2. ACETATE RAYON
• Textile fibres which are composed of ester cellulose
are called “acetate fibre”.
• Acetate means acet (i.e. come from acetic acid) and
ate (denotes a chemical salt) so acetate means a salt
of acetic acid.
• These are basically of two types :
1. ACETATE : man made , secondary cellulose acetate
filament.
2. TRIACETATE: man made , primary cellulose acetate
filament.
3. Manufacturing of acetate Rayon
• Cellulose acetate is dissolved in suitable
solvent (chloroform or acetone) and spun by
evaporating the solvent. Thus , while viscose
and cuprammonium are regenerated cellulosic
fibres, acetate rayon is regenerated modified
cellulosic fibre.
4. • Raw materials :
i. Cotton linters (fibres of short length)
ii. Wood pulp
iii. Glacial acetic acid
iv. Acetic anhydride
v. Sulphuric acid
vi. Acetone
5.
6. Acetylation process
• The pre-treated cotton linters are fed to an acetylator
(closed jacketed vessel) containing a mixture of acetic
anhydride, glacial acetic acid and small amount of
conc. Sulphuric acid . For every 100 kg of cotton linters
, 300kg of glacial acetic acid , 500kg acetic anhydride
and 8-10 kg of sulphuric acid may be used. After adding
the mixture circular door at the top is sealed.
• A stirrer having many blades rotates to mix the
ingredients. The acetylation reaction is exothermic
reaction i.e. heat is liberated during acetylation which
should be removed by circulating cold water through a
jacket fitted to the acetylator.
7. • The reaction is completed in 7-8 hrs. at 25-30
degree Celsius. Triacetate is formed in the
suspension form in the aceylation mixture ,
which is called ”acid dope”.
8. Hydrolysis (partial deacetylation)
• The acid dope is stored in jars for ageing. Water
and sulphuric acid are added and allowed to
stand for 10-20 hrs. During this period, called
ripening period, partial converison of acetate
groups to hydroxyl groups takes place. The
mixture is then diluted with water and stirred
constantly when the secondary acetate separates
in the form of white flakes. The flakes are allowed
to settle, water is removed and the jar is filled
with fresh water .
9.
10. The flakes are placed in the centrifugal machine.
When the basket revolves at a high speed, the
excess of water present in the flakes is forced out
of the cage through perforations. The flakes are
then dried in a horizontal drier, in which hot air
is forced through them.
11. Dried acetate flakes are mixed with three times
their weight of acetone with powerful stirrers.
The acetate dissolves slowly in the solvent. It
takes about 24 hrs for complete dissolution to
give a thick colored liquid, called dope. The
solution is filtered and deaerated. The spinning
solution contains 25 to 35% of cellulose
secondary acetate.
12. Spinning process
• The spinning dope is spun into acetate rayon
filaments on the dry spinning system, which
requires hot dry air. The dope is fed from a
feed tank into spinning cabinets. The dope
coming out of the spinnrette travel a distance
of 2-5meters vertically downward to a feed
roller from where it is guided onto a bobbin at
a much greater speed than that of spinning.
