Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
= CA 02745098 2011-05-30
CROSS-LINKING COMPOSITION IN PELLET FORM FOR PREPARING
CROSS-LINKED BITUMEN/ELASTOMER COMPOSITIONS
TECHNICAL FIELD
The present invention belongs to the field of bitumens, in particular to the
field of bitumen/elastomer compositions. More specifically, the invention
relates to a
cross-linking composition for bitumen/elastomer compositions, in pellet form,
making it possible to prepare cross-linked bitumen/elastomer compositions
having
reduced hydrogen sulphide omissions.
The invention also relates to the method for preparing cross-linked
bitumen/elastomer compositions using the cross-linking compositions in pellet
form,
a method in which the hydrogen sulphide emissions are reduced.
The invention finally relates to the use of the cross-linking compositions in
pellet form for preparing cross-linked bitumen/elastomer compositions while
limiting
the hydrogen sulphide emissions.
PRIOR ART
The use of bitumen in the manufacture of materials for highway and industrial
applications has been known for a long time: bitumen is the main hydrocarbon
binder
used in the field of road construction or civil engineering.
To be able to be used as a binder in these différent applications, the bitumen
must have certain chemical, physical and mechanical properties. It is well
known that
the properties of pure bitumens can be modified by the addition of polymers,
in
particular elastomers. For example, mention may be made of the addition of
styrene
and butadiene copolymers. It is also well known that the resistance to
mechanical
and thermal stresses, and the rheological, elastic, and mechanical
performances, of.
the bitumen/polymer compositions, and in particular of the bitumen/elastomer
compositions, are clearly improved when the polymers, and in particular the
elastomers such as the styrene and butadiene copolymers, are cross-linked
using
sulphur-based cross-linking agents.
During the preparation of the bitumen/polymer compositions, and in particular
of the bitumen/elastomer compositions, which are cross-linked with sulphur,
the
addition of sulphur can lead to emissions of hydrogen sulphide (also called
sulphureted hydrogen or H2S).
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Hydrogen sulphide is a colourless and fairly toxic gas, which also has a
characteristic odour at a very low concentration. The hydrogen sulphide
emissions
can therefore be a nuisance to those preparing the bitumen/polymer
compositions,
and in particular the bitumen/elastomer compositions, which are cross-linked
using
sulphur-based cross-linking agents. It would therefore be desirable for the
workers'
comfort and safety to reduce or even eliminate the hydrogen sulphide emissions
during the preparation of cross-linked bitumen/polymer compositions, and in
particular of bitumen/elastomer compositions.
In most methods for cross-linking with sulphur, différent sulphur-based cross-
linking agents are added to the bitumen/polymer, in particular the
bitumen/elastomer
compositions. These are added separately to the bitumen/polyrner, in
particular
bitumen/elastomer compositions, and therefore have to be stored and weighed
separately. Moreover, the usual various sulphur-based cross-linking agents are
compounds in the form of powder, which are sensitive to humidity and may
harden
during storage and as a result be difficult to handle. These powders are also
fairly
volatile and can cause (ires and/or explosions.
It would therefore be des irable to be able to prepare bitumen/polymer, in
particular bitumen/elastomer compositions, which are cross-linked, using
sulphur-
based cross-linking agents, while reducing the hydrogen sulphide emissions as
much
as possible, using a cross-linking system without the drawbacks of the
conventionally used sulphur-based cross-linking agents in powder form.
The patent US7402619 describes a cross-linking composition which may be
in pellet or powder form. This cross-linking composition comprises 5 to 50%
elemental sulphur, 0.5 to 10 %o sulphur derivatives, 5 to 5O% zinc
derivatives, 5 to
50% fatty acid derivatives and 10 to 85% polymer matrix. Furthermore the
quantity
of zinc in the cross-linking composition is at least 2% by mass and the mass
ratio
between the quantities of zinc and sulphur is comprised between 0.5:1 and 2:1.
This
significant quantity of zinc relative to the quantity of sulphur makes it
possible to
reduce hydrogen sulphide emissions during the preparation of bitumen/elastomer
compositions using this cross-linking composition. This cross-linking
composition is
not however satisfactory and has several disadvantages. The cross-linking
composition comprises too great a quantity of polymer matrix, a non-"active"
element which is not involved in the cross-linking of the elastomer in the
bitumen or
in the inhibition of the hydrogen sulphide emissions. This significant
quantity of
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polymer matrix is detrimental to the quantities of the "active" elements
involved in
the cross-linking or in the inhibition of the hydrogen sulphide emissions. In
particular,
the quantity of sulphur is fairly small in the cross-linking composition and
in the
bitumen/elastomer composition which does not allow optimum cross-linking of
the
elastomer, and does not make it possible to achieve the expected mechanical,
rheological and elastic properties, except by considerably increasing the
quantity of
cross-linking composition in the bitumen/elastomer composition. The quantity
of
zinc in the composition relative to the quantity of sulphur is also
unnecessarily very
significant. Finally, the presence of fatty acid derivatives in the cross-
linking
composition is required.
