Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 0220~741 1997-0~-16
The present invention relates to a thermoplastic
elastomer composition containing substantial quantities of
vulcanized rubber crumb and polyolefin. The vulcanized
crumb may be, but is not necessarily, derived from scrap
tires, and in such case may typically consist primarily of
styrene-butadiene rubber, but in such admixtures with
natural rubber, and other types of synthetic rubbers as may
from time to time be used by the tire producers in their
compound recipes.
Prior-proposed compositions of which the
applicant is aware have had relatively poor physical
properties. For example, U.S. patent 5,157,082 (Johnson)
discloses compositions comprising ground vulcanized rubber,
polyolefin and a functionalized olefin polymer.
Compositions of this type, however, tend to have relatively
low ultimate elongation and tear strength.
Applicant has found that thermoplastic elastomer
compositions having excellent physical properties,
including excellent ultimate elongation and tear strength
can be obtained by blending vulcanized rubber crumb and
polyolefin together with uncured rubber or curable
thermoplastic rubber and vinyl based polymer. The uncured
rubber or curable thermoplastic rubber and vinyl based
polymer together constitute a two stage compatibilizing
system which provides superior physical properties over
known compositions.
In accordance with the present invention there is
provided a thermoplastic elastomer composition comprising a
blend of:
(a) about 5~ to about 90~ vulcanized rubber
crumb;
(b) about 5~ to about 60~ polyolefin;
(c) about 2~ to about 30~ uncured rubber or
curable thermoplastic rubber; and
(d) about 2~ to about 30~ vinyl polymer selected
CA 0220~741 1997-0~-16
from the group consisting of vinyl homopolymers, copolymers
and mixtures thereof; all said percentages by weight based
on the total weight of the composition.
Without wishing to be bound by any theory, it is
believed that the uncured rubber or curable thermoplastic
rubber component (c) of the composition imparts excellent
strength properties to the composition as a result of the
entanglement of the molecular chains constituting the
rubber polymer molecule. These molecular chains are
believed to form interpenetrating random coils, and it is
believed that this molecular structure is capable of
imparting excellent strength properties.
Further, it is believed the vinyl polymer portion
(d) serves to provide adhesion to the tire crumb at the
molecular level, and that the excellent physical properties
result from improved adhesion or bonding between the tire
crumb and the remaining components of the composition.
In one especially preferred form of the present
invention, the vinyl polymer comprises polymer chains
having pendant oxygen-containing groups. These
compositions provide exceptionally good ultimately
elongation values and tear strengths. The rubber molecules
in the tire crumb tend to have polar sites as a result of
the chemical composition of the rubber and minor oxidation
occurring during mechanical commination. Without wishing
to be bound by any theory, it is believed that the polymers
having pendant oxygen-containing groups provide improved
adhesion tO the rubber crumb as a result of the affinity
with these polar sites on the rubber crumb.
The vulcanized rubber crumb used in the present
composition may be obtained by grinding or otherwise
comminuting any source of vulcanized rubber compound, such
as road vehicle tires, roofing membrane, hoses, gaskets and
the like, and is preferably obtained from recycled
CA 0220~741 1997-0~-16
passenger car tires using any conventional procedure. Any
steel or other metallic inclusions should be removed from
the ground tires before use in the compositions of the
invention. Since the compositions of the invention are
preferably fiber-free, all fibrous material such as tire
cord fibers is preferably likewise removed from the ground
rubber using conventional separation procedures before use
in the compositions of the invention. Desirably, the
vulcanized rubber crumb is of a particle size in the range
about 20 to about 100 mesh (Tyler standard sieve). The use
of rubber crumb of a particle size substantially coarser
than about 20 mesh tends to result in molded products which
are insufficiently homogeneous and tend to have relatively
poor strength properties. The use of crumb which is
substantially finer than about 100 mesh tends to
significantly increase the energy costs of the comminution
operation, without significant improvement of the
properties of the compositions. As noted above, desirably
the compositions of the invention comprise about 5 to about
90 weight percent of the vulcanized rubber crumb.
Compositions comprising greater than about 90~ by weight of
the cured rubber crumb can exhibit processing problems and
tend to have poor strength properties, while compositions
containing less than about 5~ of the rubber crumb tend to
be excessively costly, as a result of their low content of
the relatively low cost cured rubber crumb material.
Preferably, the composition comprises about 25 to about 75
by weight of the rubber crumb, more preferably about 40 to
about 60~.
