Temperature Coeficient of Vulcanization Determination for Mixes Accelerated with Mercaptobenzothiazole and a Crotonalde hyde - Aniline Condensation Product C. R. PARKAND R. B. MAXWELL, Goodyear Tire 4 Rubber Co., Akron, Ohio
D
ATA accumulated over of similar areas over the platen T H E T E i l / l P E R A T U R E of the inside of a a considerable period surface. Thermocouples a t the rubber article during rulcanization is much have i n d i c a t e d that , surface of the thermoboard were lower than that of the outside because of the low when employing certain acceleraused directly in contact with the heat conductivity of rubber compounds. Since tors, the temperature coefficient platen surface. The check was the curing intensity akpends upon the temperaof vulcanization is not the same repeated a t each temperature as when a rubber-sulfur mix is used. The press selected had ture, the cure of theinside of the article is often used. The values obtained in the smallest temperature variawidely diflerent f r o m that of the outside. I n the past have been subjected to tion of any press available (maxiorder to evaluate the cure, it is necessary to considerable criticism, and curmum, 1" F. or 0.55" C.). know accurately how curing intensity varies ing results from tires have indiA range of cures was made with temperature. Satisfactory data f o r mercated that the values commonly a t each of a series of temperaused for stocks containing mertures separated from each other captobenzothiazole stocks have been lacking. captobenzothiazole were t o o by steps at 10" F. (5.56" C.). The temperature coejicients have been dehigh. The v a l u e s u s e d have The sheets were cured in fourfor mercaptobenzothiazole mixes and termined varied for different experimentcavity steel m o l d s , m e e t i n g JIG7 a m i x accelerated by a crotonaldehydeers between 1.45 and 1.60 per t h e recommendations of t h e aniline condensation product. Special care was 10" F., or 1.94 to 2.35 per 10°C. Physical Testing Committee of I n some quarters i t seems to have the Rubber Division, AMERItaken to eliminate errors in temperature regulabeen the practice to use the same CAN CHENICALSOCIETY.One tion, etc., by the use of thermocouples in the temperature coefficient regardmold was placed in each opensamples during cure. The values derived ,from less of the type of mix or type of ing of the press, allowing eight modulus and combined-sulfur data were found accelerator employed. The pressheets to be cured a t one time. to be 1.91 and 2.30 (av.), respectively, f o r ent experimental work was conB e f o r e l o a d i n g the mold, a ducted with the purpose of deterthermocouple was i n s e r t e d in rnercaptobenzothiazole; and 2.32 and 2.67, remining more accurately the value each sheet. Each couple was spectively, for crotonaldehyde-aniline. of the temperature coefficient for placed in such a way as to be mercautobenzothiazole mixes. as nearlv as uossible a t eaual I n the procedure of vulcanizing test samples, there are distances from the flat surfaces of th;! moid and in the ceker several conditions which introduce errors of some magnitude. of the sheet. The time required to load the molds was Two of these errors were thought to be important enough considerably increased by this procedure, approximately 10 minutes being consumed in inserting the sheets in the to warrant the correction of the data: mold and placing the mold in the press. This practice was 1. It has frequently been observed that the test sheets do not attain the temperature registered by the press thermometer. followed in all cures up to and including the 250" F. (121' C.) 2. When a mold is removed from the vulcanizing press for series, The duplication of temperatures from sheet to refilling, it drops considerably. in temperature. When it is sheet was so good that from 260" F. (125" C.) to 310" F. replaced in the press, some minutes elapse before the mold (154.4" C.) only one couple was used in a single sheet placed regains the equilibrium temperature. This mold lag may always in the same stock and in the same mold cavity. This reduce the effective curing time. reduced the time of loading of the molds to about 3 minutes The first of these errors may be reduced to a large extent by and hence reduced the temperature lag due to mold radiation. proper adjustment of the press temperatures. The second is a TABLEI. COMPOSITIONS OF STOCKS difficulty inherent in the curing method. Both may be corSTOCK0 rected by following the temperature of the test sample with a A B C D E F G H Pale crepe 100 100 ... 100 100 100 100 100 thermocouple. Extracted pale orepe 100 . . . No previous data were available regarding the effect of Mercaptobenzothiasole 0 : i 0:i 0.3 0.2 0 : i 0 : i i:0 5 5 5 5 131 131 5.0 6" varying sulfur or accelerator ratios, or the effect of the quan- ZnO Sulfur 3 3 3 6.03 3 3 3 tity of pigment used in the mix. '"
EXPERIMENTAL PROCEDURE With a view to supplying information on the above points, eight stocks were prepared according to the formulas shown in Table I. It may be seen that these stocks include a number of the common variations to be expected in tire stocks. A large enough batch of each stock was mixed to fill all the curing requirements. Sheets were then cut and stored for use. A t,wo-opening hydraulic press was selected after exploration of the platens with a "thermoboard." This device makes it possible to determine the temperature of a small area of the platen and compare it with the temperature
Stearic acid Carbon black Crotonaldehyde-aniline oondensation
... . . . 4. ..0 . .1.5. . .. .. .. .. .. .. .4.0 ..
