June 1951
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INDUSTRIAL AND ENGINEERING CHEMISTRY
yellow birch was 22.5% and from hard maple, 21.0%. These values are all substantial increases over those from the untreated woods (Table V). Because the values are reported as acetic acid, they are lower than the actual yields. The actual yields can be estimated by calculating the percentage distribution of the three acids in the acid mixture. A basis for doing so is given in the distribution of the acids, if calculated as acetic acid, from the fermentation of the second sample of commercial hemicellulose in Table I. This calculated distribution is 48% each for acetic and butyric acid, and 4% for lactic acid. Thus, the yield of 26.6% acetic acid from sweet gum (Table VI) would approximate 33.0%, if calculated on the basis of the three individual acids. LITERATURE CITED
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(1) Acharya, C. N., Biochem. J., 24, 1459 (1935). (2) Fontaine, F. E., Ph.D. thesis, Univ. of Wisconsin (1941). (3) IND. ENG.CHEM.,ANAL.ED., 1, 52 (1929). (4) Langwell, H., .J, Soc. Chem. I n d . ( L o n d o n ) , 51, 988 (1932). (5) MacFayden, A., and Blaxall, F. R., Trans. Jenner, I n s t . Preu. M e d . , Ser. 11, 162 (1899).
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(6) Olson, F. R., Peterson, W. H., and Sherrard, E. C., IND.ENG. CHEW,29, 1026 (1937). (7) Paper Trade J . , 94, 38-9 (1932) (corrected Dee. 15, 1937). (8) Rogers, S. C., Mitchell, R. L., and Ritter, G. J., A n a l . Chem., 19, 1029-32 (1947). (9) Saeman, J. F., Bubl, J. L., and Harris, E. E., IND.ENG.CHEM., ANAL.ED.,17, 35 (1945). (10) Staudinger, H., and Reinecke, F., Papier-Fabr., 36, 489 (1938). (11) Tetrault, P. A., Zentr. Bakt., Parasitenk., Abt. 11, 81, 28 (1930). (12) Virtanen, A. I., and Hukki, J., S u o m e n Kemistilehti, 19B, 4 (1946). (13) Virtanen, A. I., and Koistinen, 0. A., Svensk K e m . Tid., 56, 391 (1944). (14) Virtanen, A. I., Koistinen, 0. A., and Kiuru, V., S u o m e n Kemistilehti, 11B, 30 (1938). (15) Virtanen, A. I., and Nikkila, 0. E.. Ibid., IQB, 3 (1946). (16) Virtanen, A. I., and Pulkki, L., J . Am. Chem. Soc., 50, 3138 (1928). RECEIVEDJune 30, 1950. Presented before the Division of Cellulose SOCIETY, Chemistry a t the 118th Meeting of the AMSRICANCHEMICAL Chicago, Ill. The Forest Products Laboratory, U. S. Departmemt of Agriculture is maiutained a t Madison, Wis., in cooperation ivith the University of Wisconsin.
Aqueous Dispersion of Carbon
Blacks E. M. DANNENBERG AND K. P. SELTZER Godfrey L. Cabot, Inc., Boston, Mass.
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4
T h e development of carbon black-synthetic rubber masterbatch is one of the most progressive advances made by the synthetic rubber industry in recent years. In the preparation of black masterbatch an aqueous dispersion of carbon black is mixed with latex, and the mixture is coprecipitated, washed, dried, and baled. The wetting and slurrying behavior of carbon blacks is of great importance in this process, since it has been observed that carbon blacks of the same grade or type may show marked variability in these properties. This paper presents information on the factors responsible for such differences. The rate of wetting of carbon black is influenced by traces of benzene extractable material and to the bulk density of the dry black. The quantity of dispersing agent required to give a stable and fluid slurry is related to bulk density, surface area, water-soluble inorganic contaminants, and surface oxidation. An understanding of the factors influencing the slurrying behavior of carbon blacks is necessary in order that carbon black and masterbatch manufacturers, may modify their operations to mutual advantage.