The polyolefin component (b) may comprise any
solid high molecular weight polyolefin homopolymer or
copolymer, or mixtures thereof. Examples of olefin polymers
polymerisable or copolymerisable to provide suitable
polyolefins for use in the present compositions include
ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-
butene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 5-
methyl-1-hexane and mixtures thereof. Preferably, the
CA 0220~741 1997-0~-16
polyolefin comprises polyethylene, polypropylene or a
copolymer of ethylene and propylene.
Preferably, as noted above, the compositions of
the invention comprise about 5~ to about 60~ by weight of
the polyolefin homopolymer, copolymer or mixtures thereof.
Compositions having a polyolefin content of greater than
about 60~ may tend to be excessively stiff and to exhibit
poor elongation values, while polyolefin contents of less
than about 5~ by weight tend to result in the composition
may exhibit processing problems and tend to have relatively
poor strength properties. More preferably, the composition
comprises about 10 to about 40~ by weight of polyolefin,
still more preferably about 20 to about 30~ by weight of
the total composition. Preferably, the composition
comprises polyethylene and polypropylene in a weight ratio
of about 1.5 to 3 parts by weight polyethylene per part by
weight of polypropylene, more preferably about 1.8 to about
2.8 parts by weight polyethylene per part polypropylene.
The uncured rubber or curable thermoplastic
rubber component of the present composition is considered
to provide adhesion or bonding between the remaining
components of the composition and the vulcanized rubber
crumb component and to provide elasticity for the
composition.
Compositions that contain less than about 2~ by
weight uncured rubber or curable thermoplastic elastomer
tend to be excessively stiff, while compositions containing
greater than about 30~ by weight of uncured rubber may tend
to be excessively soft and have insufficient strength
properties. Preferably, the composition comprises about 4
to about 20 weight percent of uncured rubber or curable
thermoplastic elastomer, more preferably about 5 to about
15 ~ uncured rubber or curable thermoplastic elastomer,
based on the total weight of the composition.
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The term "rubber" as used herein is to be
interpreted as it would be understood by those skilled in
the art, to mean natural rubber and all natural or
synthetic polymers having mechanical properties similar to
the properties characteristic of natural rubber, namely
deformability, rapid recovery from deformation, and
mechanical strength. Examples of such materials include
natural rubber, styrene-butadiene rubber, polybutadiene,
polyisoprene, polyisobutylene, isoprene-butadiene
copolymer, neoprene, nitrile rubber, butyl rubber,
polysulfide elastomers, acrylic elastomers, silicone
rubbers, polyester rubbers, diisocyanate-linked
condensation elastomers, EPDM (ethylene-propylene diene
rubbers), EPT (ethylene-propylene terpolymer rubbers), and
mixtures thereof. All such rubber materials in uncured, or
curable, form are contemplated for use in the compositions
of the invention. That is to say, the term "uncured" as
used in the present specification is to be understood
broadly as it would be understood by those skilled in the
art to refer to materials capable of undergoing
vulcanization or crosslinking. It does not exclude a
certain degree of vulcanization or crosslinking present in
the starting material. The degree of curing or
crosslinking of a particular rubber material may be
determined by standard tests well known to those skilled in
the art. For example, conventionally the degree of cure or
vulcanization of a natural rubber or styrene-butadiene
rubber compound in determined by comparing its tensile
strength before and after undergoing further curing under
standard conditions. A material which undergoes no
increase in tensile strength is 100~ cured, while increases
in tensile strength indicate various degrees of lack of
cure.
In the preferred form, component (c) comprises a
styrene-butadiene copolymer which is a curable
thermoplastic elastomer. Especially preferred are styrene-
butadiene-styrene block copolymers. The latter block
CA 0220~741 1997-0~-16
copolymers appear to provide tensile strength in the
composition as a result of entanglement of the end portions
of the polymer molecule. Further, the styrenic end
portions appear to blend or bond with the vulcanized rubber
material as a result of the affinity between the styrenic
end portions and uncured domains in the tire crumb.
As indicated above, the compositions of the
invention comprise about 2 to about 30% vinyl polymer by
weight. Said vinyl polymer may comprise vinyl
homopolymers, copolymers or mixtures thereof.
Compositions that contain less than about 2~ by
weight of the vinyl polymer may tend to be excessively
stiff, while compositions containing greater than about 30
by weight of the vinyl polymer material may tend to be
excessively soft and have insufficient strength properties.
