U.S. patent application number 10/166671 was filed with the patent office on 2003-02-13 for elastomer-modified bituminous compositions.
Invention is credited to Liang, Zhi-Zhong.
Application Number | 20030032703 10/166671 |
Document ID | / |
Family ID | 21924549 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030032703 |
Kind Code |
A1 |
Liang, Zhi-Zhong |
February 13, 2003 |
Elastomer-modified bituminous compositions
Abstract
Polymer modified bituminous compositions which are stable
against phase separation are provided at greater levels of
incorporation of elastomeric polymer having a conjugated diene
structure, such as styrene-butadiene rubbers, and/or cross-linking
agent, specifically sulfur, by incremental addition of elastomeric
polymer and/or cross-linking agent into the bitumen at elevated
temperatures of about 150.degree. to about 220.degree. C.
Inventors: |
Liang, Zhi-Zhong; (Richmond
Hill, CA) |
Correspondence
Address: |
SIM & MCBURNEY
330 UNIVERSITY AVENUE
6TH FLOOR
TORONTO
ON
M5G 1R7
CA
|
Family ID: |
21924549 |
Appl. No.: |
10/166671 |
Filed: |
June 12, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10166671 |
Jun 12, 2002 |
|
|
|
09402320 |
Dec 2, 1999 |
|
|
|
6429241 |
|
|
|
|
60042937 |
Apr 4, 1997 |
|
|
|
Current U.S.
Class: |
524/59 |
Current CPC
Class: |
C08L 95/00 20130101;
C08L 95/00 20130101; C08L 53/00 20130101; C08L 95/00 20130101; C08L
2666/08 20130101 |
Class at
Publication: |
524/59 |
International
Class: |
C08J 003/00 |
Claims
1. A method of forming a bituminous composition, which comprises:
dispersing by blending and reacting an elastomeric polymer having a
conjugated diene structure and a molecular weight of about 45,000
to about 750,000 with bitumen and a cross-linking agent at a
temperature of about 150.degree. C. to about 220.degree. C. to
stably incorporate the elastomeric polymer into the bitumen against
phase separation according to ASTM D5892, wherein at least one of
the elastomeric polymer and cross-linking agent is added
incrementally to the bitumen (or equivalently continuously) and
reacted to permit greater amounts of elastomeric polymer and/or
cross-linking agent to be incorporated into the bitumen.
2. The method of claim 1 wherein: (a) the total overall quantity of
elastomeric polymer to be incorporated into the composition is
initially added to and fully dispersed in the bitumen in an amount
of about 1 to about 8 wt % of the total composition, and (b)
sulfur, as the cross-linking agent, is added incrementally to a
total amount of about 3 to about 15 wt % of elastomeric polymer
with the sulfur being added in about 2 to about 10 increments over
a total period of about 1 to about 12 hours with about 0.5 to about
2 hours between each incremental loading or equivalently, the
sulfur being added continuously over the period of incremental
addition of sulfur, whereby a high degree of interaction and
compatibilization of the elastomeric polymer with the bitumen is
achieved while avoiding an increase in viscosity beyond workable
levels.
3. The method of claim 2 wherein the overall quantity of
elastomeric polymer is in the range of about 1.5 to about 5 wt % of
the overall composition, the total amount of sulfur is about 5 to
about 10 wt %, the elastomeric polymer has a molecular weight of
about 150,000 to about 450,000, the bitumen has a softening point
as determined by ASTM D36 of about 25.degree. to about 55.degree.
C., and the softening point as determined by ASTM D36 of the
composition is from 50.degree. to about 100.degree. C.
4. The method of claim 1 wherein: (a) an initial loading of
elastomeric polymer to be incorporated into the composition is
added to and fully dispersed in the bitumen and comprising about 20
to about 60 wt % of the total elastomeric polymer loading of about
2 to about 12 wt %, (b) the total overall quantity of sulfur, as
the cross-linking agent, to be employed is added to and dispersed
in the bitumen following said initial loading and dispersion of the
proportion of the overall quantity of elastomeric polymer to be
incorporated into the composition and the mixture reacted for about
5 to about 60 minutes, wherein the amount of sulfur employed is
about 10 to about 25 wt % of the initial loading of elastomeric
polymer and about 3 to about 18 wt % of the normal quantity of
elastomeric polymer, and then (c) the remainder of the elastomeric
polymer is incrementally loaded in about 1 to about 5 increments
over a total period of about 0.5 to about 12 hours with about 1 to
about 2 hours between each incremental loading (or equivalently,
the remainder of the elastomeric polymer being added continuously
over the period of incremental addition of the remainder of the
elastomeric polymer), whereby a high degree of dispersion and
compatibilization of the elastomeric polymer with the bitumen is
achieved while avoiding an increase in viscosity beyond workable
levels while avoiding an increase in viscosity beyond workable
levels.
5. The method of claim 4 wherein the overall quantity of
elastomeric polymer is in the range of about 2 to about 7.5 wt %,
the total amount of sulfur is about 5 to 10 wt % of the total
amount of elastomeric polymer, the elastomeric polymer has a
molecular weight of about 150,000 to about 450,000, the bitumen has
a softening point of about 25.degree. to about 55.degree. C. and
the composition has a softening point of about 50.degree. to about
110.degree. C. as determined by ASTM D36.
