Silk Dyeing Process

Silk Dyeing Process
S M Hossen Uzzal
B.Sc. in Textile Engineering
Noakhali Textile Engineering College
Facebook: http://www.facebook.com/sm.h.uzzal




Silk Dyeing:

Silk being a natural polyamide or polypeptide fibre, its dyeing properties are very similar to those of other natural polypeptide fibre, wool as well as synthetic polyamide fiber, nylon. They can be dyed by similar methods. Very fine fibrillar structure and high orientation of fibre molecules are the two characteristic properties of silk which determine its dyeing behaviour.

Silk is comparatively easier to dye and is less sensitive to temperature. However, there is always a risk of damage of silk filaments during dyeing and the dyeing on the damaged material may apparently look like faulty dyeing.
Silk Dyeing Process
Silk Dyeing Process
Since silk fiber has a slightly cationic character with the isoelectric point at about pH 5.0, . So silk is dyed using various dyes such as Acid dyes, metal-complex, reactive dyes etc. Acid dyes are more suitable for silk and wool. Dyeing and printing makes it possible to bring about the choicest colours and shades on silk leading to value addition of the silk materials. Silk offers a wide colouration possibility covering almost the entire spectrum of colours and hues due to its ready acceptability for a large range of dyestuffs.

For dyeing with milling, supermilling acid dyes and 1:2 metal-complex dye, the recipe (% o.w.m.) is:
  • x % dye
  • 0.5-1.5% Lyogen MF or SU liquid
  • 1-2% Imacol S liquid,
  • 1-2 g/l sodium acetate and acetic acid for pH 4.5-7, depending on depth.
The chemicals are added in the bath at 20-30ºC and then the dissolved dyes are added slowly or in instalments. The temperature is raised slowly to the ambient temperature of 60-70ºC or 80-90ºC depending on the material and the dyeing is continued for 60 and 45 minutes for the respective temperature ranges.

For dyeing in soaping bath:
  • x% dye
  • 1-2 g/l Marseilles soap
  • 5-20% Glauber’s salt
  • pH 8.0-8.5
The wet fastness of silk dyed with acid and metal-complex dyes may be improved by aftertreating with a cationic product such as Sandofix WE (Clariant) or stronger fixing agents like Indosol E-50 or Lanasan MW (Clariant).

Silk may be dyed by pad-batch method with Drimalan F or Drimarene K dyes by padding the material at room temperature with a liquor containing:
  • x% dye
  • 50-100 g/l urea (solubilising agent)
  • 10-20 g/l sodium bicarbonate
  • 0-2 g/l wetting agent, e.g. Sandozin AMP
The padded material is batched for 24 hours. Adequate colour yield and fixation may not be achieved with certain large-molecular dyes such as turquoise and green types.

Conclusion:
Both wool and silk are costly and delicate fibres. Under adverse conditions, they are damaged severely. High alkalinity and high temperature are harmful for these fibres. Apart from stiffening of fibres during dyeing, wool may be felted into an entangled mass, while silk filaments may be broken or chafed. Both the fibres are rich in active chemical groups. A number of dye-classes are available which can provide bright and deep shades of moderate to high fastness properties. As these materials are delicate and are handled very carefully, fastness requirements are not very high. The dyed material should possess satisfactory fastness meeting washing ISO washing fastness test no. 3 standard.

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