抄録
As the first stage to clarify effects of heating on dynamic viscoelastic properties of dry wood, dynamic viscoelasticities and weight loss of dry wood were continuously measured in dry air at constant temperatures ranging from 120°C to 200°C for 100 minutes. The results obtained were as follows. 1) Relative storage elastic modulus per residual weight increased with time at all measuring temperatures. This means the elastic modulus of residual part increased by heating. 2) Relative loss modulus per residual weight at higher temperatures remarkably decreased with time in the initial stages of heating below 180°C. 3) Relative loss modulus per residual weight in the late stages of heating decreased similarly among different temperatures below 160°C, decreased slightly at 170°C and 180°C, and then decreased markedly at 190°C and 200°C. Both decrease in fluidity by developing more compact microstructures and increase in fluidity by thermal degradation affected the dynamic viscoelasticity of dry wood. The results 1) and 2) are attributable to development of more compact microstructures of dry wood caused by activation of the molecular motion. The result 3) is possibly explained that below 160°C influence of becoming more compact microstructure on dynamic viscoelasticity overcame that of thermal degradation below 160°C, both influences were almost same at 170°C and 180°C, and the former influence largely overcame the latter influence at 190°C and 200°C, at which dry lignin and hemicellulose have been considered to reach their thermal softening temperatures. 4) The changes in dynamic viscoelasticity differed in measurement frequencies. This is deduced that the sizes of responsive units affected by developing the more compact microstructures and thermal degradation were different each other.
