October 15, 1930 Table
IiYD L-STRI.4L A S D EA-GISEERISG CHEAl1ISTRY
111-Amount of Moisture Passing t h r o u g h ( S a m p l e E) C o n t a i n i n g Pinholes Gram Gram 0,0712 0 0065 0.1352 0 0338 0,0671 0 0479 0 0556
Waxed Paper
Gram 0 0434 0 0180 0 0762
Table IV-Effect of Creasing S a m p l e o n Amount of Moisture Passing t h r o u g h Waxed Paper SAMPLE A SAMPLE D Gram Gram 0 0001 0.0004 0 0002 0.0005 0 0043 0 0048 0 0002 0 00.56a 0 0126a 0
Very lieai-i!y creased.
391
small pinholes. A marked variation due to the non-uiiiformity of the paper nil1 be noted. Using papers of high moisture resistance, Table I V gives the results of creasing the sample crosswse before testing. Unless the paper is T-ery heavily creased, the decrease in the moisture resistance is very small. From the results above it is erident that in papers of high moisture resistance the presence of pinholes in the original paper has a much greater effect on the moisture resistaiicc than the handling and creasing of the paper as done in practice. This method provides a short test by nhich the moistureproof qualities of m x e d papers may he determined with results comparable with the long-time t e d s usually employed.
Laboratory Evaluation of Flex-Cracking Resistance' L. V. Cooper FIRESTOXE TIRE & R U B B E R COMPASY,XKROS,OHIO
A machine has been designed for laboratory evaluapressible as bronze ( 1 ) the ANY factors are intion of the flex-cracking resistance of any stock from movement is practically all volved in the proper compoundingofrubwhich a dumb-bell strip may be cut. The conditions elongation, and therefore flex eracaking may be considered ber stock. I n tread cornunder which the stock is tested may be varied at the pounding wear resistance is will of the operator. The results obtained on this as the result of elongation. tile major consideration, but machine on tread and sidewall stocks have always Therefore, a machine which subjects the rubber stock to other factors c l o s e l y apevaluated the flex-cracking resistance of stocks in the preach i t in importance, same order that actual road tests have. repeated elongation should produce flex cracks. Among these is the ability Since the rigidity of a tire 1s due chiefly to the carcass fabric, to withstand repeated flexing without cracking. Fles cracking produces an unsightly appearance which conveys the idea of the conditions under which the tread and sidewall operate inherent weakness in the tire, and also, if the flex cracking be- are almost independent of the stress-strain properties of these comes very pronounced, the tire may fail froin carcass break two stocks. A laboratory evaluating machine should therefore work to a definite elongation and not to a definite a t that point. A satisfactory tire must not flex-crack. load. Flex-cracking resistance is dependent on two things-the Ordinarily flex cracking does not become noticeable on stock itself and the stress under which it is working. The design of the tire-that is, size and shape of the buttons, the road test, even in poor tires, until 4000 or more miles have size and position of the side ribs, and the amount of lettering been run. If the machine duplicated road conditions, one on the s i d e r e g u l a t e s the working stress under which the sidewall and tread are operating. This accounts for the fact that two tires made b y different companies may be different in flex-cracking resistance although of very similar or even identical compounding. Various reasons have been advanced as to why one stock is better than another in regard t o flexing resistance. A few of these reasons are: (1) better dispersion of the pigments, (2) better surface continuity, (3) fewer stock folds during forming and curing, and (4) better stress-strain properties. Arguments for and against these reasons have been advanced without any definite conclusion as yet. Laboratory duplication of road-test conditions is the goal of all rubber technologists, as road testing is costly and timeconsuming. B short study of the stresses under which the stocks in a tire work should tell us some things concerning what the laboratory machine for evaluating flex-cracking resistance should be like. A normally inflated tire is under less than 5 per cent elongation. If the tire were of uniform thickness and construction from bead to bead, the elongation would be uniform. However, such is not the case and therefore the tire has points of greater and lesser stress. As a result some part of the tread or sidewall may be subjected t o an Figure 1-Apparatus for Evaluation of Flex-Cracking Resistance elongation of possibly 10 per cent as i t makes a revolution under load. Some parts of the tire are under compression test would last 100 or more hours, or the equivalent of about during road contact, but inasmuch as rubber is only as com- 12 working days. The ideal machine would be one that could be set to duplicate road conditions and also one that could be 1 Received June 2, 1830. Presented a t the meeting of t h e Akron so changed as to give accelerated teste. Rubber Group, M a y 1 2 , 1930
