I
W. K. TAFTl, JUNE DUKE', and DOROTHY PREM' Government laboratories, Akron, Ohio
Oil-Masterbatched Butadiene-Styrene Polymers Influence o f V a r i o u s Antioxidants o n Polymer B r e a k d o w n
v-A
Antioxidants 0-conidendrol and 2246 were superior antioxidants from the point
of
stability.
view
of ultimate polymer
The former i s suggested as
being worthy of more extended study for overcoming the storage instability o f oil-polymer masterbatches, and the latter for preventing gelation with less reactive oils or for slowing the rate of breakdown with the reactive oils.
THE
TYPE and amount of antioxidant used in oil-free base polymers and in oil-polymer masterbatches (4) affect the breakdown and recombination or gelation characteristics of heat-aged polymers. From results of this earlier work it appeared that the different antioxidants permitted scission to occur at different points in the polymer chain, thus affecting the molecular weight distribution. Later work with 50 Mooney viscosity oil-free polymers containing eight different antioxidants (7) again revealed the considerable differences in the heat breakdown and gelation properties of these polymers. The physical properties of vulcanizates of premilled or pre-Banbury treated polymers were also affected by the type of antioxidant used. Other work (7) indicated that the heat stability of vulcanizates depended somewhat on the antioxidants used in manufacture of cold rubber. The change in dilute solution viscosity, DSV, of polymers during heat aging a t 140" F. has been shown (3, 5 ) by the equation 1 Present address, Olin Mathieson Chemical Corp., P. 0. Box 480, Niagara Falls, N. Y .
Be-o(t-2)
Procedure
where V = corrected dilute solution viscosity (DSV) a t time ( t ) A B = corrected DSV of the original polymer A = limiting or lowest DSV that is reached B = constant indicative of the extent of change in DSV a = constant associated with the rate of breakdown x = the induction period in days prior to the start of breakdown
+
As the constants in this equation were influenced by the type of oil, as well as the antioxidant, this work is a study of the combined effect of the type of oil with the same antioxidants used in earlier work (7).
Antioxidants Used Antioxidant PBNA BLE
P-Conidendrol Stalite
Polygard Wing-Stay S Santovar 0
2246
Chemical Type Phenyl-2naphthylamine Acetone diphenyl amine reaction product Phenolic Mixed alkylated diphenylamines Trisnonyl phenyl phosphite Mixed alkylated pheno1s 2,5-Di-tertbutyl hydroquinone 2,2'-Methylenebis (4methyl-6tert-butyl phenol)
-
Use Staining Staining
Nonstaining Nonstaining
Nonstaining Nonstaining Nonstaining
Nonstaining
T h e latex was a nonaerated high Mooney viscosity, butadiene-styrene copolymer (iron-pyrophosphate formula including potassium soap of rosin acid). T h e latex was first divided into eight parts, and a different antioxidant (1% dry rubber basis) was added to each portion. Each of the eight latex samples was then further divided into 4 parts, one portion of which was coagulated as the oil-free base polymer. Oil masterbatches were then prepared from the other portions using 37.5 parts of Circosol-2XH (naphthenic), Sundex-53 (aromatic), or Dutrex 20 (highly aromatic). Salt-acid coagulations were made in all cases. All samples were dried in a vacuum oven a t room temperature and were then heat-aged a t 140' F. for 30 days. Samples were withdrawn a t intervals for determination of gel content, dilute solution viscosity (DSV), and acetone extractables. The DSV and gel contents were reduced to a polymer basis (referred to as corrected basis) by correcting for the acetone extractable material.
Results and Discussion Constants for the breakdown equation ( 5 ) , calculated from the DSV data for each sample, are given in Table I. Breakdown curves for the base polymers and for masterbatches containing Circosol-2XH, Sundex-53, and Dutrex 20 are shown in Figures 1, 2, 3, and 4, respectively. The curves shown were derived from the appropriate equation-the actual data (corrected DSV) are represented by the symbols. The portion of the curves shown by the full line represent the period of polymer breakdown; the dotted lines represent the continuation of the derived curve, but indicate VOL. 49, NO. 8
AUGUST 1957
1293
40
381
II
B-CONIDENDROL
I 2 3
14.
12.
5 6
IO.
BLE
t3
POLYGkRO STALITE 2246
-7
0
08.
