The core principle of textile bleaching is the redox reaction between the oxidizing components of bleaching agents and chromophoric groups on fabrics, breaking down pigments into colorless substances while avoiding dye back-staining and fiber damage.
Currently, these agents are divided into two main groups: Chlorine-based bleaching agents and Oxygen-based bleaching agents.
Chlorine-based agents, including Sodium Dichloroisocyanurate, Sodium Hypochlorite, and Calcium Hypochlorite, are the most widely utilized. These compounds release hypochlorous acid (HClO) when dissolved in water, which further hydrolyzes to generate highly oxidative nascent oxygen. This oxidizes colored substances into colorless substances to achieve bleaching.
SDIC is a white crystalline solid and highly soluble. Its pure form has an available chlorine content of 64.5%, while commercial grades 55-60%. It is widely applied in wool anti-shrinking treatment, textile bleaching, breeding disinfection, civil sanitation, industrial circulating water treatment and disinfection in food and public places.
Key Advantages: High available chlorine content — equivalent to 10 times that of sodium hypochlorite disinfectant — and excellent storage stability: under proper storage conditions, the loss of available chlorine may be less than 6% over 8 years and less than 8% over 10 years.
Chemical Reaction C₃Cl₂N₃O₃Na + 2H₂O → C₃H₂N₃O₃Na + 2HClO
Sodium hypochlorite is a sodium hypohalite with a pungent odor similar to chlorine and low stability. It is mainly used in household cleaning and bleaching, food equipment disinfection, pulp and textile bleaching, and water treatment. However, its industrial application is declining.
Drawbacks: It is prone to releasing toxic gases during use and can easily damage delicate fabric fibers. Furthermore, its available chlorine content (typically 10%–15%) is unstable, requiring immediate use upon preparation. If it has been stored for a period of time, the effective chlorine content should be determined before use.
The commonly referred to "bleaching powder" is a type of impure bleaching agent produced through traditional processes. Its effective chlorine content is relatively low (28% to 35%), and it contains more insoluble substances. It is widely used in textiles, printing and dyeing, and papermaking.
Stability Issue: Available chlorine drops rapidly in open storage, losing more than 50% within about 9 days and likely becoming ineffective in 18–20 days. It must be stored in intact packaging in a dry, ventilated environment.
Oxygen-based bleaches are usually hydrogen peroxide or compounds that generate hydrogen peroxide, such as sodium percarbonate and sodium perborate. These produce hydrogen peroxide in aqueous solution and release active oxygen for bleaching.
Oxygen-based bleaches are unstable to water (except for hydrogen peroxide), heat, light and heavy metals — especially iron. They easily decompose and lose effectiveness when in contact with metals, so contact with metal surfaces should be avoided during use.
Hydrogen peroxide removes color by destroying unsaturated conjugated chromophores and is corrosive.
It requires strong alkaline and high-temperature conditions, easily damaging fibers, so it is not suitable for silk, wool, etc. To reduce fiber damage, two eco-friendly processes are used:
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Cold pad-batch bleaching: Low energy consumption, easy operation, but needs strict control and may cause uneven batches or fiber damage.
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Activated bleaching: Lower temperature and less fiber damage, but high activator cost raises production expense.
SPC, also known as solid hydrogen peroxide, is an oxygen-based bleach. It is used in starch, fabric, pulp bleaching and textile pretreatment. Pure SPC has an active oxygen content of 15.2%, while commercial products are about 13.5%. Its aqueous solution is alkaline, and its bleaching mechanism is similar to hydrogen peroxide. Its decomposition products differ from those of sodium perborate.
Sodium Perborate is a stable cyclic peroxide used as an oxidizer, bleach, detergent and bactericide. It has three hydrates; monohydrate is commonly used in dyeing and washing.
It performs well above 60°C but poorly below 60°C.
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Monohydrate: pure active oxygen 16.03%, commercial 15.10%
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Tetrahydrate: pure active oxygen 10.40%, commercial 10.00%
Note: Its bleaching mechanism is similar to hydrogen peroxide, but actual efficiency is lower. Due to environmental concerns, PBS gradually withdrew from the market.
| Feature |
SDIC (Chlorine-based) |
H2O2 (Oxygen-based) |
NaClO (Chlorine-based) |
| Active Component |
Chlorine
|
Oxygen
|
Chlorine
|
| Stability |
Excellent
|
Moderate
|
Poor
|
| Fiber Damage |
Low
|
High
|
High
|
| Eco-Friendliness |
Moderate
|
High
|
Low
|
For textile and laundry enterprises focused on production efficiency and quality stability, there is no "perfect" bleach—only the "right" choice for specific needs.
While hydrogen peroxide excels in environmental sustainability and whiteness stability, SDIC remains irreplaceable in industrial bleaching due to its storage stability and comprehensive cost-performance ratio. For the foreseeable future, dichloro will continue to be a cornerstone of industrial oxidation and cleaning.
Scientifically understanding these characteristics allows you to:
- Avoid Production Risks: Prevent unexpected fiber degradation or chemical reactions.
- Enhance Efficiency: Reduce processing times by choosing agents with appropriate activation temperatures.
- Enhance Competitiveness: Maintain a competitive edge by delivering consistent, high-quality results to clients.
