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

Wood preservative treatments are indispensable for wood used in severe environmental conditions. Decay occurs in preservative-treated woods due to the poor impregnation of sapwood; this problem has recently gained attention for Cryptomeria japonica kiln-dried logs. To clarify the causes of this phenomenon, the influence of drying temperature on the penetration of preservative into sapwood logs was investigated. Sapwood samples taken from logs dried at 20 °C to 120 °C were impregnated with copper azole (CuAz). The bordered pits of these samples were observed by scanning electron microscopy (SEM). These results revealed that CuAz absorption decreased with increased drying temperature. The CuAz penetration was deepest for the samples dried at 20 °C. The occurrence of neutral-position bordered pits tended to decrease with increasing drying temperature. These results indicated that there is a strong relationship between the drying temperature and the appearance of bordered pits. Furthermore, the preservative permeability decreased with increasing drying temperature. This result implies that one factor restraining fluid permeability is the aspiration of bordered pits.