O o d h e a d p u b L i s h I n g L i m I t e d

8.1
Introduction
Wool fabrics and wool-blend fabrics are highly prized by consumers because
of their excellent comfort properties during wear, their drape characteristics
and, not least, the ability of the fibre to be dyed and finished to give a range
of high-fashion colouristic effects. Leeder
1
 points out that wool has been
bio-engineered over millions of years to be worn next to an animal’s skin,
and is thus better than other types of fibres in terms of comfort in wear; it
possesses the properties of absorbing up to 30% of its own weight of water
without feeling wet, and even giving out heat when it absorbs water. Wool
scientists have met the challenges of possible performance deficiencies such
as felting in household laundering procedures, and attack by moths and
beetles during garment storage, by applying innovative chemistry.
Wool thus enjoys a position in the marketplace as a fine natural product
whose reputation from the environmental impact point of view must be
secure. This simple statement actually has profound implications for the
finisher, dyer and printer of wool materials. The environmental implications
result in the necessity for both the finisher and colourist to understand the
whole chemical finishing chain as well as to be an expert in the science of
wool dyeing.
Heavy metals in dyes or the dyeing processes are important issues; although
reactive dyes are being used more and more as replacements to produce dyed
materials having high wet-fastness properties they do not give the same level
© 2009 Woodhead Publishing Limited

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Advances in wool technology
184
of light-fastness in pale depths as do dyeings produced with pre-metallised
or after-chrome dyes.
The lack of brilliance in whites and pastel shades has been identified as a
major market issue; solutions must be based on research into the photo-
stability of the base wool fibre and on optimising the application of novel
bright chromophores, even those not normally suited for dyeing wool.
Millington has recently reviewed the factors influencing the photo-yellowing
of wool and possible solutions.
2,3
Increasingly shrink-resist processes based on chlorination as a pre-treatment
are under pressure due to high absorbable organo-halogen (AOX) residues –
the colourist has to be aware that up to 1000 mg/L AOX can be discharged
from the dyehouse contracted to dye these substrates; it is vital that such pre-
treatments are replaced with simple oxidation processes without adversely
affecting dyeing properties. Combined dyeing and shrink-resist processing
should be on the agenda, especially if one notes that wool is the only fibre
requiring such anti-shrink processing.
Some of the remarkable findings in wool setting chemistry and their
implications in dyeing will be reviewed, emphasising the value of using so-
called anti-setting agents in the dyeing process to improve final wool quality.
Novel technologies for ink-jet printing textile fabrics are gradually gaining
a foothold; in particular this procedure makes printing more cost effective in
short runs, a scenario ideally suited to wool printing. The special factors
limiting the rapid adoption of such digital technologies for wool fabric printing
will be considered.