CA2356580A1 - Heat and oil resistant polymer blends - Google Patents

Abstract

A conjugate is formed by blending a polyamide with a hydrogenated carboxylated nitrile rubber at elevated temperature. The conjugate is readily formable by moulding or extrusion, and it displays excellent heat, oil-resistant and barrier properties that render it suitable for use, for example, in many automotive under-the-hood applications.

Description

Heat-and-Oil Resistant Polymer Blends The present invention relates to blends of thermoplastic elastomers.
Background of the Invention Thermoplastic elastomers find many applications, for example in coatings, adhesives and in moulded and extruded parts. The latter are valued for their toughness and impact resistance, and find application in automotive parts, mechanical parts, electrical parts and other uses.
Improvements in properties are being constantly sought, however, and often for this purpose polymeric materials are mixed or blended. The present invention is directed particularly to heat-and oil-resistant materials with good barrier properties, and to processes for their manufacture.
EP-A-0364859 relates to vulcanizable rubbery compositions comprising a polyamide, a partially hydrogenated nitrite rubber and curatives in the nitrite rubber. Partially hydrogenated nitrite rubber, admixed with a curing agent, was gradually added to molten polyamide, with mixing. It is stated that it is preferred to use a polyamide having a low melting point, such as nylon 12. In a preferred embodiment the composition includes malefic anhydride or succinic anhydride.
The specification says that it is believed that the anhydride additive improves mixing between the nylon and the rubber compound. Better results are obtained in an example in which malefic anhydride is used, but the properties of the product obtained are not particularly good, and are not adequate for commercial use.
US Patent No. 4,508,867 relates to vulcanizable rubbery compositions comprising a crystalline polyamide, a synthetic rubbery polymer composed of acrylonitrile or methacrylonitrile, an a,~-unsaturated carboxylic acid and butadiene, an additive selected from the halides of lithium, magnesium, calcium and zinc, an additive selected from the oxides and hydroxides of magnesium, calcium, barium and zinc and the peroxides of calcium and zinc and further comprising sulphur vulcanization active agents. Nylon 11 is the only polyamide whose use is exemplified.
The descriptive portion of the specification suggests that the mixing of the polyamide and the synthetic rubbery polymer should take place at a temperature in the range of from about 50° to about 125°C. In Examples 1 and 2 mixing of nylon 11 and carboxylated nitrile rubber, and other ingredients, took place at 50°C. In Example 3 mixing took place at 190 to 199°C
and Example 4 does not specify the temperature of mixing.
It is believed that the compositions of US Patent No.
4,508,867 do not display adequate heat resistant properties.
Summary of the Invention In one aspect the invention provides a process which comprises blending a polyamide with a hydrogenated carboxylated nitrile rubber at elevated temperature to form a conjugate.
In another aspect, the invention provides a conjugate, or composite, of a polyamide and a hydrogenated carboxylated nitrite rubber.
The conjugates display some properties that are enhanced, as compared with corresponding properties of the polyamide, and some properties that are enhanced, as compared with corresponding properties of the hydrogenated carboxylated nitrite rubber. In particular, the conjugates display good heat-and oil-resistant properties and excellent barrier properties. These properties render the conjugates of the invention useful, for example, for containing volatile fuels such as gasoline in fuel hoses, fuel tanks, shields, fuel line and delivery hoses, inner lines for tires and industrial bladders and the like. Another advantage of the conjugates of the invention is that they are recyclable. Any excess or scrap conjugate material can be melted for re-moulding or re-extruding, for example, with no significant deterioration in properties. In this important characteristic it differs from most elastomers, which are not recyclable. Furthermore, the conjugates of the invention have a lower specific gravity than 100% hydrogenated carboxylated nitrile rubber. Hence less of the conjugate, by weight is needed to make a particular part, resulting in a material cost-saving.
Description of Preferred Embodiments Polyamides useful in the present invention are homopolymers and copolymers that have repeated amide linkages along a polymer chain. The polyamides are of high molecular weight and are crystalline or glossy polymers. Examples include polycaprolactam (nylon 6), polylaurolactam (nylon 12), polyhexamethyleneadipamide (nylon 6,6), polyhexamethyleneazelamide (nylon 6,9), polyhexamethylenesebacamide (nylon 6,10), polyhexamethyleneisophthalamide (nylon 6,IP), polyaminoundecanoic acid (nylon 11), polytetramethyleneadipamide (nylon 4,6) and copolymers of caprolactam, hexamethylenediamine and adipic acid (nylon 6,66), and also aramids such as polyparaphenyleneterephthalamide. The majority of the polyamides have softening points and melting points between about 160° and 250°C.

