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Review on Behavior of Fiber Migration

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 International Journal of Industrial Engineering, 2019;3(11-12):110-116.
ISSN: 2456-8449.
http://ijie.gjpublications.com
Review Article
Review on Study Behavior of Fiber Migration
Derseh Yilie Limeneh
Ethiopian Institute of Textile and Fashion Technology,
Bahir Dar University, Bahir Dar, Ethiopia.
*Corresponding author’s e-mail: derseh2003@gmail.com
Abstract
Fibre migration, which is expressed by various parameters and indices, depends on fibre properties, the
characteristics of the fibre assembly, and the processing conditions. The fibre properties include length,
degree of elasticity, stiffness and fineness. Short, coarse and stiffer fibres move out of the core towards
the sheath, while long, fine and flexible fibres move towards the core. Strongly crimped fibres are also
found predominantly in the sheath. In blends of fibres with substantially different processing
characteristics, preferential radial migration occurs; one component of the blend is found primarily in
the core and the other component mostly near the surface. Fibres at high tensions are tried to
relieve their tensions by migrating to the core. Relatively slack ones are displaced outwards. In ring
spinning, the fibre tensions are generated in the delta zone where the fibres leave the nip of the
front drafting rollers and pass into the twisted yarn.
Keywords: Fibre migration; Migration pattern; Fibre properties; Fibres leave.
Introduction filaments in the yarn and how the filaments are
packed in concentric shells of the yarn [3].
Fiber Migration describes the variation of radial
position of a single fiber or filament as it moves Owing to their different characteristics,
along and around the yarn axis. Migration is the fibers take up different positions in the body
permanent movement of fibers from center to of the yarn. Grouping arises mostly during
side or vice versa based on the behavior of twist drawing. Thus, long fibers are often located in
direction [1, 3]. The ideal migration pattern is the core, since they exhibit more cohesive
defined as one in which the fiber migrates friction, and therefore higher resistance to the
regularly & uniformly from outside to the center draft, and remain in the interior. Short fibers are
of the yarn and the back to outside in such a way often found on the yarn exterior. This tendency
that the density of packing of fibers in the yarn is is reinforced by fiber migration (wandering of
constant throughout the yarn. Fiber migration the fibers), since the fibers do not always stay in
can be defined as the variation in fiber position the positions they first take up. For example, if
within the yarn [2]. Migration and twist are two any traction of power (even minimal) acts on the
necessary components to generate strength and yarn, highly tensioned fibers of the outer layers
cohesion in spun yarns. Twist increases the press inward wholly or partly (the fiber ends, for
frictional forces between fibers and prevents example). In doing so, they press out the lower-
fibers from slipping over one another by creating tensioned fibers from the interior [18]. Migration
radial forces directed toward the yarn interior takes place from the sheath to the core and vice
while fiber migration ensures that some parts of versa. Such migration is, of course, most
the all fibers were locked in the structure. prevalent during yarn formation but still occurs
after yarn formation is completed.
Fiber Migration
When the smallest forces are exerted on
Migration (used in the former sense) happens as
the yarn, e.g. during bending, tensile loading,
a consequence of the twisting mechanism and is
etc., the persisting tensions in the fibers
not controllable during the textile process. The
constituting the yarn lead to continuation of the
emigrational behavior of fibres provide detailed
process of fiber migration even after the
information on the configuration of fibres or
completion of yarn formation. For example, the

