Effects of the Lignin on the Thermal-Softening Properties of the Water-Swollen Wood
Yuzo FURUTA, Masamitsu NAKAJIMA, Takeshi NAKATANI, Keisuke KOJIRO and Yutaka ISHIMARU
Abstract:To clarify effects of lignin on the thermal-softening properties of wat er-swollen wood, dynamic viscoelasticities of water-swollen wood were measured in the temperature range from 5 to 100. The results obtained were as follows. 1) Delignified wood and moso bamboo did not show thermal softening around 60`80 which was found for untreated wood and moso bamboo. From this result, it was found that the thermal softening of lingo-cellulosic materials around 60`80 were attributable to lignin. Decrease in storage elastic moduli (E') of wood and moso bamboo from 20 to 100 remarkably decreased with decreasing in their lignin contents. From this result, it can be concluded that the degree of thermal softening around 60`80 largely depends on lignin contents. 2) The thermal-softening temperatures were different among many kind of wood species (softwood, Japanese hardwood, Tropical hardwood) and between an untreated katsura (Cercidiphyllum japonicum ) sample and a sample slightly delignified. Consequently, it is deduced that the thermal-softening behaviors of water-swollen wood were largely affected by cross-linking of lignin. 3) The thermal softening behaviors of katsura were quite different among specimens experienced cooling with different rates. This suggests that the thermal-softening behaviors of water-swollen wood largely depend on th e conformation of lignin. Key Words:Thermal softening, Dynamic viscoelasticity, Water-swollen wood, Lignin content, Cross-linking of lignin, Conformation of lignin.