(7) Gurgiolo, A. E., The Dow Chemical Co., Freeport, Texas, 1953-8, unpublished work. (8) Madge, E. W., Chem. Znd. London 42, 1806 (1962). (9) Natta, G., J . Polymer Sci. 16, 143 (1955). 78, 4787 (1956); (10) Price, C. C., Osgan, M., J . Am. Chem. SOC. J . Polymer SGi. 34, 153 (1959).
water and residual contaminants to nullify any gain made in purifying these monomers even when the iron catalyst is purified. Literature Cited
(11) Pruitt, M. E., Baggett, J. M. (to Dow Chemical Co.), U. S. Patent 2,706,181 (April 12, 1955) ; Zbid.: 2,706,189; Zbid., 2,811,491 (Oct. 29, 1957 . (12) Robinson, A. E., Jr. )to Hercules Powder Co.), U. S. Patent 3,026,270 (March 20, 1962) ; Zbid., 3,026,305. (13) Winspear, G. G., “The Vanderbilt Rubber Handbook,” pp. 257, 292, R. T. Vanderbilt Co., Inc., New York, 1958. (14 Ziegler, K., Holzkamp, E., Briel, H., Martin, H., ‘4ngew. dhem. 67, 541 (1955).
(1) Bailey, F. E.: Jr. (to Union Carbide Corp.), U. S. Patent 3,031,439 (April 24, 1962). (2) Bawn, C. E. H., Ledwith, A., Quart. Rev. London 16, 408-14 (1962). (3) Belg. Patent 579,074 (May 27, 1959). (4) Borkovec, A. J. (to Dow Chemical Co.), U.S. Patent 2,861,962 (Nov. 25, 1958); Ibid.: 2,873,258 (Feb. 10, 1959); J . erg. Chem. 23. 828 (19581. (5) Generil Tire‘ t3 Rubber Co., Brit. Patent 893,274 (April 4, 1962); U. S. Appl. April 8, 1957. (6) General Tire 8r Rubber Co. (by C. C . Price), Brit. Patent 893,275 (.April 4. 1962) ; Appl. March 20, 1958.
RECEIVED for review June 3, 1963 ACCEPTED July 11, 1963 Division of Rubber Chemistry, Toronto, Canada, May 1963.
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EVALUATION OF CROSS-LINKING COAGENTS IN ETHYLENE-PROPYLENE RUBBER L
.
P
, L
ENA S
, Enjay Laboratories, P.O.
Box 45, Linden, ,V. J .
Ethylene-propylene rubber (EPR), a saturated elastomer, is usually vulcanized by a peroxide-sulfur curing system. However, several disadvantages associated with this system-undesirable odor for some applications, narrow curing range, and poor strength obtained with mineral fillers-emphasize the need for other reactive chemicals as cross-linking coagents for EPR. Certain polyfunctional monomers such as ethylene dimethacrylate, and polyfunctional polymers such as 1,2-poIybutadiene were promising cross-linking coagents for EPR. When used in place of sulfur, they decrease peroxide requirements of moderately filled EPR compounds. They also impart higher states of cure, improve the cure cycle, and decrease odor. The coagents are much superior to sulfur in mineral filled EPR compounds where, in addition to increasing the cross-linking efficiency, they also improve the wetting of the filler particles b y the rubber. However, in highly loaded (carbon black and oil) EPR formulations, the superiority of the peroxide-coagent system i s mainly due tc the ability to replace sulfur and, consequently, to improve odor. THYLEXE-PROPYLESE RUBBER
(EPR) is a saturated polymer
E and, therefore, its vulcanization requires the use of special curing systems ( 7 ) . At present, the peroxide-sulfur system is widely used for the vulcanization of EPR. However, it has the disadvantages of narrow curing range and undesirable odor (for some applications) which results from the decomposition products of peroxides and the sulfurous by-products. Furthermore, this system is only marginally effective in the curing of mineral-filled EPR compounds. I n order to overcome the disadvantages associated with sulfur, various monofunctional and polyfunctional monomers as well as polyfunctional polymers were evaluated as cross-linking coagents for peroxide-cured EPR. The mechanism of these cross-linking coagents has been discussed by Robinson, Marra, and Amberg (2) who showed that polyfunctional unsaturated compounds add relatively fast to the rubber radical (generated by the peroxide) and thus eliminate to some degree the scission of this radical. The new radical is reactive and abstracts hydrogen from a saturated rubber molecule, thus propagating a chain reaction. This propagation does not consume peroxide and. therefore, can result in a decrease in peroxide requirements or an improvement in the cure cycle. The effectiveness of various cross-linking coagents in EPR 404 is described in this paper. EPR 404 is a copolymer of ethylene and propylene, containing 43 wt. % of ethylene and having a Mooney viscosity of 40 (8’ ML a t 212’ F.). 202
l&EC P R O D U C T RESEARCH A N D DEVELOPMENT
Cross-linking Coagents in Carbon Black-Filled EPR
Polyfunctional and monofunctional monomers and polyfunctional polymers were evaluated in moderately filled (60 SRF black) as well as in highly loaded EPR, 180 p.h.r. S R F black, and 40 p.h.r. oil (p.h.r. = parts per hundred rubber).