Preferably, the composition comprises about 4 to about 20
weight percent of the vinyl polymer, and more preferably
about 5 to about 15~ polymer, based on the total weight of
the composition. The term "vinyl polymers" and "vinyl
copolymers" are used in the sense in which they would be
understood by those skilled in the art to refer to
thermoplastic polymers or copolymers made from vinyl
monomers, CH2=CHX and vinylidene monomer, CH2=CY2, but
excluding poly(~-olefins) wherein X is an aliphatic
hydrocarbon group and thermosetting resins made in part
from vinyl monomers, such as polyester resins. In the
present compositions, the vinyl polymers facilitate bonding
between the vulcanized rubber crumb molecules, the uncured
rubber or curable thermoplastic elastomer component, and
the thermoplastic component, and provide increased
elasticity. Examples of suitable vinyl polymers include
polystyrene, copolymers of styrene with other vinyl
monomers, polymers of derivatives of styrene, polyvinyl
chloride and polyacrylonitrile. Especially preferred are
vinyl polymers that have pendant groups on the polymeric
chain that comprise oxygen atoms. Examples of such
CA 0220~741 1997-0~-16
polymers include polyvinylacetate, polybutylacrylate,
polymethylacrylate, polymethylmethacrylate, polyvinyl
alcohol, polyvinylbutyral, polyvinyl pyrrolidine and
polyvinyl oxazolidinone. Especially preferred are
amorphous rubbery copolymers of such polymers with olefins.
Particularly preferred examples of such copolymers include
ethylene vinylacetate, ethylene butylacrylate and
ethylenemethylacrylate. The homopolymers and copolymers
comprising oxygen-containing pendant groups are considered
to provide adhesion to the tire crumb as a result of
affinity between the oxygen-containing pendant groups and
polar sites on the vulcanized rubber polymer.
Particularly preferred is amorphous rubbery
ethylenevinyl acetate copolymer that comprises about 5 to
about 60 weight percent vinyl acetate based on the total
weight of the copolymer more preferably about 10 to about
40 percent by weight vinylacetate and still more preferably
about 20 to 40 weight percent vinylacetate.
The compositions of the invention may if desired
be pre-melted together, for example in a conventional
internal mixer at a temperature of about 275~F to 400~F
sufficient to melt the vinyl polymer, polyolefin, and
uncured rubber and form the mixture into a uniform blend.
The blend may then be divided into particulate form, for
example by pelletization or the like, in conventional
manner, to provide pellets or other particles that may be
used in conventional thermoplastic elastomer molding
applications. Alternatively, the blend of polymers and
tire crumb in finely divided form may be simply pre-mixed
to provide a dry uniform mixture that may be used directly
as the feed to a molding process. For example, such dry
mixture may be used as the feed for a conventional screw
extruder operating at a temperature typically in the range
275~F under conditions adequate to melt the fusible
components of the polymer mixture and provide a molded
polymer product in conventional manner.
CA 0220~741 1997-0~-16
The composition may comprise small qualities of
processing aids, such as plasticizers, lubricants, mould
release agents and the like. For example, it may comprise
small quantities, typically less than about 10% and more
typically less than about 5~ by weight based on the total
weight of the polymer of processing oils, such as SUNPAR
110 paraffinic oil, antioxidants, such as TMB (
. The composition
may comprises mold lubricants, such as stearic acid.
Further, the composition may comprise a reordorant, such as
vanillin, in order to mask the somewhat sulphurous smell of
the tire crumb component.
The compositions of the invention are black,
thermoplastic, general purpose elastomers with good fluid
resistance, that can be used to replace thermoset rubbers
in a variety of applications. The thermoplastic elastomer
compositions of the invention can be processed using
standard injection molding, extrusion and other melt
processing techniques. The material contains significant
quantities of recycled rubber from scrap passenger car
tires, and may contain recycled plastic materials from
post-industrial or post-consumer waste streams.
An advantage of the present compositions is that
many of the major components may be derived from post
industrial and post consumer waste streams, thus providing
benefits of disposal of waste materials as well as taking
advantage of the ready availability and lower cost of such
materials. In most localities, polyethylene,
polypropylene, ethylene vinylacetate copolymer and uncured
rubber are readily available from waste streams.
While the above description provides ample
information to one of ordinary skill in the art to make and
use the compositions of the invention, for the avoidance of
doubt some detailed Examples will be given.
