Bicomponent Fibers:
Bicomponent (bico) fibres represent a special class of synthetic fibres / filaments that
are made up of two different polymers. It is also called heterofil fibre. There are a
number of arrangements that can be used, but the three most common are side-by-
side, core-sheath and mixed polymer or islands in the sea effect. A bicomponent fiber
is made from two or more polymers of different chemical (e.g. composition, additives)
and/or physical (e.g. average molecular weight, crystallinity) nature, extruded from
one spinneret to form a single fiber. This type of fiber is common in the carpet
industry where one polymer has a different shrinkage temperature compared to the
other.
How we will manufacture bi-component fibers: Through spinneret design, it is
possible to form fibers containing more than one polymeric component. In this
arrangement, the polymers are not blended together but remain as discrete regions
within the fiber. A range of bicomponent designs exist, but the principle types are side
by side, core-sheath, segmented pie, and islands-in-the-sea (Figure-1). The segmented
pie and islands-in-the-sea styles are often fibrillated to produce microfibers with
excellent flexibility and softness. The 4DG fiber is a high surface area fiber designed
for particle capture and wicking applications.
Figure 1: Common types of bicomponent fiber
Bicomponent fibers can have unusual physical and aesthetic properties, which make
them a high-value product compared to conventional fibers. It is often done to
combine the characteristics of polymers or to exploit the differences in a property such
as melting point. For example, bicomponent astroturf produced from a core-sheath
with a polyamide core and polyethylene sheath retains the resilience of the core but
reduces incidence of friction burn through the polyethylene. Formation of such
bicomponent material is not widespread but is relatively established as a technique.
Bicomponent fibers are those fibers which may consist of two or more components of
different polymers and extruded as a single filament.
Bicomponent fibers consist of two components divided along the length of the fiber
into two more or less distinct regions.
Bicomponent fibers are also referred to sometimes as composite, conjugate, and
hetera fibers. Some different types of bi-component fiber cross-sections are illustrated
in Figure-2.
Figure 2: The principles of bicomponent spinning and the cross-section
Types of Bicomponent Fiber:
Bicomponent fibers are sometimes referred as ‘composite’, ‘conjugate’ or ‘hetro’
fibers. There are special features and applications for each type of bicomponent
fiber. These can be divided into several groups according to the component
distribution within the fiber cross section area, as given below:
1. Core-sheath (C/S),
2. Side-by-side (S/S),
3. Segmented-pie (orange),
4. Islands in-the-sea (I/S) and
5. Polymer blends
Those are the most common types of bicomponent fibres.
Manufacturing Process of Bicomponent Fibers:
Melt spinning is the most commonly used method for manufacturing commercial
synthetic fibers. A trend in polymer melt spinning is variation of fiber morphology by
bicomponent (conjugated) spinning, one of the most interesting developments in the
field of synthetic fibers. Bicomponent fibers pass through common melt-drawing
processes similar to conventional synthetic fibers. The main objective of bicomponent
melt spinning is to exploit capabilities not existing in either polymer alone, as
advantageous mechanical, physical, or chemical properties of two materials can be
combined in one fiber, expanding the range of possible applications.
Manufacturing of side-by-side component fibres can be classified into three groups:
1. In the first group, the two components either solutions or melts are fed
directly to the spinneret orifices, being combined into bicomponent fibers
at or near the orifices.
2. In the second group, the two biocomponents of the fiber are formed into
a multi-layered structure (either flat sheets or concentric cylinders) and fed
without turbulence to the spinneret, the rows of orifices in the spinneret
being so positioned as to intersect the interfaces of the various layers of
polymer.
3. In the third group, the two components are also formed into a
nonturbulent layer structure (e.g. a mixed stream) and fed to the
spinnerets; here, however, no attempt is made to align the rows of
spinneret orifices with the component interfaces, and so bicomponent
fibers of wide range of compositions are produced.
It is possible that a bicomponent fiber may vary in the lateral distribution of the two
components along the fiber length. It is also possible to prepare yarns consisting of
mixture of bicomponent fibers and monocomponent fibers.
These bicomponent fibers are suitable for the production of bonded fabrics, floor
coverings, upholstery fabrics, high crease resistant fabrics, etc.
Aftertreatment of Bicomponent Fibers:
Usually fibers undergo diverse processing steps to increase the strength, to texturize
yarns, or to crimp and cut fibers for a staple fiber or wet-laid process. Heat setting is
often applied to crystallize the fibers in order to avoid shrinkage. It is obvious that the
heat setting must be achieved without a hot contacting surface, but by hot air flow at
reduced temperature and low speed.
In the very most cases, splitable fibres are produced by segmented-pie technology.
