Note: Descriptions are shown in the official language in which they were submitted.
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WO 97/30121 PCT/CA97/00102
TITLE OF INVENTION
STABILIZED BITUMINOUS COMPOSITION BASED
- ON POLYMER IN-SITU BLEND
FIELD OF INVENTION
The present invention is related to a process of
combining polystyrene (PS) or PS-based plastics with an
elastomer or rubber as a dispersion agent to form a
novel stabilized bituminous composition, which
comprises:
a) bitumen,
b) a PS-based plastic (PS homopolymer or PS
blend or graft copolymer) which is itself not
compatible with bitumen, and
c) an elastomeric triblock copolymer containing
styrene which is compatible with bitumen.
The principles embodied in such composition are
applicable to other polymers which are compatible in the
molten state with polystyrene, as described herein.
BACKGROUND TO THE INVENTION
PS or PS based plastics are among the most commonly
used thermoplastic polymers and generate a considerable
amount of recoverable scrap material. Like other
polymeric materials, such as polyethylene (PE),
polypropylene (PP) and ethylene-vinyl acetate (EVA), due
to their high stiffness over a range of service
temperatures, PS would also seem very suitable for
addition to bitumen and could thereby contribute
effectively to the stiffness and strength of bitumen.
Unfortunately, PS has problems similar to those of other
polymer~.c materials, in that it does not significantly
' increas? the elasticity of the asphalt binder and blends
or dispersions with a range of different type of
bitumens demix quite rapidly during hot storage. In
additio, PS has been found to be very difficult to
disperse into bitumen even using high shear, because of
SUBSTITUTE SHEET (RULE 26)
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its intrinsic structural features of rigid molecular
_ _ chains with high melt strength. Although it is
economically attractive to consider PS based scrap
thermoplastics as a modifier for asphalt, the above
discussed obstacles have limited such an application.
The use of polymers (plastics orrubbers), whether
singly or in combination, as asphalt modifiers has been
known in the construction industry for many years. Many
of these applications have received varying degrees of
success in bituminous modification. The degree of
success for each product is mainly dependent on the ease
of processing, on the compatibility of the polymerwith
bitumen and on the final property of the bituminous
composition. These prior art applications have provided
the skilled technologist with many means for modifying
bitumen properties, namely:
(a) by taking advantage of the plastics, such as
PE, PP and their copolymers, with their
crystallinity and their ease of mixing, to gain the
stiffness and strength of bitumen;
(b) by using different synthetic elastomers, such
as polyurethane, neoprene, NBR, EPDM and styrenic
block copolymers (such as SBS, SIS, SB and SEBS),
to improve the elastic recovery and viscosity of
bitumen at high service temperature and the
flexibility at low service temperature by selecting
polymers compatible with bitumen according to its
chemical composition;
(c) by adding different types of process oil
and/or treating the binder with inorganic acids to
improve the compatibility of polymer to bitumen;
(d) by using different crosslinking agents to
vulcanize rubbers (mostly butadiene-based
copolymers) into bitumen to build up chemical
interaction and tc obtain miscible rubberized
bitumen; and
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{e) by tailoring PE copolymers (such as EVA)
_ _ through controlling the proportion of polymer
components such as vinyl acetate (VA) in Eva, which
enhance their compatibility and performance as
bitumen modifiers.
Furthermore, the prior art (U. S. Patents Nos. 5,280,064
and 5,494,966, and assigned to the assignee hereof) also
disclosed a reactive process of in-situ producing a
copolymer highly miscible with bitumen from incompatible
plastics (using PE of high MW) and compatibilized rubber
components. The situ-prepared elastomer reagent was
found to function as stabilizer for both PE based
plastics and butadiene based elastomers when used alone
or together as bituminous modifiers (WO 94/22957,
assigned to the assignee hereof).
Although there are other types of polymers
described in the prior art as modifiers for bituminous
application, two types of polymers, namely PE and its
copolymers (as a representative of the plastics field)
and styrenic-dime copolymers (as a representative of
the rubber field) still remain the most useful as
modifiers in the asphalt industry, but only when they
are stabilized or compatibilized in bitumen using
technologies described elsewhere.
