INDUSTRIAL AND ENGINEERING CHEMISTRY
960
a t 80 ' C. for 1hour in 250 ml. of dry, thiophene-free benzene. Benzoyl peroxide (0.5 mole %) mas used as catalyst. The product was collected on a filter and dried t o constant weight undcr a vacuum on the steam bath. The yield of copolymer n-as 17.2 grams or 85Yc of theoretical. .Iceording to reports in the literature ( 1 9 ) )this method of preparation probably gives a copolynic~i. having a 1 to 1 ratio of nioiioniers in the chain. The poir-i.1er.y copolymer was molded into a solid, transparent, hrittlrl disk with a density d i i of 1.286 and a refractive index nzi of 1.564 60.002. These values give a n observed unit refractivity 01 51.25 (calculated for the 1 to 1 copolymer, 51.29). An elcctrometric titration of this coplymer gave a neutral equivalmt oi 100, 103 (calculated for the 1 to 1 copolymer, 101). LITERATURE CITED 11)
Brubaker, J I . .\I. (to Du Pont Co.) U. S. Patent 2 , 3 9 3 , 9 0 i
(Feb. 5 , 1946). ( 2 ) Brubaker, XI. AI., and Hanford, IT. E., I b i d . , 2,100,099 (May 14,
1946). 13) Carbide & Carbon Chemicals Corp., "F?nylite Polyrinyl .Icetart, Resins", p. 4 (1913) : "Vinylite Resins", p. 18 (1942). (4) Carothers, W. H.. Williams, I.. Collins. d.J I . , and.Kirby, J. E.. J . Am. Chem. Soc.. 53. 4203 11931). 15) Dogadkin, B. d.,Sandomirskii, D. M,,and Sharkel-ich, P.. Colloid J . (U.S.S.R.), 6, 199 (1940). 16) Du Pant Co.. "Du Pont Plastics". 1943. ~I
Vol. 38, No. 9
I'ordyce, It., Lorell, E;. L., and Hibbert, H., J . Am. C'hem. ,bur 61, 1905 (1939). H a h n , F. C., Macht, .\I. L., and F l e t r h e r , D. A , , ISD. I.:YG, CHEM.,37, 526 (1945). Jones, H. C., Ibid., 32, 331 (1940). Klatte, F., and Rollett, 1.(to Chemische Fabrik Greish. I I I P Clektron), U. 9 . 1,241,735 (Oct. 2 , 1917). SI(,Phemon,-1.T., Bur. Sta7icZai~dsJ . Research, 8 , 751 (19.32~. IIcPherson, -1.T., and Cummings, -1.D., I b i d . , 14, 55:3 (lW5 Marvel. C. S.. arid Hornung, E. C., in Gilrnaii's "Organic C'lieniistry", 2nd ed.; p. 7 5 7 . Sew York. ,John JViley d Sori> Inc.. 1943. l l e n d . D. J . , arid Fuon,, I!. 11.. J . A m . C'hem. Soc., 63, (19411.
S1ons:into Clieniiral ( ' o . , "The Family of 11ons:into Plastictn' pi). 12-13 (1943): Dow Cheniiral Co., "Styron (Dow Polyntyrene)", 1942: Catalin Corp., "Laolin, a Perfected PolyStyIene", 1941. J l o r g a n , G., JIegsoii, K. J. L., and Pepper. K. JT., Chenaistru & I J d u s f r u ,57, 669 (1938). Plastics Catalog Corp., "Plastics Catalog", 1916. Ileinliardt, R. C.. ISD. EKG.C H E W . , 35, 422 (1913). Staudiiiger, H., "Die liochmolekularen organischen T.'erhindur~gen". p. 164, Berlin, Julius Springer, 1932. Sraudinger, H.. Geiger, E., H u h e r , E.. Schanl, IT., and Scliwalbarli, -1.. Helt. C'hina. A c t a , 13, 1331 (1930). Stnudinger, H . , and Urech. E., Ibid.. 12, 1107 (1929). Strain. 11. E., Kelley, It. G., and Dittniar, H . R., ISD. 1.:sc2 CHEM., 31, 352 (1939). Whitby, G. 8.. a n d Katz, l f . , Ibid., 25, 1338 (19333). Wood. L. -1.. U . S . Dept. Comniei.cc C'irc. C424 (1940)
PROPERTIES OF LACTOPRENE EV T. J. DIETZ, W. C. I I I S T , R. L. DEdN, AND C. H. FISHER
.
