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INDUSTRIAL AND ENGINEERING CHEMISTRY
1948
1473
used the usual rapid reaction takes place and level8 out after about 160 hours. The GR-S ebonite 7 dust took 3 hours t o settle t o the bottom of the flask against 15 minutes for natural rubber ebonite 4. I n general, however, the reactions of natural rubber and GR-S ebonites with methyl iodide are very much alike. No indication of the presence of polysulfide linkages in ebonite is given by the extraction or the methyl iodide experiments. The sulfur elimination curve is hard to interpret because the controlling rate factor is probably the diffusion through the ebonite, even though 60-mesh ebonite dust was used in all the experiments reported here. SUMMARY
REACTION TIME
Figure 5.
IN HOURS
Reaction of Methyl Iodide with GR-S Ebonite 7 at 24' C.
quantities of crystalline trimethyl sulfonium iodide are liberated from the hard rubber as well as small quantities of iodine. The shape of this curve is nearly identical with that of the unextracted rubber-sulfur SBlA stock (Figure 1). About 1% of the iodine is combined i n the rubber. When mercuric iodide is used a rapid reaction takes place in the first 72 hours, down t o 24% sulfur, whereupon only 4% more sulfur is eliminated in the next 900 hours. Prior acetone extraction has no influence on the reaction. The hard rubber retains nonextractable mercuric iodide to the extent of 48 to 52y0 of the final weight of the treated ebonite. As in the soft rubber reactions the mercury and iodine are in the proportions represented by HgIz I. The reaction start,s immediately and the hard rubber powder, which normally floats in methyl iodide, sinks to the bottom in 15 minutes. Within a few hours iodine isliberated. The reaction of extracted GR-S ebonite 7 with inethyl iodide is shown i n Figure 5. With methyl iodide alone the reaction is directly proportional to time. The rate of removal of sulfur is slower than t h a t obtained with natural rubber ebonite 4 (Figure 4) and shows no inclination to level off. When mercuric iodide is
1. For the soft rubber stock SBlA there is no evidence for the change: polysulfide + free sulfur on acetone extraction. 2. Evidence for the c b n g e : polysulfide + other sulfur links on acetone extraction is indicated by increased reactivity of extracted SBlA t o methql iodide. 3. Natural and GR-S ebonites lose about one third of their combined sulfur on reaction with methyl iodide a t 24" C. Trimethyl sulfonium iodide is found in large quantities. 4. Neither extraction experiments nor methyl iodide reactions offer evidence for occurrence of polysulfides in 32% sulfur natural ebonite. LITERATURE CITED
Am. Boc. Testing Materials, Standards on Rubber Products, D297-43T, pp. 10-11, 1946.
Armstrong, R. T., Little, J. R., and Doak, K. W., IND.ENG. CHEM.,36, 628-33 (1944) ; Rubber Chem. Technol., 17,788-801 (1944).
Bloomfield, G. F., J . Polymer Sci., 1, 312-17 (1946). Farmer, E. H., and Shipley, F. W., Ibid., 1, 293-9 (1946). Meyer, K. H., and Hohenemser, W., Helv. Chim. Acta, 18, 106166 (1936) ; Rubber C h e n . Technol., 9,201-5 (1936). Naylor, R. F., J.Polymer Sei., 1, 305-11 (1946). Selker, .M. L., and Kemp, A. R., IND.ENG.CHEM.,36, 20-28 (1944) ; Rubber Chem. Technol., 17, 314-30 (1944). Selker, M. L., and Kemp, A. R., IND. ENQ.CHBM.,39, 895-900 (1947).
Selker, M. L., Ibid., 40, 1467 (1948). RECEIVED February 11, 1947.
