Note: Descriptions are shown in the official language in which they were submitted.
CA 02310645 2000-OS-18
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TITLE OF THE INVENTION
BITT7MINOUS COMPOSITIONS PREPARED WITH PROCESS
TREATED VOLCANIZED RUBBERS
FIELD OF THE INVENTION
The present invention relates to a process for
digesting ground rubber vulcanizate into bitumen to
form a rubberized bitumen concentrate whereby the
concentrates may be used on their own or for blending
with various types and grades of bitumen and polymeric
additives to prepare rubber and/or plastics stabilized
bituminous compositions for diverse asphalt
applications.
REFERENCES TO RELATED APPLICATION
This application is a continuation-in-part of
United States Patent Application No. 08/964,874 filed
December 29, 1993.
BACKGROUND TO THE INVENTION
It is well known that many desirable
characteristics of bitumen can be improved by combining
with it certain polymeric materials, especially
elastomeric materials. For example, European Patent
Publication No. 317,025 to Shell International Research
disclosed a bitumen composition useful in road paving
applications containing an asymmetric radial block
copolymer which exr~ibits increased toughness and
tenacity. PCT Publication No. WO 90/02776 to Elf
Aquitaine, disclosed a rubberized bituminous
composition which was modified through in-situ
vulcanization of a copolymer of styrene and a
conjugated diene with a coupling agent, such as sulfur.
The incorporation of crumb rubber from recycled
automobile and other tires into bitumen or asphalt is
CA 02310645 2000-OS-18
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2
desirable in view of the potentially improved
properties of composition attained thereby and the
recycle of scrap rubber achieved thereby.
Scrap crumb rubber represents a significant source
5 of rubber vulcanates, which contain a variety of rubber
polymers, predominantly styrene-butadiene rubber. Crumb
rubber generally is recycled rubber that has been
reduced to ground or particulate form by mechanical
shearing or grinding. It has been proposed that scrap
10 crumb rubber be incorporated into asphalt paving
materials. In general, crumb rubber is blended into
asphalt paving materials by one of two processes,
namely a wet process or a dry process.
In the dry process, the rubber crumb is added to
15 the heated aggregate, not the asphalt cement, or to the
hot mix asphalt mixture during production of the mix.
In such dry mix processes, beneficial chemical changes
to the asphalt binder, such as bond-cleavage or
stabilization of additives, are extremely unlikely.
20 In wet processes, on the other hand, beneficial
changes to the properties of the binder, such as those
disclosed in the present invention, can be readily
achieved by the appropriate blending of additives,
usually polymers. In practice, the crumb rubber is
25 blended into the asphalt cement, by batch blending in
which batches of crumb rubber and asphalt are mixed in
production, by continuous blending with a continuous
production system, br by terminal blending. An asphalt
cement binder that has been modified with crumb rubber
30 is termed asphalt rubber.
In one wet procedure in which polymers are used,
hot asphalt (about 190° to 220°C) is mixed with
approximately 25 to 30 wto crumb rubber and the mixture
then is diluted with kerosene. A variation of this
CA 02310645 2000-OS-18
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3
procedure uses about 22 wt% crumb rubber with dilution
being effected using extender oil. It is thought that
blending the crumb rubber and asphalt at elevated
temperature may promote limited chemical bonding of the
5 components. However, these compositions exhibit only
short-term stability and, therefore, must be employed
shortly after formation.
A recent variation of the wet process is described
in US Patent No. 4,992,492. The process involves a
10 mixture of asphalt or sulfur-treated asphalt (81 to
86~), crumb rubber (8 to l0a), extender oil (4 to 6°s)
and a high molecular weight (>100,000) olefinically-
unsaturated synthetic rubber (2 to 3~) which is blended
together at 175° to 180°C for about two hours.
15 As claimed, this process differs from the present
invention in a number of important facets. In the
referenced process, the ground crumb rubber is
dispersed in the bitumen, however, the vulcanizate
network undergoes limited, if any, chemical
20 disassociation. Such crumb rubber compositions would be
unstable without the incorporation of the claimed high
MW (> 100,00) olefinically-unsaturated synthetic
rubber. The high MW free solvated synthetic rubber
chains likely act to minimize changes in viscosity and
25 softening point over periods of up to 10 days in a
"hermetically-sealed vessel without agitation at 160°C
to 165°C" to promote stability. Other variations of the
wet process are described in WO 95/20623 and EP
439,232.
30 In WO 93/17076, ground rubber particles are
heavily oxidized, particularly at the surface of the
particles, with air injected under pressure at a high
temperature (220°C to 260°C) , in a procedure similar to
that employed conventionally for producing an oxidized
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4
or "blown" asphalt for roofing-grade asphalt. Such
treatment of the fine rubber particles in situ improves
desired rubber di~spersibility and compatibility, but
also may imparts undesirable brittleness to the asphalt
5 matrix.
