Note: Descriptions are shown in the official language in which they were submitted.
- 1 - 13~9940
The present invention relates to a process for the
production of a bituminous binder modified with thermoplastic
synthetic material for use as a binding agent of a construction
material, especially a road building material, in which process
during the production of the binder melting-liquified bitumen,
together with a thermoplast or a thermoplast mixture, preferably
an olefin polymer, is subjected to a homogenization treatment.
A number of processes for the production of bituminous
binders of the aforementioned type are known by which an
improvement in properties is accomplished when ordinary bitumen is
combined with an added thermoplast or thermoplast mixture. Such
modifying of the bitumen often requires a relatively large expendi-
ture of labour because a number of different thermoplasts, the
addition of which to bitumen can improve its properties consider-
ably, are not readily soluble in bitumen. Although bitumens,
which have better solution properties in bitumens ! do exist !
these thermoplasts often are relatively expensive.
Moreover, construction materials produced with bitumens combined
with such soluble thermoplasts often have lower physical strength
than those construction materials whose binder is a bitumen
combined with the relatively non-soluble thermoplasts.
It is an objective of the present invention to provide a
process of the type mentioned above using relatively non-
soluble thermoplasts, e.g., polyethylene, which allows not only
the achievement of a rapid homogenization process, but also
yields a bituminous binder which presents clearly better
properties than like or similarly composed bituminous binders
which have been produced by known processes.
- 2 - 1339940
To accomplish this objective in the process of the present
invention a mix which contains molten bitumen together with a
thermoplast or a thermoplast mixture is subjected to a
homogenization treatment. During this homogenization treatment
there is fed in the form of kinetic energy to said mix an amount
of energy corresponding to at least the difference between the
treatment temperature and the disintegration temperature of the
thermoplast or thermoplast mixture, and said mix is braked
abruptly on an impact surface to form readily reacting molecular
fragments of said thermoplast or thermoplast mixture. The term
"treatment temperature" is defined as the temperature of the
mixture as macroscopically measured by conventional means. The
term ~disintegration temperature of the thermoplast~ is defined as
the temperature at which the molecules of the thermoplast
disintegrate into fragments. These fragments then enter into a
reaction with the bitumen, thereby forming new substances. These
fragments also amalgamate mutually.
By this procedure, by means of the process of the Present
invention, the above-mentioned objective can be met and it is
possible to produce binders comprising bitumen and modifying
thermoplasts or thermoplast mixtures in a relatively short time,
despite the fact that these thermoplasts or thermoplast mixtures
may be, per se, relatively insoluble in bitumens. Furthermore by
the inventive process by this modification additional improvements
in the properties of the binder may be achieved, for example, in
the adhesion of the binder to rock material and in the strength of
the construction materials prepared with such a binder.
In the accompanying drawings:
FIGURE 1 is an X-ray spectra of various substances; and
FIGURE 2 discloses sectional views of various substances.
1~399~~
It is well known in the art to feed mechanical energy to a
heated bitumen-thermoplast mix by more or less strongly thorough
mixing said mix in the highly heated state. However, all such
processes hitherto known have a disadvantage in that it has so far
been impossible to apportion correctly the total energy feed. This
leads in.the case of too low an ener~y feed to end products with
poor physical properties and in the case of too high an energy
feed to an unnecessary expenditure of energy or excessively severe
disintegration, especially of the bitumen, which leads likewise to
mechanically inferior products. By the teaching of the
present invention,it is possible to use the energy input into the
system with the greatest possible conservation of the material,
especially of the bitumen, and especially differentially and
concertedly for the desired regulated decomposition of the
thermoplast or thermoplast mixture contained in the mix.
The term mix is used here as an abbreviation of the term
binder mixture, which mixture contains bitumen and synthetic
thermoplastic material.
The preferred embodiment of the process of the invention
comprises driving the mix containing bitumen and a thermoplast or
a thermoplast mixture through a narrow gap, on the average having
a width less than 3 mm, and preferably a width less than 0.3 mm,
existing between two mixing tools. These tools stand opposite to
one another and rotate relatively to one another. Preferably these
tools are arranged coaxially. The working of the mix through this
gap is continued until a clear structural change in said mix is
ascertainable, for example from the X-ray spectrum lines of the
mix. Often it is advantageous to interrupt said working by pauses
after each gap run-through.
It should be understood that the data given above regarding
the width of the gap between the mixing tools are only average
values. The gap can also be interrupted by recesses, grooves or
- 4 - 133994~
the like. However, the greater spacing present due to the presence
of such recesses or grooves on the mixing tools is not to be taken
into account when determining the average gap width.
