U.S. patent application number 10/357977 was filed with the patent office on 2004-08-05 for process for preparing bitumen/rubber compositions.
Invention is credited to Buras, Paul J..
Application Number | 20040152805 10/357977 |
Document ID | / |
Family ID | 32771112 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040152805 |
Kind Code |
A1 |
Buras, Paul J. |
August 5, 2004 |
Process for preparing bitumen/rubber compositions
Abstract
In methods of preparing asphalt and elastomeric polymer
compositions, it has been discovered that for a given crosslinker
or vulcanizing agent there is an optimum crosslinking temperature
to give a composition that has top and bottom softening points that
are close. That is, rubber/asphalt compatibility is improved, where
the crosslinking is performed within the optimum temperature
range.
Inventors: |
Buras, Paul J.; (West
University Place, TX) |
Correspondence
Address: |
ALDESIGNS INC.
RR #2
THAMESFORD
N0M 2M0
CA
|
Family ID: |
32771112 |
Appl. No.: |
10/357977 |
Filed: |
February 4, 2003 |
Current U.S.
Class: |
524/59 |
Current CPC
Class: |
C08L 21/00 20130101;
C08K 3/011 20180101; C08L 95/00 20130101; C08K 5/0025 20130101;
C08L 95/00 20130101; C08L 2666/04 20130101 |
Class at
Publication: |
524/059 |
International
Class: |
C08J 003/00 |
Claims
I claim:
1. A method for preparing asphalt and polymer compositions
comprising: (a) heating a mixture of asphalt and an elastomeric
polymer to within an optimum crosslinking temperature range; and
(b) adding a crosslinker to the mixture, where the crosslinker is
selected from the group consisting of a sulfur-containing
derivative and elemental sulfur and mixtures thereof. where the
optimum crosslinking temperature range is that where the resulting
asphalt/polymer composition has a difference between the top and
bottom softening points of 20.degree. C. or less.
2. The method of claim 1 where in heating the mixture, the
elastomeric polymer is a vinyl aromatic/conjugated diene
elastomer.
3. The method of claim 2 where the elastomeric polymer is a
styrene-butadiene copolymer.
4. The method of claim 1 where in adding the crosslinker, the
crosslinker is selected from the group consisting of elemental
sulfur, mercaptobenzothiazole (MBT), thiurams, and mixtures
thereof.
5. The method of claim 4 where in adding the crosslinker, the
crosslinker comprises a thiuram polysulfide.
6. The method of claim 5 where the thiuram polysulfide has the
formula: 2where R.sup.1 and R.sup.2 are the same or different alkyl
substitutents having from 1 to 4 carbon atoms, and wherein M is a
metal selected from zinc, barium or copper, and n is 0 or 1, and
where the optimum crosslinking temperature range is above
180.degree. C.
7. The method of claim 6 where the optimum crosslinking temperature
range is between about 185 and about 190.degree. C.
8. The method of claim 1 where the elastomeric polymer comprises
from about 1 to 20 wt % of the asphalt/polymer mixture and where
the asphalt has a penetration of between about 20 and 320 dmm.
9. The method of claim 1 where the crosslinker is present in an
amount ranging from about 0.01 to 0.1 wt %, based on the weight of
the asphalt/polymer mixture.
10. A method for preparing asphalt and polymer compositions
comprising: (a) heating a mixture of asphalt and an elastomeric
polymer to within an optimum crosslinking temperature range; and
(b) adding a thiuram polysulfide crosslinker to the mixture, where
the crosslinker is selected from the group consisting of a
sulfur-containing derivative and elemental sulfur and mixtures
thereof. where the optimum crosslinking temperature range is that
where the resulting asphalt/polymer composition has a difference
between the top and bottom softening points of 20.degree. C. or
less, and where the range is above 180.degree. C.
11. The method of claim 10 where in heating the mixture, the
elastomeric polymer is a vinyl aromatic/conjugated diene elastomer,
and where the crosslinker is present in an amount ranging from
about 0.01 to 0.1 wt %, based on the weight of the asphalt/polymer
mixture.
12. An asphalt and polymer composition prepared by the method
comprising: (a) heating a mixture of asphalt and an elastomeric
polymer to within an optimum crosslinking temperature range; and
(b) adding a crosslinker to the mixture, where the crosslinker is
selected from the group consisting of a sulfur-containing
derivative and elemental sulfur and mixtures thereof. where the
optimum crosslinking temperature range is that where the resulting
asphalt/polymer composition has a difference between the top and
bottom softening points of 20.degree. C. or less.
