Woven Fabrics - Fairchild Books

standard yarn 2.0 dpf microdenier yarn 1.0 dpf microdenier yarn 0.5 dpf
Figure 4.3
Assume the three yarns are the same size, e.g. 80 d. The yarn on the left at 2 dpf would have 40 filaments. The yarn in the
center at 1 dpf would have 80 filaments. The yarn on the right at .5 dpf would have 160 filaments. Thus, although the three
yarns are of the same size, as the fibers get thinner (lower denier per filament) there is a higher filament count in the yarn.
Technological developments in manufactured fiber
processes have made possible the generation of fibers
such as nylon, polyester, lyocell and others to be produced
in diameters finer than silk (microfilament) (Figure
4.3). These fine fibers are called microfibers, and are
also known as microdenier. The name also applies to
the yarns made from them (see p. 81 for an explanation
of denier). Microfibers are used as multifilament yarns
in flat or textured (see p. 76) configuration or are processed
as staple fibers and then spun into yarn. Fabrics
made from microfiber filament yarn are extremely soft
and drapable and can be almost indistinguishable from
silk. Spun yarns from microfibers can be blended with
cotton, wool, or other fibers to produce yarns that possess
much greater softness and flexibility, thus creating a
more drapable or fluid fabric.
Comparison of Spun and Filament
Yarn Properties
There are a variety of properties used to compare and
contrast spun and filament yarns. The three most
important are yarn uniformity, yarn smoothness and
luster, and yarn strength.
In general, filament yarns are more uniform in
diameter than spun yarns, although these differences are
not visible to the naked eye. In filament yarns, the same
number of filaments are present at every point along the
yarn. A multifilament yarn composed of 40 filaments has
40 filaments along its entire length. This is not the case
with spun yarns, where, for example, at one point there
may be 40 fibers, at another, 43, and at still another, 37.
Filament yarns are generally smoother and more
lustrous than spun yarns. Satin, a familiar filamentyarn
fabric, is smooth and lustrous, whereas sheeting,
FABRIC SCIENCE
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a typical spun-yarn fabric, is less smooth and somewhat
duller with a slight surface fuzz that is characteristic of
spun yarns. A filament yarn viewed against light shows
uniform diameter and no fuzziness. Because each filament
is as long as the yarn itself, there are no fiber ends
protruding from the yarn surface as in spun yarns. This
uniformity and smoothness in filament yarns is the main
reason for their greater luster and smoother surface.
The smooth surface of the filament yarns can sometimes
be disadvantageous, causing yarns to slip and slide
easily within a fabric. Excess stress on a seam, for example,
may cause slipping of yarns and opening of a seam without
the actual breakage of thread. This is more likely to occur
in fabrics of low construction, fabrics with a low number
of yarns per square inch (see p. 96) or where improper
seam allowance is taken in sewing. The test described on
page 324 should be used to determine the suitability of a
filament yarn fabric for yarn and seam slippage.
When a spun yarn is broken, some fibers break and
others just slide away from each other. When a filament
yarn is broken, every filament in the yarn breaks. Thus,
filament yarns are stronger than spun yarns of the same
diameter and fiber type because it requires more force to
break yarn if all the fibers break than if only some fibers
break while others slip apart.
More twist in a spun yarn increases its strength
by increasing the pressure exerted on the fibers. This
results in reduced fiber slippage when force is exerted
on the yarn. Up to a certain point, the more twist in a
yarn, the stronger it is. After that point, the extra twist
begins to cause the fibers to cut into each other and
the yarn strength decreases. This happens because the
fiber direction and thus the yarn’s strength is no longer
in a spiral direction but has been forced into more of a
horizontal steplike direction.