Page 282 - Handbook of Properties of Textile and Technical Fibres

256 Handbook of Properties of Textile and Technical Fibres

The ginner represents the primary supplier of cotton fibers to the cotton spinner.
Fibers must be supplied to the spinning mill in large quantities (in bale form) and at
acceptable quality. The optimization of the trade-off between quantity and quality
has been in the center of a continuous debate between the ginning industry and the
spinning industry. Historically, there has been little coordination between the two
industries regarding what constitutes cotton fiber quality. The ginner has always
operated based on purifying cotton from trash at minimum fiber damage to maintain
an acceptable staple fiber length. As a result, the ginner’s mirror of quality has always
been the fiber length distribution and the percent of short fiber content (fibers with less
than 0.5 in (12.5 mm) length). Therefore, sustaining a good strength of cotton fibers,
from a ginner’s viewpoint, is mainly to produce an acceptable fiber length distribution.
In addition, moisture content is widely used among ginners as a way to improve fiber
strength during ginning. The point, which is largely ignored in this view is that at the
substantially higher rate of ginning and cleaning compared to the opening and cleaning
rates in the spinning mills, excessive fiber damage and loss of elastic recovery are
inevitable. This problem has reached a peak in more recent years because of the
development of new high-speed spinning and weaving technologies that demand
minimum trash content.
Studies dealing with the change in fiber tensile behavior on ginning are limited
because of the difficulty of controlling the experiments of these studies. However,
some studies pointed out that hand-ginned cotton is superior to mechanically ginned
cotton in breaking strength, breaking elongation, and work of rupture (Hughs et al.,
2013; van der Sluijs, 2015). When mechanical ginning is used, the extent of fiber
damage will depend on the type of ginning and the process of lint cleaning. To produce
a fiber that has an acceptable integrity to contribute to yarn and fabric strength, both
fiber length and fiber strength must be maintained at acceptable levels throughout
the ginning and the lint cleaning process. In a recent study by Hughs et al. (2013),
it was found that there was a significant downward shift in the fiber length distribution
with the saw-ginned fiber in comparison with the roller-ginned fiber. The length shift
was a significant decrease of fibers above 2.54 cm (1.0 in) and a significant increase in
fibers between 2.21 and 0.30 cm (0.87 and 0.125 in). The percentage of fibers in the
2.21e2.54 cm (0.87e1.00 in) length range stayed relatively constant. This trend
continued on using saw lint cleaners after ginning. When more than one lint cleaner
was used, more long fibers were lost at the first lint cleaner than any subsequent lint
cleaner. When saw-ginned cotton was compared to roller-ginned cotton, for upland
cottons of long staple length (32 mm), a study by Marinus HJ van der Sluijs (2015)
revealed a slight but significant improvement (about 2%) of roller-ginned cotton in
both fiber strength and breaking elongation.

7.15 The spinning preparation process

In the spinning mill, cotton fibers are subjected to a variety of external stresses
(Elmogahzy and Chewning, 2001). Typically, cotton fibers arrive at the spinning
mill in a bale form. Each bale consists of a compressed bulk of more than 60 billion