Hydrogenated carboxylated nitrile rubbers (HXNBR) and processes for making them are the subject of our Canadian Patent Application Serial No. 2,304,501, filed April 10, 2001, the disclosure of which is incorporated by reference and a copy of which is appended hereto. Such rubbers are formed by copolymerizing a conjugated dime, a nitrite and an unsaturated acid, to form a copolymer with a random, or statistical, distribution of the dime, nitrite and acid, followed by hydrogenation. When the conjugated diene is polymerized the product contains some carbon-carbon double bonds. In the past attempts to hydrogenate those carbon-carbon double bonds have led also to reduction of nitrite and carboxyl groups, which is undesireable. The invention of Application Serial No.
2,304,501 enables hydrogenation of carbon-carbon double bonds of carboxylated nitrite rubber without concomitant reduction of nitrite and carboxyl groups, yielding novel and valuable polymers. These are commercially available from Bayer under the trademark Therban XT.
Many conjugated dienes can be used in the hydrogenated carboxylated nitrite rubber. Mention is made of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and piperylene, of which 1,3-butadiene is preferred.
The nitrite is normally acrylonitrile, methacrylonitrile or a-chloroacrylonitrile, of which acrylonitrile is preferred.
The a,~-unsaturated acid can be, for example, acrylic, methacrylic, ethacrylic, crotonic, malefic (possibly in the form of its anhydride), fumaric or itaconic acid, of which acrylic and methacrylic are preferred.
The conjugated dime usually constitutes about 50 to about 85% of the polymer, the nitrite usually constitutes about 15 to 50% of the polymer and the acid about 0.1 to about 10%, preferably 0.5 to 7%, these percentages being by weight. The polymer may also contain an amount, usually not exceeding about 10%, of another copolymerizable monomer, for example, an ester of an unsaturated acid, say ethyl, propyl or butyl acrylate or methacrylate, or a vinyl compound, for example, styrene, a-methylstyrene or a corresponding compound bearing an alkyl substitutent on the phenyl ring, for instance, a p-alkylstyrene such as p-methylstyrene. The polymer preferably is a solid that has a molecular weight in excess of about 60,000, most preferably in excess of about 100,000.
The degree of hydrogenation can be expressed in terms of residual double bonds (RDB), being the number of carbon-carbon double bonds remaining after hydrogenation, expressed as a percentage of the carbon-carbon double bonds prior to hydrogenation. HXNBR's less than 6 are preferred and HXNBR's with RDB in the range from 0.9 to 5.5 are particularly preferred, and with acrylonitrile contents of 32%, 34%, 36%, 39% and 43%.
In a preferred embodiment of the process, the polyamide is melted and HXNBR is then added to the melt, with stirring in an intensive mixer such as a Banbury or in a high-shear extruder. The mixing is preferably in a single step and is preferably without curatives. The mixing temperature can range from about 150°C to 300°C, preferably from about 170°C to about 270°C, and most preferably from about 200 to 250°C, depending upon the polyamide grade. The fill factor, i.e., the volume of material being mixed, expressed as a percentage of the volume of the mixing vessel, is preferably in the range from about 50% to about 95% preferably 65 to 80%, more preferably 55 to 75% with higher fill factors resulting in blends with better physical properties. The mixer is preferably used at, or close to its maximum RPM to ensure good dispersion of the elastomer within the polyamide matrix.
Nylon 6, for example, melts at a relatively high temperature of about 225°C, and the molten nylon 6 may be at a temperature of about 240°C. If held at this temperature for any length of time HXNBR may degrade, so it is preferred to minimise the time at this temperature. An antioxidant may also be included in the mixture, suitably in an amount up to 1 phr, preferably 0.7 phr. The mixture is stirred and if the torque required to drive the stirrer is plotted against time it is found that the torque increases with time. This indicates bonding or crosslinking between the polyamide and the hydrogenated carboxylated nitrile rubber. When the torque ceases to increase this indicates that crosslinking has substantially ceased, and also that mixing is complete.
