Bicomponent fibers are filaments made of two different polymers extruded together within the same filament. This allows the fibers to exploit the desirable properties of both polymers. There are several types of bicomponent fiber geometries, including core-sheath, side-by-side, segmented pie, and islands-in-the-sea. Bicomponent fibers find applications in areas like apparel, home textiles, and nonwovens due to properties like bonding ability, dyeability, insulation, and strength. They can be processed further to produce microfibers for high strength nonwoven materials.

1. Bicomponent Fibers
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2. Bicomponent Fibers
• Bicomponent fibers are filaments made up of two different
polymers that are extruded from the same spinneret with
both polymers contained within the same filament but
separated by a fine plane. The two polymers differ in
chemical nature or physical properties such as molecular
weight.

3. Why Bicomponent Fibers?
• The conventional fibers may not have all the desirable
properties. By the use of bicomponent fibers, the
functional properties of both the components can be
exploited in one filament. Further, the fibers can be
produced in any cross-sectional shape or geometry. The
properties of these bicomponent fibers are governed by :
• Nature /properties of two materials
• Their arrangement in the fiber
• Relative proportion of the two
• Thickness of the fiber

4. Types of Bicomponent Fibers:
• These fibers can be produced in many geometrical
arrangements. On the basis of cross section, these can
be classified as
• In addition to these main classes, a wide variety of
bicomponent fibers having different cross-sectional
geometries can be produced.

5. Typical
Applications:
• The bicomponent
fibers can have a
range of
functionality and
applications for
different end-
uses as given
in the table.
Functionality Some End-use Applications
Antistatic
Lining clothes, work wear, knitted
fabrics, underwear
Liquid
absorbing
Sports wear, felt pens, liquid
absorbers, underwear
Self-crimping
Stockings, beddings, heat
insulators, knitted fabrics, carpets
Thermal
Bonding
Nonwoven fabrics, beddings,
mattresses, printing screens,
cushions,
Electro-
conductive
Carpets, seating, work wear,
knitted fabrics
Light-conductive
Communication, decoration,
telephone
Other
Enhancement of properties such
as - mechanical properties,
aesthetics, dyeability, water
repellency, flame retardancy

6. Spinning of Bicomponent Fibers
For proper spinning of two components it is required that:
• Viscosities of the two polymer fluids are comparable. The
viscosity should be high enough to prevent turbulence
after the spinneret.
• Drawability of the two polymers should also be
comparable, otherwise splitting may occur.
• Compatibility of both components with the spinning
method that is melt spinning or solution spinning is also
important.

7. • The first commercial bicomponent fiber was introduced by
DuPont in the mid 1960s. 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 were
used for manufacturing. 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.
• These are melt-spun in a specially designed spinning manifold.
Separate extruders and metering pumps are used for both
components. Ratio of the polymers can be controlled by
varying the speed of the metering pumps.
Spinning of Bicomponent Fibers

8. Figure 1. Photograph of a
Bicomponent Spinning Machine
Figure 2. Sketch showing parts of
Bicomponent Spinning Machine

9. Core-Sheath Bicomponent Fibers
• In core sheath structure, one of the components called
core is fully surrounded by the second component known
as sheath. In this configuration, different polymers can be
applied as a sheath over a solid core of another polymer,
thus resulting in variety of modified properties while
maintaining the major fiber properties.
Figure 3. Different types of bicomponent
fibers a)-d)Core–sheath, e) Eccentric core-
sheath and f)Multiple core-sheath

10. • Concentricity/eccentricity of the core can be tuned
according to end application. 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.
Core-Sheath Bicomponent Fibers

11. Applications of Core-Sheath Bicomponent
Fibers
• Core imparts strength (reinforcing material) and sheath has dye
ability, soil resistance, heat-insulating, and adhesion properties. Some
examples include:
• bonding fibers used in carpets, upholstery etc., where the sheath is
made of PE and core is made of high melting point material like nylon.
• antisoil-antistatic fibers, made using a PET-PEG block copolymer
containing polyester core.
• Sheath can be made from expensive material to increase visual
appearance. And the core can be of low cost material to control cost.
• For making self crimping fibers. Crimp can be controlled by changing
the eccentricity. Eccentricity of core can be varied to balance strength
and bulkiness: used in pillows and furniture.
• In a simple technique to produce core sheath fibers, the two polymer
liquids are separately led to a position very close to the spinneret
orifices and then extruded in a core sheath form as shown in Figure 4.

