Page 41 - Handbook of Properties of Textile and Technical Fibres

22 Handbook of Properties of Textile and Technical Fibres

several methods have been proposed to determine the fiber dimensions, an entry point
for various mechanical properties, and considerable research has been carried out to
find repeatable and accurate measurement techniques (Brims and Hwang, 2015). Char-
acterization methods, which have been developed for conventional engineering mate-
rials, are often poorly adapted to the case of fibers. This chapter attempts to explain
how the morphology of these “single fibers” and their properties are measured.

2.2 Determining fiber dimensions

2.2.1 Weighing methods
The linear density, a measure of the mass per unit length of a fiber, is used by fiber
manufacturers as a measure of fineness. The most common units are known as the
denier, which is the traditional unit for which the weight of the fiber, in grams, is
normalized to a length of 9000 m; the tex, the internationally recognized unit normal-
ized to a length of 1000 m; and the decitex, normalized to 10,000 m. The denier and
the decitex are close in value, and for this reason both are often used in the clothing
industry. Often the linear density of individual fibers is not provided by the manufac-
turer. Rather the linear density of the entire yarn or tow and the number of fibers are
provided; simple division provides the average linear density of a filament and this
number is often used.
When evaluating fibers, it is often necessary to work with the linear density of the
individual fibers. This can be done by weighing. If d l is the linear density and w the
weight of a fiber of known length l, then

wS
d l ¼ (2.1)
l
S is the normalizing factor given above for each type of unit; denier, decitex, and tex.

d l ¼ ArS (2.2)

If the density, r, is known, the fiber cross-sectional area, A, may therefore be deter-
mined from the linear density using

d l
A ¼ (2.3)
rS
For a fiber with a circular cross section, the diameter, 4, is thus provided by
p ffiffiffiffiffiffiffiffiffi
2 A=p. Weighing methods give an average value of the fiber or fibers, and so if
the characteristics of individual tested fibers are required they are of limited use; how-
ever, linear density is insensitive to the cross-sectional shape of the fiber. As seen in
Eq. (2.3), the area is directly obtained from mass and density; fiber dimensions are
not necessary. This makes this technique especially attractive for irregular cross
sections.