PARTICLE SIZE IN LATEX As Related to Synthetic Rubber Properties and High Solids Latex Fluidity A. M. BORDERS
~ N R. D M. PIERSON Goodyear Tire and Rubber Company, Akron, Ohio
I
vears. several investigators have studied the particle sizes of latexes containing butadiene copolymers, particularly butadienestyrene rubber. Among these workers are Debye, Harkins, Heller, Maron, and many others. The purpose of this paper is to indicate the important polymerization variables that influence latex particle size; t o summarize studies directed to a determination of the influence of synthetic latex particle size on polymer properties; and t o present "
I
N R E C E N T years there has been considerable interest in the study of latex particle sizes of natural rubber latexes ahd of various synthetic polymer emulsions. Among the investigators of natural rubber latexes were Green (Y), Henri (9),Kemp ( I I ) , Langeland ( I $ ) , and Lucas ( I S ) . I n 1931 Cerothers, Williams, Collins, and Kirby (1) reported T h e important variables influencing particle sizes during polymerization of synthat particle size determinations thetic latex are discussed. By controlling the conditions of the emulsion polyfor polychloroprene latexes merization so as to produce very large particles, the successful preparation of a showed, on the average, a much fluid 60% solids butadiene-styrene latex and of very low nonrubber content has smaller particle size than Heven been achieved. This latex is being marketed i n tank car quantities. The possibility latex. With the intensive studied that properties of the polymer formed in such large particles might he significantly related to the manufacture of differeat from those of rubber prepared in the usual smaller particle size emulother synthetic rubbers in thr sions, such as GR-S, has been examined; no differences in vulcanizate properties ' United States within the last 6 attributable to the increased particle size have been found.
'
1474
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
Vol. 40. No. 8
tributions. The pronounced effects which changes in the size distribution can produce in the numerical values obtained using the different parameters have been discussed by many authors ( 4 ) . In synthetic latexes, where particle size ranges are wide ( 3 , I 6 ) , there has not been sufficient,correlating evidence to indicate which of tho averages is most significant in interpreting latex propc'rt,ics.
In this laboratory most of the measurements n-ere made by a determination of the total surface of the latex particles using R soap absorption method originally mentioned by Jordan ( I O ) for synthetic rubber latex, and more recently developed to a high stat'e of usefulness by Maron and eo-workers ( 1 4 ) . The average Xnd3 thus obtained is known as a volume-surface diameter, __ and Zndz' is distinct from the surface diameter
d-.F
Although the
absolute values obtained with bhis method may in many instances differ widely from those of other methods-because of the polydispersivity of t'he system-for comparative purposes it is convenient and very useful. Another experimental method for investigating latex particle sizes which involves measurcinent of light scatt,eriiig of greatly diluted latexes is described i n detail by Debye ( 5 ) who measured light scattered at various angles from highly diluted latexes. In this laboratory a simple turbidity measurement is made with the Coleman model 11 spectrophot'ometer, using: ;latexes diluted t'o 0.1 t o 0.5 gram per liter; wave length, 6000 A , ; cell thickness, 2.0 em. : and calculating: Turbidity = +
an application in which a knowledge of the factors controlling particle size was a n aid in the development of a process for manufacture of high solids synthetic latexes. The present study of any correlation between latex particle size and polymer characteristics is only preliminary. The problem was undertaken in this laboratory with no expectation that variation in latex particle size within a given monomer system would effect any remarkable change in rubber quality. Less pronounced effects might reasonably be looked for-for example, such properties as butadiene-styrene ratios, gel content, and the average molecular weight with various modifier concentrations, might be affected, These studies are of particular interest in their relation to theories of locus and mechanism of polymerization in aqueous emulsion. It was only after the completion of most of the n-ork described here that the predictions of Hauser and Le Beau (8) came to the authors' attention. These investigators pointed out the wellknown fact that synthetic latexes ordinarily have much smaller particles than natural rubber latexes and stated that, to their knowledge, polymerization chemists have been unsuccessful in appreciably increasing the average particle size of synthetic latexes. They concluded that, if the particle size of the monomer could be increased when the emulsion was made, or a t least during polymerization, a latex and finally a synthetic rubber could be produced which would be closer to natural rubber in its propertics than available synthetics. METHODS OF PARTICLE SIZE DETERMIN.+TIOS
There are several methods for qualitative comparison of latex particle sizes. Difficulties are encountered in attenipt,ing a quantitative interpretation of ccrt,ain of these nieamremcnts and particularly in att,empting a comparison of results obtained by different methods, without accurate knowledge of particle size distribution. Because most synthetic latexes contain particles of a wide range of sizes, any comparison of average size must indicate the type of measurement involved and the kind of average used. Thus, for example, the results of a det,ermination based on soap adsorpt,ion will represent an average diameter based on total surface of the particles. Measurements involving light scattering are presumed to represent weight average values, whereas electron and light, microscope studies are usually reported in number dis-
loglo roll concn. in g./l. X 2.0 em.