6. The method of claim 1 wherein: both elastomeric polymer and
sulfur, as the cross-linking agent, are loaded and dispersed
incrementally, either simultaneously or sequentially, into the
bitumen, to a total overall amount of elastomeric polymer of up to
about 15 wt % of the composition and a total overall amount of
sulfur of about 2 to about 20 wt % of the elastomeric polymer, each
component being added in about 2 to about 5 increments over a
period of about 0.5 to about 12 hours with about 20 mins to about 2
hours between increments, (or equivalently, said elastomeric
polymer and/or sulfur being added continuously over the period of
incremental addition of said elastomeric polymer and/or sulfur),
whereby a higher degree of loading of elastomeric polymer in the
bitumen is achieved while providing a stable composition which
avoiding an increase in viscosity beyond workable levels.
7. The method of claim 6 wherein the total overall amount of
elastomeric polymer is in the range of up to about 12 wt % of the
composition, the elastomeric polymer has a molecular weight of
about 150,000 to about 450,000, the overall amount of sulfur is
about 3 to about 10 wt % of the amount of elastomeric polymer, the
bitumen has a softening point of about 25.degree. to about
55.degree. C. as determined by ASTM D36, and the composition has a
viscosity of about 55.degree. to about 130.degree. C. as determined
by ASTM D36.
8. The method of claim 1, 2, 3, 4, 5, 6 or 7 wherein said bitumen
comprises from about 75 to about 99 wt % of the overall
composition.
9. The method of claim 8 wherein said bitumen comprises from about
85 to about 98 wt % of the total composition.
10. The method of claim 1 wherein the elastomeric polymer is at
least one butadiene-based homo-polymer or random or block
co-polymer.
11. The method of claim 1 wherein the elastomeric polymer is at
least one isoprene-based homo- or co-polymer.
12. The method of claim 10 wherein the butadiene-based polymer is
SBS or SB or a blend thereof.
13. A bituminous composition stable against phase separation
according to ASTM D5892, comprising about 1 to about 8 wt % of an
elastomeric polymer having a conjugated diene structure and a
molecular weight of about 45,000 to about 750,000, having a high
degree of interaction and compatibilization of the elastomeric
polymer with the bitumen by cross-linking with sulfur in an amount
of about 3 to about 15 wt % of elastomeric polymer and having a
workable viscosity, obtainable by the method of claim 2.
14. The bituminous composition of claim 13 wherein the amount of
elastomeric polymer is about 1.5 to about 5 wt %, the amount of
sulfur is about 5 to about 10 wt %, the elastomeric polymer has a
molecular weight of about 150,000 to about 450,000, the bitumen has
a softening point as determined by ASTM D36 of about 25.degree. to
about 55.degree. C., and the composition has a softening point as
determined by ASTM 36 of about 50.degree. to about 100.degree.
C.
15. A bituminous composition stable against phase separation
according to ASTM D5892, comprising about 2 to about 12 wt % of an
elastomeric polymer having a conjugated diene structure and a
molecular weight of about 45,000 to about 750,000, having a high
degree of dispersion and compatibilization of the elastomeric
polymer with the bitumen by cross-linking with sulfur in an amount
of about 3 to about 15 wt % of the elastomeric polymer, and having
a workable viscosity, obtainable by the method of claim 4.
16. The bituminous composition of claim 15 wherein the amount of
elastomeric polymer is about 2 to about 7.5 wt % of the
composition, the amount of sulfur is about 5 to about 10 wt % of
the elastomeric polymer, the elastomeric polymer has a molecular
weight of about 150,000 to about 450,000, the bitumen has a
softening point as determined by ASTM D36 of about 250 to about
55.degree. C. and the composition has a softening point as
determined by ASTM D36 of about 500 to about 110.degree. C.
17. A bituminous composition stable against phase separation
according to ASTM D5892, comprising up to about 15 wt % of an
elastomeric polymer having a conjugated diene structure and a
molecular weight of about 45,000 to about 750,000, having a higher
degree of loading of elastomeric polymer in bitumen while providing
a composition stable against phase separation at workable viscosity
levels therein than achievable by conventional procedures by
cross-linking with sulfur in an amount of about 3 to about 15 wt %
of the elastomeric polymer, obtainable by the method of claim
6.
18. The bituminous composition of claim 17 wherein the amount of
elastomeric polymer is up to about 12 wt %, the amount of sulfur is
about 3 to about 10 wt % of the elastomeric polymer, the
elastomeric polymer has a molecular weight of about 150,000 to
about 450,000, the bitumen has a softening point as determined by
ASTM D36 of about 25.degree. to about 55.degree. C. and the
composition has a softening point as determined by ASTM D36 of
about 55.degree. to about 130.degree. C.
19. The composition claimed in claim 13, 14, 15, 16, 17 or 18
wherein said bitumen comprises at least about 85% by wt of said
composition.
20. The composition as claimed in claim 19 wherein said elastomeric
polymer comprises at least one butadiene-based homo-polymer or
random or block co-polymer, at least one isoprene-based homo- or
co-polymer, or a blend of such elastomeric polymers.
Description
FIELD OF INVENTION
[0001] The present invention is concerned with the preparation of
bituminous compositions with high performance characteristics,
particularly compositions containing bitumen and high molecular
weight elastomer(s). The bituminous compositions provided herein
have numerous commercial uses, including road paving, roofing,
asphalt emulsions and crack fillers.
BACKGROUND TO THE INVENTION
[0002] Bituminous compositions for various applications are known
to contain elastomers, such as natural rubber (NR),
styrene-butadiene rubber latex (SBR), Neoprene latex and
styrene-butadiene block copolymers (SB). The SB copolymers having a
conjugated diene structure are most commonly used to provide
improved properties in specific applications. These elastomers
improve the mechanical properties of the bitumen and hence their
incorporation is desirable.
