812
INDUSTRIAL AND ENGINEERING CHEMISTRY
ccssful. Chlorinolysis occurrril a t temperatures above about 25 a C., yielding hexachloroethanc. E~esachlorobutadieiie g a w no reaction with sulfuryl chloride i n the presence of benzoyl p i ' oside. Hcsnchlorobut,adieneis a colorless liquid of t'aiut t,mpt.ntiiii:likt., odor having the following physical ronstants: niclting point -21" C.; boilingpoint (760 mni.), 215" C . ; di0 1.6820 grams pw nil.; and ,n"$ 1.5542. The viscosity of hesachlorobutaditiie i u 2.446 centipoises or 1.479 centistolies a t 37.8" C . and 1.131 ceiitipoises or 0.724 centistokes at 118.9" C. Hexachlorobutadicnc is an escellent solveiit for ni:i,iiy orgmiic substances. It has the distiiict advantage over the coni~iioii chlorocarbon solvonts of having a low vapor pressure and is applirahle as a n agent in the cstraction of organic materials from water, as a high tempcraturc dcgrcitsing agent, as a 11ydraulic fluid, and as a special solvent.
Vol. 41, No. 4
hesachlolobututlielle was greater at a 4.0 1.0 1 mt,io of chlorine to I)olvchloroi)ut:Lnes than itt lower ratios. Best yields of hesaciilorobut adieiie were obtained by using polychlorobut~ancshavirig :ispecific gravity of about 1.66. The chlorinolysis reaction was iavorccl b>- increases in temperaf urc? exposure t irnc., ratio of chlorinr to polychlorohutanes, or in thc siwcific gravity of st:lrting 1)olyclilorohutaLtic.s. ACKSOWLEUG%IEI\I1'
Thaiilcs >ire hereby extended to I,he Ilookei. 1 17-20) t,o satisfy the need for information on the compounding and rubber prope1,tii:s of these new products. Types of reinforcing furnace blacks are available n-hich will duplicate closely the usual rubber properties observcd with chanriel blacks in vulcanized stocks. However, because of the flcsihility of operation and the differcnt types of raw material adaptable t o t,he continuous furnace process it is also possible to produce grades of reinforcing furnace blacks which differ markedly from channel blacks in rubber properties. The range of rubber stiffness and hardness obtainable with reinforcing grad-os of furnace blacks is much great,er than tTith channel hhclis, and although final approval of a grade of black for a particular application is based on service testing, the usef1:l range of rubber
product quality has been broadenccl by t h e introtluctiori of ncs\\' varieties of furnace blacks. Processing characteristics of carbon blacks may be described as the relative workability factors of rubber stocks in the sequencc of operations preceding t,he completed manufacture of cured rubber articles. I n those compounds where carbon black is a substaritial component of the stock it is t o be expected that the properties of the black will exert a major influence on processing. The work reported here is concerned with the effect of cttrboii black properties on the forming step of semifinished stocks and includes a study of the processing shrinkage propert,iea of ( W ~ C J I ~ black loaded stocks. STRUCI'UHE IN CARBON BLACKS
Wliereas the processing characteristics of channel blacks I x n r i~ simple relation to particle size and are the basis for their prcscnt classification in the rubber industry, the processing propert,ies of furnace blacks cannot he correlated similarly with t,he same degree of fineness. It has been necessary t o introduce the concept of "structure" to explain such anomalous properties as the low processing shrinkage and t h e smooth surface appearance of cxtruded and calendered stocks observed when certain grades of reinforcing furnace blac.ks are used. Although these effects arc particularly noticeable with GR-S they can be observed also, to a lesser degree, with natural rubber. I n the cured vulcnnizates structure black8 are characterized by high modulus and hardness, lo^ breaking elongat,ions, and high electrical conductivity.
