SORPTION O F GR-5 RUBBER BY CARBOX BLACK
251
REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
ARNOLD, J. E.: J . Oil & Colour Chemists' Assoc. 31, 237 (1948). ARNOLD, J. E., AND GOODEVE, C.: J. Phys. Chem. 44, 652 (1940). BULGIN,D.: Trans. Inst. Rubber Ind. 20, 24 (1944). COHAN, L. H.: India Rubber World 117, 343 (1947). COHAN,L. H.: Proceedings of the Second Rubber Technology Conference (London) 1948, p. 365. EINSTEIN, A , : Ann. Physik 19, 289 (1906); 34, 591 (1911). EIRICH, F. R . : Repts. on Progress Phys. 7, 329 (1940). GUTH,E.: J. Applied Phys. 16, 20 (1945). GVTH,E.: Proceedings of the Second Rubber Technology Conference (London) 1948. p. 363. GOTH,E., A N D GOLD,C . 0.:Phys. Rev. 63, 322 (1938). MULLINS, L.: J . Rubber Research 16, 275 (1947). MULLINS, L . : Proceedings of the Second Rubber Technology Conference (London)
1948, p. 179. (13) MULLINS, L . , A N D WHORLOW, R . W . : In press. (14) PARKIXSOX, D . : Advances in Colloid Sci. 2, 389 (1946). D., h S D BLANCHARD, A . F.: Proceedings of the Second Rubber Technology (15) PARKINSON, Conference (London) 1948, p. 414. G . H . , A N U SCOTT. J. R . : J. Sci. Instruments 22, 206 (1945). (16) PIPER, (17) R E H X E RJ,. : J . Applied P h p . 14, 638 (1943). II. 11.:J. Applied I'hys. 16, 758 (1941). (18) SMALLWOOD, (19) VAND,V . : J. Phys. & Colloid Chem. 62, 2 i i (1948). (20) VOET, A . : J . Phys. & Colloid Chem. 61, 1037 (1947). (21) WACK,P. E . , ASTHOSY,R . L . , A W D GCTH, E.: J . Applied I'hys. 18, 456 (1947). (22) WIEG.4ND. B . : Ind. Eng. Chem. 17, 939 (1925).
w.
T H E SORPTIOS OF GR-S TYPE RIYRBER BY CARBOS BLACK. I',' SORPTIOK FROM BENZENE SOLI-TION BY GRAPHOX I . M. KOLTHOFF
AND
ALLAN KAHN
School of Chemistry, University of Minnesota, Minneapolis 14, Minnesota Received August 22. 1049 INTRODUCTIOS
The reinforcement of natural rubber by carbon black first became known about 1910.Since that time there have been many studies attempting t o correlate the properties of a given carbon black with t,he ultimate physical properties of 1 Presented a t the Twenty-third National Colloid Symposium, which was held under the auspices of the Division of Colloid Chemistry of the American Chemical Society a t Minneapolis, Minnesota, June 6-8, 1949. This investigation was carried out under the sponsorship of the Reconstruction Finance Corporation, Office of Rubber Reserve, in connection with the synthetic rubber program of the United States Government. f
252
I. Y. KOLTHOFF AND ALLAN KAHS
the rubber into which it is incorporated. These studies have been intensified since the development of synthetic rubbers in which carbon black reinforcement is more marked than in natural rubber. Previous work on the evaluation of carbon blacks has consisted of studies of such properties as iodine and diphenylguanidine adsorption; the determination of volatile matter and extractable matter, etc. (4); and more recently the determination of surface area, pH, and structure (6). The sorption of rubber from solution ( 5 ) had been considered also, but until the recent work of Baker (1) there had been no systematic investigation of this phenomenon. The present study deals with the sorption of GR-S type rubber from solution by various kinds of carbon black. With a certain type of black (Graphon) it was found that the sol part of the rubber could be sorbed completely, whereas the microge13 part was not or was hardly sorbed. TABLE 1 The variation of the amount of rubber sorbed on Graphon with time of shaking 4 g . of Gra on and 100 ml. of rubber solution: initial concentration = 0.25 a./100ml. 57 PZR CENT CONVERSION
77 PER
61 PER C E N I COhVERSION
CEh'I CONYEPSION
W E OF SEAK-
ixa
\mount sorbed
Intrinsic viscosity
imount sorbed
Intrinsic viscosity
Intrinsic viscosity
~ m O U nsorbed t
grams
hours
grams
0.00 0.25 0.50 0.75 1.00 2 4 8 16 24 48 120
0.000 0.122 0.129 0.133 0.131
1.29 1.45 1.32 1.28 1.19
0.136
0.96
0.136 0.136 0.138
0.64 0.67 0.63
0.000
1.20
0.133 0.130 0.137 0.135 0.137 0.140 0.139 0.141
1.61 1.83 1.36 1.14 1.07 1 .OO 0.85 0.83
1
0.120 0.122 0.125
I
3.68
EXPERIMENTAL
Materials Various samples of GR-S type rubber coagulated from latex of between 38 per cent and 90 per cent conversion and containing a small amount of antioxidant were used. All the latices were prepared by the so-called Mutual recipe a t 5OoC. Mallinckrodt reagent grade benzene was used as a solvent. Seven commercial samples of carbon black were obtained from Godfrey S. Cabot Inc., Boston, Massachusetts. I t was found that when shaken with benzene solutions of rubber all except one (Graphon) gave very dark suspensions of
* For a comprehensive study of microgel see reference
1.
