixed wax emulsion treatment can be potentially utilized as a highly efficient wood hydrophobization method for expanding wood applications outdoors.