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(3) Browne, F. L.,IND.ENG. CHBM.,22, 847 (1930). (4) Browne, F. L., and Brouse, D., Ibid., Pi, SO (1929). ( 6 ) Browne. F. L., and Truax. T . R . , Colloid Symposium Monograph, Vol. IV, p. 258 (1926). (6) Clark, G. L., Nature, 120, 119 (1927). (7) Clark, G. L., and Tschentke, H . L.,IND. ENG.CHBM.,21, 621 (1929). (8) Douglas, W. D., and Pettifor. C. B., Roy. Aeronaut. SOC.(Gt. Britain), Aernaut. Repf. 31 (1929). (9) Gerry, E., and Truax, T . R., Furnilure M f r . Artisan, 49 (April, 1922). (10) Lee, W. B., IND.EXG. CHEM.,22, 778 (1930). (11) Long, J. S., Zimmermann, E. K., and Nevins, S. C., Ibid., 20,806 (1928). (12) McBain, J. W., Ibtd., 19, 1006 (1927). (13) McBain, J. W., and Hopkins, D. G., Dept. Scientific and Industrial Research (Gt. Britain), Adhesives Research Comm. Rep; 2, 34 (1926).
(14) (15) (16) (17) (18) (19) (20) (21) (22) (23)
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McBain, J. W., and Hopkins, D. G., J . Phys. Chem., 29, 1S8 (1925) McBain. J. W., and Hopkins, D. G., Ibid., S O , 114 (1926). McBain, J. W., and Lee, W. B., J . SOC.Chem. I n d . , 46, 321 (1927). McBain, J. W., and Lee, W. B., Ibid., 31, 1674 (1927). McBain, J. W., and Lee, W. B., Proc. Roy. SOC.(London), 113A, 606 (1927). McBain, J. W., and,Lee, W. B., J. Phys. Chem., 32, 1178 (1928). Nelson, H. A., Proc. A m SOL. Testing Materials, 21 11, 1111 (1921); 23 11, 356 (1923). Truax, T . R.,U. S. Dept. Agr., Bull. 1100 (June, 1929). Truax, T. R . , Browne, F. L., and Brouse, D., IND. ENG.CHEM..21, 74 (1929). Weinstein, A. I., Colloid Symposium Monograph, Vol. IV, p. 270 (1926).
Reenforcing Action of Pigment Mixtures on Rubber Compounds‘ D. J. Beaver and J. W. MacKay GENERALATLASCARBONCOMPANY, LINDEN,N. J.
Data are presented which indicate that mixtures of decreases the dispersion of L T H O U G H a large varying ratios of either channel black or a soft carbon channel black in rubber, the amount of work has been done on the reenblack with whiting, lithopone, or clay show additive larger the amount of zinc oxforcing action of different pigphysical properties. Mixtures of soft carbon with ide the greater its effect on the merits in rubber compounds, zinc oxide also show additive properties, while mixtures black owing to “the &mivery little has been published of channel black and zinc oxide show poorer resistance cally active zinc oxide changto abrasion, higher modulus, and higher tensile ing the acidity of the rubber on the effect of pigment mixtures. strength than would be shown by purely additive during vulcanization and thus I n 1928 Pohle (4) claimed mixtures. affecting the degree of wetting that i t was possible to change The explanation of these results appears to be found of the inactive carbon by the the stress-strain curve from in the chemical reaction between the basic zinc oxide rubber.” convex to concave by the adand the acidic compounds in the rubber or on the black. I n order to determine which dition of small amounts of These results have been applied to the formulation of a of the above two theories is particles of different size to a solid tire stock which will give a better resistance to correct, a set of experiments given filler. H o w e v e r , he abrasion and blow-out when using a soft black than was made with two different gave no e x p e r i m e n t a l eviwhen using a channel black. types of carbon black with an dence showing the relationalkaline filler, such as zinc ship of particle sizes or of the magnitude of the effect. oxide, and with neutral fillers, such as lithopone and whiting, I n 1922 Greider (a) found that when using 9 volumes of and with an acid filler, such as clay. As was pointed out by pigment to 100 volumes of rubber the maximum tensile was Grenquist (3) standard channel black absorbs a considerable obtained with a mixture containing 6 volumes of channel amount of alkali but its absorption of acid is practically nil. black and 3 volumes of magnesium carbonate, while the This would indicate that the flocculating effect of zinc oxide modulus a t 300 per cent elongation and the permanent set might be due to a reaction with the acidic compounds on the did not show this maximum, being merely additive. All black. the properties of mixtures of other pigments, such as zinc I n order to test this point, a comparison was made between oxide, clay, and barytes, with basic magnesium carbonate a low and a high acid black, such as a channel black, with were found to be additive also. the above-named fillers, using a constant loading of 20 volDawson (1) studied the effect of mixtures of clay and zinc umes of pigment to 100 volumes of rubber. A sufficient with channel black using a loading of 9 volumes of filler to number of mixtures was prepared from each pair of pigments 100 volumes of rubber (1926). The results are rather in- to determine accurately the shape of the curve between the conclusive, since the zinc oxide-channel black mixtures show a single components. This procedure necessitated the use of a higher modulus at 300 per cent elongation, lower tensile larger number of points with mixt,ures showing non-additive strength, and hardness, while the clay-channel black mix- properties than with those that did. tures show a lower modulus, lower