Improvements in Dissolving Cellulose and Allied Compounds.
Year: 1892

page_text: Date of Application, 7th May, 1892
Complete Specification Left, 6th Feb., 1893-Accepted, 8th Apr., 1893
PROVISIONAL SPECIFICATION.
Improvements in Dissolving Cellulose and Allied Compounds.
We CHARLES FREDERICK CROSS, EDWARD JOHN BEVAN and CLAYTON
BEADLE all of No. 4 New Court Lincoln's Inn, in the County of London
Consulting and Analytical Chemists, do hereby declare the nature of this invention
o be as follows:-
Our invention relates to a new method of treating cellulose and allied compounds
to obtain them in a dissolved condition, and also to agents employed in the treatment
or process.
There are certain aqueous solutions in which cellulose, for example, bleached
cotton or linen dissolves without sensible chemical change and from these solutions
the cellulose is recoverable either by evaporation of the solvent or dilution of the
solution with water or by treatment with reagents so as to chemically modify the
solvent. Of such solutions one, namely the solution of copper oxide in strong
ammonia, has been applied on the manufacturing scale, for the preparation (1) of
the solution itself and (2) of waterproof fabrics by treatment of cotton or paper or
other similar fabrics with the solution.
The more general application of such solutions appears to have been precluded
by reason (1) of cost of production and (2) difficulties of manufacture &
manipulation.
Our invention has been perfected with the view of overcoming the disadvantages
and objections above mentioned.
Our invention consists in taking cellulose in any suitable form (by preference
loose cotton, cotton waste or rags) or jute fibre or other cellulosic compound treating
the material with a strong solution of a caustic alkali, draining and removing the
excess of the solution and exposing the material thus treated to the action of
carbon disulphide, liquid or vapour in a closed vessel or chamber or we treat the
material with the solution of the compounds resulting from the inter-action of
carbon disulphide and the caustic alkalis; so treated the cellulose gradually swells
to a gelatinous mass, finally loses all appearance of fibrous structure and being
stirred in cold water passes into a homogeneous solution.
This solution at a suitable degree of dilution is available for a number of
applications; but for some purposes a preliminary purification may be resorted to
for the removal of excess of solvent: for instance we treat the solution with
common salt which, in dissolving, throws out the dissolved cellulose as an alkaline
compound; this may be washed with strong brine pressed and then treated with
water in which it again dissolves to a solution resembling the original but of a much
lighter colour.
of May 1892.
CHAS. FRED. CROSS.
EDWARD JOHN BEVAN.
CLAYTON BEADLE.

page_text: COMPLETE SPECIFICATION.
Improvements in Dissolving Cellulose and Allied Compounds.
We CHARLES FREDERICK CROSS, EDWARD JOHN BEVAN, and CLAYTON
BEADLE, all of 4 New Court, Lincolns Inn in the County of London Consulting
and Analytical 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 :-
Cellulose in its various forms is attacked and dissolved by certain reagents, some
of which bring about chemical modifications more or less profound, others appear
to dissolve in the more simple way i.e. without sensible modification.
One of these solutions of cellulose viz., that produced by an ammoniacal solution
of oxide of copper, has received important technical applications at the same time
these are limited by reason of the properties of the solutions by the nature of the
solvent, and by the cost of production.
We have devised a method of dissolving cellulose as the result of a reaction
brought about by means of reagents of relatively low cost and yielding a product
available by reason of its properties for a large number of useful purposes.
"
It is well known that when cellulose in any of its fibrous forms,-i.e.,-bleached
cotton or flax is treated with strong solutions of the caustic alkalies, the effect of
"mercerisation is produced the fibres swell up considerably and become
transparent, as a result of combination with both alkali and water (hydration).
If now the mercerised fibre or compound of cellulose with alkali and water, is
exposed to the action of carbon disulphide, reaction ensues, the fibres swell up
still further until finally they are completely gelatinised, and in this condition, the
product is entirely soluble in water. The solution so obtained is of a yellow colonr
and extremely viscous.
In carrying out this treatment on the manufacturing scale we employ as our raw
material any of the forms of cellulose such as that obtained from flax, rhea, hemp,
wood, or bleached cotton in any of its forms. We impregnate the material in any
convenient way with a solution of caustic soda of fifteen per cent. strength i.e. con-
taining about 12% by weight of the oxide Na₂O, having removed the excess of
the solution by squeezing or by means of a centrifugal machine we expose the
material, retaining from 3 to 4 times its weight of the solution and therefore from
40 to 50% of its weight of the alkali Na.O to the action of the carbon disulphide
in a closed vessel or chamber employing from 30 to 40 per cent. (of the weight of
the cellulose) of the disulphide. In from 3 to 5 hours at the ordinary temperature,
the reaction is complete and the product ready for solution in water. Owing to the
great viscosity of the product the process of solution requires to be aided by stirring.
This solution contains in addition to the derivative of cellulose, thus obtained
dissolved, products of the interaction of the alkali and the disulphide. For a
number of applications of the solution, the presence of these by-products is
unobjectionable, but they may be to a great extent removed, or they may be
converted into colourless compounds in solution, by treatment to be subsequently
described.
The soluble derivative of cellulose has the property of becoming reconverted
into cellulose (1) spontaneously i.e. on long standing (2) on heating the solution
at 80-100° C., (3) by treatment of the solution with oxidising agents.
If the solution for instance be poured on to any surface and evaporated to dryness
at 100° C. a transparent skin or film is obtained from which the alkaline salts may
be removed by washing, treatment with dilute acid, and again washing. The final
product thus obtained has all the characteristics of cellulose; more especially as
regards resistance to the action of solvents, alkaline solutions and oxidising agents.
This modification of cellulose may also be deposited upon textile fabrics, yarn or
cloth or may be employed to coat wire or metal gauze and for a large number of
other useful purposes.

