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Keysight Technologies
Tensile Deformation of
Fibers Used in Textile Industry
Application Note
Introduction
Fibers are almost synonymous with textile industry. The word ‘Textile’ is actually defined
as a flexible woven material consisting of a network of natural or artificial fibers [1]. We
have been using different type of fibers from plants and animals to make fabric for last
several thousands of years, and knowingly or unknowingly selected these fibers based on
their different attributes. In recent years, as natural resources started to get expensive,
we have also invented many artificial fibers to replace the natural ones in our clothes,
carpets and other apparels.
Selection of fiber materials for making a fabric depends on many considerations, such
as their chemical stability, thermal and electrical conductivity, as well as the mechanical
properties. It may seem farfetched at first, but the knowledge of these physical properties of the fibers enables the designers to make new fabric for specific applications,
such as for the athletes or for the astronauts. The knowledge of mechanical property of
the fibers is also important for designing the automated textile plants where each fiber
is introduced to different amounts of tensile loads during the weaving process. In recent
years, it has also been an important research direction to understand the structureproperty relations in the natural fiber materials, which then can be successfully mimicked
in an artificial material.
Given the importance of understanding mechanical behavior in textile industry it is
reasonable to assume that mechanical behavior of these textile materials has already
been reported since long time in literature[2, 3]. Despite these efforts, very little is
available in the open literature about the mechanical behavior of single individual fibers
comprising the yarns in many textiles. It is important not only from the perspective of
a materials engineer, designing new materials for textile industry, but also from the
perspective of the person who designs advanced fabrics for specific applications based
on existing materials. This lack of information is in part due to unavailability of commercially available instruments which can precisely measure the deformation of a thin single
fiber, which are often only a few microns in diameter.
The Keysight Technologies, Inc. UTM T150 is specifically designed for the purpose of
measuring the tensile deformation behavior of extremely thin fibers[4, 5]. Along with the
high force and displacement resolution, the patented continuous dynamic analysis (CDA)
module enables the T150 to measure storage and loss modulus of a material continuously during a tensile experiment. The CDA is an important tool to characterize the change
in the inherent structure of materials during deformation, and especially important for
polymeric materials. The capabilities of the T150 along with the CDA were successfully
utilized to characterize tensile deformation of many technical fibers, including polypropylene[6], copper, tungsten[6], basalt[6] and spider silk [7] (a potential material for the textile
community). Hence it is evident that the T150 is a powerful tool to characterize the
deformation mechanisms in single fibers used in textile industry. The following section
briefly describes the natural and artificial fiber materials studied in the current study.
03 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
Fiber Materials
Cotton: Despite all the competition from their artificial counterparts, cotton is still the
best-selling fiber material in the world, and mostly in the textile industries[8]. This natural
cellulosic fiber does not contain many harmful chemical effects of the artificial fibers.
The individual cotton fibers are actually individual plant cells. The structure of a cotton
fiber is shown in Figure 1 (schematic). It is composed of concentric layers of closely
packed cellulosic crystalline fibrils. The innermost part, known as lumen, contains the
cell nucleus and protoplasm before the boll opening. However, when the cell interior
dries out it causes the twists observed in individual cotton fibers (Figure 1, image on
right). The cotton fibers also go through a number of chemical treatments (as is the
case with the fibers used in the present study) such as bleaching and mercerization to
improve their luster and sorption properties. After all these treatments, what remains of
the cotton fibers is mostly crystalline cellulose, which, in scientific language, consists of
a linear chains of hundreds or thousands of glucose units.
Lumen
Secondary wall with
several layers
Winding layer
Primary wall (1st layer)
Primary wall (2nd layer)
Cuticle
Figure 1. Schematic of the microstructure of cotton fiber (left), and electron micrograph showing the twisted
morphology of processed cotton fibers (right). (http://lizzcorner.wordpress.com/2009/06/11/fiber-files-cotton/).
Wool: The most popular natural fiber material that comes from an animal is wool. It
is mostly fibrous protein from specialized skin cells of sheep[9]. Unlike the continuous
surface of cotton fiber, wool fiber consists of scales and crimps. These qualities make
the wool fibers easy to spin, and the air retained in the crimped space gives rise to the
thermal insulation in the fabric. Figure 2 shows the hierarchical structure of a single wool
fiber. One wool fiber is also not a single cell like cotton, but consists of multiple cells.
