Praveen Kumar Jangala & Ramaiah Kotra
Bicomponent fibers can be defined as "extruding two
polymers from the same spinnerette with both polymers contained within the
same filament. " A close relative is "cospun fiber", which is a group of
filaments of different polymers, but a single component per filament, spun
from the same spinnerette. The term "conjugate fibers" is often used,
particularly in Asia, as synonymous with bicomponent fibers.
The first commercial bicomponent application was
introduced in the mid 1960s by Dupont. This was a side-by-side hosiery yarn
called "cantrese" and was made from two nylon polymers which, on retraction,
formed a highly coiled elastic fiber. In the 1970s, various bicomponent
fibers began to be made in asia, notably in Japan. Very complex and
expensive spin packs apparently were used in the manufacturing process.
These techniques were found to be technically unsatisfactory and excessively
expensive. Later in 1989, a novel approach was developed using thin flat
plates with holes and grooves to route the polymers. This process was very
flexible and quite price effective.
Worldwide, Japan and Korea led in bicomponent output with
a total of 200 million pounds annually. The production of the U.S. is
currently around 60 million pounds with Hoechst Celanese holding the lead.
Other U.S. players in the bicomponent sector include Foss manufacturing ,
International Polymers Inc. and Fiber Visions. The present production of
bicomponent fibers worldwide is only a fraction of the 25 million metric
tons of manmade fiber market, but the producers are confident of significant
growth in the next 10 years or so.
The polymers given below can be used as either of the
components in the cross sections.
PET(polyester) PEN polyester
Nylon 6,6 PCT polyester
Polypropylene PBT polyester
Nylon 6 co-polyamides
Polylactic acid polysterene
Soluble copolyester HDPE, LLDPE
PRODUCTION AND CLASSIFICATION
The main objective of producing bicomponent fibers is to
exploit capabilities not existing in either polymer alone. By this technique
it is possible to produce fibers of any cross sectional shape or geometry
that can be imagined. Bicomponent fibers are commonly classified by their
fiber cross-section structures as side-by-side, sheath-core,
islands-in-the-sea and citrus fibers or segmented-pie cross-section types.
1. Side-by-Side (S/S)
These fibers contain two components lying side-by-side
(Fig.1.). Generally, these fibers consist of two components divided along
the length into two or more distinct regions.
Side-by-side Fiber Production 
In most cases, the components must show very good
adhesion to each other; otherwise, the process will result in obtaining
oftwo fibers of different compositions. The way to connect the two
components mechanically is described in patent literature and is shown in
(Fig.1. (h), (i) ). Generally, there are several approaches for producing
side-by-side bicomponent fibers:
Two components, either in the form of solution or melt,
are fed directly to the spinneret orifices and are combined into bicomponent
fibers near the orifices.
Two components are first formed into multi-layered
structure and slowly fed (without turbulence) in the orifices. The orifices
are positioned so that they intersect the interfaces of various layers of
Two components are also formed into layered structure but
the orifices do not follow exactly the interfaces, which leads to production
of fibers of a wide range of compositions , varying from 100% of one
component to 100% of the other through all intermediate possibilities.
Two polymer components are slit-extruded into a layered
film, which is then cut into stripes, drawn, cut into staple and fibrillated
by a carding machine and then crimped by heat relaxation .
Use of Side-by-side Bicomponent Fibers
Side-by-side fibers are generally used as self-crimping
fibers. There are several systems used to obtain a self-crimping fiber.
One of them is based on different shrinkage
characteristics of each component. All commercially available fibers are of
this type. There have been attempts to produce self-crimping fibers based on
different elastomeric properties of the components; however, this type of
self-crimping fiber is not commercially used. Some types of side-by-side
fibers crimp spontaneously as the drawing tension is removed and others have
"latent "crimp, appearing when certain ambient conditions are obtained. Some
literature mentions "reversible "and "non-reversible" crimp, when reversible
crimp can be eliminated as the fiber is immersed in water and reappears when
the fiber is dried. This phenomenon is based on swelling characteristics of
the components. Several factors are crucial to the fiber curvature
The difference in the shrinkage between the components,
The difference between modulus of the components,
The overall cross-sectional fiber shape and individual
cross-sectional shapes of each components, and
The thickness of the fiber.
Different melting points on the sides of the fiber are
taken advantage of when fibers are used as bonding fibers in thermally
bonded non-woven webs. The example of such bonding fibers is EA & ES of
Chisso, Japan, with polyethylene as the low melting component (Tm = 110oC),
along with polypropylene . Side-by-side fibers have also been reported to
be a base fiber for producing so called "splittable " fibers, which split in
a certain processing stage, yielding fine filaments of a sharp-edged cross
section. One of the components could be removed by dissolving [9,10] or the
fiber could split by just heating and the fiber would split by a flexion
2.Sheath-core (S/C) Fibers
Sheath-core bicomponent fibers are those fibers where one
of the components (core) is fully surrounded by the second component
(sheath) (Fig.2). Adhesion is not always essential for fiber integrity. This
structure is employed when it is desirable for the surface to have the
property of one of the polymers such as luster, dyeability or stability,
while the core may contribute to strength, reduced cost and the like. A
highly contoured interface between sheath and core can lead to mechanical
interlocking that may be desirable in the absence of good adhesion.