tensile strength, and Experimental higher hardness than would be expected from additive properties. These results are in agreement with those obtained in The pigments used in these experiments were standard cement and paint mixtures, where it has been found that by grades used in the rubber trade. The channel black adsorbed properly proportioning particles of different sizes much better or reacted with 1.5 cc. more of 0.1 N sodium hydroxide than properties can be obtained than by the use of one size only. with 0.1 N sulfuric acid, while the high-modulus soft black However, if pigments have a chemical effect on each other (Gastex) adsorbed only 0.38 cc. more. The lithopone and or upon the dispersing medium, it is possible that these second- whiting adsorbed equal amounts of acid and alkali, the clay ary effects will mask the purely physical effect of mixtures. adsorbed 1.0 cc. excess of alkali, and the zinc oxide adsorbed Grenquist (3) has shown (1928 and 1929) that zinc oxide an excess of acid, the amount depending on the time of reaction. 1 Received September 20, 1930. Presented before the Division of the tests were made from a large batch Of Rubber Chemistry at the 80th Meeting of the American Chemical Society, masticated rubber by adding the pigments and other inCincinnati, Ohio, September 8 to 12, 1930.
A
IhTDUSTRIAI,AhTD ENGINEERING CHEMISTRY
March, 1931
295
I
45
I/ ma.% c.4eQox O$
CLlY
I 75% 25%
25%
50%
75%
S X
Figure 1-Clay-Carbon
4
im*
Mixtures 43
i
!
'
IC+ 0%
ClPBaIY
75%
WXinNC
*5%
5¶%
PZ
Figure 2-Whiting-Carbon
43
f1 tOOx
0%
I C11W
76%
I,~ORIMC
28%
50 %
*%
Figure 3--Lithopone-Carbon
25%
0%
75%
Ww.l
Mixtures
I 25%
0%
78%
/OO$
Mixtures
gredients, except sulfur, in master batches. I n each series a large batch of black and of filler stock was prepared, and these two batches were mixed in proper ratios to give the required mixture of black and filler, the sulfur being added to these final batches. -411 samples were cured in molds in a paraffin bath held a t 140" C. by means of a sensitive thermostatic regulator. After curing, the samples were allowed to rest for one day and the stress-strain data were obtained on an automatic Scott testing machine. The abrasion data were determined on a Williams abrading machine, using a separate sheet of abrasion paper for each series of tests. Therefore in order to make art accurate comparison of the different series, it was necessary to re-run all the carbon black stocks on one sheet of paper and then to calculate the data for each series to this common basis. The stocks were not aged in constant-temperature or humidity cabinets before testing,
but each series had a soft-black and a channel-black stock as a control. The time of cure was taken as 15 minutes ahead of the time required to reach the maximum modulus values. Results
In Figures 1, 2, 3, and 4 are summarized the data obtained in the tests with the two types of carbon black and the four filler pigments using the following test formula: smoked sheets, 100; zinc oxide, 5; sulfur, 3; Laures, 4; No. 808, 1; pigment, 20 volumes per 100 volumes of rubber. The curves in these figures have the following designations: A,B,C = soft black A',B',C' = channel black A,A' = ultimate tensile strength B,B' = abrasion loss
C,C' = modulus a t 400 per cent elongation
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IIVUU~~'RIAN L D ENGINEEMNO CHEMISTRY
An inspcctioii of these data suggehth that the properties of the mixtures of ~liaiinelblack or of soft black are additive with clay, hthopone, and ahiting. In every case the modulus, tensile, and abrasion curves are very nearly atraight lines, .;hoaiiig tliat ti e physical effects of these pigments are add,ti\e. I t can be concluded from these six mixtures that the pachiug effect of pignients of different particle sizes is very small, I f not entirely absent. in rubber compounds
Vol. 23. No. 3
carbon hlaek, it should be possible to prepare a solid-tire stock containing the usual amounts of zinc oxide and of soft black which woiild have a better resistance to abrasion than a similar stock containing channel black. A series of typical solid-tire stocks was prepared using channel black and a soft black to determine if such resnlta could be obtained. These data, summarized in Table I, show that the soft carbon-black stock gives better resistance to abrasion than the chaniiel-black stock, and that by substituting part of the zinc with an equal volume of soft black a stock with considerable further improved resistance to abrasion can be obhined. In order to determine whether thece stocks would be satisfactory for use in solid tires, they were subjected to a pounding test for one-half hour under a constant load. The results obtained in these tests are shown in Figure 5. These pictures show that stock 519, which contained the channel black, waa very badly deteriorated in these tests, while the corresponding stock containing soft black was only slightly affected. By replaciiig part of the zinc oxide with an equal volume of soft black considerable improvement wa6 obtained in resistance to "blow-out" as judged by this pounding test. T ~ b l rI-Tests on Solid-Tire Stocks Confsinlng Soft Black Base P"RM"S*: M . S . S............................... 1w S u l h i r .................................