SU1~1ARY OF T8E INVENTION
The present invention relates to a process for
digesting (or "devulcanizing") ground rubber
vulcanizate particles into bitumen to form a rubberized
10 bitumen concentrate and also relates to the use of the
concentrate to blend with various types and grades of
bitumen and polymeric additives to prepare rubber
and/or plastic modified bituminous compositions for
diverse bituminous applications in the paving, roofing,
15 coating, waterproofing and industrial product markets.
The invention includes the rubberized bituminous
compositions which result from the process.
According to one aspect of the present invention,
there is provided a stable rubberized bitumen
20 concentrate, comprising bitumen, and dissociated rubber
vulcanizate network comprising at least about 15 wt% of
said composition and incorporated into the bitumen to
the extent that rubber particles in the composition do
not sediment as determined by the Polymer Separation
25 Test and upon dilution by bitumen to a lower
concentration of dissociated rubber vulcanate network.
The Polymer Separation test is described below.
The rubber vulcanate network may comprise at least
' about 5 wt~, preferably at least about 20 wt%. of the
30 composition and up to 50 wto or higher. The
concentrate may be diluted by bitumen to a lower
concentration of dissociated rubber vulcanate network
for utilization at much lower concentration.
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wo ~mo~s pc~ricA9s~o~o~8
The present invention provides, in a further
aspect thereof, a bituminous composition and a
concentrate as provided herein as a modifier of the
bitumen. The modifier may be an independent modifier
5 of the bitumen or may be a co-modifier with at least
one additional polymer. Such polymer may be a homo-
polymer or copolymer, including as follows:
- styrenic copolymers, such as styrene-butadiene
rubber (SBR), styrene-butadiene-styrene block
10 copolymers (SBS), styrene-ethylene-butadiene-
styrene block copolymers (SEBS) and styrene-
isoprene-styrene block copolymers (SIS);
- olefinic copolymers, such as polypropylene
copolymers, ethylene-vinyl acetate copolymers
15 (EVA), ethylene methylacrate copolymers (EMA) and
ethylene propylene diene copolymers (EPDM).
- other polymers, such as nitrile-butadiene rubber
(NBR), polyvinylchloride (PVC), polyisobutene, and
polybutadiene (PB).
20 Mixtures of two or more of such polymers may be
incorporated into the bituminous composition along with
the concentrate.
In an additional aspect of the invention, there is
provided a stable bituminous composition comprising a
25 dispersion of particulate polyolefin in bitumen wherein
the concentrate provided herein is a component
stabilizing the 'particulate polyolefin against
sedimentation.
The present invention, in another aspect, provides
30 a method of forming a rubberized bitumen concentrate
which comprises (A) providing a mass comprising (a)
bitumen, and ('b) crumb rubber having a vulcanizate
network in an initial amount of at least about 15 wt%
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6
of the mass, wherein the crumb rubber is swollen in-
situ to form a network-like structure in the bitumen
susceptible to dissociation of vulcanizate particles in
a high shear field; and (B) subjecting the mass to
5 sufficient shear and temperature conditions to effect
dissociation of the vulcanizate network of the rubber
particles to incorporate the digested vulcanizate into
the bitumen to the extent that rubber particles in the
composition do not sediment as determined by the
10 Polymer Separation Test and upon dilution by bitumen to
a lower concentration of dissociated rubber vulcanate
network.
The crumb rubber which is processed according to
the method of the invention may have a wide range of
15 particle size generally from about '~ inch to about 200
mesh, preferably about 10 to about 80 mesh. A process
oil may be included in a manner to promote swelling of
the crumb rubber and to increase the solvency power of
the bitumen.
20 By the shear and temperature condition, the mass
may be subjected to thermal and mechanical energy at a
shear stress at least sufficient to effect intra-
particulate friction and shearing to effect breakdown
of the vulcanate network under the influence of the
25 shear stress applied to the mass of particles. The
shear and temperature conditions preferably are applied
for a time which results in any carbon black particles
released from the rubber particles remaining dispersed
and resistant to sedimentation.
30 At least one additional loading of crumb rubber
may be made to the initially-formed rubber concentrate
and the method is repeated to incorporate digested
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vulcanate network from each additional loading into the
rubberized bitumen concentrate.
The rubberized bitumen concentrate produced by the
method of the invention may be diluted to a lower
5 concentrate of incorporated rubber particles for use in
the diluted form for a variety of bitumen uses.
Definition
Since the process of vulcanization is
irreversible, the term "devulcanization" is something
10 of a misnomer. The in-situ devulcanization of rubber
vulcanizate in this invention means that the structured
network (or chemically cross-linked nature) of ground
vulcanizate rubber (i.e. tire rubber and other
industrial rubber waste) is dissociated or broken up
15 and the resulting devulcanized material is incorporated
directly into bitumen to a point where the treated
vulcanizate can be fully digested or stabilized in
bitumen and does not separate from bitumen in hot
liquid form over a long period of time at different
20 concentration levels. The present invention requires
the use of specific components to achieve the stable
incorporation of the devulcanized rubber particles into
bitumen as described in more detail below.
