When a fiber comes into contact with water or moisture it can dimensionally change because the fiber can absorb the moisture. Dimensional change due to the absorption of water or moisture is known as fiber swelling. Swelling occurs widthwise (i.e. transversely) or lengthwise (i.e. axially). The amount of change or swelling can be expressed in terms of the increase in diameter, area, length or volume. The amount dimensional change due to swelling can actually be calculated according to the swelling property of a fiber. The outcome of these expressions is usually expressed as a percentage.

 

There are four different types of fiber swelling that are based on changes in diameter, area, length and volume. These types of swelling are:

1. Transverse diameter swelling
2. Transverse area swelling
3. Axial swelling
4. Volume swelling

 

 

Transverse diameter swelling refers to the fractional increase in the diameter of a fiber after swelling. The formula for calculating transverse diameter swelling is:

 

 

Where,

 

 

Transverse area swelling refers to the increased fiber area after swelling. The formula for calculating area swelling is:

Where,

 

 

Axial swelling refers to the increase in fiber length after swelling. The formula for calculating axial swelling is:

Where,

 

 

Volume swelling refers to the volume of the fiber after swelling. The formula for calculating volume swelling is:

Where,

 

 

 

Fibers consist of polymer chains. Polymers are large molecules made of long chains or networks consisting of smaller molecules called monomers. These chains of molecules have a so-called property of “molecular space”.  Molecular space refers to empty spaces in the polymer chains. When a fiber comes into contact with water (part of) the water molecules will occupy these empty spaces. This occupation of the empty space cause an outward push, which is known as swelling.

 

Fibers consist of polymer chains which have empty spaces. When moisture enters these spaces, the occupation of these spaces will cause an outward push which is known as swelling. Fiber swelling is a type dimensional change that is due to the absorption of water or moisture. There are four basic types of fiber swelling:

Transverse diameter swelling, refers to an increase in diameter after swelling.

Transverse area swelling, refers to an increase in area after swelling.

Axial swelling, refers to an increase in fiber length after swelling.

Volume swelling, refers to an increase in volume after swelling.