--
~
o i
o
PBNA
4
~
[
~
~
i i 4 5 6
+
~ AX ~
~
y
O
s
a b io
15
20
DAYS
30
25
AGED AT 140.F.
that gelation occurred during this period. Gel content of the various samples and the increase in gei content with time of heating are shown in Figure 5. For samples not included i n Figure 5, no gel was formed. Of all the samplcs tested, rhe base polymer and oil masterbatches containing P-conidendrol had the longest induction periods and generally broke down the least and a t the lowest rate. In addition, the Dutrex 20 masterbatch containing antioxidant 2246 showed a remarkably low rate of breakdown. 'The base polymers containing /3-conidendrol, phenyl-r-naphthylamine IPBS'A), and 2,2'-merhylenebis (4-methyl-6-tertbutyl phenol) (2246) did not gel during the 30-day heating period. From the standpoint of the sta hility of
Breakdown of oil-free base polymers
Figure 1.
Table 1.
Parameters for Equation
(Nonaerated latex about 4 months old) Base Polymer B a 0.05 0.46
6-Conidendrol
A 3.10
Polygard
2.90
St alit e
3.00
BLE PBNA Wing-Stay S 2246 Santovar 0
Circosol-PXH -__ X
A
B
a
A
X
9
2.80
0.90
0.08
6
2.20
0.67
0.2
4
2.10
1.60
0.20
3.5
0.50
0.2
2.5
2.39
1.27
0.3
1
1.50 1.40
3.00
0.53
0.15
3.05
0.65
0.15
1
3.20
0.36
0.10
2.70
0.83
0.10
1.60
1.93
0.7
4 4 1.5
1.28
2.41
2.50
1.03
0.1
0.5
2.00
1.58
0.8
0.5
1.70 2.10
Sundex-53 a B 0.07 1.52
Dutrex 20 B a
-__
_ _ I
z
-4
~-
~
2'
6.5
1.10
2.58
0.25
5
2.18
0.25
3.5
0.96
2.68
9.4
2.5
2.26
1
1.18
2.56
1,4
0
0
1.16
2.30
0,s
0.8
I.
1.07
2.48
0.4
0.5
2.31
3
1.40 1.70
1.84
0.6 0.07 0.1
0.4
0.9
1.10
2.55
0.6
2.5
1.08
2.66
0.8
0.9
2.02
0.08
0
1.40
2.23
0.08
0
1.00
2.71
0.085
0
1.53
0.4
0
1.30
2.33
0.3
0
0.96
2.75
0.35
0
5 v
STALITE
4.0
3.8 5.6 3.4
3.2
3.0 2.8 2.8
2.4
2.2 2.0 1.8 1.6
I. 4 1.2
1
0.8 "O 0,6J 0
, 1
, 2
,
,
3
4
5
,
,
6
'
,
I
1
8
, 9
1
, 0
I
IS
20
DAYS AGED AT 140.F. Figure 2.
1 294
INDUSTRIAL AND ENGINEERING CHEMISTRY
Breakdown of Circosol-2XH masterbatches
2s
30
BUTADIENE-STYRENE POLYMERS
L
I
oil masterbatches in storage, P-conidendrol (a staining antioxidant) appeared to be the best antioxidant. However, during heat aging of vulcanizates, this antioxidant was not outstanding (7, 2). Tests on a n oil-free polymer of about 50 ML-4 viscosity containing P-conidendrol and compounded with added PBNA (7) showed improved vulcanizate stability at elevated temperatures (about 300" F.), compared to the stability of vulcanizates containing 0-conidendrol alone. The stability of vulcanizates protected with a combination of Pconidendrol and PBNA was comparable to that of the vulcanizates containing PBNA alone. These results indicate the desirability of further work with this antioxidant. The use of 0-conidendrol for improving storage stability of oil masterbatches with later addition of PBNA during compounding might offer advantages to the users. p-Conidendrol seemed to offer more protection against breakdown or gelation than 1 part of Versene Fe-3, which aided (3) in increasing storage stability of polymers made with a similar polymerization formula. The staining antioxidants, PBNA and the acetone-diphenylamine reaction product (BLE), differed in their ability to prevent gel formation. With PBNA, no gel was found in either the base polymer or any of the masterbatches during the period of heat aging, while with BLE, gel formed in both the base
I
o
4
o
2 3 A
5 9 6 D 7 A 8 X
38
36
CONIDENOROIL PBNA BLE POLYGARO STALITE 2246 SANTOVAR 0 WING-STAY S
34
32 30
2
28. 26
22
v
18. IS.
a
0.8 OS 0
1
2
3
4
15
10
DAYS
Figure 3.
30
21 2 2
AGED AT 140.F.
Breakdown of Sundex-53 masterbatches
polymer and in the masterbatch containing the naphthenic oil but not in the masterbatches with the more aromatic oils. These antioxidants protected the base polymer for about 4 days followed by breakdown, which proceeded a t a rate similar to that found with &conidendrol. BLE protected the polymer somewhat less than PBNA from breakdown. The patameters of breakdown (Table I) show the quantitative relationship.
