Sulphur Black Used For Dyeing Cotton Yarn,jeans,denim

Sulphur Black (C.I. Sulphur Black 1, CAS 1326-82-5) is the most produced and widely used dye in the sulphur dye family, accounting for 75%–85% of global sulphur dye output . Known as the "King of Black Dyes," it is prized for its deep black shade, low cost, and excellent lightfastness on cellulose fibers like cotton, linen, and viscose .

Basic Properties

It appears as black flakes or powder, insoluble in water but soluble in sodium sulfide solution, forming a dark green leuco compound . Common types include BN (blueish), BRN (blueish-red), and RN (reddish) shades, with double-strength grades like BR 200% available .

Product Types

Traditional powder forms require dissolving with sodium sulfide before use . Modern eco-friendly liquid Sulphur Black is pre-reduced, allowing direct dilution with water-eliminating sodium sulfide, reducing wastewater, and improving rubbing fastness by 0.5 grade . Solubilized versions (C.I. Solubilized Sulphur Black 1) are water-soluble (≥160g/L at 25°C) and used for leather and paper dyeing without anti-tendering treatment .

Key Concern: Fiber Tendering

The dye contains unstable polysulfide bonds that can oxidize in humid conditions, forming sulfuric acid and weakening cellulose fibers . Prevention includes thorough washing, anti-tendering aftertreatment (using urea or sodium acetate), and using tender-resistant grades treated with formaldehyde and monochloroacetic acid .

Fastness and Application

At 6% depth, it offers lightfastness grade 6, wash fastness grade 3–4, but limited wet rubbing fastness (grade 1–2) . It is essential for dyeing denim, workwear, and heavy cotton fabrics .

Trends

Development focuses on liquid and eco-friendly forms that are safer, more stable, and more sustainable-already standard in Western industrial countries .

Regarding the stability and storage performance of Sulfur Black, covering both powder and liquid forms.

Sulfur Black Stability and Storage Performance

Sulfur Black is available in both powder and liquid forms, each with distinct stability characteristics.

Powder Form: The powdered form is hygroscopic, meaning it readily absorbs moisture from the air. In humid environments (above 60% relative humidity), the powder can clump or form hard lumps, which negatively impacts dissolution and dyeing uniformity. Therefore, it must be stored in a sealed, dry, and cool place, ideally below 35°C and away from direct sunlight, as UV radiation can degrade the dye. Under proper conditions (e.g., sealed bags, low humidity), the shelf life can reach 12 to 24 months. However, prolonged storage may still cause caking at the bottom of the bag due to gravity and trace moisture. It is advisable to check for lumps before use and, if necessary, crush or sieve the powder.

Liquid Form: Liquid Sulfur Black is a pre-reduced solution that is chemically more sensitive. It requires a strongly alkaline environment (pH > 11) to maintain stability; a drop in pH can cause the dye to precipitate. It is also temperature-sensitive: the ideal storage range is 5°C to 35°C. High temperatures accelerate hydrolysis or oxidation, reducing dye strength, while freezing can cause crystallization and irreversible separation. Separation and stratification are common after long-term storage-the solution may split into a lighter upper layer and a denser dye-rich lower layer. This is not a sign of failure but requires thorough stirring or shaking before use to ensure consistent concentration. The shelf life of liquid Sulfur Black is generally 6 to 12 months, and it should not be stored in iron containers, as metal ions can catalyze decomposition.

In summary, both forms require careful storage: powder must be kept dry to prevent caking, while liquid must be maintained at a stable temperature and strong alkalinity to avoid stratification.

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