GENERAL DESCRIPTION OF INVENTION
25 The Elements (as defined in Table 1 below)
required for the provision of the composition of the
present invention ,and used in the process of the
invention are described in detail below. The Elements
are:
30 1) Bitumen or Asphalt (sometimes abbreviated
"AC" herein)
2) Ground Rubber
3) Swollen rubber particles in AC or AC-oil
combination (from elements (1) and (2))
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8
4) Minimum loading level of ground rubber in
asphalt of at least about 25 wt~
The combination of Elements 1, 2, 3 and 4 is
sometimes referred to herein as a "mass". The
5 following Table I provides more detailed information
relating to the Elements.
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TABLE 1
Element Comments
Bitumen/Asphaltmay be from a wide variety of sources, including
straight
run vacuum residue, mixtures of vacuum residue
with a
variety of diluents, such as vacuum tower
wash oil, paraffin
distillate, petroleum flux, aromatic and
napthenic oils.
Other asphaltic materials, such as rock asphalt,
naturally
occurring asphalt or air blown asphalt and
coal tar may also
be used.
Ground Rubbermost types of crumb rubber (vulcanizate)
from whole tire,
(GR) tire treads, tire buffing, tire side wall
and other
industrial/commercial waste, such as EPDM
scrap,
conveyor belt and so on.
The particular size range can be from about
lh inch to about
200 mesh, referabl about 10 to about 80 mesh.
GR Swollen the GR particles in the bitumen need to be
in- swollen
situ sufficiently in bitumen or bitumen-oil combination
while
mixin under hi h shear condition.
Minimum the GR swollen in bitumen is required to
be at a certain
effective initial loading level of at least about 15
loading k by wt.
level of GR
Along with the minimum initial loading level,
the particles
are required to be swollen sufficiently,
in order to form a
network-like-structure in the bitumen medium
to facilitate
the dissociation of vulcanizate particles
in a high shear
field.
If the loading level is too low, the vulcanizate
particle will
swell but do not become dissociated in the
high shear field.
An optimized higher starting load level can
vary depending
upon multiple factors, such as vulcanizate
source, type,
composition/formulation and additives involved
and also
largely upon the parameters of the blending
equipment.
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WO 99/Z7018 PCT/CA98/01078
The use of process oil may be considered optional
with many types of ground rubber vulcanizate and may be
required with other types of ground rubber due to
differences in rubber formulation, cross-linking
5 chemicals, rubber solubility, and so on. Such process
oils include aromatic and naphthalene oils, petroleum
flux, and other hydrocarbon oils. Addition of any oil
is intended to promote the swelling of the crumb rubber
(or vulcanizate) in the bitumen medium and to improve
10 the solvency power of the bitumen, rather than reducing
the viscosity of the end product.
Some ground rubber types, for example, nitrile
rubber and neoprene rubber are highly resistant to
bitumen or any other hydrocarbon oils in terms of
solubility, and hence their crumb vulcanizate may not
be processed according to the invention.
In summary of the above discussion with respect to
Table I, some GR types work well with asphalt only:
some GR types work well only with aromatic oil in
asphalt to facilitate particle swelling; some GR types
work well in either case; and some GR types do not work
in either case.
Only with the presence of all four of the above
described Elements and optionally process oils is it
possible to provide the essential materials and
conditions for carrying out the present invention. The
crumb rubber is mixed with asphalt at the required
loading level and' the crumb rubber particles are
swollen in-situ by hydrocarbon oils present in the
asphalt, either in-situ or added, as required to permit
penetration of the oil into the surface of the crumb
rubber particles and the softening and swelling of the
structure. The resulting "mass" is processed.
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11
The "mass" comprising the four essential or
optionally five elements must then be subjected to
sufficient shear and temperature conditions in order to
effect devulcanization of the rubber particles. The
mass is subjected to thermal and mechanical energy at a
shear stress at least sufficient to effect intra-
particulate friction and shearing to commence breakdown
of the vulcanized rubber particles, probably through
breakdown of sulfur-sulfur bonds, sulfur-carbon bonds
and cross-links between polymer molecules, under the
influence of the shear stress applied to the mass of
particles. This operation increases the solubility and
compatibility of the at least partially dissociated
rubber vulcanizate network into the bituminous phase.
With these conditions of shear and temperature
acting upon the "mass", the cross-linked network
present in the rubber vulcanizate can become
substantially disassociated (or broken down). This
mass must be processed to a point where the vulcanizate
can be fully digested, or completely incorporated, into
the asphalt to form a rubberized asphalt concentrate.
The conditions used for the dissociation of the
vulcanized rubber particles depends on a number of
factors, as discussed below. In particular, the
temperature may range from about 100° to about 300°C
with mechanical energy being applied to the particles to
produce intra-particulate friction and shearing at a
shear stress which~may vary significantly depending on
. other processing parameters, but which is at least
sufficient to effect breakdown of the mass of particles.
