Page 201 - Advances in Textile Biotechnology

182 Advances in textile biotechnology

post-treatment with transglutaminase can regain 3–5% fabric strength from
10–18% strength loss during the peroxycarboximidic acid oxidation and
protease treatment of wool. Transglutaminase has also been shown to graft

protein polypeptides, or fluorescein cadaverine onto the surface of the wool

fibre for special effects. It is reported that the crosslinking within wool fi bres
by transglutaminase can improve the resistance to enzyme attack, and
increase the resistance of wool to chemical and mechanical disruption. This

was claimed to be beneficial for protecting wool garments from detergent
damage (Cortez et al., 2005, 2007). However, the amount of lysine and glu-
tamine residues available for linkage by transglutaminase may be limited,

especially on the surface of undamaged wool fibre, restricting the extent of
enzyme reaction. Therefore, this may affect the wide application of trans-
glutaminases on wool.

8.4 Application of enzymatic treatments to silk fi bres
Silk is a natural protein fibre. The best-known type of silk is mulberry silk

(Bombyx mori) obtained from cocoons produced by silkworm larvae, which
are cultivated in provided habitats and fed with fresh mulberry leaves.
There are other less cultivated silkworms, classified as wild silk, such as the

Tussah silkworm, the Muga silkworm and the Eri silkworm, which feed on
oak, polyanthus and castor oil leaves, respectively.
Raw silk spun by the silkworm Bombyx mori is a continuous strand

(about 300 to 900 m) of two fi broin filaments cemented together by a
gummy substance called silk sericin or silk gum. Silk fi broin fi lament is the
fibrous component that gives silk its unique physical and chemical proper-

ties. Sericin gum in raw silk provides protection during processing and so
is usually retained until the yarn or fabric stage. Removing harsh and stiff
sericin from silk fibroin leaves the silk fibre lustrous and with a soft handle.

Silk is regarded as a luxury fibre and widely used for textile fabrics, gar-

ments and bedding materials including silk-fi lled duvets.

Natural raw silk is composed of about 70–80% fibroin and 20–30% sericin
on the weight of the raw silk, respectively, with the trace of other natural
impurities such as wax, carbohydrates and mineral salts. Fibroin and sericin
are two different types of protein which differ in their composition and
structure. The difference between fibroin and sericin makes the removal of

sericin gum from fibroin possible without causing considerable damage to

the fi broin filaments. A manufacturing process for removing sericin gum

from silk fibroin is known as the degumming process. This can be carried
out in the stages of unreeled silk cocoons, yarns or fabrics. Some papers
have comprehensively reviewed degumming processes (Gulrajani 1992;
Mitra et al., 2009). Degumming processes have been developed based on
extraction with boiling water and superheated water at about 115 °C,

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