Page 96 - Handbook of Properties of Textile and Technical Fibres

Properties of wool 77

180

140

100
T g (ºC) 60

20

–20
0 10 20 30 40
Regain (%)
Figure 3.17 Glass transition temperature of wool as a function of moisture regain. The curve is
a fit of the Fox equation.
Adapted from Kure JM, Pierlot AP, Russel IM, Shanks RA: The glass transition of wool: an
improved determination using DSC, Text Res J 67:18e22, 1997.

dries (Huson, 1998)(Fig. 3.19). This is attributed to a matrix modulus, which increases
from 0.5 to 6e7 GPa during drying and a moisture insensitive modulus of 8e10 GPa
for the intermediate filament (Zahn et al., 2003). The mobility can similarly be
increased or decreased by altering the temperature (Fig. 3.18(b))(Speakman, 1927;
Mason, 1964; Cook and Fleischfresser, 1990; Aksakal and Alekberov, 2009). Slowing
down the rate of testing allows more time for molecules to move and so has the same
effect as increasing temperature or moisture levels; decreased stress in the yield region
(Speakman, 1927; Rigby, 1955; Mason, 1964), and the failure point moving to lower
stress and higher elongation (Speakman, 1927; Mason, 1964; Cook and Fleischfresser,
1990). Fig. 3.18(c) shows the results for fibers tested wet at an extremely slow rate
(10 mN/2 days), a normal rate (18 mN/min), and an instantaneous rate obtained by
extrapolation of strain/time data collected at a variety of constant stresses (Speakman,
1927).
It is well accepted (Speakman and Hirst, 1933; Feughelman, 1973) that outside of
the isoelectric region (pH 4e8) wool fibers are more readily extended. These studies,
however, did not extend fibers to break and there are no studies to show the effect of
pH on failure properties. In addition to changes in mobility, if wool fibers are exposed
to moisture and heat for extended periods, degradation will occur leading to a loss of
strength. This is covered in more detail in Section 3.5.5 (Effect of chemical
processing).

3.5.2 Effect of diameter and gauge length
Wool fibers vary naturally in diameter, both between fibers and along the length of
individual fibers (Fig. 3.16). It has been shown (Collins and Chaikin, 1965, 1968,
1969, 1971; Shah and Whiteley, 1966; He et al., 2001), both experimentally and