For example, processing of the ground crumb rubber at
lower temperatures may require use of higher intra
particulate shear stresses while lower intra-particulate
shear stresses may be possible at more elevated
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12
temperatures. The heat and mechanical energy may be
applied over a period of time which may vary widely,
from about 15 minutes to about 8 hours or more,
depending on the components employed, processing
5 parameters and the nature of the product desired. In
addition, the process may be effected continuously.
In general, the process according to the present
invention to effect at least partial dissociation of the
crumb rubber vulcanizate network is controlled by a
10 number of variable factors, including type of
hydrocarbon oil, initial concentration of oil in
bitumen, process conditions employed, such as equipment
type, intra-particulate shear stress, temperature and
the interrelation of shear rate and temperature, the use
15 of additional devulcanization agents, the timing of
addition of crumb rubber, size and loading rates, amount
and timing of addition of a cross-linking agent, as
discussed below, and the molecular weight and type of
any rubber added to the composition, as well as the
20 functionality of the rubber, if applicable. By
utilizing this combination of parameters, the degree of
dissociation of the scrap rubber may be controlled to
produce a variety of products.
The application of heat and mechanical energy to
25 the dispersed swollen crumb rubber particles in the
bitumen is carried out at a shear stress at least
sufficient to effect intra-particulate friction and
shearing to cause 'dissociation of the rubber vulcanate
network and a continuous reduction in the rubber
30 vulcanate particle size, the degree of particle size
reduction depending on the length of time for which the
shear stress is applied to the composition, in addition
to the other process parameters discussed above. If
such processing is effected for a sufficient duration,
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13
all the rubber particles become dissociated and
incorporated into the bitumen, so that rubber particles
in the composition do not sediment according to the
Polymer Separation Test, as outlined below, and upon
5 dilution with bitumen to a lower concentration of
dissociated rubber vulcanate network.
However, such shear stress processing may be
effected for a sufficient duration that the rubber
vulcanate network is heavily dissociated, in which case
10 an oil-like liquefied material is produced, which may be
less desirable for use in hot mix paving and roofing
related applications. Such oil-like liquefied materials
may be better suited for use as a diluent in asphalt and
non-asphalt based coatings and sealants.
15 The ability to disassociate the rubber vulcanizate
in situ leads to a lower viscosity product than the
rubber/bitumen mixture at its starting loading level.
This result, in turn, permits incremental loading of
crumb rubber into the rubberized asphalt concentrate.
20 Within the scope of the invention, it is possible to
achieve loading levels of rubber in the asphalt up to
about 50~ or greater by effecting such incremental
loadings. This result is in contrast to conventional
procedures wherein the mixture runs dry at relatively
25 low levels.
The rubberized concentrate which results from the
process of the invention is also unique in that the
composition is stabilized indefinitely against phase
separation of the devulcanized rubber from the bitumen
30 composition. The dramatic improvement in stability of
the concentrate which results from the present
invention, as compared to a similar formulation not
prepared according to the conditions of the invention,
may not be fully appreciated until both materials are
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14
re-examined at diluted concentrations as in the form
that they would ultimately be used. Subsequent
dilution of the rubberized concentrate which results
from the procedure of the present invention, may be
5 effected to virtually any lesser concentration, with no
phase separation of the devulcanized rubber from the
asphalt matrix.
Further materials may be added to the devulcanized
composition to impart particular properties thereto, for
10 example, additional loadings of carbon black and/or
addition of gilsonite.
Crumb rubber from automobile tyres generally
contains a significant proportion of carbon black. The
dissociation procedure used herein tends to cause a
15 release of carbon black particles from the crumb rubber.
Typically, such carbon black particles would separate
from the continuous bitumen phase, by means of
sedimentation. In the present invention, the stability
of the released carbon black is improved through the
20 surface grafting of the at least partially dissociated
rubber vulcanate network onto these particles during
free radical chain transfer reaction and carbon black
particles dispersed in the liquid vulcanate rather than
sediment.
25 In general, the highly dissociated material may be
dispersed in bitumen and remain in the liquid phase as a
colloidal dispersion. However, at intermediate stages
between the commencement of dissociation and the
formation of highly dissociated material in which
30 sedimentable dispersed degraded rubber particles remain,
in order to provide a stable dispersion of such degraded
rubber particles in bitumen, it is necessary for
chemical reaction to be effected by way of cross-linking
of an unsaturated rubber component, which may comprise
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WO 99127018 PCT/CA98/01078
vulcanate from a prior degradation, in order for the
degraded rubber particles to be stabilized against
sedimentation from the bitumen.
An important aspect of the present invention is the
5 ability to control the degree or level of dissociation
of the rubber vulcanate network. Materials of certain
levels of disassociation may be used independently or
advantageously combined together, with or without
additional modifiers, as discussed above.
10 The highly dissociated rubber vulcanate network
which has been solubilized or compatibilized in the
bitumen can subsequently be re-vulcanized in-situ
through the use of commonly employed cross-linking
agents. This revulcanized modified bitumen exhibits
15 improved elasticity and stiffness without risk of phase
separation due to irreversible chemical bonding into the
bitumen.
