Page 109 - Handbook of Properties of Textile and Technical Fibres

90 Handbook of Properties of Textile and Technical Fibres

2015). The fiber is pretreated with chlorine to promote adhesion by increasing the sur-
face energy, followed by the deposition of a thin layer of polymer (Hercosett, a
polyamideeepichlorohydrin resin) to mask the scales. Strength loss due to the chlori-
nation is still possible but in recent years the concentration of chlorine has been
reduced and loss of strength is typically limited to 5%e10%. The generation of
adsorbable organo halogen (AOX) by-products during chlorination remains a problem
for this technology, thus research in this area continues (Rippon, 2008; Udakhe et al.,
2011; Rippon and Evans, 2012). Non-AOX producing oxidizing agents, ozone,
plasma, and enzymes have all been explored, and continue to be explored, as alterna-
tives to chlorination but to date only a very small number of commercial processes
based on these strategies have emerged (Rippon, 2008; Udakhe et al., 2011; Rippon
and Evans, 2012; Kettlewell et al., 2015; Shahid et al., 2016).

3.6.2 Antipilling treatments

Pilling has been the subject of extensive research, and it is now understood that the life
of a pill comprises four stages: fuzz formation, entanglement, growth, and pill wear off
(Ukponmwan et al., 1998). Attempts to eliminate pilling have focused on increasing
fiber security to prevent fuzz formation or weakening the fiber so that, once formed,
the pill readily wears off. The former strategy is indistinguishable from the approach
to prevent wool from felting and so typical shrinkproofing treatments generally have
the added benefit of improving the pilling performance of wool fabrics. The second
approach involves degradation of the wool using chemical oxidants such as chlorine
or sodium dichloroisocyanuric acid. These treatments have been shown (Naylor and
Williams, 1988) to result in a small decrease in fiber tenacity and a significant decrease
in torsional fatigue lifetime; the maximum pilling decreasing exponentially with a
decrease in torsional fatigue lifetime. Other approaches have involved degradative
treatments using UV light (Millington, 1998) and enzymes (Ukponmwan et al.,
1998; Prabhu and Kanoongo, 2005).

3.6.3 Dyeing

The negative impact of dyeing on tensile properties has already been discussed in Sec-
tion 3.5.5 (Effect of chemical processing). Both general degradation and the setting of
curvature into fibers have been shown to result in a decrease in tensile properties. Two
strategies are employed to minimize these strength losses.
It has been shown that reactive dyes (Lewis, 1989) and a range of oxidants (Hird
and Yates, 1961a,b; Cookson et al., 1991; Huson, 1992) minimize the fiber degrada-
tion during dyeing via their ability to either cross-link the protein or inhibit the thiole
disulphide interchange reaction. The latter strategy has the added benefit of reducing
setting, which in turn reduces hygral expansion of the fabric (Cookson et al., 1991), a
trait that can sometimes cause shape retention problems such as seam pucker or flag-
ging of garment fronts, lapels, or vents. For this reason the oxidants are often marketed
as antisetting agents.