Manufacture of Cellulose Acetate.
Year: 1894

page_text: Date of Application, 17th May, 1894
Complete Specification Left, 14th Feb., 1895-Accepted, 23rd Mar., 1895
We, CHARLES FREDERICK CROSS and EDWARD JOHN BEVAN both of
No. 4 New Court, Carey Street in the County of London, Analytical and
Consulting Chemists, do hereby declare the nature of this invention to be as
follows:
This invention relates to the manufacture of a certain intermediate product
consisting of cellulose and zinc acetate, and to the manufacture of cellulose acetate
by treatment of the said intermediate product.
For this purpose, cellulose hydrate is thoroughly mixed with zince acetate
solution, and the mixture, dried and dehydrated, constitutes the intermediate
product above referred to.
This intermediate product is then treated at a moderate temperature with acetyl
chloride (which may be diluted with a little anhydrous chloroform or ethyl acetate)
and the product of the reaction is thoroughly washed and dried. In order to
separate unattacked cellulose from the cellulose acetate, the latter is dissolved off
by chloroform, giving a solution of cellulose acetate, from which the solvent may
be evaporated.
Dated 1
1004
ABEL & IMKAY,
Agents for the Applicants..
Manufacture of Cellulose Acetate.
We, CHARLES FREDERICK CROSS, and EDWARD JOHN BEVAN, both of.
No. 4 New Court, Carey Street, in the County of London, Analytical and
Consulting Chemists, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained in
and by the following statement:—
This invention relates to the manufacture of cellulose acetate from a certain..
intermediate product, consisting of cellulose and zinc acetate in a state of:
combination or of intimate mixture.
To prepare this intermediate product, we take cellulose in one of its hydrated
forms which, as is well known, can be obtained by precipitation from the
solution of cellulose in zinc chloride or cuprammonium solutions, or from the
solution obtained by treatment of crude cellulose with caustic alkali and carbon
disulphide, as described in the Specification of the Patent No. 8700 of 1892. The
cellulose hydrate obtained in any of the above ways is added to and thoroughly
mixed with a concentrated solution of zinc acetate in the proportion of from one to
two equivalents of zinc acetate to one equivalent of the cellulose, that is to say
about 150 parts by weight of the crystallised zinc acetate (weighed before solution)
to 100 parts by weight of the dry cellulose contained in the cellulose hydrate. The
mixture, after thorough incorporation of its ingredients, is dried and then dehydrated
by heating it to 110° C. The dry dehydrated substance is the intermediate product

page_text: which is employed, according to this invention, for the manufacture of cellulose
acetate.
For this purpose it is finely powdered and carefully mixed by successive doses
with a definite quantity of acetyl chloride, the mixture being stirred and cooled so
that the temperature is kept below 30° C. until the whole of the acetyl chloride is
added; the quantity taken being calculated at two molecular equivalents (that is
2. C,H,O. Cl) to one equivalent of the zinc acetate that is [Zn (OC,H₂O),] in the
intermediate product. The agitation is continued until the reaction is completed,
care being taken to prevent the temperature from rising above 30° C. The
product of the reaction is treated with water to remove such zinc salts as may be
present, and after thorough washing is pressed and dried.
In order to separate residues of unattached cellulose from the cellulose acetate,
the dried product is treated with solvents, such as chloroform, which dissolve the
cellulose acetate but not the cellulose itself.
The solution of cellulose acetate is filtered or clarified by long standing and the
solution filtered or poured off from the insoluble matter may then be used.
The acetyl chloride used in the process may be diluted with chloroform or ethyl
acetate (free from water and alcohol) in order to moderate the reaction and the
resulting temperature.
The product closely resembles the cellulose nitrates in physical properties but of
course from its constitution is non explosive.
From its solution in chloroform it is obtained in transparent films or sheets
according to the thickness of the layers evaporated. Hence it may be used as a
substitute for collodion in many applications, such as surgical work, to supply a
temporary and artificial skin, or in closing down bandages; also as a varnish in
special cases where collodion varnish is now used. The product itself is of course
solid and takes various forms, according to the way in which it is prepared; it may
may be obtained in lumps, or, as described, viz. in transparent sheets and films. It
also has the property of mixing or combining with oils in suitable solvents of both.
It holds the oils in such a way as to give films of much softer texture without any
loss of transparency and only a slightly diminished lustre.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The manufacture of an intermediate product consisting of cellulose and zinc
acetate by mixing cellulose hydrate with zinc acetate solution, drying and
dehydrating the compound, substantially as described.
2. The manufacture of cellulose acetate, by treating with acetyl chloride the
intermediate product manufactured as above set forth, washing the crude product
of the reaction, pressing and drying, treating the dried substance with chloroform
or other solvent, whereby a solution of cellulose acetate is obtainted free from
cellulose, and finally, evaporating the solvent, substantially as described.
Dated this 14th day of February 1895.
ABEL & IMRAY,
Agents for the Applicants..