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Sodium Hydroxide, commonly known as caustic soda, lye, or
sodium hydrate, is a caustic compound which attacks organic matter.
(caustic soda is sodium hydroxide, caustic potash is potassium
hydroxide and silver nitrate is lunar caustic.) Caustic soda is
available commercially in various white solid forms and as a
solutions of various concentrations in water.
It is very soluble in water, alcohol, and glycerin and absorbs
carbon dioxide and moisture from the air. Sodium hydroxide is
prepared by the reaction of sodium carbonate (soda) in concentrated
solution form with calcium hydroxide (slaked lime). But the
principal method for its manufacture is by the electrolysis of
brine. (the two current technologies are the diaphragm and the
membrane). The electrolyte is saturated brine (about *5% aqueous
sodium chloride).
The chloride ion is oxidized at the anode to chlorine gas.
chlorine gas is a coproduct. Sodium hydroxide is a strong base and
inexpensive which find many applications in the chemical industry.
Sodium hydroxide provides fuctions of neutralisation of acids,
hydrolysis, condensation. saponification and replacement of other
groups in organic compounds of hydroxyl ions.
The major use of sodium hydroxide is as a chemical and in the
manufacture of other chemicals. It is used in textile industry.
Sodium hydroxide is used mainly for two processes in textile
manufacture. Mercerizing of fibre with sodium and hydroxide
solution enables greater tensional strength and consistent
lustre.
It also removes waxes and oils from fibre to make the fibre more
receptive to bleaching and dying. Sodium hydroxide is also used in
the production of viscose rayon. Cellulose is extracted from pulp
using sodium hydroxide and subsequently treated with high purity
sodium hydroxide to produce soda cellulose. Further chemical
treatment results in a rayon fibre.
This is a declining market due to the competition from synthetic
(ie petrochemical) fibres. It is used in making paper and
pulp.Sodium hydroxide aids separation of cellulose fibres from
lignin; this breaks down wood into pulp.
Sodium hydroxide also helps bleach paper to required whiteness
and brightness. In alumina production industry, a strong alkali
solution separates pure alumina from bauxite ore. Alumina is then
recovered through precipitation and finally, calcination. Sodium
hydroxide is also widely used in in making soaps and detergents,
Sodium hydroxide was originally used for soap manufacture, but now
has a wider variety of functions.
As well as an extractant and refining agent for certain oils,
sodium hydroxide is used to produce active agents, or builders in
modern synthetic detergents. Sodium Hydroxide is used for sodium
hypochlorite which is used as a household bleach and disinfectant
and for sodium phenolate used in antiseptics and for the
manufacture of Aspirin.
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