Such cross-linking and/or grafting may be effected
using any convenient cross-linking agent, including
20 sulfur, sulfur donor, with or without accelerating
additives, and other free-radical initiators, such as
hydrogen peroxide. In general, the amount of cross-
linking agent employed is about 0.05 to about 5 wt~,
preferably about 0.2 to about 3 wto of bitumen. The
25 cross-linking agent may be added at any convenient stage
of processing.
In another embodiment of the invention, vulcanized
crumb rubber particles may be added and incorporated
into the above described highly dissociated rubberized
30 asphalt composition, without partial degradation
thereof. In such compositions the at least partially
dissociated rubber network may chemically bind on the
surface of the rubber vulcanate particles thereby
creating stable compositions.
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16
Incremental batch loadings of crumb rubber
particles may be employed to provide a very high overall
loading of dispersed stabilized rubber in the product
bitumen composition, generally in the range of about 15
5 to about 80 wt$, preferably about 20 wt~ to about 50 wto
and up to about 75 wt~. Such concentrated material, or
masterbatch, may be diluted with bitumen to form a
composition containing a desired concentration of
stabilized crumb rubber, generally in the range of about
10 3 to about 40 wt$, for a variety of asphalt
applications, including all types of paving, preformed
paving bricks, roofing membranes, shingles,
waterproofing membranes, sealants, caulks, potting
resins and protective finishes. Alternatively, such
15 masterbatch may be compounded with fillers and/or
polymers and the compounded composition may be
pelletized to produce a pelletized composition for
subsequent incorporation into asphalt compositions for
such uses.
20 In published International patent application WO
93/07219 (corresponding to U.S. Patents Nos. 5,280,064
and 5,494,966, the disclosures of which are incorporated
herein by reference), there is described the provision
of stable asphalt compositions in which polyethylene
25 particles are maintained as a dispersed phase by steric
stabilization. As described therein, the bitumen
comprises the major continuous phase of the polymer-
modified bitumen compositions and the polymer is
dispersed in the bitumen by steric stabilization
30 achieved by a first component anchored to the polymer
phase and a second component bonded to the first
component and soluble in the bitumen.
In addition, as described in published
International Patent Application No. WO 94/14896, in the
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17
name of Polyphalt Inc., additional homopolymer or
copolymer components, including styrenic copolymers,
olefinic copolymers and E-P rubbers may be provided in
the bitumen composition, in the form of particle
5 dispersions, strand-like dispersions, solutions and
combinations in which the additional homopolymer and
copolymer components are stabilized against separation.
The at least partially dissociated rubber vulcanate
network produced in the manner described above may be
10 added, as is or stably dispersed in bitumen, to these
bitumen compositions so that the residual rubber crumb
particles form part of the stable dispersed phase and
may provide supplementation to or partial replacement
for the polyethylene.or other polymer particles in such
15 compositions. The unsaturated components of the at
least partially dissociated rubber vulcanate network and
any unsaturated rubber added may be employed to replace
polybutadiene-based stabilizer, in whole or in part, as
the steric stabilizer. If the unsaturated rubber is
20 used in the production of the at least partially
dissociated rubber vulcanate network and is
functionalized, then this unsaturated rubber can be used
to replace the second component which is bonded to the
first component and anchored to the dispersed polymer,
25 as described above.
The formation of stable dispersions of crumb rubber
in bitumen by the procedure employed herein may be
combined with stabilization of dispersed polyethylene
and other olefinic polymers and copolymers, as described
30 above, to improve the characteristics thereof. Paving
materials generally include aggregate, such as crushed
stone pebbles, sand etc, along with the bitumen
composition. Similarly, other additives to the bitumen
composition may be employed, dependent on the end use to
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18
which the bituminous composition is put. For example, a
roofing material may be obtained by the addition of
suitable fillers, such as asbestos, carbonates, silica,
wood fibres, mica, sulfates, clays, pigments and/or fire
5 retardants, such as chlorinated waxes. For crack-filler
applications, an oxide may be advantageously added.
Mechanism
The mechanisms by which the shear force acting on
the mass composition described above can serve to
10 effect dissociation of the swollen rubber network
present in the vulcanizate/bitumen mixed in a
conventional high shear mixer under a specified process
condition are not at present fully understood. But
without wishing to.be restricted to any theory, the
15 process of the invention is considered to result in the
breakage of sulfur-sulfur, sulfur-carbon or other
cross-linking bonds and possibly breakage of carbon-
carbon bonds present in the vulcanizate cross-linking
structure to a point such that the treated vulcanizate
20 rubber can be fully digested or stabilized in bitumen
and does not separate from bitumen in hot liquid form
over a long period of time at different concentration
levels.
