Investigation on stability and moisture absorption of superhydrophobic wood under alternating humidity and temperature conditions

Abstract The application of superhydrophobic wood is majorly limited by its durability when subjected to natural conditions. Herein, the stability of two representative superhydrophobic woods (i.e., Poplar ( Populus tomentosa ) and Chinese fir ( Cunninghamia lanceolata )), were prepared via a one-step hydrothermal process using tetrabutyltitanate (Ti(OC 4 H 9 ) 4 , TBOT) and vinyltriethoxysilane (CH 2 CHSi(OC 2 H 5 ) 3 , VTES) as a co-precursor and sequentially tested under different humidity and temperature conditions. The variables including morphology, water contact angle (WCA), color parameter, chemical components of the surface, and moisture absorption property were characterized using a scanning electron microscope (SEM), WCA measurement, a colorimeter, a Fourier transform infrared (FTIR) spectroscopy, and a moisture absorption test, respectively. It was found that initial static WCAs of superhydrophobic wood were larger than 150°. Micron-sized cracks were formed on the coatings after the alternating humidity and temperature aging cycles. This lowered the water repellency, but the WCA was still greater than 140°. There was nearly no chemical change of wood after the aging test; the color change between the same species of untreated and superhydrophobic wood was very small, only with a difference of 0.42 and 4.05 in overall color change ΔE ∗ values for Chinese fir and poplar, respectively. The superhydrophobic coatings had a trivial influence on wood moisture absorption property, which only lowered 3% in poplar and 2% in Chinese fir, respectively.