SUMMARY OF THE INVENTION
The applicant company has also sought to develop a cross-linking
composition in pellet form, allowing reduction in hydrogen sulphide emissions
during the preparation of cross-linked bitumen/elastomer compositions, while
retaining satisfactory mechanical, rheological and elastic properties in the
cross-
linked bitumen/elastomer compositions.
The applicant company has surprisingly established that the combination of a
zinc carboxylate and a triazine derivative made it possible to obtain a cross-
linking
composition in pellet form which is stab le, handleable, simple to use and
very
effective in terms of cross-linking and reduction in hydrogen sulphide
emissions,
even with very low zinc contents, in particular relative to the sulphur
contents.
To this end, the invention proposes a cross-linking composition in pellet form
comprising at least one polymer matrix , at least one cross-linking agent and
at least
one hydrogen sulphide inhibiting agent, the hydrogen sulphide inhibiting agent
comprising at least one zinc carboxylate and at least one triazine derivative.
One of the objectives of the present invention is therefore to propose an
alternative cross-linking composition in pellet form which is stable,
handleable,
simple to use, soluble in bitumen, reacting rapidly, leading to cross-linked
bitumen/elastomer compositions having satisfactory mechanical, rheological and
elastic characteristics, and making it possible to reduce hydrogen sulphide
emissions
during the preparation of said cross-linked bitumen/elastomer compositions.
Another objective of the invention is to propose a simple, rapid and sure
method for preparing cross-linked bitumen/elastomer compositions with reduced
hydrogen sulphide emissions, in particular during the cross-linking of the
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bitumen/elastomer compositions and leading to cross-linked bitumen/elastomer
compositions having satisfactory mechanical, rheological and elastic
characteristics,
this method involving a cross-linking composition in pellet form.
Another objective of the invention is the use of a cross-linking composition
in
pellet form for preparing cross-linked bitumen/elastomer compositions, with
reduced
hydrogen sulphide emissions, the cross-linked bitumen/elastomer compositions
thus
prepared having satisfactory mechanical, rheological and elastic
characteristics.
BRIEF DESCRIPTION.
The invention relates to a cross-linking composition in pellet form
comprising at least one polymer matrix , at least one cross-linking agent and
at Ieast
one hydrogen sulphide inhibiting agent, the hydrogen sulphide inhibiting agent
comprising at least one zinc carboxylate and at least one triazine derivative.
Preferably, the zinc carboxylate is chosen from zinc acetate, zinc ethanoate,
zinc propionate, zinc butyrate, zinc pentanoate, zinc hexanoate, zinc
heptanoate, zinc
octoate, zinc 2-ethyl hexanoate, zinc nonanoate, zinc dodecanoate, zinc
undecanoate,
zinc benzoate, zinc laurate, zinc palmitate, zinc stearate, zinc oleate, alone
or in a
mixture.
Preferably, the triazine derivative is chosen from the tri-alkyl
hexahydrotriazines, the tri-hydroxyalkyl hexahydrotriazines, the alkyl group
of
which comprises 1 to 12 carbon atoms, preferably 2 to 8 carbon atoms, alone or
in a
mixture.
Preferably, the polymer matrix is chosen from the polyethylenes,
ethylene/propylene copolymers, ethylene/acrylic ester copolymers,
ethylene/glycol
monostearate copolymers, ethylene/vinyi acetate copolymers, alone or in a
mixture.
Preferably, the cross-linking agent comprises sulphur optionally in
combination with vulcanization (curing) accelerators chosen from the
mercaptobenzothiazole derivatives and dithiocarbamates, alone or in a mixture.
Preferably, the quantity of zinc carboxylate is comprised between 5% and
50%, by mass, with respect to the total mass of the cross-linking composition
in
pellet form, preferably between 10% and 40%, more preferentially between 20%
and
30%.
Preferably, the quantity of triazine derivative is comprised between 5% and
40%, by mass, with respect to the total mass of the cross-linking composition
in
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pellet form, preferably between 10% and 30%, more preferentially between 15%
and
20%.
Preferably, the mass ratio of the quantities of zinc carboxylate and triazine
derivative is comprised between 0.5 and 8, preferably between 1 and 5, more
preferentially between 2 and 3.
Preferably, the quantity of zinc in the cross-linking composition in pellet
form is comprised between 1% and 15% by mass, with respect to the total mass
of
the cross-linking composition in pellet form, preferably between 2% and 10%,
still
more preferentially between 3% and 5%.
Preferably, the quantity of sulphur in the cross-linking composition in pellet
form is comprised between 5% and 50% by mass, with respect to the total mass
of
the cross-linking composition in pellet form, preferably between 10% and 40%,
more
preferentially between 20% and 30%.
Preferably, the mass ratio between the quantities of zinc and sulphur is
comprised between 0.01 and 0.3, preferably between 0.02 and 0.2, more
preferentially between 0.04 and 0.1, still more preferentially between 0.05
and 0.08.
The invention also relates to the rnethod for preparing a cross-linking
composition in pellet form as defined above, in which the cross-linking
composition
in pellet form is obtained by extrusion at a temperature below 110 C.
The invention also relates to the use of the cross-linking composition in
pellet
form as defined above, for preparing cross-linked bitumen/elastomer
compositions.
