Bicomponent Nonwoven Fabric: Analysis of Fiber Structure Advantages and Disadvantages, and Nonwoven Production Line Requirements

Introduction

Bicomponent nonwoven fabric is a new type of high-performance material, often abbreviated as “Bico,” and is widely used in fields such as medical, hygiene, filtration, industrial wipes, and construction. With the development of nonwoven production line technology, bicomponent fibers have gradually become one of the core technologies for producing high-quality nonwoven fabrics. The common structural forms of bicomponent nonwoven fabrics are mainly sheath-core (S/C) and side-by-side (S/S), each with different characteristics, suitable for various applications.

1. Advantages, Disadvantages, and Applications of Common Bicomponent Structures

The machine is designed for continuous, efficient operation, delivering products that meet the most demanding industry standards. Its wide 3.2-meter production capacity makes it suitable for high-volume manufacturing environments, and the triple-layer SSS technology ensures high-quality spunbond nonwovens with excellent strength and uniformity.

1.1 Sheath-Core (S/C) Bicomponent Nonwoven Fabric

The sheath-core structure is one of the most common structures in bicomponent fibers. In this structure, the outer “sheath” of the fiber is usually made of one polymer, while the inner “core” consists of another polymer. This design allows the fiber to combine the advantages of different materials, thereby achieving superior performance.

Applicable Materials:
The material selection for sheath-core nonwoven fibers is very broad, and common combinations include:

• Sheath materials: PP, PE, CoPP, CoPE, etc.
• Core materials: PET, PP, etc.
  By selecting different materials, sheath-core fibers can achieve various properties such as strength, softness, and biodegradability. For example, a combination of PP as the sheath and PET as the core often provides better strength and heat resistance, while PE as the sheath and PP as the core enhances softness.

Advantages:

1. High strength and durability: The core layer typically uses materials with higher strength, such as PET or PP, making sheath-core nonwoven fabrics outstanding in mechanical strength and durability, suitable for applications requiring high strength.
2. Versatility: By selecting different sheath materials, sheath-core fibers can combine strength and softness, making them ideal for hygiene materials and personal care products that require a soft touch.

Disadvantages:

1. High material cost: To achieve the multifunctionality of bicomponent fibers, two different types of polymers are typically required, which can increase production costs, especially when using more expensive materials.
2. High technical requirements: It is necessary to precisely control the ratio of the sheath and core, and ensure uniform distribution during spinning, which places high demands on the equipment and process.

Application Fields:
Due to the combination of strength and softness, sheath-core bicomponent nonwoven fabrics are widely used in the following fields:

• Medical protection: Such as surgical gowns and medical masks that require products with high strength and protection.
• Hygiene materials: Such as baby diapers and feminine care products that require soft and comfortable products.
• Industrial applications: Such as filtration materials and geotextiles that require durable and high-strength products.

1.2 Side-by-Side (S/S) Bicomponent Nonwoven Fabric

The side-by-side structure is another common bicomponent nonwoven fiber design. Unlike the sheath-core type, in side-by-side fibers, two different polymer materials are distributed side by side in the fiber cross-section. This structure allows both materials to play their respective roles in the fiber, making it suitable for elastic materials and multifunctional products.

Applicable Materials:
Common materials used in side-by-side fibers include:

• Side-by-side materials: PP, CoPP, PE, PET, CoPET, PLA, etc.
  Common combinations such as PP and PE, PET and PP, PET and CoPET, can achieve different fiber properties to meet diverse nonwoven production line needs. For example, the side-by-side structure of PP and PE offers excellent softness and elasticity, while the combination of PET and PP enhances fiber strength and heat resistance.

Advantages:

1. Good elasticity and crimp: Side-by-side fibers naturally possess crimp characteristics, with excellent bulkiness and elasticity, making them suitable for hygiene nonwoven fabric materials.
2. Strong functionality: Since two materials are distributed side by side, the ratio of the two can be adjusted as needed to achieve more diverse properties for different application requirements.
3. Improved softness: The design of side-by-side fibers offers excellent softness, making them suitable for products requiring a high level of comfort.

Disadvantages:

1. Processing difficulty: Due to the different melting points of the two materials, precise temperature control is required during spinning and thermal bonding to prevent material deformation or performance degradation.
2. Lower strength: Compared to the sheath-core structure, side-by-side fibers have slightly lower mechanical strength, making them less suitable for applications requiring high strength.