Received: 02.12.2019; Received after Revision: 21.12.2019; Accepted: 23.12.2019; Published: 25.12.2019
©2019 The Authors. Published by G. J. Publications under the CC BY license. 110
Limeneh, 2019. Review on study behavior of fiber migration
short fibers work their way to the surface and are Migration due to tension variation
then partly rubbed off [19]. Moreover, some Migration due to tension variation has been
fibers in the body of the yarn lose their helical
postulated by Morton. Since the length of the
dispositions during fiber migration; this effect is fiber path in a yarn increases from the core to the
more prominent the shorter the fibers and the surface, the tension in the yarn cross-section will
more random their arrangement. experience a different level of tension depending
In addition to its dependence on length, upon the radial position they occupy, i.e., fibres
fiber migration is dependent upon degree of on the surface will have higher tension than
elasticity, stiffness, fineness, crimp, etc. Short, those remaining in the core. Now if the external
coarse, stiff fibers move out towards the sheath restraint is withdrawn (i.e., spinning tension
while long, fine, flexible fibers move towards the becomes zero), the resultant yarn would be one
core [4]. Strongly crimped fibers are also found in which the surface fibres remain under slight
predominantly in the sheath, since they can exert tension and the core fibres are buckled. This is,
greater resistance to binding-in. Fiber migration of course, the kind of structure that is obtained
should be adequately taken into account in when a number of filaments are twisted on a
determining the composition of blends. twister (Figure 1).
Technique of fiber migration
Tracer fiber technique
This technique involves immersing a yarn, which
contains a very small percentage of dyed fibers,
in a liquid whose refractive index is the same as
that of the original undyed fibers. This causes the
undyed fibers to almost disappear from view and
enables the observation of the path of a black Figure 1. Twisted yarn
dyed tracer fiber under a microscope [5, 6].
Dyed fibers are added to the raw stock before The situation is, however, different in
spinning to act as tracers. This technique was continuous spinning or twisting. In this case, a
introduced by Morton and Yen. Or a small number of filaments are fed by a pair of front
proportion of colored fiber (less than 1%) adds rollers to the twisting zone and, at any given
to the stock from which the yarn is spun. It is instant, some fibres go to the center of the yarn
essential that the properties of the colored fibers and some take up their positions on the surface.
should by identical or almost identical with those The fibres at the surface will be taut and those
of the main stock of uncolored fibers then the remaining in the core will be slack or even
colored and uncolored fibers are twisted together buckled. Now it can be assumed that fibres on
to form yarn [8]. This yarn is immersed in a the surface will try to release their strains by
liquid of the same refractive index as the fibers. working their way into the core and in doing so,
As a result, the uncolored fibers in yarn become push the core fibres to the outer region. In this
almost transparent, whereas the colored can be way, over a certain interval, the fibres will move
easily seen. Now the fiber in the yarn is observed radially to relieve the resultant unstable stress.
in a micro projection and thus migration is Onions and co-workers suggested a
measured. different migration mechanism based on
Cross sectional method diameter and length differences of staple fibres.
During drafting, the longer components are
In this method first the fibers in the yarn are under higher constraints due to more fibre
locked in their original position by means of a contact points and tend to pull in or straighten
suitable embedding medium, then the yarn is cut into the centre of the drafting sliver. Where there
into thin sections, and these sections are studied are differences in diameter in the fibres, the
under microscope [9]. As in the tracer fiber coarser and stiffer fibres can resist the twisting
technique, the yarn consists of mostly undyed moment for a longer time than the finer ones,
fibers and a small proportion of dyed fibers such and thus tend to come to the outside of the yarn.
that there is no more than one dyed fiber in any
yarn cross-section.