The invention also relates to the use of the cross-linking composition in
pellet
form as defined above, for reducing hydrogen sulphide emissions during the
preparation of cross-linked bitumen/elastomer compositions.
The invention finally relates to a method for preparing cross-linked
bitumen/elastomer compositions utilizing at least one bitumen, at least one
elastomer
and at least one cross-linking composition in pellet form as defined above.
Preferably, the method for preparing cross-linked bitumen/elastomer
compositions comprises the following stages:
(i) heating at least one bitumen to a temperature comprised between 160 C and
200 C,
(ii) adding at least one elastomer and stirring the bitumen/elastomer mixture,
at a
temperature comprised between 160 C and 200 C,
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(iii) adding a cross-linking composition in pellet form as defined above,
stirring
the bitumen/elastomer mixture/cross-linking composition in pellet form, at a
temperature comprised between 160 C and 200 C.
Preferably, the quantity of bitumen is comprised between 75% and 98% by
mass, preferably between 80% and 96%, more preferentially between 85% and 95%,
with respect to the total bitumen/elastomer composition/cross-linking
composition in
pellet form,.
Preferably, the quantity of elastomer is comprised between 1% and 15% by
mass, preferably between 2% and 10%, more preferentially between 3% and 5%,
with respect to the total bitumen/elastomer composition/cross-linking
composition in
pellet form,.
Preferably, the quantity of cross-linking composition in pellet form as
defined
above is comprised between 0.05% and 5% by mass, preferably between 0.1% and
2%, more preferentially between 0.15% and 1%, still more preferentially
between
0.2% and 0.5%,.with respect to the total bitumen/elastomer composition/cross-
linking composition in pellet form,
Preferably, the ratio between the quantities of sulphur and elastomer is
comprised between 0.005 and 0.05, preferably between 0.01 and 0.03, more
preferentially between 0.02 and 0.025.
The invention finally relates to a cross-linked bitumen/elastomer composition
capable of being obtained by the preparation method as defined above.
DETAILED DESCRIPTION
The cross-linking composition according to the invention is in pellet form and
comprises at least one polymer matrix , at least one cross-linking agent and
at lcast
one hydrogen sulphide inhibiting agent, the hydrogen sulphide inhibiting agent
comprising at least one zinc carboxylate and at least one triazine derivative.
One of the essential elements of the cross-linking composition according to
the invention is the presence of at least one hydrogen sulphide inhibiting
agent,
which traps the hydrogen sulphide emissions released during the introduction
of the
cross-linking agent into the bitumen/elastomer composition, said agent being a
combination of at least one zinc carboxylate and at least one triazine
derivative. This
combination is essential to the invention and makes it possible for the pellet
to be
handleable and is very effective in terms of reducing the hydrogen sulphide
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emissions with very low zinc levels and zinc to sulphur ratios in comparison
with the
prior art.
By zinc carboxylate is meant all the compounds corresponding to the general
formula [RCOO]2Zn in which R represents a hydrocarbon group chosen from the
cyclic or non-cyclic, linear or branched alkyls, aryls, aralkyls or alkaryl
groups,
having 1 to 29 carbon atoms, preferably 6 to 20 carbon atoms, more
preferentially 7
to 17 carbon atours, still more preferentially 11 to 15 carbon atoms.
Among the preferred zinc carboxylates the following can be mentioned: zinc
acetate, zinc ethanoate, zinc propionate, zinc butyrate, zinc pentanoate, zinc
hexanoate, zinc heptanoate, zinc octoate, zinc 2-ethyl hexanoate, zinc
nonanoate.
zinc dodecanoate, zinc undecanoate, zinc benzoate and the zinc carboxylates
derived
from fatty acids such as zinc laurate, zinc palmitate, zinc stearate, zinc
oleate. The
preferred zinc carboxylates are zinc acetate, zinc benzoate, zinc octoate and
zinc
stearate, in particular zinc stearate which is a zinc carboxylate that is
available and
inexpensive. Independently of the nature of the zinc carboxylate used, an
inhibition
of the hydrogen sulphide emissions is noted. The inhibition would appear to be
more
effective in the case of the carboxylates comprising an R group having 1 to 6
carbon
atours, such as for example zinc acetate or zinc benzoate. The presence of
fatty acid
derivatives and in particular of zinc carboxylates derived from fatty acids is
not
indispensable.
The quantity of zinc carboxylate in the cross-linking composition in pellet
form is comprised between 5% and 50% by mass, preferably between 10% and 40%,
still more preferentially between 20% and 30%;. with respect to the mass of
the
cross-linking composition in pellet form. The range between 10 iô and ".0'/'0
is
preferred. This quantity of zinc carboxylate is an ideal compromise vis-à-vis
the
quantities of cross-linking agent and polymer matrix in the cross-linking
composition
in pellet form. This makes it possible both to sufficiently trap the hydrogen
sulphide
emissions, to sufficiently cross-link the bitumen/elastomer composition and to
have a
handleable and stable pellet. A smaller quantity of zinc carboxylate is not
suitable, as
a certain quantity of zinc carboxylate in the pellet is necessary to trap the
hydrogen
sulphide released. A greater quantity of zinc carboxylate does not make it
possible to
formulate a pellet allowing both good cross-linking and easy handling, as this
would
involve reducing the quantities of cross-linking agent and/or polymer matrix.
