1096
I N D U S T R I A L A N D E N G I K E E R I NG C H E M I S T R Y Fichter and Becker, Ber., 44,3473 (1911). Fichter, Steiger, and Stanisch, VeThand. Natur. Gesell. Basel, 28,66 (1917).
Isambert, Compt. rend., 92, 919 (1881). Krase, H.J., Gaddy, V. L., and Clark, K. G., IND. ENG.CHEY., 22, 289 (1930).
Krase, H. J., and Gaddy, V. L., J. Am. Chem. Soc., 52, 3088 (1930).
Krase, N. W., and Gaddy, V. L., J. IND.ESG. CHEY.,14, 611 (1922).
Vol. 25, No. 10
Lewis and Burrows, J. Am. Chem. Soc., 34, 151.5 (1912). Matignon and Frejacques, Bull. SOC. chim.,31, 394 (1922). Matignon and Frejacques, Compt. rend., 171, 1003 (1920). Matignon and Frejacques. Ibid., 174,455 (1922); Ann. chim., 17,257 (1922). (15) Neumann and Sonntag, 2.Elektrochem.,37,807 (1931). (16) Unpublished results a t Fixed Nitrogen Research Laboratory. (17) Yakovkin, J . Applied Chemistry (U. S . S . R.), 1, 69 (1928).
(11) (12) (13) (14)
RECEIVED April 29, 1933.
Effect of Temperature on Tensile Properties of Vulcanized Rubber A. A. SOMERVILLE AND W. F. RUSSELL,R. T.
T
HE amount of published d a t a on t h e physical properties of vulcanized rubber a t widely different temperatures is meager considering the wide range of temperatures over which rubber products are expected to give service. Temperature v a r i a t i o n s d u e t o seasonal causes alone are large, but these may be g r e a t l y accentuated in rubber articles such as tires, tubes, f a n b e l t s , and motor mounts, by severe conditions of s e r v i c e . An u n d e r standing of t h e b e h a v i o r of vulcanized r u b b e r a t wid e 1y different temperatures, and particularly a t high temperatures, is therefore b e c o m i n g more and more essential for the development of suitable compounds for rubber particles that must withstand large temperature variations.
Vanderbilt Company, Inc., N e w York,
The tensile properties and tear resistance of a large number of commercial inner tubes, before and after aging by different methods, are studied at 0", 25", and 100" C. A number of uncured bus-truck tube stocks are also studied f r o m the point of view of their capacity to withstand high temperatures. T h e effect of testing rubber at 100" C. as compared with room temperature is discussed; how some compounds collapse at 100" C., while olhers have tensile properties equal to, or better than those at 25", is shown. The effect of testing artificially aged specimens at 100" C., as well as at 25" C., is discussed; ihe high-temperature test m a y reveal conditions qf deterioration and overcure that are not noticeable in the 25' tests. The compounding and curing conditions that lead to high tensile properties at 100" C., as well as those which cause inferior quality, are discussed.
PREVIOUS WORK A report in 1926 by van Rossem and van der Meijden (3) on the influence of high temperatures on the stress-strain curve of vulcanized rubber was the first systematic attack upon this problem. These investigators did not use commercial compounds but a pure gum mix (92.5 rubber, 7.5 sulfur by weight). Tests were made a t temperatures from 24" to 147" C. It was found that, as the temperature increased, the stress-strain curve shifted progressively toward the elongation axis-i. e., the rubber softened; that the amount of shift was further influenced by the degree of vulcanization and the time of heating; that the tensile strength reached a maximum a t about 70" C. and then decreased; that higher temperatures imparted brittleness to the rubber, which disappeared on cooling-i. e., was not apparent in room temperature tests; and that the brittleness appeared in cures with high vulcanization coefficients sooner than in those with low coefficients. The authors suggested that high-temperature testing might be considered as a method of artificial aging. A further communication in 1927 by the same authors (4) deals with changes in the stress-strain curve, hardness, and plasticity of vulcanized rubber heated up to 147" C. Breuil ( I ) in 1910 gave data on four compounds (including ebonite) over a range of -10' to +loo" C. Le Blanc and
