Penetration and distribution of styrene in pressure treated hardwoods

A styrene impregnation method was used to compare liquid distribution in several species as affected by flow direction, sapwood/heartwood, and method of impregnation. Twenty-five mm ( 1") cubes were cut from the sapwood and heartwood of red maple (Acer rubrum), white birch (Betula papyrifera), yellow poplar (Liriodendron tulipifera), trembling aspen (Populus tremuloides), red oak (Quercus rubra), basswood (Tilia americana), red pine (Pinus resinosa) and American beech (Fagus grandifolia). Samples at 20-25% MC were sealed to permit either radial only or tangential only penetration or left unsealed and vacuum or pressure treated with catalysed and pigmented styrene. The styrene was polymerized in situ and the gross retention and penetration evaluated and the distribution in various cell types evaluated by light microscope. There were higher retentions and penetrations for tangential flow than for radial flow for all examined hardwoods except for red oak; red pine also was penetrated more readily in the radial direction. For transverse flow, the fibres were the most important flow paths in most hardwoods, with relatively little ray penetration, except in oak and the red pine (softwood). In uncoated samples, the vessels were the main flow paths, as expected, but the fibres were also significantly penetrated.