Temperature Coefficient of Vulcanization 111. Determination for Mixes Accelerated with Various Compounds' R. E. MORRIS,^ Municipal University, Akron, Ohio Temperature coeflcients are determined for stocks accelerated with ( A ) mercaptobenzothiazole, ( B ) mercaptobenzothiazole with diphenylguanidine, (C) mercaptobenzothiazole with diphenylguanidine neutral succinate, (D) dibentothiazyl disulfide, and ( E ) dibenzothiazyl disulJide with zinc dimethyldithiocarbamate. Cures are made at intervals f r o m
F
ORMERLY it was thought that the temperature coefficient of vulcanization of rubber by sulfur was independent of the accelerating agent used. Sheppard (8) obtained a temperature coefficient for a litharge compound which was practically the same as that found by Spence and Young (9) for an unaccelerated compound. Twiss and Brazier (10) found no change in the temperature coefficient when aldehyde-ammonia was added t o a rubber-sulfur mix. However, curing results from stocks accelerated with mercaptobenzothiazole showed that in this case the temperature coefficient commonly used must have been too high. Park
223" to 306" F., and also in a constant-temperature oven in a bolted mold at 194' and 172" F. The calms obtained from modulus and combined sulfur data are found to be ( A ) 1.41 and 1.54, ( B ) 1.41 and 1.54, ( C ) 1.43 and 1.43, (D)1.50 and 1.52, ( E ) 1.48 and 1.51, respectively Cfor 10" F. intervals). tained similar results in his work with stocks accelerated with tetramethylthiuram disulfide and with a butyraldehydeaniline condensation product.
EXPERIMENTAL PROCEDURE The rubber, zinc oxide, and sulfur were master-batched on a factory mill, sufficient stock for all the experimental work being milled a t one time. The base formula is as follows: Smoked sheet Pale crepe Zinc oxide Sulfur Accelerator
50 50 5 3
As specified
The accelerator was weighed out on a watch glass on an analytical balance in the following proportions: STOCK
A B C
2
2
D
E I
I
TIME OF CURE IN MINUTES
DATAFOR STOCKD FIGURE 1. MODULUS-TIME CUREDIN KNOXSCREW PRESS
TIME OF W
E W HOURS
DATAFOR STOCK D CURED FIGURE 2. MODULUS-TIME IN BOLTED STEEL MOLD
and Maxwell (6) found this to be true with mercaptobenzothiazole and also with stocks accelerated with a crotonaldehyde-aniline condensation product. Sandstrom (7) ob1 2
For Parts I and I1 see references ( 6 ) and (7). Present address, Goodyear Tire and Rubber Company, Akron, Ohio.
ACCELERATORB Mercaptobensothiarole Mercaptobenzothiazole hlercaptobenzothiasole neutral succinate Dibensothiaayl disulfide Dibensothiazyl disulfide carbamate
+ diphenylguanidine + diphenylguanidine + zinc dimethyldithio-
Ra~10/100R 0.5
0.13
0.13 1.0
0.5
+ 0.17 + 0.28 + 0.1
Approximately 400 grams of the master batch were milled on an experimental mill for exactly 5 minutes to soften it, accelerator was added, and the milling continued for 5 minutes to mix the batch thoroughly. The stock was sheeted off and allowed to stand overnight before curing. The stock was cured in a small Knox screw press a t temperatures of 223O, 241°, 262", 275", 289", and 306" F. (106', 116", 128", 135", 143O, a n d 152" C.). The temperature was c h e c k e d by a p r e s s standardizing block as suggested b y the Physical Testing Committee of the Division of Rubber Chemistry (11). The thermometer used was 'Ompared FIGURE 3 . TI&~E-TEMPER.ATuRE with one certified by CURVES FOR MODULUS DATAON STOCK D the Bureau of Standards. This block was used every time the temperature was changed. The temperature could be maintained constant within e 0 . 2 " F. (* 0.11O
C.). The sheets were cured in two-cavity steel molds. I n order to see whether temperature lag was appreciable, a cure was made with thermocouple wires imbedded in the sheet, and a
1400
I N D U S T R I A L A ND E N G I N E E R I NG C H E
December, 1933
1401
I ST R Y
modulus of 20 kg. per sq. cm. is plotted against the temperature of cure in Figure 3. Figures 4-6 are similar curves based on combined sulfur data. The time to reach 0.40 per cent combined sulfur is plotted against the temperature of cure in Figure 6. COEFFICIENTS~ TABLEI. D.4~ao s TEMPERATGRE INVESTIGATOR
TYPEOF STOCK AND Mnaxs OF DETERMINATION
Litharge accelerated Pure gum stock; combined sulfur Physical properties Combined sulfur Combined sulfur Extensibility a t given elongation Time to reach max. tensile Free sulfur Sheppard ( 8 ) Hand tear, modulus, and combined Park (4) 2.5 sulfur Park and Maxwell (6) Mercaptobenzothiasole accelerated; 1.91 modulus 2.30 Same' combined sulfur Crotohdehyde-aniline accelerated: 2.32 modulus 2.67 Same' combined sulfur Tetrakethylthiuram disulfide acSandstrom (7) 1.92 celerated. modulus 2.20 Same, combined sulfur Butyialdehyde-aniline accelerated; 2.52 modulus 2.40 Same; combined sulfur 1.82 A ; modulus Author A ; combined sulfur 2.11 1.81 B; modulus 2.11 B; combined sulfur 1.87 C. modulus 1.87 C f combined sulfur 2.00 D ; modulus 2.08 D: combined sulfur 1.98 E ' modulus 2.08 E f combined sulfur 0 Part of the data is taken from Sandstrom (7).