Application Fields:
Due to its excellent bulkiness, elasticity, and multifunctionality, side-by-side bicomponent nonwoven fabric is mainly used in the following fields:

Clothing and decorative materials: Suitable for garment linings and soft decorative materials.

Hygiene materials: Such as baby diapers and sanitary pads that require soft and bulky products.

Medical materials: When used in medical applications, they exhibit excellent softness.

2. How Does the Selection of Polymer Pairs Affect the Choice of Nonwoven Production Line?

Currently, popular spunbond nonwoven production lines (such as SSS lines, SMS lines) are primarily designed for single raw materials (PP, PET) and are not suitable for producing bicomponent nonwoven fabric materials. In the production of bicomponent nonwoven fabrics, the most significant impact on the selection of nonwoven production line equipment is the drawing method of the spinning system, due to the different polymer requirements for drawing speed. Additionally, polymers have varying moisture content requirements during the spinning process, meaning the drying pre-treatment configuration of raw materials differs. These are the two main factors that influence the selection of nonwoven production lines.

3. What Principles Should Be Followed When Choosing Polymer Pairs for Bicomponent Fibers?

• When selecting the two polymer materials for bicomponent fibers, factors such as melt temperature, melt viscosity, melt pressure, surface tension, tensile strength, crystallization rate, and fluidity should be considered.
• Under spinning process conditions, the melt viscosity of the two fiber components should be as similar as possible to avoid the phenomenon of “bending” when extruded from the spinneret due to large viscosity differences. The two polymer materials should also have good compatibility, meaning they should adhere well together after spinning without clear boundaries or delamination. Additionally, the two components should have significant thermal shrinkage differences to form a distinct spiral three-dimensional crimped structure.
• Some fibers exhibit significant bending as soon as they leave the spinneret, which can easily cause them to stick to the spinneret surface, affecting spinning stability. This can also result in deviations from the desired fiber shape for side-by-side fibers, making this pairing less ideal.
• For sheath-core fiber spinning, the spinnability requirements are slightly lower than for side-by-side fibers, but the melting points of the two polymer components should not differ too much. The low melting point sheath can be used for thermal bonding, with pairings such as PE/PP, PE/PET, CoPET/PET, etc.
• The melt of the two components must have sufficient tensile strength to withstand high drawing speeds and forces, avoiding fiber breakage of one component during the drawing process.
• The two polymer components must have good thermal stability to prevent changes in morphology (e.g., crimp) and properties during temperature fluctuations, post-processing, or storage.
• Some fiber pairings result in a better tactile feel for the product, while others may feel less pleasant. Production cost, including recyclability, should also be considered—if the cost is too high, it reduces practicality.
• For processes such as splittable fibers, PET/PA6 pairs are more easily split, whereas PET/PP pairs are more difficult to split. In PET/PE sheath-core fibers, the PE sheath tends to peel off, which is why these pairings are less commonly used.
• In the case of PP/CoPP pairings, the two components are essentially the same polymer, with little difference in melting points, making it unsuitable for hot air bonding and only feasible for thermal calendaring. However, the recyclability of such products is better. If the polymer properties of the two components differ greatly, the recyclability of the product will be poorer.
• For eccentric fibers, the spinnability requirements are slightly higher than for concentric fibers. The melt viscosities of the two components under spinning conditions should still be similar to avoid the “bending” phenomenon, which can affect spinning stability when extruded from the spinneret.
• Eccentric composite fibers made from two polymers with different chemical structures and properties can produce three-dimensional spiral crimp, giving the nonwoven fabric a more bulky hand feel.
• The sheath polymer material of sheath-core fibers greatly affects the bonding method of the nonwoven web. For example, using low melting point PE (LDPE or HDPE) as the sheath and pairing it with PP provides good low-temperature processing performance and can be bonded using hot air.
• When CoPP is used as the sheath and paired with PP, thermal calendaring is required, resulting in nonwoven fabric products with higher strength. When HDPE is used as the sheath and paired with PET, the large melting point difference allows for hot air bonding, giving the nonwoven fabric better heat resistance and bulkiness.
• When PP is used as the sheath and paired with PET, ultrasonic bonding can be used, resulting in nonwoven fabric products with bulkiness.

4. Can the Ratio of Bicomponent Materials Be Freely Adjusted? What Are the Limitations?

In theory, the ratio of the two components can be adjusted freely, but due to the limitations of the nonwoven production line, if the component with a larger original proportion is reduced, the key issue becomes whether the nonwoven production line can run at a significantly reduced speed while maintaining spinning stability. The smaller component, whose hardware performance is generally lower, has limited space for increasing its proportion, and often, this can only be achieved by reducing the proportion of the other component.

