WO2001023464A1

WO2001023464A1 - Process for devulcanizing a rubber

Info

Publication number: WO2001023464A1
Application number: PCT/NL2000/000621
Authority: WO
Inventors: Martin Duin Van; Jacobus Wilhelmus Maria Noordermeer; Miriam Adriënne Lambertina VERBRUGGEN; Leen Van Der Does
Original assignee: DSM NV
Current assignee: Koninklijke DSM NV
Priority date: 1999-09-28
Filing date: 2000-09-05
Publication date: 2001-04-05
Anticipated expiration: 2002-03-28
Also published as: NL1013155C2; AU7458100A

Abstract

Process for devulcanizing a rubber, which rubber is obtained by vulcanizing with the aid of a sulphur-containing compound a copolymer which contains ethylene monomer units, monomer units of an α-olefin and monomer units of a polyunsaturated compound, by heating the rubber to such elevated temperature that devulcanization occurs and a recyclable product is obtained. Monomer units of a polyunsaturated compound are monomer units according to the formula X-R0, where: X is a group having 2-20 C atoms, which group can polymerise with the aid of a co-ordination catalyst, R0 is a chain having 2-30 C atoms and containing at least one double carbon-carbon bond, with none of the C atoms of the double bond forming part of a ring structure.

Description

PROCESS FOR DEVULCA IZING A RUBBER

The invention relates to a process for devulcanizing a rubber, which rubber is obtained by vulcanizing with the aid of a sulphur-containing compound a copolymer which contains ethylene monomer units, monomer units of an α-olefin and monomer units of a polyunsaturated compound, by heating the rubber to such elevated temperature that devulcanization occurs and a recyclable product is obtained.

A similar process is known from IRC '98 Conference Proceedings, Societe de Chimie

Industrielle, Paris, 12-14th May 1998, pages 289-290.

These proceedings describe the devulcanization of a rubber vulcanized with a sulphur- containing compound and containing ethylidene norbornene (ENB) as a polyunsaturated compound, with devulcanization taking place only after the rubber that has been vulcanized with a sulphur-containing compound is heated for a long period of time and a devulcanizing agent is added to the rubber. A drawback of the known process is that devulcanization is incomplete and, additionally, occurs only after prolonged heating at high temperatures and at high concentrations of a devulcanizing agent, so that the process is an unfavourable one. As a result, the product obtained is not well recyclable.

The object of the invention is to provide a rubber devulcanization process in which a higher degree of devulcanization is effected in a simpler manner and at a shorter heating time. This object is achieved through application of the process, which is characterised in that use is made of a rubber obtained by vulcanizing a copolymer which contains monomer units of a polyunsaturated compound according to the formula

X-R° (I)

where X is a group having 2-20 C atoms, which group can polymerise with the aid of a co-ordination catalyst and R° is a chain having 2-30 C atoms and containing at least one double carbon-carbon bond, with none of the C atoms of the double bond forming part of a ring structure .

A further advantage is that the rubber can be devulcanized with lower concentrations of the devulcanizing agent. Indeed, complete or substantially complete devulcanization of the rubber can be achieved even without adding any devulcanizing agent.

The process of the invention can be caried out using polymer processing equipment referred to in the literature. Examples of suitable equipment are a press, an oven, a kneader, a stirred vessel, an autoclave or an extruder. Preferably an extruder or a kneader is used. Heating during the process of the invention is effected at a temperature of for example 50-400°C, preferably at a temperature of 150-350°C, in particular at a temperature between 250 and 350°C inasmuch as at this temperature devulcanization proceeds very rapidly, the backbone chains of the copolymer decompose only to a limited extent and the devulcanized product obtained is well recyclable.

The time during which the rubber is heated is normally less than 5 hours, preferably less than 3 hours, more preferably less than 1 hour and still more preferably less than 30 minutes. In general, a higher temperature calls for a shorter period to obtain a recyclable devulcanized product than a lower temperature .

The rubber is preferably heated in an atmosphere which is substantially free of oxygen. This can be achieved by for example saturating with nitrogen the reaction vessel containing the rubber to be devulcanized.