[0003] In general, low molecular weight (MW) elastomers, those
having a MW of less than about 70,000, are readily dispersed in
bitumen to form a compatible bitumen composition. However, low MW
elastomers do not offer significantly improved properties when
compared with those resulting from the use of high molecular weight
elastomers as bitumen modifiers, unless the low MW rubber chains
are expanded and strengthened using a cross-linking agent, such as
elemental sulfur. Even when so cross-linked, the low MW elastomeric
bituminous compositions are still inferior to those prepared from
high molecular weight elastomers, those having a MW greater than MW
about 200,000. Unfortunately, compositions prepared from the high
MW elastomers, in most cases, give rise to compatibility problems
for the elastomer in the bitumen, resulting in phase separation
when the bituminous compositions are stored.
[0004] The prior art has disclosed that the comparability as well
as the properties of high MW elastomer-modified compositions can be
improved by in-situ vulcanization using sulfur as a cross-linking
agent. However, the processes described in the prior art result in
severe limitations on the proportions of sulfur and/or elastomer
which can be reacted in the bitumen before the composition forms an
un-processible gel. As noted above, a vulcanization reagent, such
as elemental sulfur in combination with elastomers, is frequently
employed to enhance the properties or to improve the compatibility
of the elastomer in modified bitumen.
[0005] Specific examples of such prior art include U.S. Pat. Nos.
4,154,710, 4,145,322, 4,242,246 and 5,371,121, EP 2023, BE 877 112,
AU 59,875, WO 90/02776, GB 460854, GB 1 548 541 and GB 1 330 425.
In each of these prior art patent publications, elemental sulfur
was used to improve the performance and/or the compatibility of the
elastomer-bitumen compositions. In other prior art patent
publications, other types of reagents, such as sulfur-donors and
peroxides, are disclosed. However, these additives are so expensive
that they have not, in general, been used commercially.
[0006] In general, superior performance enhancement of bituminous
compositions at a fixed loading of elastomer can be achieved by
using higher molecular weight elastomers. However with these higher
MW elastomers, poor storage stability and relatively high viscosity
can result in difficult material handling (processing, pumping,
polymer separation and reblending), even at high temperatures. A
number of examples from the prior art teach that successful
stabilization and property enhancement can be achieved in
bitumen/styrene-butadiene/sulfur blends using relatively low
molecular weight elastomers, normally well below about 150,000.
Some examples, including those used in U.S. Pat. No. 4,154,710,
have even been based on the use of very low molecular weight liquid
rubber, to initiate the sulfur reaction, thereby forming a high
molecular weight elastomeric network in-situ through vulcanization,
avoiding both storage and processing problems. However, these
compositions show sub-optimal performance, high cost or both.
[0007] Some other examples from the prior art (EPA 0174795) have
used high MW elastomers (over about 150,000) which have reacted
with sulfur to provide blends with good mechanical properties.
However, such prior art examples have all suggested that
sulfur-initiated reaction or vulcanization of a high molecular
weight elastomer be carried out in bitumen/oil blends (that is, the
bitumen is fluxed with a hydrocarbon oil). The reaction product may
then be further diluted with a light fluxant oil to reduce the
viscosity to prevent the formation by gellation of a highly viscous
product. A similar prior art (BE 87712) discloses that the bitumen
may be chemically modified by a mother solution in which a high
molecular weight elastomer (SB di-block copolymer) and sulfur have
been dissolved and pre-reacted into a light petroleum fluxant.
[0008] In a recent patent (U.S. Pat. No. 5,371,121), a process was
disclosed for producing a stable bituminous composition without
using light fluxant, and in which a high molecular weight (over
about 150,000) tri-block thermoplastic elastomer was reacted with a
defined amount of sulfur from 0.015% to 0.075% by wt. However, this
disclosure is relevant to only one specific grade of bituminous
asphalt cement (AC20R) and at relatively low sulfur loadings. At
only slightly higher sulfur loadings of 0.1 and 0.25%, as disclosed
in Examples 15 and 16 of the patent, gel formation resulted in
viscosities exceeding the standard for AC20R. The process of the
present invention overcomes these difficulties.
[0009] Most recent prior art (WO 97/45488) disclosed a new
bitumen-polymer blend that utilizes a combination of two types of
elastomers (SB di-block copolymer with 100,000 MW and SBS tri-block
copolymer with 300,000 MW) at effective amounts and ratios, along
with defined amounts of sulfur which is to be added and reacted
into the asphalt to enhance performance. The remainder of the prior
art refers only to the use of a single elastomer to be reacted in
the system. However, all examples given in WO 97/45488 are limited
to sulfur loading which do not exceed 4% by wt, based on the total
amount of elastomers, otherwise the viscosity is too high to permit
workability of the asphalt-polymer mix.
[0010] In principle, under reactive process conditions, especially
those using a cross-linking agent, such as sulfur, increasing the
quantity of high MW elastomer incorporated into bitumen should
require an equivalent relative increase in the quantity of sulfur,
in order to achieve better stability of the dispersed elastomer,
and acceptable mechanical properties of the product which is
processable in varied industrial applications. However, to achieve
this result represents a challenging combination of requirements.
In practice, as disclosed above in the prior art on the practice of
reactive processing of bituminous compositions, the skilled artisan
tends to proceed with considerable caution when utilizing high
molecular weight elastomers which are to be chemically vulcanized
into bitumen alone or in combination with oil or fluxing agents.
