Calcium Hypochlorite or Sodium Hypochlorite may be used in Hypochlorite bleaching. Calcium Hypochlorite has cheap sources and hence less expensive than sodium Hypochlorite. But sodium Hypochlorite has some technical advantages.
Common Recipe :
- Wetting Agent
- Soda Ash
When calcium hypochlorite or sodium Hypochlorite is hydrolyzed, hypochlorous acid is formed which ionize under a certain condition and give per-hydroxide Ion (OCl–) which are responsible for bleaching action.
Ca(OCl)2+2H2O———-> Ca(OH)2+ 2HOCl (HOCl = Hypoclorus Acid)
HOCl ======== (H+) (OCl–) Where (OCl–) is responsible for bleaching.
Like Ca(OCl)2 we can bleach with NaOCl.
NaOCl + H2O————-NaOH + HOCl Where, HOCl is hypochlorus Acid.
It cause Bleaching like as above
HOCl ========(H+) ( OCl–)
When Calcium Hypochlorite is used, it reacts with atmospheric carbon-dioxide to give calcium carbonate.
Ca(OCl)2+H2O +CO2 —————— CaCO3↓ + 2 HOCl
Calcium carbonate is deposited on the fabric surface and cause harsh handling and uneven dyeing. Hence, it have to separate and (Acid Treatement) / scouring is done to remove it.
CaCO3+2HCl ———————- CaCl2+ CO2+H2O
Sodium hypochlorite does not react with atmospheric carbon-dioxide and hence no additional treatment is required. This is the technical advantage of sodium hypochlorite over calcium hypochlorite.