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Limeneh, 2019. Review on study behavior of fiber migration
Hearle and Merchant have put forward higher force driving it to migrate than a similarly
another migration theory, a modification of located fibre in a coarse yarn [10, 11].
Morton's tension theory, with their study of a
Geometric mechanism
seven-ply structure. They assumed that
migration will only take place when the tension Hearle and Bose have described an alternative
on the central ply has dropped to zero and some geometric mechanism which, in fact, was a by-
slack has accumulated. In other words, even product of their larger investigation on the nature
though the outer plies may be under higher of ribbon twisting. They claim that this
tension, the central ply will not be displaced as mechanism may either combine with or replace
long as it is held taut under some tension in the the tension mechanism.
twisting zone. But when it becomes slack and Yarns are often regarded as twisting in
begins to buckle, it will easily be pushed out and the form of cylindrical bundles of fibres, but they
replaced by one of the outer fibres. However, if may also twist in the form of flat ribbons.
the tension during twisting is high enough to Indeed, it is much more common in practical
keep the central ply under tension, migration will twisting operations for the yarns to be presented
not occur. as a ribbon rather than a cylinder [13].
Gupta and Hamby have put forward a With the geometric migration
migration theory - a modified form of Hearle's mechanism, there will be differences in paths
tension theory. They argued that the practical followed by the fibres depending on their
values of twisting tension in ring-spinning or in positions in the yarn before twisting. Fibres on
an up- or down-twister remains much lower than the outside would show a very marked
the tension necessary to keep the axial fibre in a migration, but those originally near the centre of
tensioned conditions. On the contrary, slackness the yarn would take up an intermediate position
in the fibres of the inner most layers occurs in the wrapped structure and would show little or
which creates a situation where fibres can no migration. This may explain the difference in
migrate. They assume that somewhere between the migration correlograms found by Riding.
the layer of slack axial fibres (helix angle = 00)
and the outer most layers of the highest Gupta has further described that the
tensioned fibres (helix angle = α = twist angle), migration due to the geometric mechanism could
there remains an intermediate layer where the include components due to the presence of
fibres, lying at a certain angle, have zero tension. producer twist as suggested by Hearle and Bose
An equation was proposed showing the relation as well as the deviations of regular, irregular or
between the helix angle of this intermediate layer random nature in fibre paths from that parallel to
and the twisting tension. They have also related the fibre bundle axis.
the buckling of the fibres in any other layers, but It should be noted that the geometric
within the intermediate layer, to the spinning mechanism would be expected to give a regular
tension [7]. migration because of the regularity of the
Gupta (neglecting migration due to producer twist and the mode of formation of the
geometric causes) has proposed yet another wrapped structure [14]. On the other hand, the
migration model based upon Hearle's tension tension mechanism can be expected to produce a
theory of migration. This concerns the tendency more random migration.
of a fibre situated at a given radial position, viz Hearle, Gupta and Goswami have
at the surface, in the yarn to migrate as a suggested that the two migration mechanisms are
function of yarn size, twist and axial tension, i.e., not mutually exclusive. If ribbon twisting occurs
twisting tension. The theory argues that a fibre then the geometric mechanism must basically be
migrates because it develops a force to drive it present. However, if the frequency of migration
during processing. This force, termed as provided by the mechanism is not sufficient to
migration force, is directed towards the yarn prevent buckling of the filaments, then the
centre in a plane perpendicular to the yarn axis. tension dependent mechanism will be
The force has been shown to depend on twisting superimposed upon it [15].
tension, yarn twist (helix angle) and yarn Tex
(yarn radius). It shows that for a given twist
multiplier, a fibre in a fine yarn would develop a

©2019 The Authors. Published by G. J. Publications under the CC BY license. 112

Limeneh, 2019. Review on study behavior of fiber migration
Variables affecting fibre migration in filament number for both nylon and acetate
yarns.
The various properties which are likely to
influence fibre position in yarn can conveniently Yarn factors in spun yarns
be considered in the following groups: Yarn count, amount of twist, blends proportion
1. Fiber related factor and fibre tangle, all might reasonably be
expected to affect the fibre migration (Figure 2).
2. Yarn related factor, and
3. Process factores
Fibre factors in spun yarns
Fibre material, cross-sectional shape and
fibre mechanical properties are inherent
characteristics of a given type of fibre. In most
cases, however, fibre friction may not be an Figure 2. Different twist level yarn
inherent property since it can be modified by a The effect of yarn count was studied by
suitable finish. In fact, fibre type, staple length Morton. He stated that the greater the number of
and denier are the three basic parameters which fibres in the yarn cross-section, the greater is the
can reasonably determine the migration pattern. obstruction which each fibre has to overcome in
On the other hand, it is found from the migrating through a given fraction of yarn
literature that the effect of fibre mechanical radius. In other words, greater tension
properties on migration is complex and differences should be created among the fibres in
sometimes even a contradictory one. coarse yarns in order to produce the same effect.

