Penetration of SiO2 sols in sapwood of Scots pine and loblolly pine.

In order to investigate the penetration of micro or nano emulsion modifiers in wood, SiO2sols with two different particle sizes (30 and 150 nm) and three concentrations (5%, 15% and 30%) were used to impregnate sapwood of Scots pine (Pinus sylvestris) and loblolly pine (Pinus taeda) under vacuum for 30 min followed by atmospheric pressure for 24 h. Then the time-dependent liquid absorption curves during 24 h and the weight percent gain at 24 h were tested. In addition, the longitudinal SiO2 concentration gradients of wood samples treated by 30 nm, 15% silicasols were obtained by mass method, and their longitudinal silicon distribution in wood cell wall was analyzed by using scanning electronic microscope coupled with energy dispersed X-ray analyzer (SEM-EDXA). The research results indicated that: 1) smaller particle sized silica sols are easier to penetrate in wood during the initial impregnation. With the impregnation proceeding, the influence of particle size weakened, and a reverse trend could even be observed. The concentration of silica sols also showed an obvious impact on liquid adsorption. Lower concentration usually resulted in higher liquid adsorption. The effect of particle size on liquid absorption was more obvious for wood treated with modifiers at high concentrations. 2) Wood species greatly affected the penetration of SiO2 sols. The liquid adsorption of sols in Scots pine sapwood was generally higher than that in loblolly pine. However, numerous SiO2 particles deposited at the opening end of Scots pine samples, resulting in non-simultaneous penetration of silica sol particles and water in Scots pines. As a result, the longitudinal SiO2 concentration gradient in Scots pines was much greater than that in loblolly pines. 3) SEM-EDXA analysis showed that the silicon could enter the wood cell walls in each axial depth profile. The scanned silicon concentration distribution was consistent with the results obtained by mass methods. These results are of great importance on improving the penetration of micro or nano emulsion modifiers in wood.