N. Y.
Kroeger ( 2 ) in 1926 gave some data on the effect of low temp e r a t u r e s , chiefly on rubbersulfur mixes, and concluded that the presence of organic accelerators did not m a t e r i a l l y affect their results. The 1J. S.Bureau of Standards (6) in 1928 published data giving physical t e s t s on six different types of rubber compounds a t temperatures f r o m -70" t o f147" C. The results showed that a t very low temperatures the specimens became rigid, with greatly increased tensile strength which gradually decreased with rising temperature until, at 147" C., it became practically negligible. All six compounds showed the same type of behavior, and it was concluded that the differences due to compounding ing r e d i e n t s were differences in degree rather than in kind. In 1928 Sornerville and Cope ( 5 ) published results on the effect of temperature on the stress-strain properties of several different types of laboratory compounds. It was shown that wide variations appeared in the stress-strain curves of the same stock a t different temperatures; that there was a progressive drop in the stress values as the temperature was raised from 0" to 100" C.; that the amount of sulfur used was a factor in the stress-strain relationship a t different temperatures; that the stress-strain properties a t different temperatures varied for different rubbers; that the state of cure caused a wide variation in tests at different temperatures; that successive stretchings of the same specimen caused large decreases in the stress after the first or second cycle; that stripping tests on frictions showed much lower strength a t 100" than a t 0" C.; and that overcures were indicated prominently a t 100" C. by shortness and low tensile, whereas a t room temperatures this shortness might remain concealed. These results were limited by the dimensions of the teniperature control chamber attached to the testing machine, which permitted tests only up to 500 per cent elongation. Since then the tester has been equipped with a 48-inch tank which allows test pieces to be stretched at the desired temperature to rupture, so that complete stress-strain data and ultimate tensiles can be obtained.
otlier haial, if tlie coinpourids nrc teated at liigli tenprriLtmrv and f i n d to ljc rensonably strolig am11firm, particuInrly after aging, it. may be assiiiritd t.llat,, when t,Iie tirc he~ o n i e shot, the rulrlier in the cnreass will coiitinue t o perform t.orily it.; proper hinctioir during service. 011the
Figure 1 s h o w tlic Scott test,er with tlrc r x v tmni control tank att,ached. The rcctangnliir tank has dinicnsions of about 7 (front,) x 0 (side) X about 48 iiicliiw, a i d is cquiiqied in> the bottoni witli :i
coiieideratims apply to tillies; tire main tuhe is .;iipijortcd and kept from rupture Hcnct! a tulle that has softened from oiiretitncs coiit,inire to perfom, its oflice Exterrmlly the tank is t!quipi"l front and back with loiig, of lidding air as long as tlic tire is good. More frequmtly, wire-glass wiiidows wliiolr permit rloiigatbiri iiieasuremeiits t,o liinvewr, it will tliirr out on softening and cliafr tlirougli :it l i e ma*lr ill the usual way: a lringcil porthole door is locatcrl mire rongli spot in tire casing. Moreover, tulres in this co~rt i n the front at. the bottom for clearring puryroses and the 1'ditirm arc iiseh:ss ~ n c they e are renioved from tiic tire because rnural of liroken tcst pieces. Int,erriirlly the tank is divided t,liey c m t i o t be rcinsertcd witliailt, bnckliiig. In ovcrhmtni loiigitudinally into three parnllel scetioris by means of two triick tires tnbcs ametirnes practically nielt a i d liecome iiipcrforated metal plates fitted into grooves, one on each side capal~leof holding air, so that a good easiiig may he ruined of the stretching rod. In tlie right-hand compartment a long lip a siiddcn let-down. &ring rod having two sets of small blade&', operated by