There are mainly two different types of cells in a wool fiber – the internal cells of the
cortex and external cuticle cells. Other than their usual application in warm clothing,
wool is safer for fire hazards compared to cotton and synthetic fibers and is used in
clothing and carpets in environments where there is a likelihood of fire exposure.
Cell membrane complex
outer cuticle layers
4
Macrofibril
Complex inner matter
Macrofibril
Matrix
Left-handed
coiled coil rope
Para cell and
ortho cell cortex
Right-handed a-helix
Figure 2. Schematic of the microstructure of a wool fiber (http://www.wool.com/Topmaking_Fibre-Modification.htm)
04 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
Polyester: Polyester, also known as polyethylene terephthalate (PET), fibers are the
most extensively used man-made material in the textile industry. Polyester fabrics show
improved wrinkle resistance, durability and high color retention. Most characteristic
properties of polyester fibers are usually attributed to the benzene rings in the
polymer chain, which leads to chain stiffness. PET fibers consist of crystalline, oriented
semi-crystalline as well as noncrystalline (amorphous) regions [10].
Rayon: Another widely used fiber in the textile industry is rayon. It is a regenerated
cellulose fiber made from naturally occurring materials[11]. Rayon fibers exhibit a lot of
similarity with natural fibers like cotton and wool; however, it does not insulate the body
heat. So, rayon fabrics are ideal for hot and humid climate.
Experimental Details
Commercially available yarns of 100% mercerized cotton, wool, polyester and rayon were
purchased. Individual fibers of each material were carefully separated from the yarn and
mounted on card templates. The gage section of each fiber specimen is measured using
a caliper, and the cross-sectional areas of the fibers were measured using scanning
electron microscopy (SEM). The template was then mounted on the T150 (Figure 3) using
the template-grips and the sides of the template were clipped to release the fiber for
testing. The micro-positioner is used to make sure proper alignment of the fibers before
testing.
The NanoSuite test method named “UTM T150 Standard Toecomp CDA” was used for
tensile testing of the textile fibers, along with continuous dynamic analysis. All the tests
were performed with a strain rate of 1x10 -3 s-1. The continuous dynamic analysis during
each test was performed using a force amplitude of 2 mN at a frequency of 20 Hz.
The fiber morphology and the fracture surface of the fibers were imaged in the SEM.
Figure 3. Individual textile fiber mounted on the
Keysight UTM T150. Note that the sides of the
card template were cut to release the fiber before
testing.
05 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
(a)
(b)
Figure 4. Continuous dynamic analysis of cotton fiber during tensile test. (a) Variation in engineering stress and storage modulus with increasing strain; (b) Variation in loss
modulus and loss factor with increasing strain.
Results and Discussion
Cotton: The engineering stress-strain curve for a typical test on a single strand of cotton
is shown in Figure 4. The elastic modulus, measured from the slope of the initial linear
region, the tensile strength, and the strain at failure for individual cotton fibers are listed
in Table 1. As expected of a natural fiber, there were higher variation in sizes of the cotton
fibers, which resulted in the variation in elastic modulus and tensile strength (Table 1).
Although the cellulose crystals in the mercerized cotton fibers exhibit high modulus and
strength, they are also the least ductile compared to the other fibers studied herein. The
electron micrograph in Figure 5 clearly shows the anisotropic cross-section of the cotton
fiber. Hence, the fiber sizes were measured post-test and a modified fiber dimension was
entered in NanoSuite to recalculate the tensile test results. At this point, it is difficult
to compare the results with literature as most of the previous tensile studies of cotton
have been conducted on yarns [3], rather than individual fibers. Moreover, the mechanical
properties of cotton also vary with the length of the fiber and the chemical treatment it
undergoes before application.
The variation in dynamic storage and loss modulus with increasing strain is shown in
Figures 4(a) and 4(b), respectively. The loss factor (ratio of loss modulus and storage
modulus) is also plotted in Figure 4(b) to get a better understanding of the damping
behavior.
Table 1. Mechanical properties of individual textile fibers.
