IMPROVEMENTS IN RECOVERING RUBBER FROM RUBBER WASTE
Year: 1881

page_text: LETTERS PATENT to Charles Aubrey Day, of 95, Navarino Road, Dalston
Rise, in the County of Middlesex, Patent Agent, for an Invention of
A com-
"IMPROVEMENTS IN RECOVERING RUBBER FROM RUBBER WASTE."
munication from abroad by Nathaniel Chapman Mitchell, of Philadelphia,
Pennsylvania, in the United States of America.
PROVISIONAL SPECIFICATION left by the said Charles Aubrey Day at the
Office of the Commissioners of Patents on the 17th November 1881.
CHARLES AUBREY DAY, of 95, Navarino Road, Dalston Rise, in the County of
Middlesex, Patent Agent. "IMPROVEMENTS IN RECOVERING RUBBER FROM RUBBER
WASTE." (A communication from abroad by Nathaniel Chapman Mitchell, of
Philadelphia, Pennsylvania, in the United States of America.)
The object of this Invention is to effect the thorough and economical recovery of
rubber, whether raw or vulcanized, from rubber waste.
In the manufacture of many articles, such as wearing apparel, overshoes, belting,
hose, packing, and other such articles, rubber, or the compound of which rubber
forms a part, is usually combined with fibrous or textile material, such as woollen
or cotton cloth, the rubber or rubber compound being generally applied to the
cloth in the form of a coating, and the rubber being sometimes raw or sun-cured,
and sometimes vulcanized.
Many attempts have heretofore been made to recover the rubber or rubber
compounds from the scraps or cuttings resulting from the manufacture of rubber
goods, or from the goods themselves after they have become so worn as to be no
longer available for the purposes for which they were intended.
Amongst the plans hitherto proposed may be mentioned the subjecting of the
scraps or waste to the action of boiling water or steam, or to heated solutions of
caustic alkali or diluted sulphuric acid; but all of these processes have been so far
from practical that the waste is generally considered as having but slight value.
The inventor of the present improvements has ascertained that the rubber in
the waste will effectually resist the action of strong sulphuric or muriatic acid'

page_text: heated to a high temperature, but that the textile material will yield to the
corrosive influence of the acid, the zinc and whiting with which the rubber is
usually combined also yielding to the acid, thus leaving the rubber in the condition
of a practically pure and marketable article.
The following is a descriptien of a convenient arrangement of apparatus suitable
for carrying out the present Invention.
The apparatus is constructed with a tank having detachable covers, both the
tank and covers being lined with lead to resist the action of the acid. In the
bottom of the tank is a perforated pipe having suitable perforated branches, and
provided at one end with a vertical branch which passes through an opening in one
of the covers, and is connected to a supply pipe by means of a section of rubber
tubing, which can be readily detached from the vertical branch pipe when it is
desired to remove the covers in order to gain access to the inside of the tank.
The apparatus is provided with a vapor discharge pipe, one section of which is
carried by one of the covers of the tank, and is connected to a fixed section by
means of a sliding section which can be elevated when it is desired to disconnect
the first mentioned section from the fixed section of the pipe. A leaden plate
serves as a valve or damper to control the flow of vapor through the vapor discharge
pipe.
In carrying out the Invention the acid is deposited in the bottom of the tank,
and the waste is then introduced into the tank, after which the covers are applied,
and steam under pressure of from fifty (50) to seventy-five (75) pounds is permitted
to pass through the perforated pipe and its branclies, the steam escaping from the
perforations and imparting a high degree of heat to the acid.
The treatment is continued for from one to five hours in accordance with the
character of the material, and the thick pasty mass which results from the treatinent
is then removed from the tank and subjected to the action of a washing machine,
the effect of which is to separate and carry off the sulphuric acid and impurities,
leaving the rubber in a pure or almost pure condition. The recovered rubber is
subsequently dried and passed between rolls or mullers, whereby it is kneaded into
a compact homogeneous mass ready for the market.
The strength of the acid and the quantity employed in respect to the quantity of
material treated will depend upon the proportion of fibre in the waste. In practice,
acid of a strength of 66° Baumé is used, employing for every thousand pounds of
waste from 300 to 500 pounds of sulphuric acid, or from 400 to 750 pounds of
muriatic acid. When the rubber is combined with woollen fabric having long
fibres of extra strength, the inventor sometimes adds to the sulphuric or muriatic
acid about one-twentieth part of its weight of fluoric acid to facilitate the
operation.
So far as the vegetable fibres are concerned, they are entirely eliminated by the
corroding action of either the sulphuric or muriatic acid; but the zinc and whiting
with which the rubber is usually combined are differently affected by the two acids,
the sulphuric acid forming comparatively insoluble sulphates of zinc and calcium
which inust afterwards be removed from the mass by washing, whereas the muriatic
acid unites with the zinc and whiting to form soluble chlorides of zinc and calcium
which are afterwards more easily removed, so that while the use of sulphuric acid
is preferable on the score of economy, muriatic acid is preferred when it is desired
to recover the rubber in a state as nearly pure as possible.
When the material to be treated is in the form of closely cemented lumps which
cannot be easily broken up, the inventor introduces into the tank with the acid a
quantity of. benzine, say, from one to two gallons for each thousand pounds of
waste. On the application of steam this benzine is vaporized, the vapors permeating
every part of the mass in the tank, and exercising a softening or disintegrating
effect on the mass, so as to facilitate the subsequent action of the acid thereon.
A valve in the vapor discharge pipe is kept closed until the vaporization of the
benzine is effected, the valve being then opened and the vapors allowed to escape.
In some cases the acid may be heated by other means than the direct injection

