Mechanism for De-aspirating Pits in Subalpine Fir by Steam Explosion Prior to Drying

Abstract

Subalpine fir with wet wood (wet pocket wood) is regarded as a species that is difficult to dry. Aspirated pits are one of the principal reasons to block water paths up in wood tracheids. Steam explosion is a technology to improve the dryability of subalpine fir by creating water paths in some aspirated pits. In this study, green subalpine fir lumber was treated with steam explosion. Samples taken from the lumber before and after the treatment were observed with a scanning electron microscope (SEM). Amechanism for de-aspirating pits during the process of steam explosion was proposed based on the understanding of wood anatomy. A series of observations with the SEM verified the mechanism for de-aspiration. The observations also discovered that the fractures in the pits between ray parenchyma cells and earlywood tracheids occurred during the process of steam explosion.