Polystyrene (PS) plastics represents a line of
rigid polystyrene based products from crystal
homopolymer, toughened graft copolymers, to blends or
alloys with various rubbers. The rigidity and high melt
strength of PS plastics causes them to be very difficult
to disperse into hot liquid bitumen. The coarsely
dispersed phase produced under high shear force
separates quickly once agitation stops. Of all the
prior arm related to the use of plastics as bitumen
w modifiers, the inventor knows of none involving the use
of any types of polystyrene rigid plastics for such
purpose.
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Of the prior art related to elastomeric modifiers,
_ _ many have disclosed the application of styrenic block
copolymers, commonly called thermoplastic rubbers (TR),
which are produced by a sequential chemical operation of
successive polymerisations of styrene-butadiene-styrene
(SBS), styrene-ethylene/butylene-styrene (SEBS) and of
styrene-isoprene-styrene (SIS) systems.
TR dispersions can render their strength and
elasticity to bitumen from a physical crosslinking of
styrene segments into a three-dimensional network as
disclosed by Holden et al. in the Proceedings of
International Rubber Conference, 1967 Maclaren. This
result can be achieved by the agglomeration of the
styrene polymerized block (or polystyrene segments of
triblock copolymers); forming very fine domains (down to
the nm scale), which provide the physical cross-linkage
for a three-dimensional butadiene, ethylene/butylene or
isoprene polymerized rubbery matrix. It is known, in
all related prior art, that the chemical structure of
the styrenic block copolymers which enhances bitumen
performance modifier is not related to the chemical
structure of the styrenic block copolymers used as a
dispersing and/or compatibilizing agent which could
promote dispersion and/or stabilization of another
separate polymer. Specifically, most of the prior art
is focused on processes by means of which the styrenic
block copolymers may be compatibilized with bitumen.
SUMMARY OF INVENTION
In accordance with the present invention,
homopolymers or copolymers of styrene and styrene
derivatives, normally incompatible with bitumen and
tending to separate therefrom, can be stably dispersed
in bitumen by employing a triblock copolymer which is w
readily dispersed or dissolved in the bitumen and which
comprises an elastomeric copolymer containing styrene
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which is compatible with bitumen.
_ _ Accordingly, in one aspect of the present
invention, there is provided a stable bituminous
composition, comprising:
5 a continuous bitumen phase,
an elastomeric triblock copolymer comprising
polystyrene segments and stabilized and compatibilized
in said bituminous phase, and
a dispersed particulate polymer phase miscible in
the molten state with polystyrene dispersed in said
bituminous phase and normally incompatible with said
bituminous phase and stabilized against separation from
said bituminous phase by said triblock copolymer.
The bitumen-soluble elastomeric copolymer
containing a styrene segment serves a dual function,
namely {1) effects a uniform dispersion of polystyrene-
based rigid polymers normally incompatible with bitumen
and (2) provides a styrene domain as a receiving unit
for stabilization of the dispersed polystyrene-based
rigid polymer against separation from the bitumen with
bitumen. The polystyrene domains, which are dispersed
throughout the bitumen by reason of the stabilization or
compatibilization of the elastomeric triblock copolymer
in the bitumen enable the normally-incompatible
polystyrene macromolecules to be incorporated into the
bitumen by receiving the polystyrene particulates into
the domains. The domains in the rubberized bitumen
continuous phase become larger once the polystyrene
macromolecules are blended in and increase in dimension
with increasing levels of dispersed polystyrene.
6ENERAh DESCRIPTION OF INVENTION
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
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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.
The domain of the elastomeric copolymer of styrene
which is readily dispersed or stabilized in the bitumen
is provided by an elastomeric triblock copolymer in
which the butadiene rubber segments are compatible with
or soluble in or are able to be compatibilized with or
solubilized in bitumen. Elastomeric triblock copolymers
may comprise about 20 to about 800 of terminal styrene
blocks, preferably about 24 to about 450.
Examples of block copolymers which may be employed
include styrene-butadiene-styrene triblock copolymers
(SBS), styrene-ethylene/butylene-styrene triblock
copolymers (SEBS) and styrene-isoprene-styrene block
copolymers (SIS). These triblock polymers may be
employed for forming stable dispersions of the rigid
styrenic polymers in the bitumen.
Elastomeric block copolymers which may be used in
the composition of the present invention may have a
molecular weight (Mn) of from about 30,000 to about
375,000, preferably about 75,000 to about 275,000.