Polyfunctional Monomers Ethylene dimethacrylate Allyl methacryPolyethylene glycol dilate methacrylate SR-210 Divinyl benzene Trimethylol propane tri- Diallyl itaconate methacrylate
Vinyl toluene Vinyl pyridine
Triallyl cyanurate Diallyl phthalate
Monofunctional .LfonomerJ Cyclohexyl methacrylate Acrylic acid
Polyfunctional Polymers Buton 150, butadiene polymer where the ratio of 1,2 to 1,4 addition is about 3 to 1 Buton 100, copolymer of butadiene and styrene Polybutadiene R-15, approximately 30 % 1,2-polybutadiene, 70 % 1,4-polybutadiene Oxiron 2002, unsaturated epoxy resin Laminac 4192, unsaturated polyester resin Diene 35, cis-l,4-polybutadiene Pale crepe
Contrary to Robinson, Marra, and Amberg ( Z ) , a crosslinking coagent for EPR does not have to be a polyfunctional monomer. Certain monofunctional monomers are moderately effective in increasing the cross-linking of EPR. All the polyfunctional monomers were found to cross link the rubber. However, among the monofunctional monomers tested, only the aromatics (vinyl pyridine and vinyl toluene) were effective; these coagents were inferior to polyfunctional monomers. Of the monomers tested, ethylene dimethacrylate, divinyl benzene, diallyl itaconate, and triallyl cyanurate were the most effective cross-linking coagents for EPR. However, ethylene dimethacrylate and divinyl benzene appear to be the most practical coagents owing to their relatively low cost. Trimethylol propane trimethacrylate, despite its trifunctional structure was inferior to ethylene dimethacrylate owing, possibly, to its greater tendency to homopolymerization. The cross-linking efficiency of allylic monomers appreciably decreases with large amounts of black and oil. Triallyl cyanurate and diallyl itaconate are the most effective monomers in moderately filled EPR compounds. However, in highly loaded EPR, they are only as effective as ethylene dimethac-
Most of the compounds tested were effective replacements for sulfur in peroxide-cured EPR formulation, thus appreciably improving the odor of the vulcanizates by eliminating the undesirable odor of sulfurous by-products. The coagents tested are given on the preceding page. p-Quinone dioxime, a polyfunctional agent, was also studied. The chemical names and suppliers, where available, are given in Table I for the propriety materials used in this work.
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Cross-linking Monomers
The results obtained with cross-linking monomers in moderately and highly loaded EPR are given in Tables I1 and 111. respectively. The higher modulus and hardness and shorter elongation obtained with promising monomers show that these compounds increase the cross-linking efficiency obtained by a standard peroxide-sulfur curing system. However, tensile strengthswere somewhat lower than thoseofperoxide-sulfur cure. This is believed to be a characteristic of these cross-linking agents and was not unexpected since in many cases high modulus is associated with a someirhat low tensile strength.
Proprietary Materials Used in This Studya Description
Table 1. Trade .\'ame Buton 100 Buton 150
Supplier
A liquid resinous copolymer of butadiene and styrene A liquid resinous butadiene polymer where ratio of 1,2 to 1,4 addition is about 3 to 1 Buton 300 A concentrated oxygen containing form of Buton 100 Approximately 40% dicumyl peroxide supported on CaC03 Di-Cup 40C Diene 35 .4czs-l,4-polybutadiene elastomer An elastomer, which is a copolymer of ethylene and propylene EPR 404 Flexon 845 Paraffinic process oil Hi-Si1 233 Hydrated silica Laminac 4192 Unsaturated polyester resin 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (457, active) on an inert Luperco lOlXL filler Mistron Vapor Talc Magnesium silicate Oxiron 2002 Unsaturated epoxy resin Polybutadiene R-15 Approximately 3oy0 l,Z-polybutadiene, 70y0 1,4-polybutadiene SR-210 Polvethvlene dvcol dimethacrvlate S-890 Undisclosed geroxide Hydrated sodium silico aluminate Zeolex 23 Other materials comparable i n chemical composition and acticity should be equally as satisfactory.
