An experimental study on pore structural changes of ultrasonic treated Korean paulownia (Paulownia coreana)

This study investigated the effects of ultrasonic treatment on the pore structure of the Korean paulownia (Paulownia coreana). Cylindrical samples (10 mm thickness and 29 mm in diameter) were taken from heartwood in longitudinal direction and divided into two groups; Group (A) consisted of samples with 2 to 3 annual rings, while the samples of Group (B) had 5 to 6 annual rings. Changes in pore structure, gas permeability, and sound absorption were measured after ultrasonic treatment for between 30 and 90 min. This study confirmed that open-pore porosity significantly increased as a result of ultrasonic treatment. However, gas permeability increased only within the first 30 min of ultrasonic treatment, but then did not increase proportionally with increasing treatment time. This study determined that during the early stage of ultrasonic treatment the number of through pores increased, but as treatment time was extended the number of blind pores increased but not the number of through pores. The sound absorption coefficient increased after ultrasonic treatment, but similar to gas permeability, only up to a certain point, beyond which increased treatment time did not result in further improvements. In addition, paulownia’s tyloses were broken by ultrasound treatment, which was responsible for the increase in blind-pore porosity.