Bourne ( 8 ) Spence and Young (9) Bourne ( 1 ) Rossem (6) Twiss and Brazier (IO)
L
I n n l l l l l l x l l l l l l l l l I 1
10
40
€0
8c
TlflE OF CURE
100
IN
120
140
160
180
200
MINUTES
SULFUR-TIMEDATAFOR STOCKD FIGURE 4. COMBINED CUREDIN KNOXSCREWPRESS temperature-time plot was made. The temperature lag was found to be negligible. The stock was cured a t 172' and 194" F. (78" and 90" C.) in a two-cavity bolted steel mold in a constant-temperature oven. The temperature of the oven could be maintained constant within *l.O" F. (*0.56" C.). Three 0.25-inch (0.635-cm.) test strips were died out and tested on a Scott testing machine by the two-observer method. Modulus at 500 and 700 per cent, tensile strength, and elongation were taken. For the calculation of the temperature coefficients the modulus a t 500 per cent was used. For determining the combined sulfur, the Kelly method (3) was used. This gives only the sulfur combined with the rubber hydrocarbon.
TIMP. COEFFICIENTS loo C. loo F. 1.8 1.37 2.65 1.72 3.1 1.87 2.0 1.47 2.3 1.59 2.3 1.59 2.4 1.63 2.59 1.70 1.66 1.43 1.59 1.60 1.73 1.44 1.55 1.67 1.63 1.41 1.54 1.41 1.54 1.43 1.43 1.60 1.52
1.48 1.61
Park and Maxwell (5) have found the temperature coefficient for mercaptobenzothiazole based on modulus to be 1.43 and that based on combined sulfur t o be 1.59 [for 10" F. DISCUSSION OF RESULTS (5.56' C.) intervals]. These values are the average for a That modulus may be determined with greater accuracy number of stocks containing various quantities of accelerator, t h a n other physical properties was shown by Sheppard (8). zinc oxide, sulfur, stearic acid, and carbon black. For their The elongation is arbitrarily chosen; for this determination pure gum stock of composition 100 pale crepe, 0.3 mercapto500 per cent was used. The modulus-time curves for each b e n z o t h i a z o l e , 5 temperature were plotted, and the time to arrive a t a given zinc oxide, 3 sulfur, 'C It9 modulus for each temperature was read from the chart. It they found the temwas assumed that a t the same modulus the state of cure was perature coeficients 38 equivalent. When the log of the time to reach equal modulus to be, respectively, was plotted against the temperature] a straight line was ob- 1.45 a n d 1.60. 27 tained. From the slope of this line the temperature coef- These values agree i6 ficient may be computed. 24 f a i r l y w e l l with I n determining the temperature coefficient from combined those of the present 104 sulfur, a similar procedure was carried out. Here it was as- a u t h o r g i v e n i n '' sumed that a t the same percentage of combined sulfur the Table I for mercapI 93 state of cure was equivalent. The results of these determina- t o b e n z o t h i a z o l e 82 tions are given under "author" in Table I, together with the (stock A). best data available in the literature. P a r k a n d hlaxm well state from their TIPIC IN MINUTES 0 b s e 1v a t i 0 n s on FIGURE6. TIME-TEMPERATURE mercaptobenzothiaCURVESFOR COMBINEDSULFUR DATAON STOCKD zole, "It is a n outstanding fact that the temperature coefficient calculated from physical data is lower than that calculated from combined sulfur data." This is not necessarily true for all organic accelerators. Using a butyraldehyde-aniline condensation product (du Pont's 808), Sandstrom (7) found 1.67 for 10" F. based on modulus and 1.63 based on combined sulfur. Table I shows that for mercaptobenzothiazole with diphenylguanidine neutral succinate TIME OF W R E IN HOURS (stock C) the coefficients are equal. FIGURE 5 . COMBINED SULFUR-TIME DATAFOR STOCKD ACKNOWLEDGMENT CUREDIN BOLTEDSTEELMOLD The author wishes to express his indebtedness to M. J. Figures 1-3 give curves based on modulus for the stock ac- DeFrance for directing the work and to L. B. Sebrell for pereelerated with dibenzothiazyl disulfide. The time to reach a mission to publish the results. 16
I N D U S T R I ,4L AS D E N G I N E E R I S G C H E M I S T R Y
1402