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
?io conclusive evidence is available showing whether these structure blacks consist of strong pearllike aggregations held together by primary valence bonds or whether their state of aggregation is of a weaker type depending on secondary valence forces. Since oil absorption determinations on the blacks themselves give good correlations with those properties of rubber attribut,ed to structure (10, 2 1 ) it, is. probable t h a t the structure is not, formed necessarily in the rubber matrix by flocculation but is present in the original black before .compounding. Dobbin and Rossman {ii) recently have demonstrated t h a t structure blacks are fluffy and are difficult t o densify by direct compression or pelletization processes. These investigators were able to destroy structure characteristics by prolonged ball milling; this procedure caused higher bulk densit,ies and a lowering of modulus in rubber. K O changes in particle size, surface area, tensile strength, and resilience accompany this change in modulus. Although t h e concept of struct,ure is helpful in explaining high modulus, smooth-out, and low processing shrinkage, other rubber properties of these blacks such as tensile strength, abrasion resistance, resilience ( 1 4 , 15), and dynamic modulus ( 3 ) can be correlated with particle size and are not particularly affected by st.ructure. It is apparent t h a t if such structure exists it must consist of relatively weak particle-particle association which can restrict t o a small degree the elastic properties of the raw rubber matrix and t o a much smallcr degree t'hat or the cured rubber mat'rix without affecting those properties depending on the extent or degree of carbon particle-rubber matrix bonding. Thus the high structure blacks may bo considered as characterized by a nonuniformity of dispersion in rubber compared t o nonstructure blacks, although both types of blacks may be relatively conipletely wetted by the rubber matrix. EVALUATIONOFCARBONBLACK STRUCTURE
Sweitzer and Goodrich ( 2 1 ) have defined a structule index of carbon blacks based on oil absorption and surface area measurements. This index gives a n indication of structure but suffers from the inherent inaccuracy of oil absorption determinations. Variations in oil absorption values arise from the difficulty in estimating the end points; difficulties in maintaining a controlled degree of mechanical working of the oil-black mix; and may depend 011 the mechanical agitation the black has received prior to testing. Also it would be more satisfactory to measure a rubber property directly affected by structure than a property of an oilblack system. Electron micrographs of carbon black cannot give any quantitative estimation of structure in rubber because the observations are not made usually in the actual rubber medium. Electron micrographs can vary in the degree of aggregation displayed depending on the method of sample preparation employed, and also on the particular sample preparation under observation. Figure 1 illustrates this last point. Electron micrographs are shown of two sample preparations of the same black; both display some aggregates of high strhcture whereas other aggregates in the same pictures show lesser structure. Differences in stiffness or modulus of loaded rubber stocks containing a series of blacks of approximately the same particle size is one of the experimental observations leading t o the postulation of structure. T h e moduli for such a group of loaded stocks could be used as a n index of structure. This procedure is not satisfactory because of the experimental difficulties involved in comparing moduli at equivalent states of cure which is often an impossible condition t o achieve. Even if this could be done relative moduli ratings may vary with elongation, depending on the shape of the itress-strain curves. Because of the large differences in mill shrinkage and smoothness of furnace black loaded GR-S stocks i t was felt t h a t such processing properties could be used t o characterize these blacks. The practical utility of shrinkage measurements as a measure of
813
Figure 1. Electron Micrographs Showing Results of Different Preparation of T w o Samples of the Same Carhon
