*2.3.4.1. Side-by-side*

Two components are arranged side by side and are divided along their length into two or more distinct regions (Figure 6). The geometrical configuration of side-by-side bi component fibers, particularly asymmetry, makes it possible to achieve an additional three-dimensional crimp during thermal bonding by differential thermal shrinkage of the two components, for example. This latent crimp gives rise to increased bulk stability and a softer fabric handle [40].

**Figure 6.** Cross Sections of Side-by-Side Bicomponent Fibers

#### *2.3.4.2. Sheath core fibers*

In sheath core bicomponent fibers (Figure 7), one of the components (the core) is fully sur‐ rounded by another component (the sheath). The arrangement of the core is either eccentric or concentric depending on the fabric properties required. If high fabric strength is required, the concentric form is selected, whereas if bulk is required, the eccentric type is used. One advantage of sheath core fibers is the ability to produce a surface with the required luster, dyeability, and handle characteristics while having a core that dominates the tensile properties. The core sheath structure also provides a means of minimizing the cost by engineering the relative proportions of the two polymer components. Commercially, the ratio of the polymer components is typically 50:50 or 30:70, but in some cases, a ratio of 10:90 is used [40].

**Figure 7.** Cross Sections of Sheath Core Bicomponent Fibers

The first industrial exploitation fiber involved the use of Co-PET/PET or PE/PP fibers for hygiene applications as well as high-loft batting, wiping cloths, medical wipes, and filters. The difference in the sheath core melting temperature in PE/PP is about 40°C. In Co-PET/PET bicomponents, the sheath melts at 100-110°C while the core melts at 250-265°C [40]. Bicompo‐ nent fibers are generally used in blend ratios of 10-50% depending on the application and process parameters. A useful experimental guide is given in Table 5.


**Table 5.** A practical guide for producing nonwoven fabrics with different handle characteristics from Co-PET/PET bicomponent fibers [8]

## *2.3.4.3. Island in the sea or segmented pie*

segmented pie. Of these, the side-by-side and sheath core arrangements are relevant for

Two components are arranged side by side and are divided along their length into two or more distinct regions (Figure 6). The geometrical configuration of side-by-side bi component fibers, particularly asymmetry, makes it possible to achieve an additional three-dimensional crimp during thermal bonding by differential thermal shrinkage of the two components, for example.

In sheath core bicomponent fibers (Figure 7), one of the components (the core) is fully sur‐ rounded by another component (the sheath). The arrangement of the core is either eccentric or concentric depending on the fabric properties required. If high fabric strength is required, the concentric form is selected, whereas if bulk is required, the eccentric type is used. One advantage of sheath core fibers is the ability to produce a surface with the required luster, dyeability, and handle characteristics while having a core that dominates the tensile properties. The core sheath structure also provides a means of minimizing the cost by engineering the relative proportions of the two polymer components. Commercially, the ratio of the polymer

components is typically 50:50 or 30:70, but in some cases, a ratio of 10:90 is used [40].

The first industrial exploitation fiber involved the use of Co-PET/PET or PE/PP fibers for hygiene applications as well as high-loft batting, wiping cloths, medical wipes, and filters. The

This latent crimp gives rise to increased bulk stability and a softer fabric handle [40].

thermal bonding applications [40].

**Figure 6.** Cross Sections of Side-by-Side Bicomponent Fibers

**Figure 7.** Cross Sections of Sheath Core Bicomponent Fibers

*2.3.4.2. Sheath core fibers*

*2.3.4.1. Side-by-side*

18 Non-woven Fabrics

Island in the sea is one type of bicomponent fiber whereby many fibrils of one polymer are dispersed in the matrix of another polymer. The fibrils are known as islands and the matrix is the sea. The island in the sea fibers have excellent tensile properties, and provide good feel, softness, and bursting and tearing strength for the nonwoven fabrics.

Bicomponent filaments can be used to produce a bonded fabric, with one of the components being thermoplastic to facilitate heat bonding and the other component having properties that will enhance the quality of the final fabric [4]. Bicomponent fibers are also used for spunlaced nonwoven products like medical disposable textiles, filtration products and air-laid nonwoven structures as absorbent cores in wet wipes [14].