When the melting-liquified mix of bitumen and synthetic
thermoplastic material is driven through a narrow gap between two
mixing tools, preferably having a width of less than 0,3 mm, there
exists, besides the thermal influence, a special kinetic energy
stress on the mix which affects especially the thermoplast
component having a higher molecular mass or molecular weight than
the bitumen. In the decomposition of the molecules present in the
mix which occurs under these loads shorter molecule fragments
(that means molecule fragments having lower molecular masses or
molecular weights) originate which have a strong tendency to
mutual amalgamation. When such a mix, e.g. a mix of bitumen and
polyethylene, on the other hand is subjected to a combined thermal
and mechanical load by intensively ordinary stirring upon
completion of this treatment there is found a mere weakening or a
full disappearance of the spectral lines of the X-ray spectrum
which relate to the characteristic of the crystal structure of the
synthetic material constituent, assuming, of course, the treatment
has been continued long enough at the disintegration temperature
of the constituent or constituents.
In the examination of a mix driven according to the process
of the present invention through a gap of small width between
rotating mixing tools, there appear, however, clearly recognizable
X-ray spectrum lines which indicate the presence of a new crystal
type structure. Corresponding to this appearance of X-ray spectrum
lines, which indicate a crystal type structure, construction
materials that have been manufactured with a binder produced using
the process of the present invention have better mechanical
properties than those building materials that have been formed
with binders containing bitumen and thermoplastic synthetic
material that have been mixed only by intensively stirring while
in the molten state.
1~399~0
Moreover, there exists a further advantage of the
aforementioned inventive procedure, in which a mix of molten
bitumen and thermoplastic synthetic material is driven through a
narrow gap between rotating mixing tools. In this manner the
production of the bituminous binder modified with thermoplastic
synthetic material may be carried out in a clearly shorter time
than by intensively stirring such a mix. In addition, and this
being an important advantage, it is possible to work the
aforementioned synthetic thermoplastic material and bitumen mix at
a clearly lower mean temperature or treatment temperature than it
is possible using the known homogenizing of such a mix by
intensively stirring. It should be recognized that this is
possible due to the fact that, on the one hand, the synthetic
material molecules during the driving of the mix through the
narrow gap undergo a mechanical stretching and, on the other hand,
the particles of the thermoplastic synthetic material are heated
for a short time substantially higher than the bitumen by the
conversion of kinetic energy applied to the mix, this being due to
the synthetic's higher molecular mass or molecular weight. This
brief heating is sufficient to divide the molecules of the
thermoplastic synthetic material into highly reactive fragments.
Such fragments then combine into a partially crystalline
structure. This change is evidenced also upon comparing the X-ray
lines with respect to the state present before the driving through
of the mix through the gap, and those lines present after this
driving occured. Because said structure which is at least partly
crystalline arises in the bitumen said structure is also closely
interwoven with the bitumen.
The close interweaving of the thermoplast with the bitumen
can also be perceived from the behaviour of a binder produced
according to the invention in a relatively long-lasting hot
storage. A mix of the bitumen and thermoplast treated according to
the process of the invention upon illumination with light of the
visible wavelength range is visually homogeneous immediately after
its production, and shows upon illumination with ultraviolet light
a dense pattern of bright points or spots on a darker background.
- 6 - 1~39940
After hot storage for many hours at a temperature that is clearly
above the melting temperature of the thermoplast, the particles
previously visible as points or spots unite to form a bright cover
layer whose volume is about four to eight times the volume of the
thermoplast constituent of the mix. By simply brief stirring this
cover layer can be combined again with the remaining part of the
binder into a visually homogeneous substance. This behaviour
differs clearly from the behaviour of a homogenized product
obtained in known manner by long stirring of a molten mix of
bitumen and thermoplast. In such a product, after hot storage for
a number of hours, a bright cover layer is formed whose volume
corresponds approximately to the volume of the thermoplast
constituent of the mix, and for the rehomogenizing of the cover
layer with the main part of the material from which the cover
layer has separated, virtually the same stirring work is required
as has been expended in the first homogenizing stirring procedure.
The two mixing tools between which the aforementioned gap
lies, through which the mix intended for the formation of the
binder is driven, should rotate relatively to one another. This
can be accomplished simply by fixing one mixing tool and rotating
the other. It is also possible, however, for both mixing tools to
rotate, either in opposite turning directions or with the same
turning direction but at different speeds of revolution.