S o corrections were made for secondary scattering. Kithin certain limitations the turbidity values determined under these conditions may be used as a rough index of latex particle size. This method has been found t o be the most convenient for rapid laboratory evaluation of the effect of various emulsion variables. Electron microphotographs represent the only direct method for investigating latex particle size distribution. However, information gained from photographs is influenced to a high degree by preparation techniques and subjective interpretation of the pictures. If valid results are t o be obtained, extreme care must be taken to avoid agglomeration or overlapping in the preparation of the specimen for the microscope. Only a few microphotographs have been made in the work reported here, as in most cases relative and approximate comparisons of latexes were required rather than absolute measurements. DEVELOPMENT OF HIGH SOLIDS LATEX USING INCREMENT SOAP ADDITION
In several industrial applications of natural latex it is essential t,hat the solids content be high. (In this paper reference to high solids latex indicates a latex of greater than 55% tot'al solids.) High solids Hevea latex was commercially available before the war from several methods of concentration: evaporation, ccntrifuging, and creaming. Early attempts to apply these t'hree met'hods t o the ordinary synthetic GR-S latexes showed that the viscosity of t,he latex increased rapidly at a solids content well below those required for most commercial uses. Thus, an ordinary GR-S latex evaporated to 45'% solids is scarcely mobile. Although the first semiquantitative determinations of particle sizes had shown GR-Sparticles to be very small compared t o those of Hevea, this fact. was not immediately connected with poor fluidity a t high concentrations. It is true that creaming has been successfully applied as a method of concentrating dilute GR-S latexes, but successful applicat,ion involved a preliminary agglomeration with acids or ot'hcr electrolytes t o increase the latex particle size before addit,ion of a creaming agent. In attempts t o make a. high solids latex of the GR-S type by reducing the water content of the polymerization charge, i t was found that the proport,ion of water to monomers may be reduced only moderately below that ordinarily used in producing 25 to 30% solids l a t e k . Two factors become important as the r a t e r content is decreased: the heat of polymerization per unit volume becomes greater and the emulsion viscosity increases. Thus, be-
August 1948
INDUSTRIAL AND ENGINEERING
CHEMISTRY
1475
yuiicl a crrtain puint,, further reduction in water charged caujcs viscosity increases so severe that during at least onc'periodof the reaction the entire emulsion is a thirk paste wherein thc temperature rises t o excessively high values bccausc of the poor heat tranjier. Accordingly, adjustment of water content alone doesnot permit preparation of a 5510 6OmCsolids latex directly in the reactor. 011esolution to the problem, described by Cliittenilen, .\IcClear)-, and Smith (P), is special agirarion and addition of viscosity reducing agents to the emulsion t o produce stable, fluid latcxcs of 55 to GOc; totalsolidsdirectlyin thcreactor. In thclon water iormulations used by these workers t,he amount of soap charged was of the smic ordcir as that u-.cd in making ordinary dilute syrithetic latexes. Hence, the average particle size of those laFigure 2. Electron Microscope Photographs of Latexes texes is probably only slightly larger than t h a t of the dilute GR-S latexes. ( L e f t ) Ordinary GR-8, type 11. (Right) High solids, large particle size type V latex I n earliest attempts in this laboratory t o make synthetic latexes directly in the reactor i t was found, as Observed by others, t h a t by reducing the soap content One hypothesis which may explain the phenomenon is: a s of the initial charge-that is, t o less than 2% soap on the appreciable quantities Of polymer are formed during the monomers-the average particle size of the resulting latex was stages of conversion the polymer is distributed mostly in latex markedly increased. The effect of varying the charged soap