August 1949
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
insulation resistance of four samples has dropped after 5 months to about 0.01 of the initial value, whereas in the two control samples in water the resistance has remained constant. I t is known that gutta-percha deteriorates unless stored under water. The deterioration of the samples in soil may be due to ordinary oxidation rather than to microbial attack. Parallel tests in sterilized soil which would be necessary for a conclusive proof of microbial attack were not made. The large resin content nould be expected to have some effect on the rate of microbial attack. The insulation resistance of wire samples insulated with polyethylene and with polyvinyl chloride has remained high and practically constant after 2 years’ exposure to soils 3 and 4 ( p H 6 and 8). A recent report ( I ) states that polyvinyl chloride insulation showed good physical and electrical properties after 12 years’ exposure t o soils of p H 4.8 and 5.3. Because of the acidity of these soils microbial attack might be suppressed. In soils 3 and 4, however, such attack would be favored. Thus polyvinyl chloride insulation appears to be stable in various soils. In view of the much higher activity of soil 5, a large number of polyethylene and polyvinyl chloride insulated samples are under prolonged tests in it. Neoprene compounds appear to be inherently resistant to soil ecposure. The proper function of neoprene compounds is as a protective covering rather than as insulation. The initial values of insulation resistance are so low that any effect of attack by microorganisms is masked. The most significant tests of neoprene compounds are made by applying them in a thin layer over insulation known to be susceptible to microbial attack, burying the samples in soil, and measuring the insulation resistance of the cumbination periodically.
1641
BIBLIOGRAPHY
Bakelite Corp., Kabelitems, No. 30 (September 1948). Bushnell, L. D., and Haas, H. F., J . Bact., 41,653 (1941). Dawson, T. R., J . Rubber Research, 15, No. 1, 1-9 (1946). Dimond, A. E., and Horsfall, J. D., Science, 97, 144 (1943). Erikson, D., J. Bact., 41, 277 (1941). Erikson, D., J. Gen. Microbiol., 1, 39 (1947). Frobisher, M., Jr., “Fundamentals of Bacteriology,” 3rd ed., p. 47-8, 382, Philadelphia, W. B. Saunders Co., 1947. Gray, P. H. H., and Thornton, H. G., Centr. Backt., 11, Abt. 73, 7 4 (1928).
Henrici, A. T., “Biology of Bacteria,” 2nd ed. p. 203, Boston, D. C. Heath & Co., 1939. Henrici, A. T., “Molds, Yeasts, and Actinomyces,” New York, John Wiley & Sons Co., 1930. Kalinenko, B. O., Microbiology (U.S.S.R.),7, 119 (1938). Leutritz, J., Jr., A.S.T.M. Bull. No. 152, p. 88 (May 1948). Leutritz, J., Jr., and Herrmann, D. B., Ibid., 138,p. 25 (January 1946).
Novogrudski, D. M., Microbiology (U.S.S.R.), 1, 413 (1932). Porter, J. R., “Bacterial Chemistry and Physiology,” p. 451, New York, John Wiley & Sons Co. (1946). Rahn, O., “Physiology of Bacteria,” Philadelphia, P. Blakiston’s Son & Co. (1932). Rahn, O., and Richardson, G. L., J . Bact., 41,225 (1941). Sisler, G. D., and ZoBell, C. E., Science, 106, 521 (1947). Sohngen, N. L., and Fol, J. G . , Centr. Backt., 11, Abt. 40, 87 (1914).
Spence, D., and Van Niel, C. B., IND. ENQ.CHEM.,2 8 , 4 7 (1936). Stief, J. L., Jr., andBoyle, J. J., Ibid., 39, 1136 (1947). Stone, R. W., Fenske, M. R., and White, A. G. C . , J . Bact., 44, 169 (1942).
Tanner, F. W., and Tanner, F. W.,Jr., “Bacteriology,” p. 287, New York, John Wiley & Sons Co., 1948. Tausz, J., and Peter, M., Centr. Backt., 11, Abt. 49, 497 (1919). ZoBell, C. E., “Marine Microbiology,” p. 20, Waltham, Mass., Chronica Botanica Co., 1946. ZoBell, C. E., and Beckwith, J. D., J. Am. Water W o r k s Asaoc., 36, No. 4 , 4 3 9 (1944). ZoBell, C . E., Grant, C. W., and Haas, H. F., BdZ. Am. Assoc. Petrdleum Geol., 27, 1175 (1943).