Black rubber processing has been discussed in a number of publications (8, IS,32-25). It has been found that the effect of carbon black on processing shrinkage can be del ermined easily with a laboratory extruder equipped with a circular die. The data can be expressed as the shrinkage of a given weight of extruded stock or t h e equivalent expression of die swelling. Extrusion shrinkage is calculated from the difference in the length of extruded stock and the theoretical length calculated from the diameter of the die opening and the weight and specific gravity of the extruded section. This extrusion shrinkage value is related t o die swelling by the following simple expression :
yo extrusion shrinkage
=
100 s
s + 100 ~
where S is the percentage of die sielling. Extrusion shrinkage measurements as described give about the same value as mill-shrinkage determinations and measure the same phenomenon' of processing shrinkage. METHOD FOR MEASURING EXTRUSION SHRINKAGE
The recipes given in Table I were used for all extrusion shririkage measurements. All mixing was done using a Type B Banbury, followed by a 12-inch roll mill having a roll s eed ratio of 1t o 1.3. Batch factors of 5 for GR-S and 6 for naturayrubber were used t o determine the actual weight in grams of each batch. The GR-S stocks were mixed in the Banbury using a n &minute cycle followed by 3-minute roll milling at a mill gap of 0.10 inch. The Banbury and roll-mill circulating water temperature mas 120" F. Natural rubber processing procedure consisted in mixing black, rubber, and softener in the Banbury using a 6-minute cycle. A zinc oxide-antioxidant masterbatch was added on the mill a t N mill gap of 0.12-inch and the milling continued for 3 minutes. Stocks were allowed t o stand overnight at room temperature. After remilling these stocks and sheeting-off at a gap opming of 0.075-inch, strips approximately 1 inch wide and 12 inches long were cut from the sheets in a direction across the milling grain. About 100 grams of these strips were fed into a KO. 1/2 Roylr estruder equipped with a die having a circular opening 0.109-inch diameter and heated by 168" F. circulating water. The 100 grams of stock were recycled through the extruder three times; the last time care was taken not t o stretch or pull the extruded section as it emerged from the die opening. Slightly over a meter length of the extruded section was cut off and placed on a Holland cloth which had been lightly dusted with talc. After resting for a minimum of 4 hours a length of exactly 1 meter was cut off and weighed. The specific gravity of the stock was determined independently. For both recipes the specific gravity was 1.15 a t a 50 part black loading. The extrusion shrinkage was calculated as follows:
W = weight of 100 cm. of extruded stock in grams; A = area in square cm. of die opening; and S.G. = specific gravity of stock.
814
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE
I
FOR EXTRUSION SHRINKAOX R h A SUREMENTS
V I S U A L DIFFERENCES I N SM0,OTHOUT
1. RECIPESUSED
100 o 3 5 2 1
Varied a As omitted
S a t u r a l Rubbera Components Parts Components GR-S 100 Smoked sheets 3 Pine tar Bardol Pine tar 3 Stearic acid Zinc oxide 5 Zinc oxide 1 Agerite Hiuar Sulfura Santocurea Varied Carbon black Carbon black a precaution against scorching the sulfur and accelerator were a t the 80 part loading in GK-F and a t all loadings in natural rubber.
MAXIMUM
GR-S
Parts
Vol. 41, No, 4
60
1
+
I
c
0 0 I
~ 5 0 v-, (3
TABLE IT. Test h-0. 1 2
SPHEROX 9 EASY PROOESRING CARBONBI,.ACK "/o Extrusion Shrinkaw
I) P yi R t i o n f 1'o n i -4w r a g e
57.3
0 ,3 0.1 0.7
3
j7.7 58 3
?
58.8 35.3
A 7 8 9 10 11
57.3 ;i7.0 j8.7 55.7 58.7
58.4 Average 37.6 Q %Average de\-iation = 1.65%;
1.2
2.3 0.3 0.6 1.1 1.9 1.1 0.8
U
Y
5
a
I
13
a IX
30-
t-
z
GR-S EXTRUSION SHRINKAGE vs. BLACK LOADING
W
a W
EXTRUSION SHRINKAGE OF REINFORCING FURNACE BLACK GR-S TREAD STOCKS
The above procedure was followed on a series of mixings in which the type of black and the loadings were varied. 4 more extensive study was made n-ith GR-S t'han with the natural rubber mixtures because GR-Sstocks give moTe information regarding the processing characteristics of carbon blacks. A fen- of the pertinent properties of the blacks selected for extmsion shrinkage evaluation are shown in Table 111. These blacks cover a range of processing properties. Fine thermal, semireinforcing furnacr, and easy processing channel blacks 17-ere included to give a basis for