Table II.
Enjay Chemical Co. Enjay Chemical Co. Enjay Chemical Co. Hercules Powder Co. Goodrich-Gulf Chemicals, Inc. Enjay Chemical Co. Humble Oil & Refining Co. Columbia-Southern Chem. Corp. American Cyanamid Co. \%'allace & Tiernan Co. Sierra Talc Co. FMC Corp. Sinclair Chemical Co. Sartomer Resins Inc. Hercules Powder Co. J. M. Huber Corp.
Effect of Cross-linking Monomers on Moderately Filled EPR Cures
Formulation: EPR 404-1 00, SRF black-60, Di-Cup 4OC-6.75, cross-linking monomer or sulfur, os shown
Sulfur Ethylene dimethacrylate Polyethylene glycol dimethacrylate' Trimethylol propane trimethacrylate Divinyl benzene, 55%," Diallyl itaconate Triallyl cyanurate Diallyl phthalate Allyl methacrylate Cyclohexyl methacrylate Vinyl toluene Vinyl pyridine $-Quinone dioxime Acrylic acid Zinc oxide Cure, 320' F./20' Hardness, Shore A 2007, modulus, p.s.i. 300y0 modulus, p.s.i. Tensile strength, p.s.i. Elongation, 7, Odor
a
...
0.32 . . . . . . . . . . . . 3
...
. .
,
. .
. .
...
...
... . .
,
. . . .
.. .. . .
...
... . . . ..
J
. . . . . . . . . . . ... .
.
3
. . . . . . . . . . . .
3 . . . . . . . . . ,.. . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . 3 . . . ... . . . . . . . . . . . . . . . 3 .
.
.
.
.
. . . . . . . . .
. . . . .
.
. .
... ... ...
... ...
...
...
.
.
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.
. .
. .
. .
. . . . . 3
...
.
. .
3
. . . . . . .
,
. .
.
.
.
. .
. .. .
.
. . . . .
. . . . . . . .
. . . . . . . . . . . . . 3 . . . . . . . . . . . 3 . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . 3 3 . . . . . . . . . . . . 5
61 63 410 750 850 1360 1550 2030 450 420 Poor Very poor
66 65 65 66 67 68 65 63 62 64 65 65 63 64 860 760 780 1100 1150 1750 710 710 320 620 730 600 590 630 1600 1470 1440 1460 1460 640 1290 1440 1150 1000 1250 1810 1810 1800 1800 1790 1750 1900 1940 1550 2000 1970 1820 1700 1800 310 340 360 280 270 200 350 370 630 420 400 430 530 430 Fair Fair Fair Fair Fair Fair Fair Fair Poor Fair Poor Fair Fair Fair to to to to poor poor poor poor 5 5 7 ~by m i g h t dioinyl benzene i n vinyl ethyl benzene and diethyl benzene.
VOL. 2
NO. 3
SEPTEMBER 1 9 6 3
203
Table 111.
Effect of Cross-linking Monomers on Highly loaded EPR Cures
Formulation: EPR 404-1 00, SRF black-1 80, Flexon 845 oil-40, Di-Cup 4OC-6.75, cross-linking monomer or sulfur, as shown
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Sulfur Ethylene dimethacrylate Polyethylene glycol dimethacrvlate Trimethylol propane trimethacrylate Divinyl benzene, 557,. Diallyl itaconate Triallyl cyanurate Diallyl phthalate Allyl methacrylate Vinyl toluene Acrylic acid Zinc oxide Cure, 320' F./20' Hardness, Shore A 200% modulus, p ' Tensile strength, p.s.i. Elongation, 70 Odor a
0 32
2 2' ,
,
. . . . ,
.
. .
. . . .
. . . . .
...
. .
. .
2
...
...
... . . . .
... ... ... ... ...
...
... . . . . . . ...
. . ...
,
.
, . .
. .
...
... ...
... ... ... ...
70 73 74 710 770 650 1090 1010 855 350 270 310 Very Fair Fair poor 55Tc by zoeight divinyl benzene i n vinyl ethyl benzene and diethyl benzene.
