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Bleaching cotton with hydrogen peroxide
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Bleaching cotton with hydrogen peroxide

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Transcript

  • 1. Bleaching cotton with Hydrogen Peroxide
  • 2. Discovery
    • Discovered in 1818
    • Used for cotton bleaching 1866
    • High cost, Limited use
    • Industrial use as bleaching agent 1935
  • 3. Properties
    • Colourless liquid
    • Corrosive to skin
    • Stable under acid pH
    • Stabilized by phosphoric acid
    • Activated under alkaline pH
    • NaOH, Na2CO3, Trisodium phosphate alone or in combination may used as alkali for activation
    • Decomposition in presence of alkali alone is very rapid
    • Uneven bleaching
  • 4. Stabilizer
    • Compounds whioch control the rate of decomposition of H2O2 under alkaline conditions.
    • Sodium silicate is the most common and economical stabilizer
    • Other non silicate based stabilizers include
    • Metal chelating agents like EDTA
    • Decomposition products of protein
    • MgCO3 and CaCO3 present in hard water
    • Polyacrylates etc.
  • 5. Mechanism of H2O2 bleaching
    • Initial understanding
    • 2 H2O2  2H2O + O2
    • Not correct because beaching not achieved by atmospheric oxygen
    • Present understanding
    • In presence of alkali
    • H2O2 +OH  HO.