M
A X A L Y TI CA L EDI T I O S
392 0 to
looyo
0 t o 75%
3 Hours Figure 2-Effect
Yol. 2 , s o . 4 0 t o 507,
6 Hours of Varying Working Elongation
421/1 Ibs. of Black
6 Hours
50 lbs. of Black
Lennth of test, 21/2 hours, elongation 0 to 100 per cent Figure 3-Effect of Increased P i g m e n t a t i o n
Description and Operation of Testing Apparatus Clay
1 Hour
Reclaim
2 Hours
Control
2 Hours
Elongation, 0 t o 100%
Figure 4-Effect
of Adding Filler P i g m e n t a n d Clay to Tread Stocks
For several years a machine for evaluating flex cracking has been in use in the Firestone laboratories. This machine has won the confidence of the organization because the results obtained with i t and the results obtained by actual road test hare always been in accord. This machine is illustrated in Figure 1. The test strip is the dumb-bell strip used in stressstrain testing, eight of which may be tested at one time on this machine. The upper beam oscillates vertically, and as the c'aiiis which actuate the driving arm and the sides of the upper beam are slotted, it is possible to obtain any initial setting between 1 and 41/2 inches and to r a r y the magnitude of the oscillation from practically 0 t o 3 inches. The power is s u p plied b y a 1/4-horsepo\T-ermotor. The pulleys are of such size that the upper beam oscillates about 400 times per minute. The strips are fastened to the lower beam b y means of a bar which is held d o x n b y four bolts n i t h wing nuts. The upper beam is then set a t the top of its stroke arid each strip is individually secured to the top b e m i by means of a special screw clamp. These clamps are flattened eyelets and secure the strip by pulling it u p into a slot in the upper beam. The slot in the upper beam is so tapered that strips of any thickness may be securely fastened. The strip is so p!aced in the upper beam that it is under maximum desired elongation.
I S D C S T R I A L AND EA7GIiYEERIAVGCHEMISTRY
October 15, 1930 Control
1% Diphenylamine
Figure 5-Effect
of Adding 1 Per C e n t D i p h e n y l a m i n e
This elongation is measured in a manner similar to its measurement on a stress-strain machine. By adjusting t'he position of the driving arm in the cams at one end and in the upper beam a t the other end, it is possible to subject the strip to any elongation desired. Early experimental work with this machine established the fact that strips must be allowed to return to a position of 0 stress in each oscillation if any rapidity of checking is to be secured. After studying various conditions of test, the following procedure was adopted: Minimum distance between beams. . . . . . . . . . . . . . . . ZS,'r inches . 5l/z inches Maximum distance between beams.. . Maximum elongation of the strip und . 100 per cent Under these conditions it is possible to obtain flex cracks on the average present-day tread stock in about 8 hours with the machine making 400 flexes per minute, which is the number of flexes to which a tire in actual service is subjected when running 35 to 40 miles a n hour. I n running a test on a series of strips the test is cont'inued only long enough definitely t o rank t.he several stocks under test, and it is desirable, if possible, t o stop the test before any st'rip actually breaks. Effect of Varying Working Elongation
The effect of varying the working elongations under which the strip is flexed on this machine is shown in Figure 2 . The stock used in this test was a tread stock containing 42l/2 pounds of channel black per 100 pounds of rubber; formula used is S o . 1 in the acconipanying table. PIGMENT
F o r m u l a s Used in Various T e s t s So. 1 KO. 2 hTo.3 No. 4 100 100 100 100 421/i 50 42-)/2 42'/2 5 5 a 5 3 3 3 3 3 3 3 3
Smoked sheet Channel black Zinc oxide Sulfur Stearic acid Pine tar Captax Clay Whole-tire reclaim Diphenylamine
4 1
... ... ...
