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

particular interest is that the coated fibres were subsequently spun into yarns,
then knitted into fabric. SEM assessment showed the coating appeared to be
basically smooth with a large number of granular deposits present, which
were largely removed by the mechanical processes that the fibre was subjected
to as it was processed into a fabric. This suggests that the granular deposits
were not well bound to the fibres, so were probably polypyrrole that formed
in the solution and then accumulated on the fibre surface. The frictional
forces of fibres rubbing against each other and against surfaces of the processing
machinery then dislodged the particles, with the result that the processed
fibre surface was relatively clean. The coating was obviously quite thin, as
the familiar overlapping scale structure of the wool fibre surface was not
obscured by the coating.
In the same paper (Varesano et al., 2005) an extensive study of durability
properties was reported. They assessed the effect on electrical properties (of
wool–polypyrrole fabrics) of laundering with either perchloroethane (dry
cleaning) or a typical domestic washing system; exposure to light and
temperature (45
°C); and abrasion. They used the relative resistance (the
resistance after a designated test, relative to its original resistance) as a
simple way of tracking the change in electrical properties. There was only a
small change in resistance with dry cleaning (relative resistance after five
cycles was 1.2), but a very large change with domestic laundering (relative
resistance increased exponentially, and was about 45 after five cycles). De-
doping was identified as the likely cause of this drastic deterioration in
electrical properties. Exposure to light caused a linear increase in relative
resistance, to about 5.5 after 160 hours. Heat exposure increased the relative
resistance asymptotically until approximately 80 hours, after which there
was no further increase. At this point the relative resistance was about 3.3.
Oxidation of the polypyrrole coating was identified as the likely cause of
both these increases. A third mechanism for the loss of conductivity is physical
erosion of the coating; after 40 000 abrasion cycles (using a Martindale-type
tester) the relative resistance had increased to about 8.5.
Pyrrole variants have been one focus of recent research by a team at
Deakin University. In two papers, Foitzik et al. (2005, 2006a) described the
© 2009 Woodhead Publishing Limited

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Advances in wool technology
316
preparation of soluble poly(3-alkylpyrrole) and its application to wool
substrates. Initially the work focused on preparing and comparing a range of
poly(3-alkylpyrrole) variants, with differing carbon chain lengths (Foitzik
et al., 2005). As the carbon chain length increased (across the range 0 to 22),
the polymer’s solubility in chloroform increased, but its conductivity dropped.
The optimum carbon chain length was between 10 and 14, giving a balance
between solubility and conductivity. The conductivity of all variants up to a
carbon chain length of 10 was comparable to that of unmodified polypyrrole.
The poly(3-alkylpyrrole) with a carbon chain length of 10 was employed
in their subsequent work (Foitzik et al., 2006a), which evaluated various
techniques for depositing poly(3-decanylpyrrole) onto fabrics. Three solution-
based techniques (spray, brush and dip coating) were compared with in situ
polymerisation of 3-decanylpyrrole in solution polymerisation and by a mist/
vapour technique. The initial resistance of the in situ polymerised specimens
was lower, but all showed increased resistance after abrasion, as the ICP
coating was worn away. The main advantage of the deposition of the ICP
from solution is that the substrate is not exposed to the potentially damaging
oxidising agent that is required for in situ polymerisation. However, the
electrical properties of solution deposited poly(3-decanylpyrrole) were inferior
to in situ polymerised.
Other pyrrole variants synthesised and polymerised onto wool by the
Deakin group team include 3-iso-butyl- and 3-iso-pentyl-pyrrole (Foitzik et
al., 2006b) and 3-menthyl carboxylate pyrroles (Foitzik et al., 2007a). Of