Page 222 - Advances in Textile Biotechnology

Functionalisation of wool and silk fi bres using enzymes 203

treatments has recently been highlighted by Ge et al. (2009). They also
investigated the dyeing behaviour of wool and reported that treatment with
microbial TGase resulted in an increase of initial dyeing rate and shorten-
ing of dye exhaustion time, which were attributed to the higher wettability
of the wool fi bres.
The beneficial effects of microbial TGase on wool were further enhanced

when primary amine ligands were grafted onto the fi bres (Cortez et al.,
2007). Silk-derived sericin peptides were used as bridging agents. Depend-
ing on reaction conditions, sericin peptides were grafted not only at the fi bre
surface but could penetrate inside the cuticle reaching the outer cortex
layer. The increased crosslinking density improved not only wool fi bre
strength, but also resulted in better resistance to felting, which allowed
TGase-treated wool to be classified ‘machine washable’ according to Wool-

mark standards. The perceived softness of wool fabrics, a property highly
appreciated by end-users, was also signifi cantly improved.
In an attempt to overcome current limitations in the use of proteases as
antifelting agents, a simultaneous one-batch protease-TGase treatment of

wool fabrics was designed with the aim of exploiting the benefits of the
individual enzymes (Gaffar Hossain et al., 2008). The protease is expected
to erode the wool scales, which would bring about shrink resistance while
opening the wool fibre texture for the penetration of TGase and formation

of isopeptide crosslinks leading to improved dimensional stability and

mechanical performance. The results reported seem to confirm the initial
hypothesis. Higher level of shrink resistance, lower weight and strength
losses, and less fi bre damage were achieved in the combined enzyme treat-
ment compared with a single protease treatment.
The issue of recovering more or less extensive tensile strength losses
caused by antifelting treatments was also addressed by Cardamone (2007).
In an attempt to remediate the high strength losses caused by a two-step

chemo-enzymatic shrink-proofing process, a third processing step based on
the use of microbial TGase was performed. However, only a moderate
recovery of tensile strength of about 3–5% was achieved by TGase treat-
ment against an initial strength loss of 10–18% caused by the shrink-
proofing treatment. In another study, wool knits were subjected to only one

oxidative chemical treatment and then were treated with TGase in the pres-
ence of solubilised keratins with the aim of improving the dimensional
stability (Cardamone and Phillips, 2007). Good results were obtained under

optimised processing conditions in terms of shrink-proofing, which could
be minimised to about 5%, whereas strength loss was reduced to 4.7%.
According to SEM results, the solubilised keratins smoothed the fi bre
surface by filling the voids at the protruding scale edges. The mechanism of

TGase-mediated grafting of solubilised keratin peptides onto wool fi bres
was reported in a subsequent paper (Cardamone, 2008).

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