INDUSTRIAL AND ENGINEERING CHEMISTRY
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the consumption of alcoholic beverages by passengers. The phenolic bodies are apparently derived from the smoke of the locomotive, The condensate also had a distinct petroleumlike odor, which may be accounted for by the fact that the train passed through a district where large oil refineries were located, or it may have been due to lubricating oil on machinery in and about the car.
Summary A freezing-out method has been developed for determining the concentration of odors in air-conditioned structures. Solid carbon dioxide, contained in a properly insulated box, was the refrigerant used to freeze out moisture and odor in an efficient condenser tube through which measured amounts of
VOL. 9, NO. 1
air were drawn a t a low velocity. Liquid air was not used on account of the expense and danger involved. The osmoscope was employed to determine the relative odor value of the condensate by the air-dilution method. Values obtained in this manner were verified by quantitative chemical determinations and also by individuals who entered the car and tested the air by smelIing. Activated carbon was demonstrated to be a safe, very efficient, and economical means of removing the odor in an air-conditioned structure.
Literature Cited (1) Fair and Wells, J. Am. Water W O TAssoc., ~ 26, 1670-7 (1934). (2) Gant, J. Pharmacal., 49, 408-27 (1933). RECEIVED October 17, 1936.
An Air-Bomb Aging Test for Tread Compounds E. W. BOOTH AND D. J. BEAVER Monsanto Chemical Company, The Rubber Service Laboratories Division, Nitro, W. Va.
T
HE comparative age-resisting properties of tire tread compounds are determined in the laboratory by either oxygen-bomb or Geer-oven aging tests. The conditions under which these tests are carried out are standardized and from their results reliable predictions are made concerning the natural aging life of the tread compounds. A few years ago oxygen-bomb aging tests, comparing firstquality tread compounds, could be satisfactorily carried out in from 39 t o 48 hours, in which time the tread compound lost about 50 per cent of its original tensile. Today, largely because of the development of better antioxidants and organic accelerators, oxygen-bomb aging tests carried out under the same conditions require between 4 and 10 days to cause the same percentage loss in tensile, and the time necessary to carry out a Geer-oven aging test has been correspondingly increased. Therefore it is very desirable to develop a shorter laboratory aging test which can be correlated with the oxygen bomb or the Geer oven and which should be indicative of natural aging results. The use of the air bomb as a laboratory method of carrying out a g i n g t e s t s h a s be e n previously suge . %+ gested (1, 2). How3' 9 3 Oxygen-BombAgad ever, papers recognized that the c o n d i t i o n s 4000 281. therein employed were too severe to permit 3500 246. reliable comparisons of 3000 111. the aging properties of tread compounds.
in this paper, and the D428-35T recommendations were followed in carrying out the oxygen-bomb and Geer-oven aging tests, with the exception that in both cases only two test pieces were broken instead of three, and in the case of the oxygen-bomb and Geer-oven aging tests one-half of the usual press-cured sheet was employed instead of the usual dumbbell test pieces. The air-bomb aging conditions referred to as being too severe consist in placing the usual dumbbell test piece in a rack, and elongating 50 per cent; the rack is then placed in the air bomb, and a temperature of 260' F. (126.7' C.) and an air pressure of 100 pounds per square inch (7 kg. per sq. cm.) are maintained for the duration of the test. These conditions were employed in carrying out the first serieS of tests in which the ratio of sulfur to rubber was varied. The results are shown in Figure 1. In the second series of tests the elongation was varied between 0 and 50 per cent, the air pressure between 50 and 100 pounds per square inch (3.5 and 7 kg. per sq. cm.), and the temperature between 210Oand 260OF. (98.9Oand 126.7' (2.). Only a single variation was made in any one 4 . test and the duration Air-Bomb Ryad of the test was kept c o n s t a n t a t 5 hours, as shown in Figure 2. From the data obtained in these as well as additional tests, the following c o n d i t i o n s 2500 t 7 6 . were adopted as more suitable for the com2000 /41. paring of tread compounds : e l o n g a t i o n , I500 to6 0; pressure, 50 pounds iooo 70. p e r s q u a r e inch (3.5 TrnE = kg. per sq. cm.); temFIGURE 1. AGINGTESTS p e r a t u r e , 220' F. Cure 75 minutes at 274OF. (134' C.). (104.4' C.); and time, Base'stock: smoked sheets, 100.00; carbon blapk,. 50.0; zinc oxide, 5.0; stearic acid, 3.0; 10 h o u r s . These Dine tar. 2.0: antioxidant, 1.5. Added t o base stock: "modified" conditions Sulfur Accelerator Sulfur Accelerator were e m p l o y e d i n E 1.25 2.20 A 2.25 1.25 F 1.00 2.40 B 2.00 1.50 c a r r y i n g out all the 0 0.80 2.80 C 1.75 1.75 later tests shown. H 0.60 2 80 D 1.50 2.00 0
I
Experiment a1 Procedure T h e procedure recommended by t h e American Society for Testing Materials, designated as D41235T, was followed in carrying out the milling, vulcanizing, and testing of the rubber compounds described