Sheath-core Fiber Production
The most common way of production of sheath-core fibers
is a technique where two polymer liquids are separately led to a position
very close to the spinneret orifices and then extruded in sheath-core form.
In the case of concentric fibers, the orifice supplying the "core" polymer
is in the center of the spinning orifice outlet and flow conditions of core
polymer fluid are strictly controlled to maintain the concentricity of both
components when spinning.
Eccentric fiber production is based on several
approaches: eccentric positioning of the inner polymer channel and
controlling of the supply rates of the two component polymers ;
introducing a varying element near the supply of the sheath component melt
; introducing a stream of single component merging with concentric
sheath-core component just before emerging from the orifice ; and
deformation of spun concentric fiber by passing it over a hot edge .
Other, rather different techniques to produce sheath-core fibers, are
coating of spun fiber by passing through another polymer solution  and
spinning of corepolymer into a coagulation bath containing aqueous latex of
another polymer .
Modifications in spinneret orifices enable one to obtain
different shapes of core or/and sheath within a fiber cross section. There
is considerable emphasis on surface tensions, viscosities and flow rates of
component melts during spinning of these fibers.
Use of Sheath-core Bicomponent Fibers
Besides the sheath-core bicomponent fiber used as a
crimping fiber, these fibers are widely used as bonding fibers in nonwoven
industry. The sheath of the fiber is of a lower melting point than the core
and so in an elevated temperature, the sheath melts, creating bonding pints
with adjacent fibers - either bicomponent or monocomponent. The first
commercial application of sheath-core binding fiber (I.C.I. Heterofil, )
has been in carpets and upholstery fabrics. The newest trend in bicomponent
fiber production is to focus on tailoring a fiber according to the
customer's needs. A considerable emphasize was put on the processing
optimization (depending strictly on machinery used) and on the desired look
of the final product. It appears that concentricity/eccentricity of the core
plays an important role. If the product strength is the major concern,
concentric bicomponent fibers are used; if bulkiness is required at the
expense of strength, the eccentric type of the fiber is used .
Other uses of sheath-core fibers derives from
characteristics of the sheath helping to improve the overall fiber
properties. A sheath-core fiber has been reported  whose sheath is made
of a polymer having high absorptive power for water, thereby having obvious
advantages for use in clothing. Other sheath-core fibers showed better
dyeability , soil resistance , heat insulating properties ,
adhesion  etc. Production of ceramic sheath-core bicomponent fibers is
another application utilizing the difference of sheath and core . The
fiber precursors are first spun in a sheath-core arrangement and then cured
by oxidation, UV and electron beam, heating or by chemical means. These
fibers are used as a composite reinforcement.
3. Matrix-fibril (Biconstituent ) Bicomponent Fibers
These are also called islands-in-the-sea fibers.
Technically these are complicated structures to make and use. In cross
section they are basically areas of one polymer in a matrix of a second
polymer. This types of bicomponent structure facilitate the generation of
microdenier fibers. The
are usually a melt spinnable polymer such
as nylon,polyester or polypropylene. The sea or matrix can be formed by
polysterene water soluble polyesters and plasticized or saponified polyvinyl
alcohol. The finer deniers that can be obtained are normally below 0.1
Production of Matrix-fibril Bicomponent Fibers
Basically, these fibers are spun from the mixture of two
polymers in the required proportion, where one polymer is suspended in
droplet form in the second melt. An important feature in production of
matrix-fibril fibers is the necessity for artificial cooling of the fiber
immediately below the spinneret orifices. Different spinnabilities of the
two components would almost disable the spinnability of the mixture, except
for low concentration mixtures (less than 20%).
Use of Matrix-fibril Bicomponent Fibers
A matrix-fibril fiber called "Source" is produced by
Allied Chemicals Ltd. . The fiber is based on PET fibrils embedded in a
matrix of Nylon 6. The presence of PET fibrils is supposed to increase the
modulus of the fiber, to reduce moisture regain, to reduce the dyeability,
improve the texturing ability and give the fiber a unique lustrous
The fine fibers produced by this method are used in
synthetic leather, specialty wipes, ultra-high filtration media, artificial
arteries and many other specialized applications.
pie cross section type
A segmented pie cross section fiber is split by
chemical,mechanical or heat treatment to result in microdenier fibers
.typically fibers of 0.1-0.3 denier can be obtained.the most usual polymer
combination is polyester /nylon.these fibers are used in high performance
wipes,synthetic suede,heat insulators,battery seperators and specialty
Polyblends, of polymer alloys, are defined as homogenous
or heterogeneous mixtures of structurally different homopolymers or
copolymers. The purpose of blending is either to improve processability or
to obtain materials suitable for specific needs by tailoring one or more
properties with minimum sacrifice in other properties. The behavior of
polyblends may be expected to depend on the individual properties of the
components in the blend, their relative proportions, degree of heterogeneity
and the properties of the interface between the components.