concentration of a dilute GR-S type recipe over a fifty fold range is particles of the polymer-plus-monomer type rather than forming illustrated in Figure 1, where turbidity values for a series of 5particles of pure polymer to give a mixture of exclusively monogallon reactor latexes are shown. These dilute latexes were polymer pnrticles. As such the polymermer and made when properties of rubbers obtained from large particle plus-monomer particles tend to retain their identity instead of size latexes were first being studied. The effect of reducing soap concentration is more pronounced in continually merging and reforming as monomer droplets are prcthe low water charges necessary for making 55% latex. Even sumed t o do. As conversion increases the partirles become inwith ~ other ~particles t ~ ~ t ~ ~ $ creasingly ~ e less~likely~ to blend ~ ~ $ on colliding, and soap added after certain minimum Polymer contents have critical point during polymerization made necessary the development of s ecial agitation which decreased the duration and been reached will tend to become sorbed onto these already severity o t t h e instability period and permitted heat transfer formed particles rather than to increase the total number of sufficient t o prevent extreme temperature rise of the emulsion. particles by forming new particlfs from the large droplets of unWith agitation used in the standard GR-S plants temperature reacted~onomers. control could not be maintained and latexes partiaily coagulated Thus, latexes of large particle size may be formed which conin t h e reactor. Particle size measurements of latexes made in this manner tain sufficient soap for product stability, inasmuch as stability is indicated a higher average value than for ordinary GR-S latexes. surface area 'Overed by governed by the fraction Of Methods of further increasing the particle size were sought in the rather than by the absolute amount of soap Present. The same hope t h a t even larger particles might further decrease the peak total amount of soap causes extremely fine particles if all of it is viscosity during polymerization and eliminate t h e necessity for extremely vigorous agitation as required for the process outlined charged initially. The large particles are important not only t o fluidity of the final latex but t o stability of the emulsion during , Although several modifications indicated improvements in this polymerization. With the soap addition technique, low water direction, the outstanding innovation involved careful control of charges necessary for making 60% solids latex do undergo a n inthe initial particle size by a very low soap concentration in the crease in viscosity during a certain period in the reaction, but the original charge, together with addition of more soap during extent of the increase and the emulsion instability are much less polymerization. It was found that soap addition at carefully than when no soap additions are made. selected points during the reaction significantlj improved staTo indicate very roughly how latex viscosity is dependent on bility without appreciably decreasing average latex particle size. average particle sizc, approximate solids contents are given for
~ ~ ~ ~ ~ g ~ h e , ~yd;~ ~ i ' ~ e ~ ~ ~ ~ ~ ~
TABLEI.
Process used t o obtain concentrated form Type of recipe
Vo1.-surf. av. particle diam., A.
% solids
a b C
Concentrated GR-S Evaporation of ordinary GR-S latex Regular GR-S; high water t o monomer ratio; 4 t o 5% soap 800-900
42 to 46 max.
Nonrubber content, % of rubber Viscosity
COMPARISON OF IIIGH SOLIDSBUTADIENE-STYRENE RUBBERLATEXESMADEUNDER VARIOUSCONDITIONS
c,
poise
6 to 8
Heavy paste
Creamed GR-S Treating GR-S latex with agglomerating and creaming agents Same as GR-S
High Solids GR-S Directly in reactor
GR-S withlow water t o monomer ratio; 5 % soap
.......... 55 to
1 to 3
..........
1
1
Becomes heavy paste a t low conversions
..........
Low Soap Directly in reactor
Low water to mono-
mer ratio: low soap in charge
Commercial High Solids GR-S Latex Containing Daxad Directly in reactor
Low water to monomer ratio: 3 to 4 % soap plus vis-
cosity agents
.......... Preooagulates in reactor a t 35 to 4 5 % solids b
..........
