Thermal-softening properties of water-swollen wood - VII. The effects of lignin

In order to clarify the effects of lignin on the thermal-softening properties of water-swollen wood, we measured the temperature dependence of dynamic viscoelastic properties from 5 to 100 degrees C with the following four specimens; (a) cellulose sheet, (b) cellulose sheet holding milled wood lignin, (c) unlignified juvenile green moso bamboo and (d) considerably lignified juvenile green moso bamboo. In the measurement of (b) or (d), the relaxation process was observed around 80 degrees C. On the other hand, the relaxation process was not observed in the measurement of (a) or (c). This result revealed that this relaxation process was derived from lignin. Moreover, this relaxation process might be based on the micro-Brownian motion of lignin because of the appropriate value of the apparent activation energy and the relevant peak location of the loss tangent.