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
2602
fa) Bush, V., Gage,
F. D., and Stewart. H. R.,Ibid., 208, 63-84
(1927).
(4) Carlwn, H. C . , private communication, 1947. (6)Colburn, A. P., and Carison, H. C.,private communication, 1942. (6) Colbnm, A. P., and Stearns, R. F., Tram. Am. Inst. Chem. M S . , 37,291-309 (1941). (7) Crank, J., “The Differential Analyaer,” New York, Longmans, Green,and Go., 1947. ( 8 ) McAdams, W. H., “Heat Transmission,” 2nd ed., pp. 3 W 3 , New York, MaGraw-Hill Book Co., 1942. (9) Marshall, W. R., Jr., and Pigford, R. L., “The Application of
Differential Equations to Chemical Engineering Problem,” pp. 144-62,Newark, Del., Univerdty of Delaware, 1947.
Vol. 43, No. 11
(10) Rose, A., and Welshans, L. M., IND. ENCI.CHEM.,32, 668-72 (1940). (11) Rose, A., Weishans, L. M., and Long, H.H.,Ibid.,32, 673-6 (1940). (12) Schmidt; E., “Foppls Festschrift.” p. 179, Berlin, Springer, 1924. (13) Sherwood, T. K., and Reed, C. E., “Applied Mathematics i n Chemical Engineering,” pp. 24145, New York, McGrawHill Book Co., 1939. (14)Smoker, E. H.,and Rose, A,, Trans. Am. Inst. Chem. Engrs., 36, 285-93, 675-7 (1940).
RECEIVED July 28, 1949. Presented a t the Delaware Chemioal Symposium held by the Wilmington Seotion of the AMERICAN CEESICAL SOCI~TT January 1949.
Banbury Mixing of Zinc Oxide -
development H. C. JONES
AND
E. G.
SNYDER
DEVELOPMENT ENGINEERING DIVISION, TECHNICAL DEPARTMENT THE NEW JERSEY ZINC CO. (OF PA.), PALMERTON, PA.
A this
NUMBER of years ago R e c e n t l y a s t u d y was It is common factory practice to premix in a Banbury l a b o r a t o r y remade of the factors involved many rubber-compounding ingredients, and pigments in p o r t e d e x p e r i m e n t s with in the Banbury mixing of partioular, in substantially higher concentrations than Banbury mixing of zinc oxide several zinc oxides in a “nonare ultimately employed in commercial rubber articles. In rubber (S). More recently productive” master batch These “nonproductive” compositions, known as master attention has been directed by the upside-down method, batches, improve dispersion and facilitate the subsequent to the importance of power and the work is described handling of the materials. consumption of Banbury mixin this paper. The experiExperiments were undertaken to study the Banbury ing by Nellen, Dunlap, and ments were conducted in a mixing characteristicsof propionic acid-treated zinc oxide Glaser (3). Since the intrclaboratory 00 size Banbury in master batches containing 60 parts of zinc oxide and duction and wide acceptance with a 4300-ml. free volume. 40 parts of natural or synthetic rubber. of GRS, more emphasis hw The Esterline graphic wattr The propionic acid-treated pigment required somewhat been placed on Banbury meter and the Westinghouse less electrical energy for incorporation in rubber than the power consumption. Standw a t t - h o u r m e t e r for the base oxide. Furthermore, the treated oxide eliminated the ard GR-S and thelow reaction power measurements were peak electrical load that was apparent during the early temperature polymers, in pararranged as shown in the stages of the mixing cycle with the untreated oxide. Pigticular, consume more elecw i r i n g d i a g r a m in Figment dispersion and processing properties were enhanced trical energy in mixing than ure 1. by the presence of the surface treating agenf on the oxide. natural rubber. FurtherIn other words, substantial power savings and improved In Figure 1, A is an Estermore, GR-Srequires a higher l i e universal current transdispersion and processing are the advantages claimed for level of pigmentation for former, 25 v o l t - a m p e r e s , the surface-treated oxide. adequate reinforcement than 2500 v o l t s , 25-60 cycles, natural rubber and this calls current ratio 25-50-100-20&400-800 to 5 amperes. for greater mixing capacity. B is a Westinghouse rotating watbhour meter, Style 362661A, Modern high speed mixing schedules and other means of increasType OA,normal voltage 200 to 400,normal amperes 1,5, 10,20, ing unit output impose greater demands upon processing equip and 40. With both A transformers set a t 25 to 5, the potentials