GR-S type V latex (formerly X-276) is a commercially available late? made in Rubber Reserve plants. Can be made without precoagulation if very high power agitation is used to help increase latex particle size. Brookfield Synchro-Lectric viscometer used, rotating cylinder type.
reducing
1700
]
Type Va Directly in reactor
Low water t o monomer ratio. soap totaling 2' to 3% added partly i n charge and partly during reaction 3000
57
60
6to7
3 to 4
1 to 3
1to 3
1476
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 40, No. 8
Vulcanizates of the resulting polymeis, whose particle dianietrr TABLE11. TREADSTOCKPHOPERTIES OF MEDIUMLARCII. was approximately t,wo and a half times that of GK-S, had properPARTICLE SIZE TATEX COMPARED WITH GR-8 ties similar to standard production rubber. Typical tread stock values are shown in Table 11. A moderate advantage in the cold processing properties was found for the low soap rubbrrs when (,ompared t o regular GR-S a t a given plasticitv but this advantage disappeared under factory conditions of hot breakdown. Yol.-surf., av. dixin., a. 900 210(1 Rest cure The importance of grl in affecting prore\iability (16) was juit beTensile, Ib./sq. in. 2376 2125 ginning to become knoun a t that time, and the slight iuperioritj 650 m Elongation %, SOOYo m o d h u s , lb./sq. I I I 700 ti60 in cold processability, plus the failure of thie superioritr to carry 01 32 , ; reeound (75' F.) Flex life, ?in. (200" V.1 60 7C through a t the high temperature4, x a i awribed to the prewnce of 101 128 Heat rise. F. gel. Rerentl? , since increint.iit *ciap addition technique in low u ater rharge emulsions has e n a b l ~ dachievement of considrrablj' larger particles, the queqtion whether such changes in the polymerization environment. can wbstantiallp affect the polymer formed the ranges within which slrithetic butadieue-styrene latexes havr was again examined. i high fiolids type run was made in a 5heen found to possess the fluidity of 63 t o 65% centrifuged gallon reartor N ith especially vigorous agitation and low initial ~iaturallatex; above thew solids ranges factory handling tIecomr+ wap concentrations in order to obtain the largest possible particle irnpractical: qize. Gum stocks rather than tread stocks wrre tmted as a more Volume-Surface 3ensitive measure of any quality change. Results of these tests, dv. Dism., b Solids, 5% showing romparisons with regular GR-S and natural rubber, are 41-44 shown in Table 111. Alco included in the last h o rolumns are 51-54 69--6l data for centrifuged fractions of the latex having larger and smaller average particle sizes than the original latex. These 'These apply only to latexes niade from fatty acid or robin h o a p shomed n o significant qiiality tlifferenres. and substantially frec from salts or other viscositv reduring materials. Some possible methods of arriving at a high solids latex anti the resulting properties are given in Table I. A comparison of the particle sizes of a iegular GR-S latex (type 11) and the high solids type V is shomn in the elertron mirroqcope photographs of Figiire 2. H o t h of thew latexi= xwre p r e p m 4 in a production plant. PLANT PRODUCTION OF HIGH SOLIDS SYNTHE'rI(: 1 . i T E X
Based on the soap addition technique, improved knoil-lrdyc. ( i f agitation, and other factors, a 55 to 60% total solids latex of a 70:30 butadiene-styrene rubber is now in commcwial production 'Office of Rubber Reserve designation: GR-S latex type V). There is one outstanding advantage of the above method of producing high solids latexes over that which involves control of latex viscosity by addition of viscosity reducing agents: the artual rubber content of a latex with a given total solids is sub-tantially higher for a latex made with low initial soap conccntration and later soap addition than the rubber content of a late\ riiatle with the customary initial w a p concentration plus substantial amounts of a viiruhity ieduring material. 'This adi~aiilsgeis shown in Table 1. In several uses of latex the high conrentration of rubber hydrocarbon and as low a concentration of nonrubber substances as possible are important. The latex made by the process just described appears entirely satisfactory with respect to mechanical stability both on the basis of laboratory tests and actual tank car handling experience. EFFECT OF PARTICLE SIZE OK CURED RUBBER PROPERTIES
For several years in connection Kith the government-sponsored ..vnthetic rubber research program the authors have been iniereited in any relation of colloidal environment during emulsion polymeiization to polymer chaiacteiistics. Laboratory studies u pie initiated t o determine the effects, if any, of variation in latex tiroplet size on pioperties of synthetic rubber. Thcse tests u-crc carlied through the pilot plant stage, where a number of runs with ,O of the prescribed amount of soap used for GR-S were made in dilute activated recipes (Figure 1). Rubber from large partirlt' y i ~ eemulsions containctl more gel than rubber of the sanii, \looney viscosity horn normal 5 % :p emulsion5 (per cent soap 1- rx-nrersed on monomcrr)
0.7
0.8
0.9
1.0
1.1
1.2
1.3
TURBIDITY
Figure 3. Gel Contents of Polymer from Latex Particles of Varying Size, Fractionated by Centrifuging Latex was made in a dilutr, low soap GR-5 t y e recipe, G P in ~ polymer of unfractionated latex = 33.?$; turbidity of unfractionated latex = 0.95; centrifuging was carried out in a De Lava1 orram separator. Circles represent fractions removed froin the cream end and solid dnt? a r e fractions from the skim end.