Prior to being devulcanized, rubber articles obtained by vulcanizing the copolymer with a sulphur-containing compound, whether or not in the presence of other substances such as fillers, additives, plasticizers and oils, are preferably pretreated using equipment referred to in the literature for the fragmenting, crushing, cutting, grinding and crumbing of rubber or plastic articles.

As α-olefins that may be used as a monomer besides ethylene there may be mentioned propylene, butene-1, pentene-1, hexene-1, octene-1 or the branched isomers thereof, such as 4-methylpentene-l, as well as styrene and α-methylstyrene . Mixtures of these alkenes are also suitable; it is preferred for propylene and/or butene-1 to be used.

The molar ratio of ethylene to propylene normally is between 5:1 and 1:5. Preferably between 3:1 and 1:1.

A group X that can be polymerised with a co-ordination catalyst is any group that contains at least one double carbon-carbon bond that can be polymerised in the presence of a co-ordination catalyst such as a Ziegler-Natta catalyst or a metallocene catalyst . Examples of a group X that can be polymerised with a co-ordination catalyst are vinyl, norbornyl, dinorbornyl and dicyclopentadienyl .

R° is a chain having 2-20 C atoms and at least one double carbon-carbon bond, with none of the C atoms of the double bond forming part of a ring structure. It is preferred for R° to be chosen from chains that satisfy either formulae II or III:

CH

R 10

where Rι-R_8/ Rio and R₁₄ may be the same or different and may be hydrogen or a hydrocarbon group having 1-5 C atoms; R₉ represents a hydrogen group or a hydrocarbon group having 1-5 C atoms if p and q are equal to 1 or a group represented by the formula - (CH₂) _m-CRιι=CRι₂Rι₃ if p and q are not equal to 1, where R₁₁-R₁₂ may be the same or different and may represent hydrogen or a hydrocarbon group having 1-5 C atoms and where R_i3 represents a hydrocarbon group having 1-5 C atoms; p and q are, independently of each other, 0 or 1 but not at the same time 0; f = 0-5, but if p and q are equal to 1 , f cannot be 0 ; g = 1-6; n = 1-5; r = 0-5 and m = 1-5.

Monomer units of a polyunsaturated compound according to formula (I) serve to incorporate unsaturation in the copolymer and may be aliphatic or alicyclic.

An aliphatic polyunsaturated compound preferably is a compound with formula (I) , where X is vinyl and R° satisfies formula (II) or (III) and where the double carbon-carbon bonds present may be conjugated or unconjugated. The double carbon-carbon bonds preferably are unconjugated. Examples of aliphatic, conjugated polyunsaturated compounds are 1, 3 -butadiene, isoprene, 2-ethylbutadiene-l , 3 and piperylene. Examples of aliphatic, unconjugated polyunsaturated compounds are 1 , 4 , 9-decatrienes, 1,4- hexadiene, 1 , 5-hexadiene, 4 -methyl -1 , 4-hexadiene, 4- ethylidene-10-methyl-l, 6, 9-decatriene, 9-methyl-l, 5,8- nonatriene, 4-ethylidene-l , 7-nonadiene, 4-ethylidene-8- methyl-1, 7-nonadiene . Preferably, 1 , 4-hexadiene or 4- ethylidene-8-methyl-l, 7-nonadiene is used as aliphatic, unconjugated polyunsaturated compound.

An alicyclic polyunsaturated compound preferably is a compound with formula (I) , where X may be monocyclic or polycyclic, preferably norbornyl , dinorbornyl and dicyclopentadienyl and R° satisfies formula (II) or (III) and where the double carbon- carbon bonds present may be conjugated or unconjugated. The double carbon-carbon bonds preferably are unconjugated. Examples of such polyunsaturated compounds are unconjugated alicyclic dienes, alicyclic trienes or alicyclic tetraenes. Mixtures of the aforementioned polyunsaturated compounds may also be used.

Monomer units of a polyunsaturated compound are present in the copolymer in amounts of for example up to 30% by weight, preferably up to 15% by weight, in particular between 2 and 10% by weight relative to the other monomer units.

The copolymer needs to be vulcanized in order to obtain a rubber article that is dimensionally stable. The dimensionally stable article is obtained by chemical cross-linking of freely movable macromolecules of the copolymer, as a result of which the article becomes a large, single macromolecules or network, as it were.

