Polyethylene glycol and silica sol penetration improves hydrophobicity and dimensional stability of wood after a short-time treatment

Abstract

Polyethylene glycol (PEG) and silica sol were used to improve the dimension stability and hydrophobicity of wood with different moisture contents (MC after oven drying, air drying: 10–12% and steam conditioning: 38–40%) via 24 h immersion treatment. The water in wood served as a medium for helping PEG diffusion into cell wall, resulting in a better dimensional stability for 38–40% MC wood. PEG impregnation could improve the dimensional stability but decrease the surface hydrophobicity due to its moisture affinity. PEG concentration (10, 20, and 30 wt.%) showed little influence on water contact angles (WCA) of treated wood. Silica sol impregnation could improve the dimensional stability and WCA. It was ascribed to the -OH consumption and filling effect in wood caused by silica sol networks. After combination treatment (one-step or two-step method), PEG and silica sol could provide a synergistic effect on improving dimensional stability and hydrophobicity of wood owing to the bulking effect and filling effect, respectively. In one-step method, as a lubricant and bulking agent, PEG could improve the ductility of the film formed by stiff silica via Si–O–Si cross-linked sol in wood. Moreover, the decreased surface hardness and compression strength of PEG treated wood were compensated by silica incorporation.