Pyrolysis Characteristics of NH₄Cl Impregnated Wood

Abstract

In our previous studies, heat treatment of cedar (Cryptomeria japonica D. Don) sapwood was carried out with a diluted NH4Cl aqueous solution impregnated. As a result, it was clarified that the decomposition of wood is promoted even by heat treatment at 150℃, and the decay resistance was improved. In addition, the heat-treated wood had an increased amount of acid insoluble components that contributed to the improvement of decay resistance.Therefore, we aimed to investigate the involvement of ammonium in the increased acid-insoluble components of wood in the heat treatment of NH4Cl impregnated wood. After impregnating wood with some ammonium salts and carried out heat treatment, the acid-insoluble components and nitrogen content of the heat-treated wood were quantified. In addition, we measured the thermogravimetric analysis of salt alone and cedar sapwood impregnated with salt aqueous solution and investigated the mechanism by which salt acts on wood components. The following became clear as that result.1) When the heat treatment was carried out by impregnating with an ammonium salt, the acid-insoluble component increased when all the salts were used. 2) Heat treatment of NH4Cl impregnated wood resulted in a darker color up to the interior of the wood. However, the NH4H2PO4 and (NH4)2SO4 impregnated woods had a darker color near the surface, but the color inside did not become so dark. 3) When the ammonium salt was heated at 170℃, NH4Cl disappeared by decomposition in about 4.5 hours, but other salts hardly decomposed at 170℃. 4) Only the NH4Cl impregnated wood had a significantly increased nitrogen content compared to the untreated wood.In the heat treatment of NH4Cl impregnated wood, it was clarified that the gas generated by sublimation and decomposition of NH4Cl salt by heating acted in a wide range and was reformed to the inside of the wood. In addition, ammonium or ammonia in the generated gas may react with wood components to form substances that are insoluble in acid, contributing to the improvement of decay resistance.