( R F ) VULCAN
v)
0
Accurate temperature control of t,he extruder does not seem to be necessary in the case of GR-S. A variat,ion in jacket water temperat'ure from 100" to 200" F. caused a decrease of only a few per cent, in extrusion shrinkage. Check values on a given GR8 recipe over a period ot 6 months on separate mixings have shown excellent reproducibility. The data (Table 11)on a 50 part loading of easy processing black in GR-Sillustrate this point,
STERLING SO
(HMF) PHILBLACK A (RF) KOSMOS 6 0
z 4012
~
Average deviation O , Q 5 u (standard deviation) = 1.14
(HMF)
v)
n
IO 1 0
I
20
I
40
I
60
1
00
LOADING Figure 2
comparison with the relatively- new grades of reinforcing furiiaoc. blacks. The surface appearance of extruded GR-S stocks (Table 111) is riot related to either t>hesurface areas or the mean particle diameters. Ilowever, oil absorption values do characterize the high structure smooth-out, blacks; the higher values indica,t,e smooth stocks. Figure 2 illustrates the marked variat,ions obtained in the (?xtrusion shrinkage4oadiIig curves. The effect of loading on shrinkage is almost negligible in the case of P-33 (fine thermal;, a black characterized by large __ particle size, loiv oil absorption, and low modulus. The blacks having the largest effect. on reducing shrinkage vary conTABLE 111. PPOPERTIES O F C l R B O N B L A C K S FOR EXTRUSIoV siderably in particle size but have in common t,he 8HRINXAGE ~7.4LU.4TION properties of high oil absorption, high modulus, Surface Electron Oild and impart t o GR-S stocks a smooth surface apAreao, Microscope Absorption, GR-Sh sei. Mean Lb./100 pearance. The blacks falling between these two Trade S a n i e Classificdtlon Smooth-out aI./G. Diameter, Lb. Black extreme types show varying ability in retarding n1P Fine thermal P-33 Rough 15 134 40 shrinkage and are also intermediate in those propSterling S Semireinforcing Rough 23 A0 70 erties associated with structure. It is therefore Easy processing Spheron 9 Rough 100 33 81 channel suggested that such a processing shrinkage measSterling 105 Reinforcing furFairly sniooth 87 39 76 nace urement affords a quantitative means of rating Philblaok 0 Reinforcing furFairly snioot,h 7; 33 110 the structure properties of all carbon blacks. nace Philblack A High modulus Smooth 43 ... 116 The broken line in Figure 2, labeled the smoot,hfurnace out line, has been drawn through t,he particula,r Sterling SO High moduluP Smooth 46 45 105 furnace loading a t which the surface of the stocks apKosinos 60 Reinforcing furSniooth 90 35 110 nace peared t o develop a n arbit'rary degree of smoothVulcan Reinforring furSmooth 11.7 32 124 nace ness. Those blacks having the maximum effect in reducing shrinkage are also the most effective a Classification of carbon blacks is in a confused atate a t the present time due to the introduction of 'new furnace blacks possessing qualities not adequately Characterized by an17 of for giving high surface smoothness at low loadthe accepted classifications; all blacks possessing reinforcing properties about the equal of or ings. The smooth-out line is not horizontal at: better than easy processing channel black are shown as reinforcing furnace Slacks; high modulus furnace blacks are less reinforcing than reinforcing furnace blacks but Inore reinwould be the case if shrinkage were the major forcing than semireinforcing. b Appearance of 50 part loading tread recipe after extrusion. factor responsible for surface smoothness. Conc L o r temperature nitrogen adsorption method (a). d Gardner method ( 7 ) . sidering the fact t h a t one rubber stock showing a n extrusion shrinkage of t5070 may be p c ~ -
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
1,OAI)IriG 20
LOADING 35
815