Fiber
Diameter
Young’s modulus
Tensile strength
Strain at failure
(µm)
(GPa)
(MPa)
(%)
Cotton
9±1
30 ± 4
1066 ± 41
5±1
Wool
41 ± 1
3.4 ± 0.1
135 ± 37
27 ± 12
PET
17.0 ± 0.2
10.5 ± 0.4
868 ± 31
21 ± 1
Rayon
13.0 ± 0.5
23 ± 2
545 ± 92
12 ± 2
Figure 5. SEM micrograph of the cotton fi ber
near the fractured surface. Note the anisotropic
shape of the cotton fi ber.
06 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
(a)
(b)
Figure 6. Continuous dynamic analysis of wool fiber during tensile test. (a) Variation in engineering stress and storage modulus with increasing strain; (b) variation in loss
modulus and loss factor with increasing strain.
The storage modulus is about 20 GPa during the initial linear elastic regime, but it
increases significantly up to about 100 GPa, before failure. This increase in storage
modulus is due to the increased alignment of cellulose crystals along the fiber axis. The
macroscopic twists in the mercerized cotton fiber may also cause some changes in the
measured storage modulus. However, more work is needed to understand the exact
microstructural changes during tensile deformation. The initial increase of the loss factor
is also in agreement with the alignment phenomenon. Once most of the crystallites are
aligned along the fiber axis, the deformation is mainly due to stretching of bonds in the
cellulose crystals, which in turn reduces the loss factor.
Wool: The tensile deformation behavior in an individual wool fiber is shown in Figure 6.
The tensile strength, the initial elastic modulus and the strain to failure are listed in
Table 1. The wool fibers exhibited the lowest strength and modulus among the four
different types of fibers characterized during this study. However, these fibers can
be stretched about 30% of their original length before failure, much higher strains
compared to other fibers. The surface morphology of wool fibers can be seen in Figure 7.
Although the fiber diameter is uniform along the length of the fibers, the expected defect
distribution in the natural fiber is higher. This causes the variation in tensile strength and
elastic modulus of wool fibers (Table 1).
When the variation in dynamic storage modulus with strain is plotted (Figure 6(a)),
there is a slight drop corresponding to the yield in engineering stress-strain curve. This
correlates to the molecular movement in the microfibrils (Figure 2) to align themselves
along the fiber axis. As this alignment process dissipates energy, it increases the loss
factor (Figure 6(b)). After the molecules in the microfibrils are aligned, the deformation
is mostly due to stretching of various hierarchical layers along the fiber axis. The drop
in loss factor in this regime suggests that the deformation of the hierarchical structure
dissipates less energy compared to the molecular alignment. However, more systematic
microstructural characterization is needed to completely understand the deformation
process.
Figure 7. SEM micrograph of the wool fiber. Note
the crimps on the fiber surface.
07 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
(a)
(b)
Figure 8. Continuous dynamic analysis of cotton fiber during tensile test. (a) Variation in engineering stress and storage modulus with increasing strain; (b) variation in loss
modulus and loss factor with increasing strain.
Polyester: A typical engineering stress-strain curve from tensile test of individual
polyester (PET) fiber is shown in Figure 8. The initial modulus, tensile strength and
strain to failure are listed in Table 1. As shown in Figure 9, the PET fibers, used during
this study, had very uniform diameter. According to previous literature[12], one PET fiber
consists of microfibrils aligned along the fiber axis. These microfibrils, in turn, consist of
crystalline and amorphous regions, and connected to other microfibrils by another kind
of amorphous phase, known as mesamorphous phase. The different regions observed
in the tensile stress-strain curve can be explained by the deformation of the different
microstructural regions mentioned above. During the initial deformation, the amorphous
regions within the microfibrils align themselves in the similar orientation as the mesamorphous phase. The stress-strain curve goes through another point of inflexion when
the applied load starts to strain the bonds in both amorphous and crystalline phases.
The final part of the curve represents slippage between microfibrils.
When the storage modulus, calculated from the continuous dynamic analysis, were
plotted together with the engineering stress and strain (Figure 8(a)), it shows almost a
monotonous increase in stiffness of the material with strain. The alignment of amorphous
regions, as discussed earlier, supports the small drop observed in the storage modulus.
