EPDM rubber blend vulcanizates

PolymerDegradationand Stability 62 (1998) 471-477 PII:

© 1998 Elsevier Science Limited. All rights reserved Printed in Northern Ireland 0141-3910/98/S--see front matter

S0141-3910(98)00030-5

ELSEVIER

Thermal stability of butyl]EPDM rubber blend vulcanizates S. H. Botros Polymers Department, National Research Centre, Dokki-Cairo, Egypt

(Received 8 November 1997; accepted 30 December 1997) Butyl rubber has some disadvantages such as marginal green strength and only fair heat and ozone resistance. These disadvantages can generally be overcome by the partial replacement of butyl rubber (IIR) with ethylene propylene diene monomer rubber (EPDM). EPDM has a highly saturated backbone which gives it excellent resistance to the effect of oxygen and ozone. However, IIR has some unsaturation due to the isopreneunits in its structure. In this investigation,data and observations on the heat resistance behaviour of IIR/EPDM blend vulcanizates over a range of compositions and temperatures are highlighted. The results show that blending of IIR with EPDM is beneficialbecause of the enhancement of heat resistance of the blend vulcanizates. © 1998 Elsevier Science Limited. All rights reserved 1 INTRODUCTION

This paper concerns preparation of I I R / E P D M rubber blend vulcanizates with various types and ratios o f E P D M rubber. The physico-mechanical properties after and before thermal ageing, at various temperatures, were evaluated.

Butyl rubber (IIR) is most noted for its excellent resistance to air permeation and, hence, is widely used in the production o f inner tubes 1 and tire inner liners. 2,3 The fair heat resistance o f I I R can be overcome by blending it with E P D M . The blends obtained can also be used for high temperature conveyor belt application, 4 mainly for carrying hot coal. Various properties o f a heat resistant conveyor belt cover c o m p o u n d based on E P D M blends, have been reported. 5,6 With the increased emphasis on weight reduction and the resulting downsizing of the automobile, additional demands are put on. the elastomeric components. 7 Butyl and E P D M rubbers are often used in m a n y applications among which are engine mounts, body mounts, transaxle mounts and bushing o f various types. The problem with blending is that it is often difficult consistently to obtain parts with the same properties on a batch-to-batch basis. The inconsistency in properties can be attributed to a different degree of mixing in the blend system. A heterogeneous blend usually results when two chemically dissimilar rubbers are mixed. Several investigators have examined this morphology. 8-12 M a n y scientists have established the factors which are important in determining the mechanical properties o f such blends. 13 other researchers have investigated the compatibility o f rubber blends. 14-16

2 EXPERIMENTAL

2.1 Materials Butyl rubber:IIR-268 E P D M rubber types: • Buna R AP-447:ethylene-propylene-ENa terpolymer, unsaturation b 8, ethylene content 70% (from Enie Chem. Elastomer). • Vistalon-5600:ethylene-propylene-EN terpolymer, unsaturation 9, ethylene content 65% (from ESSO CHIMIE). • Vistalon-6505:ethylene-propylene-EN terpolymer, unsaturation 9, ethylene content 55% (from ESSO CHIMIE). • Keltan-820:ethylene-propylene-DCPD c terpolymer, unsaturation 4.5, ethylene content 60% (from DSM): (a) Ethylidene norbornene; (b) Unsaturation (DB/IO00C); (c) Dicyclopentadiene. 471

S.H. Botros

472

Compounding ingredients: they are of pure grade and customarily used in industry. 2.2 Techniques 1. The rubber mixes were blended on a tworoll mill of 460 m m diameter and 3 0 0 m m working distance. The speed of slow roll was 16rev/min, and the gear ratio was 1:1.25. 2. The rheometric characteristics of the rubber mixes were determined using a Monsanto Oscillating Disc Rheometer R-100 according to a standard method. 17 3. The rubber mixes were vulcanized in a hydraulic press at 172+1°C for their optim u m cure time (tc90). 4. Mechanical properties of the rubber vulcanizates were measured using a tensile testing machine Zwick-1101 according to a standard method. TM 5. The rubber vulcanizates were subjected to thermal ageing w in an air-circulating oven at temperatures as stated, for different periods. The retained values, %, in tensile strength, elongation at break and 100% modulus of the vulcanizates were calculated.

Table 1. Vulcanizing systems, rheometric characteristics and physico-mechanical properties of IIR vulcanizates Sample no.