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Preferably, the zinc carboxylate according to the invention comprises a
quantity of zinc comprised between 5% and 30% by mass, preferably between 10%
and 20%, with respect to the mass of zinc carboxylate,. The quantity of zinc
in the
cross-linking composition in pellet form is limited due in particular to the
low zinc
content in zinc carboxylates.
Preferably, the quantity of zinc in the cross-linking composition in pellet
form is comprised between 1% and 15% by mass, preferably between 2% and 10%,
still more preferentially between 3% and 5%., with respect to the total mass
of the
cross-linking composition i n pellet form, The zinc comes mainly from the zinc
carboxylate, but also from the vulcanization accelerators when they are used.
Contrary to what was advocated in the prior art, the quantity of zinc in the
composition in pellet form according to the invention is not very great but
sufficient
to trap a significant quantity of hydrogen sulphide. The quantity of zinc in
the cross-
linking composition in pellet form is limited due in particular to the low
zinc content
in zinc carboxylates and vulcanization (curing) accelerators.
By triazine derivative is meant the derivatives of 1,2,3-triazine, 1,2,4-
triazine
and I ,3,5-triazine (or s-triazine). The hydrated derivatives of triazine are
preferred.
Similarly, as regards the substituents borne by the nitrogen atoms of the
triazine, the
alkyl and/or hydroxalkyl substituents comprising 1 to 12 carbon atoms,
preferably 2
to 8 carbon atoms are preferred. The tri-hydroxyalkyl hexahydrotriazines, the
alkyl
group of which comprises 1 to 12 carbon atoms, preferably 2 to 8 carbon atoms,
are
the preferred triazine derivatives, and in particular N,N',N"-tris(2-
hydroxyethyl)-
hexahydrotriazine.
The quantity of triazine derivative in the cross-linking composition in pellet
form is comprised between 5% and 40% by mass, with respect to the mass of the
cross-linking composition in pellet form, preferably between 10% and 30%,
still
more preferentially between 15% and 20%. The range between 10% and 20% is
preferred. A greater quantity of triazine derivative does not make it possible
to
correctly shape the cross-linking composition in pellet form. In fact, the
triazine
derivatives which can be used according to the invention are liquid compounds
at
ambient temperature. If the quantity of these liquid compounds is too great,
the
cross-linking composition in pellet form has the appearance of a foam and is
unusable. The cross-linking composition in pellet form is sticky and cannot be
cut
and formulated in pellet form. A smaller quantity of triazine derivative is
also not
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suitable, as a certain quantity of triazine derivative is necessary in the
cross-linking
composition in pellet form in order to trap the hydrogen sulphide emissions.
The combination of zinc carboxylate and triazine derivative is therefore
essential in order to obtain both a cross-linking composition which can be
extruded
and eut in pellet form and in order to best trap the hydrogen sulphide
emissions.
The quantity of hydrogen sulphide inhibiting agent in the cross-linking
composition in pellet form is compri sed between 10% and 60% by mass, with
respect to the mass of the cross-linking composition in pellet form,
preferably
between 20% and 50%, still more preferentially between 30% and 40%.
The mass ratio between the quantities of zinc carboxylate and triazine
derivative is comprised between 0.5 and 8, preferably between 1 and 5, more
preferentially between 2 and 3. This ratio makes it possible to obtain a cross-
linking
composition in pellet form which is stable and handleable and to b est trap th
e
hydrogen sulphide emissions. It is preferred to use a combination of hydrogen
sulphide inhibiting agent comprising a little more zinc carboxylate than
triazine
derivative in order to obtain a pellet which is more stable and easier to
extrude. The
mass ratio between the quantities of zinc carboxylate and triazine derivative
is
therefore preferably greater than or equal to 1, or even greater than 1.
In order to prepare the cross-linked bitumen/elastomer compositions, the
cross-linking composition in pellet form also comprises at least one cross-
linking
agent.
The quantity of cross-linking agent in the cross-linking composition in pellet
form is comprised between 5% and 50% by mass, preferably between 10% and 40%,
more preferentially between 20% and 30%, with respect to the mass of the cross-
linking composition in pellet form. The quantity of cross-linking agent is
adjusted as
a function of the quantity of elastomer to be cross-linked in the
bitumen/elastomer
composition. The quantity of cross-linking agent must be sufficient to allow
the
cross-linking of all the elastomer present in the bitumen/elastomer
compositions to
be cross-linked.
Preferably, the cross-linking agent comprises sulphur optionally in
combination with vulcanization (curing) accelerators.
Advantageously the sulphur used is elemental sulphur or flowers of sulphur
and preferably the orthorhombic crystallized sulphur known by the narre of
alpha
sulphur.
