Bleaching

• The purpose of bleaching is to remove stains caused by lignin.

• Major bleaching agents

  • chlorine, sodium hypochlorite, hydrogen peroxide, chlorine-dioxide, and oxygen.

• Chlorine gas is one of the different bleaching systems that are used to remove lignin that remains in the pulp.

  • Chlorine gas is passed into the pulp-water mixture.
  • The gas reacts with whatever lignin that is left and becomes chlorinated.
  • The chlorinated lignin is then removed when treated with the caustic soda NaOH (Sodium Hypochlorite)

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