4
1
... ... ...
393
4 1 40
... ...
KO.5 100
4
42l/i 5 3 3 4
...
...
...
1
1
20
1
...
The stripe on the left were subjected to 100 per cent elongation for 3 hours, at the end of which time they were loosened from the upper beam and allowed to hang free while the test was continued on the other four strips. After 6 hours the stripe under a maximum elongation of 75 per cent mere in a condition similar to those which were messed a t 100 per cent maximum elongation and loosened after 3 hours. The strips which were flexed a t only 50 per cent elongation were still in xrery good condition, T o obtain flex cracks on the two strips
shown a t the right, i t mould have been necessary to run t h e test 10 to 12 hours longer. Effect of Increased Pigmentation
Figure 3 shows the effect of increased pigmentation. The three strips a t the left contain 421/2 pounds of channel black and are of the same stock used in the preceding test. T h e three strips at the right are identical, except that 50 pounds of channel black to 100 pounds of rubber were used (Formula 2 ) . The detrimental effect of the increased pigmentation is very evident, and this is one of the reasons why more carbon black on the rubber is not used commercially. Effect of Adding Filler Pigment and Reclaim
The results of the third test (Figure 4) illustrate the effect of adding to a tread stock filler pigment and reclaim, respectively. A t present quotations whole-tire reclaim and the better grades of clay are about identical in cost on a volume basis. Although clay costs less than reclaim on a pound basis, the gravity of this material is twice that of whole-tire reclaim. Formula 1 was again taken as the basis of the test, and the strip on the left is the compound to which 40 pounds of clay have been added. The middle strip is from a compound made u p b y adding 20 pounds of whole-tire reclaim to Formula 1 (Sos. 3 and 4 in table). The volume costs on compounds 3 and 4 are identical and are about 10 per cent cheaper than that of the control, Formula 1. After 1 hour of flexing the clay stock was in very poor condition and was loosened from the upper beam, and the test continued on the other two stocks. After 2 hours the stock containing the reclaim began to shon- serious checking, and so the test was stopped. The control stock on the right showed only a very few niinor checks. Effect of Adding Diphenylamine t o Stock
Figure 5 shows the effect on flex checking of adding 1 per cent diphenylamine to the control stock. The new formula is Formula 5 . The beneficial effect of this aniine is outstanding and would be of considerable coinniercial importance, except for the fact that other materials are available on the niarket d i i c h ha\ e tlie same property and other desirable properties as well. dinong these materials are many of the antioxidants. Comparison with Other Flex-Testing Machines
Several other flex-testing machine6 have been designed, and one which is highly regarded is the so-called India machine
A S d L Y l ' I C A L EDITIOS
394
( 2 ) . This machine consists of a rotating disk inside of an off-center ring. I n the rotating disk are cut radial slots in which specially cured test samples are inserted. As the disk rotates the free end of each test strip is bent down so that its plane is at approximately a 90-degree angle to the plane of that part of the strip which is secured in the radial slot. In comparing the two machines, several desirable features are evident in the Firestone machine. With this machine it is possible to evaluate the flex-checking resistance of any stock from which a dumb-bell strip may be cut. This makes the machine valuable t o compounders who are working with stocks that are air-cured. The conditions of test niay be varied so as to simulate any stressing condition desired. Furthermore, all types of stocks may be tested, as the resist-
Yol. 2 ,
so. 4
ance to abrasion of the stock does not enter into the test a t all. The machine flexes the strips to a definite elongation and therefore the rigidity of the test strip in no wise affects the working elongation. Also, this machine can be mounted in the direct sunlight and run under conditions which are very comparable t o actual road test, a feature which recent experience has shown to be highly desirable. Furthermore, the niachine is small enough so that it can be encased and flexing determinations made a t higher or lower than normal temperatures. Literature Cited (1) International Critical Tables, Vol. 11, p. 269. (2) Torrance and Peterson, India Rubber World, 8 , 6 2 (1929)