LITERATURE CITED Bourne, A. O., I n d i a Rubber J., 45, 120 (1913). Bourne, A. O., I n d i a Rubber World, 33, 93 (1905). Kelly, J., IND.EXQ.CHEM.,12, 196,875 (1920). Park, C. R., Ibid., 22, 1004 (1930). Park and Maxwell, Ibid., 24, 148 (1932). Rossem, A. van, Communications Netherlands Gout. Inst. advisino rubber trade and ind., VI,179 (1917).
Vol. 2 5 , s o . 12
(7) Sandstrom, R.V., IND.ENQ.CHEM.,25, 684 (1933). (8) Sheppard, J. R., I n d i a Rubber World, 80,56 (1929). (9) Spence and Young, Z . Chem. I n d . Kolloide, 11, 28 (1912). (10) Trriss and Brazier, J. SOC.Chem. Ind., 39,125T (1920). (11) Vogt (chairman), IND.ENQ.C H m . , 17, 535 (1925). RECEIVEDSeptember 20, 1933. Presented before the Division of Rubber Chemistry a t the 86th Meeting of the American Chemical Society, Chicago, Ill.. September 10 t o 16,1933.
Adsorption of Copper Sulfate by Aluminum Floc C. J. BROCKMAN, University of Georgia, Athens, Ga.
T
HERE is a n enormous quantity of data on the use of
copper sulfate in the control of algae in the raw water supplies of municipalities, and there has been much disagreement as to the quantity which can be safely used without exceeding the tolerance of the human body for copper salts. In order to eliminate any differences of opinion on the matter of tolerance, it will be considered that anything over 5 parts per million will be dangerous because this concentration of copper ions imparts t o water a decided flavor. Many references in the literature indicate that very little, if any, of the copper ions get through the filters into the city clear water supply. However, no study has been made of the case in the light of modern methods of control in water works, especially control of the p H of raw and filtered water. During the past decade the problem of floc formation in water works has been put on a scientific basis by the investigations of the men connected with the U. S. Public Health Service and others (1, 4, 5 ) who have studied the conditions under which the best aluminum flocs are produced and then extended the study to include the floc from ferrous sulfate (copperas). From an examination of these publications on alum and iron flocs, the electrometric titration curves for aluminum sulfate with sodium hydroxide (5) and the similar curve for copper sulfate and sodium hydroxide (S), the writer was led t o believe that at least some of the copper salt would be flocced out in the ordinary alum treatment of raw water and consequently be retained on the filters.
EXPERIMEKTAL PROCEDURE The first series of experiments on this problem was made on the raw water supply of Athens, Ga. Jar tests according to the method of the New York State Department of Health were used. Filter alum from the Athens city water works was dissolved in distilled water so that, when 1 cc. of this solution was added to 1 quart of water, the alum concentration was 0.5 grain per gallon-that is, 8.1 grams of alum were dissolved in 1000 cc. of distilled water. The copper sulfate solution was prepared by dissolving 0.3928 gram of CuSOa5H10 in 1000 cc. of distilled water, which made the concentration 0.1 mg. of copper ions per cc. or about 0.1 p. p. m. when 1 cc. was diluted to 1 quart. A quantity of copper sulfate solution and then alum solution were added t o the raw water in quart jars. When the floc had settled, it was filtered through a large funnel. The filtrate was evaporated in a Pyrex vessel to 50 cc., analyzed for copper ions by slightly acidifying with dilute sulfuric acid, then made slightly ammoniacal in order to separate the aluminum hydroxide from the copper ions by filtration. The copper ions in this filtrate were determined after evaporating the excess of ammonia, by the ferrocyanide method according t o Yoe (6). Treatment with ammonia was necessary in order t o remove any residual aluminum salts which were not flocced out. The pH of the filtered water was determined colorimetrically on a 10-cc. sample of the clear filtrate.
