Cellulose
Acetate
Although cellulose
acetate was first prepared in 1865 by the French
chemist Paul Schützenberger, it was not until
1894 that the first industrial process for its
manufacture was patented in the UK by Charles
Cross and Edward Bevan. At about the same time,
Little in the US made cellulose acetate filaments
experimentally, as did Bronnert in Germany.
However, this material was essentially cellulose
triacetate, a rather intractable polymer, not
readily soluble in commonly available solvents.
In 1904 George Miles, an American chemist,
discovered that if the polymer was partially
hydrolysed, it became soluble in acetone.
The Swiss brothers Henri and Camille Dreyfus used
this procedure for lacquer and film production at
Basle in 1910, and at the outbreak of World War I
set up a factory in Spondon, Derbyshire, England
to make acetate 'dope' for waterproofing and
stiffening fabric covered aeroplane wings. They
set up a similar plant at Cumberland, Md., for
the US army in 1917.
 After the war they
concentrated their efforts in England, and in
1919 introduced the first acetate yarn Celanese.
In 1924, they switched entirely to the US where
acetone and acetic anhydride were cheaply
available. In the same year, rayon became adopted
as a generic term for all 'artificial silk'.
Cellulose acetate (CA) in combination with
plasticizers, such as diethyl and dimethyl
phthalate, produces a plastics material which can
be heat softened and forced under pressure into a
cool mould. This injection moulding process was
developed by Dr Arthur Eichengrün of Celonwerke
to exploit the moulding properties of the
plasticized CA moulding materials he had produced.
His first injection moulding machine had a
maximum shot weight of about 8 gm provided by a
hand-operated plunger mechanism, a far cry from
today's machines, some of which have a maximum
moulding size in excess of 100 kg.
CA plastics are tough with deep gloss and high
transparency. They possess a 'feel' which is
different to other plastics and which is often
described as more 'natural'. This may explain why
CA has retained its popularity for making items
which are handled frequently such as spectacle
frames and tool handles, many transparent tool
handles are still made from cellulose acetate and
its sister material cellulose butyrate. Other
items made from CA included combs, fashion
accessories, pen barrels and toys, but these are
now more likely to be moulded from more modern
thermoplastics.
Early spectacle frames were cut from sheet
material, mostly in imitation tortoiseshell which
was often referred to as 'optical shell'.
Reinforcing nickel wires for the side arms were
forced into heat-softened strips of CA sheet.
Nowadays, frames are generally moulded into shape
- a more economic process. However, certain high-class
frames are still made using the old process,
especially to achieve special colour effects not
possible using injection moulding.
Despite being much less flammable than cellulose
nitrate, acetate film did not become established
for photographic use until after World War II
because of the technical excellence of celluloid
and the vested interests of film manufacturers.
There was, however, a demand for transparent
sheet material in laminated safety glass,
especially car windscreens before toughened glass
became available for this purpose.
Ironically, cellulose triacetate which was
unsuccessful initially, returned to favour when a
suitable, relatively non-toxic solvent (dichloromethane
) became available in the 1940s. Since then
photographic film has been almost entirely based
on cellulose triacetate and Tricel cellulose
triacetate fibres were introduced in 1954.
Few plastics can boast such a long pedigree as
cellulose acetate and, being made entirely from
renewable resources, CA may yet have a long way
to run.
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