Eastern Regional Research Laboratory, C S. Deppartment of Agriculture, Philadelphia 18, Pa. hrilling characteristics and ph?sicaY properties of' a \ ulcanizable copolymer of %yo ethyl acrjlate and 5 % chloroethyl tiny1 ether (Lactoprene E\ ) h a l e been inFestigated. The pol) mer does not require preliminar) hreahdow n or1 the mill and, when properly fornlulated, the stock m a j be compounded without difficult?. Tensile properties of lactoprene vulcanirates are well abote a serticeable minimum, but the cured product exhibits low resilience on the formulations studied. In the field of specialty rubber$, the product possesses two outstanding propertie-resist ance to oils and to dry heat. In its resistance to organic solvents, Lactoprene EV compares falorabl? with butadiene-acrylonitrile copoljmers. The heat resistance of the vulcanized polymer is markedly superior t o that of any of the present diene sjnthetirs.
-
0
I
S recent years t,he development of synthetic rubber6 hac progressed along many lines which have produced useful rubberlike polymers of widely divergent properties. As technological requirements became more stringent, the specialty rubbers, whose exceptional properties made them valuable for ~ p o cific applications, were demanded. A recently developed specialty rubber with new properties i. the polyacrylic elastomer. Early work on the development oi vulcanizable pol-acrylic resins Tvas first reported by Fisher and eo-workers in 1944 (1). The generic name "lactoprene" T W P proposed for acrylic esters copolymerized Lvith small amounts of a polyfunctional monomer. Shortly thereafter it was demonstrated that saturated copolymers of ethyl acrylate and halogen-cont,aining acrylic derivatives could be vulcanized n-ith the aid of suitable curing agents (8). One of these, Lactoprene EV, a copolymer of 95% ethyl acrylatr,
xid 5:; chlorocthyl vinyl ethcr, has since been studied erteii-ir-ely; the results are reported in this paper. The compounding recipes tested are merely suggestive, and only one loading, 50 parts SRF black, was used. Furthermore. no attempt n-as made to improve the resilience of the vulcanizatcis hy the addition of plasticizers. These limitations on compounding ingredients vere exercised to demonstrate the basic propert i w of the rubber. Data on compounding and curing characteristics, as ne11 a:: stress-strain properties of Lactoprene ET, are given. In addition, the effect of solvents, steam, and dry heat are discussed. COMPOUh-DING
The milling characteristics of acrylic polymer differ markedly I'rom those of natural rubber and of the butadiene copolymer typtof synthetic rubber. The ethyl acrylate polymer bands readily \\-lien placed on the compounding mill, and no initial brcakdowri i': required. The crude polymer is plastic even on a cold mill, and tlierc is a strong tendency for the stock to adhere to both roll? iintil the filler has been incorporated. Furthermore, unless a *uitable release agent, such as stearic acid, is included in the coni-pounding formula, the stock adheres to the back roll throughout the process. One or two parts of stearic acid per 100 parts of polymer are usually sufficient to cause the stock to cling to the, front roll. Formerly, it ryas customary in this laboratory to compound the acrylic polymers on a cold mill to reduce the tendency of the stock to adhere to both rolls. I n a felv cases the data to be presented were obtained ir-ith vulcanizates compounded o n cold rolls. The effect of milling on the intrinsic viscosity of the ra\\ polymer is shown in Figure 1. .4 cold, tight 0 X 12 inch lahoratory mill complying with requirements of tlic rlmerican Society for Testing Materials (Dl5-21) \vas used; samples of the batrii
September, 1946
'T(iR1.E
INDUSTRIAL AND ENGINEERING CHEMISTRY
1. R E P R E - E X T ~ T ICVOEV P O L S D I V C FOR\fVL.iS 77 TTH L 4 C T O P R E I E ET
Forniu1,i t'uljnier G1.57 Red lead Zinc oxide Stearic acid p-Quinone dioxime ( G U F Tetramethvithiurani morro~ulfidr Triethylenetetramine Trimrne Bnsr
FOR 1-9E
B
.i 100
c' IO0
100 10 5
3
1
2 1
9
961
does not require premastication, it is well suited to compounding in a Banbury mixer. If this 1s done, the stock remains on the front roll and is released without difficulty. Whenever possible, the authors employ the master batch technique in compounding lactoprene. I t is possible to utilize higher temperatures in incorporating the black, and the over-all mixing schedule is shortened. As a consequence, breakdown of the stock appears to be materially reduced.