Several criteria are used to define the nature of
Miscibility or compatibility
Relative moduli of the components
The classification also depends on the polyblend method
of manufacture (melt, solution and emulsion mixing).
Homogeneity of Blends
Two polymers are thermodynamically compatible when their
free energy of mixing is negative. Because mixing of two materials is
generally endothermic and the entropy of mixing long polymer chains is
small, the free energy of mixing is rarely negative. This is the reason why
blending two polymers usually leads to heterogeneous blend. If the blend
shows homogeneity, than the behavior of the blend behaves as a single
polymer (for example, a single Tg and Tm)
In this more common category, two polymers are segregated
into spatial regions composed essentially of one or the other pure
component. Usually, the two polymers are immiscible but they can be
compatible. Considerable emphasis is put on the adhesion between the phases
of the blend because it is crucial factor for mechanical properties of the
Moduli of the Components
The theory of modulus tailoring is mainly used in
matrix-fibril type of bicomponent fibers. Classification based on the
relative moduli of the two components depends to a great extent on the
properties and use of the blends. For example, adding of a disperse phase of
higher modulus generally increases the overall modulus and is frequently
used to reduce the creep of elastomers. In contrast, adding of a low modulus
polymer in the blend is generally used to improve the impact resistance and
elongation-to-break of rigid plastics.
Rheological Aspects of Bicomponent Fiber Production
It is essential that the viscosities of both polymer
fluids are of comparable value; otherwise, the higher viscosity component
will not tend to rearrange during spinningcausing the distortion of the
distribution of the components in the cross section of the fiber.
Considerable attention should be also paid to the rate of
solidification of each component. It has been shown that during high speed
spinning of PP/PET sheath-core fibers  that the PET component achieved
higher orientation than would be obtained if the fiber was just
monocomponent, while PP component orientation was decreased. This phenomenon
is explained in terms of difference in activation energy of the longitudinal
viscosity and solidification temperature of both polymers.
APPLICATIONS IN NONWOVENS
Bicomponent fibers made of pp/pe are important material
in the nonwoven market. The main applications include:
 Kikutani, I, Radhakrishnan, J., Arikawa, S., Takaku,
A., Okui, N., Jin, N., Niwa, F., Kudo, Y.: "High-Speed Melt Spinning of
Bicomponent Fibers: Mechanism of Fiber Structure Development in Poly
(ethylene terephtalate)/Propylene System", J.Appl.Pol.Sci. Vol.62, 1996,
 Paul, D.R., Seymour, N.: Polymer Blends, vol.2,
Academic Press, Inc., 1978
 "High technology Fibers", part A, Handbook of Fiber
Science and Technology, vol. III. edited by Menachem Lewin and Jack Preston,
Marcel Dekker, Inc., 1985
 Morgan, D.: "Bicomponent Fibers: Past, Present and
Future", Hoechst Celanese, Charlotte, NC, Inda Journal of Nonwovens
Research, vol.4, no.4, fall 1992
 IDEA 92 Exhibition handouts from Chisso, Japan and
 Jeffries, R.: "Bicomponent Fibres", Merrow Publishing
 B.P. 1048370, Kanegafuchi Boseki
 NA.P. 66-12238, Shell International Research
 B.P. 1066418, DuPont
 NA.P. 65-15218, DuPont
 B.P. 1016862, DuPont
 B.P.805033, DuPont
 B.P.1100430, I.C.I. Ltd.  B.P.950429, DuPont
 B.P. 1083008, Kanegafuchi Boseki
 Belg.P. 631744, Monsanto Co.
 U.S.P. 3316336, Dow Chemical Co.
 West, K.: "Melded Fabrics", Paper presented at
Second Shirley International Seminar, Manchester, 1970
 Marcher, B.: Tailor-Made Polypropylene and
Bicomponent Fibers for the Nonwovens Industry, Tappi Journal,Dec 1991,
 B.P.1094688, Snia Viscosa
 U.S.P. 3472608, I.C.I.
 B.P. 1199115, I.C.I.
 NA.P. 65-09283, A.K.U.
 OLS.P.1816138, Kanegafuchi Boseki
 Curran, G.: Bicomponent Extrusion of Ceramic Fibers,
Advanced Materials and Processes, 1/95, 25 - 27
 Papero, P, V., Kubu, E., Roldan, L.,: Text.Res.J.,
37, 823, (1967)
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