The rigid styrenic polymers which are stably
dispersed in bitumen according to the invention may be
polystyrene homopolymers, such as crystal polystyrene
and polystyrene foam, or may be grafted copolymers and
physical blends/alloys with various rubbers, or may be
polymers of styrene derivatives, such as poly(alpha-
methylstyrene), polyp-tert-butylstyrene) and
polychlorostyrene. The rigid styrenic polymers also may r
comprise styrene based rigid copolymers, such as
polystyrene-co-vinylacetate) and polystyrene-co-
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7
vinylthiophene). The styrenic polymers may be natural '
_ _ or recycled polymer, including comingled blends of
styrenic polymers.
' The SEBS, SBS or STS triblock copolymers also may
be used to disperse and form stable dispersions of other
polymers in place of polystyrene, provided that the
polymer is miscible with polystyrene in the molten state
and hence particulates can be received by the
polystyrene domains. One such polymer is polyphenylene
IO oxide (PPO), which is difficult to disperse in bitumen
but which is miscible with polystyrene in a molten state
at any ratio and may be dispersed and incorporated into
the bitumen by the domain effect.
Such styrenic polymers may have a molecular weight
of from about 40,000 to about 1,400,000, preferably
about 100,000 to about 300,000.
The bitumen-compatible elastomeric triblock
copolymer may be provided in any desired amount in the
bitumen consistent with the amount of normally non-
dispersible polymer to be dispersed and the properties
desired to be imparted to the bitumen by the dispersed
polymer. Generally, the quantity of elastomeric
triblock copolymer dispersed in bitumen may range from
about I to about 20 wto, preferably about 3 to about 15
wt~, of the bituminous composition. Generally, the
quantity of styrenic polymer dispersed in the bitumen
may vary from about 1 to about 35 wto, preferably about
3 to about 15 wt~, of the bituminous composition.
The stabilized bituminous compositions of the
invention show no tendency to phase separate at elevated
temperatures in the range of about 100 to about 200C
and remain stable in the absence of stirring,. i.e. the
compositions exhibit no tendency for the dispersed
particulate phase to separate from the continuous
bituminous phase.
The stabilized bituminous compositions of the
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invention also may be cooled to ambient temperature, may
_ _ be reheated up to about 160°C or more up to about
200°C, several times, and may be maintained at such high
temperatures for several days, without any tendency to
phase separation of the dispersed particulate phase.
The stable dispersions of rigid styrene polymers or
other rigid polymer miscible in the molten state with
the polystyrene in the continuous bituminous phase may
be produced in any convenient manner. The elastomeric
triblock copolymer first is uniformly incorporated into
the bitumen, usually by dissolving the elastomeric
triblock copolymer in the bitumen as to establish very
fine polystyrene domains (sized down to the nm scale)
and a cross-linked rubbery matrix in the continuous
bituminous phase. The polystyrene or other polymer then
is added to the composition for dispersion therein, at a
temperature of about 150° to about 200°C, preferably
about 170° to about 180°C, which may be effected under
high shear conditions. As mentioned above, the styrene
component of the elastomeric triblock copolymer provides
domains which assist first in the dispersion of the
styrene polymer in the continuous bituminous phase and
then in stabilizing the dispersed styrene polymer
against phase separation from the continuous bituminous
phase. Alternatively, the elastomeric triblock
copolymer and rigid styrene polymer may be blended into
the bitumen simultaneously to provide the stable
composition.
The stabilized bituminous compositions provided
herein may be used as a paving material for all types of
paving as well as finding applications in roofing
membranes, shingles, waterproofing membranes, sealants, '
caulks, potting resins and protective finishes. Paving
materials generally include aggregate, such as crushed '
stone pebbles, sand etc., along with the bitumen
composition. Similarly, other additives ~o the bitumen
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9
composition are employed, depending on the end use to
_ _ which the composition of the invention is put. For
example, a roofing material may be obtained by the
addition of suitable fillers, such as asbestos,
carbonates, silicas, wood fibers, mica, sulfates, clays,
pigments and/or fire retardants, such as chlorinated
waxes. For crack-filler application, an oxide may
advantageously be added.
Examples
A series of experiments was performed to attempt to
provide a stable dispersion of molten polystyrene in
bitumen.
Eight runs were performed using various polymer
systems in two different bitumens (Asphalt 1, Asphalt 2)
respectively and a variety of properties was evaluated.