ACKNOWLEDGMENT
The authors are greatly indebted to Orison S. Pratt, Constance 11. DeMello, and a number of other associates for their interest and assistance in this work.
ZoBell, C. E., and Stadler, J.,J . Bact., 3 9 , 3 0 7 (1940). RECEIVED January 6, 1949. Presented before the meeting of the Division of Rubber Chemistry, AMERICAX CHEMICALSOCIETY, in Detroit, Mich.. November 1948.
Rubber Reinforcing Properties of High-Abrasion Furnace Black L. R. SPERBERG, J. F. SVETLIK, AND L. A. BLISS Phillips Petroleum Company, Phillips, Tex.
x
T h e properties characteristic of HAF black in a GR-S system over the loading range of 10 to 65 parts per 100 parts of elastomer are described and compared to EPC, HMF, and SRF type blacks. Physical test data illustrate the improved reinforcement possible with this new carbon in both GR-S and natural rubber. Road tests with GR-S tires containing HAF in the treads show 18 to 20740 greater abrasion resistance than EPC black. HAF also contributes somewhat better flex crack growth characteristics to the finished tires. HAF imparts good electrical conduc-
tivity to rubber stocks; this conductivity can be decreased by increasing the amount of mixing the stock receives. Bound rubber data on GR-S-carbon black master batches show that HAF attracts more rubber to its surface and holds it more tightly than does EPC; these data substantiate data reported previously (3) which showed the HAF black to have P greater surface area than EPC and a higher physical energy per unit of surface than other blacks. The percentage of bound rubber appears to correlate in general with actual road-test abrasion results.
A
Since a greater degree of improvement in the properties of vulcanizates can be obtained by the use of colloidal carbon pigments, much research and development work have been directed toward the production of new and improved varieties of this versatile element. Until a few years ago the bulk of commercial carbon black was manufactured by the channel process with natural gas as the
LTHOUGH the phenomenon of pigment reinforcement of elastomeric materials is not yet fully understood, the effects of reinforcement by pigments, particularly colloidal carbons, are readily distinguished. Reinforcement in a vulcanized rubber matrix may be recognized by improved stress-strain properties, higher tear strength, greater stiffness, and increased resistance to abrasive wear, to mention but a few of the commonly used criteria.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1642
Vol. 41, No. 8
power requirements for the mixing operation are deterEPC Blackb, Mixed for H A F Blacka, Mixed for mined in suitable equipment. 3 min. 4 niin. 5 min. 3 min. 4 min. 5 min. After being discharged from Black not incorporated, yo 4.0 2.5 0.8 12.2 5.5 2.2 the Banbury, the resultant Attained mixing temp., 268 280 270 293 285 290 E. stock is massed twice on the 111 101 110 110 131 Mooney plasticity (ML4) 139 mill and extruded through n a t 212' F. 75.5 75.6 77.7 61.9 Extrusion rate, cc./min. 81.3 79.5 Garvey die (9)in a No. Extrusion swell, cc./in. 1.97 1.95 2.16 2.06 2.23 2.33 4-,3+,42 + , 3 + , 3+ 4-,3+,44--,4--, 3 + Extrusion ratingc 3 + , 4--, 3 + 4 - - , 4 - - , 3 f Royle extruder operating a t 5 Philblack 0. a screw speed of 45 r.p.m. b Wyex. and a jacket temperature of c Garvey ratings (8) for edge, smoothness, a n d coriiw, respectively. 250" F. Tables I and I1 give comparative results of a mocessahilitv study of the H A F and EPC blacks in GR-S. It is evident feed stock; in recent years great impetus has been given to the that the H A F incorporates into the GR-S a t a much fastei manufacture of various types of carbon blacks from natural gas rate than the EPC, and that the heat generation resulting or mixed gas-liquid feed stocks in continuous-type furnace from the rapid incorporation is not excessive. The H A F operations. The original blacks produced by this method were compounds extrude at a faster rate, undergo less swelling, and classified as semireinforcing furnace blacks (SRF) since they fell have higher extrusion ratings than the correspoiiding E P C between the thermal decomposition and the channel black types compounds. These results have been verified in factory-scale in reinforcing characteristics. Since the inception of S R F mixing operations by a number of different manufacturers. blacks, several