Hydrophobic treatment of bamboo with rosin

Abstract Bamboo is an eco-friendly and sustainable material that has great potential in construction. However, the excellent hydrophilic properties of bamboo restrict its further application in building materials. Rosin is a natural resin with low molecular weight. Its main component is resin acid, which is highly hydrophobic. It is also an eco-friendly material for treating bamboo. The objective of this study was to improve the hydrophobicity of bamboo with rosin. A rosin-ethanol solution was prepared, and bamboo was subjected to vacuum pressure impregnation with this solution at room temperature. During treatment, the rosin retention rate in bamboo increased rapidly with increased soaking time and tended to become stable after 4 h. After rosin treatment, the water uptake of bamboo decreased by 24.7%, meanwhile the swelling coefficient from air-dry to water-saturated conditions in the radial and tangential directions decreased by 23.11% and 21.36%, respectively. The water vapor sorption behavior of bamboo was investigated using a dynamic vapor sorption apparatus, and the results were analyzed using the Guggenheim-Anderson-de Boer model. After rosin treatment, the sorption isotherms of bamboo were still type II, with a decrease in the equilibrium moisture content of bamboo across relative humidity values. Bamboo surface wettability also decreased after rosin treatment, with an initial contact angle of 93°. Scanning electron microscopy revealed that the rosin formed a continuous and uniform film on the surface of bamboo and covered the vessels and pits.