Morton's experiments with viscose and The influence of the amount of twist has
acetate blends reveal that the latter fibres also been studied by Morton. He observed that
predominate on the surface of the yarn [13]. an increase in the amount of twist decreases the
Apparently, the fibre with higher tensile modulus interval between reversals of the helix envelope.
would be expected to lead to a greater tangential Similarly, Hearle and Gupta and Gupta
or hoop tension in the fibre helices, leading to demonstrated that rapid irregular migration
inward migration. However, Hearle and Gupta occurs in spun yarns and migration increases
observed that a difference of 45 per cent in the with increase in twist. They also showed that
initial modulus of red and black spun-dyed tracer frequency of migration has almost a constant
fibre of the same type (bright staple rayon, 38 relation with frequency of twist which is, in fact,
mm and 0.17 tex) had no appreciable effect on in good agreement with Morton's findings.
its radial position. Furthermore, Hearle and Gupta and later Gupta
have shown experimentally that roving twist has
In another experiment on the effect of influence on the migration in spun yarns. This is
fibre length, Morton observed that the shorter based on the theory of ribbon twisting as
fibres tend to migrate towards the surface. described before.
Fibre factors in continuous filament yarns Gupta and Hamby, working with staple
Migration applied to continuous filament yarn is fibre yarn, have shown an interesting
very limited. Hearle and Goswami have reported phenomenon of fibre migration. Using statistical
the observations of filament size and number on techniques, they concluded that migration
migration behavior. With acetate, nylon and behavior of a fibre depends, to a large extent, on
polyester yarns, they concluded that decrease in its average radial position in the yarn. Fibres
filament size decreases the migration and this is which stay close to the yarn axis show a high
more pronounced in the case of nylon yarns [12]. rate of short term migration together with a high
However, Riding's experiments show that the intensity and low deviation from their average
migration pattern is independent of filament size position. On the other hand, fibres whose
as well as filament number. In contrast to this, average position is close to the yarn surface
Hearle and Goswami have shown that there is show the least tendency to migrate. However, the
appreciable decrease of migration with decrease fibres which occupy intermediate layers show a