.....................
4.0 40
... ...
1
The effect of the temperature lag of the molds was much smaller than was anticipated. The time required for the sheet to reach temperature equilibrium was 5 to 7 minutes. I n order to convert these values to equivalent cure units a t the scheduled temperature, a time-intensity curve was drawn for each cure, using a preliminary value of 1.50 for the temperature coefficient of vulcanization. From this curve, with the aid of a planimeter, the equivalent cure was computed. The method used has been outlined in detail
148
February, 1932
I N D U S T R 1A L A N D E N G I N E E R I N G C H E M I S T R Y
119
Combined sulfur was determined as follows: A 0.5-gram sample of the stock was extracted overnight in an Underwriter's apparatus. The extracted stock was then transferred to an Underwriter's flask. -4 mixture of concentrated nitric acid saturated with bromine was added, and digestion carried out at low heat until the bromine fumes were completely expelled. The volume was reduced to 20 cc., and 3 grams of potassium chlorate were added The solution was then evaporated to dryness. Expulsion of nitric oxide was accomplished by repeatedly evaporating to dryness after addition of hydrochloric acid. The sulfates were then precipitated and ignited in the usual way.
by Sheppard and Wiegand (4). I n spite of the time required to reach temperature equilibrium, the reduction in equivalent cure in no case amounted to more than 3 minutes a t the temperature used. I n most cases it was less than 1 minute. This amounts to about 1 to 2 per cent of the total equivalent cure a t temperatures up to 250" F. (121' C,), At higher temperatures the percentage loss in equivalent cure was higher because of the shorter times of cure. Differences in equivalent cure in a given time between two individual cures at the same temperature never amounted to more than 2 per cent. I n practically all cases, a t a given temperature the curves relating intensity of curing effect with time were identical during the period of rise. Mold lag, although taken into consideration in the plotting and calculation of data, affected the results to a very small extent. For example, stock C calculated from the curve as drawn in Figure 4 gives a value of 1.764; stock C calculated from the curve uncorrected for mold lag gives a value of 1.750. The equilibrium temperatures reached by the sheets in the press were in all cases so close to the temperatures scheduled as to produce no measurable effect on the results.
FIGURE 2. STOCK F After curing, the sheets were tested, using the Goodyear testing machine. Combined sulfur data were obtained on a sufficient number of sheets to determine the temperature coefficient. The combined sulfur data are given in Table 11. TABLErr.
FIGURE 3. TIMEOF CURE FOR STANDARD PROPERTIES
PHYSIC4L
Stocks A and B
values, read from the stress-strain curves a t the chosen elongation, were plotted as modulus-time curves of the type shown in Figures 1 and 2. Figure 1 shows stock C and Figure 2 shows stock F. Similar curves were d r a m for each stock. At each temperature the time of cure required to produce a given modulus was read from these curves. I n the case of stock C, for example, the times read were those required t o produce a modulus of 60 kg. per sq. cm. The times of cure so determined were plotted in Figures 3 to 6, against the temperature. The above method is the one in most common use and has been outlined in a previous paper (1). A similar procedure was used with the combined sulfur data (Figures 7 to 10). The temperature coefficients have been calculated ( 3 ) from these curves and are given in Table 111. TABLE111. TEMPERATURE COEFFICIENTS STOCK0
A
B
C
D
E
F
G
H
CALCULATED FROM MODULUS DATA
COMBINED SULFUR
CUREIN MINUTESAT TEMPERATURE SPECIFIED ( " C,)5 2.3/ 4.6/ 9.1/o 14.25/ 24.2!/ 34.25/ 69.7/ 89/o 117.5,' STOCK310' 300' 290 280' 270 260' 250' 240 230" % % % % % % % % % -4 0.38 0.82 0.75 0.74 0.58 0.77 0.55 0 . 8 2 0.68 B 0.24 0.51 0.45 0.52 0.38 0.49 0.55 0.53 0.45 C 0.45 0.75 0.58 0.71 0.53 0.80 0.83 0.81 0.61 D 0.52 0.80 0.65 0.74 0.64 0.85 0.85 0.88 0.67
E F 0 H
C.tLCUL.4TIOS AKD DISCUSSION RIodulus may be determined with a greater degree of accuracy then tensile, elongation, or any other commonly used characteristic of the stress-strain curve. For this reason modulus alone was used in calculating the temperature coefficient. I n any given case the elongation a t which modulus studies were to be made was chosen arbitrarily for convenience in plotting. The elongation selected for study of stock C was 800 per cent. T-alues used for other stocks are show11 in the line labeled "Strain" in Table 111. The modulus
178.5/ 220 % 0.72 0.48 0.70 0.38
0.41 0.59 0.48 0.74 0.42 0.64 0.62 0.67 0.54 0.58 0.28 0.37 0.34 0.96 0.34 0.42 0.36 0.44 0.34 0.68 0.41 0.56 0.54 0.52 0.48 0 . 6 2 0.81 0.55 0.44 0.34 0.82 0.83 0.92 0.89 0.88 0.78 0.74 0.69 0.54 0.50 O.The cure a8 given has been correoted for temperature lag of the mold.