I n the masterbatches containing the naphthenic oil (Circosol-2XH) and antioxidants PBNA or BLE, essentially the same breakdown results were obtained as with the base polymer, except that the degree of ultimate breakdown was reversed with these two antioxidants. Among the nonstaining antioxidants used in the base polymer, Wing-Stay S and Santovar 0 offered very little protection against gelation. Polygard and Stalite protected the polymer against
I B CONIDENDROL 2 4 PBNA 3 A BLE 4 0 POLYGARD 5 T STALITE 6 0 2246 7 A SANTOVAR 0 8 X WING-STAY S
0
1
2
3
4
5
6
7
8
9
1
0
15
25
20
x)
DAYS AGED AT 140'F. Figure 4.
Breakdown of Dutrex 20 masterbatches VOL. 49, NO. 8
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-
loo 80
I'P
60
POLYGARD
d/
40
0'9
CIRCOSOL- 2X-4
89
WING-STAY S
60
40
BLE
f+-'
20
100
0 .
20
0 2
100
SUNDEX- 53 100
~
-
80
60.
60
80
4
7
10
15
21
30
DUTREX 2 0
40
20
SYALITE -li
0
0
2
4
7
IO
I5
21
30
DAYS Figure 5.
gelation about as well as BLE, and the sample containing 2246 formed no gel. Wing-Stay and Santovar 0 also provided the least protection with respect to the breakdown of the oil-free polymer. Polygard was more effective than Stalite in lengthening the induction period; however, polymers with these two antioxidants broke down to approximately the same level, with the former having a higher rate of breakdown. Antioxidant 2246 provided little initial stability of the base polymer although a low rate of breakdown was found in every case with this antioxidant. With the naphthentic oil masterbatches (Circosol-ZXH), approximately the same relationships were obtained as with the base polymer, except that the rate and amount of gelation were less, the stltbility before breakdown started was less, and the rate of breakdown was higher. An exception was the masterbaich containing Santovar 0, which formed relatively less gel and broke down less than the base polymer. I n the masterbatches containing the aromatic oil (Sundex-53): the amount of gel formed was less, the breakdown rate was higher: and extent of breakdown was greater than with the masterbatches containing the naphthenic oil. Wing-
1 296
2
4
IO
15
y7 21
30
AGED AT 14OOF.
G e l formation during heat aging
Stay S was the exception in that it provided an apparent initial stability (which may be experimental error). The relative order of the antioxidants regarding their influence on the polymers was similar except for a reversal in position of Stalite and Polygard. Generally, the more reactive oil (higher aromatic type) lowered the rate and amount of gel formed and increased the rate and amount of breakdow-n When the masterbatches contained the highly aromatic oil (Dutrex 20), more polymer breakdown occurred than with the less reactive oils (less aromatic), although the relative behavior with the various antioxidants was comparable with all the oils. '4lthough practically no preliminary polymer stability was found with antioxidant 2246, this material was very effective in preventing the high rate of breakdown associated with nonstaining antioxidants in the presence of aromatic and highly aromatic oils. With the aromatic oils, the polymer containing 2246 was similar in break-down characteristics to polymers containing PBNA or BLE. Antioxidant 2246 in masterbatches with the highly aromatic oii showed significantly lower rates of breakdown.
INDUSTRIAL AND ENGINEERING CHEMISTRY
7
Acknowledgment
The authors are indebted to the following for supplying the antioxidants used: PBNA and Stalite, Goodrich Chemical Co.; BLE and Polygard, Naugatuck Chemical Co.; Wing-Stay S, Goodyear Tire and Rubber Co. ; Santovar 0, Monsanto Chemical Co.; p+ conidendrol, Crown-Zellerbach Corp. ; and 2246, .4merican Cyanamid Co. Literature Cited
(1) National Science Foundation, private communication. ( 2 ) Schade, J. W.,India Rubber TVarid 123, 311-14 (1950). ( 3 ) Taft, W. K . , Duke, J., Larchar, T. B., Sr., Kitzmiller, W., Feldon, M., IND.ENG.CHEM.48, 1220 (1956). ( 4 ) Taft, W. K., Duke, June, Laundrie, R. W., Snyder, A . D.? Prem, D. C.: Mooney, Howard, Ibid., 46, 396 (1 954). ( 5 ) Taft, W. K., Snyder, A. D., Duke, J. T., Mooney, H. R., Zbid., 48, 336 (1956). RECEIVED for review May 31, 1956 ACCEPTED January 16, 1957 Division of Rubber Chemistry, ACS Meeting, Cleveland, Ohio, May 1956. Work performed as part of the research project sponsored by the National Science Foundation.
