Sodium Hypochlorite for Textile Bleaching — NaOCl vs H₂O₂, Process & Safety
Table of contents
TL;DR: Sodium Hypochlorite (NaOCl) is a strong oxidizing bleach used in the textile industry for cotton and linen fibers. This article compares NaOCl vs H₂O₂ on bleaching performance, fiber strength impact, anti-chlor treatment requirements, and the ZDHC/documentation questions export factories are often asked by brands. Loc Thien supplies NaOCl 10% and 12% with batch COA/MSDS, delivered to industrial parks nationwide.
What Is Sodium Hypochlorite and Its Role in Textile Bleaching?
Sodium Hypochlorite (NaOCl, CAS 7681-52-9) is a strong alkaline solution at pH 11–13, containing 10–12% active chlorine. It is a chlorine-based oxidizing bleach used in the textile industry since the late 18th century. The bleaching mechanism relies on the reaction of hypochlorous acid (HOCl) — the active form of NaOCl in aqueous environments — releasing atomic oxygen that breaks the color bonds of chromophores (natural pigments) on cotton, linen, and other cellulosic fibers.
In modern textile technology, there are two main bleach groups: chlorine-based (NaOCl, Ca(OCl)₂) and peroxide-based (H₂O₂). Hydrogen peroxide now accounts for over 70% of global bleaching production due to its better environmental profile. However, NaOCl remains widely used in Asian textile mills, especially for orders that do not require maximum whiteness, thanks to lower cost and faster bleaching at room temperature.
Technical Specifications of NaOCl for Bleaching
| Parameter | Value |
|---|---|
| Chemical formula | NaOCl |
| CAS | 7681-52-9 |
| Active chlorine concentration | 10% ± 0.5% |
| Solution pH | 11–13 |
| Density (20°C) | 1.16–1.20 g/mL |
| Redox potential | 1,400–1,550 mV |
| Optimal bleaching temperature | 30–40°C |
| Optimal bleaching pH | 9.2–11.0 |
| Bleaching time | 30–120 min |
| Usage concentration | 1.5–5.5 g/L (active solution) |
| Documents | Batch COA/MSDS |
Comparing NaOCl and H₂O₂ in Textile Bleaching
The choice between NaOCl and H₂O₂ depends on fiber type, whiteness requirements, operating costs, and factory environmental standards. The table below compares the two bleaches across key technical criteria.
| Criterion | NaOCl (Sodium Hypochlorite) | H₂O₂ (Hydrogen Peroxide) |
|---|---|---|
| Bleaching mechanism | Chlorine-based oxidation, releases HOCl | Peroxide-based oxidation, releases [O] |
| Operating temperature | 30–40°C (room temperature) | 80–100°C (requires heating) |
| Optimal pH | 9.2–11.0 (alkaline) | 10–11 (alkaline + stabilizer) |
| Bleaching time | 30–120 min | 30–60 min (at high temperature) |
| Optimal concentration | 3.5–5.0 g/L | 3.5–4.5 g/L |
| Maximum CIE whiteness index | 75–85 | 85–95 |
| Fiber strength impact | 10–20% reduction if pH < 9 | < 5% reduction with stabilizers |
| AOX (Adsorbable Organic Halides) | > 1 mg/L (requires treatment) | < 0.1 mg/L |
| COD in wastewater | 300–500 mg/L | 200–500 mg/L |
| Chemical cost per kg of fabric | 15–25% lower | Higher |
| Anti-chlor requirement | Mandatory | Not required (catalase) |
| ZDHC MRSL documentation | Depends on each product’s documents | Depends on each product’s documents |
| Suitable for | Cotton, linen, low-cost cellulose fibers | Cotton, wool, silk, high-quality fabrics |
On Whiteness Index
Research on single jersey cotton fabric (GSM 160) showed that at the same concentration of 3.5 g/L, NaOCl achieved a whiteness index of approximately 50 (CIE scale), while H₂O₂ at 4.5 g/L achieved an index above 70. However, increasing NaOCl concentration to 5.5 g/L yielded negligible whiteness improvement while tear strength decreased noticeably due to cellulose hydrolysis. The optimal concentration for NaOCl is 3.5–4.5 g/L, depending on fabric type and bleaching time.
On Environmental Impact
NaOCl generates AOX (Adsorbable Organic Halides) — a group of persistent halogenated compounds that are bioaccumulative and toxic to aquatic life. AOX levels in NaOCl bleaching wastewater typically exceed 1 mg/L, higher than the 0.1 mg/L limit under EU BAT standards. Therefore, textile mills using NaOCl require dedicated AOX treatment systems (activated carbon adsorption or ozone oxidation), increasing operating costs by 15–20%. H₂O₂ decomposes into water and oxygen, producing no AOX, making it more suitable for mills aiming to reduce AOX in wastewater.