12. Figure 4. Technique for Core-Sheath Fiber formation

13. Core-Sheath Bicomponent Fibers
• In case of concentric fibers the core polymer is in the center of the
spinning orifice outlet and flow of the core polymer fluid is strictly
controlled to maintain the concentricity of both components, while
eccentric fiber production is based on following approaches:
• Eccentric positioning of the inner polymer channel and controlling of
the supply rates of the two component polymers.
• Introducing a stream of single component merging with concentric
sheath-core component just before emerging from the orifice.
• Deformation of spun concentric fiber by passing it over a hot edge.
• Coating of spun fiber by passing through another polymer solution.
• Spinning of core polymer into a coagulation bath containing aqueous
latex of another polymer.

14. Side by Side Bicomponent Fibers
• These fibers contain two components lying side-by-side.
Both components are divided along the length into two or
more distinct regions. These are generally used to make
self-crimping fibers due to different shrinkage
characteristics of the two components. In some
applications, different melting temperatures of the fibers
are taken advantage of when fibers are used as bonding
fibers in thermally non woven waves.
• Generally, the two components must show good
adhesion. however, side by side fibers can also be used
for producing the so called splitable fibers which split in a
certain processing stage yielding fine filament of a sharp
edge cross section.

15. Figure 5. Schematic showing melt
spinning of side by side bicomponent
fibers

16. Multi layer, fine or microfibers
• After the commercialization of self-crimping bicomponent
fibers in 1960’s, attempts were made to multiply the
conjugating structure to produce much complicated
bicomponent fibers, also sometimes referred to as
multilayer fibers. After development of multilayer fibers
around 1965, the fibers were split (as shown in Figure 6)
to produce super fine fibers /microfibers.

17. Figure 6. Evolution of Microfibers

18. • Besides direct spinning most other techniques for the
production of microfibers involve the spinning of a
multicomponent filament from which smaller sub units are
isolated by splitting. Some examples of microfibers
produced by separation /splitting are summarized in
Figure 7.

19. Figure 7. Microfiber produced by
separation/splitting

20. Segmented Pie
• These are made from alternate wedges made from two
different polymers. The number of wedges is around 16 to
32 and the spinning manifold is complicated. The fiber is
drawn to high draw ratio and sometimes splitting may
occur while drawing.
• The splitting is carried out by partial or complete
dissolution of one component. Fibers obtained are of fine
denier and sharp cross section.
• These are used for making non-woven web with ultra fine
fibers. The resultant fabric is stronger and has higher
surface area.

21. Figure 8. Segmented pie bicomponent fibers
Figure 9. Schematic showing melt spinning
of segmented pie structured fibers

22. • PET and Nylon
bicomponent fiber is
split by soaking in a
hot caustic solution
of 5-10% NaOH.
PET and Nylon are
separated due to
swelling.
Figure 10. Schematic showing melt
spinning of segmented pie fibres

23. • Sanding and
brushing can also
be used for splitting
fibers. But it works
only with fibers that
are easily splitable
such as hollow fiber. Figure 11. Radial petal like conjugate
fibres: (a) without central hole and (b)
with central hole

24. Islands in the sea
• These are also called as matrix-fibril fibers. In cross
section there are areas of a polymer (island) in the matrix
of the other (sea). These are also used to produce finer
fibers. Sheath is made up of a dissolvable material and
core is made up of desired material. Sheath is dissolved
in proper solvent giving micro denier fibers.