Usually, even at a fixed level of sulfur, as the concentration of
the elastomer is increased, the viscosity of the asphalt mixture
increases rapidly due to gellation and phase separation of the
asphalt and elastomer may occur because of excessive inter-polymer
cross-linking. Therefore, it is generally considered difficult to
incorporate high MW elastomer into bitumen at higher loadings,
especially for the situation in which the proportion of sulfur is
also increased proportional to the increased load of elastomer. In
addition, the limitation on the load level of elastomer which can
be vulcanized into asphalt has restricted the application of the
reactive process in important industrial applications, such as
roofing, crack filler and so on.
[0011] The present invention is directed towards solving the above
described problems whereby a sulfur reactive process is proposed
for producing unsaturated elastomer/bitumen compositions with high
loadings of high MW elastomers and corresponding high loadings of
sulfur. More particularly, the present invention is directed
towards the provision of a novel process of preparing stable, high
performance elastomer-bitumen compositions, which can be applied in
many fields of industrial application. The compositions consist of
the high MW elastomers (over about 150,000) which has been reacted
into bitumen using sulfur as a cross-linking agent, resulting in a
high performance product at desirable high loadings of sulfur and
elastomer, generally from about 2% to about 30% by wt of sulfur,
depending on the total amount of elastomer contained in the
compositions.
SUMMARY OF THE INVENTION
[0012] The present invention relates to the preparation under
reactive process conditions of stable bituminous compositions
modified with high MW elastomers using sulfur or other
cross-linking agent as a reagent, to provide compositions with
superior performance. More particularly, the present invention is
concerned with elastomer reacted bituminous compositions, in which
high MW elastomers having molecular weight of over about 150,000
and with a conjugated diene structure have been well reacted
through the agency of sulfur or other cross-linking agent, into
bitumen, resulting in high performance products at desirable load
levels of sulfur and/or elastomer.
[0013] In accordance with the invention, the elastomer with a
conjugated diene structure can be a butadiene based homo-polymer or
random or block (di- or tri-) co-polymer or an isoprene based homo
or co-polymer. Elemental sulfur is selected as the preferred
cross-linking agent due to economics and availability, whereby it
is used as a reaction reagent, to effectively in-situ vulcanize the
elastomer into bitumen under defined procedures disclosed herein to
achieve stable bituminous compositions with a good performance/cost
balance, which may be applied over a broader range of applications.
Other cross-linking agents, such as sulfur donors and peroxides,
may be employed.
[0014] According to the present invention, these result are
achieved by employing a defined procedure, in which the addition
and mixing of the elastomer and/or sulfur are staged/programmed by
controlling the timing and amount of incremental addition of sulfur
and/or elastomer to achieve in-situ vulcanization of the elastomer
into bitumen under agitation at elevated temperature. The time- and
mass-controlled addition of elastomer and/or sulfur may also be
achieved continuously within an equivalent period of time using the
principle of the invention.
[0015] Accordingly, in one aspect of the present invention, there
is provided a method of forming a bituminous composition, which
comprises dispersing by blending and reacting an elastomeric
polymer having a conjugated diene structure and a molecular weight
of about 45,000 to about 750,000 with bitumen and a cross-linking
agent at a temperature of about 150.degree. C. to about 220.degree.
C. to stably incorporate the elastomeric polymer into the bitumen
against phase separation according to ASTM D5892, wherein at least
one of the elastomeric polymer and cross-linking agent is added
incrementally to the bitumen (or equivalently continuously) and
reacted to permit greater amounts of elastomeric polymer and/or
cross-linking agent to be incorporated into the bitumen.
[0016] As described in more detail below, the method aspect of the
present invention is preferably carried out using one of three
different embodiments to provide the bituminous compositions which
are stable against phase separation. In the three embodiments,
sulfur or other cross-linking agent, elastomeric polymer or both
are added incrementally or equivalently over the same overall time
period to the bitumen at the elevated temperature. The invention
extends to bituminous compositions which are stable against phase
separation and which are obtainable by the procedures described
herein.
[0017] The advantages of the present invention include the ability
to employ high molecular weight elastomers at relatively high load
levels in a reaction process with better viscosity control to
confer enhanced performance on the bituminous composition at
relatively low cost towards diverse applications. Further, the
procedure of the present invention enables the use of a wide range
of bitumens, many of which cannot normally be compatibilized with
the elastomers, especially when their molecular weight is high/or
the load level is high.
GENERAL DESCRIPTION OF INVENTION
[0018] The term "bitumen" used herein means a class of black or
dark-colored (solid, semi-solid or viscous) cementitious
substances, natural or manufactured, composed principally of high
molecular weight hydrocarbons of which asphalts, tars, pitches and
asphaltites are typical. The term "asphalt" used herein means a
dark, brown to black, cementitious material, solid or semi-solid in
consistency, in which the predominating constituents are bitumens
that occur in nature, as such, or are obtained as residue in
petroleum refining.
[0019] The bitumens which may be used in the present invention vary
widely in softening point, generally from about 20.degree. to
65.degree. C., preferably about 25.degree. to 55.degree. C. The
bitumen may comprise about 75 to about 99 wt % of the total
composition, preferably about 85 to about 98 wt % of the total
composition.
[0020] The ability to use bitumens of widely varying properties is
an advantage of the present invention. Normally only a narrow range
of asphalts is suitable for phase stable incorporation of
elastomers.
[0021] The elastomers which may be used in the present invention
have a conjugated diene structure and may vary from elastomeric
polymers to elastomeric copolymers or thermoplastic elastomers. The
elastomeric polymers may be those conjugated diene polymers
selected among butadiene, isoprene and their functionalized
polymers, such as those with halogenated or carboxylated groups.
