Page 101 - Handbook of Properties of Textile and Technical Fibres

82 Handbook of Properties of Textile and Technical Fibres

3.5.3 Effect of torsion and abrasion

During wear, fibers in a fabric are subjected to the repetitive application of a range of
different forces, generally resulting in low levels of strain, but eventually resulting in
fatigue failure of the fibers. Many attempts have been made to simulate wear in the
laboratory, using a variety of abrasion and flex fatigue tests (Morton and Hearle,
1993). While agreement with wear trials is only tenuous, abrasion tests remain popular
and the belief is that torsional fatigue plays an important role in the failure mechanism.
These repetitive low level strains have been shown to result in failure at the CMC
(Orwin and Thomson, 1975; Tester, 1984), resulting in fibrillation of fiber ends
(Anderson and Robinson, 1971; Wan et al., 2014)(Fig. 3.24). Others have shown
that subjecting wool to chemical treatments (such as sodium dodecyl benzene sulfo-
nate or the proteolytic enzyme trypsin) that damage the CMC results in a dramatic
decrease in abrasion resistance (Anderson et al., 1971). Attempts to modify the
CMC showed that treatment with o-chlorophenol (Anderson et al., 1971) and swelling
solvents such as ethanol (K€ orner, 1990), formic acid (Feldtman and Leeder, 1984), and
n-propanol (Feldtman and Leeder, 1984) led to significant improvements in abrasion
resistance. The mechanism by which this improvement is gained is not yet known but
the extraction of lipids and proteins from the cell membrane is believed to play a role
(Feldtman and Leeder, 1984; K€ orner, 1990). The treatment did not, however, lead to
any change in tensile properties as measured by wet bundle strength tests (K€ orner,
1990) or dry fabric tensile tests (Feldtman and Leeder, 1984).

3.5.4 Effect of crimp

Several workers (Barach and Rainard, 1950; Evans, 1954; Dusenbury and Wakelin,
1958; Gullbrandson, 1958; Collins and Chaikin, 1968; Ross, 1971; Bendit, 1980)
have investigated the effects of both natural and artificial crimp on the tensile proper-
ties of wool. A number of these studies (Evans, 1954; Dusenbury and Wakelin, 1958;
Collins and Chaikin, 1968; Bendit, 1980) showed that the modulus or Hookean slope
decreases with increasing levels of crimp. Evans (1954) interpreted the results by

Figure 3.24 Scanning electron micrograph of a piece of wool fabric (left) after failure by
abrasion and a close-up of the fibrillated fiber end (right).