As indicated, an antioxidant may be used in the mixing process. Examples of suitable antioxidants include -p-dicumyl diphenylamine (Naugard 445), Vulcanox DDA (a diphenylamine derivative, Vulcanox ZMB2 (zinc salt of methylmercapto benzimidazole) and Vulcanox HS (polymerized 1,2-dihydro-2,2,4-trimethyl quinoline).
It is possible to achieve further crosslinking.
Thus, when the torque ceases to increase a crosslinking agent can be added, while mixing continues. The crosslinking agent can be a peroxide crosslinking agent, a diamine crosslinking agent or sulphur or a sulphur containing crosslinking agent.
In many embodiments of the invention it is desired that the conjugate have good high temperature properties, and sulphur-curing tends to have a deleterious effect on high temperature properties. It is therefore expected that sulphur curing agents will be used only rarely, but their use is not outside the scope of the invention.
There are known many peroxide crosslinking agents, including dicumyl peroxide, di-tert.-butyl peroxide, benzoyl peroxide, 2,5-dimethyl-2,5-di(tert.-butylperoxy)-hexyne-3, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane and the like. The high temperature of the polyamide melt limits selection, however. A
preferred peroxide curing agent is commercially available under the trademark Vulcup 40KE. The peroxide curing agent is suitably used in an amount of 0.2 to 5 parts per hundred parts of rubber (phr), preferably 1 to 3 phr. Too much peroxide may lead to undesirably violent reaction.
Diamine crosslinking agents that can be used include aliphatic diamines, for example a,~ alkylene diamines such as 1,6-hexamethylenediamine and cycloaliphatic diamines such as 1,4-cyclohexanediamine. One convenient source of 1,6-hexamethylenediamine is hexamethylenediamine carbamate, available under the trademark DIAK 1. The diamine crosslinking agent is suitably used in an amount of 0.2 to 20 phr, preferably 1 to 10 phr.
Vulcanizing co-agents can also be used. Mention is made of triallyl isocyanurate (TAIC), commercially available under the trademark DIAK 7 from DuPont.
The ratio of polyamide to hydrogenated carboxylated nitrite rubber can vary between wide limits, say from 90 parts to 10 parts by weight to 10 parts to 90 parts by weight.
Properties of the conjugate vary, depending on the ratio of polyamide to elastomer. A conjugate of 30 parts polyamide and 70 parts elastomer was flexible and was suitable for use in flexible hoses for use, for example, as fuel lines. A 50:50 conjugate was hard and a 70:30 conjugate was like a plastic, and acceptable for rigid fuel lines but not flexible ones. The ratio can of course be varied to optimise particular properties, and tests of conjugates of different proportion can be carried out routinely by persons skilled in the art.
It is possible to include a plasticizer in the conjugate. Suitable plasticizers include those well known for use with nitrile polymers such as the phthalate compounds, the phosphate compounds, the adipate compounds, the alkyl carbitol formal compounds, the coumarone-indene resins and the like. An example is the plasticizer commercially available under the trademark Plasthall 810. The plasticizer should be a material that is stable at high temperature and will not exude from the conjugate. If plasticizer is to be used it is preferred to melt the polyamide, add a first portion of the hydrogenated carboxylated nitrite rubber, say about half, mix, then add the plasticizer, mix and then add the remainder of the HXNBR and continue mixing. The amount of plasticizer used will depend upon the proposed end use of the conjugate, but may be between 1 and 40 phr, preferably between 5 and 20 phr.
It is possible to use a blend o.f polyamides. It is also possible to use a mixture of HXNBR's or a mixture of the HXNBR and another elastomer, for example a carboxylated nitrite rubber (XNBR), a hydrogenated nitrite rubber (HNBR) or a nitrite rubber (NBR). Suitable XNBR's are commercially available from Bayer under the trademark Krynac and suitable HNBR's are commercially available from Bayer under the trademark Therban and suitable NBR's are available from Bayer under the trademark Perbunan. If the HXNBR is used in admixture with another elastomer it is preferred that the HXNBR
shall be at least 25%, preferably at least 50%, of the HXNBR-elastomer mixture.