fectly smooth whereas another stock showing the same shrinkage may be rough it, must be concluded t h a t smoothness is related to the uniformity of shrinkage. This uniformity of shrinkage seems to be anot'her property associated wit'h structure blacks. The ability of struct,ure blacks to. reduce procrssing shrinkage limy be explaiiied possibly by assuming t h a t the carbon particles are not dispersed uniformly because of their origiiial. aggregation habit. This would cause variations in black concentration tlhroughout, the volume of the loaded rubber stock and result in a partial restrict,ion of the elast>icproperties of the rubber matrix involved in the regions of higher black concentrat,ioris. Thus the same effect is produced as would be observed in going to a higher loading of black; tlhe effective volume of the stock posseEsing elastic properties is ieduced. This explanation therefore post,ulates a phenomenon similar to gel formation in the rubber phase, using the term gel loosely, on t,he part of the structure blacks. rinalogous changes in processing characteristics are observed if the gel content of standard GR-S 1s increased (16). Deformation of such gelled systems is more irreversible than less restricted systems and will result in a decrease of raw elasticity a i d procpssing shrinkage. These effects can be expressed in rubber cheqistry terminology as a reduct,ion of nerw. It follows that if t,he above mechanism is correct the rubber phase of the gelled fraction after deformation, must be under a higher degree of strain than the remainder of the rubber inatr ' For comparing differences in surface srnoothueas it was found that at, a 35 part loading the largest gradations were obtained. St the 20 part loadings all stocks were rough :tnd ttt the 50 part loadings the smooth-out, effect is so pronounced t'hat small differences between blacks are obscured. Visual differences in roughnew are easily recognized whereas there are no differences apparent once a degree of high smoothness is obtained. Figure 3 shows extruded sections of the stocks corresponding to the curves shown in Figure 2. I t is evident that smoot,hness increases with loading and that the structure blacks smooth out a t lower loadings. The 35 part loadings have different surface textures for each section. This is not t>hecase for any other loading.
LOADING 50
PROCESSING SHRINKAGE INDEX
It is desirable to be able to assign a number to a black which
LOADING 63
LOADING 80
will rate its effectiveness for reducing processing shrinkage. Actually the extrusion shrinkage value a t a 50 part, loading in GR-S 'could be used, but it is felt that a more useful number arid a less specific rat'ing is obtained if the shrinkage is expressed in terms of t,he shrinkage of a standard black. Accordingly, a processing shrinkage index has been defined in terms of Spheron 9, a grade of easy processing channel black, as the extrusion shrinkage for each black stock divided by the extrusion shrinkage obtained for the channel black stock using GR-S and a 50 part loading. Processing shrinkage index values for a large number of blacks are given in Table IV. Processing shrinkage index values show a rough correlat,ion with oil adsorption values in that the low oil absorption blacks give the highest shrinkage and the high oil absorption blacks give the lowest shrinkage values. However, oil absorpt'ioii cannot give a generally consistent index of processing because of the inaccuracy of the determination. The samples of furnace blacks given in Table IV show lwo main groupings. One group has index values of 0.95 t o 1.06 and is characterized by the processing shrinkage properties of channel black although definite and reproducible differences exist in this group. The second group consists of high st,ructure blacks in the narrow range of index values of 0.76 to 0.78. Philblack 0 and the lampblacks are intermediate in shrinkage between these two ex-
+ Figure 3.
Extruded Sections of Stocks Corresponding to Curves Shown i n Figure 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
816
Vol. 41, No. 4
I
I20
81
'
7
w (3 U Y
za 61 I
v)
I-
(HMF) STERLING S O (HMF) PHILBLACK A ( R F ) KOSMOS 60 ( R F ) VULCAN
z
W
0
a
w 5
n.
4
GR-S RUBBER MATRIX SHRINKAGE\ vs BLACK LOADING 20 I
40 I
60
LOADING
\1
\\
80
Figure 5
Figure 4
NATURAL RUBBER MOONEY VALUES vs BLACK LOADING
6C
W 0
a
x 5c
z
a L cn Z
0 (0 4c 3
a
L 5 3c W
W
0
a
w
N A T U R A L RUBBER EXTRUSION SHRINKAGE vs BLACK LOADING
a
10
I
0
I
I
I
20
40
60
80
LOADING
Figure 6
Figure 7
t
1
April 1949 TABLEIV.