13. The composition of claim 12 where in the method, in heating the
mixture, the elastomeric polymer is a vinyl aromatic/conjugated
diene elastomer.
14. The composition of claim 13 where in the method, the
elastomeric polymer is a styrene-butadiene copolymer.
15. The composition of claim 12 where in the method, in adding the
crosslinker, the crosslinker is selected from the group consisting
of elemental sulfur, mercaptobenzothiazole (MBT), thiurams, and
mixtures thereof.
16. The composition of claim 15 where in the method, in adding the
crosslinker, the crosslinker comprises a thiuram polysulfide.
17. The composition of claim 16 where in the method, the thiuram
polysulfide has the formula: 3where R.sup.1 and R.sup.2 are the
same or different alkyl substituents having from 1 to 4 carbon
atoms, and wherein M is a metal selected from zinc, barium or
copper, and n is 0 or 1, and where the optimum crosslinking
temperature range is above 180.degree. C.
18. The composition of claim 17 where in the method, the optimum
crosslinking temperature range is between about 185 and about
190.degree. C.
19. The composition of claim 12 where in the method, the
elastomeric polymer comprises from about 1 to 20 wt % of the
asphalt/polymer mixture and where the asphalt has a penetration of
between about 20 and 320 dmm.
20. The composition of claim 12 where in the method, the
crosslinker is present in an amount ranging from about 0.01 to 0.1
wt %, based on the weight of the asphalt/polymer mixture.
Description
FIELD OF THE INVENTION
[0001] The present invention is related to hydrocarbon-based
binders, such as bitumens, asphalts and tars, modified with
elastomers, and including a vulcanized stage, which are
particularly useful as industrial coatings and road bitumens, or
the like. It relates more particularly to processes for obtaining
vulcanized compositions based on bitumens and on styrene/butadiene
copolymers that have close top and bottom softening points.
BACKGROUND OF THE INVENTION
[0002] The use of bitumen (asphalt) compositions in preparing
aggregate compositions (including, but not just limited to, bitumen
and rock) useful as road paving material is complicated by at least
three factors, each of which imposes a serious challenge to
providing an acceptable product. First, the bitumen compositions
must meet certain performance criteria or specifications in order
to be considered useful for road paving. For example, to ensure
acceptable performance, state and federal agencies issue
specifications for various bitumen applications including
specifications for use as road pavement. Current Federal Highway
Administration specifications require a bitumen (asphalt) product
to meet defined parameters relating to properties such as
viscosity, stiffness, penetration, toughness, tenacity and
ductility. Each of these parameters define a critical feature of
the bitumen composition, and compositions failing to meet one or
more of these parameters will render that composition unacceptable
for use as road pavement material.
[0003] Conventional bitumen compositions frequently cannot meet all
of the requirements of a particular specification simultaneously
and, if these specifications are not met, damage to the resulting
road can occur, including, but not necessarily limited to,
permanent deformation, thermally induced cracking and flexural
fatigue. This damage greatly reduces the effective life of paved
roads.
[0004] In this regard, it has long been recognized that the
properties of conventional bitumen compositions can be modified by
the addition of other substances, such as polymers. A wide variety
of polymers have been used as additives in bitumen compositions.
For example, copolymers derived from styrene and conjugated dienes,
such as butadiene or isoprene, are particularly useful, since these
copolymers have good solubility in bitumen compositions and the
resulting modified-bitumen compositions have good rheological
properties.
[0005] It is also known that the stability of polymer-bitumen
compositions can be increased by the addition of crosslinking
agents (vulcanizing agents) such as sulfur, frequently in the form
of elemental sulfur. It is believed that the sulfur chemically
couples the polymer and the bitumen through sulfide and/or
polysulfide bonds. The addition of extraneous sulfur is required to
produce the improved stability, even though bitumens naturally
contain varying amounts of native sulfur.
[0006] Thus, there is known a process for preparing a
bitumen-polymer composition consisting of mixing a bitumen, at
266-446.degree. F. (130-230.degree. C.), with 2 to 20% by weight of
a block or random copolymer, having an average molecular weight
between 30,000 and 300,000. The resulting mixture is stirred for at
least two hours, and then 0.1 to 3% by weight of sulfur relative to
the bitumen is added and the mixture agitated for at least 20
minutes. The quantity of added sulfur cited in this patent is 0.1
to 1.5% by weight with respect to the bitumen. The resulting
bitumen-polymer composition is used for road-coating, industrial
coating, or other industrial applications.