It is especially preferable if the mix containing the
bitumen and thermoplastic synthetic material is driven through a
gap between the mixing tools having an average width of about 0.1
mm or narrower. By this further development of the measure to
process the mix to be homogenized in a very narrow gap, it is
possible to further intensify the decomposition of the synthetic
material leading to the production of highly reactive molecule
fragments that show a special tendency to recrystallize. It has
been determined that it is possible to achieve this effect at
lower and lower mean temperatures of the mix by decreasing the gap
width. It is also advantageous to form the gap in such a way that
the mix in the gap is subjected to pressure built up by
13399~0
hyd~odynamic action.
- The decomposition of the synthetic material molecules and
the formation of the especially reactive fragments can be promoted
by the application of high centrifugal forces on the mix of
bitumen and thermoplastic synthetic material. Toward this end, it
is very favorable to impart to the mix a velocity of revolution as
high as possible and then to brake the mixture from this velocity
in a brief period of time. The promotion of the decomposition of
the synthetic material molecules can be explained in the following
manner. The synthetic material molecules, through their high
molecular mass or molecular weight, take on a high velocity under
the influence of the centrifugal forces. The transformed energy
arising during rapid braking, viewed energetically, corresponds to
attaining a very high temperature, which extremely favors the
molecular decomposition mentioned. These high velocities and the
energies or temperatures arising during the braking occur during
very short periods of time only, so that no disadvantageous
disintegration of the thermoplastic synthetic materials arises.
The bitumen does not experience, practically speaking, any adverse
effects corresponding to this brief period of high heating, this
being explainable in that the bitumen having a much lower
molecular mass or molecular weight than the thermoplastic
synthetic material present in the mix.
The kinetic energy of the molecules, which is given by the
mass and the square of the velocity, is proportional to the
absolute temperature of these molecules. There is produced, in the
aforementioned treatment of a mix in which molecules are present
whose molecular weights differ markedly, for example by a factor
of 20, with fully abrupt braking a difference in the temperature
rise that corresponds to this factor, the molecules with the lower
molecular mass or molecular weight undergoing a lesser and the
molecules with the higher molecular mass or molecular weight
undergoing a greater temperature increase.
- 8 - 1~39940
For the mentioned form of execution of the process of the
invention, in which the mix is driven through a gap it is
preferred that the mix be driven through a gap which extends
radially at least at the emergence edge between two coaxially
rotating mixing tools. An especially good result may be achieved
if the mix is abruptly braked on an impact surface in the gap
zone, preferably immediately after its emergence from the gap,
since in such a manner the high velocity imparted by centrifugal
force to the synthetic material molecules being transformed
particularly efficiently into a state corresponding to brief high
heating.
It is possible to carry out the treatment of the fusible mix
consisting of bitumen and thermoplastic synthetic material in an
atmosphere of protective gas or in vacuo.
The invention is further explained with the aid of examples
having supplementary references to the drawings.
E x a m p 1 e
A molten mix which consisted of 94 % wt. of bitumen B 100
and 6 % by weight of high density polyethylene was first lightly
stirred in a supply container. This mix was fed from the supply
container to a run-through mixing apparatus which had two discoid
mixing tools standing opposite one another in which the one mixing
tool was at a standstill and the other was turnably borne
coaxially to the first one and was connected to a driving means.
Both the standing mixing tool and the rotating mixing tool were
provided with ribs on sides facing one another. On the facing
sides of the two mixing tools there was a gap of about 0.1 mm
between the ribs of the one mixing tool and the ribs of the other
mixing tool through which the mix to be treated was driven. The
circumferential velocity of the rotating mixing tool at the outer
edge of the gap was about 30 m/s. Likewise, the flow velocity of
the mix through the gap was about 30 m/s. In the gap zone there
were provived impact surfaces, where the mix was braked abruptly.
- 9 - 1~39940
The mix was driven six times through the run-through mixing
apparatus, requiring about 20 minutes. The bituminous binder thus
obtained was mixed with a preheated rock material and rock meal
filler with a standardized composition for asphalt concrete 0-8.
Using the construction material thus obtained in standardized
procedure, Marshall test bodies were produced which were thereupon
examined for their mechanical properties. The measurement values
obtained are presented in column 1 of the Table.
E x a m p 1 e 2
A procedure analogous to that of Example 1 was followed.
However, the mix for the production of the binder consisted of
94 % by weight of bitumen B 100 and 6 % by weight of low density
polyethylene. The measurement values obtained are listed in column
2 of the Table.
E x a m p 1 e 3
A procedure analogous to Example 1 was followed. However,
the mix for the production of the binder consisted of 94 ~ by
weight of bitumen B 100 and 6 % by weight of ethylene-propylene-
diene copolymer. The measurement values obtained are listed in
column 3 of the Table.
