Improvements in Reclaiming Rubber.
Year: 1898

page_text: Date of Application, 22nd Mar., 1898-Accepted, 23rd Apr., 1898
Improvements in Reclaiming Rubber.
I, PERCY LEMON CLARK, of 1410 Marquette Building, in the City of Chicago,
County of Cook, State of Illinois, and United States of America, Rubber Manufacturer,
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:
The purpose of this invention is to deprive vulcanized rubber of its vulcanized
character and adapt it for re-moulding or other re-shaping and for vulcanizing in
new form.
By experiment, I have ascertained that the essential conditions for the attainment
of this purpose are the following:-First, the employment of a solvent of rubber
and sulphur whose boiling or vaporizing point is lower than the point at which rubber
is disorganized by heat, which is commonly spoken of as the melting point, and which
with different grades of rubber varies from a point somewhat below 150° Centigrade,
to a point several degrees above 150° Centigrade; second, soaking the vulcanized
rubber thoroughly in such solyent; third, maintaining the rubber in a soaked or
approximately saturated condition while exposing it to heat sufficient to vaporize the
solvent; fourth, avoiding a degree of heat sufficient to disorganize the rubber.
The best method which I have found for practising this invention consists in first
soaking the rubber thoroughly in such a solvent as gasoline, benzine or any common
grade of naphtha, though I have used kerosene in connection with the more volatile
of those oils. The rubber thus soaked I place in a chamber containing a similar
solvent, gasoline being most convenient and satisfactory, the rubber being not placed
in the liquid, but in a position where it will be exposed to the vapor which will result
from heating the liquid. The chamber being tightly closed and heat being applied,
vapor of the solvent
produced and pressure developed therein, the air originally
contained in the chamber being permitted to escape after vapor is formed, so that the
latter, substantially free from air, envelopes the rubber. The quantity of liquid
solvent placed in the chamber should preferably be such, relative to the size of the
latter, that considerable pressure may be developed by a temperature below the dis-
organizing point of rubber. The exposure of the saturated rubber in the vapor of the
solvent at a temperature which, in my experiments, has varied from 95° to 150°
Centigrade, but sometimes a little higher, for a period of time which has varied from
one hour to three hours, and with an indicated pressure of vapor ranging from slight
pressure up to one hundred pounds per square inch, results in reducing the rubber
to a condition in which it can be re-massed together and re-worked and vulcanized in
any form, substantially as new rubber. Although the rubber is thus apparently
devulcanized, no considerable loss of sulphur occurs in the process, and re-vulcaniza-
tion may usually be effected perfectly without the addition of any sulphur. The
apparatus which I have used is illustrated in the drawing, which is an axial section
through two chambers which comprise it. A is a chamber to which a proper solvent
may be supplied through a pipe A¹ controlled by a valve A². This chamber is
enclosed in a steam jacket B, through which steam for heating is supplied through a
pipe B controlled by the valve B². B³ is a drain-cock for the water of condensation.