~ CA 0220~74l l997-0~-l6
EXAMPLES
All percentages or parts by weight herein are by
weight based on the total weight of the composition.
EXAMPLE 1
The composition set out in Table 1 below was
blended in an internal mixer at a temperature of 350~F for
a period of about 5 minutes sufficient to melt the fusible
ingredients and form a uniform blend.
TABLE 1
Micron tire crumb51
Polyethylene 16
Polypropylene 8
EVA 12
SBS co-polymer 12
Antioxidant 1~
For testing purposes, plaques were injection
molded from the blended composition, and were tested and
values obtained in accordance with the procedures indicated
in Table 2 below.
TABLE 2
PROPE~TY TEST METHODTEST UNITS TYPICAL VALUE
Tire crumb % 63
component
Hardness ASTM-D-2240Shore 'A'77
Specific Gravity ASTM-D-792 1.04
Tensile ASTM-D-412 MPa 5.20
strength,
ultimate*
Elongation, ASTM-D-412 % 260
O ultimate*
100% modulus* ASTM-D-412 MPa 3.5
Compression set, ASTM-D-395,% at 23~C 60
168 hrs Method "B"
Tear strength ASTM-D-624kN/M @ 23~C 32
Brittle point ASTM-D-746 ~C ~-40~C
Ozone resistance BP-101-1 Cracks 0
Flammability SAE J369Mm/Min 25
~Properties measured across the flow.
CA 0220~741 1997-0~-16
- 10 --
EXAMPLE 2
The procedure of Example 1 was followed except
the composition was as indicated in Table 3 below.
The physical properties were tested and
evaluated, and were as indicated in Table 4 below.
Table 3
Formulation
Tire Crumb 40 micron (1) 52.0
2035 Polyethylene (2) 18.4
Polypropylene pm 6100 (3) 7.0
sunpar 110 (4) 4.4
Krayton 1102 (5) 8.6
EVA 2510M (6) 8.6
TMB6 (7) 1.0
15 stearic acid (8) 0.5
Vanillin (9) 0.1
total 100.0
.otes
(1) Ground passenger car tire crumb. Average particle
size 40 microns.
(2) ex
(3) ex
(4) ex Suncor Inc. Calgary, Alberta. Paraffinic oil
processing aid.
(5) styrene-butadiene-styrene block copolymer ex Shell
Canada Limited, Calgary, Alberta.
(6) ethylene vinyl acetate copolymer ex A.T. Plastics
Inc., Brampton, Ontario.
(7) ex
(8) Processing aid.
(9) Reodorant.
CA 0220~741 1997-0~-16
Table 4
Physicals
Tensile strength MPa 7.2
Elongation ~ 200
5 Hardness Shore A 89
Compression set 75
100 ~ mod. MPa 5.3
Tear ckN/m 52
Density 1.01
10 Low Temp. flexibility -40C
Ozone resistance/BplO1-01 0
flammability/ SAE J369 mm/min 75
heat aged 168 70 C
change in hardness points +1
15 change in tensile ~ +10
change in elongation ~ -25
heated aged 1000 hrs
change in hardness points +3
change in tensile ~ +3
20 change in elongation ~ -30
Comparative Testing
In order to illustrate the combined effect of the
vinylpolymer (ethylenevinyl acetate copolymer) and uncured
rubber (styrene-butadiene-styrene block copolymer) on the
compositions of the invention, four compositions A, B, C
and D were mixed, blended, molded and tested as described
in more detail in Example 1 above. Formulation D is in
accordance with the invention. The compositions, and the
tensile strengths, elongations, tear strength, hardness and
viscosity values are given (in the units of and by the test
CA 0220~741 1997-0~-16
methods of Table 2), together with the particulars of the
compositions, in Table 5 below.
Table 5
Formulations
A B C D
tc 50 50 50 50
pe 36 25 25 22
pp 14 10 10 8.4
eva 10 10
1102 10 10
Tensile 5.9 5.6 5.7 7.2
elongation 24 133 56 207
Tear 24 20.3 30.5 52.2
hardness 97 91 92 91
Viscosity 3.2 2.7 3.5 4.7
~otes:
tc = tire crumb
pc = polyethylene
pp = polypropylene
eva = ethylene vinyl acetate copolymer
1102 = styrene-butadiene-styrene block copolymer
The synergistic effect of the combination of the
vinyl polymer and uncured rubber on the elongation and tear
strength is particularly marked.
