抄録
Mechanical stress relaxation was measured for raw and degummed silk in relation to the effects of sorbed water. The relation modulus of sericin was derived therefrom by assuming the additivity, where E(t)r•s, E(t)f and E(t)s are relaxation modulus of raw silk, degummed silk and sericin component, respectively. Vsis the volume fraction of sericin.
Time-humidity superposition was successfully applied to the stress-relaxation curves for raw silk, degummed silk and sericin. The obtained composite curve for sericin was similar to that for raw silk. Relaxation spectra were determined from these composite curves by means of the usual first approximation method. Both of the relaxation spectra for raw silk and sericin exhibited rather broad humps, while for degummed silk, a spectrum with a distinct maximum at ca. 105.3 second was observed.
The relation between the shift factor ac and water content was represented by Fujita-Kishimoto's equation. It was found that the increase of free volume is largely affected by the content of dissolved water, C2, which contributes fractionally to the total sorbed water. However, in case of degummed silk, the content of water of Langmuir type sorption, C1, could not be neglected in this respect. The value of the parameter, β, in the Fujita-Kishimoto's equation increased to another value over 55% R. H. for raw silk and sericin, whereas degummed silk gave three values for 0-55, 55-85 and 85-% R. H. regions. The equation was not applicable for raw silk and sericin, when R. H. was higher than 85%.
