Effects of NH₄Cl and MgCl₂ on Heat Treatment and Evaluation of Decay Resistance Given to Heat-treated Wood

Abstract

Heat treatment is one of the techniques to improve the resistance to decay and dimensional stability of wood. In this study, paid attention to those inorganic salt of NH4Cl and MgCl2, dilute NH4Cl and MgCl2 aqueous solution were impregnated into cedar (Cryptomeria japonica D. Don) sapwood and subjected to heat treatment at 160℃ to 180℃, and then the decay resistance was evaluated by a decay test using Fomitopsis palustris.The mass loss rate by heat treatment was about 3% for the wood without impregnation, whereas the impregnated wood exceeded 11% under the treatment condition of 180℃, and the accelerated thermal decomposition by inorganic salt was observed. As for the decay resistance, the mass loss rate of wood without heat treatment was 57%, whereas NH4Cl impregnated wood was suppressed to about 10%, and there was no significant decrease in the decay resistance due to the leaching treatment. On the other hand, it was suggested that MgCl2 impregnation wood had a large decrease in the decay resistance by performing the leaching treatment in advance, and that the composition after the thermal decomposition differed depending on the inorganic salt used. In addition, NH4Cl impregnated wood showed higher resistance to decay with a lower mass loss than that for MgCl2 impregnated wood under the same temperature and the heat-treated wood under higher temperatures.