ment. As a result of this situation many rubber manufacturers connected as shown, and switch set to 400 volts, 5 amperes, dial are operating closer to or are exceeding rated equipment capacity. reading of B is multiplied by 40/3 to obtain total watt-hours durThey may also be more conscious of peak electrical loads and the ing period that push button is pressed. Push button has lock and release buttons so that one is pressed to start and the other to atop danger of utility company penalties for exceeding demand rates. meter. Within the past few years an upside-down mixing technique C is an Esterline-Angus graphic wattmeter, Type MS, 5 amhas been adopted by some rubber processors. This is a method in peres, 100, 200, and 500 volts. With connection as shown (the which the pigments are charged into the Banbury before the potential connections on 500-volt posts) and A transformers rubber. According to Comes (I)an improved pigment dispersion connected 25 to 5, full scale of instrument is 25 kw. The standard batch consisted of 2400 grams of zinc oxide and is realized by the upside-down mixing cycle because of the high 1600 grams of GR-SX-346,and this amount of material occupied power input required by the stiff consistency of the batch. He 50% of the Banbury capacity. A ram pressure of 40 pounds per also adds that just as good results may be obtained in the same square inch and a rotor speed of 69 r.p.m. for one rotor and 60 period of time by incorporating the ingredients in a more regular r.p.m. for the other rotor were employed. The temperature of the manner so that the rubber or other base material may adsorb the stock in the Banbury was Qbtained from a thermocouple projecting into the mixing chamber and recorded autographically. fillers more readily.
November 1951
INDUSTRIAL A N D ENGINEERING CHEMISTRY
2603
treated pigments. Similar power charts were obtained for the mixings at 65' and 80" C. The total power consumed for the mixing of the batches apd the final batch temperatures are listed in Table I. The mixings a t 65" and 80" C. Eequired essentially the same amount of power and slightly less than the batches milled at 60" C., but with each stepup in mixing temperature there waa a corresponding increase in final batch temperature. In every case less power waa required and a lower temperature d e veloped with the batches containing the treated oxide than in the case of corresponding mixings with the untreated pigment. The interpretation of the power charts is fitcilitated by the following information. The standard mixing cycle was 3 minutes with the only deviation occurring in the rotor speed study. The charta read from right to left as indicated in Figure 2. The abscissa ie time of mixing and the ordinate, electrical energy. The exact units of time in minutes and energy in kilowatts are not indicated because the charts are utilized for a number of time interval and energy settingfl. BACK OF INSTRUMENT
Figure 1. Electrical Connections of Watt-Hour Meter and Graphic Wattmeter on Banbury Mixer Roll
TABLE I. EFFECT OB BANBURY TEMPERA'IWRE ON MIXINQ Final
A. Eatdine universal ourrent tranoformer B. Weatinghouw rotating watt-hour meter C. Eaterlino-Anguo graphic wattmeter
Mixing Temperature C.'
Power Consuinption Watt-€&a
Mooney Viscosity ML Elastio recovery, at 100" C., 3-minute degree8 readings at 30 seconds
Banbury Temperature 50' C.
EFFECT OF TEMPERATURE
Four zinc oxides, zinc oxide A, XX-4 American process type;
zinc oxide B, Protox-166 Amencan process type treated with
propionic acid; zinc oxide C, Kadox-72 French process type; and &c oxide D, an expenmental Kadox-72 surface treated with proionic acid, were incorporated in GR-S a t 60", 65", and 80 C. &he the and Banbu maintained watertemperature through theinrotor j a g e was t of the mixer a tby thecirculating indicated temperature. The charts in Figure 2 illustrate the substantially higher initial power requirements of the untreated oxide as compared with the
Zinc oxide A, untreated Zinn oxide _, €3 trrrshd _.-zinc oxide C untreated Oxide D:
----
92.5 R7 _..0_ 90.5 87.0
_--
398
49.0
396 368
4116
a_ _m_
164
42.5
1.53
45.85
180
i58
Banbury Temperature 66* C.