Textile Bleaching Process Using NaOCl
The NaOCl bleaching process consists of 5 steps: preparation, bleaching, anti-chlor treatment, neutralization, and rinsing.
Step 1: Scouring
Grey fabric is treated with NaOH and auxiliaries at 80–95°C to remove pectin, wax, and natural impurities from fiber surfaces. Basic scouring formula: NaOH 1–3 g/L, wetting agent 0.5–1 g/L, ML ratio 1:4, temperature 90°C, time 30–45 min.
Step 2: Bleaching
After scouring, the fabric enters the NaOCl bleach bath. Typical parameters:
- NaOCl concentration: 3.5–5.0 g/L (equivalent to 2.5–5°TW — Twaddell degrees)
- NaOH (pH adjustment): 0.2–0.8%
- Soda ash: 2–3%
- Temperature: Below 40°C (optimum 30–35°C)
- Time: 30–120 min (depending on whiteness requirement)
- ML ratio: 1:4
pH control is critical when bleaching with NaOCl:
- pH 2–4: generates toxic chlorine gas, corrodes equipment
- pH 4–6: HOCl dominates, easily damages fibers
- pH 7 (neutral): the “Damage Point” — NaOCl decomposes very rapidly, severely destroying cellulose
- pH 9.2–11: optimal bleaching zone — solution stable, fabric does not yellow after bleaching
- pH 11–13: slower bleaching; pH 11 requires 130 hours, pH 13 requires 40 hours
Step 3: Anti-Chlor Treatment (Mandatory)
This is the most important step when bleaching with NaOCl. After bleaching, residual hypochlorite ions (OCl⁻) in the fibers react with residual proteins to form chloramines — corrosive, unhygienic compounds. When chloramines encounter moisture, they hydrolyze to produce HCl, causing the fibers to gradually yellow and rot over time.
Typical anti-chlor formula:
- Reducing agent: NaHSO₃ 0.2–0.6% (or Na₂S₂O₃ 0.5–1%)
- Temperature: Room temperature (30–35°C)
- Time: 10–20 min
- pH: 6–7
Anti-chlor reaction equation with Na₂S₂O₃ (thiosulfate): 4NaOCl + Na₂S₂O₃ + 2NaOH → 4NaCl + 2Na₂SO₄ + H₂O
Step 4: Neutralization
After anti-chlor treatment, the fabric is treated with formic acid (0.5–2%) or dilute acetic acid to bring fiber pH to 6–7, preparing for the dyeing or finishing stage.
Step 5: Rinsing
Rinse the fabric with clean water 3–4 times, each for 10 minutes, until the rinse water pH reaches 6–8 and no residual chlorine remains (test with KI indicator paper).
Sample NaOCl Bleaching Parameters for 1 Ton of Cotton Fabric
| Parameter | Value |
|---|---|
| Fabric batch weight | 1,000 kg |
| ML ratio | 1:4 |
| Water volume | 4,000 L |
| NaOCl 10% | 12–16 L |
| NaOH 32% | 1–2 L |
| Soda ash | 5–8 kg |
| Wetting agent | 0.5 kg |
| Temperature | 35–40°C |
| Time | 60 min |
| Anti-chlor (NaHSO₃) | 1–2 kg |
| Rinse water | 16,000 L (4 cycles) |
NaOCl Concentration and Dilution for Bleaching
To achieve optimal bleaching without damaging fibers, active chlorine concentration must be calculated precisely:
Formula for diluting NaOCl 10% → working bleach solution:
V (L NaOCl 10%) = (C (g/L) × V_solution (L)) / 100
Where C is the desired active chlorine concentration (g/L).