Although the sizes of the largest particle synthetic latexes obtained in this work are still somewhat smaller than most a r repted values for Hcvea latex, evidence secured to date fails to -tiox that particle size, as such, has any more than a slight effert on the quality of vulcanizates of eniulsion diene copolymers. On thc basis of this stud> no support can be given to the hypothesib and picdiction of Haiiser and Le Beau (8)
INDUSTRIAL AND ENG INEERING CHEMISTRY
August 1948
TABLE111. COMPARISONOF GUM STOCK PROPERTIES OF BUTADIENE-STYRENE RUBBERFROM LARGE’ PARTICIA:SIZE LATEXWITH THOSE OF H ~ v e . 4AND GR-8
VoL-surf. av. diam.,
b.
Relative heat generation at constant force
Hevea
GR-9
2500 to 10,OOOb
High Solids, Increment Soap Addition Larger Smaller particle particle size size Whole fraofraclatex tionQ tiona
800
4600
5000
2800
2400 690 240 87 141 960
240 410 190
290 410 190
30 115
350 400 240 67 31 120
410 370 280 69 35 65
27 77
32 47
33 46
33 45
100
193
190
194
67
64
38 95
37 48 161
a Separated by centrifuging. b Approximate range of various investigators’ number average values. Attempts to determine surface average values of Hevea latexes using soap titration techniques have not met with much success because of the unknown extent to which the particles are covered with naturally present adsorbed materials. 0 Dynamic tests run as described in (6).
EFFECT OF PARTICLE SIZE DISTRIBUTION ON PROPERTIES OF UNCURED POLYMERS
Distinct from the problem of the effect of average particle sizes of different latexes are the properties of the polymers contained in the different size particles within any one latex. This approach relates to the mechanism and locus of polymerization in aqueous emulsion. Although no attempt will be made here to discuss in detail these still incompletely clarified phases of emulsion polynerization, one or two observations on the properties of polymers obtained from fractions of different particle sizes may be worthy of mention. Very crude fractionations of two diffepent large particle size latexes were obtained by centrifuging in a D e Lava1 cream separator type machine. For effective separation into different sizes, the important variables are the acceleration, the rate of latex feed, and the setting of the machine with respect to the relative volumes of the heavy and light end take-offs. Only a rough fractionation of sizes is obtainable with this comparatively mild centrifugation. A phenomenon of considerable interest was the observation that gel appears to be concentrated chiefly in the smaller particles. The correlation shown in Figure 2 was obtained for one of the dilute low soap GR-S type latexes referred to above. The fractions obtained with this method are extremely broad and can give only qualitative indications of the true distribution in a latex. Thus, similar intormation on well separated, closely cut fractions might show a much sharper division of properties than is ‘indicated here. Centrifuging a high solids type latex, wherein large particles were achieved by increment soap addition, caused a similar segregation of gel wi;h respect to particle size as shown in Table IV.
