Variations in Processing and Physical
Properties of Oil Masterbatches with Increasing Oil Content W. IC. TAFT, B. G. LABBE, AND R. W. LAUNDRIE Government Laboratories, University of Akron, Akron, Ohio
A
SYSTEMATIC study was needed of the effect of the amount of oil on the processing and physical properties of masterbatches prepared from low temperature synthetic rubbers of various Mooney viscosities. I t was believed that data should be collected to indicate the preferred level of Mooney viscosity in making the masterbatches. KO data were available in the literature on this kind of systematic study. Swart and others ( 4 )and Harrington and others (.2) in their earlier work approached the same problem, but not in the same manner. D'Ianni and others ( 1 ) reported results a t one oil level only. T o simplify the experimental approach, the amount of carbon black used was on the basis of the polymer plus oil, the quantity ofblack being varied, The quantities of accelerator based on the polymer content, exclusive of the oil, were kept constant. It was recognized that with increase in oil content more sulfur would be needed, and consequently the sulfur was increased 0.5 part with every 35 parts of oil, although no claim is made that this adjustment is the optimum one.
masterbatcbed with Circosol-2XH by usual techniques as discussed, to obtain masterbatches having about 40, 60, and 80 RIL-4 viscosity, washed, and dried a t 140' F. Circosol-2XH was used because it is low in nitrogen bases and therefore should not affect the cure, which is import,ant in a compounding study.
PROCEDURE
Table 11. Effect on ML-4 Viscosity of Oil Addition to Base Polymers
A series of latices was made a t 41' F. by a sugar-free ironpyrophosphate formula to 60% conversion and the modifier was varied to obtain base polymers of varying viscosities. The reaction was shortstopped with 0.14 part of sodium dimethyl dithiocarbamate-sodium polysulfide mixture per 100 parts of monomers and stabilized with 1.5% phenyl-2-naphthylamine per 100 parts of polymer. The polymers were coagulated alone or latex
60 ML-4
240
-
4 0 ML-4
Table I.
Compounding Recipes
Tread Type" 100 parts polymer parts oil 40, 50, or 60% of above
+
Polymer plus oil
Carcass Type" 100 parts polymer parts oil
+
Black EPC or HAF Black HMF ... 3O'or 40% of above 5 5 Zinc oxide Stearic acid 0.75 1.5 2.0 0 . 5 per 35 parts oil 2 . 0 0 . 5 per 35 parts oil Sulfur Benaothiazyl disulfide 2 . 3 5 1.5 25y0 DPG mdsterbatch .. 1.0 ParaAiix .. 5.0 a Values represent parts by weight unless otherwise noted.
+
+
Requirements for Masterbatches of 40 ML-4 45 58 90 Oil used, parts per 100 rubber 0 12 30 ML-4 of base polymer 40 61 95 120 150 2OOa ML-4 of masterbatch . . 42 40 38 44 41
107 235" 39
Requirements for Masterbatches of 60 AIL-4 42 63 70 Oil used, parts per 100 rubber 0 13 25 61 95 120 150 2005 235O ML-4 of base polymer 61 62 59 60 60Q ML-4 of masterbatch
,.
Requirements for Masterbatches of 80 hIL-4 Oil used, parts per 100 rubber 0 4 15 25 46 ML-4 of base polymer 76 95 120 150 2005 ML-4 of masterbatch . 80 82 82 78 5 Estimated values from Williams plasticities, modifier charge, dilute solution viscosities, and Figure 1.
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Effect of oil content on Mlooney viscosity of base polymers
Figure 2. 2401
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INDUSTR IAL AND ENGINEERING CHEMISTRY
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Compound Mooney viscosity
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November 1955
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INDUSTRIAL AND ENGINEERING CHEMISTRY
-
40% 50%
60%
50%
2403
The Mooney viscosities of the compounded stocks for each masterbatch decreased linearly with an increase in the amount of oil in the masterbatch, as shown by the graphs in Figure 6. The larger amounts of oil with the masterbatches of 60 and 80 ML-4 viscosity im-
2404
pp,
INDUSTRIAL AND ENGINEERING CHEMISTRY 40 M L - 4 STOCKS
60 M L - 4 STOGKS ELONGATION
80 M L - 4 STOCKS
300% MODULUS
1
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Figure 10.
