Research On The Permeability In Scots Pine And Southern Pine Of Silica Sols

Permability is one of the important physical properties of wood, which has a very important meaning in wood drying and wood impregnation modification. Wood permeability directly influences the selection of impregnation processes and improvement effect of wood drying and wood impregnation modification, which makes it a consistent focus in wood science area. The development of the traditional solution-based modifiers to novel micro or nano aqueous modifiers puts forward new requirements to permeability research. Two particle sized silica sols (30nm and 150nm), with the maximum concentration of 30%, were used to impregnate Scots pine (Pinus sylvestris) and Southern pine (Pinus spp.) sapwood to investigate the influence of particle size and concentration, initial moisture content of different species, and different impregnation parameters (impregnation pressures and times), so that providing specific and instructive data for the permeability research of micro or nano modifiers in wood and laying the foundation for later research. The main conclusions of this study are drawn as follows:1. For both vacuum-atmospheric and vacuum-pressure processes, the influence of particle size on silica sol penetration in two different wood species was consistent and significant. Namely, the liquid adsorptions (LAs) and weight percent gains (WPGs) of 30nm silica sol impregnated wood were significantly higher than those of 150nm. Furthermore, the axial distribution gradients of silica after impregnating with 30nm silica sol were lower than those of 150nm silica sol, suggesting that the permeability of 30nm silica sol was better than 150nm, namely, the lower particle size of silica sol resulted in the better the permeability.2. The study on vacuum-atmospheric process showed that the influence of concentration on permeability was also significant. Generally, the higher concentration corresponded to the lower LAs and higher WPGs, and more obvious axial distribution gradients of silica in wood specimen. Namely, the higher the silica sol concentration was, the worse the permeability in wood would be. In addition, the combined effect of particle size and concentration was much larger, that was to say, when high concentration silica sol was used to treat wood, the influence of particle size on permeability was more significant; while big particle size silica sol was used, the influence of concentration on permeability was more significant.3. There was a great difference between the penetration of SiO2 sol in sapwood of Scots pine and Southern pine because of their different anatomic structure and pit membrane constitution. There are more incrusting substances on the pit membrane of Scots pine. Generally, by using vacuum-atmospheric process for longer time (24h) and low pressure impregnation for shorter time (0.2MPa-60min), LAs and WPGs of Scots pine were higher compared with Southern pine, whereas, for long-time low pressure impregnation (0.2MPa-120min) and high pressure impregnations (0.4,0.8MPa), LAs and WPGs of Scots pine were lower than those of Southern pine. Numerous SiO2 would react with the extactives in Scots pine and disposited at the unsealed end of samples, which resulted in the great longitudinal concentration gradients and nonuniform distributions. But the penetration of water and silica sol particles was simultaneous in Southern pine.4. The influence of initial moisture contents on silica sol penetration in wood was also significant, which was related to different silica sol particle sizes and wood species. The LAs of 30nm and 150nm silica sols achieved the highest at air dried and conditioned moisture contents, respectively. What should be noted was that regulations of the deposition of silica in wood were different from LA, namely, the penetration of water and SiO2 was not silmultaneous in some cases.5. Both impregnation pressure and pressure time showed effect on penetration of silica sol in wood, namely, both impregnation pressure increment and pressure time prolonging could imcrease the silica sol penetration in wood to some extents. However, the prolonging of treatment time could only increase the whole LAs of wood samples, and numerous silicas could only deposite at the unsealed end of wood specimen and could not enter inside. The elevated pressure could not only improve the whole LAs, but also improve the permeability of silica particles and the uniformity of its distribution.6. The distribution of silicon in wood cell walls was uneven according to the EDXA results.