THERMAL-SOFTENING PROPERTIES OF WATER-SWO LLEN WOOD V - THE EFFECTS OF DRYING AND HEATING HISTORIES

The effects of drying and heating histories on the temperature depende nce of viscoelasticity in the radial direction for wet hinoki (Chamaec yparis obtusa Endl.) wood were investigated. Remarkable differences be tween green and wet specimens with drying histories were recognized in dynamic viscoelastic measurements with increasing temperatures. The d ynamic modulus (E') of wet specimens changed around 50 degrees C and 8 0 similar to 90 degrees C. These relaxations were considered to be due to the drying history and the micro-Brownian motion, respectively, of lignin molecules. However, the green specimens showed only one relaxa tion due to lignin. With increases of the time left in water, the E' a t room temperature of wet specimens with a drying history increased, a nd their loss peaks due to their drying histories were reduced. In the second measurement, the green specimens and the wet specimens with dr ying histories showed similar results. The E' at room temperature for green specimens decreased remarkably. The green specimens showed the l argest static Young's moduli (E) at 20 degrees C. The E in wet conditi ons at 20 degrees C decreased remarkably immediately after drying or h eating, but increased with time. These results suggested that drying o r quenching induced strains due to the orientational changes of the mo lecules composed of amorphous regions of cell walls, and long time imm ersions were necessary to release the strains.