Agriculture Reference
In-Depth Information
Endocuticle
Exocuticle
Epicuticle
Tyrosin
rich
protein
protein
Cuticle
Inter
microfibrile
material
Matrix
Cell
membrane
complex
Right hand
helix
Microfibrile
Figure 15.3 Structure of adult
mohair fi ber (from Smith, 1988).
Orthocortex
dyestuffs, other chemicals, and moisture throughout the
structure. The mohair cortex is predominantly (more than
70%) orthocortex that is chemically less resistant than the
remainder, paracortex. In contrast, fi ne wool usually con-
tains both types arranged bilaterally in approximately equal
amounts in the same fi ber. This arrangement is associated
with wool crimp and imparts to wool greater resistance to
chemicals and heat compared with mohair. In contrast,
cashmere down fi bers are composed of a mixture of ortho-
cortical and mesocortical cells, the latter having a structure
intermediate between that of ortho and paracortical cells.
Cuticle cells cover the fi ber surface in the form of
protective, overlapping scales (Figure 15.4). The protrud-
ing edge of each scale points from the fi ber root to the
tip. It has been suggested that an important function of
this structure is to anchor the fi bers in their respective
follicles. In wool, relatively thick scales (0.8-1.0
be the outside layer of the CMC. As mentioned previ-
ously, a third component of the fi ber, the medulla, is
contained in some of the fi bers produced by P follicles
and consists of a continuous or fragmented central core
composed of air-fi lled cell residues.
Mohair
The morphology and physical properties of mohair
have been reviewed in detail by Zahn (1990) and
Hunter and Hunter (2001), among others. Fine mohair
fi bers are round in cross section. As the fi bers become
coarser, the cross section becomes more elliptical. Some
kemp (highly medullated) fi bers are collapsed and have
the appearance of a fl attened straw. Mohair is more
crystalline than wool of comparable dimensions, which
helps to explain why mohair is stronger, more wear
resistant, less extensible, and stiffer than wool. Mohair is
characterized by excellent whiteness, luster, durability,
elasticity, resilience, resistance to soiling, soil shedding,
setting, strength, abrasion resistance, draping, moisture
and perspiration absorption and release, insulation, comfort
and pleasing handle, and low fl ammability, felting, and
pilling (see Table 19.2) (Hunter and Hunter, 2001).
Mohair's high luster, smoothness, soil resistance, very low
propensity for felting, and durability are largely a result of
the structure of the scales on the fi ber surface, which are
thinner, less pronounced (since they hardly overlap), and
longer (approximately 20
m)
protrude to such a degree that the fi bers felt or mat easily
when rubbed together in the presence of moisture
and heat. Because the scales on mohair are thinner
(0.2 - 0.5
μ
m) and lie closer to the core of the fi ber, the
felting propensity of mohair is lower than for cashmere
and wool. Scale height has been used to estimate the
composition of wool/mohair blends and to identify
unknown animal fi bers. Currently, DNA testing is con-
sidered to be more accurate for the latter purpose, but the
analysis is only capable of differentiating species (e.g.,
ovine versus caprine) and not breed (e.g., Angora versus
cashmere goat). The cuticle is made up of three distinct
structures termed the endo-, exo-, and epicuticle, the
latter being a hydrophobic, semipermeable, fl attened
sheath on the very outside of the fi ber that may in fact
μ
μ
m) than those in wool of com-
parable fi neness.
Two main types of medullated fi ber are distinguished in
mohair (Figure 15.5). The objectionable kemp fi bers gen-
erally have a medulla that is continuous along the fi ber
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