Page 140 - Handbook of Properties of Textile and Technical Fibres

Physical, chemical, and tensile properties of cashmere, mohair, alpaca 119

4.2.2.4 Ellipticity

Animal fibers are not circular in cross-section but elliptical. The ellipticity, sometimes
called the contour, of a fiber refers to the ratio between the major and minor cross-
sectional diameters of a fiber. Limited studies have shown the ellipticity of most
rare animal fibers are greater than that of Merino wool. Higher fiber diameter vari-
ability is associated with increased ellipticity of wool and this is likely in all animal
fibers. Increased ellipticity reduces spinning performance and may reduce the bending
rigidity and increase softness of animal fibers. Medullated fibers, which tend towards
kidney shaped in cross-section, have the highest ellipticity.
Ellipticity of Peruvian alpaca increases as MFD increases from a ratio of 1.15 at
22 mm to 1.28 at 32 mm(Villarroel, 1959). Using samples with an MFD of 28 mm,
Huacaya fibers were more circular than Suri fibers between MFDs of 21e44 mm.
The ellipticity of cashmere (1.20) is less than that of alpaca and qiviut (1.32e1.33)
with mohair and bison intermediate (1.22 and 1.24, respectively) (McGregor and
Liu, 2017). Nutritional manipulation of cashmere goats changed the ellipticity of cash-
mere from 1.14 to 1.29 (McGregor and Liu, 2017).
4.2.2.5 Frictional properties

Frictional properties affect the processing performance of fibers, fabric handle attri-
butes, fabric wear characteristics, and fabric felt shrinkage. Frictional properties of an-
imal fibers are greatly affected by the cuticle scale frequency, scale edge height, and
fiber crimp (curvature). With wool, Shah and Whiteley (1971) reported that the greater
the directional friction effect (the difference in friction between down the fiber or
against the scales and up the fiber or with the scales), the harsher the handle. This rela-
tionship was arrived at when both MFD and directional friction effect were used
together. Such a finding indicates that rare animal fibers with a low directional friction
effect would have softer handle than wools with higher directional friction effect.
As mohair differs from wool in frictional properties, the property has attracted some
research attention. Martin and Mittlman (1946) and Frishman et al. (1948) reported the
lower friction and lower differential friction of mohair due to less-prominent cuticle
scales. Smuts and Slinger (1972) related fiber friction in mohair to fabric handle. Hunt-
er and Kruger (1972) examined mohair yarn friction. It was found that the friction of
waxed mohair/wool blend yarns actually increased with increasing mohair content. By
scouring or extracting the yarns with a solvent prior to waxing, the yarn friction, sub-
sequent to waxing, could be reduced considerably and became approximately indepen-
dent of the mohair content of the yarn. It was suggested that it was not inherent
differences between the mohair and wool fibers, as such, that influenced the yarn fric-
tion but that it was extractable matter (grease, additive applied during processing, etc.)
present on the mohair that adversely affected the performance of the paraffin wax. The
effect of scouring methods and chemical modifications, such as chlorination and buff-
ering, on fiber friction coefficient and the differential fiber friction for mohair and cash-
mere were investigated by Holt (1995). A slightly lower directional frictional effect
was measured in Suri alpaca compared with Huacaya alpaca (Table 4.3). Camel hairs
were investigated by Matsukawa et al. (1997).