19
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FIGURE 2. EFFECTOF VARIATIONS IX CONDITIONS OF AIR-BOMB AGING Cure, 60 minutes a t 274' F. (134' C.) Aging time 5 hours. Base stock. smoked sheets 100.0; carbon black, 50.0; zinc oxide, 5.0; sulfur,:2.75; stearic acid, 3.0; pine tar, 2.0; accelerator, 1.25; antioxidant, 1.50,
I n the third series of tests the oxygen concentration was varied by dilution with nitrogen. The usual dumbbell test pieces were employed here and the end point of the test was the time necessary to cause a loss of 40 per cent in tensile,
improvement being greater in the case of the air bomb. However, even the G and H compounds show a loss of about 50 per cent in tensile due to 7 hours' aging in the air bomb, whereas previous tests showed that a heat-resisting inner-tube compound lost only about 30 per cent in tensile through aging 18 hours under the same conditions ( I ) . Therefore, these air-bomb aging conditions are too severe, and since the main difference between the composition of the heat-resisting inner-tube compounds and tread compounds G and H is the use of P33 black and carbon black, respectively, the conclusion seems obvious that carbon black does not age as /
Discussion The results of previous laboratory comparisons of heatresisting inner-tube compounds, which were carried out in the ercenf ,oo 0 80 BO 50 40 30 2 0 Oxy9en air bomb, established the theory that a low ratio of sulfur to rubber was necessary ( I ) . Therefore the first series of tests FIGURE 3. EFFECTOF OXYGENCONCENTRATION in this study was carried out to determine whether or not Same base stock as in Figure 2. E n d point, loss of 40 per cent of origitread compounds with low sulfur ratios aged better than nal tensile. Total pressure, 300 pounds per square inch (21.1 kg. per sq, om.). Temperature, 158' F. (70' CJ. Oxygen concentratlon tread compounds containing normal sulfur ratios and to prevaried from 0 to 100 per cent. sent data to show that these air-bomb aging conditions were too severe to permit reliable comparisons of tread compounds. well as some of the other compounding ingredients. SchoenThe results are shown in Figure 1. feld (3) recognized the relatively poor aging properties of It is known that tread compounds such as those shown in carbon black and attributed them t o oxygen or oxygen comFigure 1 are not practical because of their poor resistance to pounds in the carbon black. flex cracking and abrasion. The unaged results are not shown, The second series of tests was carried out to determine but to maintain the same rate of cure for all the compounds it which of the air-bomb aging conditions had the greatest effect was necessary to increase the accelerator ratio as the sulfur on the results. The data shown in Figure 2 indicate that the ratio was decreased. A range of cures was carried out and temperature employed has the greatest effect. These results, aging tests were made on several cures. However, the 75together with a few confirming tests, led to the adoption of minute cure a t 274" F. (134" C.) was chosen to make up this the "modified" air-bomb aging conditions given above. chart because it was the optimum cure. The unaged tenThe compound employed here and in all the later tests is siles of all the compounds were the same within the usual probably higher in accelerator and antioxidant ratio than is laboratory error of * 5 per cent. The unaged modulus figures usual in commercial compounds. The accelerator employed varied between about 3000 pounds per square inch (211 kg. in all the compounds in this paper is dibenzothiazyldimethylper sq. cm.) in the case of the A compound to about 2300 thiol urea and the antioxidant employed is a ketone-primary pounds per square inch (161.7 kg. per sq. cm.) in the H comaromatic amine reaction product. This compound has an pound. Figure 1 represents the results of the A , B, and C compounds as being e x c e l l e n t range of alike, but actually cure, showing no inflir.Bombflghg 7 /ohrs. Oxygen-Bomb flg1ng:Tdays t h e r e s u l t s shown dications of o v e r Geer-Oven Aging =z8d04s are the averages of cure up to the 105the three r e s u l t s . minute cure. The The same is true, in abrasion index and the case of the D, E , flex cracking resistand F and the G a n c e are excellent. and H compounds. T h e 400 p e r cent This was d o n e i n 246 3500'0 m o d u l u s figure of E order to present a the cure shown was 2// 3000 % clearer picture. about 3200 pounds The results show per square inch 116 2500 t h a t reducing the (225 k g . p e r sq. sulfur ratio has imcm.) and the tensile 141 2000 p r o v e d t h e agewas a b o u t 4400 Oxygtn Bomb 4dOp s&43 7doyz resisting properties 0 /od?qs 20 30 40 SO pounds per square Air Bomb 3bn sbr3 mhs. l5bf3. Pelcent Carbon Black of the tread comi n c h (309 kg. per Geer Owcn 7doqs i4dap ildoqs ZSdays pounds in the caseof sq. cm.). OF OXYGEN-BOMB, AIR-BOMB,AND GEER-OVEN AGING FIGURE 4. COMPARISON both the air-bomb I n the third series Left, base stock same BS in Figure 2 and t h e oxygenof tests the oxygen Right, same stobk except carbon black varied from 0 t o 50 parts bomb aging, t h e concentration was Cure, 60 minutes at 274' F.(134' C.)