74 550 640 310 Fair
69 200 300 210 Poor
Table IV.
...
...
2
...
... ... . .
2
. . . .
. . ..
...
2
...
. .
... ...
. .
. . . .
73 750 895 270 Fair
71 710 935 280 Fair
...
. .
...
...
. .
...
...
...
. .
. . . .
. . . .
... . . ...
72 780 1000 270 Fair
. .
,
,
.
,
.
.
...
...
. .
...
...
. . ...
...
2 ... ...
2 ...
... 2
..
...
...
, . .
2 5
63 200 580 500 Fair
74 410 500 400 Fair
... ...
70
...
. .
...
70
...
...
230 300 Fair
250 300 Fair
,.. ...
Effect of Cross-linking Polymers on Moderately Filled EPR Cures
Formulation: EPR 404-1 00, SRF black-60, Di-Cup 4OC-6.75, cross-linking polymer or sulfur, as shown
Sulfur Buton 150 Buton 100 Oxiron 2002 Laminac 4192 Polybutadiene R-15 Diene 35 Pale crepe Cure, 320" F./20' Hardness, Shore A 200Y0 modulus, p.s.i. 3007, modulus, p.s.i. Tensile strength, p.s.i. Elongation, 7, Odor
...
0.32
...
. .
...
3 ...
... . . . .
. .
. .
...
61
410 850 1550 450 Poor
...
..
...
...
3
...
...
... ...
... 63 750 1360 2030 420 Very poor
... .
.
. .
3 ..
I
68 1200
66 1070
1800 260 Fair
1850 290 Fair
rylate. The decrease in efficiency is most apparent with diallyl phthalate and allyl methacrylate, both of which give good and very poor cures with moderately and highly loaded compounds, respectively. This phenomenon is attributed to the low polymerization reactivity of allyl groups, which is enhanced by the dilution effect of oil and black. On the other hand, large amounts of oil and black do not adversely affect the efficiency of polyfunctional monomers containing highly reactive vinyl groups. The poor performance of monofunctional monomers tested in highly loaded EPR was expected since most of them are marginally effective even in moderately filled compounds. Zinc oxide increased the cross-linking efficiency of acrylic acid in moderately filled EPR owing, probably, to the formation of zinc diacrylate, a polyfunctional monomer. This combination, however, did not effectively cross-link highly loaded EPR. Cross-Linking Polymers
Thermosetting resins and unsaturated elastomers were evaluated as cross-linking coagents for EPR. The results with 60 SRF black-filled EPR are given in Table IV. All of the thermosetting unsaturated resins tested were effective replacements for sulfur and aided in the cross-linking of EPR with a varying degree of efficiency. They gave higher modulus and hardness, and shorter elongation than those of 204
... . .
..
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
65 740 1510 1750 320 Fair
67 530 1150 1720 390 Fair
65 540 1170 1700 390 Fair
...
3
63 370 700 1700 560 Poor
64
Poor
peroxide-sulfur cure. However, the rubber polymers tested do not function as cross-linking coagents. I t appears that reactive olefinic groups are necessary for the cross-linking behavior of the polymers and that backbone unsaturation may not be sufficiently reactive to contribute to their cross-linking efficiency. This is further evidenced by comparing the results obtained with Diene 35, Polybutadiene R-15, and Buton 150 where the latter compound contains the highest amount of vinyl groups.
Table V.
Effect of Buton 150 on Highly loaded EPR Cures
Formulation: EPR 404-1 00, SRF black & oil-as shown, Di-Cup 4OC-6.75, Buton 150 or sulfur, as shown
SRF Black Flexon 845 oil Sulfur Buton 150
130 130 20 20 0.32 . . . ... 5
180 180 180 40 40 40 0.32 . . . . . . ... 3 9
Cure, 320" F./20' Hardness, Shore A 2007, modulus, p.s.i. 300%modulus, p.s.i. Tensile stren th, p.s.i. /o Elongation, 5
70 1020 1530 1670 350
70 1200 1600 250
1090
Odor
Very poor
Fair
Very poor
..