Table I indicates that in the ordinary alum treatment of water, up to 1 p. p. m. of copper ions is completely removed in the process of filtration. The mechanism by which this removal is accomplished need not concern us at present. It may be either co-precipitation with the alum floc or an adsorption on the alum floc. At any rate, there are no copper ions in the clear filtered water. TABLE I. TESTSON ATHESSWATERSUPPLY 7
TEST
PH
1 2 3 4 5 6
7.0 7.0 7.0 7.0 7.0 7.0
.
R A WWATER FILTERED WATER Alum solution Copper solution pH Copper Cc. Grains/gal. Cc. P.p . m. P. p . m. 1.0 8.55 1.0 0.1 6.4 0 . 0 0 1.0 8.55 2.0 0.2 6.4 0 . 0 0 1.0 8.55 3.0 0.3 6.4 0.00 4.0 0.4 1.0 8.55 6.4 0.00 6.4 0 . 0 0 1.0 8.65 5.0 0.5 6.4 0 . 0 0 1.0 8.65 10.0 1.0
TABLE 11. TESTSWITH BUFFERSOLUTIONS TEST
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 31 33
34 35 36 37 38 39 40 41 42 43 44 45 46
-BUFFERED WATER-pH Alum solution Copper solution cc. P . p . m. Cc. P. p . m.,, 10 1160 10 14.3 7.4 10 16.7 0 0 7.4 10 1160 10 14.3 7.2 10 1000 20 25.0 7.2 10 1160 10 14.3 7.0 1 150 3 5.5 7.0 10 16.7 0 0 7.0 15 20.0 10 1080 7.0 20 25.0 10 1000 7.0 2 1 153 3.8 7.0 10 14.3 10 1160 6.8 10 1160 10 14.3 6.6 3 5.5 1 150 6.6 10 1000 20 25.0 6.6 7.3 4 1 148 6.6 3.8 2 1 153 6.6 10 1160 10 14.3 6.4 5.5 1 150 3 6.4 5 550 20 26.7 6.4 20 25.0 10 1000 6.4 10 16.7 0 0 6.4 1 1.9 1 156 6.4 2 3.8 1 153 6.4 5 8.8 2 285 6.4 5 9.0 1 144 6.4 10 14.3 10 1160 6.0 3 5.5 1 150 6.0 20 26.7 5 550 6.0 25.0 20 1 0 1000 6.0 15 20.0 10 1080 6.0 25 29.4 10 950 6.0 30 33.3 100 900 0 6.0 10 16.7 6.0 10 1160 10 14.3 6.0 5.5 3 1 150 5.6 10 16.2 2 130 5.6 20 28.6 0 0 5.6 10 14.3 10 1160 5.6 20 25.0 10 1000 5.6 10 16.: 0 0 5.6 10 1 6 . f 0 0 5.2 10 1160 10 14.3 5.2 20 25.0 10 1000 5.0 10 16.7 0 0 5.0 10 1160 10 14.3 5.0 20 25.0 10 1000 5.0
FILTERED WATER Copper p H Copper removed 7.2 7.3 7.0 6.9 6.8 7.0 6.9 6.7 6.7 7.0 6.6 6.4 6.5 6.4 6.5 6.6 6.0 6.3
...
6.0 6.2 6.4 6.3 6.2 6.2 5.2 6.0
... ...
...
... ... ,..
Mg.
%
0.00 0.00 0.00 0.00 0.00 0.00
100.0 100.0
0.05 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.10 0.00
0.10 0.00
0.00
0.05 0.10 0.05
0.05 0.20
0.10 0.05 0.20 0.10 0.10
, . .
0.00
5.5
0.05 0.30 0.20 0.50
... ,..
...
... ...
.. .. .. ...
... ...
...
1.00
0.10 0.50 0.50 1.00 0.70 0.50 1.00
100.0 100.0 100.0
100.0 95.0. 100.0 100.0 100.0 100.0 100.0 100.0
100.0 100,0
100,0
100.0 100.0 95.0 100.0 90.0 100.0 100.0 90.0 80.0
95.0 84.0 90.0 95.0 97.0 92.0 90.0 90.0 100.0 85.0
70.0 90.0 50.0 50.0 90.0 50.0 50.0 50.0 30.0 50.0 50.0
These preliminary experiments on raw water indicated that the problem should be further studied, This was done.