new types of furnace blacks have been produced The power consumption data in Table I1 indicate that the which, in general, have been characterized by progrersively HAF black requires slightly more total pover than E P C for an increasing degrees of reinfoi cement. These newer furnace blacks equal mixing cycle. This would be expected since HAF incorcomprise the H M F (high modulus furnace), FF (fine furnace), porates more readily into the clastomer and the mixing is being and VFF (very fine furnace) or RF (fully reinforcing furnace) conducted on a tougher mix. However, since H A F is essentially classifications. As Stokes and Dannenberg ( 4 ) pointed out, incorporated in appioximately 4 minutes as compared with EPC: the reinforcement level of FF blacks is roughly 80 t o 90% of that in 5 minutes, the total power requirement may be less for RSF. of channel black, whereas the VFF blacks approach or excel. The processing investigation of IlAF black was extended to the reinforcement level of channel black. include both unpremasticated and premasticated No. 1 ribbed Concurrently with the VFF blacks, a new type of colloidal smoked sheet as the basic elastomers. The same rapid rate of carbon, Philback 0, which is 10 to 20% more reinforcing than E P C incorporation of HAF was observed as in GR-S. black, was introduced to the rubber industry. 'This black The extrusion data in Table I11 show that HA\Fblack gives a has been classified as an H A F (high-abrasion furnace) type black better processing stock with all three elastomers, and that the because of its superior resistance t o abrasive wear. The chemical smoothing or plasticizing action is most pronounced in the very and physical properties of H A F blacks have already been detough, unpremasticated natural rubber where the H A F compound scribed ( 3 ) . This article is confined to the properties of this extrudes at twice the rate of the E P C black compound. With black in different elastomeric systems. the more plastic GR-S the difference in the action of the two PROCESSABILITY blacks becomes smaller, as would be expected. T o determine the processability of different carbon blacks, rubbers, etc., this laboratory has developed a mixing test utilizing TABLE TIT. EXTRKSJON RATESO F 17ARIOUS RUBBERS a midget Banbury which, when coupled with the laboratory E P C Black extrusion test, gives good correlation with factory processability __ H A F Black Mixing, Extrusion, MiTing, Extrusion ratings. The midget Banbury has a capacity of approximately min. cc./min. min. cc./niin. 260 cc., and can be operated a t variable speeds and a t different, Unpreniasticated S o . I 6 38.2 6 20.0 ribbed smoke sheet jacket temperatures. The ratio of total surface to volume is Broken-down iSo. 1 smoked 5 48.8 6 43.5 sheet much greater for the midget Banbury than for a No. 11 factory GR-S (chunk) 4 79.5 6 75.5 Banbury, which results in much better heat transfer characteristics for the midget Baabury; therefore the only way to get comparable batch temperatures in the two Banburies is to operate P R O P E R T I E S O F H A F BLACK IN GR-S the midget at a jacket temperature of approximately 250" F. To show the over-all reinforcement characteristics of HAF I n brief, a batch composed of 1.8 times the basic recipe of 100 in GR-S, representatives of the EPC, H M F , and S R F types were parts of elastomer, 50 parts of carbon black, and 10 parts of selected for comparison. The basic recipe follows: softener is loaded into the midget Banbury, masticated for a GR-S (X-346) 100 parts definite time at a rotor speed of 33 revolutions per minute, and HAF, EPC, HRIF, SRF blacka, each a t 10,20, 30, 40, 5 0 , 6 5 Zinc oxide 3 then discharged. The unincorporated black is weighed, and the 10 (6 for H M F and SHF: Asphalt KO.6 percentage of black not incorporated into the elastomer is calSulfur 1.75 0 8 ( 1 . 2 for EPC) Santocure culated. The final temperature of the rubber batch and the a Pliilblaok 0, Wyex, Philblark A, Gastex, respectively.
DATA TABLE I. LABORATORY MIXING AND EXTRUSION
TABLE11. Blaok
HAF EPC AF
PC
POWER
REQUIREMENTS O F h11DCET BANBURY
0 Min. 1 hlin. 2 &En. 3 hlin. 4 Min. &&fin. Mauimum Power a t Each 1-Min. Interval, Kw. 13.4 9.5 8.3 8.0 8.2 8.2 13.5 9.0 8.2 7.6 7.2 7.0
Total Power Consumed in 1-hlin. Intervals, Watt-Hr. 135 140 130 180 153 ... 120 11.5 140 160 ... 165
Total
. .