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The quantity of sulphur in the cross-linking composition in pellet form is
comprised between 5% and 50% by mass, preferably between 10% and 40%, more
preferentially between 20% and 30%, with respect to the mass of the cross-
linking
composition in pellet form. The range between 30% and 40% is preferred. The
quantity of sulphur is adjusted as a function of the quantity of elastorner to
be cross-
linked in the bitumen/elastomer composition. The quantity of sulphur must be
sufficient to allow the cross-linking of all the elastomer present in the
bitumen/elastomer compositions to be cross-linked. This quantity of sulphur
represents the quantity of flowers of sulphur in the cross-linking composition
in
pellet foret. The sulphur present in the vulcanization accelerators is not
taken into
account.
The quantity of sulphur in the pellet is preferably chosen so as to obtain a
mass ratio between the quantities of zinc (in the zinc carboxylate and
vulcanization
accelerators when they are present) and of sulphur comprised between 0.01 and
0.3,
preferably between 0.02 and 0.2, more preferentially between 0.04 and 0.1,
still more
preferentially between 0.05 and 0.08. Contrary to what was advocated in the
prior art,
the ratio between the quantities of zinc and sulphur in the cross-linking
composition
in pellet form according to the invention, is very low but sufficient, in
combination
with the triazine derivative, to trap a significant quantity of hydrogen
sulphide.
It is also possible to add vulcanization accelerators in order to accelerate
the
cross-linking of the bitumen/elastomer compositions. These vulcanization
accelerators are chosen from hydrocarbyl polysulphides, thiuram polysulphides,
thiuram monosulphides, mercaptobenzothiazole derivatives and dithiocarbamates,
alone or in a mixture. These différent vulcanization accelerators are well
known in
the state of the art and reference can for example be made to the patents
FR2528439,
EP0360656 and EP0409683.
It is preferred to use as vulcanization accelerators the mercaptobenzothiazole
derivatives and the dithiocarbamates, preferably in combination, more
preferentially
a 50 /50 combination of m ercaptobenzothiazole derivatives and
dithiocarbamates .
The preferred mercaptobenzothiazole derivative is zinc 2-mercaptobenzothiazole
(ZMBT). The preferred dithiocarbamate is zinc dibutyldithiocarbamate (ZDBC).
The quantity of vulcanization accelerators in the pellet is comprised between
0% and 5% by mass, preferably between 0.1 % and 3%, more preferentially
between
0.5% and 2%, with respect to the mass of the cross-linking composition in
pellet
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form. The presence of vulcanization accelerators is preferably recommended, as
they
would make it possible to accelerate the cross-linking of the elastorner in
the bitumen.
The sulphur would react more rapidly on the elastomer and in this way the
hydrogen
sulphide emissions would be reduced.
The quantity of vulcanization accelerators in the pellet is preferably chosen
so
as to obtain a mass ratio between the quantities of vulcanization accelerators
and
sulphur cornprised between 0.02 and 0.10, preferably between 0.03 and 0.08,
more
preferentially between 0.05 and 0.06.
Preferably, the vulcanization accelerators include a quantity of zinc
comprised between 5% and 30% by mass, preferably between 10% and 20%. more
preferentially approximately 15%, with respect to the mass o f the vul
canization
accelerators,.
In order to be able to shape the cross-linking composition in pellet fonn, the
latter must comprise a polymer matrix, which makes it possible to bind the
différent
constituents of the pellet to each other. This polymer matrix allows shaping
by
extrusion in pellet form. The polymer matrix preferably comprises a plastomer.
This
plastomer is, preferably, a plastomer comprising ethylene units. Preferably,
the
polymer matrix is chosen from the polyethylenes (PE), ethylene/propylene
copolyrners, ethylene/acrylic ester copolymers, ethylene/glycol monostearate
copolyrners, ethylene/vinyl acetate copolymers (EVA) clone or in a mixture.
The quantity of polymer matrix in the pellet is comprised between 5% and
50% by mass, with respect to the mass of the cross-linking composition in
pellet
form, preferably between 10% and 40%, more preferentially between 20% and 30%.
A greater quantity of polymer matrix is not desirable as the latter is not
invoived in
the elastomer cross-linking and the inhibition of hydrogen sulphide emission
processes (it serves only to make it possible to shape the cross-linking
composition in
pellet form). It is therefore sought to limit the quantity of polymer matrix
to a
minimum, the limit clearly being imposed by the shaping in pellet form.
Preferably the composition in pellet form according to the invention
comprises:
10% to 50% cross-linking agent,
10% to 40% hydrogen sulphide inhibiting agent,
5% to 40% polymer matrix.
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More preferentially, the composition in pellet form according to the invention
comprises:
- 10% to 50% sulphur,
- 0% to 5% vulcanization accelerators,
- 5% to 20% zinc carboxylate,
- 5% to 20% triazine derivative,
- 5% to 35% polymer matrix.
Still more preferentially, the composition in pellet form according to the
invention comprises:
- 10% to 50% sulphur,
- 1% to 5% vulcanization accelerators,
- 5% to 20% zinc carboxylate,
- 5% to 20% triazine derivative,
- 5% to 35% polymer matrix.
The invention also relates to the method for preparing cross-linking
compositions in pellet form according to the invention. The cross-Iinking
compositions in pellet form according to the invention are obtained by
extrusion and
sieving the différent constituents. The extrusion temperature is below 110 C,
preferably below 90 C. It is possible to carry out pre-mixing of the hydrogen
sulphide inhibitors when one of the inhibitors is a powder at ambient
temperature and
the other inhibitor is a Iiquid at ambient temperature, before passing through
the
extruder, then the sieve.
