Caustic Soda for Textile Processing: Uses, Grades and Bulk Supply

Caustic Soda for Textile Processing: What It Does and Why Mills Depend on It

Content reviewed: 28 October 2026 · SUHA International Trading L.L.C., Dubai & Ankara

Caustic soda is also called sodium hydroxide, NaOH, lye or caustic. Textile mills buy it as flakes, pearls (prills) or liquid lye, and use it at almost every wet-processing stage for cotton. SUHA International Trading supplies membrane-grade caustic soda for textile mills, dyehouses and chemical distributors, loading at Mersin (Türkiye) and Jebel Ali (UAE).

• FormulaNaOH
• CAS No.1310-73-2
• HS code2815.11 / .12
• Grades98% · 99%
• UN / Class1823 / 1824 · 8
• MOQ1 FCL

Why the Textile Industry Uses Caustic Soda

Cotton is about 90% cellulose, but raw cotton also carries natural waxes, pectins, proteins, seed-coat fragments and, on woven fabric, size from weaving. Water alone cannot remove them, and dyes cannot penetrate evenly while they remain. Caustic soda solves this because it is:

• The strongest common alkali – a 1% NaOH solution has a pH of about 13.4, high enough to saponify waxes and break down pectins.
• Able to swell cellulose – at mercerising strength it changes the cotton fibre itself, something no weaker alkali can do.
• Fully soluble and easy to dose – 111 g dissolves in 100 mL of water at 20 °C, and liquid lye is pumped straight into dosing systems.
• Cheap per unit of alkalinity – it is made in very large volumes by the chlor-alkali industry and traded worldwide.

Uses of Caustic Soda in the Textile Industry, Stage by Stage

In a cotton or cotton-blend mill, caustic soda for textile wet processing appears at five of the eight main stages:

1. SingeingBurns off surface fibres. No caustic.
2. DesizingRemoves starch or PVA size; caustic is used in oxidative or combined desize-scour.
3. ScouringHot caustic removes waxes, pectins and oils so fabric becomes absorbent.
4. BleachingCaustic sets the pH that activates hydrogen peroxide.
5. MercerisingConcentrated caustic swells cotton for lustre, strength and dye uptake.
6. DyeingFixes reactive dyes; dissolves vat, indigo and sulphur dyes.
7. PrintingAlkali in reactive print pastes; mainly soda ash or bicarbonate.
8. FinishingNeutralising, softening, resin finishing. Caustic must be fully washed out first.

Textile scouring with caustic soda

Scouring – also called kier boiling or alkaline boiling – treats greige cotton with dilute caustic soda near the boil, together with a wetting agent and detergent. NaOH saponifies the natural waxes into soluble soaps, dissolves pectins and hemicelluloses and loosens seed-coat fragments. The result is fabric that absorbs water instantly and dyes evenly. Polyester-cotton blends are scoured with milder alkali and shorter times, because hot caustic attacks polyester.

Exact concentration, temperature and time depend on the machine (kier, J-box, pad-steam, jet), the fabric and the auxiliaries, so mills set their own recipes with their dyehouse chemist or auxiliary supplier.

Textile Mercerisation: The Largest Single Use of Caustic Soda

Mercerisation (also spelled mercerization) treats cotton yarn or fabric with concentrated caustic soda – typically 20–26% NaOH – while it is held under tension, then washes the alkali out. John Mercer discovered the treatment in 1844; Horace Lowe found in 1889 that tension produces the silk-like lustre that mercerised cotton is known for.

The caustic swells each cotton fibre so that its flat, twisted shape becomes round. On washing, the cellulose re-forms in a different crystal structure (cellulose II), which gives:

• A higher, silk-like lustre
• Higher tensile strength
• Better dye uptake, so less dye is needed for the same depth of shade
• Better dimensional stability and lower shrinkage

Mercerising is where a cotton mill's caustic volume is concentrated. A 2025 review in the Euro-Mediterranean Journal for Environmental Integration puts mercerising consumption at 170–350 g of caustic soda per kg of fabric (Musaoglu & Unlu, 2025). Most mills therefore recover the weak lye from the washers by evaporation and reuse it, which cuts both caustic purchases and the alkali load in the effluent.

Caustic soda concentration: %, Baumé, Twaddell and g/L

Mercerising and dosing lines often measure lye strength in degrees Baumé (°Bé) or Twaddell (°Tw). This conversion table is calculated from standard NaOH solution densities at 20 °C:

°Bé = 145 − 145 ÷ SG · °Tw = 200 × (SG − 1) · g/L = % × SG × 10.

Caustic Soda in Textile Bleaching with Hydrogen Peroxide

Hydrogen peroxide is the standard bleach for cotton, and caustic soda is what makes it work. Peroxide is stable in neutral water; adding NaOH raises the pH to about 10.5–11, where peroxide forms the perhydroxyl ion (HOO⁻) that oxidises the natural colour in cotton.

How caustic soda and hydrogen peroxide react: H₂O₂ + NaOH → Na⁺ + HOO⁻ + H₂O. Too little caustic and bleaching is slow; too much, or traces of iron or copper, and peroxide decomposes fast, wasting chemical and attacking the cellulose (pinholes and strength loss). Mills therefore add a stabiliser – sodium silicate or an organic stabiliser – and control iron in both the water and the caustic soda.

Scouring and bleaching are often combined in one bath on modern continuous ranges, which reduces water and energy use.

Caustic Soda in Textile Dyeing

Reactive dyeing of cotton

Reactive dyes bond chemically to cellulose only under alkaline conditions. Soda ash is the usual fixing alkali; caustic soda, alone or mixed with soda ash, is used where a higher pH is needed – for low-reactivity dyes, deep shades, short fixing times and cold pad-batch dyeing, often with sodium silicate. Alkali is usually added in portions so the dye fixes evenly instead of hydrolysing in the bath.