Applications for Devulcanized Rubberized Concentrate
25 The rubberized bituminous concentrates which
result from the procedure of the present invention may
be employed in a variety of applications, in undiluted
or bitumen-diluted form, as described above and
summarized below:
30 1) The rubberized bituminous concentrate which
results from the process of the invention is
characterized by:
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19
~ a processable binder containing a high loading
from about 15 up to about 50~ or higher at
elevated temperature.
~ a stable, unique heterogeneous compound mixture
with all the rubber vulcanizate digested.
The concentrate may be used as an end product in some
industrial applications, such as in sealants, or may be
directly compounded with some polymers and/or inorganic
fillers for the provision of mechanical goods.
2) Bitumen-diluted rubberized concentrate may be
used, independently or combined with different polymers
and/or other additives, in order to prepare a broad
range of final products. These products are suitable
for diverse bituminous applications in the paving,
roofing, coatings, waterproofing and industrial product
markets. The rubberized concentrate may be used with
regular AC, air blown AC and/or polymer-modified
asphalt:
~ as an independent modifier with no rubber phase
separation at different dilution levels
~ as a co-modifier in combination with at least one
additional polymer, which may be a plastomer or
elastomer, preferably an elestomeric unsaturated
polymer, which may be cross-linked to provide a
stablilized final composition
as a stabilizer in the in-situ reactive
stabilization of polyolefinic plastic dispersion in
hot liquid bitumen, in which case, the treated
vulcanizate is a substitute for the non-vulcanizate
rubber component in the In-Situ Steric Stabilization
Process of WO 93/07219.
rvTrenr r~
In the Examples which follow, the stability of the
bituminous compositions during hot storage was
CA 02310645 2000-OS-18
wo ~mo~s PcTicw9sio~o~s
evaluated using a Polymer Separation Test of
conditioned asphalt samples as follows. The
conditioning procedure consists of placing approx. 70g
of the binder in ~," aluminum tubes and storing such
5 tubes in a vertical position at 320°F in a oven for 48
hr (or 2 days). Following hot storage, a viscosity
ratio was determined by comparing the viscosity of the
binder tested at 275°F or 356°F from the top section of
the tube with the binder and from the bottom section of
10 the tube. A ratio in the range of 0.80 to 1.20 is
generally considered acceptable with respect to
separation of the dispersed phase.
Usually, if the viscosity for the polymer modified
bitumen systems before hot storage is about 3000 cp or
15 below at 275°F, the storage condition specified at
320°F for 48 hr is commonly acceptable. However, if
the viscosity is higher due either to high loading of
polymer in bitumen or to the bitumen itself (for
example, oxidized bitumen), the polymer phase
20 separation (if unstable) in bitumen may be relatively
slower in some cases. It is necessary either to dilute
the composition to a lower polymer inclusion level or
to use a higher storage temperature and/or longer time
to insure that the stability/non-stability of polymers
25 included in bitumen medium are correctly reflected.
Mixing in all Examples was effected in a 1 liter
mixing vessel using Brinkman Polytron high shear (Model
PT45/80) homogenizer.
Example 1:
30 A first series of experiments was carried out
using both a conventional procedure and a procedure
according to the invention to provide the same final
compositions of crumb rubber in the same type of
CA 02310645 2000-OS-18
WO 99lI?018 PCT/CA98/01078
21
bitumen to permit direct comparison. The results of
this set of experiments are shown in Table 2 below.
Four scrap rubber vulcanizate sources from three
different manufacturers were used in this set of
5 experiments. The scrap rubber vulcanizates came from
the side-wall of tires but may be formulated
differently by each manufacturer. The mesh sizes of the
ground rubbers (GRs) were quite different varying from
" to 100 mesh. The specified mesh no. with each GR
specified in Table 2 is an average value.
The bitumen used in this set of experiments had
the same viscosity grade (AC-5) with the following
properties: 148 dmm penetration at 77°F, 113°F
softening point and 233 cp Brookfield viscosity at
15 275°F.
A series of blends of four different crumb rubbers
and the bitumen (AC-5) at different blending ratio (5$,
8o and 12~ by wt as shown in Table 2) were prepared
respectively using conventional steps as described in
20 the prior art.
The bitumen was heated to 356°F in the mixer
followed by dispersing the ground rubber particles
under high shear at higher temperature around 392°F for
2 hours. Although the swollen crumb rubber particles
25 were fully dispersed under such high shear mixing, they
were not broken down and/or digested into bitumen at
the low rubber loadings of less than 15o by weight. The
results for all compositions indicated that the rubbers
treated in the conventional steps (i.e. prior art)
30 tended to' show phase separation (or crumb rubber
sedimentation at the bottom) from the hot liquid
bitumen during 'storage without agitation. However, the
results also showed differences to a certain degree in
the rate of phase separation because of both the
CA 02310645 2000-OS-18
- wo ~mois PrricA9s~oio~s
22
different crumb sources at the same loading and the
different loadings for the same source. Nevertheless,
all treated crumb under the conventional wetting
process conditions were not stable in hot liquid
bitumen.