S1

$2

$3

IIR Neoprene-w MBT TMTD ZDEDC S P h e n o l f o r m a l d e h y d e resin

100 -0.6 1.2 -1 --

100 ---2 2 --

100 8 ----12

53 10 13 3.5 10.5

58 12 17 2 6.7

30 9 34 6 3.6

Rheometric characteristics M a x i m u m torque, d N m M i n i m u m torque, d N m Cure time tc90, rain Scorch time ts2, rain Cure rate index (CRI), min -1 Physico-mechanical properties 100% modulus, M P a Tensile strength, M P a Elongation at break, %

0.88 0.92 0.90 14 13 11.2 700 650 700

However, the cure time (tC9o) and the scorch time (ts2) of resin cured vulcanizate are longer than S cured vulcanizates. It can be noticed that the 100% modulus and the elongation at break for the three vulcanizates, under investigation are, almost, unchanged. But the tensile strength of resin cured vulcanizate ($3) is lower than those obtained for S cured vulcanizates (S1 and S2).

3 R E S U L T S AND D I S C U S S I O N The rubber mixes were prepared in an open two roll mill. The rubber blend compositions are shown in Table 1. The base recipe contains: rubber 100, ZnO 5 phr, stearic acid 1.5 phr, SRF carbon black 40 phr and processing oil 5 phr. 3.1 Effect of the vulcanizing systems on the heat resistance of IIR vulcanizates In order to study the thermal stability of IIR vulcanizates, three vulcanizing systems were used: (1) MBT/TMTD/S; (2) Z D E D C / S and (3) neoprene-w/phenolformaldehyde resin-1054. The formulations are indicated in Table 1.

3.1.1 Rheometric and physico-mechanical characteristics The rheometric and physico-mechanical data are shown in Table 1. It is clearly seen that the m a x i m u m and minimum torques of resin cured IIR are lower than those obtained by S cured IIR.

3.1.2 The physico-mechanieal properties after thermal ageing The three vulcanizates under investigation were subjected to thermal oxidative ageing at 90°C for various periods up to 7 days. The retained values of tensile stregth, elongation at break and 100% modulus were calculated and plotted versus the ageing time (Figs 1-3, respectively). Those values are taken as a measure for the heat resistance of IIR vulcanizates. It is clear from Figs 1 and 2 that resin cured IIR retains tensile strength and elongation at break to a higher extent than S cured IIR (S1 and $2). Also $3 shows moderate values of 100% modulus u p o n ageing as shown in Fig. 3. Therefore, it can be concluded that resin cured IIR has superior performance to the other vulcanizing systems used, against thermal ageing. The heat resistance of the vulcanizates can be arranged according to the vulcanizing systems used, in a descending order, as follows: resin cure > S / Z D E D C > S / M B T / T M T D .

Thermal s.tability of butyl/EPDM rubber blend vulcanizates 3.2 Effect of E P D M types on the heat resistance of I I R / E P D M vulcanizates

In order to select the suitable type of EPDM which improves the thermal ageing resistance of IIR,

120

• 51 052 x $3

100 "

80

60

40 |

I

I

I

I

I

I

1 2 3 4 5 6 7 Ageing t i m e at 9 0 ' C , d a y s

473

various types of EPDM were blended with IIR, then the other compounding ingredients were added to the blend.

3.2.1 Rheometric and physico-mechanical characteristics The rheometric characteristics of the I R R / E P D M blends and the physico-mechanical properties of their vulcanizates are given in Table 2. It is clearly seen that blending of IIR with Keltan-820 does not affect the rheological characteristics of IIR. However, blending of IIR with Vistalon-5600, Vistalon-6505 and Buna AP-447, results in increasing maximum torque and decreasing minimum torque, cure time and scorch time. It can be also noticed from Table 2 that blending IIR with Vistalon-5600 and Vistalon-6505 produces vulcanizates with lower tensile strength and elongation at break than does Keltan-820. Blending IIR with Vistalon-6505 and Buna AP-447 results in increasing of 100% modulus of the blend vulcanizates. Therefore, Keltan-820 shows no adverse effect on characteristics of the vulcanizates.

I

8

Fig. 1. Retained tensile strength versus ageing time of IIR with various vulcanizing systems: S1 (S/TMTD/MBT), $2 (S/ ZDEDC) and $3 (Ph. resin).