Example: Preparing 4,000 L of bleach solution at 3.5 g/L from Javen 10%: V = (3.5 × 4,000) / 100 = 140 L NaOCl 10%
Reference concentration table by fabric type:
| Fabric Type | NaOCl (g/L) | Time (min) | Temperature (°C) |
|---|---|---|---|
| 100% Cotton (grey fabric) | 3.5–5.0 | 60–120 | 30–40 |
| 100% Cotton (scoured) | 2.5–3.5 | 30–60 | 30–35 |
| Linen | 4.0–5.5 | 90–120 | 35–40 |
| PE/Cotton blend | 1.5–2.5 | 30–45 | 30–35 |
| Terry towel | 3.0–4.0 | 45–90 | 30–35 |
Safety When Using NaOCl for Bleaching
Personal Protective Equipment (PPE)
NaOCl at 10–12% concentration is a corrosive, strong oxidizer. Operators must wear:
- Chemical splash goggles
- Long-sleeve nitrile or PVC gloves
- Chemical-resistant clothing (HDPE coated)
- Rubber boots
- Vapor respirator when working in confined spaces
- Emergency eyewash station within a 10 m radius
Incompatibilities and Reaction Risks
- DO NOT mix NaOCl with strong acids (HCl, H₂SO₄) — generates toxic chlorine gas (Cl₂), causing acute lung injury
- DO NOT mix NaOCl with ammonia or amine compounds — generates toxic chloramine
- DO NOT use metal tools (304 stainless steel corrodes at >200 ppm Cl₂)
- Use PP, PVC, or FRP equipment rated for alkali
- Store in a cool, ventilated area away from direct sunlight and temperatures >40°C
ZDHC Documentation and Paperwork for NaOCl in Textile Bleaching
ZDHC (Zero Discharge of Hazardous Chemicals) manages input chemicals through the MRSL. The Gateway Levels 1–3 are tied to chemical products and issued by a ZDHC Approved MRSL Certifier; ZDHC does not issue certificates to mills. Brands/ZDHC may ask for MRSL documentation for input chemicals; Javen is a process chemical, so it depends on the documentation of each product. Loc Thien supplies NaOCl Javen 10% and 12% with:
- Batch COA stating active chlorine content (declared ±0.5%)
- MSDS/SDS and UN/GHS labelling
- Batch traceability through the COA, so textile mills can support customer audits
If a brand requires ZDHC documentation, contact Loc Thien to confirm the documents currently available for each product. For output wastewater, mills using NaOCl need AOX and COD treatment systems meeting regulatory standards.
Technical Support & B2B Procurement Hotline
Loc Thien Chemical specializes in direct manufacturing of FeCl₂ / FeCl₃ and direct industrial supply of basic chemicals (NaOH, HCl, H₂SO₄, PAC, NaOCl, H₂O₂, FeSO₄) with direct B2B pricing and dedicated 5–30-ton tanker delivery across Vietnam.
- Hotline / Zalo: +84 979 891 929
- Official Email: [email protected]
- Direct Manufacturer: Ferrous Chloride (FeCl₂ 30%) & Ferric Chloride (FeCl₃ 38–40%)
- Primary Supplier: NaOH 32%/45%/50%/99%, HCl 32%, H₂SO₄ 98%, PAC 30–31%, NaOCl 10–12%, H₂O₂ 35%/50%
- Compliance & Quality: FeCl₂ ZDHC MRSL v3.1 test report (Smart testing, 5 substance groups, TUV Rheinland Vietnam), ISO 9001:2015, Quatest 3, Full COA & GHS SDS
Frequently Asked Questions (FAQ)
Why is anti-chlor treatment required after NaOCl bleaching?
Residual NaOCl in fibers forms chloramines — corrosive compounds that cause yellowing and fabric deterioration over time. Anti-chlor treatment neutralizes residual chlorine, protecting fiber strength and worker safety.
Can vinegar be used to neutralize NaOCl?
Absolutely not. Acetic acid (vinegar) reacts with NaOCl to form hypochlorous acid (HOCl), which corrodes fibers and can generate chlorine gas if the pH drops low enough.
What is the optimal NaOCl bleaching temperature?
30–40°C. Above 40°C, NaOCl decomposes rapidly, reducing bleaching efficiency and increasing fiber damage risk.
Does NaOCl affect spandex/elastane fabric?
NaOCl completely destroys spandex/elastane fibers. Fabrics containing spandex require H₂O₂ or non-chlorine bleaches.
Does NaOCl affect reactive dyes on fabric?
Yes. NaOCl can destroy reactive dyes upon direct contact. Therefore, NaOCl is used only for bleaching greige (undyed) fabric or pre-dyed fabric requiring color stripping for re-dyeing. Reactive-dyed fabrics should not be bleached with NaOCl.
How do ZDHC documents apply to NaOCl in textile bleaching?
Brands/ZDHC may ask for MRSL documentation for input chemicals; Javen is a process chemical, so it depends on the documentation of each product. Loc Thien supplies batch COA and MSDS for Javen NaOCl; if a brand requires ZDHC documentation, contact us to confirm the documents currently available for each product.
Can polyester fabric be bleached with NaOCl?
No. NaOCl has no bleaching effect on synthetic fibers such as polyester, nylon, or acrylic. For these fibers, use H₂O₂ or optical brighteners. NaOCl is only effective on natural cellulosic fibers such as cotton, linen, and rayon.
What are the signs of fabric damage from excessive NaOCl bleaching?
Significant reduction in tensile strength, surface fiber pitting visible under microscope, white color turning yellow (over-bleaching), and fabric easily tearing when pulled. Strength can decrease by 30–50% with excessive dosage or prolonged exposure.
🛒 Need NaOCl Javen for textile bleaching? Buy Javen NaOCl 10% and 12% — batch COA/MSDS, delivered to industrial parks nationwide. Hotline 0979 891 929.
Quality control: QC Specialist Phan Cam Thuy inspects and Vo Thi Nhu Hoa approves each batch of Javen NaOCl. Every batch comes with a COA and MSDS.