I
P. 0.TAWNEY, J. R.
LITTLE, and PAUL VIOHL
Research Center, United States Rubber Co., Wayne, N. J.
Another High Temperature Elastomer
Vulcanization of Butyl Rubber with PhenolFormaldehyde Derivatives Vulcanizates of butyl rubber cross-linked with phenol-formaldehyde derivatives are finding uses in high temperature applications, such as tire curing bags which were formerly cross-linked with sulfur D u R r i w the vulcanization of natural and Butyl rubber with sulfur two competing reactions occur-cross linking or vulcanization and reversion or devulcanization. These reactions have been described for Butyl rubber by Zapp and Ford (6). The present authors, as well as Zapp and Ford and others, have long recognized the need for a more stable cross link in vulcanized Butyl rubber. This study deals with formation of extremely stable cross links in Butyl rubber by vulcanizing with 2,G-dimethylol-4-hydrocarbylphenols or condensation polymers derived therefrom (4). Vulcanization of natural rubber with palkylphenol-formaldehyde condensation products has been reported (7), and others (2, 5 ) studied these cures extensively, working chiefly with monomeric dimethylol-palkylphenols. Few data were shown on the effects of heat or oxygen, and there is little evidence to indicate commercial use. Curing Agents and Vulcanization
Condensation polymers of 2,G-dimethylol 4 hydrocarbyl phenols can best be presented by I where R is
- -
-
OH
r
an alkyl or hydrocarbyl group and n varies from 0 to 5 or 6. The essential feature is that the structure is bifunctional with respect to o-methylolphenol groups. Much of the detailed structure is not known. Undoubtedly, this representation is oversimplified. Important structural features of the cross links in Butyl rubber vulcanized with condensation polymers such as I can be represented by 11.
CH? CHa
/-\
R ;Vulcanization rates and thermal stabilities of more or less typical sulfur and phenolic derivative cures of Butyl rubber were studied for compositions S1 and R1 (Table I). Composition S1 cured to optimum or maximum stress a t 20OY0 elongation in approximately 1 hour a t 322' F., and continued heating caused rapid devulcanization or reversion. Composition R1 cured with Super Beckacite 1001 was slow curing, but the extreme thermal stability of the vulcanizate is exemplified by absence of reversion after 16 hours a t 322' F. The extreme stability of the phenolic vulcanizate is further shown in Table 11. Tensile, and particularly stress at 20070 elongation, indicate rapid reversion in the sulfur vulcanizate with no reversion in phenolic vulcanizates even after 20 days. OH
1
R hydrate, zinc chloride, and tin( 11) chloride dihydrate. For exploratory work on catalysis, tin( 11) chloride
$ R-7- 4
I,
;
6
p ' $00 g 8
3 10 TIME IN MIN. AT 2 5 0 .
13
LO
F.
Figure 1. Effect of tin(l1) chloride dihydrate on scorch rate of Butyl rubber cured with phenolic condensation polymer Compounds R6 and R 7 would b e considered unsafe for most factory operations
OH
Rate and Catalysis
The extreme thermal stability imparted to Butyl rubber by vulcanizing with phenolic condensation polymers led to the search for catalysts or vulcanization accelerators. Peterson and Batts ( 3 ) showed that vulcanization of Butyl rubber by phenolic condensation polymers is strongly catalyzed by metallic halides, such as iron(II1) chloride hexa-
PARTS OF PHENOLIC
CONDENSATION POLYMER
Figure 2. Effect of varying concentration of phenolic condensation polymer on cures of Butyl 2 15 Ultimate state of cure was higher in the cat. alyzed formulation
VOL. 51, NO. 8
AUGUST 1959
937
Table I.
Typical Sulfur and Phenolic Derivative Cures of Butyl Rubber Parts s1 R1 52 R2 R3
Enjay Butyl 215 HAF black Hydrocarbon plasticizing oil Zinc oxide Stearic acid MBTS MBT Tetramethylthiuram disulfide Sulfur Super Beckacite lOOla 2,5-Dimethylol-4-tert-butylphenol Amberol ST 137b Vulcanization temp., ' F. Vulcanization time, hr.
100 60
100 50 5
100 50 5
...
...
5
5 1
... ...
0.5
0.5
...
*..
...
0.5 1.5 2
... ...
... ... 6 ...
322 0.2516
322 0.2516
1.25 2
... ... ...
...
...
307 1
100 60
100 60
.. .. .. ..
.. * . .. .. ..
..
.. ..
.. 8 .. 330 2
..
..
..
..
8 330 2
a Reichhold Chemicals, Inc., believed to be a condensation polymer of p-lert-butylphenol and formaldehyde. Rohm & Haas Co., believed t o be condensation polymer of p-octyiphenol
The role of polymer unsaturation in vulcanization with phenolic condensation polymerswas investigated in butyl rubbers 035, 150, 215 and 325 which differed from one another only in increasing order of percentage unsaturation. The following general formulation was used : Po1ymer HAF black Stearic acid Plasticizing oil Amberol ST-127 SnCl?.2H20
Part100 50 2 7 Variable (2-12)
Ultimate state of cure was d e p p d e n t on polymer unsaturation, and for Butyl 035, excess curing agent dppeaied ro have a plasticizing effect.
and formaldehyde.
