Page 110 - Handbook of Properties of Textile and Technical Fibres

Properties of wool 91

The degradation of the fiber is directly linked to the time spent at elevated temper-
ature and the pH of the dye liquor. The damage is minimized if dyeing is carried out at
pH 4e5 for as short a time and at as low a temperature as possible. The balance of
course is to minimize damage while still achieving good dye exhaustion, penetration,
and levelness (Brady, 1985). This has led to a large number of methods for increasing
dye penetration at low temperature (Brady, 1985; Harrigan and Rippon, 1988; Lewis,
1989; Rippon and Harrigan, 1994; Rippon, 1998). The Sirolan LTD Process, devel-
oped by the CSIRO, uses a special chemical (Valsol LTA: APS Chemicals) to modify
the fiber surface and the CMC in a simple pretreatment, allowing effective dyeing at
lower temperatures (Rippon and Evans, 2012).

3.6.4 Stretched wool
The finer the wool the more soft and comfortable it is, which is of particular impor-
tance in “next to the skin” applications. For this reason fine wool attracts a premium
price at auction. A process to stretch wool, thereby reducing its diameter, was devel-
oped in the mid 1990s (Phillips and Warner, 1994; CSIRO, 2011). Wool sliver was
false twisted into a cohesive bundle of fibers, which, after chemical reduction to break
disulfide bonds, was stretched and then permanently set in the extended state.
The resultant fiber, trademarked Optim fine, was typically 3e4 mm finer with a
cross-sectional shape that was polygonal rather than round, leading to a much more
lustrous fiber (CSIRO, 2011; Rippon and Evans, 2012; Rippon et al., 2016). The
dry fiber strength and modulus were relatively unaffected, or in some cases increased
(Liu and Yu, 2007), whereas the wet properties were severely compromised, leading to
difficulties in dyeing. Modified dyeing methods were developed where the fibers were
stabilized resulting in commercially acceptable dyeings. The use of transglutaminase
to improve the properties has also been investigated (Motaghi et al., 2012, 2014).
An alternative fiber, Optim max, was also commercialized. These fibers were only
temporarily set, thus when exposed to hot water or steam, they shrunk by about 25% in
length. When Optim max, blended with normal wool in a spun yarn, was treated in hot
water the blended yarn retracted and bulked up. Garments knitted from such yarns
were 20%e30% lighter than garments knitted to the same cover factor from normal
wool yarns (Rippon and Evans, 2012), resulting in warmer garments without added
weight.

3.7 Future trends

Wool is a medium strength fiber and, for the most part, performs more than adequately.
In recent years, however, with the advent of synthetic microfibers, there has been a
push to soft, next to skin, lightweight fabrics, and the easiest way to achieve this
goal is to reduce the diameter of fibers. The Australian clip, for instance, has changed
significantly in the last 2 decades. In 1993e94 the mean fiber diameter (MFD) was
22.4 mm and only 8.8% of the total clip was classed as fine wool (<19.5 mm). Ten