Study of the transverse liquid flow paths in pine and spruce using scanning electron microscopy

Samples of pine (Pinus sylvestris) and spruce (Picea abies) were impregnate d with a low-viscous epoxy resin using a vacuum process. The epoxy was cure d in situ and the specimens sectioned. Deposits of the cured epoxy was then observed in the wood cavities using a scanning electron microscope. The in vestigation concentrated on tracing the transverse movements of a viscous l iquid in the wood. and special attention was therefore given to the cross-f ield area between ray cells and longitudinal tracheids. A damage hypothesis is proposed based on the results obtained in the present investigation in combination with those from earlier studies on linseed oil-impregnated pine : In addition to the morphology of the bordered pits, viscous liquid flow i n wood is dependent on damage that occurs during the impregnation procedure . For pine sapwood. liquid flow is enabled through disrupted window pit mem branes. which divide the longitudinal tracheids and the ray parenchyma cell s. A mechanism accounting for the reduced permeability of pine heartwood is believed to be deposits of higher-molecular-weight substances (extractives ) in the ray parenchyma cells and on the cell walls. In spruce the thicker ray cells in combination with the smaller pits, which are connected to the longitudinal tracheids, reduce permeability considerably.