... 738 700
The increase in the accelerator quantity required by the E;PC formulations is necessitated by that black's so-called retarding effect upon the rate of cure. For the various furnace blacks, an accelerator correction for the activating effect of increased loadings was not made since it was felt that a valid comparison of the different compounds could be made a t equal states of cure by slightly varying the cure time. Figures 1 and 2 give Ohe results; the various properties are shown at an optimum state of cure for each carbon black at each loading level.
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1949
'
TENSILE' S T R N~G T H 80 OF.
4000-
BLACK' PHR Figure 1.
I
I
- 4000-
I
1643
I
I
I
T E N S I L E STRENGTH-AGED 80°F-
-
B L A C K PHR
Tensile Strength, Modulus, and Elongation of GR-S at Various Black Loadings
'
INDUSTRIAL AND ENGINEERING CHEMISTRY
1644
IC-
Vol. 41, No. 8
2IO0F,
,
LEGEND
.-
PHILBLACK 0 PHILBLACK A - - - - - - - - EPC B L A C K n---SRF BLACK
I
x-0
5-
6
-
2
I
I
I
I
I
ocI
I
I
IO Figure 2.
20
I
30
I
40
1
50
i
\'\
I
I
I
I
' D Y ~ A M IHARDNESS ~
I
I
\
4'
I
SHORE HARDNESS
I
1
I
60
1
0
r IO
Resilience, Flex Life, Abrasion LOSS,and Hardness of G R - S a t Various H1ack:Loadings
I
'
I
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
August 1949
1645
TABLE IV. SUMMARY OF PHYSICAL PROPERTIES IN NATURAL RUBBER [Rubber 100, black 50, antioxidant 1.0, stearic acid 3, pine t a r 3, sulfur 3, accelerator 0.6 part (0.9 for EPC)] At 80° ~~. ..
300% Black HAF EPC H4IF
modulus, Ib./sq. in. 2725 1900 2600
At ZOOo .-. ..
~
4460 4500 3725
'
300% modulus, Ib./sq. in.
480 580 440
1600
1100
1625
F.. Ultimate Tensile, ElongaIb./sq. in. tion, %
2925 2825 2475
Heat Buildup, F.
530 505
Abrasion Loss, cc.
Flex Life, Min.
68
2.62 3.32 4.30
80 28 28
% 58 54
67 68
61
FROM
Test C a
Test Da
Test E a
113 100
114
108
Test F b 113
83
..
114 100 82
100
..
ROADTESTS
100
100
..
100
size. GR-S or GR-8-10 treads. size. Natural rubber treads.
b 9.00-20
w
&looney Plasticity, ML4
Test Bo 119
Test Aa
6.00-16
6-
Shore Hardnees 67 65 67
TABLEv. ABRASION INDEXES Black HAF EPC
HMF
PHILBLACK 0
Resilience (Lupke),
29 31 27
630
I
\
SI-
z F z
F. Ultimate Tensile, ElongaIb./sq. i n . tion, %
5-
0
m
3
4-
0 '
I
E 0
Y
3-
J
I
2b
30
I
40 B L A C K - PHR
I
1
50
60
Figure 3. Abrasion Loss of Natural Rubber at Various Black Loadings (in Parts per 100 Parts Rubber)
The greater reinforcing characteristics of HAF are shown in improved tensile strength, particularly a t the elevated temperature, higher modulus, superior flex life, and improved abrasion resistance. I n general, this superiority is evident a t all black loadings studied in both the oven-aged and original properties. Thp resilience data show that HAF possesses approximately the same hysteresis properties as E P C and the H M F exhibits approvimately the same hysteresis level as SRF. H A F black shows the greatest degree of reinforcement, followed in order by EPC, HMF, and SRF, respectively. PROPERTIES OF HAF BLACK IN NATURAL RUBBER
*
A similar compounding evaluation of HAF black in natural lubber was carried out with the black loadings varied between 20 and 60 parts per 100 parts of elastomer, and compared t o EPC and H M F blacks. The results parallel closely those obtained in the GR-S loading study, with the possible exception of stress-strain properties. Since natural rubber gum stocks characteristically give high tensile strengths and elongations, the values obtained a t low loadings of black in natural rubber are considerably higher than the tensile properties of the corresponding GR-S compounds. Over-all results parallel closely those obtained with GR-S rubber, and curves similar to those of Figures 1 and 2 did not seem necessary. Table IV summarizes results. These data show the same general ieinforcement characteristics for the HAF black as did the GR-S study. Since reinforcement of rubber is often associated with resistance to abrasion, the abrasion loss curves of the three blacks over the entire loading range are reproduced in Figure 3. The superior reinforcement level attainable with the HAF type black is evident.
