Cotton Dyeing With Direct Dye

In this article, we are going to describe the process, recipe, and steps for the dyeing of cotton with direct dye.

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Introduction

Direct dyes are one of the most versatile classes of dyestuff applicable to cellulose, wool, silk, and nylon fibers. These dyes have inherent substantively for cotton and for other cellulose fibers. Their aqueous solutions dye cotton, usually in the presence of an electrolyte such as NaCl or Na2SO4. The light fastness of (dyed with direct dyes) cellulose fibers varies from poor to fairly good. Direct dyes give bright shades but exhibit poor wash fastness. Various after-treatments are used to improve the wash fastness of direct dyes. Direct dyes are molecules that adhere to the fabric molecules without help from other chemicals. Direct dyes are defined as anionic dyes with substantively for cellulose fibers.

Objectives

1. Comparative low time required to produce supply garments.

2. No possibility of shade variation.

3. Easy process.

4. Cost-saving.

Recipe

Chemicals/Parameters	Quantity
Direct dye	2%
Common salt	10 g/L
Soda ash	2 g/L
Sequestering agent	1 g/L
Wetting agent	1 g/L
pH	7-8
M:L	1:40
Time	20 minutes
Temperature	100℃

Calculation

M:L (Material: Liquor) = 1:40 (M:L is more because it is done in the open bath)

Fabric: 5 gm

So, liquor (5 ✕ 40) : 200 ml

So, M:L: 5:200

We know, Dye = (Sample weight ✕ Shade %) / (Stock solution %)

For 2% shade and 1% stock solution,

= (5 ✕ 2%) / (1%) = 10 ml

also, Chemical : (g/L ✕ Total liquor) / (1000 ✕ Stock solution %)

For 5% stock solution = (1 ✕ 200) / (1000 ✕ 5%) = 4 ml

Thus, calculated the total amount of chemicals.

Now, freshwater needed = (200- Total chemicals) ml

Direct Dyed Fabric

Direct Dyeing Curve

Auxiliary Chemicals Functions

Direct dye: Direct dyes are molecules that adhere to the fabric molecules without help from other chemicals. It is the primary chemical substance to color the fabric, and it is an anionic dye.

Soda ash (Na2CO3): It maintains suitable pH for direct dyeing.

Sequestering agent: In the absence of a water softening plant in an industry, it is also possible to reduce the unwanted interference of heavy metal ions during soaping or dyeing by a sequestering agent. A sequestering agent is a substance that suppresses a property or reaction of metal ions without the removal of that metal from the system. The most common sequestering agent is EDTA, known as ethylenediaminetetraacetic acid.

Wetting agent: It accelerates the wettability of material in solution, thus helping to easy penetration of chemicals into the substance.

Common salt (NaCl): This common salt is used as an electrolyte. We know that direct dye is an anionic dye, and cotton fiber assumes a negative charge when immersed in water. Electrolyte reduces or extinguishes the change in the fiber, to color the fabric.

Conclusion

Direct dyeing is the most popular dyeing process in Bangladesh. It is not an expensive dye. But it generally cannot meet today's more stringent washing fastness requirements for apparel and linens. In recent years, their share of the market has gradually declined in favor of reactive dyes. But for low cost and easy process, it is still popular in some sectors of dyeing.