[0007] Similarly, there is also known an asphalt (bitumen) polymer
composition obtained by hot-blending asphalt with 0.1 to 1.5% by
weight of elemental sulfur and 2 to 7% by weight of a natural or
synthetic rubber, which can be a linear butadiene/styrene
copolymer. A process is additionally known for preparing a
rubber-modified bitumen by blending rubber, either natural or
synthetic, such as styrene/butadiene rubber, with bitumen at
293-365.degree. F. (145-185.degree. C.), in an amount up to 10% by
weight based on the bitumen, then adjusting the temperature to
257-320.degree. F. (125-160.degree. C.), and intimately blending
into the mix an amount of sulfur such that the weight ratio of
sulfur to rubber is between 0.01 and 0.9. A catalytic quantity of a
vulcanization-accelerator is then added to effect vulcanization. A
critical nature of the sulfur to rubber ratio is sometimes
reported, for instance that weight ratios of sulfur to rubber of
less than 0.01 gives modified bitumen of inferior quality.
[0008] The second factor complicating the use of bitumen
compositions concerns the viscosity stability of such compositions
under storage conditions. In this regard, bitumen compositions are
frequently stored for up to 7 days or more before being used and,
in some cases, the viscosity of the composition can increase so
much that the bitumen composition is unusable for its intended
purpose. On the other hand, a storage stable bitumen composition
would provide for only minimal viscosity increases and,
accordingly, after storage it can still be employed for its
intended purpose.
[0009] Asphaltic concrete, typically including asphalt and
aggregate, asphalt compositions for resurfacing asphaltic concrete,
and similar asphalt compositions must exhibit a certain number of
specific mechanical properties to enable their use in various
fields of application, especially when the asphalts are used as
binders for superficial coats (road surfacing), as asphalt
emulsions, or in industrial applications. (The term "asphalt" is
used herein interchangeably with "bitumen." Asphaltic concrete is
asphalt used as a binder with appropriate aggregate added,
typically for use in roadways.) The use of asphalt or asphalt
emulsion binders either in maintenance facings as a surface coat or
as a very thin bituminous mix, or as a thicker structural layer of
bituminous mix in asphaltic concrete, is enhanced if these binders
possess the requisite properties such as desirable levels of
elasticity and plasticity.
[0010] As noted, various polymers have been added to asphalts to
improve physical and mechanical performance properties.
Polymer-modified asphalts (PMAs) are routinely used in the road
construction/maintenance and roofing industries. Conventional
asphalts often do not retain sufficient elasticity in use and,
also, exhibit a plasticity range that is too narrow for use in many
modern applications such as road construction. It is known that the
characteristics of road asphalts and the like can be greatly
improved by incorporating into them an elastomeric-type polymer
which may be one such as butyl, polybutadiene, polyisoprene or
polyisobutene rubber, ethylene/vinyl acetate copolymer,
polyacrylate, polymethacrylate, polychloroprene, polynorbornene,
ethylene/propylene/diene (EPDM) terpolymer and advantageously a
random or block copolymer of styrene and a conjugated diene. The
modified asphalts thus obtained commonly are referred to variously
as bitumen/polymer binders or asphalt/polymer mixes. Modified
asphalts and asphalt emulsions typically are produced utilizing
styrene/butadiene based polymers, and typically have raised
softening point, increased viscoelasticity, enhanced force under
strain, enhanced strain recovery, and improved low temperature
strain characteristics as compared with non-modified asphalts and
asphalt emulsions.
[0011] The bituminous binders, even of the bitumen/polymer type,
which are presently employed in road applications often do not have
the optimum characteristics at low enough polymer concentrations to
consistently meet the increasing structural and workability
requirements imposed on roadway structures and their construction.
In order to achieve a given level of modified asphalt performance,
various polymers are added at some prescribed concentration.
[0012] Current practice is to add the desired level of a single
polymer, sometimes along with a reactant that promotes
cross-linking of the polymer molecules until the desired asphalt
properties are met. This reactant typically is sulfur in a form
suitable for reacting.
[0013] However, the cost of the polymer adds significantly to the
overall cost of the resulting asphalt/polymer mix. Thus, cost
factors weigh in the ability to meet the above criteria for various
asphalt mixes. In addition, at increasing levels of polymer
concentration, the working viscosity of the asphalt mix becomes
excessively great and separation of the asphalt and polymer may
occur.
[0014] It is common in the preparation of polymer-modified asphalts
to include activators and accelerators to make the crosslinking
reaction proceed faster. Zinc oxide (ZnO) is a conventional
activator, and mercaptobenzothiazole (MBT) is a conventional
accelerator. ZnO is also sometimes used to control the tendency of
the polymer to gel. The zinc salt of mercaptobenzothiazole (ZMBT)
combines features of both of these conventional additives.
