Wednesday, September 1, 2010

Garment Dyeing - Part-3 - Chemicals and Auxiliary Chmicals - Selection and Analysis

In garment processing we are using a lot of basic chemicals, auxiliary chemicals, enzymes and natural resources such as water. All the above said ingredients play its own important role.

  • Water plays the key role in any textile wet processing. The quality of water decides the quality of your product and rework percentage.  In all climatic condition no water quality would remain same. Rainy season will bring more turbidity and mineral content in running water (river) and more soft and less saline water in bore wells. Providing a good quality water for processing is the basic requirement for any processing unit. How to test and treat water and make it suitable for dyeing is a separate line of discussion.

  • Basic Chemicals: In garment processing we are using the following basic chemicals. The purity of these chemicals is also very important from the point of dyestuff behavior and economy. Some examples are:
      • Common Salt - Common salt is used in reactive, direct and sulphur dyeing processes as a dye exhausting agent. The high impurities present in salt will precipitate on the garment being processed during the addition alkali (soda or caustic) in to the dyeing bath. The unwanted metal ions present in the contaminated salt, like Calcium, Magnesium, Manganese, Iron, Aluminium etc some time replaces the metal ions present in the dyestuff and make the shade appear duller and different in tone. By using a good quality salt like Galuber's salt (Na2SO4) or pure vacuum salt (common salt purified), would save you from these problems. While selecting a basic chemical, buy it from reputed manufacturer and ask them provide you purity certificates. If necessary you can also test the purity of chemicals.
      • Soda Ash - Purity testing of soda ash is very important because the concentration decides the correct pH requirement for fixation of reactive dyes.
      • Hydrogen Peroxide - Hydrogen Peroxide is being sold under two concentrations viz., 35% and 50%. According to the strength the dosage in bleaching varies. Being water like adulteration very easily possible and this decides the batch whiteness. If whiteness between varies, then the final shade also will vary in tone and depth.
      • Acetic Acid - Acetic Acid is used as a neutralizing  agent in two stages of processing, viz., after bleaching and after dyeing. Both stages are very important to achieve the required results. Improper neutralization before dyeing leads to patchy dyeing and after dyeing results in fastness related problems and tonal variations of many shades.
  • Auxiliary Chemicals  - inclusion of too many products for processing leads to loading of effluent and creates complications in treatment. Moreover poor quality products purchased only with the aim to reduce cost of production ends up in many quality problems. If you have a simple analytical lab you can test all auxiliary chemicals at your end itself as a standard practice. We can suggest you the optimum number of essential products for any type of dyeing or finishing.

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