,
70 710 930
350
72 390 440 450 330
73 740 1000 1000 300
Fair
Fair
A polybutadiene resin having its unsaturation present primarily as vinyl groups (Buton 150) was the most efficient cross-linking polymer followed by Buton 100 and Oxiron 2002. The somewhat poor performance of polyester resin indicates the low activity of fumarate unsaturation in the cross-linking reaction. Buton 150, a viscous resin, is the cheapest effective crosslinking coagent for 60 SRF black-filled EPR. It is convenient to handle because of its lack of toxicity, very low vapor pressure, lack of odor, and it can be easily incorporated into the rubber. In highly loaded EPR formulations, the cross-linking effi-
- 2000
. I
7
m
a w-
2
I/
z
/ s s - C K
+ w
6 . 7 5 GI-CUP 4 0 C
E; 1400
BUTON 1 5 0 ETHYLENE GIMETHACRYLATE
m
3 J 3
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g
I
I
iaoo
1000
0
-- - - - -E L O N G A T I O N
i
hlODULUS' CURE' 33O0F/10'
c
:
200
-___
__
*-----+-
k===---L
1
-----------.
x
I
- - - - - - - a
L
I
1
5
3
I 7
1 1 9
I
10
CONCENTRATION, PHR
Figure 1. Effect of cross-linking coagent concentration on the physicals of EPR cures
ciency of polymers is appreciably decreased. However, they can still be used in place of sulfur and, consequently, they reduce odor (Table V). In highly loaded EPR, the crosslinking polymers are inferior to monomers in that large amounts of the former are required to obtain peroxide cures competitive with those resulting from a peroxide-sulfur curing system. Concentration of Cross-linking Coagents
The effect of cross-linking coagent concentration on EPR cures was investigated with Buton 150 and ethylene dimethacrylate, which were the most promising coagents. Table VI shows that only 1 to 2 p.h.r. of ethylene dimethacrylate can be used in place of sulfur in both moderately and highly loaded EPR formulations. One p.h.r. Buton 150 can also be used instead of sulfur in moderately filled EPR. However, about 9 p.h.r. of Buton 150 are required in highly loaded EPR compounds. Figure 1 shows graphically the effect of cross-linking coagent concentration o n the modulus of moderately filled EPR cures. At 1 p.h.r. concentration level, ethylene dimethacrylate is more effective than Buton 150. However. a t greater concentrations, Buton 150 becomes much superior to ethylene dimethacrylate. As the concentration of Buton 150 is increased from 1 to 10 p.h.r., the modulus continuously increases resulting in very high states of cure. O n the other hand, the modulus obtained with ethylene dimethacrylate does not appreciably change with concentration, probably because of the homopolymerization of the highly reactive cross-linking monomer. Peroxide Requirements
Cross-linking coagents, as expected, decreased the peroxide requirement, with several peroxides, of moderately filled EPR formulations (Table VII). Ethylene dimethacrylate was somewhat less efficient in decreasing the peroxide requirements of 60 p.h.r. S R F black-filled EPR (Figure 2). The resulting ?SO0
1600 -
1400
-
v; 1000 3 3 J 0
5
0'
800-
N 0
A
S U L F U R : 0 . 3 2 PHR
600 -
E T H Y L E K E DIF.1ETHACRYLATE:
CURE
320'F
30'
400 -
7 .BUTON 150 5 PHR * B U T O N 150 1 0 PHR
200 200
CURE TlAlE
-
1 03
4
=
20 hllN.
I I 5
I
I
6
6.75
1 0
2
9
0
I 300
DI-CUP 4 0 C , PHR
Figure 2. Effect of peroxide concentration on moderately filled EPR cures
310 CURE TEMPERATURE, ' F
320
Figure 3. Effect of temperature on the modulus of Di-Cup-Buton 150 and Di-Cup-sulfur cures VOL 2
NO. 3
SEPTEMBER 1943
205
Table VI.
Effective Cross-linking Coagent Concentrations at Various loading levels
Formulation: EPR 404-1 00, SRF black and oil-as shown, Di-Cup 40C-6.75, cross-linking coagent, as shown
SRF black Flexon 845 oil Sulfur Ethylene dimethacrylate Buton 150 Cure, 320' F./20' Hardness, Shore A 200y0 modulus, p.s.i. 30OYp modulus. p.s.i. Tensile strength, p.s.i. Elongation, Table VII.
60
60
...
60
0.32
,
...
.. 1
...
...
63 750 1360 2030 420
65 830 1620 1800 330
130 20 0.32
... ... ...
...
,
130 20
...
,.
... ...
...
70 1020 1530 1670 350
73 1050 ... 1500 290
1
66 720 1500 1670 320
130 20
...
1
5 70 1200 ...
1600 250
180 40 0.32 ...
