Page 146 - Handbook of Properties of Textile and Technical Fibres

124 Handbook of Properties of Textile and Technical Fibres

similar MFD. Highly medullated or kemp fibers showed a very low stress at break and
poor extension. It is probable that this decrease in stress at break was due to an
increase in the size of the medulla in alpaca fibers with increase in the diameter of
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these fibers. Zak and Kobielarz (2010) reported that for 30 mm alpaca the Young’s
Modulus was 2.7 GPa (standard deviation 0.5 GPa) and the strength of single fibers
was 190 MPa. The Young’s Modulus and strength of alpaca yarns were respectively
350 and 50 MPa.
When comparing the single fiber tenacity of Australian alpaca (MFD 24.3 mm) with
Australian wool (MFD 23.0 mm), Liu et al. (2005) reported that the alpaca had a higher
tenacity (1.44 vs. 1.23 cN/dTex) and higher initial modulus (28.22 vs. 25.71 cN/
dTex), which may have been related to the higher variation in fiber diameter along
the wool fibers.
Cashmere and alpaca are sold in a range of natural colors. Much of this natural color
is bleached to enable the resultant paler fiber to be dyed to a greater range of end prod-
ucts (von Bergen, 1963; Forté, 1985). Similarly, yak wool is often bleached and then
dyed. Bleaching of fine yak hair knitwear resulted in a change in amino acid content
and reduced handle and fullness properties and reduced bending rigidity and shear ri-
gidity (Yan et al., 1998). The authors concluded that bleached fabric had a poorer
three-dimensional form, which may result in sewing difficulties and poorer garment
fit. Bleaching damages alpaca, reducing fiber strength and colorfastness and so for
most samples of these fibers the final textile product may not perform as desired
when compared with the highest quality of white fiber or with the unbleached tops
and yarns (Liu et al., 2004).

4.3.1 Staple strength

Most rare animal fibers have not been tested for staple strength and position of break as
is common with wool. This is because the raw fleeces are often a mixture with long
coarse medullated guard hairs, e.g., cashmere, and so the measurements are
confounded; the staples have low friction and slip or are tippy and do not measure
correctly in wool measuring equipment, e.g., mohair, Suri alpaca (McGregor,
2006a); the traded fiber does not have staples as it has already been dehaired, e.g.,
cashmere; or the fibers are harvested by combing the moulted downy fibers and the
resulting combed fiber resembles an entangled ball assemblage rather than aligned fi-
bers in a staple.
Wuliji et al. (2000) found New Zealand alpaca had a staple strength of 28e32 N/
ktex, values lower than desired, and more likely to result in significant fiber breakage
during processing. Australian Huacaya alpaca from five farms, covering the range in
MFD of 18.5e45.0 mm, indicated that staple strength averaged 76 N/ktex with a range
of 25e140 N/ktex (McGregor, 2006a). Huacaya staple strength increased as MFD
increased. For Huacaya alpaca from USA, staple strength was affected by sex and
age, with older heavier alpacas producing coarser fiber with higher staple strength. Sta-
ple strength for 1-year-old alpacas (MFD 24.3 mm) was 28 N/ktex, less than that for
older alpacas (41e56 N/ktex) (Lupton et al., 2006).