The miles per 0.001 inch nonskid loss of the H A F tires in the five GR-S or GR-S-10 tests were 78, 77, 84, 68, and 106, respectively, which correspond to tread design mileages of 22,000 to 35,000 miles. The crack growth resistance of all the tires was good, and no tires failed during bhe tests because of a defect in this property. The natural rubber tire test has not been completed, but the abrasion index of the H A F black tires has leveled out a t 113% in comparison to the channel black control pegged a t 100%. The improved abrasion resistance and flex life characteristics of HAF over E P C as shown in the laboratory data of Figure 2 are verified by the road test data. EhECTRICAL CONDUCTIVlTY
The electrical conductivity of rubber compounds is an important property which must be taken into consideration in many applications. To locate the electrical conductivity of H A F relative t o other blacks of the carbon spectrum, compounds were mixed containing 50 parts each of HAF, EPC, H M F , and S R F per 100 of GR-S. Since it was known that the degree of mixing has a marked effect upon electrical conductivity, samples of the mixes were taken a t various stages of the milling procedure
r
GUM1
:I $10 4
w
I z
l
ROAD TESTS
The HAF type black has been road-tested in tire treads during the past two years on Phillips Petroleum Company test vehicles as well as by several commercial tire manufacturers. The results to date indicate that HAF imparts 10to 2O%superior abrasion resistance in addition t o improving the flex crack growth characteristics of the tires. Table V gives a brief summary of results on six separate tire tests conducted privately to compare HAF black directly to EPC. I n two tests H M F was also included.
1 L
i
I 6
A
Figure 4. A. B. C. D.
E.
C
D
Electrical Conductivity Data
Sampled 1 minute after incorporation of black Sampled after 3 minutes Sampled after six cuts and three endwise rolls Sampled after hot remill Sampled after cold remill
E
INDUSTRIAL AND E N G I N E E R I N G C.HEMISTRY
1646
TABLE Vi. Black Type
Vol. 41, No. 8
HOUNDRUBBER DATA
Hound Rubber, %
HAF
Swelling Index of Bound Rubber 39.4 33.4 39.8 33.9
EPC Acetylene HMF SRF ... FT Ob ... a Partially dissolved. The benzene was discolored blaok owing t o partis1 “solubilization” of the carbon black-rubber master batch which formed a black colloidal solution in the benzene. The gel remaining did not contain all of the carbon black originally presenz in the master batch: therefore, t h e per cent of bound rubber a.nd swelling index of the bound rubber could not be determined. b Completely dissolved t o give black colloidal solution of carbon blackrubber master batch in the benerne.
e5
I
90
Figure 5.
