When two or more polymers that do not mix are present in the cross-section of a single fiber, it is called a composite fiber. This type of fiber, developed in the 1960s, is a form of physically modified fiber. Composite fiber manufacturing technology allows the creation of various modified fibers, such as bicomponent fibers, permanently crimped fibers, ultrafine fibers, hollow fibers, and differently shaped fine fibers, each combining the characteristics of the two polymers.
Classification and Characteristics
Currently, there are hundreds of types of composite fibers. Based on the number of components, they can be categorized into bicomponent and multicomponent composite fibers. Most developed fibers are bicomponent fibers (also known as conjugate fibers). Bicomponent fibers can be further classified into four types based on their cross-sectional morphology: side-by-side, sheath-core, island-in-sea, and segmented pie.
Composite Fiber Cross-sectional Morphology
1. Side-by-Side Composite Fibers
Side-by-side composite fibers are made by aligning different polymers with varying properties or structures along the fiber axis. The proportions of each component can be symmetrical or asymmetrical. The key feature of these fibers is their ability to utilize the differing shrinkage properties of each element to produce an ideal helical three-dimensional crimp similar to wool, thus producing permanently crimped chemical fibers with self-crimping properties.
Currently developed side-by-side composite fibers mainly include PBT/PET and CDP/PET composites. (To know more about CDP Chip, please check https://www.polyestermfg.com/cationic-dyeable-polyester-chip/. PBT and PET are polyester polymers with very similar macromolecular structures, providing good compatibility and adhesion, allowing the creation of side-by-side composite fibers without delamination. After composite processing, the asymmetric distribution of the two components and their different shrinkage rates produce three-dimensional crimps after stretching and heat setting, achieving high elasticity without deformation processing. This shortens the process flow, reduces costs, and avoids strength loss during deformation processing. PBT/PET composite fibers combine the high elasticity of PBT with the characteristics of PET fibers. These fibers are not only highly elastic and quick to dye with vibrant colors but also soft to the touch, combining softness with firmness, and possess excellent heat resistance, chlorine resistance, and alkali resistance. Various denier composite filaments have found applications in silk, knitting, dyed fabrics, ribbons, wool, and linen industries, suitable for making various pantyhose, tights, elastic jeans, swimwear, and various high-end sportswear and distinctive new silk products.
2. Sheath-Core Composite Fibers
Sheath-core composite fibers are made by encapsulating one polymer component with another, forming concentric or eccentric layers along the fiber axis. Sheath-core composite fibers can be divided into several types, such as concentric, eccentric, and irregular cross-section types. These fibers can produce different morphologies and effects by leveraging the differing properties of each component. For instance, polyamide/polyester sheath-core composite fibers, mainly using polyamide as the sheath and polyester as the core, combine the advantages of nylon and polyester.
These fibers have good elastic modulus and a soft yet firm hand feel. They exhibit excellent dyeability due to the easy dyeing properties of nylon, allowing for dyeing at normal pressure with convenience. Typically, this type of composite fiber is dyed using acid dyes with good color fastness and bright colors, along with dispersing dyes for good-level dyeing.
Polyamide/polypropylene sheath-core composite fibers, using polyamide as the sheath and polypropylene as the core, maintain the excellent elasticity, abrasion resistance, and dyeability of nylon while overcoming the difficulties of dyeing, low moisture absorption, and easy aging of polypropylene. Moreover, polypropylene is a low-cost raw material and the lightest among synthetic fibers. Additionally, through composite spinning, the core layer polypropylene can be colored with a masterbatch, eliminating the dyeing process and reducing costs.
Adding various functional additives such as antibacterial, aromatic, UV-resistant, photosensitive, and conductive substances to the sheath or core layer can produce various functional fibers. For example, by using polyester (antistatic or semi-dull polyester) as one component and carbon black conductive medium with a polymer as the other, sheath-core conductive fibers can be manufactured using composite spinning technology. The carbon black polymer can be either the sheath or the core, both having good conductivity, now used in explosion-proof and dust-proof clothing. White conductive polyester with CuI as the conductive component in sheath-core form has also been developed successfully.
