To produce colored fabric whether dyed or printed, needs pre-treatment of those fabrics before dyeing and printing. Pre-Treatment of Fabric before dyeing the pre-treatment operations involved for cotton fabric are described systematically below:
Pre-Treatment of Fabric before Dyeing and Printing
Singeing: Pre-Treatment of Fabric before dyeing it is the process of burning out projecting hairy fibers from surface of the grey fabric by passing the fabric through a gas flame. Both sides of the fabric is burnt out by the flame, it helps in subsequent chemical process of the fabric. After dyeing or printing of singed fabric, brightness and luster of the color and fabric becomes better.
Desizing : Pre-Treatment of Fabric before dyeing it is the process of removing starch materials present in the grey fabric. Generally enzyme is used to degrade and remove the starch present in the grey fabric. If those size materials are not removed from the grey fabrics, then the subsequent chemical treatments on the fabric will be irregular, which will cause the defective dyeing and printing.
Scouring : Pre-Treatment of Fabric before dyeing it is the process of removing natural impurities present in the cotton fiber. The natural impurities are pectins, pectose, ash, wax, mineral compounds, and etc materials. If those impurities present in the cotton fibers are not removed, then it will be difficult to dye or print the fabric uniformly. Normally caustic soda and soda ash is used as main reagent for scouring of cotton fabric.
Bleaching: Pre-Treatment of Fabric before dyeing it is the process of removing natural coloring matters present in the cotton fiber. For this purpose, hydrogen peroxide, bleaching powder or other bleaching agents are used. Hydrogen peroxide is the best and most commonly used bleaching agent. If this bleaching treatment is not carried out before dyeing or printing then the color yield and shade matching may be a great problem.
Mercerization: Pre-Treatment of Fabric before dyeing it is a special chemical pre-treatment on cotton fabric to improve the properties and performance of cotton fabric. The cotton fabric is treated under tension in the 20 % caustic soda solution which is called mercerization. Due to mercerization many properties of cotton fabric is improved, some of them are mentioned below:
- Increases fabric strength
- Increases absorbance power.
- Increases fabric luster.
- Increases fabric softness and handle property.
- Reduces dye consumption.
- Reduces chemical consumption in dyeing.
All the above mentioned five pre-treatments are not compulsory before fabric dyeing and printing. Specifically all the five pre-treatments are done for high quality cotton fabric coloration but only desizing, scouring and bleaching are done for common qualities of cotton fabrics.