Bicomponent Fibers: Bicomponent (bico) fibers represent a special class of synthetic fibers / filaments that are made up of two different polymers. It is also called heterofil fiber. 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 forma single fiber. This type of fiber is common in the carpet industry where one polymer has a different shrinkage temperature compared to the other.
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:
Core-sheath (C/S),
Side-by-side (S/S),
Segmented-pie (orange),
Islands in-the-sea (I/S) and
Polymer blends
Those are the most common types of bico fibers.
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 fibers can be classified into three groups:
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.
In the second group, the two bicomponents 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.
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, splittable fibers 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 behavior 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.
Splittable fibers 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 behavior. 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: Manyfiberapplicationshavebeenrevolutionizedby Bicomponenttechnologies.Productshavebeenmadelighter, 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.
Figure-3: Bulky acrylic yarn using shrinkable, non-shrinkable and bicomponent fibers.
References:
Introduction to Textile fibers (Revised Edition) by H. V. Sreenivasa Murthy
Textile and Clothing Design Technology by Tom Cassidy & Parikshit Goswami
Handbook of Fibrous Materials Edited by Jinlian Hu, Bipin Kumar and Jing Lu
Synthetic fibers: Nylon, Polyester, Acrylic, Polyolefin Edited by J. E. McIntyre
Forensic Examination of Fibres, Third Edition Edited by James Robertson, Claude Roux and Kenneth G Wiggins
Md. Khalilur Rahman Khan, Mohammad Naim Hassan. A Review Study on Bicomponent (Bico) Fibre/ Filament. J Textile Sci & Fashion Tech. 8(2): 2021. JTSFT.MS.ID.000681. DOI: 10.33552/JTSFT.2021.07.000681.
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