Using the inventive procedures on the same
compositions, a rubberized concentrate was first formed
and then diluted with bitumen to the final composition
tested, in which the treated crumb rubber was
stabilized in the binder at any lesser concentration of
rubber.
In this set of experiments, the rubberized
concentrates were prepared using an incremental loading
procedure in the same high shear mixer. About 17o by
wt of the crumb rubber initially was added while
stirring to hot liquid bitumen at about 356°F. A high
viscosity mixture, which was still workable or
processable in the Polytron high shear mixer, was
provided at this initial loading level. The blending
was carried out under high shear force for half hour at
around 392°F. The viscosity of the mixture started to
drop down to a point where it was possible to make an
incremental loading of the crumb rubber to the mixture,
yielding a final loading at 25o by wt for this Example.
The mixture then was subjected to the same high shear
conditions. The total processing time was 2 hours to
provide a smooth rubberized concentrate mixture in
which all crumb vulcanizate added was digested and/or
incorporated into bitumen. The resulting concentrates
were diluted with the same bitumen to different rubber
loadings in the final compositions, the same as in the
conventional prior art examples. All compositions
prepared from four sources of crumb rubber at different
loadings according to the invention (shown in Table 2)
CA 02310645 2000-OS-18
WO 99/17018 PCT/CA98/01078
23
were stable, and exhibited no residual crumb rubber
sedimentation during storage.
CA 02310645 2000-OS-18
WO 99/27018 PCT/CA98/01078
24
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CA 02310645 2000-OS-18
WO 99/Z7018 PCT/CA98/01078
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CA 02310645 2000-OS-18
wo ~mo~8 Pc~ric~9sioio~8
26
Example 2:
In a second set of experiments, the bitumen used
was the same asphalt (AC-5) as used in Example 1. Tire
rubber was ground rubber (designated GR-5) manufactured
from discarded tires. GR-5 had a particle size on
average about 40 mesh and was produced from passenger
tire (with fiber and wire removed) by Baker Rubber Inc.
A process oil employed was a hydrolene recycling agent
(H-90) having total aromatics of 83.6%, saturates of
16.3% and asphaltenes of 0.1%.
The blends of this GR with the bitumen at two
different rubber loading (5% and 7.5% by wt) were
carried out by using the conventional prior art method
(as shown in Table 3 below) . The GR-5 unlike the type
of vulcanizate used in Example 1, needed to be swollen
sufficiently in the bitumen containing a certain
portion of the process oil. Following the conventional
steps, although the swollen GR-5 particles were well
dispersed in the bitumen under high shearing mixing at
high temperatures form 428°F to 469°F, they were still
not broken down and/or digested into bitumen. The
result also showed a higher rate of phase separation at
same rubber loading during hot storage in comparison
with the results on different type of tire rubber in
Example 1.
A blend with the GR-5 at the same rubber load was
also prepared (see sample GR-5-3 shown in Table 3)
according to the principle taught in the prior art (EP
0439232). The tire rubber (GR-5) was mixed at 338°F
under high shear and then transferred to a separate
vessel and subjected to a low shear agitation to
circulation at a higher temperature at 410°F for 10
more hours. T.he result indicated that the rubber
CA 02310645 2000-OS-18
WO 9917018 PCT/CA98101078
27
treated according to the conditions of EP 0939232 also
tended to show phase separation during storage without
agitation.
Using the inventive procedure to achieve the same
final composition, a rubberized concentrate was first
formed and then diluted with bitumen to the final
specified composition to be tested.
The rubberized concentrate with GR-5 rubber was
prepared using an incremental loading procedure in the
same high shear mixer. About 20o by wt of the crumb
rubber was added while stirring to hot liquid
bitumen/process oil blend at 1:1 ratio. The high
viscosity of the mixture, which was still workable or
processable in the .Polytron high shear mixer, was
achieved from this starting effective loading level
together with a higher degree of swelling of the
dispersed; rubber particles. The blending was carried
out under high shear force for one and half hours at
around 464°F. The viscosity of the mixture started to
drop down to a point where an incremental loading of
the rubber was possible, achieving a final loading at
50~ by wt for this example, which is shown in Table 4
below. The mixture was subjected to the same high shear
condition and a total processing of time was about 4
hours, to yield a smooth rubberized concentrate binder
in which all crumb vulcanizate added was digested
and/or incorporated into bitumen. The resulting
concentrates were diluted with the same bitumen to the
same final composition, which was stable without crumb
rubber sedimentation at the bottom during storage (see
the results in Table 3).
The diluted concentrate contains a devulcanized
rubber which was used as a substitute for non-
CA 02310645 2000-OS-18
WO 99127018 PCT/CA98/01078
28
vulcanizate rubber as one of stabilizer components for
preparing a stable polyethylene dispersion in the same
bitumen used to prepare the concentrate, according to
the procedure disclosed in prior art Steric
Stabilization Process described in WO 93/07219. The
result on this sample (DGR-5/PE-1) shown in Table 3
indicated that the devulcanized tire rubber was both
compatible and reactive enough with the bitumen to
function as an elastic layer which can stabilize the
polyolefinic particulate phase according to the Steric
Stabilization Process.
