Effects of different types of bleaching

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Transcript of Effects of different types of bleaching

  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Effects of different types of bleaching
  • Name : MAZADUL HASAN SHESHIR ID: 2010000400008 Batch: 13th Batch (Session 2009-2013) Department: Wet Processing Technology Email: [email protected] Blog: www. Textilelab.blogspot.com Southeast University Department of Textile Engineering PREPARED BY right
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Prof . Engr. Dr. Ayub Nabi Khan Bleaching 3 Bleaching The process of decolorize the natural coloring matter present in the cloth treating with some oxidizing agent and reducing agent and ensure the permanent whiteness is called bleaching. Objects A high uniform absorbency of fabric to water and dye stuffs. Uniform degree of whiteness. Fabric should not damage and DP should remain high. Destruction of natural coloring matters from the fabric. To ensure a level dyeing properties. To make the textile materials suitable for subsequent processing. (Dyeing, printing, etc.)
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Types of bleaching agents Oxidative bleaching agent Hydrogen peroxide bleaching. Sodium chlorite bleaching. Hypochlorite bleaching. Percretic acid Ozone Bleaching powder Reductive bleaching Zn dust Staneous chlorite Ferous sulphate Sulpher dioxide Sodium hydrosulphate Prof . Engr. Dr. Ayub Nabi Khan Bleaching 4
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Prof . Engr. Dr. Ayub Nabi Khan Bleaching 5 Reducing bleaching is a temporary bleaching process because after bleaching there is possibility that the oxygen in the air may reoxidize and it will return to its original state. But oxidizing bleaching is permanent because it gives almost invariably a more permanent white. Bleaching can be done in various process: 1. Hypochlorite bleaching for 100% cotton (less used) 2. Hydrogen peroxide bleaching for 100% cotton (more used) 3. Sodium Chlorite bleaching only used for special sector and only for polyester and cotton blend. 4. Peracetic acid bleaching can also be done for the better improvement of the process and this is not still used in our country commercially.
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Hypochlorite bleaching Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 6
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 7 In textile hypochlorite bleaching sodium hypochlorite [NaOCl] or calcium hypochlorite [Ca(OCl)2] may be used as hypochlorite bleaching agent. Differences between Ca(OCl)2 and NaOCl bleaching Ca(OCl)2 NaOCl 1.It is unstable 1.It is stable 2.It produces CaCO3 precipitate 2. It doesnt produce any precipitate 3.It makes harsh feeling on the fabric 3.It doesnt make harsh feeling on the fabric 4.Comperatively cheaper than NaOCl bleaching 4.Higher cost than Ca(OCl)2 bleaching
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Sequence of cotton bleaching NaOCl Antichlore treatment Cold wash Ca(OCl)2 souring Antichlore treantmnet Cold was It is seen that souring is used only for Ca(OCl)2 but antichlore treatment is used for both. Cause when Ca(OCl)2 is used, it reacts with atmospheric CO2 to give CaCO3 as white precipitate. CaCO3 deposited on the fabric causing harsh handling and uneven dyeing, hence it has to separate and souring (acid treatment) is done to remove it. Ca(OCl)2 + CO2 + HO2 CaCO3 + HOCl Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 8
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Souring The treatment by which the fabrics after processing with alkali (scouring/bleaching) are treated with HCl or dilute H2SO4 for removing alkali or neutralization for alkali is called scouring. This process is necessary in case of Ca(OCl)2 bleaching. CaCO3 + 2HCl = CaCl2 + CO2 + H2 O CaCO3 + H2SO4 = CaSO4 + CO2 + H2 O Antichlore treatment In case of hypochlorite bleaching (OCl- ) hypochlorous ion is produced, which will react with residual protein to form chloramines > NCl which is corrosive and toxic. Cl2 is also produced which also unhygienic and irritate to skin. Moreover >NCl reacts with moisture and gradually cotton becomes yellowish due to forming of HCl. Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 9
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY OCl - + resedual protein >NaCl >NaCl + H2O HCl Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 10
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Treatment procedure: In an experiment the hypochlorite bleaching scoured fabric samples (10 g. each) were treated with sodium hypochlorite solutions (0.5, 1.0, 1.5 g/liter available chlorine) at different pH values (11, 12, and 13) for 15 min., keeping a liquor ratio of 30:1 at 30, 45, 60 C. the bleached samples were washed, scoured with 0.1% hydrochloric acid and washed free from the acid. For the other purpose of comparison two pieces of scoured cloth were bleached with sodium hypochlorite solution (3 g/liter available chlorine) at pH 11 and 30C for 1 hr and scoured as above. Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 11
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Result: Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 12 Conc. Of NaOCl g/liter avail. Cl2 Temp. C Whiteness pH 11 0.5 30 Yellowish white 0.5 45 Dull white 0.5 60 White 1.0 30 Yellowish white 1.0 45 White 1.0 60 White 1.5 45 White 1.5 30 Dull white
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Conc. Of NaOCl g/liter avail. Cl2 Temp. C Whiteness pH 12 0.5 30 Good white 0.5 45 Slightly white 0.5 60 Dull white 1.0 30 Yellowish white 1.0 45 White 1.0 60 White 1.5 30 Yellowish white 1.5 45 Dull white 1.5 60 White Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 13
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Conc. Of NaOCl g/liter avail. Cl2 Temp. C Whiteness pH 13 0.5 30 Dull white 0.5 45 White 0.5 60 White 1.0 30 Dull white 1.0 45 Cream white 1.0 60 White 1.5 30 Slightly white 1.5 45 White 1.5 60 White Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 14
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY At a given hypochlorite concentration, the bleaching efficiency increases with an increase in either the temperature or in the pH. Good white effects are obtained when bleached for 15 min. at 60C with 1.5 g/liter available chlorine. In case of 1 hr process with 3 g/liter available chlorine at 30Cwhite effects are obtained. Conc. Of NaOCl g/liter avail. Cl2 Temp. C Whiteness pH 11 3.0 30 (1hr) White 3.0 30 (1hr) White Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 15
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Advantages Cheapest Variety of machine can be used Large batches fabric can be processed Simple machine can be used Disadvantages There is a danger of damaging the fabric due to accidental lowering of pH. The process is slow, it is carried out at low temperature and it is therefore difficult to integrate into rapid continuous operation. There is danger of yellowish upon storage. The relatively high salt loads in the process are undesirable for ecological reason Prof . Engr. Dr. Ayub Nabi Khan Hypochlorite bleaching 16
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Hydrogen peroxide bleaching Prof . Engr. Dr. Ayub Nabi Khan 17
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Hydrogen peroxide is called universal bleaching agent and most widely used for bleaching and over 90% of all fibre can be bleached with H2O2. It can be used for vegetable fibre as well as protein fibre although the cost of H2O2 is greater then hypochlorite. Properties of hydrogen peroxide: (a) H2O2 is a clear colorless liquid. (b) Strength of H2O2 is 35% - 70%. (c) Should store away from light. (d) In presence of heavy metal like gold, silver, platinum it decomposes with the (e) liberation of oxygen. (f) This material is irritant for skin (g) This is non flammable. Prof . Engr. Dr. Ayub Nabi Khan Hydrogen peroxide bleaching 18
  • School of Science and Engineering, Department of Textile Engineering SOUTHEAST UNIVERSITY Bleaching methods with hydrogen peroxide: There are two c