[0015] In view of the above, bitumen compositions, which
simultaneously meet the performance criteria required for road
paving, and which use an alternative activator to the relatively
costly ZnO would be advantageous. Additionally, having available a
variety of different activators for bitumen compositions would
provide versatility. In preparing the composition, significant
mixing is needed to insure the uniform addition of both the polymer
and any crosslinking agents, accelerators or activators. The
crosslinking agents and other agents are usually added as a dry
powder and mixed with the asphalt compositions.
[0016] One of the methods commonly utilized in the industry to
standardize the measure or degree of compatibility of the rubber
with the asphalt is referred to as the compatibility test. The test
comprises the mixing of the rubber and asphalt with all the
applicable additives, such as the crosslinking agents. The mixture
is placed in tubes, usually made of aluminum or similar material,
referred to as cigar tubes or toothpaste tubes. These tubes are
about one inch in diameter and about fifteen centimeters deep. The
mixture is placed in an oven heated to a temperature of about
162.degree. C. (320.degree. F.). This temperature is representative
of the most commonly used asphalt storage temperature. After the
required period of time, most commonly twenty-four (24) hours, the
tubes are transferred from the oven to a freezer and cooled down to
solidify. The tubes are kept in the vertical position. After
cooling down, the tubes are cut into thirds; three equal sections.
The ring-and-ball softening point of the top one third is compared
to the softening point of the bottom section. This test gives an
indication of the separation or compatibility of the rubber within
the asphalt. The rubber would have the tendency to separate to the
top. The lower the difference in softening point between the top
and bottom sections, the more compatible are the rubber and
asphalt. In today's environment, most states require a difference
of 4.degree. F. (2.degree. C.) or less to consider the
asphalt/rubber composition as compatible. Few standards allow a
higher difference. The twenty-four hour test is used as a common
comparison point.
[0017] As can be seen from the above, methods are known to improve
the mixing of asphalt and polymer compositions. The needed elements
for the commercial success of any such process include keeping the
process as simple as possible, reducing the cost of the
ingredients, and utilizing available asphalt cuts from a refinery
without having to blend in more valuable fractions. In addition,
the resulting asphalt composition must meet the above-mentioned
governmental physical properties and environmental concerns. Thus,
it is a goal of the industry to maintain or reduce the cost of the
polymers and crosslinking agents added to the asphalt without
sacrificing any of the other elements and improving the properties
of the asphalt and polymer compositions as much as possible.
SUMMARY OF THE INVENTION
[0018] There is provided, in one form, a method for preparing
asphalt and polymer compositions involving first heating a mixture
of asphalt and an elastomeric polymer to within an optimum
crosslinking temperature range, and then adding a crosslinker to
the mixture, where the crosslinker may be a sulfur-containing
derivative, elemental sulfur and mixtures thereof. The optimum
crosslinking temperature range is that where the resulting
asphalt/polymer composition has a difference between the top and
bottom softening points of 10.degree. C. or less.
[0019] In another embodiment of the invention, there are provided
asphalt and polymer compositions made by the process described
above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a graph of the compatibility of the
asphalt/polymer compositions of this invention plotted in terms of
separation as a function of crosslinking temperature;
[0021] FIG. 2 is a graph illustrating the relationship between
penetration and the crosslinking temperature; and
[0022] FIG. 3 is a graph plotting Brookfield viscosity as a
function of crosslinking temperature.
DETAILED DESCRIPTION OF THE INVENTION
[0023] It has been discovered that improvements in rubber/asphalt
compatibility may be obtained by crosslinking with certain
crosslinkers at temperatures higher than those normally employed.
When particular crosslinkers are used to crosslink mixtures of
asphalt and elastomeric polymers there is an optimum crosslinking
temperature range at which the crosslinker is added and reacted
with the mixture. This optimum crosslinking temperature range gives
resulting crosslinked compositions with small differences between
the top and bottom softening points. In one non-limiting
embodiment, the difference between these two points is broadly
20.degree. C. or less, in one non-limiting embodiment 10.degree. C.
or less, alternately can be 4.degree. C. or less, and can be
2.degree. C. or less. This invention may be considered as a
potential alternative to the use of resins or other techniques to
reduce separation.
[0024] Care must be taken in not subjecting the asphalt/polymer
composition to elevated temperatures for too long to avoid thermal
degradation of the polymer. Thus, the mixture of asphalt and
elastomeric polymer can be maintained within the optimum
crosslinking temperature range for a minimal period of time that is
typically empirically determined. However, in one non-limiting
embodiment of the invention, the mixture is kept within the optimum
crosslinking temperature range for a time period ranging from about
30 to about 120 minutes, such as for example, 60 minutes.