1417
Although the average size was greater than for the low solids latex described, the latex feed rate was several times that employed for the latter, and hence the net efficiency of separation was probahly somewhat poorer. Presumably a fractionation before a n y gel had formed would have shown a segregation of the higher molerular weight species within the smaller particles. Another property of interest in these fractions was the somewhat higher styrene content of the smaller size particles. The phenomena of concentration of gel and of higher styrene polymers in the smaller particles are features of considerable interest in interpreting theories on the mechanism of the formation and growth of latex particles, but are outside the scope of this paper. ACKNOWLEDGMENT
The writers express their appreciation t o L. H. Willisford for the electron microscope photographs, and t o J. M. Lawrence arid J. C. Needs for much of the experimental work. Acknowlcxigment is also made for the cooperation of the Goodyear Chemic.aI Engineering Diyision, particularly to J. D. Wilkerson and P. h1. Lindstedt, for their development of the high solids latex procesr o n pilot plant and manufacturing scales. Dynamic properties of thc. gum stocks were provided by 8. D. Gehmsn. LITERATURE CITED
(1) Carotheis, W. H., Williams, I., Collins, A. M., and Kirby, J . E. J . Am. Chem. Soe., 53,4203 (1931). (2) Chittenden, F. D., McCleary, C. D., and Smith, H. S., ILD. ENG.CKEM.,40,337 (1948).
(3) Columbian Carbon Co., “Electron Microscope Study of Rubber Latices and Pigments,” April 1944. (4) Dalla Valle, J. M., “Micromeritics: The Technology of Fine Particles,” pp. 31 ff., New York, Pitman Pub. Co., 1943. (5) Debye, P.,J . AppZiedPhys., 15,338 (1944); 17,392(1946). (6) Gehman, S. D., Woodford, E. E., and Stambaugh, R. B., IND. ENG.CHEM.,33, 1032 (1941). (7) Green, H., IND. ENG.CHEM.,17,802 (1925). (8) Hauser, E. A., and Le Beau, D. S. (J. Alexander, ed.), “Colloid Chemistry,” Vol. VI, p. 403, New York, D. Van Nostrand Go., 1945. (9) Henri, V., Compt. rend. 144, 432 (1907); Caoutchouc & guttopercha, 3,510 (1906). (10) Jordan, H.F., private communication. (11) Kemp, A. R., IND. ENG.CHEM.,30, 154 (1938). (12) Langeland, E. E.,IND. ENG.CHEM.,ANAL.ED., 8,174 (1936). (13) Lucas, F.F.,IND. ENG.CHEM.,30, 146 (1938); 34, 1371 (1942). (14) Maran, S. H.,and co-workers, private communications beginning April 1945. (15) White, L. M., Ebera, E. S.,Shriver, G. E., and Breck, S., INLP. ENG.CHEM.,37,770(1945). (16) Willisford, L. H., Goodyear Tire and Rubber Co., unpublished. RECEIVED June 19,1947. Presented before the ’Division of Rubber ChemisCHEMICAL SOCIETY,Chicago, 111. try at the 110th Meeting of the AMERICAN The major portion of this work was performed in connection with the Government Synthetic Rubber Program under the sponsorship of The Office of Rubber Reserve, Reconstruction Finance Corporation. Contribution No 146from the Goodyear Tire and Rubber Company Research Laboratory.
Correction The authors of the article on “Paving Asphalt from California
OF PROPERTIES OF LARGEAND SMALL TABLE IV. COMPARISON Crude Oil” [IND. ENG.CHEM.,40,548 (1948)]incorrectly stated PARTICLE SIZEFRACTIONS OF A CENTRIFUGED LATEX
Whole Latex
Large Particle Size Fractions 3500 to 4000
34 0
32.0
* Approx. particles.
2/s
Small Particle Size Fractions 1000 to 1200
5 20 35.5
of latex not recovered, including portions containing largest
that the Petro-Chem Development Company, which msnufactured the fractionating furnace for the asphalt plant, is a subsidiary of Bethlehem Steel Corporation. Petro-Chem Develop ment Company, Inc., has no direct connection through ownership, management, or operation with the Bethlehem Steel Corporation. The authors regret that this error occurred.
M. L. K A S T E X ~ CALIFORNIA ASPHALTCORPORATION ( : 4LIFOHNIA RESEARCH cORPOR4TION