a ' I h r c is an elenrent of 1Iiinia11risk irlvolved in tire u,~eof small motor and worm gear mounted tires and t,obes which sliouIcl render tire on the top of the tank, helps to keep study of tlieir behavior a t liigli temperauniform the tcnipiirature of the liquid tures a, matter of considerable imporin t.lie tank. These cornpartments can bance. Tha actual testingof the st,reiigtlr be packed with cracked ice wlicn t.estof tires at liiglier temperatures in tlre ing at, 0" C. is undertaken, t,he perforlaboratory is difiicnlt and thus far has ated plates prevcnting the ice fmm obbeen best, ai:groaclied through frictioliscuring the descent of the s t r e t c h i n g Somerville and Cope rod aiid t l i e r e a d i n g of elongat,inn j liavc already report,ed in similar tests rneasurerrients. on I'eltiiig that t i r e friction pull at. 100" Two electric immersion heaters at the ('. \!'as about Iidf of that finind at 0". Imttom of the tank keep the liquid at 1 iilies, OIL tlie other hand, are easy tu tire temperature desired. For temperaiecause they are of suitable t,lrickt,urt?s u p to 100" C. water is the best nd can he readily cut into the ordili+ii(l; for ternperattires almve 100" C. dumb-bell test pieces of the proper glycerol, on account of its negligible shape and dimensians. action on rubber, has proved to he a The fact that tubes are expoaid to conveiiirnt maliiim. iixidizing conditions as well as heat adds importarree to the study of aging in relaON C U ~ ~ E I I I~N IK A r x tLTUIJM tion to higlr-temperature testing. Practically no &ita I i n w been pubI n order to study the behavior of inner lisircd on tlie pliysicnl properties of D ~ I t,iilres under a fairiy wide spread of tem. rnercial riibher :irticlt~sa t high tenipcraperature corrditions, t.liis laboratory retures. It is ~vcllk m w n tliat aotoinolrile cently i~urclrased on bhc open niarkct passenger car inner t,olies of practically tires aiid tulies :ire f r e i j n ~ n t l ysubjeet,ed t,ii crt,renic t o m p all tile availaiile rriakcs. These tubes nger tires iiiny reach 70" to were sntijccted to t i 100' C. iii hot rveatlier, while large busarid 100" C., covcririg tensile pri>pcrt.ies truck tires frecjneiitly reach and reiiinin Iiefore arid after aging in the air bornlr, oxygen bomb, and Gerr oven, tear resistat, vulcanizing te~npr!raiiires for coiisiiierahle periods. ance before and after aging, and perrnaNois-outs occur triost c,oninimly i n ncnt set at 0" arid 100' C. In view hot w d i e r xiid i ~ r eattributed eit,licr to the large nirrnlier of tabes tested, it was tires lioiirg worir too kir into tlrc onrcwss found iinpassilile to give all the results or to nioahitniaal ( I d ( liere, so that oiily those pertaining t,o if the tiro is relatively unworu. It is large-sized passenger car t.ubes (6.50 x gemrally understood that tile nibiier ill 17 bo 7.50 X 17 incliesj are eliuwn. The crms to insnlat,e tlie fabric data obt,ained at 70" are omitted so as cords and plies froiii one nnot,lier, as well not to complicate the graphs witli too bond these into a flexible, solid iriany poirits. The resulds arc given in If at higher t e m p c r a tu r c s the graphical forni arid witisout identificar bcaiincs short and xeak, it is tion. Each tube has a niirrilii~r,arid airy probable that the insulating function of manufacturer desiring to irlmitify iris own the rihber rnay gradually be destroyed tuhe will he so advised upon request. by constant. flexing, thus a l l o w i n g a. TESS~LE STELEKUTH. Figure 2 slro~ss separat,ion to start, tlia the tensile strcrigt,li nf nineteen largerimxiit in a l,lorr.-oiit. I sized passenger car tubes at O", 25', and 100" C. TIie leibgtli of eaeli vertical h e shows the drop in tensile strength Lieperatnres arc more or Icss ineaninglcas tween 0" and 100". The tubes are ar(IOT1' .r,,:s,.,s,% , ~ l TT f, 8 s far as tire perforznanc(~ is mneerned. ranged in the order of ascending 25" (:o\?.nO,. l