[0025] As used herein, the term "bitumen" (sometimes referred to as
"asphalt") refers to all types of bitumens, including those that
occur in nature and those obtained in petroleum processing. The
choice of bitumen will depend essentially on the particular
application intended for the resulting bitumen composition.
Bitumens that can be used can have an initial viscosity at
140.degree. F. (60.degree. C.) of 600 to 3000 poise (60 to 300
Pa-s) depending on the grade of asphalt desired. The initial
penetration range (ASTM D5) of the base bitumen at 77.degree. F.
(25.degree. C.) is 20 to 320 dmm, and can be 50 to 150 dmm, when
the intended use of the copolymer-bitumen composition is road
paving. Bitumens that do not contain any copolymer, sulfur, etc.,
are sometimes referred to herein as a "base bitumen."
[0026] "Elastomeric Polymers" are natural or synthetic rubbers and
include, but are not necessarily limited to, butyl, polybutadiene,
polyisoprene or polyisobutene rubber, ethylene/vinyl acetate
copolymer, polyacrylate, polymethacrylate, polychloroprene,
polynorbornene, ethylene/propylene/diene (EPDM) terpolymer and
advantageously a random or block copolymer of a vinyl aromatic
compound, e.g. styrene, and conjugated dienes. In one non-limiting
embodiment of the invention, styrene/conjugated diene block
copolymers may be used that are linear, radial, or multi-branched.
Styrene/butadiene and styrene/isoprene copolymers having an average
molecular weight of between 30,000 and 300,000 have been found to
be particularly useful in the present invention.
[0027] "Conjugated dienes" refer to alkene compounds having 2 or
more sites of unsaturation wherein a second site of unsaturation is
conjugated to a first site of unsaturation, i.e., the first carbon
atom of the second site of unsaturation is gamma (at carbon atom 3)
relative to the first carbon atom of the first site of
unsaturation. Conjugated dienes include, by way of non-limiting
example, butadiene, isoprene, 1,3-pentadiene, and the like.
[0028] "Block copolymers of styrene and conjugated-dienes" refer to
copolymers of styrene and conjugated-dienes having a linear or
radial, tri-block structure consisting of styrene-conjugated
diene-styrene block units that are copolymers are represented by
the formula:
S.sub.x-D.sub.y-S.sub.z
[0029] where D is a conjugated-diene, S is styrene, and x, y and z
are integers such that the number average molecular weight of the
copolymer is from about 30,000 to about 300,000. These copolymers
are well known to those skilled in the art and are either
commercially available or can be prepared from methods known in the
art. Such tri-block copolymers may be derived from styrene and a
conjugated-diene, wherein the conjugated-diene is butadiene or
isoprene. Such copolymers may contain 15 to 50 percent by weight
copolymer units derived from styrene, alternatively may contain 20
to 35 percent derived from styrene, and then again may contain 28
to 31 percent derived from styrene, the remainder being derived
from the conjugated diene. These copolymers may have a number
average molecular weight range between 50,000 and 200,000, and
alternatively have a number average molecular weight range between
80,000 and 180,000. The copolymer can employ a minimal amount of
hydrocarbon solvent in order to facilitate handling. Examples of
suitable solvents include plasticizer solvent that is a
non-volatile aromatic oil. However, when the hydrocarbon solvent is
a volatile solvent (as defined above), care should be taken to
ensure that the amount of solvent contained in the final bitumen
composition is less than about 3.5 weight percent.
[0030] The term "sulfur" is defined herein as elemental sulfur in
any of its physical forms, whereas the term "sulfur-containing
derivative" includes any sulfur-donating compound, but not
elemental sulfur. Sulfur-donating compounds are well known in the
art and include various organic compositions or compounds that
generate sulfur under the mixing or preparation conditions of the
present invention. In one non-limiting embodiment, the elemental
sulfur is in powder form known as flowers of sulfur. Other
sulfur-containing derivatives or species that can be used in the
invention include, but are not necessarily limited to
mercaptobenzothiazole, thiurams, and the like, and combinations
thereof. In another non-limiting embodiment of the invention, the
sulfur is present in an amount ranging from about 0.06% to about
0.3 wt. % based on the asphalt, abd alternatively is present in an
amount from about 0.08 to about 0.2 wt. %.