I
I
95
I
100 105 ABRASION INDEX -PERCENT
I
110
I
111
I
Abrasion Index t’s. Round Rubber
(Figure 4). The resistivities in megohm-centimeters of the various mixes are plotted against the degree of mixing in Figure 4. H A F black imparts good electrical conductivity and falls in the range of conducting blacks. A4gum stock is included t o show the resistivity of a good nonconductor. The degree of mixing, over the range investigated, had little effect on the electrical conductivity of HAF and E P C blacks, whereas H M F black varied from a good conductor t o a good nonconductor as the mixing time was increased. However, even with H A F the electrical conductivity was decreased slightly as a result of longer mixing; if the stock were milled under more severe mixing conditions, the electrical conductivity of H A F stock would continue to decrease still more to place H A F in the range of the nonconducting blacks. BOUND RUBBER
For many years i t has been known that raw rubber is made insoluble in ordinary solvents by the addition of carbon black t o rubber ( I ) . N. A. Shepard states: “Most uncured rubber mixes disperse readily in such a solvent as benzol or gasoline. In fact, it is common procedure for determining whether ‘set-up’ or premature vulcanization has occurred in a mixing to test its solubility in these solvents, for vulcanized rubber swells but will not form a sol. T o all appearances channel black mixes containing 25 or more volume per cent of black behave exactly like vulcanized rubber in this respect” ( 1 ) . This observation has led to the development of a test designed to measure the reinforcement properties of different carbon blacks. The method simply involves the preparation of a carbon black master batch (50 parts of carbon black in 100 parts of rubber), the determination of the gel content of the master batch, and the swelling index of the gel with benzene as solvent. Since the gel contains all of the carbon black plus a certain amount of the rubber which has become insolubilized in the benzene because of the powerful adsorptive forces of the carbon black, the per cent of gel may be converted to the per cent of bound rubber immobilized by the carbon black by the following equation:
% bound rubber
=
(% gel
- 33.3) x
66.7
100
The swelling index of a gel is defined as the ratio of the weight of the swelled gel to the weight of the dried gel and is a measure of the relative “tightness” or “looseness” of the gel; the higher the swelling index number, the “looser” or the more easily broken down is the gel. T h e swelling index of the carbon black-rubber gel may be converted to the swelling index (S.1.)of the rubber only by the following equation:
S.I. (of bound,rubber)
=
% gel X S.I. (of black-rubber gel) -33.3 ~
%gel - 33.3
T o show the reinforcerilelit cliaracteristics associated with different blacks, samples of HAF, EPC, acetylene, HMF, SRF, and FT type blacks were mixed into GR-S to determine their elastomer-immobilizing chaiacteristics. Fifty parts of black per 100 parts of gel-free X-224 GI1-S were milled on a standard 6 X 12 inch laboratory mill, using a batch weight in grams 1.5 times the formula weight Since the bound rubber values may vary somewhat with the severity of the milling operation--Le., size of batch, opening of rolls, time of milling, etc.-the same milling procedure was employed for the various blacks. The procedure utilized an 11-minute initial milling cycle plus a 1.5minute hot remill (at 220” F.) plus a 3-minute cold remill. The stocks were allowed to rcst a minimum of one hour between each milling operation. After the cold remill, the various batches wcre sampled and the per cent gel and the swelling indexes of the carbon black-rubber gels were determined. These data were then converted to per cent bound rubber and swelling index of bound rubber by the preceding equations (Table VI). These data show that the H A F black adsorbs more rubber on its surface and holds it more tightly than does EPC. H M F holds the bound rubber as tightly to its surface as does HAF, but the quantity adsorbed is considerably less. Acetylene black adsorbs slightly more rubber than does H M F but holds i t somewhat less tightly. S R F black adsorbed some rubber to its surface, but the milling treatment was so severe that a high percentage of the sample dissolved. Since the carbon black comprises 331/a%of the total mixture, any carbon black-rubber gel content below this figure indicates a partial solution of the gel. The partially solubilized gel discolors the benzene solvent, an indication that a portion of the carbon black-rubber master batch has colloidally dispersed. The SRF-rubber mixture contained only 10% gel, an indication that a considerable portion of the sample had dissolved. The benzene solution was also very black. The FT black-rubber master batch completely dissolved, left no gel, and turned the benzene solution very dark. Comparison of the bound rubber values for the different carbon blacks to the abrasion indexes (Figure 5) shows that a correlation does exist between the percentage of bound rubber and the tiretread wearing characteristics of the different blacks. The more highly reinforcing blacks immobilize larger quantities of rubber hydrocarbon. The bound rubber test and the laboratory abrasion test appear to be the best laboratory methods applicable to compounded stocks for defining semiquantitatively the general reinforcement characteristics of carbon blacks. LITERATURE CITED
(1) Alexander, Jerome, “Colloid Chemistry,” 1’01. 4, p, 326, New York, Reinhold Publishing Corp., 1944. ( 2 ) Garvey, Whitlock, and Freese, IND. EXG.CHEW,34,1309 (1942). (3) Sperberg and Barton, Rubber Age (N.Y.), 63, 45 (1948). (4) Stokes and Dannenberg, IXD.ENG.CHEM.,41, 381 (1949). RECEIVED April 22, 1048. Presented before t h e Division of Rubber Cheinstry a t the 113th Meeting of t h e AVERICANCHEMICAL SOCIETY, Chicago. Ill.
