INDUSTRIAL AND ENGINEERING CHEMISTRY
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when an excess of zinc oxide is present results in an increase in rate of cure. LITERATURE CITED (1) Aultman, P. M., Pennsylvania Rubber Co., private communication. (2) Bedford and Gray, IND. ENO.CHEM.,15, 720 (1923). (3) Bedford and Winkelmann, Ibid., 16, 32 (1924). (4) Davey, J. SOC.Chem. I d . , 49,338T,343T (1930). (5) Jones, H. C., and Depew, H. A., IND.ENG.CHEM.,23, 1467 (1931). (6) Martin and Davey, J . SOC.Chem. Ind., 44, 317T (1925). (7) Morris, T. C., IND. ENQ.CHEM.,24, 584 (1932).
Vol. 24, No. 5
(8) Reece, Trans. Inst. Rubber Ind., 4, 526 (1929). (9) Russell, W. F , U. S. Patent 1,467,197 (1923). (IO) Russell, W. F., IND.ENQ.CHEY.,21, 727 (1929). (11) Schidrowitz, India Rubber J.,81, 13 (1931). (12) Sebrell, L. B., and Boord, E. E., IND. ENQ.CHEM.,15, 1009 (1923). (13) Sebrell and Vogt, Ibid., 16, 792 (1924). (14) Steele, F. A., Research Division, New Jersey Zinc Co., private communication. (15) Whitby and Evans, J . SOC.Chem. Ind., 47, 122T (1928). RECEIVED March 3, 1932. Presented before the Meeting of the Rubber Division of the American Chemical Society, Detroit, Mich., February 26 and 26, 1932. The author’s present address is American Zinc Sales Co., Columbus, Ohio.
Effect of Cadmium Compounds on Typical Organic Accelerators during Vulcanization M. K. EASLEY AND A. C. EIDE,American Zinc Sales Co., Columbus, Ohio Cadmium m a y occur in zinc oxide in the f o r m of oxide, hydroxide, sulfate, sulfide, chloride, and carbonate in quantities up to 0.5 per cent or slightly more. Using 10 parts of zinc oxide which contains 0.5 per cent of cadmium, the latter would not exceed 0.05 part on the rubber. Owing to testing inaccuracies and the masking effect of impurities, small amounts of cadmium m a y be dificult to detect. To eliminate such complications, a base formula was selected using chemically pure zinc oxide to which were added various amounts of cadmium compounds. W i t h f e w exceptions, these compounds retard teiramethylthiuram monosulfide
T
HE literature contains considerable information regarding the reactions of zinc oxide with thiuram accelerators.
Some ten years ago Bedford and Sebrell
(1) published a mechanism for the reaction of zinc oxide and
but slightly advance the rate of cure of butyraldehyde aniline, diorthotolylguanidine, and mercaptobenzothiazole. General analytical practice is insu Eficient to ident i f y the various forms of cadmium present, and the action of cadmium-bearing zinc oxides is diflcult to predict. Samples of three experimental zinc oxides gave widely different results with tetramethylthiuram monosulfide. T w o samples of comparatively low cadmium content assayed approximately the same. One was ,fast- and the other slow-curing; the third, assaying appreciably more cadmium, produced an intermediate rate of cure. bearing metallic zinc (French process) or cadmium-bearing ores (American process), it is possible for many cadmium compounds to be present, but those most likely to occur are the oxide, hydroxide, sulfate, sulfide, chloride, and carbonate. I n French process zinc oxide, the preponderance of cadmium is usually present as the oxide; in American process, as the oxide or sulfate, though it is possible for all six compounds to occur, depending upon operating conditions and procedure.