page_text: of steam into the mass, but the latter method is much to be preferred, as the steam
bas a tendency to penetrate every portion of the mass, and induces the acid to
follow it. The joint action of the steam and acid is especially to be preferred when
the rubber is combined with woollen fibres, as this is by far the most effective
means which the inventor has as yet discovered of destroying the said fibres.
When the rubber contains but about one or two per cent. of sulphur, the latter
will be practically eliminated by the treatment above set forth; but when a larger
percentage of sulphur is present the rubber substantially retains its vulcanized
character, the effect of the acid treatment being mainly to eliminate the fibrous
portions of the waste.
When the perforated pipe and its branches become choked with rubber, the
perforations can be readily cleaned by filling the pipe with benzine, and allowing
the latter to remain in the pipe for a time prior to making the steam connection.
The present Invention is distinct from the plan which has been proposed of
treating the waste with exceedingly diluted acid, as the latter can have no
appreciable corroding effect in removing the fibre or impurities with which the
rubber may be combined, whereas strong sulphuric or muriatic acid completely
eliminates the fibres, and so frees and changes the character of the impurities as
herein before set forth, that they can be readily removed by subsequent washing.
There is no appreciable dilution of the acid by condensed steam in the apparatus
herein before described, as the contents of the tank are maintained at a high
temperature, and the steam or vapor as it rises above the mass in the tank passes
through the draft tube, so that the accumulation of water due to condensation of
the steam is very alight.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Charles Aubrey Day in the Great Seal Patent Office on the
16th May 1882.
CHARLES AUBREY DAY, of 95, Navarino Road, Dalston Rise, in the County of
Middlesex, Patent Agent. IMPROVEMENTS IN RECOVERING RUBBER FROM RUBBER-
WASTE." (A communication from abroad by Nathaniel Chapman Mitchell, of
Philadelphia, Pennsylvania, in the United States of America.)
The object of this Invention is to effect the thorough and economical recovery of
rubber, whether raw or vulcanized, from rubber waste.
In the manufacture of many articles, such as, for example, wearing apparel,
overshoes, belting, hose, and packing, rubber, or the compound of which rubber
forms a part, is usually combined with fibrous or textile material, such as woollen
or cotton cloth, the rubber or rubber compound being generally applied to the cloth
in the form of a coating, and the rubber being sometimes raw or sun-cured, and
sometimes vulcanized.
Many attempts have heretofore been made to recover the rubber or rubber.
compounds from the scraps or cuttings resulting from the manufacture of rubber,
goods, or from the goods themselves after they have become so worn as to be no
longer available for the purposes.for_which they were intended.-
Amongst the plans hitherto proposed may be mentioned the subjecting of the
scraps or waste to the action of boiling water or steam, or to heated solutions of
caustic alkali or diluted sulphuric acid, but all of these processes have been so
far from practical that the waste is generally considered as having but slight
value.
The inventor of the present improvements has ascertained that the rubber in
the waste will effectually resist the action of strong sulphuric or muriatic acid
heated to a high temperature, but that the textile material will yield to the corrosive
influence of the aid, the zine and whiting with which the rubber is usually
combined also yielding to the acid, thus leaving the rubber in the condition of a
practically pure and marketable article.
The accompanying Drawing illu-trates a convenient arrangement of apparatus
suitable for carrying out the present Invention, although the practice of the
Invention is not limited to the use of this particular apparatus.
1 represents a tank having detachable covers 2, both the tank and covers being
lined with lead (as shown by the thick inner line) to resist the action of the acid.
In the bottom of the tank is a perforated pipe 3 having suitable perforated branches,
and provided at one end with a vertical branch 4 which passes through an opening
in one of the covers 2 and is connected to a supply pipe 5 by means of a section of
rubber tubing 6 which can be readily detached from the pipe 4 when it is desired
to remove the covers in order to gain access to the inside of the tank. 7 represents
a vapor discharge pipe, the lower section 8 of which is carried by one of the covers
of the tank, and is connected to an upper fixed section 9 by means of a sliding
section 10 which can be elevated when it is desired to disconnect the section 8
from the section 9. A leaden plate 11 serves as a valve or damper to control the
flow of vapour through the pipe 7.
In carrying out the Invention the acid is deposited in the bottom of the tank 1,
and the waste is then introduced into the tank, after which the covers 2 are applied,
and steam under pressure of from, say, about fifty, to, say, about seventy-five pounds
is permitted to pass through the pipe 3 and its branches, the steam escaping from
the perforations and imparting a high degree of heat to the acid.
•