By devulcanization is meant the reduction of the number of cross-links until there is obtained a product that is suitable for recycling. It is possible, for example, to blend the devulcanized rubber with an as-yet unvulcanized copolymer and then to, for example, extrude or roll the so-obtained blend of the devulcanized rubber and the as-yet unvulcanized rubber to form a product. When the number of cross-links of the rubber has been strongly reduced by devulcanization, it is also possible to process the devulcanized rubber as such in the manner described above to form a product.

The number of cross-links of the rubber is reduced by heating the rubber for a particular period of time. A suitable measure of the rate of progress of this devulcanization process is the amount of polymer that dissolves in a suitable solvent such as tetrahydrofuran (THF) . The amount of polymer that can dissolve through extraction with THF is dependent on the number of cross-links of the rubber that are severed. The higher the amount of dissolved polymer, the higher the number of cross-links that are severed. The invention also relates to a devulcanized rubber of which the amount of polymer soluble in tetrahydrofuran is greater than 20% by weight, preferably greater than 30% by weight, in particular greater than 50% by weight.

As devulcanizing agent there may be used any commercially applicable devulcanizing agent that is capable of severing the cross-links in a rubber that has been vulcanized with a sulphur-containing compound. It is not necessary for the devulcanizing agent to sever all cross-links in the vulcanized rubber. The devulcanizing agent should preferably sever at least a proportion of the cross-links.

Preferably, devulcanizing agents are chosen from the group comprising aromatic and aliphatic disulphides, thiols and amines. Examples of aromatic and aliphatic disulphides are diphenyldisulphide, dixylyldisulphide, dibenzyldisulphide and dibutyldisulphide . It is preferred for diphenyldisulphide to be used.

The amount of devulcanizing agent to be added preferably is between 0 and 10% by weight, more preferably between 0 and 5% by weight.

The invention also relates to a blend of the devulcanized rubber obtained via the process as described and an as-yet unvulcanized rubber, vulcanizing agent, oil, carbon black and any additives. Blending may be by customary techniques and equipment. Preferably, blending operations take place at a temperature of between 50°C and 120°C. During blending there may optionally be added customary additives for the polymer composition, such as stabilisers, colorants, processing aids such as mould release agents and retardants and fillers or reinforcing (fibrous) materials .

The blend of the invention may be used in the customary applications of vulcanized ethylene- alpha-olefin-diene copolymers . Examples of such applications are bicycle tyres, mats, cable sheathing, hoses and shock dampers .

The invention is now explained in further detail with reference to the following examples and comparative examples without being limited thereto. The amount of soluble polymer is determined as follows. After extraction with acetone, the rubber is dried in a vacuum oven. The dry, devulcanized rubber, which now is free of devulcanizing agent and oil, is weighed and then extracted with tetrahydrofuran in a Soxhlet extraction apparatus in a nitrogen atmosphere and with exclusion of light for 96 hours. After extraction, the rubber is again dried in a vacuum oven and weighed. The difference yields the amount of soluble polymer. For samples without carbon black and free of devulcanizing agant and oil, this amount is expressed as a percentage relative to the devulcanized rubber sample. For rubber with carbon black, the amount is expressed as the percentage of polymeric portion present in the rubber that is free of devulcanizing agent and oil.

Example I

50 parts per hundred (pph) of Sunthene 4240 oil and 80 pph of N330 carbon black were added to and blended in an internal blender with Nordel 1040 (an EPDM polymer with 3% by weight of 1 , 4-hexadiene and 54% by weight of ethylene) . Next, the blend was blended in a laboratory blender with 5 pph of zinc oxide, 1 pph of stearic acid, 0.5 pph of mercaptobenzothiazol , 1 pph of tetramethylthiuram disulphide and 1.5 pph of a sulphur- containing compound and then heated. The amount of tetrahydrofuran-soluble polymer of the vulcanized rubber so obtained was between 1.9 and 3.2% by weight.

The vulcanized rubber was then heated for 2 hours at 266°C and at a pressure of 7.6 MPa in the presence of 2.5% by weight of diphenyldisulphide in a closed oven saturated with nitrogen.