loo,~
Zinc oxide A, untreated zinc oxide^ treated
96.0
Zinc oxide D: d untreated Zinc Oxide
95.6 97.0
380 350 368 340
50.5 46 0 47.5 46 0
104 152 174 174
Banbury Temperature 80a C. Zinc oxide A, untreated Zinc oxide B, treated
g: fgrgpd
107.6 106.0
{x:
379 358 368 340
51 5 47.5 47 0 46 0
163 164 165 170
The stocks were compounded with 12 grams of carbon black to provide a dark background for the detection of any undispersed zinc oxide in the batches. All of the batches with the treated oxides showed essentially a perfect dispersion at the three mixing temperatures while there was evidence of undispersed pellets of the untreated oxides, zinc oxide A and zinc oxide C, and the inferior dispersion waa more apparent aa the mixing temperature was increased. The untreated pigment, zinc oxide A, had a higher Mooney viscosity than zinc oxide B while zinc oxide C and the corresponding treated wide were essentially equal in viscosity. Miuin(l Y
a
Figure 2. Power Consumption Charts for Zinc Uxides A, B, C, and D, Mixed at 50" C.
Figure 3.
Effect of Remastication on Power Consumption
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
2604
TABLE11.
INFLUENCE OF Final Mixing Temperature
ZincOxideA Untreated Unm.ytic;ted GR-8 Masticated GR-S.30minute roll breakdown Masticated GRS f 6 6 stearic acid in r;bPber Masticated GR-S 55 etearic acid witrzinc oxide Zinc Oxide C, Untreated Unmasticsted GR-8. Masticated GR-S 30minute roll br&kdown Mastioated GR-8 5.5% stearic acid in rubber Masticated GR-8 witraino 5.5 , stearic oxide acid
+
Figure 4.
Stearic Acid Added Before and with Zinc Oxide
temperatures of 50°, 66O, and 80" C. did not influence the viscosity results. The elastic recovery data for the series of compounds showed some inconsistencies.
+ +
Unmasticated GR-S Masticated GR-8.30minute roll breakdown
0
c:
Vol. 43, No. 11
MASTICATION AND
SOFTENERS
Mooney Visoosity Power ML Elastic Consump- at 100' C. recovery. tion 3-minute degrees Watt-Hburs readinga at 30 seconds
98.5 92.5
439 398
66.0
49.0
203 164
89.0
386
39.0
147
90.0
382
43.0
132
98.0 90.6
439 396
65.0 46.5
225 158
88.0
386
40.0
148
87.5
375
39.5
142
Uncompounded polymer Uncompounded polymer
42.0
346
31.6
230
EFFECT OF MASTICATION AND SOITENERS
When the Banbury mixings weremadewith unmasticatedGRS, substantially more power was consumed and higher temperatures were developed than with 30-minute prernasticated GR-S,as ahown in Table I1 and Figure 3. Unless otherwise specified, the premasticated GR-S was used. The addition of stearic acid to the zinc oxide before incorporating in GR-S reduced the initial power surge but the effect was not so pronounced as witha surface treated zinc oxide. See Figures 2 and 4. Actually the amount of organic treating agent on zinc oxide B was only approximately one tenth oPthe amount of stearic acid added with zinc oxide A. The total power requirements and the h a 1 temperatures were lowered with the fatty acid addition to the zinc oxide. The same amount of stearic acid premixed in the polymer did not reduce the initial power surge which occurred when the fatty acid was
present with the zinc oxide. The latter batches had somewhat poorer dispersions than those in which zinc oxide was incorporated with stearic acid. The advantage of having the organic acid treating agent uniformly distributed on the zinc oxide ir further demonstrated by the following experiment: An amount of propionic acid equivalent to that present as the coating agent on zinc oxide B was added to the base oxide before incorporating in the Banbury, and the mixing and dispersion characteristics were essentially the same as the untreated pigment zinc oxide A. Increasing tenfold the amount of propionic acid
NC OXIDE"
UNTREATED
ZINC OXIDE "A" UNTREATED
. Z I N C OXIDE ';B" W I T H STEARIC A
Figure 5. Treated and Untreated Oxide Mixed at 137 and 35 R.P.M.
Figure 6.