INDUSTRIAL AND ENGINEERING CHEMISTRY
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FIGURE 5. EFFECTOF COMPOUNDING INGREDIENTS Base stock, smoked sheets, 100.00; zinc oxide, 6.0; @fur, 2.75; stearic acid, 3.0; pine tar, 2.0; accelerator, 1.25; antioxidant, 1.60. Added to base stock: A control B; calcene (CaCOI plus stearic acid), 50.0 C blano fixe 50.0 0’ iinc oxid; 50 0 E : P33 black’(soit blaok), 50.0 F clay 50 0 -= unoged U’ G a s k ‘soft black), 50.0 ~,oarbon black, 50.0 “g msm = air-bomb aged lohours
*3
.3‘
-
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I n the last series of tests a comparison was made of the effect of several compounding ingredients on the aging of rubber compounds. These results are shown in Figures 5 and 6. With carbon black i t was necessary to show the 200 per cent modulus figures, because in the Geer-oven a n d a i r - b o m b aging the elongations were less than 400 per cent. F i g u r e 5 shows the modulus results unaged and after aging in the air bomb, oxygen bomb, and Geer oven. Each compound shows an increase of the aged modulus over the unaged modulus f o r air-bomb and Geer-oven results, while the modulus decreases after oxygen-bomb aging. Figure 6 shows the t e n d eresults o b t a i n e d with the same compounds. These results show definitely that, irre-
n= Geer-oven ogad a8doys
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= oxygen-bomb aged 7doys
316.4 4500 varied in an attempt to obtain data which would explain the differences 281.2 4000 between the results of the oxygenbomb and the Geer-oven aging tests and perhaps suggest better conditions under which to carry out comparisons of tread compounds. The results are shown in Figure 3. The only 140.6 2000 obvious conclusions that can be made from these results are that a temperaMaterial -+ Confrol Co/cen@ Bl~ncfiXeLlhcOxide P3s € lay Gastex CorbonBlock ture hieher than 158’ F. (70” C.) is FIGURE 6. TENSILERESULTSWITH COMPOUNDS IN FIGURE 5 necessary materially to shorten \he time necessary to carry out aging tests, even though the oxygen concentration is 100 per cent. spective of pigment used, the “modified” air-bomb aging I n the fourth series of tests a comparison was made of airconditions parallel the Geer-oven results, but show considerbomb, oxygen-bomb, and Geer-oven aging, and the results able variation from the oxygen-bomb results. I n other are shown in Figure 4, The “modified” air-bomb aging conwords, the higher temperature employed for a shorter length ditions were employed in this comparison. The results show of time in the air bomb has practically the Bame effect on a correlation of the three aging methods. A horizontal line continuing vulcanization and oxygen deterioration as is obwas drawn which represents a loss of 40 per cent in tensile tained in the Geer-oven tests. (indicated as “correlation”) and shows that about 10 hours’ aging in the air bomb has brought about the same loss of tenConclusion sile as about 7 days’ aging in the oxygen bomb or 28 days’ aging in the Geer oven. Realizing that many more tests Data here presented demonstrate that study of tread commust be carried out before an exact correlation of the three pounds by the air-bomb aging method must include modificaaging methods can be made, this apparent correlation is shown tions of the conditions followed in the comparison of innerto emphasiae the shorter length of time necessary to carry out tube compounds. air-bomb aging tests and to explain the reason for adopting Data are presented which show the effect of air pressure, these various times in carrying out later comparisons. temperature, elongation, oxygen concentration, time, and Also shown in Figure 4 are the results of tests to determine pigment variation on the aging of rubber compounds. whether the same correlation held for various amounts of The air-bomb aging conditions suggested for the study of carbon black. As the carbon black content is increased from tread compounds, consisting in testing at 0 elongation, 50 0 to 50 per cent based on the rubber content, the unaged tenpounds air pressure per square inch (3.5 kg. per sq. cm.), and sile increases rapidly until about 40 per cent of carbon black 220’ I?. (104.4’ C.) temperature, have provided a shorter is present. At this point the tensile decreases rapidly. The laboratory test which parallels the Geer-oven aging test in its air-bomb and Geer-oven aging also show a slight initial ineffect on carbon black compounds. crease in tensile as the carbon black content is increased with a later decrease, but nevertheless the percentage loss in tensile Literature Cited increases progressively as the carbon black content is in(1) Booth, E. W., IND.ENG.CHEM.,24,555 (1932). creased. The oxygen-bomb aging shows no increase as the (2) Booth, E.W., Rubber Age (N.Y . ) ,34,268-71 (1934). carbon black content is increased. These results show that (3) Schoenfeld, F.K., IND.ENQ.CEEM.,27, 571 (1935). the correlation is not exact for these various aging methods when different amounts of carbon black are employed. HowR~C~IW September D 18, 1936. Presented before the Division of Rubber ever, the air-bomb and Geer-oven aging are probably within Chemistry at the 92nd Meeting of the American Chemical Society, Pittsburgh, Pa., September 7 to 11, 1936. the limit of experimental error. -
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