page_text: The crude solution may be treated in various ways for the modification or
elimination of the by-products of the reaction and the preparation of colourless or
nearly colourless solutions, of these we may instance the following.
(1) Acidification with certain "weak" acids such as carbonic, acetic, and lactic
acids; and removal of the hydrogen sulphide resulting from their action by passing
a stream of air through the solution.
(2). The addition of sulphurous acid, in the proportion of one half to three
fourths of the quantity equivalent to the caustic soda used in the preparation of
the solution. By this reaction thiosulphate (hyposulphite) of soda and other
colourless products are formed and a practically colourless solution results showing
none of the re-actions of sulphides.
The sulphurous acid may be added as such i.e. in aqueous solution or a con-
centrated solution of an alkaline bisulphite may be employed where it is necessary
to avoid undue dilution of the solution.
(3) Lastly the cellulose derivative itself may be precipitated by the addition of
brine; the precipitate washed with brine to further remove the alkaline salts
the washed precipitate then freed as far as possible from residual brine by pressing
or otherwise.
The purified product thus obtained has a greenish white colour and dissolves in
water to a nearly colorless solution having the properties of the original solution.
For special purposes alcohol may be employed as the precipitating agent, the
treatment being similar to that employed in the case of the brine. By this device
the alkaline by-products are much more completely removed and the final product
may be considered as the
pure cellulose derivative.
We would point out that although the reaction carried out upon the pure
cellulose and under the conditions above specified gives a product entirely soluble
in water. This is not the case with many of the raw fibrous material of the vegetable
kingdom and compound or mixed celluloses. These substances are likewise attacked
under the treatment and on treatment with water break up into a mixture of soluble
derivatives of the character already described and undissolved fibres or cells.
Thus esparto grass and straw when heated first with the strong alkali solution and
then exposed to carbon disulphide are completely disintegrated and the mass when
treated with water gives a thick pulp or magma consisting of dissolved cellulose
derivates and undissolved fibres and cells. This mixture is available for special
purposes.
It will be evident that the results herein described are similarly obtained with
the equivalent alkali, caustic potash, that is, under the joint action of this alkali
in strong aqueous solution and of carbon disulphide, cellulose is converted into a
derivative soluble in water.
The solution of cellulose resulting as it does from the simultaneous action of
alkali, water and carbon disulphide it is evident that the mode of applying these
reagents to the cellulose may be varied at will and according to circumstances.
Having now particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
The treatment of fibrous and cellular materials of the vegetable kingdom by the
means and for obtaining the results substantially as described.
D
L
Bahun 1893