It is possible to incorporate other known additives or compounding agents in the conjugate. These are preferably added after the blending of the polyamide and HXNBR. Additives include reinforcing fillers, for example carbon black, calcium carbonate, clay, silica or talc, antioxidants, antiozonants, processing oils, ultra violet absorbers, co-agents and the like.
The conjugate of the invention sets, of course, to form a solid on cooling. The conjugate can be remelted and resolidified without any significant deterioration or deleterious effect on its properties. In this respect, it differs from elastomers such as pure HXNBR, XNBR, HNBR and the like; after crosslinking these cannot be melted and resolidified. This property of the conjugate of the invention is important. It permits the conjugate of the invention to be made into the form of pellets, which pellets can be remelted to be formed into final products by, for example, moulding or extrusion. It is also possible to recycle conjugate of the invention, which is a very significant commercial advantage of the invention.
The invention is further illustrated in the following examples.
General Procedure A Brabender Plasticorder was fitted with roller mixing blades and a 369g capacity bowl. Mixer bowl temperature, fill factor, mixing time and roller speed were varied. In a typical mixing procedure polyamide was initially melted, followed by addition of elastomer and, in some instances, a cure system. The polymer blend was then passed through a hot mill once, to make a flat sheet.

A Preco Press was used to compression mould test pieces. The compound was added to a pre-heated mould and placed in the press at 0 psi at 240°C for 10 minutes. The mould was then held at 20,000 psi for 20 minutes, after which the moulded sample was transferred to a cold press and held at 10,000 psi for 5 min.
The polyamide used was Durethan B31SK polyamide 6, supplied by Bayer Plastics. B31SK is an unreinforced polyamide with low crystallinity. It has the following desirable properties:
high strength, stiffness and abrasion resistance good chemical and stress-cracking resistance vicat softening point > 200°C; melting point - 225°C
good barrier properties As HXNBR there was used a Therban XT that has carboxyl moieties, based on acrylic acid, of approximately 5.0%, an acrylonitrile content of 33%, the balance 1,3-butadiene, a Mooney viscosity of 77 and an RDB of 3.5. As HNBR's there were used Therban A3406 and Therban C3446, Therban A3406 has an acrylonitrile content of 34% and an RDB not greater than 0.9, Therban C3446 has an acrylonitrile content of 34% and an RDB of 4.
Example 1 (Comparative) 70 Parts HNBR (Therban A3406 or Therban C3446) and 30 parts polyamide 6 were blended in the presence of a peroxide cure system, namely Vulcup 40KE and TAIC and 0.7 phr of antioxidant. The Brabender mixing conditions were as follows:
55% fill factor;

80 RPM mixing blade speed;
230°C bowl temperature;
12 min total mixing time.
Results are given in Table 1 Table 1: Room-temperature physical properties for 70:30 phr Therban:Polyamide 6 blends (Peroxide/Coagent DV) Therban grade Tensile Ultimate Tensile Hardness Strength Elongation (~) set() (Sh. A) (MPa) A3406 2.24 489 >100 60 C3446 1.95 337 na 64 The products did not meet the inventor's minimum targets of a tensile strength greater than 7.0 MPa and a tensile set of less than 50%.
Example 2 HXNBR (Therban XT, 70 parts) and polyamide 6 (Durethan B31SK, 30 parts), with no curatives, were blended.
The polyamide was melted and the HXNBR and 0.7 phr of an antioxidant (Naugard 445) were then added. It was observed that mixing torque would increase for a period of about three minutes and then reach an equilibrium level, at which time mixing was stopped. Results are given in Table 2.

Table 2: Room-temperature physical properties for 70:30 phr Therban XT:Polyamide 6 blends with no curatives; mixing conditions Were varied Run Tensile Ultimate Tensile Hardness Strength Elongation set (~) (Sh. A) (MPa) A 9.5 165 Na 78 B 8.5 350 35 62 C 7.1 216 16 67 The product of these runs did meet the inventor's minimum target of tensile strength greater than 7 MPa, ultimate elongation greater than 100% and tensile set less than 50%.
The best results were achieved in run B, in which mixing was done with a high fill factor (70%), fast RPM (95) and high temperature {240°C) .
When runs similar to runs A, B and C were carried out but using an HNBR (Therban) in place of the HXNBR, no increase in mixing torque was observed in the absence of a curing system, suggesting that there was no interaction between the HNBR and the polyamide. This contrasts with the situation when HXNBR and polyamide are blended.
The products of runs A, B and C were heat aged in an air-oven at 150°C for 168 hours or for 504 hours, and properties measured. For comparison peraxide-cured Therban A3406 was heat aged and its properties measured. Results are given in Table 3.