tetramethylthiuram disulfide. Simmons and Cummings (4) showed that the monosulfide and disulfide were very similar in their action with zinc oxide. Recently Jones and Depew (3) have shown the influence of lead, and Bridgewater (2) gives data showing the influence of certain cadmium compounds. EXPERIMENTAL PROCEDURE All of these explanations are dependent upon the formation Since metallic compounds other than cadmium may be of hydrogen sulfide during vulcanization and the formation of inert metallic compounds of the thiurams. present in commercial zinc oxides and have various effects on For some time i t has been known that certain cadmium accelerators, c. P. zinc oxide (dry process) was used to elimicompounds effectively retard tetramethylthiuram mono- nate any such possibilities. Various amounts of cadmium compounds were incorporated sulfide a t various curing temperatures. A similar investigation of other typical accelerators disclosed the fact that all in the batch. It is quite probable that such a method does accelerators are not so affected. In some cases distinct not typify the dispersion of cadmium compounds found in commercial zinc oxides, where the various metallic substances acceleration results. It is not the purpose of this paper to explain, a t this time, are most intimately associated with the zinc oxide, but it is the reactions of cadmium compounds with these accelerators sufficient to indicate their respective activities. The various quantities of cadmium compounds used in this but merely to present the data obtained. The presence of cadmium in zinc ores is not a t all uncommon investigation are not, in every case, necessarily those most and in pyrometallurgical processes it is volatile a t lower probable in cadmium-bearing zinc oxide. In some instances, temperatures than zinc, which makes possible practically comparatively large quantities were selected because certain 100 per cent recovery of the cadmium with zinc metal or zinc compounds impart only a slight influence on rate of cure, and oxide. Cadmium may be removed from zinc ores by special it was necessary to use excessive amounts to show their true treatment to produce zinc metal or oxide which is substan- characteristics. tially cadmium-free. Since gum stocks give more or less erratic tensile results, the I n the commercial production of zinc oxide from cadmium- curves presented in this paper are those representative of the
I N D U S T R I A L -4N D E N G I N E E R I N G C H E M I S T R Y
May, 1932
F I G U R E 3. E F F E C T OF CADMIUM CHLORIDE ON I I U B B E R A C CELERATED WITH TETAAMETHYLTHIURAM MONOSULFIDE
569
FIGURE4. EFFECTOF CADMIUMSULFATEON RUBBERAcCELERATED WITH TETRAMETHYLTHIURAM MONOSULFIDE
f000
/
SU'IuI1
"LCC.2 ZldorrDI C"LI*I"M
3.0'9
.,a
-
1
3.00
60
90
C Y R t I N .-7,Nl@
I /20
ratr(,o,*c~
r
1
20
Jo
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1J 2>9?@26'C)
I
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10
6
I
I
8
10
/2
ZPL%(II+S)
FIGURE6. EFFECTOF CADMIUMCARBONATE ox RUBBER ACCELERATED WITH TETRAMETHYLTHIURAM MONOSULFIDE moduli a t 700 per cent elongation, which is near the breaking point. TETR.4METHYLTHIUR.kM
MONOSULFIDE:
The first accelerator investigated was tetramethylthiuram monosulfide, and various amounts of cadmium compounds were added to the following basic formula:
Rubber Zinc oxide, c. P. Sulfur Tetramethylthiuram monosulfide
100 5
3
0.18
Figure 1 presents a comparison of the effects of various amounts of cadmium oxide ranging from 0.01 to 0.20 part on the rubber, which shows this ingredient to be an effective retardant a t low curing temperatures. When the tempera-
INDUSTRIAL AND ENGINEERING CHEMISTRY
570
'
I
01 bo W 110 C U R E INnR.CZ27'I (l0B.U
1
20
I
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30 45 259'E(tZbY.I
I
I
I
IO
I
8 10 292.f. Il44W
6
60
Vol. 24, No. 5
12
FIGURE7. EFFECTOF CADMIUM CHLORIDEON RUBBERAcCELERATED WITH BUTYRALDEHYDE ANILINE
FIGURE8. EFFECTOF CADMIUM OXIDEON RUBBERACCELERATED WITH BUTYRALDEHYDE ANTLINE
CUR1 ihplIKe227'1: (l0VC.l
259.E l I Z s 4
Ze2'C(I'.'CJ
ON RUBBER FIGURE9. EFFECTOF CADMIUMCARBONATEON RUBBER FIGURE10. EFFECTOF C.4DMIUM HYDROXIDE ACCELERATED WITH BUTYRALDEHYDE ANILINE .\CCELERATED WITH BUTYRALDEHYDE AR'ILINE
01
,
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20
30
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rsrr(l>Erc.,
1
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8
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/Z
6127 ( / O W
FIGURE11. EFFECT OF CADMIUM SULFATE ON RUBBERAcCELERATED WITH BUTYRALDEHYDE ANILINE
ture is raised to 292" F. (144" C.), the retarding action is considerably lessened, and fairly good cures result in 10 and 12 minutes with 0.01, 0.02, and possibly 0.03 part. The results obtained with cadmium hydroxide and cadmium chloride (Figures 2 and 3) are somewhat similar. It will be noted, however, that larger amounts of these compounds were used than in the case of cadmium oxide since there were reasons to believe, when this work was undertaken,
that these compounds would not be as effective and that their presence in zinc oxide is more or less theoretical. The presence of cadmium sulfate in zinc oxide is permissible in appreciable quantities as shown in Figure 4. Retardation develops a t 227" F. (108" C.) when 0.25 part is used but the effect is slightly less noticeable when the temperature is raised to 259" F. (126" C.) Not only is this amount inactive a t 292" F. (144" C,), but it has a tendency to prolong the range of cure. When the cadmium sulfate content is increased to 0.50 part, a stock only slightly slower than the control is produced. Another interesting form of cadmium is the sulfide, as illustrated in Figure 5 . Small amounts show only slight retardation a t 227" F. (108" C,), and a t 259" F. (126" C.) the presence of 0.05 and 0.10 part has not affected the cure to any appreciable extent. Larger amounts, however, show marked retardation. When the temperature is raised t o 292" F. (144 " C.) this cadmium compound apparently activates tetramethylthiuram monosulfide, since 0.05 and 0.10 part produce considerably higher moduli and lengthen the range of cure. Cadmium carbonateimpartsretardationat 227" F. (108" C.) and 259" F. (126" C.), and the amount present is not very important, since 0.05 is almost as effective as 1.00 part (Figure 6). Although retardation is less noticeable a t 292" F. (144" C.), the carbonate has a marked tendency toward flattening the curing range.