The elastomeric copolymers are thermoplastic elastomers or are
conjugated diene based copolymers with another type of polymer,
such as styrene and isobutylene. The copolymers may be a random or
a block; di-sequenced; multi-sequenced; or a statistical copolymer.
Suitable elastomers include NR, SBR, SB and SBS. The potential for
compatibilizing these high molecular weight elastomers of widely
varying properties in bituminous compositions is another primary
advantage of the present invention.
[0022] The elastomers which can be used include those having a
molecular weight (MW) range from about 45,000 to about 750,000,
preferably about 150,000 to about 450,000. These polymeric
elastomers are available from a variety of commercial sources.
[0023] Such elastomers may be present in the bituminous
compositions of the invention in an amount of about 1 to about 20
wt % of the total composition, preferably about 2 to about 12 wt %,
depending on the end use to which the composition is put.
[0024] The quantity of sulfur which is employed in the process of
the invention, generally varies from about 2 to about 30 wt %,
preferably about 3 to about 15 wt %, more preferably about 5 to
about 10 wt %, based on the total amount of elastomer contained in
the composition.
[0025] The process of the present invention can be carried out in
three different procedures as follows, any one of which may lead to
different load level of elastomers, reacted/incorporated into
bitumen at a desirable amount of sulfur.
[0026] In Procedure A, the quantity of elastomer loaded is in a
range from about 1% to about 8% by wt, preferably about 1.5% to
about 5% by wt. All the elastomer needed for the final composition
is added to bitumen and is well mixed/dispersed in the bitumen at a
temperature generally in a range of about 150.degree. C. to about
220.degree. C., preferably from 170.degree. C. to about 190.degree.
C. Then elemental sulfur is added to the mixture in increments with
defined time intervals with sufficient agitation.
[0027] When the sulfur is added incrementally to the heated mixture
of bitumen and elastomer, the shearing is maintained and
predetermined weights of the sulfur are added with closely defined
time intervals between each increment of sulfur addition. Generally
about 2 to about 10 increments of sulfur addition are used over a
total period of about 1 hr to about 12 hours, with about 0.5 to
about 2 hours between each incremental loading. Alternatively, the
mass flow rate of sulfur when added continuously may be determined
within an equivalent period of time, based on these criteria.
[0028] The incremental load of sulfur in this procedure is from
about 3% to 15% by wt, preferably about 5 to about 10 wt %, based
on the total amount of elastomer.
[0029] Following Procedure A, the incremental loading of sulfur,
with certain time intervals or over a defined period of time under
agitation, leads to a high degree of interaction of the elastomer
and the bitumen. As a result, a high degree of compatibilization of
the high MW elastomer with bitumen is achieved while at the same
time avoiding rapid increased viscosity extremes due to excessive
inter-polymer cross-linking, that normally occurs in conventional
procedures for loading sulfur into compositions similar to those
with which the present invention is concerned.
[0030] In Procedure A, the bitumen preferably has a softening point
as determined by ASTM D36 of about 25.degree. to about 55.degree.
C. The compositions which are produced following procedure A
preferably have a softening point, as determined by ASTM D36, of
about 50.degree. to about
[0031] In Procedure B, all the sulfur needed for the final
composition is added at one time in the conventional manner after
some (a defined percentage) of the total elastomer has been first
loaded and well dispersed into the bitumen. The amount of elastomer
added in the first load is important. The quantity of the first
load of elastomer is controlled within a range from about 20% to
about 60% by wt of the total amount of elastomer, which is from
about 2% to about 12% by wt, preferably from about 3 to about 7.5%
by wt, in the final composition.
[0032] The amount of sulfur employed is about 10 to about 25 wt %
of the initial loading of elastomeric polymer and the total amount
of sulfur is about 3 to about 15 wt %, preferably about 5 to about
10 wt %, of the total amount of elastomeric polymer. The mixture is
reacted at a temperature of about 150.degree. to about 220.degree.
C., preferably about 170.degree. to about 190.degree. C., from
about 5 to about 60 minutes.
[0033] Then, the remaining amount of elastomeric polymer is added
all one time or incrementally to the elastomer reacted bitumen in
about 1 to about 5 increments over a period of about 0.5 to about
12 hours with about 1 to about 2 hours between each incremental
loading. Equivalently, the remainder of the elastomeric polymer may
be added continuously over the period of incremental addition of
the remainder of the elastomeric polymer.
[0034] The pre-dispersed elastomer from the first load should have
quickly reacted with the bitumen in the presence of the excess of
sulfur without gellation and effectively provides an elastomer
reacted bitumen binder matrix, which is Theologically much more
closely matched to facilitate the dispersion of the remaining
elastomer to be loaded later. The residue of un-reacted sulfur in
the matrix readily reacts in an effective manner with the dispersed
phase of elastomer added subsequently, ensuring the stabilization
of elastomer reacted bituminous compositions.
[0035] The bitumen employed in Procedure B preferably has a
softening point as determined by ASTM D36 of about 25.degree. to
about 55.degree. C. The stable bituminous composition using
Procedure B should preferably have a softening point as determined
by ASTM D36 of about 50.degree. to about 110.degree. C.
[0036] The compositions prepared according to procedure B have a
high MW elastomer chemically incorporated into bitumen at
relatively high load levels of elastomer and/or sulfur, while still
maintaining good workability (relatively low viscosity) of the
product.
