Dyeing of Cotton with Direct Dyes

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Introduction:
Direct dyes are one of the most versatile classes of dyestuff applicable to cellulose, wool, silk, nylon fibers. This dyes have inherent substantivity for cotton, and for other cellulosic fibres. Their aqueous solutions dye cotton usually in the presence of an electrolyte such as NaCl or Na2SO4. The light fastness of dyeings with direct dyes on cellulosic fibers varies from poor to fairly good, although some copper complex direct dyes have very good light fastness. As usual, the deeper the color of the dyeing, the lower the fastness to wet treatments, and the higher the fastness to light. Various aftertreatments of the dyeings improve the fastness to washing. In some cases, however, such aftertreatments decrease the light fastness. They also invariably cause a change in hue that makes shade correction and color matching more difficult. Direct dyes 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 favour of reactive dyes. The latter have very good washing fastness on cellulosic materials and often have bright colors.

Objects :

  1. Cost saving .
  2. Comparative low time required to produce supply garments .
  3. No possibility of shade variation .
  4. Easy Process .
Recipe :
  • Shade ……………………5 %
  • Wetting agent …………..1 g/l
  • Sequestering agent ……..1 g/l
  • Levelling agent ………...0.5 g/l
  • Soda ash ……………….3 g/l
  • Gluber salt……………. 4 g/l
  • pH……………………. 10-11
  • Temperature ………….70
  • Time ………………….30
  • M:L ………………….1:30
  • Sample Weight ………5 gm
Calculation :



Dyeing Curve :
Dyeing curve
Dyeing Procedure :
  1. Set the dye bath with substrate at room temperature
  2. Add dye solution with other auxilaries ad raise the temperature at 900c
  3. Run the bath for 15-20 min and add salt step according to dye bath concentration
  4. This is better to add salt afe reaching the temperature to build point since at tis period the maximum penetration is achieved all over the substrate.
  5. Run the dye bath for 30 to 5 minutes at 90-95 0c for complete the dyeing cycle
  6. Cold down the bath temperature to 60-70 0c
  7. Drop the bath and rise
  8. Carry on the aftertreatment process to improve wet fastness
Precaution :
i) All chemicals should be measured very carefully.
ii) Temp should be increased very carefully.
iii) Water should be added very carefully.
iv) Time & Temp should be maintained very sincerely.

Conclusion :
Direct dyeing is the most popular dyeing process in Bangladesh. It is not expensive dye. Our teacher is very helpful to complete this experiment. She helps us to learn about direct dye. We learned a lot of things about direct dye from our teacher. So we can say that we have done this experiment successfully. 

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