I S D U S T R I A L A N D E X G I NE E R I N G C H E Z I I S T R Y
AIay, 1932
060
Pb '
CYRZ/N*(IX
,io do 1
D dZlr(i08t)
.?J0
k
259 %(IP4'C)
571
1 7L72 ZP?f
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FIGURE12. EFFECTOF CADMIUMSULFIDEON F~UBRER AcCELERATED WITH BUTYRALDEHYDE ANILINE
CU8Z /NM/U ID 227?(/0BY)
c'uT(/'+'q
2rFP'V(/Z6'C)
FIGURE13.
EFFECT OF CADMIUM O X I D E ON RUBBERA C CELER4TEn WITH DI-0-TOLYLGUASIDIKE
I PO /ED do CURE / X M / N 0 Z 2 7 Z ( h l C )
do
0 60 1
- L PO
cum n * / IiB
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-
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-
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nl
y,
u
ZJV?(/Z/.C)
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e
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' 0
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FIGURE15. EFFECTOF CADMIUMCARBONATEON RUBBER ACCELERATED WITH DI-0-TOLYLGUANIDINE
FIGURE14. EFFECTOF CADMIUM CHLORIDE ON RUBBERAcC E L E ~ A T E D WITH DI-O-TOLYLGUANIDINE
BUTYRALDEHYDE AKILINE A similar procedure was followed with an accelerator of the aldehyde aniline type using the following formula: Rubber
Zinc oxide, c. P. Stearic acid Sulfur Butyraldehyde aniline
100.0 5.0 0.5
3.0
0.75
-4rather effective retarding agent at any temperature is found in the case of cadmium chloride, and the degree of retardation is directly proportional to the amount used (Figure 7). It is well known that certain acid radicals influence the curing properties of some accelerators and it is possible that the presence of the chloride may be responsible for the action noted, but the scope of this paper does not include other metallic chlorides. Figures 8 and 9 represent the data obtained with cadmium oxide and cadmium carbonate which are apparently very similar in their activity. Both of these compounds produce higher moduli than the control stock a t all three temperatures, and the various quantities used do not seem to influence the results to any appreciable extent. Regardless of the quantities or curing temperatures used, cadmium hydroxide, sulfate, and sulfide gave practically the same characteristic results which do not vary matwially from those obtained for the control stock, as shown in Figures 10 to 12. DIORTHOTOLYLGUANIDINE The behavior of cadmium compounds with this accelerator is very interesting since their influence is rather pronounced.
CU#'-/X a x l a zr7.C(/08'C)
2597(/26'C)
2923(/W@
C.4DMIUM HYDROXIDE ON RUBBER ACCELERATED WITH DI-0-TOLYLGUANIDINE
FIGURE16. EFFECTOF
Maintaining much of the same type of cure, the following formula was selected: Rubber
Zinc oxide, c. P. Sulfur Diorthotolylguanidine
100.0 6.0 3.0
1.25
Cadmium oxide is effective a t all temperatures as represented in Figure 13. Quantities as small as 0.01 part produce definite acceleration. When the quantity is increased to 0.07 part, the results approximate those of the control, while larger amounts definitely retard. ilction of the chloride is similar to that of the oxide as shown in Figure 14. The carbonate is another peculiar cadmium compound, inasmuch as the mide range of quantities used produces cures a t 259" F. (126" C.) showing only slight retardation as represented in Figure 15. At 227' F. (108' C.) and 292" F. (144" C.) this compound develops definite activation.
I N D U S T R I A L A N D E S G I N E E R I N G C H E hf I S T H Y
572
I
0 Po
60
30
20
(20
C U K / N MIN. @ 227*/(/08$
f5
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FIGURE17. EFFECTOF
CADMIUM SUI.FATE ON RUBBERA C CELERATED WITH DI-O-TOLYLGUANIDINE
60 90 /?a C U M /NMNY b 2 2 7 ' F ( / O # ~
CADMIUM CHLORIDE O X RUBBER ACCELER.4TED WITH MERC.4PTOBESZOTHIAZOLE
I
01
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+*77cIo#c.c3
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io
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FIGURE
01
I
Jg IJ ZJI'T(/EbV)
I
I
20
I
I
6
0 8 292.f
,o
/I
(wc)
I
30
I
I5
do
I
1
I
a
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PVE?
I
I
/o
12'
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EFFECTO F C.ADhfIUht SULFATE OV RUBBER-\CCELEHATED WITH ?V~ERCAPTOBE~ZOTH1AZO14E
20.
,; Io '
d
2 92Y (/**'Z)
FIGURE 21. EFFECTOF
CADMIUM SULFIDE ON R U B B r R -462CELERATED WITH MERCAPTOBENZOTHIAZOLE
0
10
90
120
20
CV"8 IN A?