Vat and indigo dyeing: caustic soda and hydrosulphite

Vat dyes – including indigo for denim – are insoluble in water. Sodium hydrosulphite (sodium dithionite) reduces them to a soluble "leuco" form, but only in a strongly alkaline bath, and caustic soda supplies that alkalinity. The dissolved leuco dye penetrates the cotton and is then oxidised back to its insoluble coloured form inside the fibre. Without enough caustic, the hydrosulphite decomposes and the dye precipitates. Sulphur dyes follow a similar alkaline reduce-and-oxidise route.

Polyester weight reduction

Hot caustic soda slowly hydrolyses polyester from the surface. Mills use this deliberately – "alkali weight reduction" or "denier reduction" – to give polyester a softer, silk-like handle. The same reaction is why caustic must be controlled carefully on polyester-cotton blends.

Soda Ash vs Caustic Soda for Textile Processing

Soda ash (sodium carbonate, Na₂CO₃) and caustic soda (sodium hydroxide, NaOH) are both textile alkalis, but they are not interchangeable. Caustic soda is much stronger; soda ash is a milder, buffered alkali.

Most cotton mills buy both. SUHA supplies caustic soda and soda ash, so both can be combined in one supply plan.

Which Fibres Can Be Treated with Caustic Soda?

Caustic soda is a cellulose chemical. On protein fibres it is destructive, and several textile guides get this wrong.

Caustic Soda for Textile Mills: Grades, Forms and Specifications

Textile-grade caustic soda is not a separate chemical – it is high-purity NaOH whose impurities are low enough not to cause faults in bleaching and dyeing. Membrane-cell caustic soda, which SUHA supplies, is the grade most mills prefer.

What to check on the certificate of analysis

Guaranteed limits for each form are in our technical data sheets: flakes TDS, pearls TDS and liquid caustic soda TDS. Every lot ships with a certificate of analysis.

How Much Caustic Soda Does a Textile Mill Need?

For procurement planning, mercerising is the line that decides volume. This estimator uses the 170–350 g of caustic soda per kg of fabric reported for mercerising (Musaoglu & Unlu, 2025), before any lye recovery.

Estimate of gross caustic demand as 100% NaOH, before lye recovery, which can return much of it to the line. One 20ft container of flakes carries about 25 MT (1,000 × 25 kg bags). Confirm your own consumption with your process team.

Buying Caustic Soda for Textile Mills in Bulk

SUHA International Trading is a caustic soda supplier and exporter for the textile industry – mills, dyehouses, denim and knit processors, and the distributors that serve them. We are a trading company, not a chlor-alkali producer: we source membrane-grade NaOH from approved producers and handle documents and logistics from Dubai and Ankara.

Supplying textile hubs in Türkiye, the Gulf and worldwide

From Ankara we deliver to textile mills in all 81 Turkish provinces, including the major cotton-processing centres, and by road to neighbouring markets. From Dubai we serve all seven emirates and the Gulf. By sea from Mersin and Jebel Ali we export to textile-producing countries in South Asia, Southeast Asia, Africa, Europe and the Americas.

What to include in your RFQ

• Form and grade: flakes 98% or 99%, pearls 99%, or liquid
• Monthly volume and number of containers
• Packing: palletised bags, bags in jumbo bags, or ISO tank
• Destination port or city and Incoterm
• Any iron or heavy-metal limit your bleaching process needs
• Start month and contract length

Safe Handling of Caustic Soda in Textile Plants

Caustic soda is classified as Skin Corrosion 1A (H314) – it causes severe skin burns and eye damage – and Metal Corrosion 1 (H290). Textile workers handle it daily, so the basics matter:

• PPE: chemical goggles and face shield, alkali-resistant gloves, apron and boots. Eyewash and safety shower within reach of every dissolving and dosing point.
• Dissolving: always add caustic to water slowly while stirring – never water to caustic. Dissolving releases a lot of heat and can boil and spatter.
• Storage: keep bags dry, closed and off the floor, away from acids, and away from aluminium, zinc and tin, which caustic attacks with release of hydrogen.
• Spills: contain the spill, sweep up solid caustic dry into labelled containers, then dilute the residue with plenty of water. Neutralise only dilute residues, slowly – adding acid to concentrated caustic generates heat.
• First aid: rinse skin or eyes with running water for at least 15 minutes and get medical help.
• Effluent: neutralise alkaline wastewater to the pH your discharge permit sets before release.

Full guidance is in our caustic soda MSDS (PDF).

Caustic Soda Demand in the Textile Chemicals Market

Grand View Research values the global textile chemicals market at about USD 28.6 billion in 2025, rising to about USD 40.4 billion by 2033 (4.4% a year), with Asia Pacific holding about 58% of revenue. Pretreatment – scouring, bleaching and mercerising, where most caustic soda is used – is one of the main segments.

Wet processing is resource-heavy: the 2025 review by Musaoglu and Unlu reports around 55 L of water and 8–20 kWh of energy per kg of textile. That is why mills are combining scour-bleach steps, using enzymatic scouring for some goods and recovering mercerising lye – changes that reduce, but do not remove, the need for caustic soda.

Sources: Grand View Research, Textile Chemicals Market report; N. Musaoglu & D. Unlu, "Caustic in textile processes and environmentally responsible solutions: a mini-review", Euro-Mediterranean Journal for Environmental Integration 10 (2025), doi:10.1007/s41207-025-00801-6.