[0037] In Procedure C, both elastomer and sulfur are added
incrementally and simultaneous or sequentially with sufficient
agitation and at the same processing temperature as disclosed above
under Procedures A and B. In principle, this procedure has combined
Procedures A and B in a way that leads to a higher loading of
elastomer in the bituminous compositions, which are stable and
processable, and have a good cost/performance balance.
[0038] Following this reactive procedure, the elastomer may be
loaded to levels of up to about 15% by wt, preferably up to about
12% by wt, which are suitable for those industrial applications
which require high loading of polymeric modifier to meet specific
engineering performance criteria. The quantity of sulfur which is
employed in this procedure is in the range from about 2% to about
20% by wt, preferably from about 3 to about 10% by wt.
[0039] In this procedure C, each component may be added in about 2
to about 5 increments over a period of about 0.5 to about 12 hours
with about 20 mins to about 2 hours between increments.
Equivalently, the elastomeric polymer and/or sulfur may be added
continuously over the period of incremental addition of the
elastomeric polymer and/or sulfur.
[0040] The bitumen employed in procedure C preferably has a
softening point, as determined by ASTM D36, of about 25.degree. to
about 55.degree. C. The compositions prepared according to
procedure C preferably have a softening point as determined by ASTM
D36 of about 55.degree. to about 130.degree. C.
[0041] These procedures described above enable the production of
highly compatible (stable) rubberized bituminous compositions,
which may be further processed, and which have a viscosity in a
workable range for paving, roofing or other bitumen-related
industrial applications. The viscosity of the composition generally
vary from about 200 to about 12,000, preferably about 1000 to about
6000 centi-poise. The viscosity for composition intended for paving
application generally is determined at 135.degree. C. according to
ASTM D4402 while the viscosity of composition intended for roofing
application is determined at 180.degree. C. according to ASTM
D4402.
[0042] As noted earlier, the procedure permits a high loading of a
high molecular weight elastomer without causing gellation problems
and offers enhanced performance which can be achieved at a
relatively low loading in comparison with those of the prior
art.
[0043] The rubberized bitumen compositions obtained by the
procedures of the invention may be diluted with the same or other
bitumen to provide the desired composition for the specific
contemplated end use. The rubberized bitumen products, in either
concentrated or diluted form, may be mixed with additional
identical or chemically similar elastomers to form a uniform
mixture.
[0044] In addition, the diluted rubberized bitumen products
according to the present invention may be further reacted with
sulphur or other conventional cross-linking agent under low shear
agitation to optimize the performance of the product.
EXAMPLES
[0045] Example A
[0046] This Examples describes the results of a first set of
experiments using bitumen AC-20-1 from AASTO Materials Reference
Laboratory (Grade: AC-20, MRL asphalt code: ABF).
[0047] In this first set of experiments, the elastomer used was a
styrene-butadiene-styrene tri-block copolymer (SBS), a
commercially-available thermoplastic elastomer with the trade-name
Enichem-161B. The elastomer has an average molecular weight of
278,300 and a styrene/butadiene ratio of 30:70.
[0048] In such experiments, the polymer and sulfur, when used, were
dispersed into the bitumen with a high shear mixer (Brinkman
Polytron Mixer) at a temperature of 180.degree. C. Certain
properties of the resulting compositions are listed, using ASTM
Standard procedures.
[0049] The results obtained in this first set of experiments is
shown in Table I below. There are four experiments reported in
Table 1, labelled Control, Comparative Example 1, Comparative
Example 2 and Inventive Example 1, following Procedure A described
above.
[0050] Results for the Control Example in Table I indicated that
the SBS used was not compatible with the bitumen. The blend did not
show superior performance enhancement and tended to polymer
separation during hot storage without agitation.
[0051] The following two. Comparative Examples (No. 1 and 2)
illustrate the results of using a conventional blending procedure
to carry out bitumen modification with SBS elastomer using sulfur
as a reagent for the purpose of improving both performance and
compatibility.
[0052] Comparative Example 1
[0053] In a one liter mixer, 97.5% by wt of the bitumen was heated
to 180.degree. C. 2.5% by wt of Enichem-161B thermoplastic
elastomer, was then added and dispersed in the bitumen with the
high shear mixer for one hour at a speed of about 2,500 rpm. Within
one or two minutes, elemental sulfur was added slowly to the
mixture, while still mixing, in the amount of 5% by wt based on the
total amount of the elastomer dispersed in the bitumen and mixing
was continued for a further 1.5 hours. After the mixing was
stopped, the dispersion of the elastomer was unstable (phase
separated) and a viscous polymer-rich layer was formed on the
surface of the rubberized bituminous composition.
[0054] Comparative Example 2
[0055] The method of Comparative Example 1 was repeated but 10% by
wt of elemental sulfur was added instead of 5% by wt of the sulfur
based on the total amount of the elastomer dispersed in the
bitumen. This substitution resulted in the formation of a very
viscous jelly-like rubber binder within about 0.5 hour after
addition of sulfur under the process conditions described in
Comparative Example 1. Additional mixing for two hours under high
shearing did not cause the formed rubber gel to disappear from the
bituminous composition. The resulting composition had a very high
viscosity due to gellation and could not be tested for
properties.
[0056] Inventive Example 1
[0057] This Example illustrates an inventive step using procedure A
as described above.
[0058] In a one liter mixer, 97.5% by wt of the same bitumen as
used in the above Comparative Examples were heated to 180.degree.