[0031] Acceptable crosslinkers, in one non-limiting embodiment of
the invention, are thiuram polysulfides. In another non-limiting
embodiment of the invention, the thiuram polysulfides have the
formula: 1
[0032] where R.sup.1 and R.sup.2 are the same or different alkyl
substituents having from 1 to 4 carbon atoms, and wherein M is a
metal selected from zinc, barium or copper, and n is 0 or 1. In
another non-limiting embodiment of the invention, a crosslinking
temperature range for thiuram polysulfides of formula (I) is above
180.degree. C. (356.degree. F.), alternatively, the crosslinking
temperature range may be between about 185 and about 190.degree. C.
(365-374.degree. F.). In one non-limiting embodiment of the
invention, the optimal crosslinking temperature range for a
particular crosslinker is determined empirically. In another
non-limiting embodiment of the invention, the optimal crosslinking
temperature range is 20.degree. C. wide, in one non-limiting
embodiment of the invention 10.degree. C. wide, in another
non-limiting embodiment 4.degree. C. wide, and in yet another
non-limiting embodiment of the invention 5.degree. C. wide or
less.
[0033] In still another non-limiting embodiment of the invention,
the sulfur-containing derivative excludes added elemental sulfur,
per se. Alternatively, the asphalt and elastomeric polymer mixture
may contain added elemental sulfur, but the crosslinking is
conducted at a temperature different from the optimum crosslinking
temperature for elemental sulfur, per se.
[0034] The term "desired Rheological Properties" refers primarily
to the SUPERPAVE asphalt binder specification designated by AASHTO
as SP-1. Additional asphalt specifications can include viscosity at
140.degree. F. (60.degree. C.) of from 1600 to 4000 poise (160-400
Pa-s) before aging; a toughness of at least 110 inch-pound (127
cm-kilograms) before aging; a tenacity of at least 75 inch-pound
(86.6 cm-kilograms) before aging; and a ductility of at least 25 cm
at 39.2.degree. F. (4.degree. C.) at 5 cm/min. pull rate after
aging.
[0035] Viscosity measurements are made by using ASTM test method
D2171. Ductility measurements are made by using ASTM test method
D113. Toughness and tenacity measurements are made by a Benson
Method of Toughness and Tenacity, run at 20 inches/minute (50.8
cm/minute) pull rate with a 1/8 inch (2.22 cm) diameter ball.
[0036] By "storage stable viscosity" it is meant that the bitumen
composition shows no evidence of skinning, settlement, gelation, or
graininess and that the viscosity of the composition does not
increase by a factor of four or more during storage at
325.+-.0.5.degree. F. (163.+-.2.8.degree. C.) for seven days. In
one non-limiting embodiment of the invention, the viscosity does
not increase by a factor of two or more during storage at
325.degree. F. (163.degree. C.) for seven days. In another
non-limiting embodiment of the invention, the viscosity increases
less than 50% during seven days of storage at 325.degree. F.
(163.degree. C.). A substantial increase in the viscosity of the
bitumen composition during storage is not desirable due to the
resulting difficulties in handling the composition and in meeting
product specifications at the time of sale and use.
[0037] The term "aggregate" refers to rock and similar material
added to the bitumen composition to provide an aggregate
composition suitable for paving roads. Typically, the aggregate
employed is rock indigenous to the area where the bitumen
composition is produced. Suitable aggregate includes granite,
basalt, limestone, and the like.
[0038] As used herein, the term "asphalt cement" refers to any of a
variety of substantially solid or semi-solid materials at room
temperature that gradually liquify when heated. Its predominant
constituents are bitumens, which may be naturally occurring or
obtained as the residue of refining processing. The asphalt terms
used herein are well known to those skilled in the art. For an
explanation of these terms, reference is made to the booklet
SUPERPAVE Series No. 1 (SP-1), 1997 printing, published by the
Asphalt Institute (Research Park Drive, P.O. Box 14052, Lexington,
Ky. 40512-4052), which is hereby incorporated by reference in its
entirety. For example, Chapter 2 provides an explanation of the
test equipment, terms, and purposes. Rolling Thin Film Oven (RTFO)
and Pressure Aging Vessel (PAV) are used to simulate binder aging
(hardening) characteristics. Dynamic Shear Rheometers (DSR) are
used to measure binder properties at high and intermediate
temperatures. This is used to predict permanent deformation or
rutting and fatigue cracking. Bending Beam Rheometers (BBRs) are
used to measure binder properties at low temperatures. These values
predict thermal or low temperature cracking. The procedures for
these experiments are also described in the above-referenced
SUPERPAVE booklet.
[0039] Asphalt grading is given in accordance with accepted
standards in the industry as discussed in the above-referenced
Asphalt Institute booklet. For example, pages 62-65 of the booklet
include a table entitled Performance Graded Asphalt Binder
Specifications. The asphalt compositions are given performance
grades, for example, PG 64-22. The first number, 64, represents the
average 7-day maximum pavement design temperature in .degree. C.