The storage stability of the resulting systems was
assessed by microscopical observation (magnification
400X) of the morphology of samples after about a 3 hour
maintenance of the composition at about 160°C on a hot
stage with a temperature controller. With this
approach, the polystyrene dispersibility in bitumen and
the its stability at elevated temperature can be
followed and determined from the variation in the
morphological features with time during the hot staging.
The following Table 1 sets forth the materials used
and results obtained for the various runs:
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1 ()
TABLE 1
Component E~~n~ ~~'~
....... .. ._. , .... ... ... __._...___.___ ____._..__
..... __ .._. . _ .,__ _ .. .. __
. . .., ,
..
__
.... 4 5 .....
. __..___. _ .... ~. . ..,.... . _.
. .___._ . . _.. ... .._ ._
_ _ . ._
~
r ~~ y~ ~ NN C~ ' 9(? 9~
Asphalt . ... (} ~ ....._ __.._
.... ........ . .._ ._. .. . . . .._ _ .....
_ ...._.. . ....
. ........
Asphalt 2 CI (~ ~ i.? ~~2 o 0
_ ~_ ___._ )~ 'lY ? ~_ i ~
__ _. __~ ~ _
_ . .
__ _. ___
_
Polystyrene ~ C? i (~ ~ ~ O 4
,I - ~ ____~_:_.~._.._
.e ~
.
_ _..~__
._
..____
__. _~.._._.____..._.~._______.___ ~...__.___.....__._._.
___...._____.._ ___
.
.
SBS iD 4 .S 4 4 0 0
SEBS 0 0 i) C) tt 0 4 4
_....~~_.~___.~___.._._.._...___. __.;._..._'~_.._. ... _.
._____....~_...__v.
__ _ _ . _. .. ._. _ .__._.
..... __ ..
_
.
Sulfur 0 0 0 C) (~ 0.1~0 ! 0
_.. __-. ___.__~__ ,._ __.__ _ _-_~~_.._~_
_.___ __....__.__..___
_~_
Property ' ',
Penetration ~I 46 ' ~? 4 f - 43 ' - 42
at 4C - !
(
Penetration ~ ~ 12S ' 8b 105 - 73 - 110
at 25C -
i ;
Softening Point,- ' 87 51 8r) 64 64 44 49
C
Viscosity, ~ ~ "~~8 ~~g~ 988 130i~ 32503G3 425
cp, 135C ~ ~I '
_.. ___._.__ __~ __:_.___.._ . ...... .____._..-_ _.___._~_
_ _.~.._._.__.___.___.. .. ~ ...._. yes _.__ yes
Stability . _ ._ __ _ ., . yes
no* yes ..._. yes nc
no
* Could not be dispersed property into AC
Polystyrene ~vmployed in the exl>er:.ments was .~ crystal
polystyrene pl.ast is ~.rl ~:el~.~-°t l:c~trrc ;P~~;, ~~nelt index: 5
gram/1e) min and :,uppL.ie;~ by ;~'r_>l.y:~arv li.mit~eci) anct;he two
triblock copo.lyrners were :>tax'rene.--kuata;:~:iene--styrene (CBS)
thermoplastics ru::~ber (ELm~c~pr=-,r:e'~" :;<:;:~ T _r61 ~, sW's bound
styrene, 70 o bond k~uta~:~ierre, marvufac:~tured by Enichem
Elastomers Americ:.°a :Lnc:. ) aruci ;pct yrc~nk-E-
:thylene/~utylene-
styrene (:3EBS ) tam~~rmo~.:last ~ ~ ::~ ra.:k:~~~:=.;:- i n~rwt~onT"'' G ~
652, 3G o
bound styrene, ?i7a knc:>uracl c:t::l:ylerm;'butylene, manufactured
1G by Shell Chemicals Inc. i . ~'w~'~ sourves c:~t asphalt- cements
(Asphalt 1 and Aspha.l.t ~ ) k:ease~~ w~m t:t~e same Viscosity
grade were a:.~mpl.~ysad: A:;phalt;: , i...f~t~::i f::~:r runs 1, 2, 4, i
and i3 has 167 clrn:n of': ~pc:nf~~t:~:-a.~t~i~::~ra ::al:: ?':~°C',
90°C ~oftenir~g
point and 1 '~5 ~~~.. oi~ br~ ~c~~,:f ~.1.;...:~ ~,~:Lc ~: ity at
x.35°C and
15 Asphalt 2 ~..zsed for ran ~:, ~~ :_xrac6 has i4E~ dmm of
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1. ~_
penetration at ~ :°C, 45°C, :,~c°.aa:t:.en.:i.r:~c
pc::int and 2:::i3 ep. of
Brookfield vis~~os.i.ty at 1.35°:'.
