Abstract
The complex modulus of single keratin fibres has been studied
at various extensions or times as well as at different relative humidities,
temperatures and frequencies . Two parameters of the complex
modulus were measured, namely the dynamic modulus and the loss angle.
To carry out measurements for the above studies a dynamic
mechanical tester was designed and constructed. By using a piezoelectric
element the apparatus allows for measurements to be taken in
the frequency range 6 Hz to 1500Hz, while with an environment conditioning
chamber the full range of relative humidities and the range of -100°C
to + 50°C for temperatures can be covered. Fine fibre samples can be
extended in the apparatus and tested at each extension. Considerable
precautions were taken in the apparatus to reduce noise because of the
small values of the signals detected.
By using the above equipment it was found that the modulus of
wool fibres decreases with strain up to intermediate extensions of about
20% and then increases with higher extensions. The loss angle variation
with extension is inverse to the modulus changes. The complex modulus
was also measured while fibres were extension cycled or relaxed at fixed
strains. More measurements were taken under other specific conditions
of strain. All of these results, it was shown, could be explained by
the application of the two-phase structure model of keratin: one phase
C being relatively impenetrable to water and possessing elastic properties
at all extensions, and the other phase M being water penetrable and
acting mechanically as a viscoelastic solid.
Measurements on fibres were carried out during abrupt relative
humidity changes at a constant frequency and temperature. For an abrupt
relative humidity increase it was found that the loss angle vs time
exhibits an overshoot at the time when the absorption is nearly completed,
while the modulus curve is changing markedly at the same
time. This result was compatible with the suggestion that the
structural mobility of the keratin fibre reaches a maximum at the
time when absorption is almost complete.
The complex modulus of wet keratin fibres was measured in
the frequency range of 6 - 1500 Hz at different temperatures between
0.2 and 45°C. Some measurements were taken at different relative
humidities. These results together with results of other workers
indicated the presence of a characteristic transition process in
keratin dependent strongly on the water content. This process was
attributed to the main chain motion in the M phase.