0
NE of the major achievements of the government synthetic
rubber program is the large scale production of carbon black masterbatches. Developed during World War I1 under the pressures of increased production, lack of processing equipment, and labor shortages, black masterbatch has found wide postwar acceptance by many sectors of the rubber industry. The production of black masterbatch was about 70,000 long tons in 1949. Some of the advantages of incorporating carbon black into synthetic rubber latex to form a masterbatch are inherent cleanliness, simplicity of handling, and a reduction of mixing time and power requirements. Mixing is done a t a lower temperature. A more uniform mix is obtained with less trouble and no loose carbon black is lost to the dust collecting systems.
Carbon black masterbatches can contain as much as 100 parts of black per 100 parts of synthetic rubber with most mixtures having about 50 parts of black. They are available in a number of different combinations of grades of black and types of synthetic rubber. Their use by rubber product manufacturers requires mastication and mixing in Banbury mixers and roll mills in order completely to disperse the carbon black and t o incorporate the curing, softening, and other compounding ingredients. The development and production of black masterbatch have been described in publications by McMahon and Kemp ( 6 ) ,O’Conner and Sweitzer (9),Rongone, Frost, and Swart (IO),and Madigan and Adams ( 7 ) . The sequence of operations in making masterbatch is carefully controlled mixing of an aqueous dispersion of carbon black and synthetic rubber latex, followed by creaming, coagulation, washing, drying, and baling, similar to the techniques of normal synthetic rubber manufacture. In order to incorporate carbon black satisfactorily into the synthetic latex, the pigment must first be dispersed in water. Knowledge about the preparation and colloidal properties of aqueous carbon black dispersions is therefore of importance to the masterbatch producer. This subject is also of obvious interest to the carbon black manufacturer, since it is desirable to predict and control the slurrying performance of carbon blacks used for latex incorporation. The purpose of this investigation was to determine the dispersion characteristics of various carbon blacks in water and the fundamental properties of a black that influence its dispersion characteristics. The reinforcing ability of carbon black has long been attributed to its small particle size. I n order to develop high reinforcement, carbon black must be dispersed in rubber to a degree commensurate with its particle size. In ordinary dry mixing the dispersion of carbon black in rubber is accomplished mainly during roll milling, where high shearing and elastic forces disintegrate the carbon aggregates and bring the newly exposed carbon surfaces into immediate contact with rubber. In contrast to rubber
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INDUSTRIAL AND ENGINEERING CHEMISTRY
which is a highly viscous, elastic, nonpolar dispersion medium, water has a low viscosity, is not elastic, and is highly polar. It is therefore not surprising that the predominant factors responsible for the dispersion of carbon blacks in water differ markedly from the factors responsible for dispersion in rubber. Compared to other finely divided fillers such as clays, calcium carbonates, aluminum oxides, and silicas, carbon blacks are relatively hydrophobic. Prolonged ball milling of carbon black and water does not give stable colloidal dispersions, and the quantity of black that can be added to water while retaining a fluid consistency is small, amounting to less than 5% for some grades of carbon black. The use of dispersing agents has a pronounced effect on carbon black-water mixtures, producing stable colloidal BUSpensions and allowing the incorporation of the large amounts of black required for practical masterbatch production. Dispersing agents are usually dissolved in the water in amounts u to 5% on the weight of the black to make slurries of 15 to 30& black content. The actual quantity of dispersing agent required depends on the efficiency of the dispersing agent, the grade and quality of the black, and the amount of carbon black in the slurry. Many varieties of dispersing agents have been used, but the most common are the sodium salts of lignin, of lignin sulfonic acids, and of naphthalene sulfonic acids. Since most dispersing agents exhibit maximum effectiveness in an alkaline environment, it is general practice to add alkali to maintain a pH of about 10 for the carbon black dispersion. The dispersion characteristics of a black may be described in terms of rate of wetting of the black, dispersing agent requirements for dispersion, and aggregate size of the black in the dispersed state.
Vol. 43, No. 6
black is recorded and the bulk density calculated as follows:
W / V X 62.4
=
bulk density of black (pounds per cubic foot)
-
where V = final volume of black after taming, and W = weight of black sample. DETERMINtlTION OB WETTING RATE ( 5 ) . Eighty ml. O f 5% MarasrJerse CB-water solution. 80 ml. 0.1 N sodium hvdroxide and 1100 ml. of distilled water are first mixed a