The cross-linking compositions in pellet form according to the invention have
dimensions comprised between 3 mm and 20 mm, prcfcrably between 5 mm and i 5
mm, in general.
The invention also relates to the use of the cross-linking compositions in
pellet form according to the invention, for preparing cross-linked
bitumen/elastomer
compositions. The use of cross-linking compositions in pellet form according
to the
invention makes it possible to cross-link the bitumen/elastomer compositions
with
reduced hydrogen sulphide emissions.
The invention also relates to the method for preparing cross-linked
bitumen/elastomer compositions using the cross-linking compositions in pellet
form
according to the invention. For this, the cross-linkable composition in pellet
form as
defined above, at least one bitumen and at least one cross-linkable elastomer
are used.
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The bitumen which can be used according to the invention can be a bitumen
obtained from différent origins. The bitumen which can be used according to
the
invention can be chosen from the bitumens of natural origin, i.e. those
contained in
deposits of natural bitumen, natural asphalt or bituminous sands, the bitumens
originating from the refining of crude oil such as the bitumens originating
from
atmospheric and/or vacuum distillation of oil, these bitumens being able to be
optionally blown, visbroken and/or de-asphalted. The bitumens used can also be
bitumens fluxed by the addition of volatile solvents, fluxes originating from
oil,
carbochemical fluxes and/or fluxes of vegetable origin. II is also possible to
use
synthetic bitumens also known as clear, pigmentable or colourable biturnens.
Between 75% and 98% by mass of bitumen, with respect Io the total mass of
bitumen/elastomer/cross-linking composition in pellet form, preferably between
80%
and 96%, more preferentially between 85% and 95% is preferably used. The range
between 95% and 98% is preferred.
The elastomers which can be used according to the invention are the elastomers
which can be used in a standard fashion in the field of bitumens/polymers, in
particular bitumens/elastomers, such as for example the polybutadienes,
polyisoprenes, butyl rubbers, ethylene/propene/diene (EPDM) terpolymers,
styrene
and isoprene copolymers, styrene and butadiene copolymers, alone or in a
mixture.
The preferred elastomer is a styrene and butadiene copolymer such as the
styrene/butadiene (SB) block copolymer or the styrene/butadiene/styrene (SBS)
block copolymer.
The styrene and butadiene copolymer advantageously has a styrene content by
weight ranging from 5 to 50%, preferably 20 Io 50%.
The styre ne and butadiene copolymer, advantageously has a (1,2 and 1,4)
butadiene content by weight ranging from 50 to 95%.
The styrene and butadiene copolymer advantageously has a 1,2 butadiene
content by weight ranging from 5 to 70%. The 1,2 butadiene units are units
which
resuit from polymerization via the 1,2 addition of the butadiene units.
The average molecular mass of the styrene and butadiene copolymer can be
comprised, for example, between 10,000 and 500,000, preferably between 50,000
and 200,000 and more preferentially between 50,000 and 150,000 Daltons.
CA 02745098 2011-05-30
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Between 1% and 15% by mass of elastomer, with respect to the total mass of
bitumen/elastomer/cross-linking composition in pellet form, preferably between
2%
and 10%, more preferentially between 3% and 5% is preferably used.
Are preferably used, according to the invention, between 0.05% and 5%,
preferably between 0.1% and 2%, more preferentially between 0.15% and 1%.
stil)
more preferentially between 0.2% and 0.5% by mass of cross-linking composition
in
pellet form with respect to the total mass of bitumen/elastomer/cross-linking
composition in pellet form. The range between 0.1% and 0.2% is preferred. It
is
preferable to use a smaller quantity of cross-linking composition in pellet
form. The
cross-linking composition in pellet forrn must therefore have as high a
concentration
as possible of so-called active agents such as the cross-linking agent or the
hydrogen
sulphide inhibiting agent.
The quantity of cross-linking composition in pellet form to be introduced into
the bitumen/elastomer composition is chosen so that the mass ratio of the
quantities
of sulphur and elastomer is comprised between 0.005 and 0.05, preferably
between
0.01 and 0.03, more preferentially between 0.02 and 0.025. This ratio is very
high
and allows optimum cross-linking of the elastomer. A ratio of less than 0.005
does
not make it possible to cross-link all of the elastomer present in the
bitumen/elastorner composition. The elastic properties of the
biturnen/elastomer
composition would be insufficient if this ratio were less than 0.005.
The method for preparing cross-linked bitumen/elastomer compositions
comprises the following essential stages:
(i) at least one bitumen is heated and mixed between 160 C and 200 C,
preferably
between 180 C and 190 C, preferably between 5 minutes and 120 minutes,
more preferentially between 10 minutes and 60 minutes,
(ii) at least one elastomer is added, the bitumen/elastomer composition thus
obtained is heated and mixed between 160 C and 200 C, preferably between
180 C and 190 C, preferably between 5 minutes and 240 minutes, more
preferentially between 10 minutes and 120 minutes, still more preferentially
between 30 minutes and 60 minutes,
(iii) the cross-linking composition in pellet form is added, the
bitumen/elastomer
composition/cross-linking composition in pellet form thus obtained is heated
and mixed between 160 C and 200 C, preferably between 180 C and 190 C,
preferably between 5 minutes and 120 minutes, more preferentially between 10
CA 02745098 2011-05-30
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minutes and 60 minutes, in order to cross-link said bitumen/elastomer
composition.
