Page 280 - Handbook of Properties of Textile and Technical Fibres

254 Handbook of Properties of Textile and Technical Fibres

Recall that in static tensile tests, typical values of cotton fiber initial modulus
ranged from 350 to 800 gf/tex (3.4e7.84 N/tex). The methods of dynamic modulus
summarized above yielded values of dynamic elastic modulus that varied
according to the method used and the frequency of loading of the sample. Values of
2.3e6.6 N/tex were reported at 15e30 Hz, and values of up to 10.5 N/tex were
reported at 1 kHz. This means that dynamic tensile testing of cotton fibers is far
from being standardized and additional efforts need to be made in this area. The
authors of this chapter strongly believe that revisiting the issue of testing the dynamic
tensile behavior of cotton fibers in view of the current advanced computer technology
will result in immense benefits, not only in improving the processing performance of
cotton fibers, but also in improving the manufacturing technology.

7.12.2 The effects of the tensile behavior of cotton fibers on
processing performance

The journey of a cotton fiber from the cotton boll to its final destination in apparel or
home products is characterized by enormous technological challenges associated with
different modes of strain applied on the fiber. Indeed, before fibers are finally settled in
a yarn or a fabric structure, they must undergo a combination of deformational and
deconfigurational modes in which fibers are stretched, pulled, compressed, twisted,
bent, and rubbed against each other and against metallic surfaces. Because fibers
must be aligned in subsequent processes along their length before they are finally
spun into yarn, their tensile behavior is certainly the most dominant factor in deter-
mining the fiber’s ability to withstand the various stresses and contribute effectively
to the integrity of yarns and fabrics. In the following sections, we present brief
discussions of the effects of different processes on the tensile behavior of cotton
fibers.

7.13 The harvesting process

The journey of the cotton fiber begins in the field where a mature seed cotton plant may
carry about 100 cotton bolls, and each boll may contain about 500,000 seed fibers. The
cotton is picked from the field using manual or mechanical means. Manual harvesting
represents a gentler approach of pulling the fibers, and it is expected to result in
minimum fiber damage. Mechanical harvesting, on the other hand, involves the use
of stiff wires and barbed spindles operating at high speeds, which result in an
inevitable fiber damage and alteration in the tensile behavior of fibers.
Two types of mechanical harvesting are commonly used: stripper harvesting and
spindle harvesting. In the context of cotton quality, the main difference between these
two types is the yield and the amount of trash and dust produced. Typically, stripper
harvesting gathers much more trash with the seed cotton than spindle picking. As a
worst-case scenario, approximately 2200 pounds (1000 kg) of seed cotton are
harvested using a brush stripper to obtain 500 pound (w227 kg) of cotton lint (the
typical weight of a cotton bale). In spindle harvesting, only 1500 pounds of seed cotton
is typically harvested to obtain 500 pound (w227 kg) bale of lint. From a mechanical
viewpoint, stripper harvesting deals directly with cotton bolls. The cotton stripper