Caustic soda is one of the most important chemicals in cotton textile processing. It is used to clean raw cotton in scouring and to improve lustre and dye uptake in mercerising. This guide explains both processes and the practical points that affect quality and cost.
Scouring: cleaning the fibre
Raw cotton contains natural waxes, pectins, oils and other impurities that stop water and dyes from penetrating evenly. Scouring removes them by treating the fabric or yarn in a hot alkaline bath.
- Typical bath: a few percent caustic soda with a wetting agent and detergent, near boiling.
- Result: absorbent, clean fibre ready for bleaching and dyeing.
- Watch: too much caustic or too long a treatment weakens the fibre.
Mercerising: lustre and strength
Mercerising treats cotton with concentrated caustic soda, commonly in the range of about 20 to 30% NaOH, usually cold and under tension. The fibres swell and become rounder, which gives:
- a silk-like lustre;
- higher tensile strength;
- better dye uptake, so less dye is needed for the same shade.
After treatment the fabric is washed and neutralised with dilute acid. Many mills recover and concentrate the weak caustic from the wash water to reuse it, which saves a large share of caustic cost.
Quality points for the caustic itself
- Purity: use 99% flakes or a consistent lye so bath strength is predictable.
- Iron: low iron avoids yellowing of white goods.
- Carbonate: high carbonate reduces the effective alkali and can affect results.
- Bath control: check strength by titration or density every shift.
Safety in the dye house
Concentrated caustic causes severe burns. Operators need goggles, gloves and aprons, and eyewash stations near mercerising and scouring machines. Always add caustic to water when making up baths.
For textile groups operating in Oman
If your company also runs facilities in Oman, caustic soda flakes 99% are available with a published daily price and ready stock in Barka at muscatchemical.com/caustic-soda.
