Biomimetic Textiles - Engineered Biomimicry - page 245

From those early times to the present, the
continued development of methods of textile
production has broadened the available choices
of textiles and thus influenced how people
clothe themselves and protect themselves from
their surroundings. The study of the DNA of the
body louse has allowed us to infer the length of
time during our evolution that humans have
been wearing clothing. The common louse
particular to humans diverged from its ances-
tors possibly as long as 650,000 years ago [2] .
Scientific research, based on the study of the lice
that infest modern humans estimates that
humans have been wearing clothing for at least
107,000 years [3] . Thus, it is clear that the
manufacture of clothing and related textiles is a
venerable and integral part of human culture.
In fact, the ubiquitous nature of textile materials
renders them essentially invisible; nonetheless,
as it was in ancient times, textiles remain a criti-
cal component of our modern infrastructure.
The first actual textile, instead of skins simply
sewn together, was probably felt [4] . In modern
incarnations, felts can be made from essentially
any fiber through the nonwoven fabric manu-
facturing process, which is introduced in Section
10.3.1.3 ; originally, however, felts were made
only from animal hair fibers. The surface of a
hair fiber (keratin) such as wool has scales
( Figure 10.1 ). When a bundle of such fibers, ran-
domly oriented, is subjected to mechanical
motion, especially in the presence of moisture,
the scales interlock in a ratcheting fashion, caus-
ing a relatively permanent fabric structure, i.e.,
felt, to be formed. Animal hair felt is the earliest
form of a nonwoven fabric. Other fabric types
require first that the fibers be formed into yarns.
It is not clear when humans first discovered
that fibers, such as from wool or cotton, could be
twisted together into the larger and more robust
structure of yarns, but it is clear that this has
been done from prehistoric times. Nonetheless,
the engineering aspects of the processes for
mechanized yarn formation were not well devel-
oped until the Industrial Revolution. Clothing

FIGURE 10.1 SEM micrograph of a Merino wool fiber.
(Photo: Dr. Mevlut Tascan)

production continued to be accomplished by
hand until sewing machines became common in
the 19th century, thereby facilitating production
of apparel.
In essence, to produce a yarn, the randomly
oriented fibers must first be aligned and rarefied
and then twisted together. Carding , the process of
combing the fibers into alignment, was originally
done by hand using card flats, , flat or curved
boards with wire teeth. The carding machine was
developed to increase the speed of production by
using rotating drums with the card wire on them.
The output of the card, the card web , is a thin mat
of oriented fibers. This mat is pulled together to
form the card sliver (the i is pronounced eye ).
Although there are ancillary steps in the process,
we will not review them here; the sliver is then
drawn out to a smaller diameter and fed into the
spinning machine. The familiar spinning wheel
was a human-powered machine developed to
spin the fibers into yarns. An earlier system, the
spinning bobbin , was gravity powered.
At the yarn-spinning machine, the most obvi-
ous level of hierarchical structure is introduced
by making the yarn (having a high aspect ratio)
from fibers (also with high aspect ratio, albeit of
smaller diameter). However, the fibers, which
are thin structures with a high aspect ratio, are