Smoked Sheets, Untreated and Treated Zinc Oxide with and Without Stearic Acid
INDUSTRIAL A N D ENGINEERING CHEMISTRY
November 1951
ZINC OXIDE'A"
2605
added to the base oxide continued to yield a poor dispersion and the power consumption curve resembled that of the untreated oxide. The hi4h concentrations of propionic acid, however, had a distincrt eoftenmg effect on the batch. Unmaaticated GR-Shad higher Mooney viscosity values than the 30-minute premasticated polymer which was further cized by stearic acid. Premixing the stearic acid with rubf%% adding it with the zinc oxide did not influence the Mooney values. INFLUENCE OF ROTOR SPEED
There is a significant difference in the power requirements for the mixing of the several zinc oxidea with variable Banbury rotor speeds aa shown in Table I11 and F5guw 6. At 36 r.p.m., 260 to 3(ro watt-hours were required €or mixing the oxides and more power was consumed in incorporating the untreated than the treated oxide. When the rotor speed was 137 r.p.m., approximately 600 watt-hours were needed and at this epeed the treated oxide consumed lesa power than the untreated oxide over the entire mixing cycle. It is shown in Figure 2 that the stocks mixed a t 69 r.p.m. used an intermediate amount of powelc-360 to 400 watt-hours. The Banbury mixings a t 69 r.p.m. had the best and the 36 r.p.m. mixiigs, the poorest dispersions. Milling at 137 r.p.m. were slightly better dispersed than those mixed at 36 r.p.m. The propionic acid-treated oxide yielded distinctly better dispersions than the untreated oxide. Rotor speed did not affect the Mooney viscosity values of the several batches and, although there were differences in the elastic recovery, they were not consistent. The Figure 7. Cold Rubber (X-478), Untreated and Treated Zinc Oxide with and Without Stearic Acid
T-LE 111. EFFECTOF R O ~ R BPEUD ON BANBURY MEUNQ PBOPERTIES
Zinc oxide A, untreated Zinc oxide B, treated Mixing time, minutea Rotor travel feet per minute TOM rotor &awl, feet
R.P.M.
R.P.M. 137
35 Power 69 137
Final stock temperature, 0.
consumption, watt-hourn 286 398 632 266 360 492 4 3 2
36
80.0
76.0
69
92.6 87.0
106 99.0
46 89 181 267
TABLEIV. MOONEYVISOOSITY OF BANBURY M AT V A E I A BROTOR ~ SPEBDS
174 848
~ STOCKS D
Mooney Vioosity 36
Figure 8. Butyl Rubber with Untreated and Treated Zinc Oxides
Figum 9. Buna N with Untreated a d Treated Zinc Oxides
Zinc oxide A, untreated Zipa.oxide B, treated Maxing time, rmnutee
R.P.M. 09
137
M> at 100° .C. a-rmnute reedmm 46.6 49 48.6 41 42.6 42 4
3
R.P.M. 3&astic~~cove$7
in degrees at 161 164
30 neaonda 164 160 163 160
2
F i p r e 10. Neoprene pe W with Untreated and 'I'reat~ZincOxides
VoL 43. No. I I
INDUSTRIAL AND ENGINEERING CHEMISTRY
2606 Smoked Sheet
Butyl
steario scid WBB incorporated in the Banbury with the untreated oxide, the batch did not maw and a pulverieed residue wm obtained. Additional rubber had to be charged into the Banbury to fuse the hnteh. Tabla VI shows that stearic mid incorpoomted with the aurface treated oxide did not msterially influence the mixing oycle other than reducing the total power consumption slightly. Butyl rubber, Buna X, and neoprene were compounded with the treated and untreated oxides and in every case somewhat lesa power WBB required for the mixing of the treated pigment. Table VI1 and F-res 8, 9, and 10 show the power consumption. Buns N c o sumed the greatest, neoprene intermediate and Butyl the least mount of electricsf energy. Thore WBB B sharp break in the power CODsumption cume with Buns N after the initial stsge of the mixing cycle while the reduction in power with the other polymers wsa more gradual. This behavior is believed to be saso*ated with the thermoplsaticity of the acrylonitrile polymer, which is very griezly and develops considerable hest at the outset of the mixing cycle. It suddenly softera and the mixing continues at B lower level of power oonsumption. The effect is not too elesrly illustrated by the power chart in Figure 9, preaumsbly due to the high oscillation speed of the recorder unit during the Figure 11. Actual Size Photographs of Zino Oxide Diapersiuiia initial stages of the mixing cycle when the peo A. Zinc oxide A, untraated is not feeding ink to the chart at s uniform rate. B. ZimomidaB. treated The dispersion of the treated oxide was substsntiallv better than the uotreated oxide with Mwney viscosity values and elastic recovery are shown in Table Butyl rubber, Bunn N, and neoprene. hetuel she photographs (Figure 11) ofthe zinc oxide mixinp in IV. smoked sheeb and Butyl rubber illustraLethe dispersion difPOLYMERS OTaBR T H * N GR-5 X-846 ferencae noted between the treated and the untreated oxides and these were representative for the several polymers investigated. When mixed in woked sheet, zinc oxide A required considerThe ohvioua question is: Why does a surface-treated oxide 00"ably mom power and developed B higher mixing temperature than Bume less electricst energy for inwrpcration in the several sinc oxide B. The introduction of 5.5 parts atearic mid with the polymers than the untreated base oxide?, and the answer is tm&ed oxide did not influence the power consumption while mggeeted in the power charts ahom in Figure 12. When para& samewhst lese energy wae uaed with zinc oxide A and ateario scid is incorporated in GR-S AC with the untreated oxide, the power thsn the enme oxide without the fatty wid addition. Resulta of ~~~
~~
thw tests are given in Tsble V.
