Page 151 - Handbook of Properties of Textile and Technical Fibres

Physical, chemical, and tensile properties of cashmere, mohair, alpaca 129

4.4.3 Felting and softness

Felting is a unique attribute of animal fibers being useful for the production of textiles
but also a potential disadvantage in knitwear as a consequence of dimensional
shrinkage during laundering. With rare animal fibers propensity to felt is mainly
related to variations in compressability and fiber curvature (crimp) with far lesser ef-
fects of MFD (McGregor and Schlink, 2014). Essentially increasing resistance to
compression and fiber curvature reduced the propensity to felt. There were differences
between propensity to felt and origin of cashmere and between rare animal fibers.
Cashmere grown by poorly fed goats had a lower propensity to felt compared with
cashmere grown by better fed goats probably related to differences in fiber curvature,
even though cuticle scale frequency was higher (McGregor and Liu, 2017). A conse-
quence of the progressive blending of cashmere with a low fiber curvature with super-
fine wool (high fiber curvature) was an increased propensity of the blend to felt, but
when the same cashmere was blended with low curvature superfine wool there was lit-
tle or no effect on feltability. It appears possible to source cashmere that has different
propensities to felt based on fiber curvature and therefore to produce textiles that are
likely to have different textile properties.
The factors affecting the softness (compression) of rare animal fibers showed that
fiber type, fiber curvature, and MFD were the most important (McGregor, 2014). Vari-
ation in fiber diameter coefficient of variation and fiber color were of much lesser
importance on softness. Other attributes of these rare animal fibers, which may also
contribute to differential deformation of the fibers and reduced fiber bending stiffness,
include the following: cashmere fibers have a lower number of cuticle cells found
around a fiber cross-section than Merino wool fibers (Tester, 1987); fewer cuticle cells
per unit length of fiber than wool; higher proportion of orthocortical cells compared
with wool; greater fiber ellipticity compared with wool (Tucker et al., 1988; McGregor
and Quispe, 2017); and different internal lipid content compared with wool (Logan
et al., 1989).

4.4.4 Dyeing
Because medullated fibers, and particularly kemp, tend to lie on the surface of yarns
and fabrics and are generally much thicker than the surrounding fibers, the visual
and other effects they produce can be out of proportion to the actual quantity present.
Furthermore, dyed medullated fibers generally appear much lighter than the surround-
ing dyed nonmedullated fibers, and show up prominently in the fabric. This occurs as
the medulla affects the optical properties of light passing through the fiber by diffrac-
tion, not from differences in dye uptake by the keratin of the fiber (Hirst and King,
1926; Hunter, 1993). Many animal fibers are used in blends with man-made fibers.
Sch€ afer (1994) reported that cationic dyestuffs, which are used to dye the acrylic
component of polyacrylonitrile/wool blends, may accumulate in the medulla of coarse
keratin fibers. According to Sch€ afer (1994), this is due to the lower degree of cross-
linking of the medulla by cystine bonds, to its higher porosity and to its acid character
(higher content of acid amino acids as glutamic acid, aspartic acid). Also, a preferential