&ifur
< R F hlack
ivere removed at intervals and dissolved in toluene (0.05 gram u i polymer per 100 ml. of solvent). Viscosity measurements n-ere made in a modified Ostvald viscometer a t 25" C. ( 7 ) . rls Figure 1 shoas, the polymer is exceptionally sensitive to mechanical hreakdown when masticated on a cold mill. For this reason the milling procedure was modified so that present laboratory technique on 6 X 12 inch rolls approximates that, recommended by the Rubber Reserve Company for GR-8, * w e p t for the following. The preliminary breakdown is omit'ted. and roll temperature is adjusted between 140" and 160" F. at the !wginning. S o cooling water is circulated, and the temperature is r)c,rmitted t o drift. K h e n first banded on the warm mill, the polymer tends t o split and adhere to both rolls. Addition of filler is begun immediately. Csually the filler is an S R F black t o which has been added the stearic acid called for in the formula. Hy the time half the carbon black-stearic acid mixture has been .Idded, the stock is clinging tightly to the front' roll, and a smooth rolling bank is formed. At this point it is customary to make one , cut from each side holding the stock until the bank disap~it~;trs. The remainder of the black-stearic acid mixture is added, cut is made from each side. LTsually n-hen 30 .tnd again a parts of black per 100 of polymer are required, 1 part of stearic ,tcid is sufficient as a release agent. If 50 parts of black are used, 2 parts of stearic acid may be preferred. The vulcanizing agent.* . ~ i i dother ingredients are quickly added after the incorporation < i t filler. The stock is cut and lapped so that there are three 34!' ,.tits from each side; then the stock is rolled and pz rtirough themillsix times. It is then sheeted to the desired tliickness and allowed to cool, The temperature of the stock removed lrom the mill is of the order of 175" to 18.3" F. The sheeted stock I S comparatively smooth and glossy, and shrinkage is of the order ' I f 33';. cuts The stock adheres firmly to the front roll until the first : i w made and it is difficult to make these first cuts without momcntarily stopping the mill. However, this difficulty may be obviated if the compounder prepares a master batch of the polymer, carbon black, and stearic acid as a leader. Since lactoprenc
IO
20
40
30 MILLING
50
60
TIM, MIN.
Figure 1. Change of Intrinsic Viscosity of Lactoprene E\ with Time of IIilling on Cold Rolls
{
Roll Mill Cumpounding method Stock number ES 767 ES 768 E8 769 Formula A €3 c Cumulative niixine time. min. 0.3 0.5 0.5 To band 1 1 1 Black started 10.5 10.5 10.5 Black in 17.;7 21 Off mill 183 Slixing temperature: F. 150 150 Front roll, start, 150 Hark roll, start, 150 150 I50 192 194 189 Batch, finish Plasticity, mm.b 8.2 8.2 8.2 Raw 7.5 8.5 7.9 Compounded \rill shrinkage, % 29.2 21.8 33.3 6 minutes required for master batch. 4 Williams, 5 kg., 10 minutes a t 158' F.
Banbury JIaster Batcli E S 771 ES 772 E9 773 \ R C 6.5"
6.5O
6.5" 6,ja 6 . 5 " 22..i 17.5 6.5in
150 150 175
8.2 7.6
34.4
150 150
175
8.2 7.4 29.2
6.3"
6.sa 6 5(' 14.5
I30 150 183
8 2
7.2 27 1
The temperature of the Banbury mixer is maintaiwd at 200" t o 210" F. merely because the equipment is designed for use with .team at, atmospheric pressure. During mixing the actual temperature of the stock rises t o 350" F., as .measured by a needle type pyrometer. Higher mixing temperatures have not been c q l o r e d , but it, is expected that they can be employed without serious thermal decomposition. Three representative compounds of Lactoprene EV were prepared by the open mill and the master batch procedures suggested above. Test formulas A , B, and C are listed in Table I. Formulas 4 and C are basically similar