The dynamic storage modulus during the initial deformation is in good agreement with
the elastic modulus listed in Table 1, as well as the quasistatic elastic modulus reported
earlier. Similarly, the dynamic loss modulus also increases with increasing strain
(Figure 8(b)). However, the real damping behavior can be observed form the variation of
loss factor with strain, where the loss factor reaches a maximum during the alignment of
amorphous regions, and then decreases as the crystalline and amorphous regions within
the fiber becomes more aligned with the fiber axis.
Figure 9. SEM micrograph of the cotton fiber near
the fractured surface. Note the anisotropic shape
of the cotton fiber.
08 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
(a)
(b)
Figure 10. Continuous dynamic analysis of rayon fiber during tensile test. (a) Variation in engineering stress and storage modulus with increasing strain; (b) variation in loss
modulus and loss factor with increasing strain.
Rayon: The tensile deformation behavior of individual rayon fibers is similar to wool
fibers. The tensile stress-strain curve (Figure 10(a)) exhibit an initial linear elastic region
followed by a hardening behavior. The diameter of the rayon fiber was also needed to
be modified post-test because of its irregular cross-section. The electron micrograph of
the rayon fiber (Figure 11) clearly revealed the striations on the surface of the fiber. This
is most probably due to the arrangement of cellulose microfibrils along the length of the
rayon fiber.
Similar to wool and PET, rayon fibers also exhibit a drop in dynamic storage modulus
during the yielding process (Figure 10(a)). This corresponds to the alignment of the
amorphous regions within the microfibril in a similar orientation with the amorphous
chains between the microfibrils. This alignment mechanism dissipates more energy,
which results in higher loss factor (Figure 10(b)). As both the crystalline and amorphous
regions get aligned the energy dissipation drops, decreasing the loss factor with increasing strain.
By comparing the results on four different individual textile fibers (Figures 4–11, Table 1),
it is evident that fiber morphology plays an important role in their deformation process.
However, a more detailed study is required to understand the exact nature of the
deformation.
Figure 11. SEM micrograph of the rayon fiber.
Note the striations on the fiber surface.
09 | Keysight | Tensile Deformation of Fibers Used in Textile Industry - Application Note
Conclusions
The Keysight UTM T150 is successfully employed to test four different individual textile
fibers — cotton, wool, polyester and rayon — under tensile loading. The continuous
dynamic analysis (CDA) module enabled us to study the variation in dynamic storage
and loss modulus of the textile fibers with increasing strain. The combination of storage
modulus and loss factor calculation not only confirms that the stiffness of the individual
fibers increases with strain, but also can be used to identify the energy dissipation
mechanisms during deformation of natural and artificial polymeric fibers.
References
1.http://en.wikipedia.org/wiki/Textile.
2. Eyring, H. and G. Halsey, The Mechanical Properties of Textiles, III. Textile Research
Journal, 1946. 16(1): p. 13-25.
3. Orr, R.S., et al., Physical Properties of Mercerized and Decrystallized Cottons.
Textile Research Journal, 1959. 29(4): p. 349-355.
4. Basu, S., Tensile Stress-Strain Response of Small-diameter Electrospun Fibers.
Keysight Technologies Application Note, 2014.
5. Basu, S., Tensile Test of Copper Fibers in Conformance with ASTM C1557 using
Keysight UTM T150. Keysight Technologies Application Note, 2014.
6. Hay, J., Quasi-static and Dynamic Properties of Technical Fibers. Keysight Technologies Application Note, 2014.
7. Blackledge, T.A., J.E. Swindeman, and C.Y. Hayashi, Quasistatic and continuous
dynamic characterization of the mechanical properties of silk from the cobweb of
the black widow spider Latrodectus hesperus. The Journal of Experimental Biology,
2005. 208: p. 1937-1949.
8. http://en.wikipedia.org/wiki/Cotton.
9. http://en.wikipedia.org/wiki/Wool.
10. http://web.utk.edu/~mse/Textiles/Polyester%20fiber.htm.
11. http://en.wikipedia.org/wiki/Rayon.
12. Lechat, C., et al., Mechanical behaviour of polyethylene terephthalate & polyethylene naphthalate fibres under cyclic loading. Journal of Materials Science, 2006.
41(6): p. 1745.
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