The second number, -22, represents the minimum pavement design
temperature in .degree. C. Other requirements of each grade are
shown in the table. For example, the maximum value for the PAV-DSR
test (.degree. C.) for PG 64-22 is 25.degree. C.
[0040] In accordance with one non-limiting embodiment of the
present invention, an asphalt composition is prepared by adding the
asphalt or bitumen to a mixing tank that has stirring means. The
asphalt is added and stirred at elevated temperatures. Stirring
temperatures depend on the viscosity of the asphalt and can range
up to 500.degree. F. (260.degree. C.). Asphalt products from
refinery operations are well known in the art. For example,
asphalts typically used for this process are obtained from deep
vacuum distillation of crude oil to obtain a bottom product of the
desired viscosity or from a solvent deasphalting process that
yields a demetallized oil, a resin fraction and an asphaltene
fraction. Some refinery units do not have a resin fraction. These
materials or other compatible oils of greater than 450.degree. F.
(232.degree. C.) flash point may be blended to obtain the desired
viscosity asphalt.
[0041] Rubbers, elastomeric polymers, or thermoplastic elastomers
suitable for this application are well known in the art as
described above. For example, FINAPRENE.RTM. products available
from Atofina Petrochemicals Inc. are suitable for the applications
of the present invention. This example is not limiting for the
inventive technology that can be applied to any similar elastomeric
product particularly those produced from styrene and butadiene.
[0042] Various additives suitable for the purposes of this
invention include, but are not necessarily limited to, known and
future accelerators, activators, and the like. A variety of
accelerators may be used in conjunction with this invention,
including, but not limited to, dithiocarbamates and
benzothiazoles.
[0043] The methods and compositions of this invention will be
further illustrated with respect to particular Examples that are
only intended to more fully illuminate the invention and not limit
it.
EXAMPLES 1-13
[0044] The base asphalt used was a PG 64-22. It was made by
blending an asphaltenes sample designated 97-116 with a flux oil
designated 97-134. The Triflux 250 flux oil was produced from
Boscan crude.
[0045] This blend initially showed severe incompatibility with F
411 SBS rubber. The top and bottom softening points of aged samples
differed by as much as 100.degree. F. (56.degree. C.).
[0046] The asphaltene/flux oil blend was preheated and held at the
specified mixing temperature for 30 minutes with an oil bath. The
mixing temperature was that of the asphalt as measured with a
hand-held thermocouple. The rubber was added and mixed with a
Silverson high shear lab mixer until a smooth homogeneous mixture
was obtained (approximately 30-45 minutes).
[0047] The high shear mixer was replaced with a low shear prop
mixer. The temperature of oil bath was then adjusted to bring the
asphalt/rubber mixture to the proper crosslinking temperature and
allowed to stabilize. The crosslinking additives were slowly added.
Low shear mixing was continued for 90 minutes. The samples were
then placed in a 325.degree. F. (163.degree. C.) oven overnight. On
removal, the samples were stirred for a few minutes with a low
shear mixer to insure homogeneity. The samples were then poured for
separation and other testing.
[0048] The results are shown in Table I and a plot of separation
versus crosslinking temperature is graphed in FIG. 1. It may be
seen that a dramatic improvement in separation was obtained at an
optimal crosslinking temperature of about 370.degree. F.
(188.degree. C.).
1TABLE I Evaluation of Crosslinking Temperature in Asphalt
Crosslinking Systems Ex.: Ingredients 1 2 3 4 5 6 7 8 9 10 11 12
Flux Oil (97-134) Wt % 80 80 80 80 80 80 80 80 80 80 80 80
Asphaltenes Wt % 20 20 20 20 20 20 20 20 20 20 20 20 (97-116) F 401
Wt % 4 2.67 1.33 F 502 Wt % 4 1.33 2.67 F 411 Wt % 4 3 3 3 3 3
Kraton 1101 Wt % 4 Kraton 1116 Wt % 4 Sulfur Wt % 0.05 0.05 0.05
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Methyl Zimate Wt %
0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Mixing
.degree. F. 350 350 350 350 350 350 350 370 370 370 370 370
temperature (.degree. C.) (177) (177) (177) (177) (177) (177) (177)
(188) (188) (188) (188) (188) Crosslinking .degree. F. 320 320 320
320 320 320 320 370 340 355 390 380 temperature (.degree. C.) (160)
(160) (160) (160) (160) (160) (160) (188) (171) (179) (199) (193)
Compatibility 24 hrs - 325.degree. F. (163.degree. C.) Top .degree.
