Improved Process of Devulcanizing Vulcanized India Rubber, Gutta Percha, and similar Gums, and Reclaiming the Rubber therefrom for Remanufacture without the Addition of Pure Rubber.
Year: 1891

page_text: Date of Application, 20th June, 1891-Accepted, 22nd Aug. 1691
Improved Process of Devulcanizing Vulcanized India Rubber, Gutta
Percha, and similar Gums, and Reclaiming the Rubber therefrom
for Remanufacture without the Addition of Pure Rubber.
I ALFRED FRANCIS BILDERBECK GOMESS of 244 Alfred Place West South
Kensington in the County of Middlesex Gentleman 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:-
It is well known that vulcanized rubber gutta percha and similar gums cannot
be remanufactured without the addition of pure rubber and even then the products
are of a very inferior character.
Now the object of this invention is to treat vulcanized rubber gutta percha and
similar gums in such a way as not only to devulcanize the same but to reclaim the
rubber therefrom in such a state as to render it capable of being remanufactured
into articles without the addition of fresh rubber.
According to this invention the vulcanized caoutchouc is first ground so as to
facilitate the action of chemicals upon it.
Taking by way of example vulcanized rubber which is not very old or in which
the oxidising process (all kinds of rubber being very liable to this) has not advanced
to any extent I proceed as follows:-
The free or uncombined sulphur is removed by boiling the ground rubber in a
solution of a carbonate sulphite or hydrate of an alkali.
The rubber is well washed and placed in a suitable vessel with dilute sulphuric
acid or I may use dilute hydrochloric acid but I prefer using dilute sulphuric acid
and iron containing a large amount of combined carbon such as white cast iron
spiegel or specular pig iron the acid being sufficient to cover the rubber and if
necessary a perforated diaphragm made of suitable material placed over so as to
keep the rubber under the acid. A. brisk chemical action ensues with disengagement
if nascent hydrogen and the formation if protosulphate of iron hydrocarbons
paraflins &c.
If the iron is in the form of borings or filings the acid should be
sufficient to completely dissolve it for in the form of borings or filings the excess of
iron might cling to the rubber but if the iron be in the form of sheets or large pieces
the iron may be in excess.
It is then allowed to remain in a dark place until the chemical action has ceased
when the rubber will be found not only to be deoxidized and reduced but to have
undergone certain changes. It is removed allowed to drain and gently washed
boiled for 3 or 4 hours in a solution of caustic alkali (the strength varying with the
kind of rubber under treatment) then removed well washed and pressed and the
operation last described repeated.
If now the solution (in which the rubber is last boiled on being tested) contains
sulphur in any form iz. sulphide hyposulphite &c. the operation is again repeated
until the solution is free from that element. The rubber is then well washed
pressed and dried subjected to the action of carbon bisulphide naptha and rectified
oil (spirits of turpentine) in varying proportion (the proportions I have found
answer well in practice are 1 part turpentine 2 parts bisulphide of carbon and about
8 to 10 parts of naptha) either in a form of vapour or by mixing in a masticator
when these have nearly volatilized the rubber is heated in a dry heat in a suitable
apparatus to a temperature not exceeding 120 C. until it begins to acquire its
cohesive state then mixed in a masticator and subsequently spread out in thin
layers.
If however the rubber is very old or the process of oxidation has advanced very

page_text: far I prefer to begin with the process of deoxidation substantially as herein
described.
In some cases it may be found necessary to repeat either a part or the whole of
the process.
Instead of using the above named solvents I may use any of the
series Cu H4 or I may use any of the homologues of benzine for example
toluene methylbenzine or phenyl methane (CH, CH₂) or sulphide of phenyl.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
-
1. In the process of devulcanizing vulcanized india rubber gutta percha and
similar gums and reclaiming the rubber therefrom for remanufacture without the
addition of pure rubber the boiling in caustic alkali after the treatment with dilute
sulphuric acid and iron containing a large amount of combined carbon substantially
as herein described.
11. The subsequent treatment by the hereinbefore mentioned solvents in the
manner herein described after the treatment as set forth in Claim I.
11. The process as hereinbefore described of devulcanizing vulcanized india
rubber gutta percha and similar gums and reclaiming the rubber therefrom for
remanufacture without the addition of pure rubber.
Dated this 20th day of June 1891.
BROWNE & Co.,
60, Chancery Lane, Agents for Applicant.