E x a m p 1 e 4
A procedure analogous to Example 1 was followed. However,
the mix for the production of the binder consisted of 94 ~ by
weight of bitumen B 100 and 6 % by weight of styrene-butadiene-
styrene block polymer. The measurement values obtained are listed
in column 4 of the Table.
E x a m p 1 e 5
A procedure analogous to Example 1 was followed. However,
the mix for the production of the binder consisted of 94 ~ by
weight of bitumen B 100 and 2 % by weight of ethylene-propylene-
- lo - 1339~40
- diene copolymer and 4 % by weight of low density polyethylene. The
measurement values obtained are listed in column 5 of the Table.
,.
E x a m p 1 e 6
A procedure analogous to that of Example 1 was followed.
However, the mix for the production of the binder consisted of
94 % by weight of bitumen B 100 and 2 % by weight of ethylene-
propylene-diene copolymer and 4 % by weight of high density
polyethylene. The measurement values obtained are listed in column
6 of the Table.
E x a m p 1 e 7
The properties of the bitumen used in Examples 1 to 6 and
those of a construction material analogously produced with this
bitumen were examined. The measurement values obtained are listed
in column 7 of the Table.
E x a m p 1 e 8
The finished binder obtained according to Example 1 was
subjected while in a cooled state to an X-ray spectral
examination. A spectrum was obtained and this spectrum is
designated by letter a in FIG. 1. Further, a visually homogeneous
mix mixed by mere stirring and having the same composition such as
the mix according to Example 1 was subjected to the same X-ray
spectral examination while in a cooled state. A spectrum was
obtained and this spectrum is designated by letter in FIG. 1.
The polyethylene used in FIG. 1 was also subjected to this X-ray
spectral examination while in a cooled state. A spectrum was
obtained and this spectrum is designated by letter c in FIG. 1. It
is evident from these X-ray spectra that the strong spectral lines
which are present in the spectrum designated by letter c and which
are caused by the crystalline structure of the polyethylene no
longer appear in spectrum b. It follows therefrom that this mix of
bitumen and polyethylene which was mixed by mere stirring has
- 11 - 13~9~0
virtually no crystalline structure present in the cooled state. In
spectrum a there appear spectral lines which correspond to the
strong spectral lines of spectrum c coming from the crystalline
structure of the polyethylene. Therefrom it is concluded that the
binder produced according to Example 1 in the cooled state has at
least a partially crystalline structure that has arisen from the
molecule fragments of the polyethylene.
E x a m p l e 9
A sample of a binder was produced following the process of
the invention according to Example 2 from 94 ~ by weight of
bitumen B lO0 and 6 % by weight of low density polyethylene. This
binder was allowed to harden in a beaker, whereupon the body thus
obtained was split open vertically. The cleavage surface showed a
homogeneous appearance upon illumination with visible light. Upon
illumination with ultraviolet light a dense pattern of uniformly
distributed bright points on a darker background was visible. A
figure of this cleavage surface is designated by letter a in FIG.
2. A further sample of this binder was stored for 24 hours at
160~C. in a beaker and was then allowed to cool in this beaker,
whereupon the body that had thus arisen was split open. Upon
illumination with ultraviolet light there was recognizable a
bright layer which occupied approximately a third of this body
which has been the upper one third in the preceding storage, and
the remaining two-thirds of the body lying under it had a dark
color. A figure of the cleavage surface of this body is designated
by the letter b in FIG. 2. This body was then remelted and this
melt was throughly stirred at about 170~C., the melt after a few
minutes achieving a fully homogeneous appearance.
E x a m p l e 10
A mix was formed of the substances used in Example 2 having
a composition of 94 ~ by weightof bitumen B 100 and 6 % by weight
of low density polyethylene. This mix was stirred for 1 - 1/2
hours at 2800C. to form a homogeneous product. A sample of this
- 12 - 13 393 4a
product was then stored for 24 hours at 160~C. in a beaker and
then allowed to cool, after which the body that had thus formed
was split open. Upon illumination with ultraviolet light a bright
layer was recognizable which had in its volume approximately the
volume of the polyethylene constituent of the product and which
was located on that side of the body that has been the upper side
in the preceding storage. An illustration of the cleavage surface
of this body is designated by letter c in FIG 2. Then this body
was melted and the melt thus obtained was thoroughly stirred again
at about 280OC. Said stirring had to be continued for over one
hour in order to achieve a fully homogeneous appearance of the
melt.
13- 1~3994~
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