Table 3: Heat-aged physical properties for 70:30 phr Therban XT:Polyamide 6 blends with no curatives; Aging temperature was 150°C
Run Aging Change in Ultimate Hardness Time (h) Tensile Elongation (Sh. A) Strength Heat-aged physical properties for 100 phr Therban peroxide-cured optimized for heat resistance; Aging temperature was 150°C

These results show that the long term heat aging performance of the products of runs A, B and C exceed that of Therban C3406, with good retention of physical properties such as tensile strength and ultimate elongation at high temperature. The brittle point for the product of run B
exceeded -72°C.
In contrast, the product of blending HNBR (Therban C3406) with polyamide in the absence of a curing system melted when attempt was made to heat-age it at 150°C.

The permeability of the product of run C was measured and found to be 3 . 5 (cm2/ (atm' s) ) x108, which compares favourably with the permeability of 3 of a typical bromobutyl cured time innerliner.
The products of runs A, B and C were all reprocessable. Moulded test pieces were cut and remoulded several times without any evidence of gel material. The products had excellent flow properties at moulding temperatures, for example 240°C.
Example 3 In this example HXNBR (Therban XT, 70 parts) and polyamide 6 (Durethan B31SK, 30 parts) and 0.7 phr antioxidant (Naugard 445) were blended in the presence of a peroxide curing agent, (a, a-bis(t-butylperoxy)diisopropylbenzene), Vulcup 40KE, and a coagent, triallylisocyanurate, TAIC (DIAK 7, available from DuPont). Mixing conditions were kept constant at 95 RPM, 240°C and 65% fill factor. Results are given in Table 4.
Table 4: Room-temperature physical properties for 70:30 phr Therban:Polyamide 6 blends with peroxide cure system Run Vulcup DIAK Tensile Ultimate Tear Hardness (phr) 7 Strength Elongation Strength (Sh. A) (phr) (MPa) (~) (kN/m) D 2.2 1.1 7.6 266 24 59 E 2.2 2.2 9.0 332 28 60 F 3.3 2.2 7.8 344 21 61 G 5.3 1.1 7.1 274 28 68 Example 4 HXNBR (Therban XT, 70 parts) and polyamide 6 (Durethan B31SK, 30 parts) and 0.7 phr antioxidant (Naugard 445) were blended with a bifunctional curing agent, namely hexamethylenediamine, DIAK 1. Results are given in Table 5.
Run I is comparative, as there is used an HNBR, not an HXNBR.
Table 5: Room-temperature physical properties for 70:30 phr Therban:Polyamide 6 blends with DIAK 1 cure system; various mixing conditions*
Run Therban DIAK Tensile Ultimate Tear Hardness Tensile Grade l Strength ElongationStrength (Sh. A) Set (phr) (MPa) (~) (kN/m) Ha XT .2 8.3 109 58.3 76 15 Ia A3406 .2 4.6 45 33.6 77 6.7 Jb XT .2 7.8 140 42.0 74 12 K XT .3 7.8 104 64.4 76 10 La XT .1 8.5 242 - 76 -Ma XT .05 $.1 205 - 75 19 N XT .08 9.5 288 - 71 27 Mixing conditions:
95 RPM, 70~ fill factor; DIAK 1 added after 8 min mix a= 240°C, °
time. Total mix time was 9 minutes.
b= 230°C, 95 RPM, 67% fill factor; DIAK 1 added after 8 min mix time. Total mix time was 9 minutes.
c= 240°C, 95 RPM, 70% fill factor; DIAK 1 added once polymer blend torque was minimized (approx 5 minutes into mix). Total mix time was 8 minutes.
Example 5 HXNBR (Therban XT, 70 parts) and polyamide 6 (Durethan B31SK, 30 parts) and 0.7 phr antioxidant (Naugard 445) were blended. In runs 0 and P there were used 2.2 phr Vulcup 40KE and 2.2 phr DIAK 7, added after 7 minutes of mixing. The mixing conditions in runs O, P and Q were:
temperature 240°C; speed 95RPM; fill factor 70%; total mixing time 8 minutes. The oil resistance of the formed conjugates in ASTM Oil 1 and IRM 903 was then measured. ASTM Oil 1 is a blend of aromatics. IRM 903 is a blend of naphthenics and paraffinics. The blends were heat-aged at 150°C for 168 hours in ASTM Oil 1 and IRM 903 and the results are given in Table 6 and 7, respectively.
Table 6 contains the results of heat aging for selected Therban XT/polyamide-6 blends. All blends Were heat aged at 150°C for 168 hours in ASTM Oil 1.
Compound Cure Tensile Ultimate hardness Weight Volume Number System Strength Elongation (Sh. A Change Change ($ (~ change) (~) change) change) O Peroxide 38 -1 -2 -0.7 0.3 P Peroxide 4"1 2 1 -1.4 -1.4 Q None 118 40 8 0.4 1.6 N DIAK 1 77 -17 5 0.4 1.3 HNBR Peroxide 18 -33 1 -2.1 -2.4 Control The blends cured using Peroxide, O and P, exhibited the best overall performance i.e. retention of physical properties and had minimal weight and volume change after oil-immersion aging. The tensile strength of all the blends increased during aging whereas the elongation values varied depending on the cure system. The oil resistance of the blends is comparable to the HNBR control.
Table 7 contains the results of heat aging for selected Therban XT/polyamide-6 blends. All blends were heat aged at 150°C for 168 hours in IRM 903.
Compound Cure Tensile Ultimata Hardness weight volume Number System Strength8longation(Sh. A) Change Change O Peroxide -36 -34 -10 15.6 18.1 P Peroxide -37 - -5 14.7 15.9 Q None 36 8 -5 17.9 20.3 N DIAK 1 -17 -39 -4 17.9 20.3 HIsHR Peroxide -20 -24 -8 14.6 17.9 Control The IRM 903 oil resistance of the TPE blends is comparable to the Therban A3406 peroxide cured reference formulation. All blends had a decrease in hardness and an increase in weight and volume after the testing.

