Page 139 - Handbook of Properties of Textile and Technical Fibres

118 Handbook of Properties of Textile and Technical Fibres

commercial dehaired cashmere the incidence of residual medullated fibers should
be <0.2% (McGregor, 2000a,b; McGregor and Postle, 2004a). While the occurrence
of medullated and kemp fibers are occasionally acceptable, or even desirable for spe-
cial effects such as the Shetland wool effect, the presence of even a small amount in
otherwise high-quality fiber may have a pronounced adverse effect on its value and
end-use potential (Hunter, 1993; McGregor and Butler, 2004).
Environmental factors are the largest source of variation affecting the incidence of
medullated fibers in mohair. The effects of these factors appear variable and the accu-
racy of detection is also variable making the study of medullation in fleeces difficult
(Lupton et al., 1991). The introduction of the OFDA100 made detection of medullated
fibers faster, more reliable, and substantially cheaper (Lupton and Pfeiffer, 1998;
IWTO-57, 2006). Lupton et al. (1991) reported no medullation in mohair at an
MFD of 20 mm. Medullated fibers increase with increasing live-weight of goats and
increasing MFD of mohair, and these responses are largely functionally separate
and not influenced by fiber length growth (McGregor et al., 2013a,b). Thus there ap-
pears to be some unrelated and unreported physiological mechanism that favors the
production of medullated fibers in larger Angora goats, possibly related to skin follicle
density. The occurrence of kemp and other medullated fibers in greasy and scoured
Australian mohair is influenced by grazing and nutrition management (McGregor,
2010). These results suggest that nutritional management influences the incidence of
medullated fibers, presumably via perturbed keratinization in the skin follicle bulb.
Villarroel (1959) investigated the incidence and size of the medulla in Peruvian
Huacaya and Suri alpaca fiber. At MFD of 29.0 mm, only 25% of fibers were nonme-
dullated, 27% of fibers had fragmented or interrupted medullas with fiber diameters
20e40 mm, and the remaining fibers were medullated and coarser than 40 mm. In
Australian Huacaya and Suri alpacas the incidence of medullated fibers increased
linearly from 10% to 60% by weight, as the mid-side MFD increased from 22 to
40 mm(McGregor, 2006a). For Huacaya and Suri alpaca the incidence of medullated
fibers increased 3.1% and 2.5% units respectively for each 10 kg increase in live
weight. The mean incidence of medullated fibers in animals 5e8 years of age
was about double than that of 1- to 4-year old animals probably as older alpacas are
heavier. Medullated fibers are more noticeable in fine alpaca as the fiber diameter of
medullated fiber is up to 40% greater than the MFD for the fleece, whereas in coarser
fleeces the differential between the medullated and unmedullated fiber declines to 10%
(McGregor, 2006a).
For a number of rare animal fibers, the high incidence of medullation reduces the
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average specific density from about 1.30 to 1.31 g/cm (averages for wool, cashmere,
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and mohair) to about 1.28 g/cm for alpaca and llama and for Angora rabbit
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1.20e1.26 g/cm (which may have multiple medulla channels within the fiber) (Blan-
kenburg and Philippen, 1988; Hunter, 1993). Variation in the specific density of An-
gora fiber may affect blend ratios, and other properties of Angora textiles
(Blankenburg and Philippen, 1988). They also reported differences in specific density
and medullation between samples of Angora fiber from different sources.