Sheath-core composite fibers can also use low-melting (110-130°C) polyethylene/PET as the sheath and higher melting (160-170°C or regular) polypropylene/PET as the core to produce heat-bonding fibers for non-woven fabrics, known as ES fibers. Our company can supply low melt (90°C /110°C /180°C ) PET Chip. For more information, please refer to https://www.polyestermfg.com/low-melting-polyester-chip/.
3. Island-in-Sea Composite Fibers
Island-in-sea composite fibers, also known as multi-core composite fibers, consist of one polymer as the matrix (sea component) and another polymer distributed as fine fibers (islands) within the matrix fiber. The “island” and “sea” components are continuously and densely distributed along the fiber axis. Viewed as a whole, the fiber has a conventional fiber denier. By dissolving the “sea” component with a solvent, a bundle of ultrafine fibers can be obtained, used for synthetic leather, wipes, ultra-fine filtration media, artificial arteries, and other special applications. By dissolving the “island” component, porous hollow fibers can be obtained, which can be microfibres through swelling. For instance, the PET filament product “K-21” developed by Japan’s Kuraray Company has a hollow rate of over 40%, a density of only 0.859/cm3, lighter than polypropylene and fabrics made from this fiber can float on water.
The island component of island-in-sea fibers typically uses alkali-soluble polyester (COPET) or polyamide (PA), with sea components including polyethylene (PE), polyamide (PA6 or PA66), polypropylene (PP), polyvinyl alcohol (PVA), polystyrene (PS), and acrylic copolymers or modified polyesters. The number of islands ranges from 16, 36, 64, to 200 or even 900 or more. If you want to purchase COPET, please click https://www.polyestermfg.com/alkali-soluble-polyester-chip/.
4. Segmented Pie Composite Fibers
Segmented pie composite fibers, also known as celestial or bicomponent fibers, feature one polymer component dispersed in a fibril state within another component. In the cross-section of such fibers, the size and distribution of the fibrils are random, with fibrils discontinuously distributed along the fiber axis.
These fibrils increase the fiber’s modulus, such as in Allied Chemicals Ltd.’s bicomponent fiber “Source,” which disperses PET in a PA melt. The presence of PET fibrils increases the fiber’s modulus, reduces moisture regain, and improves deformability, giving the fiber a unique luster and appearance. Tires made from this fiber maintain adhesion to rubber while improving the “flat spot” phenomenon.
Applications
Composite fibers, known for their unique styles and properties, have found extensive applications in daily life, industry, medicine, and optoelectronic communication, becoming an indispensable fiber material.
1. Apparel
Composite fiber fabrics are meeting the demand for high-end clothing with their delicate and intricate styles, soft and full hand feel, good drape, coverage, abrasion resistance, moisture absorption, silk-like feel, and luxurious appearance with unique luster. They can be used to make popular autumn and winter garments such as imitation suede, ordinary peach skin, MOSS peach skin, and artificial down. They are also used in high-quality sportswear like golf jackets, tennis wear, baseball uniforms, and ski suits. Additionally, they are utilized in protective clothing with functions like rainproof and breathable, hydrophobic and oleophobic, antibacterial, and dust-proof properties, as well as “breathable” swimwear, underwear, shirts, and portable, compressible clothing.
2. Industrial Use
Industrial textiles represent a dynamic and promising field with significant future potential. Composite spinning technology can provide high-quality raw materials for various products, including high-grade artificial leather base fabrics, high-grade imitation suede base fabrics, high-quality cleaning cloths, padding materials, ski condensation film materials, ion exchange materials, sun umbrellas, colored car covers, hygiene products (such as diapers and sanitary napkins), and paper products (like high-strength paper and ultra-soft paper).
3. Biomedical Use
The development of bio-functional textiles has become a prominent theme in the 21st-century textile industry. Due to their large specific surface area per unit weight, composite fibers can be processed into various shapes and line densities, offering excellent durability and mechanical strength. They are widely used in bioengineering and medical fields, providing raw materials for artificial arteries, artificial blood cell separators, enzyme supports, inhibitors for shellfish and seaweed, and other biological products.
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