In run 1, polystyrene ( x parts per 100 total parts)
alone was disper::ed in bi_tuznen r_nsing ;z high she4~r with a
'r Brinkman Po.lyt~xon~rM Mi:~exv fc.;~e 4. r~our: at abo~.zt 185°C.
Sampling from t:hu m:ixt:ar~:> wi7i.le t-len~inq indic:zted 1=hat
polystyrene was diff i~:ul:~ ~~o ~~li:~pe~ se in tr;e liquid
asphalt, even us.unc~ ~i h ~ c,i-; ~he,:~r ciur~ to its intrinsic
properties, name: y ins~;lu;>~~:i l.i.t~~;, t ~..gi. ~itY,~ and high melt
strength. 'The resu~~t.an~._. ~~~oaxw:~ ~:~ispersion quickly
separated from bitwimrJn ~~r~.<:~E~~ a~~i.ts:zt.i.on ato~,:~ped, as
evidenced by mic:z:,;scop~.c- e~:aminati.~.:r .
In runs c and 3, the 'v~BS (-l parts per 100 total
parts) alone wa;5 di~p~"r~s~.°~~7. i_n ~~ ~ta<~ ~:w °1 and
~~~sphalt 2
respectivel=y under: ti:e .~arnr ~.:ond'Lf , ~.or~~ ~~~; L~se~cl :inn run 1.
The SBS was easi.y dispersed in both sources of asphalt.
However, microscopic obsevt,~atioru :~>r, t~~ese two samples at
the hot stage t,r~owed that ti~u ::.E.;:~ v:ras compata.ble with
Asphalt 1 and not with Asp ha 7. t i' t. seo: Table 7. ) .
Ir: runs s aaud '., a rn-~x,:..ure ~ f: p:~i,y~.sty~rene ( ~l parts
per 100 total. par": s) anc:a ~>P~ !;-~ pa~ ::::~ x~~:~:c 1.00 total parts)
was dispersed i.n Asph<;lt 2 and ;"~;7p1-,al.t. ~' respectively
under the same c:::ondit~ion as other runs. In comparison
between run 9 arad xzzn 5, tnc~ r ~a u.zl.t s c>f mor,~knological
observation c~a: sam~>les v.rud:i.cr~t:era trl~~'t:., alt:h~::.>uc~rz the
dispersibility of po:l.~.~;tyrervr way= i~nxr:~~,red significantly
tOr botr'1 Ca:~E)S~ r t. rte ~'?C:ro )_. ; .'~t~:'r-5ril' I'll ~p~:rslC)r'1
bacame
stabil_zed i.n the bi.t.umen (J=,,s~:;l~~;~.:l.t: 7.) w:i°uic,,h
contained the
solubilized SBS block copolyn;ex- pr:ovidir2g the polystyrene
dispersion with ~~ receivi.ri:~ domain i:u the bitumen. The
dispersed domainz incxe~ase~_~ in dirnc.~rz~~:! on wi.trz itnc.reasing
polystyrene concer~trar_ i.on .
Irr the >BSi t~sp~nal t. ~::' E~:_; sy:,t:em, polystyreane still
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separated from Asphalt 2 binder because the SBS, which
was incompatible to the bitumen, could not provide a
stabilized styrene domain in the asphalt medium unless
the SBS itself was compatibilized with the asphalt by
other means, for example, using a reactive agent, such
as an elemental sulfur (see run 6).
In runs 7 and 8, a mixture of polystyrene (4 parts
per 100 total parts) and SEBS substituting for the SBS
(4 parts per 100 total parts) was dispersed in Asphalt 1
under the same condition as other runs. The SEBS was
compatible with Asphalt 1 and was able to function a
dispersion agent and stabilizer to provide a stabilized
bituminous composition (see results in Table 1).
SUNJNiARY OF DISCLOSURE
In summary of this disclosure, the present
invention provides a novel system for stably dispersing
normally-incompatible styrenic polymers, particularly
rigid styrenic polymers, in bitumen by providing
dispersed in the bitumen an elastomeric triblock
copolymer normally compatible with the bitumen and which
is an elastomeric copolymer of styrene. Modifications
are possible within the scope of this invention.
r