After devulcanization, the amount of soluble polymer was determined as a measure of the degree of devulcanization. The amount of tetrahydrofuran-soluble polymer relative to the polymeric portion was 55 ± 2 % by weight.

Example II

Example I was repeated except that the amount of diphenyldisulphide was varied as shown in Table 1. Table 1 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Example III

Example I was repeated except that the temperature was varied as shown in Table 2.

Table 2 Amount of THF-soluble polymer as a function of temperature

Example IV

Example I was repeated except that the time was varied as shown in Table 3.

Table 3 Amount of THF-soluble polymer as a function of time

Example V

Example I was repeated except that no Sunthene 4240 oil and N330 carbon black were added to the EPDM polymer, the devulcanization temperature was 200°C and the amount of diphenyldisulphide was varied as shown in Table 4.

Table 4 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Example VI

50 pph of Sunthene 4240 oil and 80 pph of

N330 carbon black were added to and blended in an internal blender with an EPDM polymer containing 3.3 % by weight of 4 -ethylidene- 8 -methyl -1, 7-nonadiene (EMN) and 56% by weight of ethylene. Next, the blend was blended in a laboratory blender with 5 pph of zinc oxide, 1 pph of stearic acid, 0.5 pph of mercaptobenzothiazol, 1 pph of tetramethylthiuram disulphide and 1.5 pph of a sulphur-containing compound and then heated.

The amount of tetrahydrofuran-soluble polymer of the vulcanized rubber so obtained was between 2 and 3% by weight.

The vulcanized rubber was then heated for 2 hours at

266°C and at a pressure of 7.6 MPa in the presence of 2.5%by weight of diphenyldisulphide in a closed oven saturated with nitrogen. After devulcanization, the amount of soluble polymer was determined as a measure of the degree of devulcanization. The amount of tetrahydrofuran-soluble polymer relative to the polymeric portion was 58% by weight .

Example VII

Example VI was repeated except that the amount of diphenyldisulphide was varied as shown in Table 5. Table 5 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Example VIII

Example VI was repeated except that the temperature was varied as shown in Table 6.

Table 6 Amount of THF-soluble polymer as a function of temperature

Example IX

Example VI was repeated except that the time was varied as shown in Table 7. Table 7 Amount of THF-soluble polymer as a function of time

Example X

Example VI was repeated except that no Sunthene 4240 oil and N330 carbon black were added to the EPDM polymer, the devulcanization temperature was 200°C and the amount of diphenyldisulphide was varied as shown in Table 8.

Table 8 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Comparative example A

50 pph of Sunthene 4240 oil and 80 pph of

N330 carbon black were added to and blended in an internal blender with Keltan ® 4802 (an EPDM polymer containing 4.5% by weight of 5-ethylidene-2 -norbornene and 49 % by weight of ethylene) . Next, the blend was blended in a laboratory blender with 5 pph of zinc oxide, 1 pph of stearic acid, 0.5 pph of mercaptobenzothiazol, 1 pph of tetramethylthiuram disulphide and 1.5 pph of a sulphur-containing compound and then heated.

The amount of tetrahydrofuran-soluble polymer of the vulcanized rubber so obtained was 1.0 % by weight.

The vulcanized rubber was then heated for 2 hours at 266°C and at a pressure of 7.6 MPa in the presence of

2.5% by weight of diphenyldisulphide in a closed oven saturated with nitrogen.

After devulcanization, the amount of soluble polymer was determined as a measure of the degree of devulcanization. The amount of tetrahydrofuran-soluble polymer was 18% by weight.

Table 9 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Table 10 Amount of THF-soluble polymer as a function of temperature

Table 11 Amount of THF-soluble polymer as a function of time

Comparative example B

50 pph of Sunthene 4240 oil and 80 pph of N330 carbon black were added to and blended in an internal blender with Keltan ® 820 (an EPDM polymer containing 4.5% by weight of dicyclopentadiene and 55 % by weight of ethylene) . Next, the blend was blended in a laboratory blender with 5 pph of zinc oxide, 1 pph of stearic acid, 0.5 pph of mercaptobenzothiazol, 1 pph of tetramethylthiuram disulphide and 1.5 pph of a sulphur- containing compound and then heated.

The amount of tetrahydrofuran-soluble polymer of the vulcanized rubber so obtained was 4.0% by weight .