SORPTION OF GR-S R U B B E R BY CARBON
253
BLACK
carbon black which would not settle out even on prolonged centrifugingP Therefore, Graphon was used exclusively in this study. TABLE 2 Sorption of rubber from solution in benzene by Graphon at dO°C. and 60°C. 100 ml. of solution; initial concentration = 0.279 g./lOO ml. AMOUXr SORBED
AUOUNTOPORAPHON
67 per cent conversion
~
1
30°C. grams
1.5 2 4 6
I
90 Der cent conversion
50°C
30°C.
grams
grams
grams
O.Oi7
O.Oi6
0.114 0.203
0.144 0,201
0 052
. .za
-
.24
-
38
X
(I6 81 90
0
SOT
grams
1
0 049
CONVERSION
0
A
-
0
5.20-
3
w
Ab-
c
2
a
.12-
FIQ.1. Amount of rubber sorbed from solution in benzene by various amounts of Graphon.
Method I n general, from 2 to 12 g. of Graphon was added t o a bottle containing 100 ml. of a 0.25 per cent rubber solution in benzene. The bottle was then clipped to the outside of a cylinder 18 in. in diameter which was rotated a t 32 R . P . Y . in a lyater ‘Later it was found t h a t clear solutions could be obtained with many of the carbon black samples when the sorption was determined in chloroform solutions of rubber
254
I. M. KOLTHOFF MVD ALLAN KAHh*
bath at 30°C. After 48 hr. (unless otherwise noted) the bottles Tvere centrifuged to settle out the carbon black. Aliquots (25 ml.) of the supernatant liquid were evaporated to determine the amounts of residual rubber. On many samples the relative viscosity a t 30°C. of the supernatant liquid mas also determined. RESULTS
Effect of time of shaking Samples (100 ml.) of rubber of 57, 61, and 77 per cent conversion mere shaken with 4 g. of Graphon for various periods of time. The results are given in table 1. Effect of temperature Sorption data for two different samples of rubber were obtained at 30°C. and 50°C. The results are given in table 2. The data show that the amount of rubber sorbed from a solution in benzene by Graphon is hardly dependent on the temperature between 30" and 5OoC. TABLE 3 Microqel content of rubber samples of various conversions ~~
~~~
CONVBPSIOY
per ccnf
38 66 72
77 81 82 86 87
90
* 12 g. of
~
I
YICROOEL
per cLnl
0 0 5 25 33 46 58 58 69
,
PWBBLP W T SORBED BY ORAPRON*
per c m l
0 0 14 25 28 40 50
51 56
Graphon shaken with benzene solution containing 0 25 g. of rubber
Sorption data for rubber samples of baraous degrees oj conversion The amount of rubber sorbed from solution in benzene by various amounts of Graphon is plotted in figure 1 for four samples of rubber of different conversions. All of the rubber in the samples of 38 per cent and 66 per cent conversion was sorbed by 12 g. of Graphon. However, with the samples of 81 per cent and 90 per cent conversion, although the initial sorption was comparable to that with the other samples, only a fraction of the rubber could be sorbed, even with large amounts of Graphon. It was thought that there might be some connection between the amount of rubber not sorbed by Graphon and the amount of microgel in the samples. Therefore the microgel content of a number of rubber samples was determined by the method of Medalia and Kolthoff (3). The amount of rubber not sorbed on 12 g. of Graphon from 100 ml. of benzene solution containing 0.25 g. of rubber was also determined. The results are given in table 3.