except that A includes the accelerator Trimene Base (triethyltrimethylenetriamine) to re11uw the curing time. Formula B is a nonsulfur recipe which tends to produce a tight, cure. Formula *4 is considered to be a general purpose recipe; the others are included to shoiv the effwt of formulation on specific propert,ies of vulcanizates. Processing characteristics of the three stocks (Table 11) are w r h that the polymer bands readily on the mill and no breakcion-n is required: thus the incorporation of carbon black may be begun immediately. The time required for milling in the black k somewhat ehorter than that required for other synthetic elastomers. Furthermore, the over-all milling t'ime is comparatively short. The temperature of Lactoprene EV stocks tends to run high during compounding. High milling temperatures serve t o plasticize the polymer and thus improve processability. Killiams plasticity values for these three stocks are also shon-n in Table 11, The plasticity t,ests were performed a t 70" C. under *tandard conditions, according t o specification D-2 for Governmcnt Synthetic Rubbers, .July 1, 1916. 4 s determined by a recrimmended method (.,:-
N-ALCOHOL
Figure 4. \-olume Increase of Lactoprene EV in Yormal klcohols
prene EV compares favorably in volume increase and retention 1 1 1 physical properties with the Hycar and Perbunan stocks. The effect of steam on dimensional stability and physical proilerties of lactoprene vulcanizates is also shoxn in Table J-. Iniprovement in steam and water resistance may be expected from the use of plasticizers or metal oxide loading; experiments art. still in progress and results arr riot available at this time. d.S.T.M. method R, designation D471-43T, was also used i ( J r a simplified evaluation of solvent re ancc. Essentially, tlik method consists in measuring the extension of 100 X 1.6 x 1.R mm. specimens immersed in the test solvent for 3 days. Tht, volume increase, AT, is e x p r e w d as fiinction of change i n 11mgtl1, AL ( 2 ) . Psing this method, the sw-elling of several oil-resistant synthetic rubbers in standard reference fluids v a s measured, and thr results are shown in Tahle 1-1. The heptane and toluc11t4c~p-
P a.;.-
=:;
--d
TABLE 1.1. CO?JPARISOS O F PERCESTAGE INCREASE IX v O L T \ I E OF REPRE~ESTATIVE SYNTHETIC RUBBERS WITH LACTOPRESF. AFTER 3 D A Y S ' IMMERSIOK A T R O O M TE1IPER;ITURE'' .
Circo Light Process Oil SR-10 0 0 0 0
5:
$arr.ple Thiokol ST Thiokol FA Seoprene 11095-8>
8 Prrhunan 26. 8926-1 3 Perbunan 18, 8925-2 9 Hycar OR-15, 1275HCR-138 0 H j c a r OR-25, 1275HCR-128 0
19 12
21 0 3
SR-6 Heptane 12 3 il l!O
n2
SZ
17 28
3 21 12
22 1.5 6.1
50% Heptane. 50% Toluene. hy Vol.
17 19 140 68 105 ~~
26
44
T.actoprene ET 2081 60/50b 0 1.; 37 1.5 42 n Method of Garvey (21. deaipnation D471-43T, method B. b After immersion in Circo light process oil for 3 days a t 212O F.. ttir volume increase was 3 7 , .
VOLUME INCREASE O F L.4CTOPRENE EV, G-137 IMMERSED FOR 7 2 HOVRS AT 77" F. IN \7.%RIol-S HYDRoChRBOSS
TABLE1.11, (2169). Solvent dkellysolve 15 Skellj-solve C Skellysolve F Skellysolve L Hexane Heptane
Volume Increase, 5 7'. 6 6.1 6.1
3.0
t5
Solvent Benzene Toluene Ethg-lbenzene Diisopropylhenzene Triisopropylbenzene
Volurlie Increase, I 413.1
333.1 287.0 24.2 0
;
INDUSTRIAL AND ENGINEERING CHEMISTRY
September, 1946
965
