Changes in Permeability and Sound Absorption Capability of Yellow Poplar Wood by Steam Explosion Treatment

Abstract

Wood is widely used as a housing material because of its environmental superiority, good mechanical properties, fine appearance, and high thermal insulation properties. However, wood is a sound reflecting material with a relatively low sound absorption capability. It is recognized that the sound absorption capability of wood is influenced by air permeability that varies by the sound incident surface structure. Wood is a porous material which has numerous cylindrical pores in the fiber direction. However, the permeability of wood is relatively low because there are very few continuous pores in wood. The pores in wood are classified into three types: through, blind, and closed. Among these pores, only the through pore has continuous vessel elements that readily permit fluid flow. Furthermore, the formation of pit–aspirations in softwoods or tylosis in hardwoods restricts the air or liquid flow in wood. Improving the permeability of wood has been an interest of many wood researchers because highly permeable solid wood can be treated easily by a functional treatment that allows the good dimensional stability, fire proofing, and other traits. It is generally recognized that wood treatability increases with permeability. Several treatments, such as steaming, extraction with solvents, and degradation with enzymes or microorganisms, have been attempted to increase the permeability of wood. However these treatments did not have a sufficient effect on increasing permeability, and a useful method has not yet been developed. In a previous paper, Kang et al. (2008 a) reported that the delignification treatment by Wise’s method improved wood permeability in the fiber direction, and that the sound absorption capability on the cross sectional surface of Larix kaemferi increased, as compared with the control wood. Also, it was found that the sound absorption capability of a mushroom bed log of Mongolian oak degraded by fungus over four years was 2–3 times higher than that of control wood (Kang et al., 2008 b). On the other hand, steam explosion is used in the field of pulp and fiberboard manufacturing or the wood– based biomass industry and is exposure to violent pressure and temperature changes via steam. For this treatment, the target material is mounted in a closed chamber, and then superheated steam is introduced from a boiler. The superheated steam heats the chamber and target material to a high temperature and pressure, which is maintained for a moment and then discharged abruptly by a blasting device. By this process, high–pressure Changes in Permeability and Sound Absorption Capability of Yellow Poplar Wood by Steam Explosion Treatment