Bleaching cotton with hydrogen peroxide

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Bleaching cotton with hydrogen peroxide

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

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