t u l e mixtures are included as checks on the SR-10 and SR-6,respectively. The Lactoprene ET' stock (2081) used in this test was compounded and cured ai follo\~-s: Lactoprene ET', G-157, 100: litharge, 8; nccclcrator 805, 3; and SIlF black, 50; cured, 60 minutes at W '208' F. The results show that Lartoz prcne E V compares favorably in diP inclnsional stability v i t h the other oil. w 3001 tnnt rubbers tested. The nooprene 'ample was a laboratory composition 220iiiid does not necesarily reprewnt a I ~v)nimc~rci:il product. 0 100 200 300 400 500 600 700 BOO 100 200 300 400 50C 0 The uystem toliiene-heptane ivas inAGING IN AIR AT 300'F., HRS. AGING I N A I R AT 300'E,HR5. vcstigated more fully, and the results are shown in Figure 3. Compounding and curing data on the test' specimen,* (ES 778) are given in Tables IT' and \'. The marked effect of aromatic hydrocarI bons on the type of acrylic polymer dlb016di \ scribed is obvious. Perhaps it i i ot Figure 3. ElTecL o f interest that the logarithm of volunio 4giiig in \ir at 300' F. incwase 11s. concentration by tveight on Teniile Properties of Three Lactoprelie ~)ftoluetiein thc toluene-heptane misturr Stocks yields a str:iight-line plot. ;ill point.. *. - A . L a c t o p r e n e EV, No. 214i with the possible exception of the low,qt. B . L a c t o p r e n e EV, No. 2148 are equilibrium values. Additional data C. L a c t o p r e n e EV, ES 771 :NGAWCN , *,-, , , ' * *-. -u n the s i d l i n g of Lactoprene ET' in various hydrocarbons are shown in Table 2 VII. -4s expected, the volume increase in aromatic hydrocarbons is large, and that 0 100 200 300 400 500 600 700 BOO 900 in the paraffinic hydrocarbons is ex4GING IN AIR AT 300.6, HRS. cseptionally small. The benzene, toluene, ethylbenzene, iaopropylbenzcmr series is of some interest. I n the ljrcxstias been demonstrated, for csaniple, CJII heat-resistant stock> ence of sufficiently bulky side groups the. .-\vLilliiig eftttiat ot t l ~ t , based on a 50-50 mixture of Hycar OR-15 and Perbunan (9), on aromatic nucleus is completely lost. GR-S compounds (3, 6,I I ) , on Butyl rubber ( i ) and , others. The s d l i n g of Lactoprene ET' for 3 days a t 77" F. in various I n a recent report on the relaxation of synthetic rubbers ( I O ) at alcohols is shown in Figure 4 and Table T I I I . 111the normal alelevated temperatures, Mesrobian and Tobolsky postulated that cohol series the swelling is inversely related to the number of the presence of double bonds or methyl groups in the polymer rarbon atoms, ending with ndecanol which produces no apparent chain tends to favor degradation. They reported that ester effect, Branched-chain alcohols cause greater swelling, as shown groups in the polymer chain, on the other hand, appear to be with 4-, 6-, and 8-carbon alcohols (Table VIII). Cellosolves responsible for improved heat resistance. D a t a on the heat rewild Carbitol also cause marked sn-elling of the vulcanizate. sist,ance of lactoprene vulcanizates gRthered in this laboratory do HEAT RESISTANCE not contradict this view. Table IX shows heat aging results on a number of lactoprene The stability of Lactoprene E\- vulcanizates in the presence of compounds aged for 72 hours a t 300 F. in a mechanical convecdry heat is outstanding in comparison with that of natural rubtion oven with the ports open. All stocks in this group wercber and the butadiene copolymer type of synthetic rubber. Escompounded on a cold mill and cured for 120 minutes a t 312 ' F. cept for Butyl rubber, the susceptibility of the diene synthetics prior to aging. The aged tensile data are reported in preference to heat aging is believed to be related to their unsaturation. This to the unaged properties because they are more representative of the various compounds. The change in each of the properties listed which occurs as a result of heat aging is given in per cent. plus or minus. Test results are arranged in order of ascending
-
i
'\.-.
.-.-.-
-4.0
z
-3.0
6 2
-2.0 +'
- 1.0
B
- .o 4 61
0
100
200 AGING
300 ik
400 AIR
500 AT
300'F.,
600
700
800
I
300
HRS.
Figure 6. Effect of Aging i n Air a t 300" F. o n Hardness and Weight of Lactoprene EV, ES 771
.