page_text: The treatment is continued for from one to five hours in accordance with tho
character of the material, and the thick pasty mass which results from the
treatment is then removed from the tank and subjected to the action of a washing
machine, the effect of which is to separate and carry off the sulphuric acid and
impurities leaving the rubber in a pure or almost pure condition. The recovered
rubber is subsequently dried and passed between rolls or mullers, whereby it is
kneaded into a compact homogeneous mass ready for the market.
The strength of the acid and the quantity employed in respect of the quantity
of material treated will depend upon the proportion of fibre in the waste. In
practice, acid of a strength of 66° Baumé is used, employing for every one
thousand pounds of waste from 300 to 500 pounds of sulphuric acid, or from
400 to 750 pounds of muriatic acid. When the rubber is combined with woollen
fabric having long fibres of extra strength, the inventor sometimes adds to the
sulphuric or muriatic acid about one twentieth part of its weight of fluoric acid
to facilitate the operation.
So far as the vegetable fibres are concerned, they are entirely eliminated by the
corroding action of either the sulphuric or muriatic acid, but the zinc and whiting
with which the rubber is usually combined are differently affected by the two
acids, the sulphuric acid forming comparatively insoluble sulphates of zinc and
calcium, which must afterwards be removed from the mass by washing, whereas
the muriatic acid unites with the zinc and whiting to form soluble chlorides of
zinc and calcium, which are afterwards more easily removed, so that while the
use of sulphuric acid is preferable on the score of economy, muriatic acid is
preferred when it is desired to recover the rubber in a state as nearly pure as
possible.
When the material to be treated is in the form of closely cemented lumps, which
cannot be easily broken up, the Inventor introduces into the tank with the acid a
quantity of benzine, say, from one to two gallons for each thousand pounds of
waste. On the application of steam this benzine is vaporized, the vapors per-
meating every part of the mass in the tank and exercising a softening or
disintegrating effect on the mass, so as to facilitate the subsequent action of the
acid thereon.
The valve 11 in the pipe 7 should be kept closed until the vaporization of
the benzine is effected, the valve being then opened and the vapors allowed to
escape.
The acid may be heated by other means than the direct injection of steam into
the mass, but the latter method is much to be preferred, as the steam has a
tendency to penetrate every portion of the mass and induces the acid to follow it.
The joint action of the steam and acid is especially to be preferred when the
rubber is combined with woollen fibres, this being the most effective means of
destroying the said fibres.
When the rubber contains but about one or two per cent. of sulphur, the latter
will be practically eliminated by the treatment herein before described; but when
a larger percentage of sulphur is present the rubber substantially retains its
vulcanized character, the effect of the acid treatment being mainly to eliminate
the fibrous portions of the waste.
When the perforated pipe 3 and its branches become choked with rubber, the
perforations can be readily cleaned by filling the pipe with benzine and allowing
the latter to remain in the pipe for a time prior to making the steam connection.
The present Invention is distinct from the plan which has been proposed of
treating the waste with exceedingly diluted acid, as the latter can have no
appreciable corroding effect in removing the fibre or impurities with which the
rubber may be combined, whereas strong sulphuric or muriatic acid completely
eliminates the fibres, and so frees and changes the character of the impurities, as
hereinbefore set forth, but they can be readily removed by subsequent washing.
There is no appreciable dilution of the acid by condensed steam in the apparatus
hereinbefore described, as the contents of the tank are maintained at a high

page_text: temperature, and the steam or vapor as it rises above the mass in the tank passes
through the draft tube 7, so that the accumulation of water due to condensation
of the steam is very slight.
Having now described the nature and object of the said Invention, together
with the manner in which the same is to be or may be performed or carried into
practical effect, I would remark in conclusion that I claim as the Invention
communicated to me by the above named Nathaniel Chapman Mitchell, —
1st. The mode hereinbefore described of recovering rubber from rubber waste
by subjecting the waste to the action of heated sulphuric or muriatic acid,
substantially as described.
2nd. The mode hereinhefore described of recovering rubber from rubber waste,
by subjecting the waste to the action of strong sulphuric or muriatic acid in
connection with that of steam, by injecting the steam into the mass of acid and
waste, substantially as described.
3rd. The mode herein before described of recovering rubber from rubber waste
by first subjecting the mass of waste to the action of hydrocarbon vapor, and then
to the action of strong sulphuric or muriatic acid heated to a high temperature,
substantially as described.
In witness whereof, I, the said Charles Aubrey Day, have hereunto set my
hand and seal, this 15th day of May, in the year of our Lord One thousand
eight hundred and eighty two.
CHARLES AUBREY DAY. (L.S.)