3.2.2 The physico-mechanical properties after thermal ageing IIR/EPDM vulcanizates with various types of EPDM were subjected to thermal ageing at elevated 200,

120

*

51 o 52 x53 •

Sl

o S2 180

x

53

100 160 .-e*

uJ

E tw

,°I

140 /

o

x~

x

120~

oL 4_~ 0

j

I , I 1 2 Ageing

I I I I I 3 4 5 6 7 time at 9 0 ' C , d a y s

J 8

Fig. 2. Retained elongation at break versus ageing time of IIR with various vulcanizing systems: S1 (S/TMTD/MBT), $2 (S/ ZDEDC) and $3 (Ph. resin).

0

1 2 Ageing

3 time

,,ii,

4 5 6 7 at 9 0 " C , d a y s

8

Fig. 3. Retained 100% modulus versus ageing time of IIR with various vulcanizing systems: S1 (S/TMTD/MBT), $2 (S/ ZDEDC) and $3 (Ph. resin).

S . H . Botros

474

temperature (120°C) for periods up to 7 days. It should be noted, here, that the ageing temperature exceeds that of the previous step (90°C). The retained values in tensile strength and elongation at break, after ageing, were calculated and taken as a measure of the heat resistance of vulcanizates, as seen in Figs 4 and 5. It is obvious that IIR/Keltan-820 vulcanizate shows the best performance against thermal ageing; since it retains tensile strength and elongation at break to a higher extent than do the other types of EPDM. This can be attributed to the low unsaturation value of Keltan-820 (4.5 DB/ 1000C). It can be concluded that heat resistance of the vulcanizates can be arranged in a descending order as follows:

oil 5 phr, Neoprene-W 8 phr and phenolformaldehyde resin--1045 12 phr. It is noticed from Table 3 that the maximum torque decreases gradually as the Keltan-820 content

120 4- ~

÷

100

8O

Z

Keltan-820 > B u n a R A p - 447

60

> Vistalon-5600 and 6505. 053 ÷ $4 "55

40 3.3 Effect of IIR/EPDM blend composition on heat resistance of the vulcanizates

In order to produce I I R / E P D M vulcanizate with outstanding heat resistance a partial replacement of IIR with various proportions of Keltan-820 was carried out. Composition of the blends, rheometric characteristics and physico-mechanical properties of the vulcanizates are indicated in Table 3. The base recipe contains: Rubber 100, Zn0 5 phr, stearic acid 1.5 phr, SRF carbon black 40phr, processing

t

0

$3

$4

$5

$6

$7

IIR Keltan-820 Vistalon-5600 Vistalon-6505 Buna R AP-447

100 ---. .

80 20 ---

80

80

20

.

80 -20 -.

-20

Rheometric characteristics Maximum torque, dNm Minimum torque, dNm Cure time tC9o, rain Scorch time ts2, min Cure rate index (CRI)

30 9 34 6 3.6

28 9 34 6 3.6

36 3 30 4 3.8

35 4 30 3.5 3.8

40 6 31 3.5 3.6

Physico-mechanical properties 100% modulus, MPa 0.9 Tensile strength, MPa 11.2 Elongation at break, % 700

0.8 11 720

0.83 7 600

1.1 9 600

1.2 10.5 650

i

m

I

i

I

l

1 2 3 z, 5 6 7 8 Ageing time at 120'C,days

Fig. 4. Retained tensile strength versus ageing time of IIR/ EPDM, with various types of EPDM: $4 (Keltan), $5 (Vista1on-5600), $6 (Vistalon-6505) and $7 (Buna AP-447).

20t

v 56 x 5 7

053 +54 •55

100

Table 2. Rheometric characteristics and physico-mechanical properties of IIR/EPDM vulcanizates, using various types of EPDM Sample no.

v S8 x S 7

LU

80

rr

60

z,0 l

I

I

I

!

I

|

I 2 3 & 5 6 7 Ageing time at 1 2 0 ' C , d a y s

I

8

Fig. 5. Retained elongation at break versus ageing time of IIR/EPDM, with various types of EPDM: $4 (Keltan), $5 (Vistalon 5600), $6 (Vistalon-6505) and $7 (Buna AP-447).

Thermal stability of butyl/EPDM rubber blend vulcanizates increases in the blend, while the minimum torque, cure time (tc90), scorch time (ts2), 100% modulus and tensile strength of the vulcanizates decrease at high content of Keltan-820 (40 and 50 phr). On the other hand the elongation at break is almost not affected by increasing the content of Keltan-820 in the blend.