Air Aging of Vulcanizates
dihydrate was selected as it can be adapted to conventional rubber practices. I t is a stable, nonhygroscopic hydrate, melts a t 37' C., and loses water of hydration readily. Vulcanization in the absence of metallic halide was slow, requiring 4 hours at 322O F. for approximately 80% of a full cure.
__ Enjay Butyl 215 HAF black Plasticizing oil Super Beckacite 1001 SnCla .2H B0
both catalyzed and uncatalyzed samples, vulcanization state reached a maximum at about 12 parts of phenolic condensation polymer per 100 parts of Butyl 215 (Figure 2). Again, however, the ultimate state of cure in the catal>-zed formulation was considerably higher than in the uncatalyzed. For the latter case Parts
R4
R5
R6
K7
100 50
100 50 5 6 1
100 50 5 6 2
100 50 5 6 4
5 6
...
Addition of tin(I1) chloride dihydrate, hoivever, in amounts of from 1 to 4 parts per 100 Butyl greatly accelerated cure. Not only does a metallic halide increase vulcanization rate but it also increases over-all state of cure obtainable. The amount of catalyst must be chosen judiciously, for in achieving fast rates of cure with metallic halides scorch life is decreased (Figure 1). Because of the dual role that the metallic halide plays in vulcanization, the effect of the catalyst was studied in compositions R8 and R9 that vary in concentration of curing agent. All compounds were vulcanized for 8 hours a t 322' F., as vulcanization would be essentially complete in that time. I n
118 100 50 5 2-20
...
Table II.
Effect of Aging in Steam at
328" F. Phenolic vulcanizates showed no reversion even a f t e r 20 days
Vulcanizate
R2b
Days Aged
0
0
5 10 15 20
R3C 16
10 15 20
DAYS AGEDAT INDICATED TEMP
Figure 3. Aging of Butyl rubber in circulating air The ~ u l f u r vulcanirate wos severely deterior a t e d a f t e r 4 days
938
0
5
~
8
5 2-20 2
Formula I1 indicates that chemical unsaturation in Butyl rubber is consumed or saturated during vulcanization. Figure 2 substantiates this to some extent.
5
4
100 50 5 8 2
Role of Polymer Unsaturation
10 15 20
2
R10
100 50
it must be concluded that some phenolic resin molecules are combined Mith Butyl rubber hydrocarbon in some way that does not involve cross linking.
S2"
I
R9
Tensile P.S.I.
Stress at 20070
2230 600 540 430 370
1180 200 170 120 140
1500 2080 2120 2180 1930
470 1140 1100 1130 1110
1970 2140 2110 2200 1940
690 1040 1030 1030 1030
Elongation
a Sulfur vulcanizate Vulcanized with 2,6-d1methylol-4-fert-butylphenol Vulcanized with Ainberol ST 137
INDUSTRIAL AND ENGINEERING CHEMISTRY
Butyl rubber vulcanized with phenolic condensation polymers showed extreme thermal stability both on long time curing a t high temperatures and on aging at 328' F. in steam. Tremendously improved resistance to aging in circulating air is also imparted to Butyl rubber by curing Lvith phenolic condensation polymers. The aging resistance of R8, vulcanized for 1 hour at 322' F., is better at 400' F. than the aging resistance of S1 at 300' F. (Figure 3) Composition R8 retained approximately 70% of its original tensile strength aftcr aging for 1 6 days a t 300' F. in circulating air. S1, the sulfur vulcanizate: was severely deteriorated at the cnd of 4 days. By vulcanizing Butyl rubber with phenolic condensation polymers resistance to air aging was improved by 100" F. over the range from 300' to 400' F. Acknowledgment
The authors acknowledge the technical contributions of A . N. Iknayan, L. C . Peterson, and H. .J. Batts. J. J. Fleming and A. J. Saulino assisted in the pioneering applications work. P. F. Gunberg and G. H. Brice made technical contributions and assisted in laboratory work. Literature Cited (1 1 Bitterich, others, Soci6t6 Francgise Beckacite A.R.L., French Patent 804,522 (Oct. 27, 1936). (2) Meer, 5.van der, Rec. trac. chirn. 63, 147
(1944). (3) Peterson, L. C., Batts, €3. J.? U. S. Patent 2,726,224 (Dec. 6;1955). (4) Tawnep, P. O., Little, J. R., Zbid., 2,701,895 (Feb. 15, 1955). (5) Wildschut, A. J.,Rec. tra7,. c h i n . 61, 898 119421.
(6)' Zapp, R. L., Fcrd, F. P.. J . Poiyrnw Scz. 9, 97 (1952).
RECEIVED for review June 2n, 1958 ACCEPTED April '3, 1959 Division of Rubber Chemistry, ACS, Cincinnati, Ohio, May 1958. Contribution No. 174 from the Research Center, United States Rubber (To., Wayne, N. J.
