The role of
twist in yarns and the part it plays in the design of textile structures .He
discusses the obvious
necessity of twist in the natural and staple fibers by
pointing out“ Twist is
essential to provide a certain minimum coherence between fibers, without a yarn
having a significant tensile strength cannot be made. This coherence is
dependent on the frictional forces brought into play by the lateral pressures
between fibers arising from the application of a tensile stress along the yarn
axis. With the introduction of continuous filament yarns, however, the role of
twist must be reconsidered. In continuous filament yarns, twist is not
necessary for the attainment of tensile strength (in fact, it reduces it) but
it is necessary for the achievement of satisfactory resistance to abrasion,
fatigue, or other types of damage associated with stresses other than a simple
tensile stress, and typified by the breakage of individual filaments, leading
ultimately to total breakdown of the structure. High twist produces a hard
yarn, which is highly resistant to damage of this kind. The role of twist in
continuous filament yarn is thus to produce a coherent structure that cannot
readily be disintegrated by lateral stresses.
From the engineering
standpoint, the interesting thing about this structural function of twist is
that, in contrast to most structure-building techniques, it produces its effect
without significantly increasing the flexural rigidity or resistance to bending
of the system. A yarn of 100 filaments has only 100 times the flexural rigidity
of single filament; if the filaments were all cemented together to form a solid
rod, it would have 10,000 times the flexural rigidity of a single filament.
Extending this
line of thought to woven fabrics, we find again that the stiffness of the
fabric is of the same order as the total stiffness of all the filaments in a
given cross section as shown by Livesey and Owen, and similar considerations
apply, no doubt, to knitted or other types of fabric structure. We see,
therefore, that the major processes of textile fabrication are concerned with
the production of coherent structures having maximum flexibility or minimum
resistance to bending stresses, and hence also to compressive or buckling stresses,
while retaining, of course, the inherent strength of the original filament
material under the action of tensile stresses. This objective is in curious
contrast to that normally encountered in engineering structures, where the
general problem is to produce maximum resistance to bending and compressive
stresses, combined with maximum tensile strength. The engineer achieves his
objective of maximizing the rigidity by the introduction of suitably disposed
fixed linkages between the various components of the structure.
In textile
structures, on the other hand, the objective of maximum flexibility is
ingeniously achieved by the introduction of geometrical restrains, which, while
strongly resisting forces of disruption do not interfere appreciably with the
small relative movements of individual elements associated with bending or
other types of lateral deformation. However, a difference of objective does not
necessarily imply a difference in method of approach, and there is no reason
why the design of textile structure should not be treated by the same rigorous
analytical techniques as the design of any other engineering structures such as
bridge or an airplane. The materials with which the textile engineer works have
an inherent strength and other mechanical properties comparable with those of
typical structural-engineering materials, and research is continually being
concentrated on the improvement of these inherent properties. If these valuable