40
Vol. 47, No. 11
70 0
Stress-strain properties
Tread-type reci e 40, 50, and 60% EPCblack
temperature, and the Mooney viscosities of the compounded stocks are shown in Figure 8 for mixes prepared in the Banbury in accordance with the carcass-type recipe using 30 and 40% H M F black based on the masterbatch. These results confirmed in general those for the tread-type recipes. To sum up the effect of increasing the oil content on the processing properties: The extrusion and the Mooney viscosity of the compounded stocks improved, lower peal: power loads resulted, and the stocks ran cooler in the Banbury. There was little or no difference in roughness or shrinkage of the stocks. Increasing the oil content of masterbatches prepared from the same latex permitted more black t o be used in order to obtain similar processing results. Shown in Figures 10, 11, and 12 are the variations in the stressstrain characteristics as the oil loading was increased in the stocks compounded according to the tread-type recipe with the three loading levels of EPC and HAF blacks and the carcass-type recipe with two loading levels of H M F black, The data for the compounds containing EPC and H M F were taken at the optimum cure times, as shown in Figure 9. For the compounds prepared according to the recipe with H M F black, the best average of optimum cure time was used. For the compounds prepared according t o the HAF recipe, the cure rates were very rapid, and the optimum cures were close to 25 minutes in all cases. This cure time has been used in Figure 10. With all the compounds of each black at each level of black, the tensile strength decreased, the modulus decreased, and the elongation increased with increase in oil. The modulus increased and the elongation
decreased regularly with each black as the black loading changed from 40 to 50 to 60y0 of the masterbatches in the tread-type recipes and from 30 to 40% in the carcass-type at all three viscosity levels of the masterbatches, but the effect of the black loadings on tensile results was irregular. As expected, the modulus and tensile strength increased and the elongation decreased with the increase in viscosity of the masterbatches. The change in per cent rebound, in set, and in temperature rise with increase in oil content at the three viscosity levels for stocks compounded according to the three recipes and cured at the optimum is shown in Figures 13, 14, and 15. At the lower viscosity level (40 ML-4) of the masterbatches, the base polymer of very high viscosity required such a large amount of oil that poor states of cure resulted, This, of course, is reflected by results for these properties. With these exceptions, a t each level of black the rebound increased in general as the oil loading increased, and the increase in the level of black a t any one masterbatch viscosity decreased tho rebound. Again a t each level of black, except for the 40 ML-4 stocks with the highest oil loadings, the set tended to increase in general with increase in oil loading and the hysteresis tended to decrease in spite of the higher sets. With increase in black loading, set and temperature rise increased, and rebound decreased. I n Figures 16, 17, and 18, the Shore A hardness is shown for the masterbatches com30 50 pounded according to the three recipes with the different black loadings. The hardness decreased a t each viscosity level of the masterbatch with increase in oil content. To some extent, this reduction in hardness can be compensated for by increasing the black loading with the sulfur formula and a t the constant accelerator level used. The effect of an increase in oil loading on the flex life of the stocks compounded according to the two tread-type recipes a t the three levels of black is shown in Figures 16 and 17; no definite trend seems apparent. The data obtained with several masterbatches of 60 ML-4 viscosity and containing different amounts of oil, when compounded according t o the tread-type recipe with EPC black to approximately 62 Shore A hardness by varying the black level, have been plotted in Figure 20 to show how the various properties are affected a t a constant hardness by oil loading. Similarly, data for stocks prepared from masterbatches of 80 MIA-4 viscosity, compounded according to the HAF recipes to 64 i2 Shore A hardness, are shown in Figure 19. It is evident that under these conditions of compounding the following tended to decrease with increase in oil loading of the polymer: tensile strength, modulus, rebound, and power consumed, as shown by the average peak power at the Banbury start-up times. The following tended to increase with increase in oil loading: elongation, temperature rise, set, extrusion index (Garvey die), and optimum cure time, t,. The Mooney viscosity of the compounded stocks, Banbury dump temperature, roughness, shrinkage, and flexlife were not affected markedly, or regularly, by increase in the oil content of the masterbatch. The foregoing discussion is based on essentially a constant compounding recipe-that is, the acceleration was kept constant and the sulfur was varied from 2 parts based on the polymer
.
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November 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
40 M L - 4 STOCKS
80 M L - 4 STOCKS
60 M L - ~STOCKS
ELONGATION
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0
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400
300
300% MODULUS 3700 3500 3300 3100
2900
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TENSILE STRENGTH
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0 OIL, PARTS
Figure 11.
40
70
Stress-strain properties
Tread-type recipe 40, 50, and 60 70H A F black
plus 0.50 part per each 35 parts of oil. To observe how the physical test results would be altered by increasing the sulfur level at constant acceleration at a 50% EPC black loading, and by increasing acceleration a t a constant sulfur loading, the masterbatch of 60 ML-4 viscosity containing 42 parts of oil was retested after the masterbatch had been stored about 2 years, and the results of optimum cure are shown in Figures 21 and 22. Some of the properties were different from those obtained earlier and shown in the previous figures, notably stress-strain, per cent set, and temperature rise. These differences probably were caused by a drop in Mooney viscosity of the masterbatch from 59 t o 35 ML-4. The results indicate, however, that the tendency of the larger amounts of oil to produce softer stocks can be overcome by increasing the amount of curatives used. The main effects of increasing the curatives were to reduce the time to optimum cure, elongation, set, flex life, and temperature rise, and to increase the modulus, rebound, and Shore A hardness. Increasing the sulfur level by small amounts had little effect on tensile values, but a large increase caused a drop in tensile strength, while an increase in acceleration within the limits used caused little or no change in this property a t optimum cure.
50
2405
2406
INDUSTRIAL AND ENGINEERING CHEMISTRY
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INDUSTRIAL AND ENGINEERING CHEMISTRY SHORE A HARDNESS 60 M L - 4 STOCKS
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Figure 17.
Shore A hardness and flex life properties at 30- to 40minute overcure
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