Effects of drying temperature for Cryptomeria japonica on the permeability of wood preservative. I: The permeability of dried logs

Treatment by wood preservative is indispensable for utilization of wood in severe environmental conditions. However, the problem of decay of preservative-treated woods because of poor impregnation in sapwood has recently gained attention for Cryptomeria japonica kiln-dried logs. In order to clarify the cause of this phenomenon, the influence of drying temperature of logs on the preservative penetration in sapwood of logs was investigated. Impregnation of CuAz into the sapwood samples derived from the logs dried at 20 °C to 120 °C and observation by scanning electron microscopy (SEM) of bordered pits revealed that the absorption of CuAz decreased with increasing drying temperature. CuAz penetrated the deepest for the samples dried at 20 °C. The occurrence of neutral-position bordered pits tended to decrease with increasing drying temperature. These results indicate that there is a strong relationship between drying temperature and the appearance of bordered pits. It was also determined that the preservative permeability decreased with increasing drying temperature. This implies that one of the factors restraining fluid permeability is the aspiration of bordered pits.