This method for preparing cross-linked bitumen/elastomer compositions is
particularly simple to implement since it involves only three components: the
bitumen, the elastomer and the cross-linking composition in pellet form which
brings
together all the components necessary for the cross-linking and for trapping
the
hydrogen sulphide.
The invention finally relates to the use of the cross-linking composition in
pellet forrn as defined above for preparing cross-linked biturnen/elastorner
compositions which can be used as bituminous binders in anhydrous form or in
the
form of an emulsion. This bituminous binder can be used in highway
applications as
a base course, binder course or wearing course and/or in industrial
applications as a
sealing membrane, membrane, impregnation layer. These bituminous binders then
being able to be combined with aggregates in order to provide surface
dressings, hot
mixes, cold mixes, cold-cast mixes, gravel emulsions.
The cross-linking compositions in pellet form are prepared by a conventional
extrusion method. Standard techniques and equipment are used. The extrusion
temperature is preferably below 110 C, preferably also below 90 C. It is also
possible to carry out premixing of the hydrogen sulphide inhibitors when one
of the
inhibitors is a powder at ambient temperature and the other inhibitor is a
liquid at
ambient temperature.
EXAMPLES
The following are used:
- A direct distillation bitumen having a penetrability measured at 25 C
according to
the standard EN 1426 of 40 1/10 mm and a Ring and Ball Temperature measured
according to the standard EN 1427 of 51.6 C,
- flowers of sulphur,
- two vulcanization accelerators: zinc dibutyldithiocarbamate (ZDBC) at a zinc
level
of 14.3% and zinc 2-mercaptobenzothiazole (ZMBT) at a zinc level of 16%,
- a linear block elastomer of styrene/butadiene/styrene type, comprising a
styrene
content by weight of 31%,
- zinc stearate at a zinc level of 10.8% or zinc acetate at a zinc level of
29%,
N,N',N''- tris(2-hydroxyethyl)6hexahydrotriazine,
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- a plastomer of ethylene/ vinyl acetate type having a vinyl acetate level of
20% by
mass and a melt index of 20 g/10 min,
- carbon black,
- a polyisobutylene tackifier with a high molecular weight on an LLDPE (Linear
Low Density Polyethylene) support.
Cross-linking compositions in pellet form are prepared as controls (G,, G2
and G3) and according to the invention (G4, G5 and G6). The cross-linking
compositions in pellet fortn according to the invention G4 and G5 comprise as
hydrogen sulphide inhibiting agent a combination of a particular zinc
carboxylate,
zinc stearate, and triazine derivative. The cross-linking composition in
pellet form
according to the invention G6 comprises as hydrogen sulphide inhibiting agent
a
combination of a particular zinc carboxylate, zinc acetate, and triazine
derivative.
The control cross-linking compositions in pellet form comprise no hydrogen
sulphide
inhibiting agent (G1) or comprise as hydrogen sulphide inhibiting agent only a
particular zinc carboxylate, zinc stearate (G2) or zinc acetate (G3).
The cross-linking compositions in pellet form are prepared by a conventional
extrusion method. Standard techniques and equipment are used. The extrusion
temperature is below 110 C, preferably below 90 C. It is also possible to
carry out
premixing of the hydrogen sulphide inhibitors when one of the inhibitors is a
powder
at ambient temperature and the other inhibitor is a liquid at amblent
temperature.
All the cross-linking compositions in pellet form, thus obtained, are stable
and handleable. The cross-linking compositions in pellet form have the
compositions
given in Table I (% by mass).
Table I
Ci, G2 G3 Gq G5 G6
Sulphur 60 40 40 40 40 40
ZDBC 1.87 1.25 1.25 1.25 1.25 1.25
ZMBT 1.87 1.25 1.25 1.25 1.25 1.25
EVA 33.86 25.1 25.1 25.1 25.1 25.1
Zinc stearate - 30 - 20 10 -
Zinc acetate - - 30 - - 20
Triazine - - - 10 20 10
Carbon black 0.4 0.4 0.4 0.4 0.4 0.4
Tackifier 2 2 2 2 2 2
The quantity of zinc (% by mass) in th e composition is calculated as a
function of the zinc level present in the zinc carboxylates and in the
vulcanization
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accelerators. The quantities of zinc in the cross-linking compositions in
pellet form
G, to G6 are respectively 0.56%, 3.61%, 9.07%, 2.53%, 1.45% and 6.17%.
The mass ratio of the quantities of zinc and sulphur in the cross-linking
compositions in pellet form G, to G6 are respectively 0.009, 0.090, 0.226,
0.063,
0.036 and 0.154.
