Caustic Soda in Textile Processing: Scouring, Mercerising and Dyeing

Walk into any cotton processing house in Surat, Sachin, Ahmedabad or Navsari and you will find caustic soda — sodium hydroxide, NaOH — near the start of the line. It prepares grey cotton for everything that follows. This guide explains where it is used, what grade to buy, and how to handle it safely on the shop floor.

Where caustic soda is used in a textile mill

Scouring: making cotton absorbent

Raw cotton carries natural waxes, oils and pectins that repel water. If they stay on the fabric, dye takes unevenly and the finished shade looks patchy. In scouring, the fabric is treated in a hot alkaline bath: caustic soda turns the fats into soap (saponification) and breaks down the pectins so they wash out. Wetting agents and sequestering agents are added alongside it.

The amount of caustic soda depends on the fibre, fabric weight, machine (jigger, winch, soft-flow or continuous range) and how much impurity the grey fabric carries. Your process chemist sets the recipe; what matters on the purchasing side is that every lot of caustic soda is consistent, so the recipe does not have to be adjusted batch to batch.

Mercerising: lustre, strength and deeper shades

Mercerising treats cotton yarn or fabric in a strong caustic soda solution — typically around 20–25% NaOH — while it is held under tension, and then washes and neutralises it. The fibres swell and become rounder, which gives:

• Lustre: a silky shine, prized in shirting and premium cotton.
• Strength: higher tensile strength and better dimensional stability.
• Dye uptake: deeper shades with less dye.

Because mercerising uses a lot of caustic soda, large ranges often run on lye from a storage tank, while smaller units dissolve flakes. Our guide caustic soda flakes vs pearls vs lye compares the two.

Dyeing and pH control

In vat and sulphur dyeing, caustic soda supplies the alkali that keeps the reduced dye soluble so it can enter the fibre. In peroxide bleaching it holds the bath at the alkaline pH the bleach needs. For reactive dyes on cotton, most mills fix the dye with soda ash, sometimes boosted with a little caustic soda for deeper shades.

Which grade and form to buy

• Grade: industrial caustic soda flakes at 98–99% NaOH cover scouring, mercerising, dyeing and cleaning.
• What to watch on the COA: NaOH content, and low sodium carbonate and iron. Iron can cause yellowing in bleached goods.
• Form: flakes in 25 kg or 50 kg bags for most units; lye for large mercerising ranges with storage tanks.
• Make: mills often standardise on one make — GACL, Grasim, DCM Shriram or Epigral — to keep results consistent.

Dissolving and handling safely

• Always add flakes slowly to water, never water onto flakes. Dissolving releases a lot of heat.
• Use a dedicated dissolving tank with a stirrer, and wear goggles or a face shield, gloves and an apron.
• Keep an eyewash station near the dissolving point; caustic soda is UN1823, Class 8 (corrosive).
• Store bags sealed, dry and off the floor; open bags absorb moisture and lump.
• Neutralise caustic effluent before discharge as your ETP requires.

Supply to Gujarat's textile clusters

From our Ankleshwar warehouse we deliver caustic soda flakes the same or next day to Surat, Sachin and Vadodara, and in 1–2 days to Navsari and Ahmedabad. For makes, packing and what affects the price, see buying caustic soda flakes in Gujarat, or send your monthly requirement through our quote form.

GACL, Grasim, DCM Shriram and Epigral are trademarks of their respective owners. Aethon Chemicals is an independent supplier and stockist of genuine material and is not affiliated with these manufacturers.