Strain, yo 800 Coefficient (10' F ~ ) 1.45 Coeffioient (10' C.) 1.94
800 800 800 400 400 300 700 1.38 1.37 1.41 1.45 1.46 1.52 1.60 1.79 1.76 1.86 1.96 1.97 2.13 2.32 CALCUL.4TED F R O M COMBINED SULFUR
Coefficient (10'F.) Coefficient (10OC)
1.60 1 56 1.55 1.60 1.55 1.57 1.65 1.72 2.34 2 . 2 8 2.21 2.34 2.21 2.25 2.46 2.67
It is a n outstanding fact that the temperature coefficient calculated from physical data is lower than that calculated from combined sulfur data. It is obvious from an inspection of Table I1 and the individual temperature-coefficient plots, that the combined sulfur data were not as reliable as the
150
INDUSTRIAL AND ENGINEERING
physical data. Kevertheless, the differences between the coefficients as calculated from the two sets of data are consistent enough both in direction and magnitude to indicate a definite difference. This being the case, it is evident that a value for the coefficient determined by means of combined sulfur data alone could not be satisfactorily used to predict physical cure. This is in agreement with the fact pointed out by Shepard and Krall (2) that degree of physical cure is not related to combined sulfur. It has been noted frequently that various accelerators seem to have optimum curing temperatures. Figures 1 and 2 indicate that higher modulus values are developed a t 220" F. (104.4' C.) to 240" F. (115.5" C.) than a t higher temperatures. This behavior seems to be characteristic of stocks accelerated with mercaptobenzothiazole. The data for stock H indicated a much higher optimum. No similar o p timum was found for a rubber-sulfur mix ( I ) , nor was there any difference between the temperature coefficient derived from physical data and the coefficient calculated from combined sulfur. The variations in the individual values obtained from the various stocks from A to G may represent an actual difference
Figure 4.
Stooks C and D
Figure 5. Stooks E and F
Figure 6.
Stooks G and H
TIME OF CUREFOR STANDARD MODULUS
CHEMISTRY
Vol. 24. No. 2
in behavior A definite conclusion to this effect should, however, be based upon careful check results. In any case, it seems entirely satisfactory for most practical purposes to use the temperature coefficient obtained by averaging the values given by the seven stocks containing mercaptobenzothiazole. In concluding, it may not be amiss to point out again that, since the present discussion is concerned primarily with physical properties, the value 1.91 per 10" C.
Figure 7.
Stocks A and B
Figure 8.
Stooka C and D
-.-
Figure 9. Stooks E and F
Figure 10. Stocks G and H
TIMEOF CUREFOR STANDARD COMBINED SULPUR
INDUSTRIAL AKD EXGINEERING CHEMISTRY
February, 1932
should be used for mercaptobenzothiazole stocks. Likewise, the lower value, 2.32 per 10" C., should be used for the crotonaldehyde-aniline condensation product. The above values have been collected in Table IV: together with the best data available in the literature. TABLEI\'.
VALUES OF TEMPERATURE COEFFICIEST
found to be 1.91 per 10" C. For crotonaldehyde-aniline, the value was 2.32 per 10" C. 2. Bssed upon combined sulfur data, the value was 2.30 (average) per 10" C., and for crotonaldehyde-aniline 2.67 per 10" C. 3. The values obtained from physical data are to be preferred for all practical purposes.
(At loo C.)
MERCAPTOCROTON- ALDERUBBER BENZOALDEHYDEHYDEAUTHORITY SULFURTHIAZOLE LITHABGEANILINE AMMONIA .. Spence and Young (6) 2.65" 2
Van Rossem (7)
0
..
..
..
..
..
..
151
ACKXO WLEDGMENT The authors are indebted to H. W. Wilson for assistance in the experimental work, and to R. P. Dinsmore for kind permission to publish the results.
2.4C
..
