Effective changes in cellulose cell walls, gas permeability and sound absorption capability of Cocos nucifera (palmwood) by steam explosion

Steam explosion is a useful method to soften and dimensionally stabilizing wood. A significant increase in air permeability and sound absorption capability of steam-exploded palmwood compared to untreated palmwood is observed due to changes in cell wall. Cell wall’s changes are characterized by instrumental techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscope and gas permeability by capillary flow porometry and sound absorption coefficient by two-microphone transfer function method. The average increase in air permeability (259.3%) and sound absorption coefficient (52.33% at frequency range of 250–6400 Hz) of steam-exploded samples is higher than that of untreated samples. Color of steam-exploded woods become black due to chemical reactions in cell wall during steam explosion. The color change, air permeability and sound absorption coefficient of wood are correlated with the findings. These results suggest that low-pressure steam explosion could be considered as an effective technique for improving the air permeability and sound absorption capability of palmwood in the longitudinal direction. This approach could be useful to manufacture sound absorption board to control the acoustical housing environment.