The power mo-ption oharts in Figure 6 again demonstrate high initial energy surges with einc oxide A but not with the treated oxide. When stearic add w88 incorporated with the untregtad oxide, there were wide fluctuations in the power cume end somewhat less with the bsteh containing the treated zinc oxide and stearic acid. Corresponding G R S batches with stearic wid did not show the power fluctuations; thia is illustrated in Figure 4. Apparently stearic acid is not 80 readily adsorbed by natural rubber as GR-S. In the former owe the chamber wall8 m luhricsted and the grinding is leas uniform than with GR-S. The p ~ s e o c sof the mrfacetrested oxide with stearie acid reduced the power fluctuations subatantially. Zinc oxide B had a mesaurshly lower Mwney Viscosity than sinc oxide A and the addition of stearic mid to the batches further reduced the viemsity by ~pproximately25 Mouney unite. Ioc o p r a t i n g stearic wid with the untreated oxide materially improved the dispersion but the hatch WBB not quite equal to the ~tedoxideinthisrespect. A similar series of Banbury mixbps were made with the low d o n tempersture polymer, X-470,and the power coraump tion o u n s s M shown in Figure 7. This polymer, which had the -e 3o.minute premastication sa standard GRS, consumed more pom~ in the Banbury mixing cycle than the G W . When
Tmm V. Nnm-
MIXING
RUBBER B-uar
. Zina oxids A. "atrested
Zins oxide A. Ulltldswd 6.6% *t+s wid
+ n t hi m oxide
Zinc orida D . 1 m t e d Zina orido D. treated $ 6 2 , s-rie wid s m o oxide Prsblsndd m o k d ohsau. wrwoirrsd
+
101
413
88
83
347
e1
I46
94
866
75.6
147
91
370
63.6
146
90.6
217
Tmm VI. COLD RWBEB(X478)Mumas
168
INDUSTRIAL AND ENGINEERING CHEMISTRY
November 1951
consumption curve is essentially the same as if the para& were not present, while in a similar experiment with the same amount of stearic acid part of the high initial power surge is observed with the untreated oxide and no fatty acid is eliminated. Approximately ten times as much fatty acid was required t o produce this effect as was applied to the surface treating agent on zinc oxide B. The pigment dispersion with stearic acid was substantially better than with paraffin. This is experimental evidence that the reaction between the organic acid and zinc oxide and the orientation of the polar soap molecule at the surface of the pigment particle are responsible for the reduced power consumption and improved dispersion. The organic group in the zinc soap projecting from the surface of the pigment particle is more readily wet by the polymer than ainc oxide without a coated surface. ~~
TABLE VII.
~~~
2601
for the treated over the untreated zinc oxide are realized only in the upside-down mixing cycle. This is not the case; power savings of 10 to 20% have been reported by the rubber industry with more conventional mixing cycles on commercial Banbury units in a similar pigment comparison. These results have not been duplicated in a laboratory Banbury mixer. Presumably with the small-scale operation, power consumption differences are not measurable when the rubber is charged to the Banbury immediately or shortly before the pigment.