CA 02310645 2000-OS-18
WO 99/Z7018 PCT/CA98/01078
29
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CA 02310645 2000-OS-18
WO 99127018 PCT/CA98/01078
TABLE 4
Rubberized Concentrate Composition
INGREDIENT\CODE RC-1 RC-2
Bitumen (AC-5) 25
Bitumen (flux type) 25
Process oil 25 25
GR-5 (40 mesh) 50
GR-6 (30 mesh) 50
CA 02310645 2000-OS-18
- wo ~mo~s pcricA98io~o~s
31
Example 3:
Another rubber (designated as GR-6) used in a
further experiment according to the procedure of
Example 2, was a recycled rubber from a mixture of
passenger tires and truck tires.
The GR-6 rubber was treated in bitumen-
flux/processing-oil combination using the same
procedure as for GR-5 described in Example 2. The
rubberized concentrate from GR-6/flux/oil mixture was
shown in Table 4. The bitumen flux came from Amoco
Clark, which was identified as a type of bitumen for
air blown applications. Properties of this bitumen
(flux) were 302 dmm penetration at 77°F, softening
point at 100°F and 32 cp of Brookfield viscosity at
350°F. The oxidized bitumen was a typical roofing grade
bitumen air blown (or oxidized) from the bitumen flux,
and had the following properties: 17 dmm penetration at
77°F, softening point at 212°F and 770 cp of Brookfield
viscosity at 350°F. Air blown bitumen is usually
considered to be a very difficult bitumen to modify due
to its very poor compatibility with polymers. The
process oil used was the same as in Example 2. However,
using the inventive procedure, the rubberized
concentrates prepared were diluted with the air-blown
bitumen to provide a highly stabilized rubberized
bitumen product, as indicated in Table 5 below. It was
more surprising to ,find that the digested tire rubber
in air-blown asphalt was also both soluble and reactive
enough in-situ to function as an elastic layer which
stabilized the polyolefinic particulate phase in the
air-blown asphalt (see result on this sample (DGR-6/PE-
1) in Table 4).
CA 02310645 2000-OS-18
WO 9927018 PCT/CA98/01078
32
TABLE 5
GR Treated and LDPE stabilized
with the treated GR in air blown asphalt
Comparative Inventive
Ingredient\Code GR-6-1 GR-6/PE-1GR-6-1 DGR-6/PE-1
Bitumen (oxidized) 80 85 80 85
Bitumen (flux type) 5 3 5 3
process oil 5 3
GR-6 (30 mesh) 10 6
process oil (in the concentrate 5 3
RC-2*)
GR-6 (in the concentrate 10 6
RC-2*)
Recycled Polyethylene (PE) 2 2
Malefic anhydride grafted 0.5 0.5
PE
FPB (Hycar reactive rubber) 0.3 0.3
Sulfur 0.2 0.2
Stability data(5 days at
425F)
Viscosity, cp at 375F
at Top section 665 595 375 1790
at Bottom section 1000 2400 373 1780
Stability Index (ratio) 0.67 0.23 1.01 0.98
Storage Stability no no yes yes
* Rubberized concentrate composition shown in Table 4.
CA 02310645 2000-OS-18
WO 99/17018 PCT/CA98/01078
33
Example 4:
The ground rubber (GR-1) was used again in a
fourth set of experiments.
GR-1 was treated in a harder base bitumen (AC-20),
using the same condition to prepare concentrate at 25%
loading as described in Example 1.
Properties of the AC-20 base bitumen were 67 dmm
penetration at 77°F, 215°F softening point and 368 cp
Brookfield viscosity at 275°F.
This rubberized concentrate was diluted with AC-20
base to 3 different concentration levels (6%, 8% and
10% by wt) of crumb rubber, followed by dispersing
1.25% of SBS in the diluted concentrates at 356°F for
30 min and then chemically reacting in-situ under high
shear and at the same temperature with 0.15% of
elemental sulfur for 90 more min.
In comparative examples, the process conditions
and final compositions were the same as in the
inventive examples, except that the ground rubber (GR-
1) was directly treated in the composition without
going through the rubberized concentrate based on the
inventive procedure. The results shown in Table 6
below indicate that the final mixtures prepared with
concentrate produced according to the procedure of this
invention, with the same composition as in conventional
Examples at three different loading were stable,
without crumb rubber sedimentation at the bottom under
standard storage conditions.
CA 02310645 2000-OS-18
WO 99/17018 PCTlCA98/01078
34
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CA 02310645 2000-OS-18
WO 99!17018 PCT/CA98/01078
SU~RY OF DISCLOSURE
In summary of this disclosure, the present
invention provides a novel solution rubberized bitumen
concentrate composition comprising the same and the
5 procedure for the manufacture of the same.
Modifications are possible within the scope of this
invention.
