Home Textile Fabrics Manufacturers introduces what is the scouring and bleaching of cotton fabrics:

Cotton fiber contains impurities, which are mixed with the slurry, oil, and contaminated dirt during the textile processing process. These impurities will hinder the smooth progress of the dyeing and finishing process. The purpose of scouring and bleaching is to remove impurities on the fabric and make The fabric is white, soft, and has good permeability to meet comfort requirements and provide qualified semi-finished products for dyeing, printing, and finishing.
The main processes of pure cotton fabric scouring and bleaching are original fabric preparation, singeing, desizing, scouring, bleaching, and mercerizing.

Mercerizing is applied to cotton fiber products. It uses a strong alkaline mercerizing agent to change the cotton fiber from a flat, twisted ribbon shape into a round, shiny, strong, and easy to absorb dye state, which can enhance the dimensional stability of the fabric (Fiber becomes more uniform) and durable gloss, breaking strength also increases. The fiber after mercerization has an increase in the absorption of water, iodine, and dyes, and dyes are more dyed during dyeing.