Différent bitumen/elastomer compositions C, to C6 respectively cross-
linked with the différent vulcanizing compositions in pellet form G, to G6 of
Table I are prepared. The bitumen/elastomer compositions C, to C6 are prepared
as follows:
A direct distillation biturnen as defined above is introduced into a 2-litre
hermetic reactor under stirring (300 rpm) and at 185 C, heated for 10 minutes,
an
elastomer of styrene/butadiene/styrene type, as defined above, is added, the
bitumen/elastomer mixture is heated at 185 C for 4 hours, and finally a
vulcanizing
composition in pellet form as defined above is added, in the proportions of
Table Il
below (% by mass). The mixture is stirred at 300 rpm and heated at 185 C for 2
hours.
A non-cross-linked bitumen/elastomer composition Co is also prepared in the
say way as above without the stage of addition of the vulcanizing composition
in
pellet form.
Table II
C0 C1 C2 C3 C4 C5 C6
Bitumen: 97 96.9 96.85 96.85 96.85 96.85 96.85
SBS Elastomer 3 3 3 3 3 3 3
Pellet - 0.1 0.15 0.15 0.15 0.15 0.15
The mass ratio of the quantities of sulphur and elastomer in the cross-linked
bitumen/elastomer compositions C, to C6 is 0.02.
Table III below shows the physical characteristics of the cross-linked
bitumen/elastomer compositions according to the invention, compositions C4, C5
and
C6 respectively cross-linked using the cross-linking compositions in pellet
form G4,
G5 and G6 and control cross-linked bitumen/elastomer compositions,
compositions
C,, C2 and C3 cross-linked respectively using the cross-linking compositions
in pellet
form G,, G2 and G3 and a control non-cross-linked bitumen/elastomer
composition
Co.
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Table III
Co C, C2 C3 C4 C5 C6
'enetrabi1ity (0.1 mm) 30 26 28 25 24 27 27
BT ( C) 60.2 62.8 63.2 65.0 64.2 63.6 63.8
'I -0.4 0.1 0.3 0.4 0.2 .3 0.4
hreshold stress (MPa) 1.75 1.67 1.58 1.62 1.54 1.68 1.60
Max elongation (%) 180 700 700 700 700 700 700
Max elongation stress (MPa) 0.18 0.74 0.7 0.66 0.68 0.72 0.72
nergy at 400% elongation (J/cm- - 13.88 12.7 13.07 12.56 12.34 12.10
otal energy (J) 0.86 2.85 2.38 2.61 2.28 2.88 2.58
According to the standard NF EN 1426.
t2 Ring and Ball Temperature according to the standard NF EN 1427.
(3) Pfeiffer index according to the standard EN 12591.
Traction test at 5 C according to the standards NF EN 13587 and EN 13703.
v~ith a stretching rate
of 500 mm/min.
In the light of the results compiled in Table III, we are able to make the
following comments:
All of the vulcanizing compositions in pellet form G1 to G6 make it possible
to
cross-link the bitumen/elastomer compositions CI to C6. Ail of the elastomer
present
in these compositions is cross-linked. In fact, it is noted that the
consistency of the
cross-linked bitumen/elastomer compositions Ci to C6 is greater than that of
the non-
cross-linked bitumen/elastomer composition Co (see the penetrability and Ring
and
Ball Temperature values). Similarly, the values obtained in the traction test
show that
the cross-linked bitumen/elastomer compositions CI to C6 are clearly more
elastic
than the non-cross-linked bitumen/elastomer composition Co. Reference can be
made
for example to the elongation values obtained, which are 700% in the case of
the
cross-linked bitumen/elastomer compositions C1 to C6 and only 180% in the case
of
the non-cross-linked bitumen/elastomer composition Co.
The hydrogen sulphide emissions released are measured in gas phase using a
probe placed in the closed reaction medium, over 2 hours starting from the
introduction of the cross-linking composition in pellet form into the
bitumen/elastomer mixture. For each composition Ci to C6, a curve gives the
hydrogen sulphide quantities released as a function of time. The curve
corresponding
to the cross-linked composition CI using a pellet comprising no hydrogen
sulphide
inhibitor is considered as the reference curve. The percentages of reduction
in
hydrogen sulphide emissions obtained during the cross-linking of the
bitumen/elastomer compositions C2 to C6, with respect to the reference CI, are
shown
in Table IV below:
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Table IV
reduction in hydrogen sulphide emissions
with respect to C
C2 20
C3 32
C4 43
CI 47
C6 49
It is noted that the use of the cross-Iinking compositions in pellet form
according to the invention G4 to G6, in which the hydrogen sulphide inhibiting
agent
is a combination of zinc carboxylate and triazine derivative, allows a clearly
more
significant reduction in hydrogen sulphide emissions. Thus, the hydrogen
sulphide
emissions are reduced by 43% and by 47% when a cross-Iinking composition
comprising both zinc stearate and a triazine derivative is used (instead of
only 20%
when the stearate is used alone). Similarly, the combination of zinc acetate
and
triazine derivative makes it possible to reduce the hydrogen sulphide
emissions by
49% (instead of 39% in the case of zinc acetate alone).
The cross -linking compositions in pellet form according to the invention
therefore make it possible to obtain elastic cross-linked bitumen/elastomer
compositions, while considerably reducing the hydrogen sulphide emissions.