F. 163.7 162.2 236.2 174.7 171.3 171.0 169.0 139.8 190.5 165.0
189.1 175.3 (.degree. C.) (73.2) (72.3) (113.4) (79.3) (77.4)
(77.2) (76.1) (59.9) (88.1) (73.9) (87.3) (79.6) Bottom .degree. F.
142.2 149.7 141.5 140.5 140.8 138.4 144.0 140.8 140.1 140.5 138.5
137.7 (.degree. C.) (61.2) (65.3) (60.8) (60.3) (60.4) (59.1)
(62.2) (60.4) (60.1) (60.3) (59.1) (58.7) Delta .degree. F. 21.5
12.5 94.7 34.2 30.5 32.6 25.0 -1.0 50.4 24.5 50.6 37.6 (separation)
(.degree. C.) (12.0) (7.0) (52.6) (19.0) (17.0) (18.1) (13.9)
(-0.5) (28.0) (13.6) (28.2) (20.9)
[0049] F 401 is a Finaprene SBS Rubber available from Atofina
Petrochemical.
[0050] F 502 is a Finaprene SBS Rubber available from Atofina
Petrochemical.
[0051] F 411 is a Finaprene SBS Rubber available from Atofina
Petrochemical.
[0052] Kraton 1101 is a SBS Rubber available from Kraton
Polymers.
[0053] Kraton 1116 is a SBS Rubber available from Kraton
Polymers
[0054] Methyl Zimate.RTM. is a trademarked name for zinc
dimethyidithiocarbamate available from R. T. Vanderbilt, Inc. and
is a thiuram polysulfide within the scope of this invention.
[0055] One potential explanation of the phenomenon illustrated in
FIG. 1 is that as the crosslinking temperature is increased, the
reaction becomes less selective with interspecies links formed
between the rubber and the asphaltenes. At still higher
temperatures, more crosslinking between asphaltene molecules occurs
which again makes them incompatible with rubber. However, the
inventor does not want the invention to be limited by any
particular theory, explanation or supposed mechanism.
[0056] Two other properties of the crosslinked asphalt were
measured as a part of the study: penetration and viscosity at
350.degree. F. (177.degree. C.). As shown in FIG. 2, there was no
significant trend in penetration at different crosslinking
temperatures. The viscosity decreased as the crosslinking
temperature increased as shown in FIG. 3, most likely due to the
improved compatibility.
[0057] One concern of raising the crosslinking temperature to
370.degree. F. (188.degree. C.) is the increased risk of excessive
thermal crosslinking occurring that may cause the asphalt to be
unusable (high viscosity gel). Thus, a balance needs to be achieved
in choosing a crosslinking temperature between obtaining good
separation and minimizing thermal crosslinking.
[0058] The data for Examples 14 through 18 presented in Table II
below demonstrates that crosslinking may be achieved at elevated
temperatures (380.degree. F.; 193.degree. C.) using the method of
this invention without causing the asphalt/polymer composition to
gel, as shown for Examples 16 and 18.
2TABLE II Evaluation of Crosslinking Temperature in Asphalt
Crosslinking Systems Example Component Units 13 14 15 16 17 SBS
Finaprene 411 Wt % 2 2 2 SBS Kraton 1184 Wt % 2 2 Sulfur Wt % 0.03
0.03 0.03 0.03 0.03 Zinc oxide Wt % 0.02 0.02 0.02 0.02 0.02 MBT Wt
% 0.02 0.02 0.02 0.02 0.02 Mixing .degree. F. 325 360 380 360 380
Temperature (.degree. C.) (163) (182) (193) (182) (193) Blend
result gelled gelled no gel gelled no gel Kraton 1184 is an SBS
rubber available from Kraton Polymers.
[0059] In the foregoing specification, the invention has been
described with reference to specific embodiments thereof, and has
been demonstrated as effective in providing methods for preparing
asphalt and polymer compositions with optimized separation between
the top and bottom softening points. However, it will be evident
that various modifications and changes can be made to the method
without departing from the broader spirit or scope of the invention
as set forth in the appended claims. Accordingly, the specification
is to be regarded in an illustrative rather than a restrictive
sense. For example, specific combinations or amounts of asphalt,
polymer, crosslinker, activator, accelerator, and other components
falling within the claimed parameters, but not specifically
identified or tried in a particular PMA system, are anticipated and
expected to be within the scope of this invention. Specifically,
the method and discovery of the invention are expected to work with
crosslinkers other than those exemplified herein.
* * * * *