From the results obtained, it can be concluded that IIR/Keltan-820 vulcanizate ($8(70:30)) shows a superior performance to the other blend compositions against thermal ageing at 140°C for 7 days. 220

X ~ x ~ x

2O0

3.3.1 The physico-mechanical properties after thermal ageing

180

IIR/Keltan-820 vulcanizates, with various compositions, were subjected to thermal ageing at an elevated temperature (140°C) for periods up to 7 days. It should be noted here, that the ageing temperature exceeds that of the previous step

O

160 140 ,,., 120

(120°C).

The retained values of tensile strength, elongation at break and 100% modulus were calculated and plotted against the thermal ageing time as illustrated in Figs 6-8, respectively. It is clear that the retained values of tensile strength increase as the Keltan-820 content increases in the blend. The replacement of 30, 40 and 50 parts of IIR with Keltan-820 shows similar but higher retained values of elongation at break than those obtained for IIR with and without replacement of 20 parts, as shown in Fig. 7. On the other hand, it is found from Fig. 8 that 100% modulus increases to a low extent (a desirable character) by replacement of 20 and 30 parts of IIR with Keltan-820, while it increases to a high extent by replacement of 40 and 50 parts of IIR. This can be attributed to the scission of IIR during oxidation and cross-linking of EPDM during oxidative ageing. Therefore, IIR/Keltan-820 vulcanizate $8 (70:30) is the least affected by thermal ageing.

475

100 80-

4-

~

~~+----~+

6O 402O

•

S 3

+

S

"

S 8

o S9 x S 10

4

0 0

1

2

3

4

5

6

7

8

Ageing time at 140"C , d a y s Fig. 6. Retained tensile strength versus ageing time of IIR/ Keltan, with various compositions: $3 (100:0), $4 (80:20), $8 (70:30), $9 (60:40) and S10 (50:50).

•

$3

100

$9 $10

o

+ S4 /" S 8

x

Table 3. I I R / E P D M blend composition, rheometric characteristics and physico-mechanical properties Sample no.

$3

S4

$8

$9

S10

IIR Keltan-820

100 --

80 20

70 30

60 40

50 50

Rheometric characteristics Maximum torque, d N m Minimum torque, dNm Cure time tc90, min Scorch time ts2, min Cure rate index (CRI)

30 9 34 6 3.6

28 9 34 6 3.6

26 9 34 6 3.6

24 5 32 3 3.4

23 4 30 3 3.7

0.9 0.8 11.2 11 700 720

0.8 9.8 730

0.7 7.3 730

0.7 5.7 740

Physico-mechanical properties 100% modulus, MPa Tensile strength, MPa Elongation at break, %

E 6O

40I

0

|

I

1

I

I

I

1 2 3 4 5 6 7 Ageing time at 1/,0 ' C , d a y s

J

8

Fig. 7. Retained elongation at break versus ageing time of IIR/Keltan, with various compositions: $3 (100:0), $4 (80:20), $8 (70:30), $9 (60:40) and S10 (50:50).

476

S. H. Botros

3.4 Effect of ageing temperature upon physicomechanical properties of IIR/Keltan-820 (70:30) vulcanizate

oo]

A severe thermal ageing test was carried out in order to evaluate the heat resistance of IIR/Keltan820 vulcanizate. The prepared vulcanizates were subjected to thermal ageing in an air-circulated oven at various temperatures up to 200°C for 48 h. Tensile strength elongation at break and 100% modulus of the vulcanizates are illustrated in Fig. 9. It is clear that tensile strength of the vulcanizate $8 (70:30) increases as the ageing temperature increases up to 120-130°C, then it decreases till the temperature reaches 200°C. It should be noted here that, at 165°C, the vulcanizate $8 retains 100% of its original tensile strength value before ageing, while the elongation at break decreases gradually as the ageing temperature increases. On the other hand 100% modulus of that vulcanizate, increases as the ageing temperature increases up to 165°C. Further increase of the ageing temperature results in a decrease of 100% modulus. This can be attributed to the cross-linking process that takes place till the ageing temperature reaches 165°C. However, a chain scission process takes place as the temperature

400

300 E

n,-

200

• S 3 +54

100

059 x 5 10

aSS

OL 0

, , 1 2 Ageing

l , i i , 3 & 5 6 7 t i m e at 1 4 0 ° C , d a y s

, 5

Fig. 8. Retained 100% modulus versus ageing time of IIR/ Keltan with various compositions: $3 (100:0), $4 (80:20), $8 (70:30), $9 (60:40) and S10 (50:50).