For example:
In a sheath-core spinning system, the total extrusion capacity is 180 kg/m/h, where the sheath (S) is designed to extrude at 60 kg/m/h with a maximum proportion of 33%, and the core (C) extrudes at 120 kg/m/h with a maximum proportion of 67%. If the sheath’s proportion is increased to 50%, since the extrusion rate of the sheath system has already reached its maximum, it cannot be further increased. Therefore, the only way to increase the sheath’s proportion is by reducing the core’s extrusion rate. To achieve a 50% ratio, the core’s extrusion rate must match the sheath’s at 60 kg/m/h, making the total extrusion rate 120 kg/m/h (=60+60), which is only 67% of the rated extrusion capacity, reducing production by 33%. In this state, the flow rate per hole in the spinneret decreases, lowering the melt pressure, which affects spinning stability. Although the fiber diameter becomes smaller, the production volume and economic efficiency decrease significantly, making it economically unfavorable. For S/C fibers, if the sheath is too thin, it requires high uniformity in melt distribution, otherwise it will be difficult to evenly coat the core material. Generally, maintaining the sheath’s proportion at around 10% is considered optimal and manageable in terms of process performance.

In laboratory conditions (small-scale experiments), some component ratios are not difficult to achieve, but in large-scale industrial production, it may not be advisable as it can lead to a decrease in the rate of qualified products and cause significant hidden losses, reducing its practical value.

The cross-sectional structure of bicomponent fibers has two aspects: one is the “weight” ratio of the polymer materials, which can be adjusted by changing the spinning pump’s speed, thus altering the melt extrusion rate. The other is the ratio of each component’s “area” in the fiber cross-section, which requires changes to the spinning assembly’s structure and cannot be modified on-site. Since the densities of the two polymers differ, the weight ratio of the polymer material differs from the cross-sectional area ratio. When adjusting the ratio of the two components, spinning stability must be considered. If the ratio of one component is too small, the spinning pump speed will be too low, affecting spinning stability. Uniformity should also be considered; for example, if the sheath proportion of S/C fibers is less than 5%, maintaining uniformity becomes difficult, making it impossible to coat the core evenly.

The ratio of the two polymer components has a significant impact on fiber performance. For example, in S/S fibers, the crimp degree is greatest at a 50:50 ratio. The higher the proportion of the more expensive component, the higher the production cost. When adjusting the ratio of the two components, if it exceeds the equipment’s performance limits, the extrusion volume of the spinning system decreases, production output decreases, energy consumption increases, and economic efficiency is reduced.

5. Can Bicomponent Nonwoven Fabrics Be Recycled On-line?

Generally, defective bicomponent nonwoven fabrics are not suitable for on-line recycling to avoid affecting the accuracy of the component ratio. If on-line recycling is necessary, only the component with the higher temperature should be used to prevent the high-melting-point polymer from failing to melt, which could clog the melt filter and spinneret holes, possibly leading to equipment damage.

The greater the difference in the properties of the two polymer components, the harder it is to recycle. If the properties of the two polymer components are similar, as with PP/CoPP fibers, they are more suitable for recycling. However, for bicomponent products like PP/PET containing polyester polymers, recycling on-site without proper drying treatment, similar to standard PP defects, would introduce too much moisture and affect stable spinning, making them unsuitable for recycling.

Since defective products have already been melted once, degradation and improved fluidity are inevitable. When such melt re-enters the spinning system, it changes some polymer characteristics, complicating the components. However, when the recycling proportion is small, the impact may not be significant.

Conclusion

Bicomponent nonwoven fabrics, especially sheath-core (S/C) and side-by-side (S/S) structures, have become key materials in nonwoven production due to their multifunctionality and wide range of applications. Sheath-core structures excel in strength, durability, and softness, making them ideal for high-performance applications like medical protection and industrial filtration. Side-by-side structures, known for their bulkiness, elasticity, and comfort, are widely used in hygiene products and elastic materials.

By selecting suitable raw materials, structure ratios, and nonwoven production equipment, high-quality bicomponent nonwoven fabric products can be manufactured to meet various market demands. As a producer of nonwoven production lines, AZX has extensive experience in bicomponent nonwoven fabric production technology. If you want to learn more in this field and achieve new breakthroughs in nonwoven materials, feel free to contact us.