SORPTION O F GR-S RUBBER BY CARBON BLACK
255
DISCUSSION
The results of the effect of time of shaking on the sorption of rubber show that the sorption takes place very rapidly. Especially with low conversion samples there was very little change in the amount of rubber sorbed after 1 hr. With the samples of 57 per cent and 61 per cent conversion the intrinsic viscositys of the supernatant liquid from each sample increased initially and then decreased. The results for the rubber of 77 per cent conversion are complicated by the presence of microgel in the sample. Separate tests showed that the intrinsic viscosity of the solutions remained unchanged when they were shaken for 120 hr. without carbon black. Therefore it seems probable that the lower-molecular-weight fractions are sorbed faster than the higher-molecular-weight fractions, but that the former are replaced by the latter upon longer periods of snaking. Thus when dealing with a heteromolecular solution of rubber, true sorption equilibrium is not reached until after a long period of shaking. As demonstrated by the results in table 1, the amount of rubber sorbed remains constant after a few hours of shaking, but the molecular weight of the sorbed rubber increased with time of shaking (up t o about 48 hr.). The relatively negligible dependence on temperature of the amount of sorption, as shown in table 2, is generally found in sorption from liquids (2). The results plotted in figure 1 are representative of those obtained with a larger number of samples. It was found that below about 70 per cent conversion all the rubber from 100 ml. of a 0.25 per cent solution in benzene could be sorbed by 12 g. of Graphon. However, above 70 per cent conversion the sorption curves are seen to be flattened before all the rubber is removed, indicating the presence of a fraction which is sorbed to only a small extent, if any, by Graphon. The results of table 3 definitely show that it IS the microgel fraction of the rubber which is not or hardly sorbed on Graphon. This difference of sorption can thus be used to differentiate between sol and microgel solutions of rubber. The agreement between the amount of microgel determined by a conventional method (3) and that indicated by the results of the sorption experiments is satisfactory. SUMMARY
The sorption of GR-S type rubber from solution in benzene by Graphon carbon black has been investigated, and it has been found that: 1. The amount of rubber sorbed remains unchanged after several hours of shaking, but the intrinsic viscosity of the remaining solution changes slo~vlywith continued shaking (up to about 48 hr.). I t seems probable that the lower-molecular-weight fractions are sorbed faster than the higher-molecular-weight fractions but that the former are replaced by the latter upon longer periods of shaking. Actually, In V , / C was determined, where v , is the relative viscosity and c is concentration i n grams per 100 ml. However, a t the concentrations used this is a close approximation t o the intrinsic viscosity: lim In vr e-0-7
256
E. A . HAUSER AND D. 9. LE BEAU
2. The amount of sorption a t 50°C. is not appreciably different from that a t 30°C. 3. The microgel fraction in rubber is not or is hardly sorbed by Graphon; the sol fraction is sorbed completely. REFERENCES (1) BAKER,W. 0.:Ind. Eng. Chem. 41, 511 (1949). (2) FREUNDLICH, H.: Colloid and CapilZary Chemistry, p. 224. Methuen and Co. Ltd., London (1926). (3) MEDALIA, A. I., AND KOLTHOFF, I. M.: Unpublished work from this laboratory. (4) SHEPARD,N. A , : “Carbon Black in the Rubber Industry,” in Colloid Chemistry, edited by Jerome Alexander, Vol. IV. The Chemical Catalog Company, Inc., New York (1932). (5) STAMBERGER, P . : Kautschuk 7, 182 (1931). (6) WIEGAND, W. B.: Can. Chem. Process Ind. 28, 151 (1944).
STRUCTURE OF LYOGELS. V1
A STUDYOF POLYMER FRACTIONS PREPARED FROM SMOKED SHEET,STANDARD GR-S, LOW-TEMPERATURE GR-S (X-435),AND
~ E O P R E N E10
E . A. HAUSER
Department of Chemical Engineerzng, Massachusetts Institute of Technology, Cambridge, Massachusetts, and Department of Chemistry and Chemical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts AND
D. S. LE BEAU Midwest Rubber Reclaiming Company, East St. Louis, Illinois
Received August 88, 194.9
Previous experiments had shown that the structure of the polymer film as observed in the ultramicroscope using incident light depended on the molecular weight of the polymer (molecular weight distribution) and on the physical structure of its chains. The effect of time and temperature on the structure of natural isoprene polymer films had been correlated with the folding and the internal structure of thenatural polymer chains (6, 7 ) .The effect of the molecular weight on the flow of isobutylene polymers had also been studied (8). Because flow can be considered a phenomenon closely related to molecular weight and its distribution as well as to the physical and chemical nature of the polymer, it was felt that it deserved more attention. Therefore smoked sheet, standard GR-S, low-temperature GR-S, and ?;eoprene were studied in greater detail by subjecting each polymer to fractionation 1 Presented a t the Twenty-third National Colloid Symposium, which was held under the auspices of the Division of Colloid Chemistry of the American Chemical Society a t Minneapolis, Minnesota, June 6-8, 1949.