180 40
180 40
180 40
.,.
...
...
2 ...
...
73 770
73 740 1000 1000 300
1
, . .
...
70 710 930 1090 350
73 640 860 860 300
,
.
1010 270
9
Cross-linking Coagents Decrease Peroxide Requirements of Moderately Filled EPR Cures
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Formulation: EPR 404-1 00, SRF black-60, peroxide and cross-linking coagent, as shown
Luperco 1OlXL S-890 Di-Cup 40C Sulfur Buton 150 Ethylene dimethacrylate Cure, 320' F./30' Hardness, Shore A 3007, modulus, p.s.i.
...
...
58 1280
60 1260
69 2100
Tensile strength, p.s.i. Elongation, 70 Odor
1995 460 Poor
1680 375 Good
2200 310 Fair
7
... 3
3 ...
... ...
5
Formulation: EPR 404-1 00, SRF black-1 80, Flexon 845 oil-40, peroxide and cross-linking coagent, as shown
&
... ...
6.75 0.32
70 710 930 1090 350
5 ..,
5
...
...
... 2
68 440 650 750 400
72 530 680 740 360
9
cures possess a very low odor since, in addition to the replacement of sulfur, the amount of undesirable peroxide decomposition products is kept to a low level. These cures may also be cheaper than those obtained with a peroxide-sulfur curing system. The peroxide requirements of highly loaded EPR, however, could not be decreased (Table V I I I ) . Cure Cycle
Cross-linking coagents could improve the cure cycle of EPR compounds by supressing undesirable reactions during the curing process-such as scission. Very likely they enter into the cross-linking reaction via polymerization. This improves the utilization of the free radicals thus making available more cross links for the rubber molecules. The over-all improved efficiency of the system permits a decrease of the curing temperature and/or time. Table IX shows that promising cross-linking coagents can appreciably improve the cure cycle of 60 SRF-filled EPR. Formulations incorporating dicumyl peroxide as curing agent can be cured even a t 290' F. for a period of only 30 minutes by the use of diallyl itaconate as a coagent. High temperature curatives such as di-tert-butyl peroxide can be used a t moderate temperatures by the use of cross-linking coagents. The di-tert206
t . .
0.32 ... ...
...
Table VIII. Cross-linking Coagents Cannot Decrease Peroxide Requirements of Highly loaded EPR Cures
Di-Cup 40C Sulfur Buton 150 Ethylene dimethacrylate Cure, 320" F./20' Hardness, Shore A 2 0 0 5 modulus, p.s.i. 300% modulus, p.s.i. Tensile stren th, p.s.i. Elongation,
2
...
...
0.32
...
...
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
...
5
...
...
...
...
, . .
6.75 0.32 ...
...
4
... 5
5
...
...
5 70 1370 (200%) 2000 260 Very good
65 1750
66 1640
68 1650
2050 360 Very poor
1900 320 Good
1950 360 Fair
butyl peroxide-ethylene dimethacrylate curing system results in almost odorless cures. However, the volatility of this peroxide limits its application. Figure 3 graphically shoivs that by the use of Buton 150, cures with acceptable properties can even be obtained a t 300' F., whereas, similar sulfur cures could be obtained only at 317' F. EPR-peroxide-Buton 150 formulations can also appreciably decrease the cure time a t constant temperature. Good states of cure can be obtained in 7 minutes a t 320' F. (Figure 4). Effect of Sulfur in EPR-PeroxideCross-linking Coagent Cures
Sulfur increases the tensile strength and per cent elongation and decreases the modulus of EPR-peroxide-cross-linking coagent cures. The gain in tensile strength, however, cannot compensate for the losses in modulus. The deleterious effect of sulfur is somewhat greater in peroxide-Buton 150 cures than peroxide-ethylene dimethacrylate (Table X). The behavior of sulfur is attributed to its inhibiting effect on vinyl polymerization of unsaturated compounds and to the low reactivity of Buton 150 at moderate temperatures. Cross-linking Coagents in Mineral-Filled EPR
Sulfur is not an effective coagent in mineral-filled EPR formulations. Even in its absence, silica-filled EPR stocks result in peroxide cures with only slightly lower physicals. Cross-linking coagents were much more effective than sulfur. The EPR-peroxide-coagent cures possess, in addition to higher modulus, higher tensile strength, as well as lower odor than those of peroxide-sulfur. Coagents also reduce the peroxide requirements. Table XI shows that epoxidized polyolefins and ethylene dimethacrylate are superior to unmodified polyolefins in cross-linking EPR. It appears that oxygenated cross-linking coagents improve the wetting of mineral fillers. The effectiveness of vinyl toluene (a low cost monofunctional monomer) in giving very low odor and low cost in silica filled
1800
lboot ~
14001
1200
A
60 S R F B L A C K 6 . 7 5 D!-CUP 40C SULFUR 0 . 3 2 PHR B U T O N 1 5 0 3 PHR B U T O N 1 5 0 5 PHR B U T O N 1 5 0 1 0 PHR C U R E TEh0PE:RATURE