~~~
BANBURY MIXINQ WITH DIFFERENT POLYMSRB Final Mooney Mixing Power ML at 100' C., Tempera- Consumpture tion 3-minute C,' Watt-Hbura readings
Zinc oxide A, untreated Butyl (GR-I blend) Buna N (H car OR) Neoprene (?we W) Zinc oxide 13, treated Butyl (GR-I blend) Buna N (H car OR) Neoprene ('fype W)
Visoosity Elastic reoovery, degrees at 80 seconds
90 112 89
877 480 891
53 129 These atooks were too stiff for testing in the Mooney visoometer
a4 90
a4a 869 364
49.5 128 Those stocka were too stiff for testing in the Mooney viscometer
86
Butyl, Buna N and neoprene rubber8 were preheated about 15 minutes in an oven at looo C'. before Banbury mixing.
Another question that might be raised by these experimenta is why some batches do not mass in the Banbury mixer. Examination of the power charta (Figures 4, 6, and 7) shows that when stearic acid is incorporated with the untreated oxide there is a distinct lowering of power consumption during the early stages of the mixing cycle. This effect is least pronounced with standard GR-S, intermediate with natural rubber, and greatest with the low reaction temperature polymer, X-478-which did not maas in the Banbury. Parallel experiments with the treated oxide show essentially no change in the power consumption curves when stearic acid is incorporated with the pigment. The striking differences between the treated and untreated oxide may be partially explained on the basis of the known behavior of these pigments in the paint industry's oil absorption test, in which the treated oxide haa a somewhat lower oil absorption than the same pigment without a surface coating. In the Banbury experimenta where the polymer and stearic acid may be considered the continuous phase, there would be less tendency for the treated pigment to absorb polymer and plasticizer and hence less drying action exerted than with the untreated oxide. The drying action of the pigment is only a single factor in influencing the fusion of the batch. The softness or the ability of the polymer to mass in the Banbury also ie important. In this study it appears that X-340 OR-S massed with the greatest ease, natural rubber intermediately, and X-478 least readily. Equally important is the pressure that is developed in the chamber during the mixing cycle and this effect was demonstrated by several load variations. The natural rubber batch in Figure 6 was remilled with 45 and 42% load factors instead of SO%, the pigmenbrubberstearic acid ratio remaining constant. With the 45% load, power consump tion gradually decreased until, toward the end of the cycle, the batch massed and the pigment dispersion was incomplete. When the loading was reduced to 42%, there was not sufficient pressure developed in the mixer to mass the charge and the batch appeared partly shredded and pulverized. An inquiry has been made aa to whether the mixing advantages
Figure 12. Incorporation of Zinc Oxide with Paraffin and Stearic Acid in GR-S AC
In the preceding discussion attention has been directed to the influence of the nature rather than the extent of the pigment surface and some mention should be made of this extent. The following Banbury mixing8 of untreated zinc oxides in GR-S AC by the previously described procedure indicate that in this type of mixing the amount of pigment surface was a relatively secondary consideration.
Zinc oxide A Zinc oxide C Zinc oxide E. Kador-15 Frenoh prooess type
Burface Area Sq.M./Grad, Low Temperature Nitrogen Adsorption 4.6 6.4 9.8
Power Consumption, Watt-Hours 627 600
512
Zinc oxide E has almost twice the surface area of zinc oxide C and yet the Banbury power requirements of these oxides were essentially the same. These pigments were made by the same process and difIered only in particle size. The slightly greater amount of power that is consumed in the mixing of zinc oxide A may be ascribed to the low concentration of basic sulfates which are present on the surface of this oxide. ACKNOWLEDGMENT
The authors wish to acknowledge the comments and assistance of B. R. Silver. Valuable suggestions were contributed by WesIey Merritt, Gates Rubber Co., Denver, Colo. LITERATURE CITED
(1) Comes, D.A.. India Rubber Wodd, 122, 178 (1950). (2) Mathews, W. C., and H a d a m , (J.S.,Rubbw Age ( N . Ye), 32, 206 (1932). (3) Nellen, A. H.. Dunlap, W. B., and Qlaser, 0. J., Zndiu Rubbrr World, 120,57 (1949).
R I E C E I V February ~D 24, 1961. Presented before the DivLion of Rubber Chemistry of the AMERICAN CXEMICAL BOCIETT,W ~ b i n g t o n ,D.C., 1OSl.
