CA2205741A1

CA2205741A1 - Thermoplastic elastomer composition

Info

Publication number: CA2205741A1
Application number: CA 2205741
Authority: CA
Original assignee: National Rubber Technology Inc
Current assignee: National Rubber Technology Inc
Priority date: 1997-05-16
Filing date: 1997-05-16
Publication date: 1998-11-16

Abstract

A thermoplastic elastomer composition containing in percentages by weight based on the total weight of the composition, about 5% to about 90% vulcanized rubber crumb;
about 5% to about 60% polyolefin; about 2% to about 30%
uncured rubber or curable thermoplastic elastomer; and about 2% to about 30% vinyl polymer selected from vinyl homopolymers, copolymers and mixtures.

Description

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.

CA 0220~741 1997-0~-16 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.

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.

Micron tire crumb51 Polyethylene 16 Polypropylene 8 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.

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 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 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.

Claims

1. 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 elastomer; and (d) about 2% to about 30% vinyl polymer selected from the group consisting of vinyl homopolymers, copolymers and mixtures thereof; all said percentages by weight based on the total weight of the composition.

2. A composition according to claim 1 wherein the content of vulcanized rubber crumb is about 25% to about 75%.

3. A composition according to claim 2 wherein said content is about 40% to about 60%.

4. A composition according to any preceding claim wherein said vulcanized rubber crumb has its particle size in the range about 20 to about 100 mesh.

5. A composition according to any preceding claim wherein the content of polyolefin is about 10% to about 40%.

6. A composition according to claim 5 wherein said content is about 20% to about 30%.

7. A composition according to any preceding claim wherein said polyolefin comprises polyethylene, polypropylene or a copolymer or mixture thereof.

8. A composition according to claim 7 wherein said polyolefin comprises polyethylene and polypropylene in a weight ratio of about 1.5:1 to about 3:1.

9. A composition according to claim 8 wherein said ratio is about 1.8:1 to about 2.8:1.

10. A composition according to any preceding claim wherein the content of uncured rubber or curable thermoplastic elastomer is about 4% to about 20%.

11. A composition according to claim 10 wherein said content is about 5% to about 15%.

12. A composition according to any preceding claim wherein said curable thermoplastic elastomer comprises a styrene-butadiene copolymer.

13. A composition according to claim 12 wherein said styrene-butadiene copolymer comprises a styrene-butadiene-styrene block copolymer.

14. A composition according to any preceding claim wherein the content of vinyl polymer is about 4% to about 20%.

15. A composition according to claim 14 wherein said content is about 5% to about 15%.