= 320°F
c
I
I
z
200
G 2
c 5
CURE T E M P E R A T U R E I 10 CURE TIR'E,
L
a
P
3 0
2 N
-1
15
21IN
I
I
I
8 0 0 t
1'400
i
330°F
=
CURE TlIuIE
c
=
5 I.lIN. i
1000
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I
400 C 600
200
60 I R F B L A C K 6 7 5 D l - C U P 40C
1 200
L+
00
1 L-
320
I
10 CURE TIME, M I N .
115
B U T O N 1 5 0 . 3 PHR
-
ETHYLENE DIMETHA C R Y L A T E . 3 PHR I 330
I
340 CURE T E M P E R A T U R E ,
0-
Figure 4. Cure rate of Di-Cup-Buton 150 and DiCup-sulfur cures
Table IX.
I
1 360
350 'F
figure 5. Effect of cure temperature and time on the modulus of Di-Cup-Buton 1 50 and Di-Cup-ethylene dimethacrylate cures
Effect of Cross-linking Coagents on the Cure Cycle of EPR Cures
Formulation: EPR 404-1 00, SRF black-60, peroxide and cross-linking coagent, as shown
Di-Cup 40C Luperco l 0 l X L Di-tert-butyl peroxide Sulfur Diallyl itaconate Buton I50 Ethylene dimethacrylate Cure Cycle, F./Min. Hardness, Shore A 300YGmodulus, p.s.i. Tensile strength, p.s.i. Elongation, yG Odor
Table X.
... ...
6.75
6.75
...
...
0.32
... ...
... 320115 63 1180 2000 515 Very poor
... 3
... ...
290130 64 1120 1600 400 Fair
, . .
7 ... 0.32 ... ...
...
... 7 . .
...
2.92
...
...
2.92 ...
...
0 64 ...
...
5 ...
... ...
... 3
320/30
300/30
58
67
1280 1995 460 Poor
1500 1800 360 Fair
. .
320/60 58 1060 2140 570 Poor
... 320/30 62 1330 1830 400 Very good
Effect of Sulfur on EPR Peroxide-Cross-linking Coagent Cures
Formulation: EPR 404-1 00, Di-Cup 4OC-6.75, SRF black, oil and cross-linking coagent, as shown
SRF black Flexon 845 oil Ethylene dimethacrylate Buton 150 Sulfur Cure, 320' F./20' Hardness, Shore X 200YGmodulus, p.s.i. 300y0 modulus, p.s.i. Tensile strength, p.s.i. Elongation, yo
60
...
3
60 ...
3
... ...
...
66 860 1600 1810 310
65 720 1240 2000
0.32
460
180 40 2 ...
...
73 770 ... 1010 270
180 40 2 ... 0.32 70 620 850 1020 370
VOL. 2
180 40 ... 7
... 73 740 1000 1000 300
NO. 3
SEPTEMBER
180 40 , . .
9 0.32 67 560 790 980 420
1963
207
Effect of Cross-linking Coagents on Silica-Filled EPR Cures
Table XI.
Formulation: EPR 404-1 00, Hi-Si1 233-60, zinc oxide-5, cross-linking coagent, as shown
...
Sulfur Buton 100 Buton 300 (100% solids) Buton 150 Epoxidized Buton 150 Oxiron 2002 Ethylene dimethacrylate Cure, 320’ F./20’ Hardness. . . Shore A 3007? modulus, p.s.i. Tensile strength, p.s.i. Elongation, yo Odor
...
... ... ...
... ... ... ...
... ...
...
...
...
73 350 1980 890 Poor Table XII.
... 3
0.32
... ...
...
74 580 1930 765 Fair
...
...
...
...
...
3 ...
... 3
... ...
...
3
...
...
...
...
...
...
...
77 1000 2060 570 Fair
78 690 2000 750 Fair
78 1280 2370 465 Fair
74 1330 2370 450 Fair
...