Claims (22)

1. A process which comprises blending a polyamide with a hydrogenated carboxylated nitrile rubber at elevated temperature to form a conjugate.

2. A process according to claim 1 wherein the polyamide is polyamide 6.

3. A process according to claim 1 or 2 wherein the hydrogenated carboxylated nitrile rubber is a copolymer of acrylonitrile, butadiene and acrylic acid, which has a residual carbon-carbon double bond content of 6% or less.

4. A process according to claim 1, 2 or 3 wherein the elevated temperature is in the range 150 to 300°C.

5. A process according to claim 1, 2 or 3 wherein the elevated temperature is in the range 170 to 270°C.

6. A process according to claim 1, 2 or 3 wherein the elevated temperature is in the range 200 to 250°C.

7. A process according to any one of claims 1 to 6 wherein the blending is carried out with a fill factor in the range 50 to 95%.

8. A process according to any one of claims 1 to 6 wherein the blending is carried out with a fill factor in the range 65 to 85%.

9. A process according to any one of claims 1 to 8 which comprises melting the polyamide and adding the hydrogenated carboxylated nitrile rubber to the molten polyamide, with stirring and in the absence of any curative system.

10. A process according to claim 9 wherein the mixing torque is observed and when the mixing torque ceases to increase a curing system is added to the blend.

11. A process according to any one of claims 1 to 8 which comprises melting the polyamide and adding the hydrogenated carboxylated nitrile rubber and a curing system to the molten polyamide.

12. A process according to claim 10 or 11 wherein the curing system is a peroxide curing system or a diamine curing system.

13. A process according to claim 12 wherein the curing system comprises (a..alpha.,.alpha.-bis(t-butylperoxy)diisopropylbenzene) and triallylcyanurate.

14. A process according to claim 12 wherein the curing system comprises 1,6-hexamethylenediamine.

15. A process according to any one of claims 1 to 14 which comprises the step of forming the conjugate into pellets suitable for use in moulding or extrusion operations.

16. A conjugate of a polyamide and a hydrogenated carboxylated nitrile rubber.

17. A conjugate according to claim 16 wherein the polyamide is polyamide 6.

18. A conjugate according to claim 16 or 17 wherein the hydrogenated carboxylated nitrile rubber is a copolymer of acrylonitrile, butadiene and acrylic acid that has been hydrogenated to a residual carbon-carbon double bond content of 6% or less.

19 19. A conjugate according to claim 16, 17 or 18 that has been formed with the aid of a curing agent.

20. A conjugate according to any one of claims 16 to 19 which also contains a hydrogenated nitrile rubber.

21. A conjugate according to any one of claims 16 to 20 in the form of pellets for use in moulding or extrusion operations.

22. A conjugate according to any one of claims 16 to 20 in the form of a moulded or extruded part.