After devulcanization, the amount of soluble polymer was determined as a measure of the degree of devulcanization. The amount of tetrahydrofuran-soluble polymer was 21% by weight.

Table 12 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Table 13 Amount of THF-soluble polymer as a function of temperature

Table 14 Amount of THF-soluble polymer as a function of time

Comparative example C Comparative examples A and B were repeated except that no Sunthene 4240 oil and N330 carbon black were added to the EPDM polymer, the devulcanization temperature was 200°C and the amount of diphenyldisulphide was varied. Table 15 Amount of THF-soluble polymer as a function of the amount of diphenyldisulphide

Claims

1. Process for devulcanizing a rubber, which rubber is obtained by vulcanizing with the aid of a sulphur-containing compound a copolymer which contains ethylene monomer units, monomer units of an α-olefin and monomer units of a polyunsaturated compound, by heating the rubber to such elevated temperature that devulcanization occurs and a recyclable product is obtained, characterised in that use is made of a rubber obtained by vulcanizing a copolymer which contains monomer units of a polyunsaturated compound according to the formula X-R° , where:

X is a group having 2-20 C atoms, which group can polymerise with the aid of a co-ordination catalyst,

R° is a chain having 2-30 C atoms and containing at least one double carbon-carbon bond, with none of the C atoms of the double bond forming part of a ring structure.

2. Process according to Claim 1, characterised in that the α-olefin is chosen from the group comprising propylene and butylene-1.

3. Process according to either of Claims 1-2, characterised in that X is chosen from the group comprising vinyl, norbornyl , dicyclopentadienyl .

4. Process according to any one of Claims 1-3, characterised in that R° satisfies either formula II or III:

CH

where Rx-Rs, Rio and R_i4 may be the same or different and may be hydrogen or a hydrocarbon group having 1-5 C atoms; R₉ represents a hydrogen group or a hydrocarbon group having 1-5 C atoms if p and q are equal to 1 or a group represented by the formula - (CH₂) m-CRιι=CRι₂Ri3 if p and q are not equal to 1, where R11-R12 may be the same or different and may represent hydrogen or a hydrocarbon group having 1-5 C atoms and where R_i3 represents a hydrocarbon group having 1-5 C atoms; p and q are, independently of each other, 0 or 1 but not at the same time 0; f = 0-5, but if p and q are equal to 1, f cannot be 0; g = 1-6; n = 1-5; r = 0-5 and m = 1- 5. Process according to any one of Claims 1-4, characterised in that the amount of monomer units of the polyunsaturated compound in the copolymer is between 2 and 10% by weight.

6. Process according to any one of Claims 1-5, characterised in that the rubber is heated in an atmosphere substantially free of oxygen.

7. Process according to any one of Claims 1-6, characterised in that the rubber is heated at a temperature of between 150 and 350°C.

8. Process according to any one of Claims 1-7, characterised in that the rubber is heated at a temperature of between 250 and 350°C.

9. Process according to any one of Claims 1-8, characterised in that the rubber is heated for a period of less than 3 hours.

10. Process according to any one of Claims 1-9, characterised in that the rubber is heated for a period of less than 1 hour.

11. Process according to any one of Claims 1-10, characterised in that a devulcanizing agent is added to the rubber.

12. Process according to any one of Claims 1-11, characterised in that the amount of devulcanizing agent added is between 0 and 5% by weight.

13. Process according to either of Claims 11-12, characterised in that the devulcanizing agent is chosen from the group comprising aromatic and aliphatic disulphides, thiols and amines.

14. Process according to any one of Claims 11-13, characterised in that the devulcanizing agent is diphenyldisulphide .

15. A devulcanized rubber obtainable via the the process set forth in any one of the preceding claims, characterised in that the amount of tetrahydrofuran-soluble polymer is greater than 30% by weight .

16. A devulcanized rubber according to Claim 15, characterised in that the amount of tetrahydrofuran-soluble polymer is greater than 50% by weight.

17. A blend containing an as-yet unvulcanized rubber, vulcanizing agent, oil, carbon black and any additives, characterised in that the blend contains the devulcanized rubber obtained via the disclosed process.

18. Use of the blend according to Claim 17 for the manufacture of rubber articles.