## Swelling of Textile Fibers

Swelling of Textile Fibers

Department of Textile Engineering
Daffodil International University

Swelling:

When the fibers absorb water, they change dimensionally (length, diameter, area). Swelling occurs in transverse direction (width wise) and axial direction (length wise). It can be expressed in terms of increase in diameter, length, area and volumes. That means the dimensionally changes due to absorbing water or moisture by any fiber is termed as swelling property.
Significance of Swelling:
• The predominant width-wise (transverse) swelling results in a shrinkage of twisted or interlaced structure.
• The closely woven fabrics will be completely blocked when the fabrics are swollen, and they may be impermeable to water. Thus this property of fiber is used to make water proof fabric.
• It is also an important factor in crepeing due to increased twist angle in swollen yarn, and in drying and dyeing.
Types of Swelling:
1. Transverse dial swelling
2. Transverse area swelling
3. Axial swelling
4. Volume swelling
1. Transverse dial swelling: Fractional increase in diameter of a fiber after swelling is called transverse dia swelling.

Mathematically,
Transverse dia swelling, SD = ∆D / D
Where, D = original diameter of fiber, ∆D =increased diameter of swollen fiber.

2. Transverse area swelling : Fractional increase in area of a fiber after swelling is called transverse area swelling.

Mathematically,
Transverse area swelling, SA = ∆A / A
Where, A = original area of fiber, ∆A =increased area of swollen fiber.

3. Axial swelling: Fractional increase in length of a fiber after swelling is called axial swelling.

Mathematically, Axial swelling, SL = ∆L / L
Where, A = original length of fiber, ∆L = increased length of swollen fiber.

4. Volume swelling: Fractional increase in volume of a fiber after swelling is called volume swelling.

Mathematically,
Volume swelling, SV = ∆V / V
Where, V = original Volume of fiber, ∆V = increased volume of swollen fiber.

Importance of Swelling:
• Improve the absorption capability of dyes and chemicals.
• It has technical consequences in the dimensional stability of the fabric, the predominant transverse swelling measurement.
• Due to swelling the pores of interlaced structure will be blocked, this idea is used to produced shower proof fabric.
• Improve fastness of dyed materials.
• Elastic properties changed.
• Static Electricity is reduced.
Rates of Swelling Depends on
• Size and form of the sample, such as - fiber, yarn, fabric etc.
• Composition of the material, such as - cotton, polyester, acrylic, nylon etc.
• External condition, i.e. Temperature.
• Chemical content, i.e. oil, wax and other impurities.
What is the reason?
• We know, a fibre is consisted of polymer chains. This chains are arranged differently in different regions. The region having parallel arrangement of chains are called Crystalline region and disoriented region is called amorphous region.
• This polymer chains have empty spaces among them, known as the ‘molecular space’. When a fibre is immersed into water, water molecules enter into these spaces and pushes the fiber chains. As a result, Swelling occures.
More orientation means less Swelling, and vice-Versa!
• In a highly oriented fiber, the moleculear chains are lying parallel to the fiber axis. Which results in low molecular space, so swelling will be lower
• For the same reason, less oriented fibre has high swelling, because they have high molecular space for water molecules to enter!
• That’s why Viscose swelling is greater than Nylon swelling, cause Nylon is much more oriented than Viscose.
Typical values of Swelling of some well known fibres:
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### Editor-in-Chief:

Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.