TABLEVI111 T'OLUME ISCREA.SE O F L.4CTOPRENE EV, G-157 (2169) IMMERSED FOR 72 HOURSAT 77" F. I N \r.IRIOT JS ALCOHOLS Volume Increase, 5% 88.4 Ethanol 40.5 n-Propyl alcohol 38.6 n-Butyl alcohol 24.2 Isobutyl alcohol 33.1 lert-Butyl alcohol 72.8 n-Amyl alcohol 20.8 2-Methyl-1-pentanol 72.8 n-Hexanol 14.1 Cyclohexanol 10.8 Solvent
11ethanol
Solvent n-Octyl alcohol Capryl alcohol n-Decanol ,3-Chloroallyl alcohol 14-Dioxane l\iethyl Cellosolve E t h l i Cellosolve Isopropyl Celiosolve Butyl Cellosolve Phenyl Cellosolve
Volume Increase, % 3.0 12.5 0 553.9 417.8 220.8 2i2.1 137.9 81.6 333.1
Vol. 38, No. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
966
I
.. 1 I
1
1
I I
1
I I
l r i ~ i ~ i * ( , i i i : i ch:ingc g(~ of moduliic ; i t :300' i,hrng:it i o i i , 'l'liiin, ir:t,.tt'i.ibtii.h ~ I I Y , 4 i o \ \ - t i i t i Figiirc 2li. Pr(,biini;tt>ly, -I)c~cinit~ns on the left-hand side uf thc. table* wliosi, i ~ I i : i ~ i ipi i g iigc~iitis prrscwt i n tlie uiiiigtd vii1vaiiiz:itt. st] t h a t tiiiiduliis is negative exhibit other signs t r f r( riil~iiigcontiniics diiririg thc: heat :igirig period. This continunt i o t i of curv i.e'inltb in a stiff vulcaniz:itc' of high teiihil(' strength cliictiiin in tensile strength and hardiir.sq. ( t IIC, right, v h i d i develop a higher rnocliilii,~c i r i aging, csliihit : t i i t 1 mt,clulns and of Ion. e1ong:ition. Furthermow, ttica c i i d -titTc.ning aiid shortening. .-tcwk sllon-s I I O signs O F I ion w h e n aged for periods as long RP i r i rnoHt of thme tests only one iigiiig p S-10 hour,- at 300" F. I n this coditions of cure are c's:iggl,l~;ltrtltc1 tht, c~stentthat, the 300" 1'. was employed. However, in the c:ise ~ l stocks ' 2147 :ind silc strcmgth and elongation plot of the type of Figure j - 1 ) itre permanently di2148 longer aging periods \wre used to investigute thc trend oi for estremc periods of aging the stock is likely t.11bet o l r ~ i l cpropc>rties. ~ The per cent retc~ntion of tensile qtrengtli. iiltini:it(i i~longation, and modulus at 30OC; t.long:ition, :ir'i' Tliiis it i': possihlis, through thc propcr ee jrlottcd :ig:iiiist time of aging for stock 2147 iii Figure 5.1. Tile, iii?: torniiil:is, to produce a vulcmizate whi t c ~ t i * i l (4~ w n p t h falls off slowly with time, h i i t t i iaarly in the :igiiig period or resist this r C ~ I Y ~ : I W ~ rapidly to a minimum and then I -1.-might lie, espectrd, lieat resistant stocks of pi':ic+ic:il u t i l i t y t l i c > incidulus rises rapidly t o a maximum : i t i d then falls I)!? i'i)Ii1.:iIl wnic.\vliere lietween these two limits. -i-tt,iit \\-ith the reversion of tensile stwngtli. 'Tlitx moi;t heat resistant ,stock studied was ES 771 (Table 111). 1)isc~ussionis facilitatcd by dividing Figiirc 5.1 into t u ir pirl'igiii'c. 3(' sammarizes retention of tensile properties, in pcr cent, t i t I i i , * tiy the dotted linc, z-N'. For agiii :ig:ii:ist Iioiirs of csposure at 300" F. The effect of heat o n Durl(,tt of this diviiding linc, the tensile piv o i i i ( , t i - i , 1i:ii.iIiiCnh and specimen n-eight is shown in Figurr, 6. : I I , I L -ritistantially unimpaired. To the Material Spec8ific:ttion 3201 B for dry lipatl i o \ t i ~ \ . i ~the r, stock undergoes serioiis therni:il dccoriil)i)~iitioIi. ? ' l i t . Ac~t.ciiiuutic~:il ri,-i*t:irit i,titiher requires that :in acceptable stock rctain 40s; I.:sc*c,jit Tor rapid-curing stocks containing a large c~sciwof frcvb 1 1 1 i t - original t r n d c strength, 30r;, of its original (.longation, : i i i t i yulcariizing agent, lactoprene vulc:zniz:itc~s, in i 1 i i . w i.w in 1)uromctcr hardness hj- not more than 20 points -iniiliii~lyto stock S o . 2147 with respect to hezit :tttc-i.70 Iioiirh of esposiire in air a t 300" F. Stock $3771 rncets C ' o i i d c r a stock which is loner in per cent c th i ~ ~ rc,qiiiwments c~ aft1.r more than 700 hours of :iging at the i'r;t1)1~3 IS)-for esnniple, stock y o . 2148. L)at:t are plotted i n . ~ i t , i , i f i i d t rmperatiire. !,7giii.i),513 for this vulcanizate. 0hjcction:ible detorieir:itioii hi,gin