LITERATURE CITED
.. 2.500
Park and Maxwell Sbeppard ( 8 ) a Combined sulfur.
.. ..
2.50b
Park ( 1 )
b
.. ..
1.91b 2.30a
..
..
Physical data.
.. .. C
2.328 2.67a
.. ..
2.59c Average value
CONCLUSIONS 1. The average temperature coefficient of mercaptobenzo-
thiazole accelerated mixes, based upon physical data, was
(1) Park, IND.ENG.CHEM.,22, 1004 (1930).
Shepard and Krall, Ibid., 14, 951 (1922). Sheppard, India Rubber World, 80, 56 (1929). Sheppard and Wiegand,
[email protected].,20, 953 (1928). Spence and Young, 2. Chem. Ind. Kolloide, 11, 28 (1912). Twiss and Brazier, J. SOC.Chem. Ind., 39, 125T (1920). (7) Pan Rossem, Comm. Netherlands Govt.Inst. Advising Rubber Trade and Rubber Ind., VI, 179-222 (1917).
(2) (3) (4) (5) (6)
RECEIVED September 10, 1931. Presented before the Division of Rubber Chemistry at the 82nd Meeting of the Bmerioan Chemioal Society, Buffalo, N. Y., August 31 to September 4,1931. C. R. Park is now with the Firestone Tire and Rubber Co., Akron, Ohio.
Fu-royl Chloride W. W. HARTMAN AND J. B. DICKEY, Eustmun Kodak Co., Rochester, N . Y .
I
N RECEKT years furfural (2-furaldehyde) has become
inexpensive and easily available in large quantities. The drop in price of furfural has stimulated research in the field and has produced correspondingly inexpensive derivatives, such as furoic (pyromucic) acid. Furoyl chloride1 is one of the most useful derivatives of furfural from a synthetic viewpoint because of its stability and multiplicity of reactions. Furoyl chloride was first prepared by the action of phosphorus pentachloride on furoic acid (6). Frankland and Aston ( 3 ) have reported a practically quantitative yield of furoyl chloride by treating furoic acid with about two equivalents of phosphorus pentachloride in dry chloroform in a special apparatus described by them. Baum ( I : ] and Gelissen and Van Roo11 (4) have prepared furoyl chloride by heating the acid with thionyl choride on a water bath over a period of 1 t o 2 hours. The yields were reported to be nearly quantitative. Bogert and Stull (2) using the same method, reported a yield of 79 per cent. Maxim ( 7 ) obtained a 40 per cent yield of furoyl chloride by treating the acid with thionyl chloride, and a yield of 70-80 per cent by the action of phosphorus pentachloride on the acid. Gilman and Hewlett (5) prepared the acid chloride in 75 per cent yield by treating the acid with thionyl chloride in dry benzene. An examination of the literature indicates that the yield of the acid chloride obtained by treating the acid with phosphorus pentachloride or thionyl chloride is variable. There is the possibility that decomposition is caused by impurities in the acid itself or in the reagents used. 1 Attention is called to the fact that furoyl chloride is a vigorous lachrymator and must be handled with care.
EXPERIMENTAL The preparation described here is an extension and modification of the method of Gilman and Hewlett ( 5 ) . It is believed that the method described is applicable to quantities many times that described in this report. The reaction was carried out in a 22-liter flask fitted with an inverted Liebig condenser, an S-tube, and a dropping funnel for the introduction of the thionyl chloride, and suitable means for removing the hydrogen chloride and sulfur dioxide which were evolved in the preparation. Five thousand six hundred grams (50 moles) of a commercial grade of furoic acid? were placed in the flask, and 10 liters of dry benzene3 added. The reaction mixture was then placed on a steam bath and heated to gentle refluxing, and 8294 grams (75 moles) of a commercial grade of thionyl chloride were added dropwise over a period of 4 days. The reaction mixture was not heated overnight. After the addition of the thionyl chloride, the reaction mixture was refluxed for an additional 12 hours and filtered into a 22-liter flask. The flask was fitted with a 1.5-foot (45.7-em.) fractionating column, and the benzene and excess thionyl chloride were distilled over on a steam bath. After removal of the benzene and thionyl chloride, the acid chloride was distilled from a 12-liter flask fitted with a 2.5-foot (76.2 em.) fractionating column, Liebig condenser, and water-cooled 5-liter receiver. The first fraction boiling up to 59.5" C./T mm. weighed 90-100 grams and was mostly 2 The crude acid was an air-dried material which contained 97 per cent furoic acid and about 2 per cent moisture ' T h e benzene was'dried by distilling a commerdal grade of benzene through a 1.5-foot column until the distillate was no longer milky. About 15 per cent of the benzene was distilled over
