Study on hydrophobic characteristics of wood surface modified by a silica/silicone oil complex emulsion combined with thermal post-treatment

Silica and silicone oil complex silicon emulsion (short as complex silicon emulsion, CSE)was composed of silica (micron- and nano-scaled silica) and silicone oil (hydroxy silicone oil and hydrogen silicone oil) as raw materials and formulated in high pressure homogenization. After dilution to different concentration levels, CSE was mixed with catalyzer and used to treat poplar (Populus cathayana) sapwood samples in vacuum-pressure process and then post-treated with 180 ℃ thermal process to fabricate superhydrophobic wood surface. Water contact angle (WCA), water sliding angle (WSA), surface roughness (SR) of modified samples were measured and analyzed, and the microscopic morphology and element distribution in wood cell wall were investigated by field emission scanning electronic microscope coupled with energy-dispersed X-ray analyzer (FESEM-EDXA) and atomic force microscope (AFM). The results indicated that: 1) WCAs and WSAs on the three section surfaces of samples treated with 2.7% CSE combined with thermal modification meet the requirements for superhydrophobic surface. However, the hydrophobicity of modified wood surfaces decreased with CSE concentration; 2) compared with other high CSE concentrations, SR values on the three section surfaces of 2.7% CSE/thermally modified wood showed the most proximity to that of lotus leaf. Depending on the roughness of the wood surface or the silicone film, the surface roughness of the lotus leaf could not be simulated; 3) two-level compound mastoideus consisting of both micro- and nano-scaled protrusions emerged on the surface of modified wood, which can mimic the structure of lotus leaf; 4) silicon element distributed in wood cell wall, with much deposited on the surface of wood.