page_text: The chamber A has connected with it a thermometer C adapted for indicating the
interior temperature, that is, the temperature of the vaporized:solvent.
E is a
pressure gauge connected with the vapor-chamber. At the center of the top is a
hand-hole provided with a tight cover A+, and within the chamber adapted to be
inserted through the hand-hole and suitably suspended is a wire cage F, to contain
the rubber articles to be treated, which are illustrated as suspended or lying on wire
shelves therein. From the upper end of the chamber, a pipe G, controlled by a
valve G2, leads to a condensing coil G¹, which drains into a receptacle J. The coil is
enclosed in a chamber H, which is supplied with water through a pipe H³, which
drains out through a waste-pipe H2, and in thus circulating, cools the coil and con-
denses the vapor of the solvent which is collected in the receptacle J, thus preventing
any considerable waste. Any vessel answers for the preliminary soaking of the rubber
in the solvent, and none is illustrated. The length of time necessary to soak it
varies somewhat with the quality of the rubber. The visible effect of soaking with
solvent is to swell the rubber, and when the swelling ceases, the rubber is sufficiently
saturated.
The quantity of a given solvent necessary in a given sized chamber to develop the
most desirable degree of pressure at the most desirable temperature may be
ascertained by a little experiment by the operator. As above stated, the solvent
must be one having a vaporizing point (at atmospheric pressure) lower than the
melting or disorganizing point of rubber, that is to say, not much exceeding
150° Centigrade, and I have found that at a given temperature, the greater the
pressure, the more rapid the process. It is therefore desirable to employ a solvent
whose vaporizing point considerably below 150° Centigrade, so that considerable
pressure may be developed before reaching the limit of temperature. Commercial
gasoline, in quantity equal to say one-seventh of the capacity of the chamber, I have
found yielding a pressure of 70 to 75 pounds per square inch at temperature of
150° Centigrade. With a larger quantity in the same chamber, a greater pressure
would be obtained at a lower temperature. The time necessary with a given solvent
at a given temperature and a given pressure, varying somewhat with different
qualities of rubber, may be determined for each quality by a little experiment.
But
so long as the temperature does not exceed the disorganizing point of rubber, the
exposure may continue for some length of time after the result is accomplished,
without injury, and the ascertainment of exact time necessary is desirable only to
economize time and heat. I have found, moreover, that, with a given solvent and a
given quality of rubber and given average temperature the product of the time by
the pressure is substantially constant, but that other conditions being constant, the
product of the time by the temperature exhibits wide variation, so that while the
time varies inversely as the pressure, no definite relation can be predicated between
the time and the temperature, except that, in general, increase of average temperature
shortens the time somewhat.
To afford guidance in the practice of the invention, the details of certain successful
experiments are given, as follows:-
Experiment A -Pure rubber vulcanized in a chamber one-seventh filled with
gasoline, at an average temperature of 850 Centigrade (maximum temperature,
106° Cent.) at an average pressure of 54 lbs., was found devulcanized at the end of
1 hour and 7 minutes.
Experiment B:-Pure rubber in the same chamber with the same quantity of
gasoline at an average teinperature of 123° Cent., (maximum temperature, 137° Cent.)
at an average pressure of 42 lbs., was found devulcanized at the end of 1 hour and 30
ninutes.
Experiment C-Mechanical rubber, composed of about one-third pure rubber and
one-half shoddy rubber, and the remainder earthy material and oils, in the same
chamber one-sixth filled with gasoline, with an average temperature of 108 Cent.
(maximum temperature, 130° Cent.) average pressure, 48 lbs., was found devulcanized
at the end of 2 hours and 23 minutes.

page_text: Experiment D-In the same chamber one seventh filled with gasoline, rubber of
the same character as in Experiment C, exposed to an average temperature of 102°
Centigrade (maximum temperature, 113° Cent.), at an average pressure of 65 lb. was
found devulcanized at the end of 1 hour and 50 minutes.
I conclude from all my experiments: -That it is important to retain the solvent in
the interstices of the rubber, and thus to maintain the substantially saturated condition
of the rubber during treatment; that this is effected notwithstanding the temperature
is adequate to vaporize the saturated solvent, when such vaporization takes place
under pressure of the vapor of a solvent; and that the result obtained is due to the
intimate association of the solvent vapor with the molecules of the rubber, which is
not injured by the temperature necessary to such vaporization, but which, although
probably more susceptible to the action of the solvent at higher than at lower tem-
perature, is more affected in a manner tending to devulcanize it by the intimacy of
association of the solvent with it due to the pressure, than it is by the mere increase
of temperature.
I do not limit myself strictly to any of the specific details mentioned, nor to the
use of the apparatus described.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The process of devulcanizing rubber, which consists in first thoroughly soaking
the rubber with a solvent of rubber and sulphur whose vaporizing point is below the
melting or disorganizing point of rubber, and maintaining it in such saturated con-
dition while heating it in a vapor of such solvent, to a temperature adequate to
vaporize the saturating solvent, but lower than the melting or disorganizing point of
rubber, until the rubber is devulcanized.
2. The process of devulcanizing rubber, which consists in saturating it with a solvent
of rubber and sulphur adapted to vaporize at a temperature below the melting or
disorganizing point of rubber, and maintaining it in such saturated condition by the
pressure of vapor of such solvent while heating it in such vapor, to a temperature
adequate to maintain the pressure therein, but lower than the melting or disorganizing
point of rubber, until devulcanization is effected and the rubber is in condition to be
inassed.