Bicomponent Fiber Spinning: Factors, Principles and Technologies

Bicomponent Spinning:
Bicomponent fibers are fibers that in a single fiber consist of two distinct raw material components. It is made by simultaneously spinning two compositions in each capillary of the spinneret. The growing demand for nonwoven fabrics is one of the growth drivers of the global bicomponent fiber industry. The growing demand for nonwoven fabrics is one of the growth drivers of the global bicomponent fiber industry. In addition, bicomponent fibers are also used in the manufacture of bulky goods, microfiber fabrics, advanced textiles, etc. Various types of commercial bicomponent fibers as well as bicomponent fiber fabrics are manufactured by many companies around the world. However, factors affecting bicomponent spinning, principles of bicomponent spinning, bicomponent fiber spinning technologies are briefly reviewed in this paper.

Bicomponent spinning is a two-step process that involves spinning two polymers through the spinning die (which forms the bicomponent fiber with island-in-sea (IIS), side-by-side, sheath–core, citrus or segmented-pie structure) and removal of one polymer. The first bicomponent fibers were spun by Dupont in 1960; a side-by-side fiber made from two types of polyamide fibers with different retraction. Although bicomponent fibers of different cross-sectional shapes and geometries with micrometre diameter can be produced with the existing fiber-forming techniques, fabricating smaller diameters especially in nanometres is a real challenge.

The production of webs of IIS structure (nylon 6 island and PLA sea) by spunbonding process and subsequent removal of sea for the production of micro and nanofibers have been reported. Hill Inc. produced nanofibers of 300 nm diameter from the IIS structure.

Bicomponent spinning can be used for the fabrication of smaller nanofibers by sacrificing one of the polymer components as well as to create multicomponent nanofibers. Several research studies on bicomponent polymeric nanofibers of sheath– core structure by electrospinning process using a coaxial two-capillary spinneret have been reported. The use of melt-coaxial electrospinning for the fabrication of core–shell nanofibers having potential for temperature sensors and composites based on phase change materials have been investigated. The segmented-pie structure forms micro-and nanofibers (diameters 500 nm–2 μm) with non-circular cross section. A modified coaxial electrospinning process has been developed to prepare polymer fibers from a high-concentration solution of PVP. This process involved a pure solvent concentrically surrounding polymer fluid in the spinneret and was able to produce fibers with a smooth surface morphology and good structural uniformity.

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Factors Affecting Bicomponent Spinning:
Choice of polymers is a highly crucial factor in bicomponent spinning. If the viscosities of the polymers are close, a continuous phase would exist. The morphology would strongly depend on the relative amounts of each phase and the relative viscosity of the two polymers. It has been observed that when polymers have varying viscosity, the lower viscosity polymer tends to encapsulate the one with a higher viscosity. This is extremely important for sheath-core spinning where, in the final fiber, the sheath is of lower viscosity polymer and the core has a higher viscosity. Final diameter of fibrils, in case of matrix fibril type bi-constituent fibers, can be achieved through the control of particle size of the discontinuous phase, the amount of spin draw, and post spinning parameters.

Principles of Bicomponent Spinning:
Following principle follows during bicomponent spinning process.

1. Structure formation during spinning and drawing
2. Mutual influence of components on orientation and crystallinity
3. Interfacial adhesion
4. Coextrusion instabilities
5. Encapsulation
6. Volatiles
7. Simulation and modeling

Bicomponent Fiber Spinning Technologies

1. Spin Pack Design:
In bicomponent fiber spinning, one can differentiate between single die andmultiple die spinneret, depending on the position where the molten polymers meet. In the first, by far most common type, two pressurized polymer melts meet within the spinneret. Ensuring a laminar flow prevents mixing of the two phases. The development of etched stacked plates to create polymer channels in the spin pack led to smaller packs with higher hole densities and shorter residence times, as well as larger number of segments or islands in the fibers.

In the second, less prominent type, each polymer is extruder separately, and the melts meet just at the capillary exit. This geometry is complex to realize but can lessen rheological disparities between the components and enable an exact position of the core within the sheath polymer.

2. Cross-Sectional Geometries:
The three main geometries of multicomponent fibers are side-by-side, core–sheath, and multiple core configurations. Side-by-side and eccentric core–sheath bicomponent fibers are most commonly used to produce self-crimping yarns applied in voluminous products. By combining two polymers that undergo differential shrinkage, the yarn curls up after thermal treatment or relaxation and develops crimp contraction.

3. Melt Spinning Equipment:
Atypical bicomponent melt spinning plant comprises two screw extruders, a spin pack with discrete polymer conduits, and a set of spinnerets allowing for elaborate fiber cross sections.

4. Special Spin Pack Designs:
As nonlinear and elastic flow properties of polymer melts would lead to flow instabilities in coextrusion of a molten polymer and a liquid core, a special spin pack was designed that enabled the stable melt spinning of a bicomponent fiber with a liquid core.

In order to produce bicomponent thermoplastic core–sheath fibers with a high tenacity core, a wire-coating spin pack was modified to enable coating a high tenacity thermoplastic filament with a polymeric sheath. The other important part in bicomponent spinning is to maintain and control the polymers as long as possible at their optimal temperatures during extrusion.

References:

1. Fibers to Smart Textiles: Advances in Manufacturing, Technologies, and Applications Edited by Asis Patnaik and Sweta Patnaik
2. Handbook of Fibrous Materials Edited by Jinlian Hu, Bipin Kumar and Jing Lu
3. Advances in filament yarn spinning of textiles and polymers Edited by Dong Zhang
4. 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.

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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