PROCESSINQ SHRINXAQE INDEX
Carbon Black Trade Name P-33 Sterling S Sterling L Spheron 9
Classification Fine thermal Semireinforcing High modulus furnace Easy processing chnnne1 Statex K Reinforcing furnace Sterling 105 Reinforcing furnace Philblack 0 Reinforcing furnacc Monsanto 10 Lampblack Monsanto B5 Lampblack Monsanto 1 Lampblack Philblack A High modulus furnace Sterling SO High modulus furnace Kosrnos 60 Reinforcing furnacc Vulcan Reinforcing furnace Acetylene Conductive furnacc: (Shawinigan)
Absorptions,
Oil
Surface Area,
70 74 81
23 31 100
Lb./100 Lb. Black 40
75
76 110 93 103 84
116 105
110 124 144
S M.7b.b 15
GR-S, % Extrusion Shrinkage (50 parts) 63.4
61.7 59.2 60.0
55’
87 75
13
...
69 43 46
90 117 65
a Gardner method (7). 6
817
INDUSTRIAL AND ENGINEERING CHEMISTRY
Nitrogen adsorption method ( 8 ) .
treme groups. Acetylene black gave the lowest processing shrinlrage index in line with its high oil absorption value. The decrease in processing shrinkage with an increase in black loading is expected simply from the fact that the volume of .actual rubber in the stock is proportionally reduced. By expressing the per cent shrinkage on t.he basis of the volume of the rubber phase, where all the shrinkage occurs, interesting loading relations are observed as shown in Figure 4. In each case except. P-33, a definite maximum in rubber phase shrinkage value is evident. At the low loadings this shrinkage actually is increased by the presence of black, but a t the higher loadings the effect of black structure reverses this trend. The loadings corresponding t o the maximum values decrease with the effectiveness of the blacks in lowering processing shrinkage. It is felt that the increase in rubber phase shrinkage a t the lower loadings is due t>othe greater strain imposed on the rubber phase by the presence of black during the process of extrusion. On emerging from the die opening this enhanced strain causes a greater elastic retraction and higher shrinkage value. That the incorporation of carbon black causes the development of a higher degree of strain in the rubber phase on stretching has been demonstrated by x-ray studies of Gehman and Field (9). As loading increases, the blacks, depending on hheir structure tendencies, overcome this effect of strain and restrict the elastic properties of the rubber phase. This retardation of elastic recovery caused by particle-particle associat,ion must freeze the rubber matrix in a state of higher strain than would be the case if blacks of lower structure had been used. The effects of structure can be detected also from the variatiop of Mooney values with loading. Figure 5 shows curves of lLIooney values against loading determined on the same stocks used in the extrusion shrinkage studies. The high structure blacks cause a sharper increase i n Mooney values with increase loading than do the lower structure blacks. The plasticity of black-rubber stocks therefore must be a function of both particle size and the degree of black structure. Thus, structure tendencies of carbon black not, only cause B reduction in t,he elasticity but also increase the plasticity of raw sbocks. STRUCI‘URE FURNACE BLACKY’IN NATURAL RUBBER
The processing properties of natural rubber stocks are much less affected by carbon black struct~urethan is observed in the case of similarly loaded GR-S stocks. This probably arises from the great’er mobility of natural-rubber chain units compared to GR-S and the larger number of possible configurations of such units. A consequence of such a condition is enhanced rubberlike elasticity which would be less sensitive to restricting influences imposed by carbon black structure. I n Figure 6 it can be seen that at loadings of 50 to 80 parts of black the effect of structure in natural rubber i s definitely present. The results correlate with those described