©2019 The Authors. Published by G. J. Publications under the CC BY license. 113

Limeneh, 2019. Review on study behavior of fiber migration
tendency to undergo complete cycles of short case of multi-roving spinning, the position of the
term migration around the intermediate position. roving bobbin with respect to the roller nip has
also some effects on migration as shown by
Yarn factors in continuous filament yarns
Morton and Boswell and Townend. For his study
The effect of twist on migration in continuous Morton used the tracer fibre technique and
filament yarn has been studied by Riding, Hearle Boswell and Townend used rovings of different
and Gupta and Hearle and Goswami. In general, colours. Their experiment showed, with triple
they have shown that twist has a marked effect roving spinning, that fibres from certain roving
on migration which increases with increase in bobbins did show a tendency to predominate at
twist. In addition, Hearle and Gupta suggest that the yarn surface but Morton found this effect is
migration in continuous filament yarn is made up negligible with his double roving spinning.
of a rapid irregular migration superimposed on Differences in colour shades have been observed
slower regular migration. It has also been shown by Boswell and Townend, when the positions of
by Riding and later by Hearle and Gupta that in two coloured rovings were interchanged.
the case of continuous filament yarn producer
The effect of twisting tension has been
twist controls the migration period.
studied by Hearle and Merchant. They calculated
The effect of the mechanism of twisting a theoretical value of tension needed to stop
has been studied by Hearle and Goswami and migration. Experiments on staple fibre yarns by
Gupta. Hearle and Goswami used rectangular Hearle and Gupta have shown that the effect of
and cylindrical spacers. The position of the twisting tension on migration is small and the
tracer filament in the spacer was varied between level of twisting tension which is found in
centre, left and right. It was very difficult to practice is much less than the value which would
draw any firm conclusions from their results; be needed to stop migration. This has also been
however, migration intensity was found to confirmed by Townend and Dewhirst and Gupta
increase drastically when the yarn was twisted and Hamby [16]. The latter have shown that
without spacers. spinning tension and spindle speed influence
Gupta concluded from his results that fibre migration, but to a lesser extent than the
about half of the total migration in commercial radial position of a fibre in a twisted yarn.
yarns must arise from causes whose origin does The effect of drafting tenacity and
not lie in the operation of buckling and drafting ratio on spun yarn migration, as has
geometric mechanisms, i.e., it must have come been reported by Gupta, is insignificant and
from some undetermined causes. This, of course, these contribute very little to the formation of
supports the earlier conclusion by Hearle and geometric mechanism of migration as proposed
Goswami that migration increases drastically by Hearle and Bose [17]. This is possibly
when the yarn is twisted without spacers. because of several irregularities which occur in
Similarly, when only a tension mechanism was the drafting zone.
made operative, the magnitude of migration was
The effect of machine parameters on
found to be quite small. Gupta concludes that 25
fibre migration in open-end spun yarns and a
per cent of the total migration observed in
comparison between open-end and ring-spun
commercial yarns comes from the tension
yarns have been reported by Pillay and co-
mechanism and the other 75 per cent or more
workers and Hearle, Lord and Senturk.
from geometric and random causes. This lower
value associated with the tension mechanism, he Processing factors for continuous filament
argues; arise from the high surface frictional yarns
restraints of the filaments. Riding has compared the migration behaviour of
Processing factors for spun yarns statically twisted yarns - where a fixed length of
yarn is twisted on a twist tester, model yarn - 100
Processing factors include yarn manufacturing
stands of 75 denier cellulose acetate yarns
systems (ring spinning or core-yarn spinning,
twisted on an up twister, and actual viscose yarn
open-end spinning, etc), machine geometry,
- a yarn consisting of 201 stands each of
machine settings and possibly the type of
1.5denier. He has shown that statically twisted
twisting, ie, ring-traveller system or spindle or
yarn shows a much greater irregularity in the
friction twisting in the case of texturing. In the

©2019 The Authors. Published by G. J. Publications under the CC BY license. 114

Limeneh, 2019. Review on study behavior of fiber migration
path of the filaments. In addition, calculation of sections cotton/polyester yarn it was found that
Morton's coefficient of migration shows that the location of different fibres in cross-section of
there is less migration in the actual yarn than for blended yarn depends on the percentage of these
the model yarn. fibres in the yarn components and their
following properties: density and Young's
Hearle and Gupta and later Gupta studied
modulus. With the increasing Young's modulus
the effect of tension on continuous filament yarn
of fibres of one kind, the mass percentage of
and concluded that twisting tension has a marked
these fibres in external layer is reduced. With the
effect on migration [18]. Unlike staple fibre
reduction of fibres density increases the
yarns, where the tension mechanism
proportion of the area occupied by these fibres in
predominates to give a rapid migration (though
external layer of yarn. – The obtained formulae
this is superimposed on a slow migration which
can be used for prediction of fibres distribution
appears to be related to roving twist), in
in the cross-section of blended yarns from any
continuous filament yarns both mechanisms
mixtures of heterogeneous components. The
(tension and geometric) play a significant part.
usage of the calculation results allows drawing
Recently, the migrational behaviour of conclusions about the necessity of adjustments in
filaments in the twisted thread line, collected settings of subsequent processing of the yarns.
from a conventional texturing zone, has been
studied by Backer and Yang, though this study is Conflicts of interest
very limited. With the application of the tracer No conflict of interest.
fibre technique, they have reported, for 94/28
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