Page 193 - Advances in Textile Biotechnology

174 Advances in textile biotechnology

increased protein stability and increased resistance to chemical and proteo-
lytic degradation.

8.3 Application of enzymatic treatments to
wool fi bres
8.3.1 Wool fi bres

Raw wool sheared from sheep contains a high level of grease which con-
tains valuable lanolin as well as dirt, dead skin, suint, and vegetable matter.

A typical Merino fleece contains about 13.6% wool wax, 3.1% suint and
12.9% dirt (inorganic and organic) (Prins, 2009). The average yields of clean
dry wool vary according to the breed, but generally Merino types yield
60–70% of clean wool after processing.

Electron scanning microscopy shows that the wool fibre is covered by a
thin sheath of overlapping scales like the slates on a roof (Fig. 8.1). These
scales are responsible for the felting and shrinkage that occurs during laun-
dering. This is due to the differential frictional effect (DFE) caused by the
difference in friction between μ a (friction coefficient when rubbing in the

against-scale direction) and μ w (friction coefficient when rubbing in the

with-scale direction). Finishers can make use of this property in a process
known as milling to achieve consolidation of the fabric and make it fuller
and denser. On the other hand, felting shrinkage can be detrimental to the

performance of wool fabrics. Shrink-resist finishing is required to give wool
fabrics and garments machine washability.

10μm
EHT = 12.00 kV WD = 10 mm Mag = 1.75 K X
3μm Photo No. = 1147 Detector = SE1
8.1 Scanning electron micrograph of wool fi bres.

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