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

Key words: wool, colour, photostability, free radical oxidation, bleaching,
fluorescent whitening.
9.1
Introduction
Wool has many excellent qualities that other fibres are unable to emulate, but
its achievable whiteness and its photostability when exposed to sunlight are
both areas where wool compares rather poorly. Current commercial bleaching
processes for wool are far less efficient than those used on cotton and synthetics
and can sensitise the wool to photoyellowing on exposure to sunlight. The
use of fluorescent whitening agents (FWAs) on bleached wool improves
whiteness significantly, but commercial use of FWAs is limited owing to the
very poor photostability of FWA-treated wool, in particular when garments
are wet after laundering and exposed to direct sunlight during line drying. A
single laundering and drying cycle can cause an unacceptable level of yellowing,
rendering the garment unwearable. This inability to produce photostable
products in bright white and pastel shades affects wool’s ability to compete
effectively with other fibres in some major textile markets, especially the
current growth areas of casual fashion knitwear, sports and leisurewear.
The chapter opens with a section on wool colour and discusses the evolution
and genetics of the natural cream colour of wool, how it is measured and the
effects of wool processing on colour, including commercial bleaching and
whitening processes (
Sections 9.2
 and 
9.3).
 These sections include a comparison
of the achievable whiteness on wool with cotton and synthetic fibres and
highlights the technical challenges that exist to allow wool to compete on a
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© 2009 Woodhead Publishing Limited

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Advances in wool technology
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level playing field with these fibres with regard to colour attributes (
Section
9.3).
 The chemistry of wool colour and photostability is discussed in 
Section
9.4,
 with particular emphasis on the current understanding of the mechanisms
involved in photoyellowing. 
Section 9.5
 describes the current methods available
for improving whiteness and photostability, followed by a discussion of the
prospects for further improvement (
Section 9.6).