Liquid Flow Paths Into Wood Using Polymerization Techniques– Douglas-Fir and Styrene

The path of flow of a liquid into Douglas-fir was studied by forcing catalyzed monomeric styrene into wood and polymerizing the liquid to a solid condition. Microtome sections were prepared and studied by microscope to determine the characteristics of liquid movement and the paths of flow. Wood blocks were injected longitudinally, radially, and tangentially. In the longitudinal direction, the bulk of the flow was through the tracheids. Some penetration of resin canals occurred. Liquid also moved into many of the ray tracheids and spread laterally by this means. In radial impregnation, the liquid moved mainly in the ray tracheids. Ray parenchyma cells were mostly impermeable. The liquid moved from the ray tracheids occasionally into longitudinal tracheids. Radial intercellular spaces between ray parenchyma cells and longitudinal tracheids sometimes conducted liquid. In tangential impregnation, the penetration was comparatively slow. Movement was through tracheid bordered pits, and into and across ray tracheids to some extent. The sapwood showed a larger number of penetrated cells than the heartwood. Tracheids in either zone often had broken columns of liquid in the lumens. The degree of filling varied from a coating of the cell, walls to completely full. Liquid, moved along by gas pressure, often lodged in the angles of the walls and in the bordered pits. Partial solvent seasoning increased the degree of cell penetration of the wood. The results give a clearer idea of what is taking place in liquid treatments of wood such as in empty-cell preservative treatments, resin impregnations, gluing, and coating applications. All cells do not contribute equally to flow, some appear impermeable. This makes for uneven treatments. Liquids may form a discontinuous system between the surface and the interior of the wood. In impregnated small pieces, there probably exist small pockets of liquid and of air.

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