ROLE OF SALT IN TEXTILE CHEMICAL PROCESSING TREATMENT

Introduction

An exhausting agent used during the dyeing process is normally a salt. The fabric will be immersed in water during dyeing which will generate negative charges on the fabric surface and this is called as Zeta potential. Anionic dyes, which produce negative charges, are mostly used in the dyeing process (eg: Reactive dyes, Direct dyes, Acid dyes) it must repel. It requires attraction to bind the dye molecules to the fabric surface.

An exhausting agent used commonly is NaCl. It attracts Na+ and cl- ions (common ion effect) when dissolved in water. Depositing Na+ ions on fabric creates a positive charge. So, the fabric will draw it as and when the dye is applied.

Need for salt in textile chemical processing

The purpose of the information given here is to help in understanding the role of using salt during Textile Wet Processing especially in dyeing. This article represents an outline of information, collected from some sources and experiences.

Why do use salt in textile chemical processing?

Is a fascinating and fundamental question to be asked in the field of textile chemical processing. Particularly in the dyeing sector. To intermingle with each other, it should have homogeneous characteristics. But it is not naturally available between the textile substrate and the dye molecule. In such cases, some medium is needed to facilitate the action while dyeing the fabric. Salt plays a crucial medium because it has an extremely high water-attraction nature.

In the textile industry, industrial salt is used in the processing of fabrics and materials, such as for dyeing cotton and other cellulose materials. Salt causes the dye to completely penetrate in the fabric when used in a dye bath thereby making the dyeing process uniform and easier.

Types of salt:

Two types of industrial salt called Vacuum and rock salt are available for textile dyeing. Both types of salts are having a very high content of sodium chloride and are offered in various grain sizes. If the salt used is pure, superior will be the dye results. Usually, vacuum salt is preferred in the textile industry due to its high degree of purity. Rock salt can also be used for dyeing because of its high sodium chloride content.

Usually,  in three ways salt is acted during the dyeing process, first, the dye molecule will get transported into fibre molecule. Secondly, dispersing the dye molecules fully into the fibres. Thirdly, it is used as an electrolyte for the dyes to get fixed to the cellulose fibres.

Glauber’s salt / Common salt:

Salts play a crucial role in reactive dyeing by increasing the dyestuff’s attraction towards the fibre and accelerate the association with the dyes. For this purpose, either Glauber’s salt or common salt is used.

The Glauber’s salt can always be preferred over the common salt because the presence of chlorine ion in the common salt may cause dyeing equipment to become corrosive.

Glauber’s salt is the decahydrate form of sodium sulfate. The chemical formula of Glauber’s salt can be written as Na₂SO₄.

Common Salt is a chemical compound belonging to the larger class of salts composed primarily a mineral of sodium chloride (NaCl).

Functions of salt in reactive dyeing:

1. The salt added during the reactive dyeing process increases the dye’s attraction to the Cellulosic material.
2. The reactive dyestuff exhaustion is high during dyeing because of adding salt.
3. Reactive dyes have a lower affinity towards cellulosic material. So, more inorganic salt to be used to accelerate the absorption while using reactive dyes.

Generally, either Glauber’s salt or the common salt (sodium chloride) are used in dyeing. Because of its efficiency and less cost. These two are essentially the same in terms of their place as an inorganic salt. Because of the presence of sodium cation in both the salts.