and elasticity. Wool is often degreased to remove the natural oils (lanolin in
the case of sheep’s wool) that coat it and give it water-resistant properties.
Wool is particularly valued as a textile fibre for its desirable properties in
terms of comfort. When it absorbs water, heat is liberated, making woollen fab-
rics ideal for cold, wet conditions; this ability to trap and retain water also keeps
the relative humidity at the skin comparatively high, making it a suitable
material for hot, dry environments. However, wetting weakens the fibres and
may promote bulk dimensional changes in fabrics. The bulky, crimped nature
of wool fibres ensures that the textiles contain a high proportion of air space,
giving them good insulative properties.
Wool fibres may be subjected to fullering– the fibres are treated with an
appropriate agent (traditionally mercury compounds were used), which causes
the individual scales on the fibre to stand proud of the surface, causing adjacent
fibres to become entangled, and increasing the bulk of the material. The process
can be employed to make non-woven woollen textiles (i.e.felt), but is also
employed to modify the properties of fibres used for yarns and fabrics, and
can give a durability to wool fabrics that is not found in the individual fibres.
Wool and hair fibres can be taken from a wide range of animal species such
as sheep, goats, camels, yak, musk ox, llamas and related species, and ‘fur’ ani-
mals (rabbits, foxes, beavers and the like), among others. The properties of these
fibres are dictated by the source, and these variations can influence length,
diameter and fineness, mechanical characteristics and durability, colour and
dyeability.
5.3 Degradation of Wool
Like other natural fibres, wools are subject to attack by heat, light, acid and alka-
line hydrolysis, the action of fungi and other microorganisms, and by mechan-
icaldamage (wear and tear), but in contrast to the other fibres, wool is also
particularly prone to insect attack. As wool is primarily a proteinaceous fibre,
the chemistry of wool is largely dictated by protein chemistry. In general these
fibres are more susceptible to chemical deterioration than are silks, due to dif-
ferences in the chemistries, structures and micro-structure of the fibres. The
composition of silk fibroin ensures that it can adopt extensive -sheet struc-
tures, which in turn form chemically-resilient crystallites. Wool, on the other
hand, is significantly more amorphous in structure, allowing degradative reac-
tions to propagate much more rapidly, particularly once the resilient outer
layers of the fibre cells have been damaged. Oxidation will attack the protein
chain in general, especially at susceptible side-chains, and most notably will
lead to the scission of the structurally-important disulfide bridges; this oxi-
dised wool is soluble in basic solutions. However, wool fibres tend to exhibit
a greater resistance to photodegradation than do silks.
88 Chapter 4