MECHANICAL AND DIELECTRIC RELAXATIONS OF WOOD IN A LOW-TEMPERATURE RANGE .1. RELAXATIONS DUE TO METHYLOL GROUPS AND ADSORBED WATER

The dynamic viscoelastic and dielectric properties of spruce (Picea si tchensis Carr.) wood along the grain were measured in a temperature ra nge from -150 degrees C to 0 degrees C. A mechanical relaxation and a dielectric relaxation were observed in the absolutely dried condition. The relationships between logarithms of the frequencies at loss peaks and reciprocals of absolute temperature were represented by a linear equation. The apparent activation energies for these relaxations which were considered to result from the motions of methylol groups in the amorphous region of the cell mall were 9.8 kcal/mol. Other mechanical and dielectric relaxations appeared in the presence of a small amount of water. With increasing moisture content, the loss peaks for these r elaxations increased and their temperature locations shifted to lower temperatures. The apparent activation energies for these mechanical an d dielectric relaxations were 16 kcal/mol and 17 kcal/mol, respectivel y. These relaxations were considered to result from the motions of ads orbed water molecules. With increasing moisture content within 1%, the dynamic elastic modulus increased, and the loss peak due to the motio ns of methylol groups decreased slightly. These results show that the adsorbed water molecules increase the cohesive forces between the cons tituent molecules of the cell wall and slightly influence the motions of methylol groups.