characteristics are to be utilized to the fullest extent, it is equally
important to see that the problem of design from the engineering standpoint
receives something like the kind of attention.”
The physical and mechanical properties of
various textile fibers that concern the
Engineers and Textile Technologists
as well as the consumers are
summarized in
Physical Properties of Textile
Fibers for twist structure
Fiber type
|
Name
|
Range of Diameter (m)
|
Density (g/cm3)
|
Initial Modulus (gf/tex)
|
Tenacity (gf/tex)
|
Breaking extension (%)
|
|
Natural
Vegetable
|
Cotton
|
11-22
|
1.52
|
500
|
35
|
7
|
|
Flax
|
5-40α
|
1.52
|
1830
|
55
|
3
|
||
Jute
|
8-30
α
|
1.52
|
1750
|
50
|
2
|
||
Sisal
|
8-40
α
|
1.52
|
2500
|
40
|
2
|
||
Natural Animal
|
Wool
|
18-44
|
1.31
|
250
|
12
|
40
|
|
silk
|
10-15
|
1.34
|
750
|
40
|
23
|
||
Regenerated
|
Viscose rayon
|
12+
|
1.46-1.54
|
500
|
20
|
20
|
|
High tenacity rayon
|
12+
|
1.46-1.54
|
600
|
51
|
10
|
||
Polynosic rayon
|
12+
|
1.49
|
800
|
30
|
8
|
||
Fortisan
|
5+
|
1.49
|
1700
|
60
|
6
|
||
Acetate
|
15+
|
1.32
|
350
|
13
|
24
|
||
Triacetate
|
15+
|
1.32
|
300
|
12
|
30
|
||
Casein
|
17+
|
1.30
|
350
|
10
|
60
|
||
Nylon
|
6
|
14+
|
1.14
|
250
|
32-65
|
30-55
|
|
6.6
|
14+
|
1.14
|
250
|
32-65
|
16-66
|
||
Qian(du Pont)
|
10+
|
1.03
|
25
|
26-36
|
|||
Polyster
|
Dacron (du Pont)
|
12+
|
1.34
|
1000
|
25-54
|
12-55
|
|
Kodel (Estman)
|
12+
|
1.38
|
1000
|
40-50
|
35-45
|
||
Acrylic
|
Orlon (du Pont)
|
12+
|
1.16
|
650
|
20-30
|
20-28
|
|
Acrilan( monsanto)
|
12+
|
1.17
|
650
|
18-25
|
35-50
|
||
Polyolefin
|
Polypropylene
|
091
|
800
|
60
|
20
|
||
Polyethylene
|
0.95
|
30-60
|
10-45
|
||||
Aramid {Nomex(dupoint)}
|
12+
|
1.38
|
36-50
|
2-32
|
|||
Novolid{Kynol(Carborandum)}
|
1.25
|
16
|
35
|
||||
Spandex{ycra(dupoint)}
|
1.21
|
6-8
|
444-555
|
||||
Inorganic
|
Glass
|
5+
|
2.54
|
3000
|
76
|
2-5
|
|
Asbestos
|
0.01-.30 α
|
2.5
|
1300
|
||||
α = Actual fibers – usual textile fibers are coarse bundles.
b = Much lower antistatic agents.
Name
|
Work of Rupture(g/tex)
|
Elastic resistance 65% rh.
(ohm-cm)
|
Moisture Regain 65% rh. (%)
|
Melting Point(°c)
|
Strength Retentions 20 days
130°c-(%)
|
Attack by Chemicals
Dissolved //Deraded by
|
|
Cotton
|
1.3
|
107
|
7
|
c
|
38
|
Strong
acid
|
|
Flax
|
0.8
|
107
|
7
|
c
|
24
|
Strong
alkalis
|
|
Jute
|
0.5
|
107
|
12
|
c
|
Mildew
|
||
Sisal
|
0.5
|
107
|
8
|
c
|
Light
|
||
Wool
|
3
|
109
|
14
|
c
|
Strong
alkali
|
||
silk
|
6
|
1010
|
10
|
c
|
Acids,
lights
|
||
Viscose rayon
|
3
|
107
|
13
|
c
|
44
|
Acid,
Strong
alkalis, light, mildew
|
|
High tenacity rayon
|
4
|
107
|
13
|
c
|
|||
Polynosic rayon
|
1
|
107
|
11
|
c
|
|||
Fortisan
|
2
|
107
|
11
|
c
|
28
|
||
Acetate
|
2
|
1013b
|
6
|
230
|
Acids,
alkalis, light, acetone acid & alkali light
|
||
Triacetate
|
2
|
>1012b
|
4
|
230
|
|||
Casein
|
4
|
109
|
14
|
c
|
|||
Nylon
|
6
|
6-7
|
>1012b
|
2.8-5
|
225
|
21
|
Strong
Acids
|
6.6
|
6-7
|
>1012b
|
2.8-5
|
250
|
21
|
Oxidizing
agents
|
|
Qian(du Pont)
|
2.5
|
274
|
Light
|
||||
Polyster
|
Dacron (du Pont)
|
2.9
|
>1012b
|
0.4
|
250
|
95
|
Strong
Alkalis
|
Kodel (Estman)
|
9
|
>1012b
|
0.4
|
250
|
95
|
Strong
Alkalis
|
|
Acrylic
|
Orlon (du Pont)
|
5
|
>1012b
|
1.5
|
Sticks at 235
|
Strong
Alkalis
|
|
Acrilan( monsanto)
|
5
|
>1012b
|
1.5
|
d
|
91
|
Strong
Alkalis
|
|
Polyolefin
|
Polypropylene
|
8
|
>1012b
|
0.1
|
165
|
Light
|
|
Polyethylene
|
3
|
>1012b
|
0
|
115
|
Very
resistant
|
||
Aramid {Nomex(du Pont)}
|
7.5
|
6.5
|
Decomposed at 380°c
|
Resistant
|
|||
Novolid{Kynol(Carborandum)}
|
5
|
6
|
Chars-Carbon 300-580
|
Strong
Alkalis
|
|||
Spandex{yacra (du Pont)}
|
18
|
1.3
|
230
|
Resistant
|
|||
Glass
|
1
|
109
|
0
|
800
|
100
|
Very
resistant
|
|
Asbestos
|
1
|
1500
|
Very
resistant
|
||||
c =
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