on GR-S. However, a t the 50 part loadings the range of extrusion shrinkage values going from blacks of low to high structure tendencies is narrow Processing compared to GR-S. At the higher loadings of 65 Shrinkage Index and 80 parts the spread becomes appreciable, but 1.06 these loadings are not practical for routine evalua1.03 0.99 tions of tread type recipes. 1.00 Since natural rubber is inherently smooth processing the effect of black structure on this property is difficult to observe. Only at the 80 part loading does there seem to be a definite effect of the structure blacks on the smoothness of extruded sections of natural rubber stocks. The reproducibility of cxtrusion shrinkage measurements with natural rubber also is not as good as with GR-S. Since the effects of milling, temperature, and oxygen are more prqnounced with natural rubber than GR-S, variability in processing shrinkage may be attributed to these factors. Because of the difficulties associated with natural rubber, GR-S was selected as a more suitable rubber for characterizing the processing characteristics of furnace blacks. Figure 7 shows the Mooney viscosity-loading curves for a few types of furnace blacks. I n line with the extrusion shrinkage results in natural rubber, the structure blacks are not sharply differentiated from the other blacks, Sterling SO, a definite smooth-out structure black gives the same shape of curve as does Sterling 105, a black of much less structure. Only in the case of Vulcan at the 65 part loading is a sharp increase in Mooney value observed. This black is a much smaller particle size black than Sterling SO and extrusion data places it in the same structure category. LITERATURE C I T E D
(1) Braendle, H. A,, Steffen, H. C., and Sheppard, J. R., presented before the Division of Rubber Chemistry at 113th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill. (2) Brunauer, S., Emmett, P. H. and Teller, E., J . Am. Chem. Soc., 60,309 (1938). (3) Buist, J. M., and Mottram, S., T r a n s . I n s t . Rubber I n d . , 22, 82 (1946). (4) Crayno‘r, D. F., Snyder, J. W., and Cobbe, A. G., I n d i a Rubber W o r l d , 117, 749 (1948). (5) Dobbin, R. E., and Rossman, R . P., IND. ENG.CHEM.,38, 1145 ( 1946). (6) Drogin, I., and Bishop, H. R., presented a t the Meeting of the Division of Rubber Chemistry, AMERICAN CHEMICAL SoCIETY, Cleveland, Ohio, May 1947. (7) Gardner, H. A., “Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors,” 6th ed., p. 475, Washington, D. C., Inst. of Paint and Varnish Research, 1933. ( 8 ) Garvey, B. S., et al., IND. ENG.CHEM.,34, 1309 (1942) (9) Gehman, 5. D., and Field, J. E., Ibid., 32, 1401 (1940). (10) Hall, R., Buckley, B., and Griffith, T., Can. Chem. Process Inds., 29,587 (1945). (11) Holbrook, E’. L., and Hunter, B. A., presented before the Division of Rubber Chemistry at the 113th Meeting of the AMERICAN CHEMICAL SOCIETY, Chicago, Ill. (12) McCollum, 0. H., IND.ENG.CHEM.,to be published. (13) Mooney, M., J. Colloid Sci., 2, 69 (1947). 114) Parkinson, D., Trans. I n s t . Rubber I n d . , 19, 131 (1943). (15) Ibid., 21,7 (1945). (16) Schoene, D. L., Green, A. J., Bunes, E. R., and Vila, G. R., ISD. ENG.CHEM.,38,1246 (1946). (17) Schuhe, W. A., et al., I n d i a Rubber W o r l d , 117, 739 (1948). (18) Sperberg, L. R., Svetlik, J. F. and Bliss, L. A., IND. ENG.CHEM., to be published. (19) Staff Report, Chem. Eng. News, 25, 1115 (1947). ENG.CHEM., in press. (20) Stokes, C. A., and Dannenberg, E. M., IND. (21) Sweitzer, C. R., and Goodrich, W. C., Rubber A g e , 55, 469 (1944). (22) Taylor, R. H , Fielding, J. H. and Mooney, M., Ihid., 61, 705 (1947). (23) Vila, G. R., IND. ENG,CHEM.,36, 1113 (1944). (24) White, L. M., Ebers, E. S., and Schriver, G. E., Zbid , 37, 767 (1945). (25) Zapp, R. L., and Gessler, A. M., Ibid., 36, 656 (1944). I
RECEIVED June 28, 1948. Presented before the Division of Rubber Chemistiy at the 113th Meeting of the Ahrnnrc~1-CHEMICAL SOCIETY, Chicago, I11