4
S t e a t i c a ~ i d............................ D . P . G...............................
619 25
Stuck No.
iio
Fieure 5 -Results of Pounding Testa on Solid Tire Stocks
Crn.
1.81 94
520
..
25 150 1.81
540 000 .. 73
91 130 500 570 5 71
2.77
4 88
l5X
In the ~ i n cuxidi-carboii black mixtures the modulus .&adtensile rui\eh show that the soft carbon iriixtures have additive properties while the channel-blach curves show a distinct curvature, with the intermediate points lying above tlie straight line loining the two base mixtures. The abraiioii curves of these two blacks with zinc oxide show that the soft black has additive properties while the channel black shows a more rapid decrease in the resistaiice to abrrasion than would be expected from purely additive properties. The data given in Figure 4 indicate that the res'stance to abrwioii of the soft black-zinc omde mixture at the 50-50 ratio is approximately equal to that of the channel black-zinc oxide miuture, while for lower percentages of black it is slightly better, This difference 1s probably due to the reaction hetween the zinc oxide and the acidic compounds present in the rubber or on the black causing the medium to become more alkaline. As shown by Grenquist (Y), this change in acidity causes a decrease in the dispersion of the channel black while, because of the lack of acidity oE tlie soft black or because it is less sensitive to a change in acidity of the rubber, its dispersion is not affected so much This explanation is in partial agreement with the r e d t s of Greider (2)TI ith basic magnesium carbonate, since this pignient would have as much of a neutralizing effect on the acidity of the rubber a8 the zinc oxide and thus cause the channel blach to Roccdate. Howsever, he fourid that only the tensile propertie8 of tlie mixtures were not additive while in the present tests with ~ i n coxide, tensile, modulus, and abrasion resistance were non-additive. On tiie basis of tiiis assumption, it i b possible to offer an explanation for tiie poor "blowout" cliaiacteristics of sohdtire trcad stocks containing cliaiiiicl blach, because this type of stock contains high percentages of zinc oxide which would have a very strong flocculating effect on the channel black. Since the shove results also indicate that zinc oxide does not have such a pronounced effect on the flocculation of the soft
5
1.25 523
..33
125 1.72 130 144 488
5w
21 75
V24
.. 41
iw
1.61 148
160
420
(40 35
75
3.29 8.30 4.45 6.12 4.05 4.93 Cure, 80 minateS at 140' C..which wag the time required to reach maxi-
mum tensile.
Conclusion Mixtures of varying ratios of either channel black ur n soft carbon black with whiting, lithopone, or clay show additive physical properties. Mixtures of soft carbon with ziiic oxide also show additive properties, while mixtures of channel black and zinc oxide show poorer resistance to abrasion, higher modulus, and higher tensile strength than would be shown by purely additive mixtures. The explanation of these results appears to be found in the chemical reaction between the basic zinc oxide and the acidic compounds in the rubber or on the black. These results have beon applied to the formulation of a solid-tire stock which will give a better resistance to abrasion and blowuut when using a soft black than when using a channel black. Acknowledgment
The authors wish to express their appreciation to the Geueral Atlas Carbon Company for permission to publish t,hese results and to C. J. Wright, vice president of this company, whose interest and support have made it possible to carry on this work. Literature Cited (1) Uhwjou, T. R . , Tronr. Inst. Rubber Ind., 1, 350 (19261. (2) Greider, X. W.. IN^. ENO.Caear., 14, 385 (1922). (3) Grcnqiiist, E.A., I M d . , 20, 1073 (1928): 21, 665 (19291. (4) Pollie, H.,Gummi-218.. 42, 2887 (1928).