Easy splitting is desired, which may be achieved by hollow segmented-pie fibers. Yet
during fiber melt spinning, drawing, crimping, and carding, the fibers must not split, as
this would significantly impair these processes. To avoid splitting during processing,
but enabling it in post treatment, the polymer melts should be compatible, but show
almost no inter diffusion of macromolecules across the interface, and the polymers
should have similar drawing behaviour and extensibility to allow deformation during
the crimping process at low force. Steam supports the crimping process but can lead
to shrinkage and thereby to splitting.
Splitable fibres are processed into knits, woven fabrics, or nonwovens. For splitting,
woven and knitted materials are brushed, needled, or treated by water jet, where the
mechanical force separates the segments. The filaments are bound in the fabric, which
allows a harsh procedure yet limits a spreading of the mechanically induced splitting.
Other mechanisms to split are heat treatment through air or infrared heating if both
of the fiber components have different shrinkage behaviour. Chemical splitting is
realized by hot water, sodium hydroxide, caustic soda, and benzyl alcohol solutions,
eventually supported by ultrasonic force. Hot drawing and heat setting for
bicomponent fibers are more complex than single-component fiber.
Application / Uses of Bicomponent Fibers:
Many fiber applications have been revolutionized by Bicomponent technologies. Pro
ducts have been made lighter, stronger and simpler to work with. This type of fiber is
expected to develop as an advanced material across many end-use
applications, including hygiene, textiles, automotive, home furnishings, and many
others to solve problems and meet customer needs. In nonwovens, bicomponent
staple fibers have been one of the most significant fibers. Major uses of bicomponent
fibers are given below.
1. Fibers as bonding elements in nonwovens:
In the through-air thermal bonding of bicomponent fibers for the production of
nonwoven fabrics, a fiber web mixed with thermo-bondable core–sheath
bicomponent fibers is treated by blowing hot air through the web. Bicomponent fiber
is utilized for the production of nonwoven fabrics with soft touch, which are applicable
for diapers and hygiene products.
2. Microfibers:
One of the first and best-known microfiber products is the artificial leather called
Alcantara. It is produced from bicomponent fiber. A solvent-free alternative to
produce microfibers is the application of mechanical stress to separate the different
parts of segmented-pie fibers.
3. Fibers with special cross sections:
A special feature of the islands-in-the-sea technology is the logotype fiber, where the
islands polymer has a different color or has different dyeability compared with the
matrix (e.g. PA vs. PET).
4. Fibers with high-performance core:
The reinforcement of concrete with fibers can be an economical alternative to
conventional steel bar reinforcement. Polyolefin-based bicomponent fibers, with
high tensile strength and elastic modulus in the core, nanoparticles and other
additives in the sheath, and a structured fiber surface were successfully applied to
enhance the mechanical properties of concrete.
5. Fibers with functional surface:
Core–sheath fibers offer the chance to modify the surface while leaving the bulk
unchanged. The majority of commercialized bi-component fibers are binder fibers
with a low melting temperature sheath.
6. Fibers for fully thermoplastic fiber-reinforced composites:
Core–sheath and islands-in-the-sea bicomponent fibers can be utilized for the
production of fully thermoplastic fiber-reinforced composites.
7. Shape memory fibers:
Two polymers with different phase transition temperature can be combined to form
a composite material with a shape memory character. Bicomponent spinning
provides a useful platform for engineering shape memory composites or blends.
8. Polymer optical fibers:
To obtain thin and flexible polymer optical fibers (POFs) for textile applications,
bicomponent melt-spun fibers with a cyclic olefin polymer (COP) as the core and a
tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV).
Use of bicomponent fiber in manufacturing bulked yarn for knitting:
Acrylic bicomponent fibers exhibit a reversible crimp on steam wetting and drying,
similar to what is observed in the case of wool. In fact, acrylic bicomponent fibers were
developed after studying the morphological structure of wool fiber. The typical hand
and bulkiness of wool fibers is largely attributed to the bilateral structural asymmetry
of the fiber which is due to the presence of two components namely ortho and para-
cortex units in the cross-section. Acrylic bicomponent fiber is normally prepared by
spinning fibers from the acrylic copolymers having different longitudinal shrinkage
characteristics.
When bicomponent fiber is subjected to heat, differential shrinkage is developed in
the fiber itself and as a result a three-dimensional crimp is formed. This three-
dimensional crimp in the fiber in turn generates a very good feel, high elasticity, high
resiliency and improved dimensional stability of the yarn. The crimp configuration of
acrylic bicomponent as well as monocomponent fiber in producing bulky hand knitting
yarns is as shown in Figure 3.
