Abstract
To clarify the dynamic viscoelastic properties of wood in nonequilibrium states, dynamic viscoelasticity of water-swollen wood with different drying or heating histories were measured at several frequencies. In the measurements after soaking in water at 10% of moisture content or after quenching from boiling state, the storage elastic modulus (E') increased and the loss elastic modulus (E'') and the loss tangent (tanδ) decreased with time at 30°C at all frequencies, except E' of the sample measured at 50Hz after soaking. The changing rates of these properties increase with decrease in frequency. In the measurement under stepwise heating and cooling cycles (5°C→35°C→5°C→65°C→5°C→95°C→5°C), lager E', and less E'' and tanδ were found during cooling processes than heating processes in the every cycles. This trend was remarkable at lower frequencies and for the samples with higher lignin contents. Each curve of E', E'' and tanδ in the every heating processes traced each curve of them in the every latest cooling processes. These results suggest that the dynamic viscoelasticity of water-swollen wood largely depend on the conformation of lignin, i.e., the thermodynamic states of lignin.