Separation of Alkyl and Aryl Halogen' A Modification of the Stepanow Method, with Particular Reference to the Analysis of Certain Insecticides Quick Landis? and H. J. Wichmann FOOD,D R C G ,A N D INSECTICIDE ADMIXISTRATION, SAN FRASCISCO, CALIF
The Stepanow method for organic halogen is modiset-up is required. Tlie Asfied (Method 1) by refluxing with a ten to fifteen fold tance and increase in sociation of Official dgriculexcess of sodium in kerosene or xylene and a few cubic the use of insecticides tural Chemists ( I C ) has decentimeters of amyl alcohol. Benzenoid halogen is containing chlorinated hydroveloped a method, applied reported t o be completely decomposed by this procarbons bring with them the principally to carbon tetracedure. Aliphatic halogen in the presence of aryl is desirability of d eve1 o p i n g c h l o r i d e and t r i c h l o r o determined (Method 2) by decomposition in kerosene methane, in which the comsimplified methods for the solution with butanolic potash at 110" C . ; in the case pound is heated under presa n a l y s i s of such mixtures. of volatile compounds the reacting mixture is covered Sprays frequently c o n t a i n sure to 100" C. with methwith a layer of solvent to prevent the escape of vapors anolic potash, using pressure carbon tetrachloride or p-dibefore decomposition. Total halogen is in this case bottles. Francois ( 1 2 ) has chlorobenzene or both, and determined by Method 2 followed by Method 1, using, thus the problem becomes recently reported good results however, a twenty to twenty-five fold excess of sodium. essentially the determination in the case of carbon tetraAnalytical data are presented to show that the method of alkyl chlorine in the preschloride by refluxing the cornis probably generally applicable. ence of aryl chlorine. Alpound with ethanolic potash though methods for the deunder a trap of glass beads. termynation of the two compounds separately h a r e been de- The writers, working independently, were ;nahG to obtain scribed, some of them require special apparatus or reagents, complete recovery by this means, even when a slow counterand do not appear to be suited t o the separation of the two current of solvent down the condenser was used. The "overlaying" procedure described below seems, however, to be effecconstituents. tive in preventing the escape of the volatile compound. Review of Methods ~PECIAL !lhrHoDs-Krishna and Swarup (16)have adapted GENERALRIETHoDs-The ultimate standard for halogen Kus's iodine method (1) to the determination of certain lidetermination is the Carius method, but many laboratories able halogens such as occur in acyl chlorides and chloramines, do not possess the equipment required for heating under pres- involving decomposition in alkaline solution. The separasure. The Parr bomb ignition Kith sodium peroxide and tion of p-dichlorobenzene from certain other halogenated comstarch has been adapted t o halogen determination ( I ? ) in- pounds by fractional distillation has been described by several cluding fluorine ( I S ) . Rlarcusson and Doscher (20) ignite investigators (6,12, 14). The authors were able to detect as the compound in a n atmosphere of oxygen and subsequently little as 2 per cent p-dichlorobenzene in a kerosene insecticide absorb the inorganic halide in alkali. R h e n liquid ammonia by suitable fractionation followed by the chilling of the 165is available the halogen compound may be determined ac- 175" C. fraction to - 10" C., but failed in the case of a solvent cording t o Clifford (4) or Dains and Brewster ( 7 ) by decom- naphtha preparation, the amount of petroleum hydrocarbon position with sodium. Several investigators have described distilling with the halogenated one being too great to permit methods involving catalytic reduction with various metals and separation of the latter. Cappenberg (3) has described a hydrazine (2, I S , 25'). Stepanom (26) has described a general method suitable in certain cases in which the compound is method based upon the action of a twenty-five fold excess of decomposed by potassium hydroxide in methanolic solution. sodium upon the compound in ethyl alcohol solution. Principles Involved VOLATILECovpoums-The combustion method of PlimpOf the above listed methods that of Stepanow, in conjuncton and Graves (24) appears to be well adapted to the treatment of volatile compounds, although a rather elaborate tion with the A. 0.A. C. alcoholic potash saponification, appeared to offer the most promise. A large number of trials 1 Received June 4, 1930. of various modifications finally led to the development of the Present address, The Fleischmann Laboratories, N e w York. N. Y.
HE g r o w i n g i m p o r -
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