... . .
...
... ...
... ... ...
...
...
73 450 2050 900 Very poor
...
3
... ...
3 83
1-
950 2100 575 Fair
Effect of Cross-linking Coagents on Mineral-Filled EPR Cures
Downloaded by CENTRAL MICHIGAN UNIV on September 13, 2015 | http://pubs.acs.org Publication Date: September 1, 1963 | doi: 10.1021/i360007a008
Formulation: EPR 404-1 00, mineral flller, as shown, zinc oxide-5, Di-Cup 4OC-6.75, cross-linking coagent, as shown
Hi-Si1 233 Hard clay Zeolex 23 Mistron vapor talc Sulfur Vinyl toluene Oxiron 2002 Ethylene dimethacrylate $-Quinone dioxime Vinyl pyridine Cure, 320’ F./20’ Hardness. Shore A 300% modulus, p.s.i. Tensile strength, p.s.i. Elongation, yo Odor a
Di-Cup 40C, 4p.h.r.
60 ...
...
... 0.32
...
... ...
...
... 100
...
100 ... ... 0.32
...
...
60° ... ...
...
5
,..
... ...
... ...
73 450
75 370 1830 790 Good
2050 900 Very poor Failed to cure.
... ... , . .
...
...
...
... 3
... ...
... 100 ... ... ... ... ... ...
...
...
... ... 100
0.32
...
, . .
...
...
...
...
2
68 260
67 680
77 590
510 1100+ Poor
1200 745 Very poor
770 510 Very poor
...
b
c
b
c
b b
c c
..,
Fair
...
...
...
100
... ...
...
...
... ...
3
...
...
... 100 ...
... ,..
100 0.32
... ,..
...
100 ...
, . .
... ...
...
... ...
...
...
81 920 (200%) 1130 260 Fair
55 240
610
...
3
... , . .
...
400 ll00f Very poor
3
... 70
1540 730 Fair
Undercured.
EPR cures with a reduced amount of peroxide, is presented in Table XII. The same table also shows that EPR compounds filled with a n acidic filler, such as hard clay, can successfully be cured in the presence of coagents containing nitrogen. Acidic fillers consume the peroxide curative by promoting its ionic decomposition. However, coagents, such asp-quinone dioxime and especially vinyl pyridine, in addition to improving cross-linking of the rubber in the presence of peroxide, increase the p H of the medium and, therefore, give good cures by decreasing the acid catalyzed decomposition of the peroxide. Cross-linking coagents also were very effective in a sodium silico aluminate and a platy talc-filled EPR compound. The superiority of coagents over sulfur was more pronounced with the platy talc, where the tensile strength obtained with a peroxide-sulfur system was considerably increased by replacing sulfur with ethylene dimethacrylate.
reactive. As the curing time or temperature is increased, it is likely that some of the ethylene dimethacrylate homopolymerizes (Figure 5). The tendency to homopolymerization and low vinyl concentration of ethylene dimethacrylate overcomes its advantageous high reactivity. When EPR is diluted appreciably with carbon black and oil, the concentration and, therefore, the rate of coagent addition to the rubber radical (generated by the peroxide) is decreased. Consequently, some peroxide is consumed by the scission of the rubber radical and its requirements cannot be decreased with reasonable amounts of cross-linking coagents. Buton 150 is affected more than the ethylene dimethacrylate because of its already low reactivity towards the mentioned reaction. The superiority of ethylene dimethacrylate over Buton 150 in mineral-filled EPR formulations is attributed to its polarity and, therefore, to its better compatibility with mineral fillers.
Buton 150 vs. Ethylene Dirnethacrylate
literature Cited
Buton 150, despite its low reactivity a t moderate temperatures, is superior to ethylene dimethacrylate in 60 SRF loaded EPR probably owing to its higher unsaturation and its very low rate of homopolymerization. In the early stage of the curing process, however, the performance of ethylene dimethacrylate is as good as, or better than, that ofButon 150 since it is highly
(1) Natta, G., Bruzzone, M., Rubber Plastic Age 42, 53 (1961). (2) Robinson, A. E., Marra, J. V., Amberg, L. O., IND. ENC. CHEM.PROD.RES.DEVELOP. 1, 78 (1962).
208
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
RECEIVED for review June 17, 1963 ACCEPTEDJuly 15, 1963 Division of Rubber Chemistry, Toronto, Canada, May 1963.
