The Basic Principle and Purpose of Scouring of Cotton Fabrics
Scouring is to use chemical and physical method to remove natural impurities on cotton fabrics, which is to achieve the purpose of scouring and purifying cellulose. Scouring is a very important process in the pretreatment.
For mature cotton fiber, the cellulose content is more than 94%. In scouring process, it needs to remove 6% impurities.
If the outer layer is closer to the surface, the content of impurities will be higher. These impurities are mainly on the surface of the primary cell wall and form a hydrophobic mesh layer with pectin as the skeleton through the adhesion of the main chain and the branch chain of pectic substances. The purpose of scouring is to destroy and remove this hydrophobic mesh layer, especially remove the wax.
The Basic Principle and Purpose of Bleaching of Cotton Fabrics
There will produce a kind of pigment that is like acid dye in the growing process of natural cellulose. This kind of pigment cannot be thoroughly removed in the scouring process. It can be removed by bleaching process.
The main purpose of bleaching is to remove natural pigment and increase the whiteness of fabric. At the same time, it needs to remove other impurities remaining on the cotton fabric, such as cotton seed shell, wax and nitrogen substances, etc. to further improve the wetting ability of cotton fabric.
Oxidants and reducing agents can bleach natural fibers. But reducing agents cannot thoroughly destroy the pigment in the natural fibers. The fabric that is reducing bleached has limited whiteness and will yellow after long time. But oxidants can destroy the pigment molecules in natural fibers, which can achieve durable bleaching effect.
The commonly used reducing bleaching agents are sodium sulfite, low sodium sulfite and sodium hydrosulfite, etc. And the commonly used oxidation bleaching agents are hypochlorite, sodium chlorite, hydrogen peroxide and potassium permanganate, etc.
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Post time: Aug-15-2023