C., 2.5% by wt of Enichem-161B thermoplastic elastomer were added
and dispersed in the bitumen with the high shear mixer for one hour
at a speed of about 2,500 rpm. Sulfur then was added incrementally
to the heated mixture of bitumen and the elastomer while
maintaining high shearing with a defined interval between each
increment of sulfur addition. Three increments of sulfur addition
were used over a total period of about 2.5 hours, with about 40
minutes between each incremental loading, in a total amount of 10%
by wt of sulfur based on the total amount of the elastomer
contained in the composition. The resulting composition was very
homogeneous and showed a high degree of compatibility of the
elastomer into the bitumen while at the same time no extreme
viscosity or gel formation resulted using the reactive procedure
described above. The results of the property tests are given in
Table I below.
[0059] Example B
[0060] This Example describes the results of a second set of
experiments using bitumen AC-20-2 from the Huntway Refinery,
California, USA. This bitumen grade is a typical AC-20 grade from
this region. In this second set of experiments, the elastomer
employed was the same as that used in Example A.
[0061] The results obtained in this second set of experiments are
shown in Table 2. There are eight experiments reported in Table 2,
labelled Control, Comparative Example 1, Comparative Example 2,
Inventive Example 2, Inventive Example 3, Inventive Example 4,
Inventive Example 5 and Inventive Example 6.
[0062] The Control Example in Table II indicated that the SBS used
was also incompatible with the bitumen (AC-20-2). Polymer
separation can be seen in the Table.
[0063] The first two Comparative Examples (Sample Nos. 1 and 2)
were prepared using the conventional procedure in attempts to
produce homogeneous compositions of modified bitumen with SBS
elastomer at load levels of 4% by wt using sulfur as a
cross-linking agent at load levels of 2.5% by wt and 5% by wt
respectively, based on the total amount of elastomer dispersed in
final composition.
[0064] Comparative Example 1
[0065] In a one liter mixer, 95.9% by wt of bitumen was heated to
180.degree. C. 4% by wt of Enichem-161B thermoplastic elastomer,
was then added and dispersed in the bitumen with a high shear mixer
for 1.5 hours at a speed of about 2,500 rpm. Within one minute,
elemental sulfur was added slowly to the mixture, while still
mixing, in the amount of 2.5% by wt based on the total amount of
the elastomer dispersed in the bitumen, which was continuously
mixed for 1.5 hours. After the mixing was stopped, the dispersion
of the elastomer was unstable and a viscous polymer-rich layer was
formed on the surface of the rubberized bituminous composition.
[0066] Comparative Example 2
[0067] The method of Comparative Example 1 was repeated but 5% by
wt of elemental sulfur was added instead of 2.5% by wt of the
sulfur based on the total amount of the elastomer (4% by wt)
dispersed in the bitumen. This substitution resulted in a very
viscous jelly-like rubbery binder within about 20 min after
addition of sulfur under the process conditions described in the
Comparative Example 1 above. Additional mixing became quite
difficult because of the highly viscous mixture formed due to the
significant gellation of the bituminous composition. As a result,
no property tests could be performed on the sample.
[0068] The Inventive Examples that follow illustrate the inventive
examples using Procedure A, Procedure B and Procedure C
respectively, which have been described in the General Description
of Invention. The stable compositions at different SBS elastomer
load levels were produced based on these defined Procedures.
[0069] Inventive Example 2
[0070] This Example again illustrates the inventive process using
procedure A to compatibilize the SBS into bitumen (AC-20-2), in
this case at a 4 wt % loading level.
[0071] In a one liter mixer, 95.8% by wt of the same bitumen as
used in the above Comparative Examples were heated to 180.degree.
C., 4% by wt of Enichem-161B thermoplastic elastomer were added and
dispersed in the bitumen with the Polytron Mixer for about one hour
at a speed of about 2,500 rpm. Sulfur then was added incrementally
to the heated mixture of bitumen and the elastomer while
maintaining high shearing with a defined interval between each
increment of sulfur addition. Three increments of sulfur addition
were used over a total period of about 2.5 hours, with about 40
minutes between each incremental loading, to a total amount of 5%
by wt of sulfur based on the total amount of the elastomer
contained in the composition. The resulting composition appeared to
be very homogeneous and to display a high degree of compatibility
of the elastomer into the bitumen while at the same time no extreme
viscosity or gel formation occurred during the above described
reactive procedure. The results of property measurements are given
in Table II.
[0072] Inventive Example 3
[0073] This Example illustrates an inventive example using
Procedure B to compatibilize 4% by wt of the SBS into bitumen
(AC-20-2).
[0074] In a one liter mixer, 95.8% by wt of the same bitumen as
used in the above comparative example were heated to about
185.degree. C., 2% by wt of Enichem-161B thermoplastic elastomer
were added and dispersed in the bitumen with the Polytron Mixer for
about one hour at a speed of about 2,500 rpm. The total amount of
10% by wt of sulfur based on the amount of the already dispersed
elastomer in the composition then was added quickly within 1 or 2
minutes to the mixture with agitation. About 15 minutes after the
sulfur was added, the remaining SBS (another 2% by wt) was added
and dispersed with high shear for one and half-hours. The resulting
composition also showed very homogeneous properties, and a high
degree of storage stability as found in the sample with the same
final composition prepared by the Procedure A. The results are
given in Table II.
[0075] Inventive Example 4
[0076] This Example again illustrates an inventive example using
Procedure B to compatibilize 6% by wt of the SBS into bitumen
(AC-20-2).