1000

200 x T.S.

oE •

~0

Mocl.

t

160

:E

600

120 0.~ :E

LIJ

-

400 -

80

20O -

4

40

0

0

x 0

i

0

40

I

I

I

I

I

80 120 Ageing t e m p . , ° C

I

160

1

I

200

Fig. 9. Tensile strength, elongation at break and 100% modulus of IIR/Keltan (70:30) versus ageing temperature for 48 h.

Thermal stability o f b u t y l / E P D M rubber blend vulcanizates

increases over 165°C. This result agrees with the data obtained for the tensile strength. From the above results it can be concluded that the IIR/Keltan-820 (70:30) blend vulcanizate shows outstanding resistance to thermal ageing; since it can retain 100% of its tensile strength value, even after the exposure to thermal ageing at 165°C for 48h.

4 CONCLUSIONS The following conclusions can be extracted from the observations and the data obtained. 1. Resin cured IIR is characterized by low maximum torque, longer cure and scorch times and comparatively having the same physicomechanical properties as those for sulphur cured IIR. 2. Resin cured IIR vulcanizate has superior performance to sulphur-cured vulcanizates, against thermal ageing at 90°C. 3. Of all EPDM types, Keltan-820 shows the best performance against thermal ageing of IIR/Keltan-820 vulcanizate at 120°C. 4. Of all IIR/Keltan-820 blend compositions investigated, 70:30 is superior because of good retension of the tensile strength and the elongation at break of the vulcanizates, beside the least increase of 100% modulus, upon the thermal ageing at 140°C for 7 days. 5. From severe thermal ageing test, indications are that the IIR/Keltan-820 (70:30) vulcanizate has an outstanding thermal resistance, since it retains 100% of its original tensile strength, after ageing at 165°C for 48h; likewise; that vulcanizate undergoes scission

477

after ageing at temperatures above 165°C. Therefore, the stated vulcanizate can be recommended for high temperature application.

REFERENCES 1. Jablonowski, T. L. and Faiman, D. T., J. Elastomers and Plastics, 1991, 23, 199. 2. Jablonowski, T. L., Mitchell, J. M. and Suryanarayanan, B., The use of EPDM in butyl inner tubes for improved performance. Presented at the 14th Rubber Conference of the India Rubber Manufacturers Research Association, January 1988. 3. Morton, M., Rubber Technology, 3rd edn. Van Nostrand Reinhold, New York, 1987, pp. 284-321. 4. Bhaumik, T. K., Gupta, B. R. and Bhowmick, A. K. J. Mater. Sci. 1987, 22, 4336-4342. 5. Bhaumik, T. K., Bhowmick, A. K. and Gupta, B. R., Plast. Rubber Process. Applic., 1987, 7, 43. 6. Bhaumik, T. K, Gupta, B. R. and Bhowmick, A. K., J. Adhesion, 1987, XX, 915. 7. Trexler, H. E. and Lee, M. C. H., Kautschuk & Gummi Kunstoffe Jahrgang, 1987, 40, 945. 8. Waiters, M. H. and Keyte, D. N., Trans. Inst. Rubbers Ind., 1962, 38, T 10. 9. Gardiner, J. B., Rubber Chem. Technol., 1970, 43, 370. 10. Kazhdan, M. V., Bakeyev, N. F. and Berestneva, Z. I., J. Polym. Sci., 1972, 38, 443. i 1. Corish, P. J., Rubber Chem. Technol., 1967, 40, 324. 12. Rehner Jr J. and Wei, P. F., Rubber Chem. Technol., 1969, 42, 985. 13. Hamed, G. R., Rubber Chem. Technol., 1982, 55, 151. 14. Yehia, A. A., Helaly, F. M. and E1-Sabbagh, S. H., Modeling Measurements and Control., 1992, 32, 53-64, AMSE Press. 15. Yehia, A. A., Abdel-Aal, N. S., Helaly, F. M. and E1Sabbagh, S. M., Proceedings of the 2nd Arab International Conference on Advances in Material Science & Engineering (Polymeric Materials), Cairo-Fayom, Egypt, Sep 6-9, 1993. 16. Yehia, A. A., Mansour, A. A. and Stoll, B., J. Thermal Analysis, 1997, 48, 1299. 17. ASTM Designation D 2084 76T, 1972. 18. ASTM Designation D 412 66T, 1967. 19. ASTM Designation D 573 55T, 1968.