To clarify effects of lignin on the thermal-softening properties of water-swollen wood, dynamic viscoelasticities of water-swollen wood were measured in the temperature range from 5°C to 100°C. The results obtained were as follows. 1) Delignified wood and moso bamboo did not show thermal softening around 60∼80°C 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°C were attributable to lignin. Decrease in storage elastic moduli (E') of wood and moso bamboo from 20 to 100°C remarkably decreased with decreasing in their lignin contents. From this result, it can be concluded that the degree of thermal softening around 60∼80°C 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 the conformation of lignin.