[0077] In a one liter mixer, 93.8% by wt of the same bitumen as
used in the above comparative example were heated to about
185.degree. C., 2% by wt of Enichem-161B thermoplastic elastomer
were added and dispersed in the bitumen with the Polytron Mixer for
about one hour at a speed of about 2,500 rpm. The total amount of
10% by wt of sulfur based on the amount of elastomer already
dispersed in the composition then was added quickly within 1 or 2
minutes to the mixture with agitation. About 15 min after sulfur
was added, 2% more by wt of SBS was added and dispersed with high
shear for about one hour. Additional SBS (the second 2% by wt) were
added and dispersed with high shear for one and half-hours. The
remaining SBS (the last 2% by wt) was added and dispersed into the
mixture for about one hour. The resulting composition also showed
good storage stability as shown in Table II.
[0078] Inventive Example 5
[0079] This Example illustrates an inventive example using
Procedure C to compatibilize 6% by wt of the SBS into bitumen
(AC-20-2).
[0080] In a one liter mixer, 93.7% by wt of the same bitumen as
used in the above Comparative Examples were heated to about
185.degree. C., 2% by wt of Enichem-161B thermoplastic elastomer
were added and dispersed in the bitumen with the Polytron Mixer for
about one hour at a speed of about 2,500 rpm. Then, 10% by wt of
sulfur based on the amount of the already dispersed elastomer in
the composition was added quickly within 1 or 2 minutes to the
mixture with agitation. About 15 minutes after the sulfur was
added, 2% more by wt of SBS was added and dispersed with high shear
for about one hour. Additional SBS (the second 2% by wt) was added
and dispersed with high shear for one and half-hours. The remaining
SBS (the last 2% by wt) was added and dispersed into the mixture
for about 45 min, followed by the addition of about 1.7% by wt of
sulfur based on the total amount of the elastomer in the final
composition. Additional mixing for two hours resulted in a SBS
modified bitumen composition with relatively better properties with
respect to the Example 4 having the same SBS load level. The
resulting composition showed good storage stability and performance
as shown in Table II.
[0081] Inventive Example 6
[0082] This Example illustrates again an inventive example using
Procedure C but to compatibilize 8% by wt of the SBS into bitumen
(AC-20-2).
[0083] In a one liter mixer, 91.6% by wt of the same bitumen as
used in the above Comparative Examples were heated to about
185.degree. C., 2% by wt of Enichem-161B thermoplastic elastomer
was added and dispersed in the bitumen with the Polytron Mixer for
about one hour at a speed of about 2,500 rpm. The 15% by wt of
sulfur based on the amount of the already dispersed elastomer in
the composition was then added quickly within 1 or 2 minutes to the
mixture with agitation. About 15 min after the sulfur was added, 4%
more by wt of SBS were added and dispersed with high shear for
about one hour. The remaining sulfur was added in two increments
with about 30-min time intervals to the mixer. The remaining SBS
(the last 2% by wt) was added and dispersed into the mixture for
about two hours. The resulting composition showed good storage
stability and good mechanical performance as shown in Table II.
SUMMARY OF DISCLOSURE
[0084] In summary of this disclosure, a unique reactive process of
preparing rubberized bitumen products at high loadings of high
molecular weight elastomers, such as styrene-butadiene block
copolymers, is provided in which the elastomer is compatibilized
into the bitumen by incremental loading techniques. Modifications
are possible within the scope of this invention.
1TABLE I Examples Control Comparative 1 Comparative 2 Inventive 1
Blending Procedure Conventional Conventional Conventional Procedure
A Composition Bitumen AC-20-1, % by wt 97.5 97.375 97.25 97.25 SBS,
% by wt 2.5 2.5 2.5 2.5 Sulfur, % by wt 0 0.125 0.25 0.25
Sulfur/Elastomer ratio -- 1/20 1/10 1/10 Properties and Test Method
Softening point, C., ASTM D36 55 86 -- 61 Viscosity, cp at
135.degree. C., ASTM D4402 758 1080 -- 1340 Viscosity, cp at
180.degree. C., ASTM D4402 -- -- -- -- Polymer Separation, ASTM
D5892 Softening point, C. at top, ASTM D36 98 75 -- 59 Softening
point, C. at bottom, ASTM D36 52 55 -- 59 Storage Stability, ASTM
D5892 no no gellation yes
[0085]
2TABLE II Comparative Comparative Examples Control 1 2 Inventive 2
Inventive 3 Inventive 4 Inventive 5 Inventive 6 Blending Procedure
Conventional Conventional Conventional Procedure A Procedure B
Procedure B Procedure C Procedure C Composition AC-20, % by wt
(AC-20-2) 96 95.9 95.8 95.8 95.8 93.8 93.7 91.6 SBS, % by wt 4 4 4
4 4 6 6 8 Sulfur, % by wt 0 0.1 0.2 0.2 0.2 0.2 0.3 0.4
Sulfur/Elastomer ratio -- 1/40 1/20 1/20 1/20 1/40 1/20 1/20
Properties and Test Method Softening point, C., ASTM D36 83 86 --
95 85 91 100 112 Viscosity, cp at 135.degree. C., ASTM 1050 1780 --
3000 2135 -- -- -- D44025 Viscosity, cp at 180.degree. C., ASTM 253
345 -- 565 413 1042 1505 11775 D4402 Polymer Separation, ASTM D5892
Softening point, C. at top, ASTM 112 102 92 83 92 100 127 D36
Softening point, C. at bottom, 52 63 92 82 94 101 125 ASTM D36
Storage Stability, ASTM D5892 no no gellation yes Yes Yes Yes
Yes
* * * * *