DYNAMIC VISCOELASTIC PROPERTIES OF WOOD I N VARIOUS STAGES OF SWELLING

Viscoelastic properties of wood (hinoki; Chamaecyparis obtusa Endl.) s wollen in ten different organic liquids (Table 1) were studied and com pared with those swollen by moisture and liquid water. The dynamic mod uli of elasticity (E') and the dynamic losses (E '') in the radial dir ection were measured over the temperature range of 10 to 90 degrees C under forced stretching vibration of 0.05 Hz. At a constant temperatur e of 20 degrees C, the E' of the samples swollen by moisture were almo st constant in the range of 0 to about 30% relative swelling, they the n decrease with increasing relative swelling (Fig. 1), and E '' of the samples swollen by moisture became a maximum at a relative swelling o f about 30% (Fig. 2). Most of samples swollen in organic liquids had l arger E' and E '' than those swollen by moisture to a similar degree. This tendency was more obvious for E '' than for E' (Figs. 1 and 2). T his behavior of E '' was very similar to that of the moduli of rupture in bending (MOR) obtained in a previous study(3)) (Fig. 2). In most s wollen samples, temperature ranges in which E' decreased and E '' incr eased extensively were recognized except in the samples in relatively small and very large swelling states. The E '' of these samples decrea sed with increasing temperature after becoming maximum. The temperatur e regions differed among samples swollen in different organic liquids (Figs. 5 and 6). The behaviors of E' and E '' mentioned above could be explained by a simple viscoelastic model which takes into accounts th e packing effect by the proper adsorption of liquids and the thermal s oftening of the wood in a swollen state (Figs.4 and 7). From these res ults, viscoelastic properties of wood in various swelling states shoul d be related to the packing effect by the adsorption of swelling liqui ds, differences in broken numbers of hydrogen bondings between molecul es of the wood constituents among the samples swollen by different liq uids having different molecular sizes, cohesion forces of liquids, ads orption forces between liquids and wood, and temperature dependencies of the latter two properties.