Influence of Moisture Content of Carbon Black on
Rubber Properties LEONARD H. COHAN AND C. R. JOHNSON Continental Carbon Company, New York, N. Y.
The modulus at 400 per cent, abrasion resistance, and age resistance of a tread stock decrease as the moisture content of carbon black increases. Tensile at break shows no trend with moisture content. The extrusion time of a carbon black-rubber master batch and of an uncured tread stock are markedly decreased by the presence of adsorbed water on the carbon black.
water. I n no case, however, was liquid water used in preparing blacks of moisture contents less than 4.2 per cent.
Extrusion Results The very pronounced effect of moisture on the extrusion time of a carbon black-rubber master batch containing 40 per cent carbon black by weight is shown in Figure 2. A Firestone plastometer was used in all extrusion experiments a t a diaphragm pressure of 18 pounds and a thermostat tempera1
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1
HE large quantity of carbon black used in rubber tread stocks and the tendency of blacks of this type t o adsorb
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an appreciable amount of water vapor bring up the question of the influence of the adsorbed water vapor on the properties of the resultant stock Although other compounds present can also adsorb water vapor, only carbon black is capable of carrying appreciable quantities into a tread stock. The following series of experiments was conducted chiefly with the purpose of determining the extent to which this moisture affects the accuracy of testing carbon black, and thus to remove one of the uncertainties which enter into the evaluation of carbon black in rubber. I n Figure 1a water ON FIUURE 2. EFFECTOF MOISTURE ID0 vapor adsorption isoEXTRUSION TIMEOF CARBON BLACKtherm a t 27" C. RUBBERMASTER BATCH (81" F.) is shown for HUMIDITY RELATIVE the carbon black which was used as a ture of 190" F. The three curves are for three different grades of rubber carbon black. Particularly in the case of standard in most of the experiments (3). blacks A and B, an S-shaped curve fits the experimental Points more closely than the straight lines. However, in This black was the %Mcx5TURE slow-curing small view of the limits of accuracy of the plastometer measureparticle type, had a ments, it was felt advisable to await additional evidence beFIGURE1. WATER VAPORADvolatile content of fore deciding on the exact nature of the moisture contentSORPTION ISOTHERM AT 27 C. 5.1 per cent (4, and extrusion function. diphenyl guanidine Figure 3 shows the dependence of extrusion time of an uncured tread stock on moisture content of the carbon black. adsorption of 47.5 (g). Figure 1 indicates that a change in humidity of only 10 per cent can change the moisture content The tread stock used in this and the following experiments contained by weight: of the black by as much as 1 per cent, Thus small changes in atmospheric humidity can alter the moisture content of the Smoked sheet 100 black appreciably. The maximum amount of water vapor Standard carbon black 50.6 Zinc pxide 7.85 adsorbed by this black is about 4 per cent by weight. I n Stearite 3.30 Sulfur 2.81 those experiments in which moisture contents higher than 4.2 Mercaptobenzothiasole 0.743 _ _ per cent are reported the blacks were allowed t o adsorb liquid Total 165 2 1183
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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A du Pont abrader was used for the abrasion loss experiThe three sets of points in Figure 3 correspond to carbon ments, and the results are calculated in cubic centimeters lost black run in three separate master batches of the above per horsepower-hour on Figure 4 The change in abrasion formula. loss with increasing moisture content is in the same direction Although the presence of as would be expected from the corresponding decrease in moisture on the carbon loading. black decreases the carbon Aging tests were made in a Geer oven. Samples were aged loading, experiments have for 4 days a t 85" C. The tensile strength a t rupture of the shown that the difference in _aged sample decreases about 20 per cent over the range 0 to 8 loading between 0 and 4 per am 8h per cent moisture. The four series of points shown in Figure 4 cent moisture content proare for four separate batches made up on the standard formula, $i duces no change in extrusion %MOSTLIRE but milled and aged a t different times. The cure selected for time within the limits of error aging tests was in each case the cure which corresponded to the Of the Plastometer' For exFI~cR 3. ~DEPENDEX\TCE maximum value for unaged tensile a t rupture. This optimum ample, the dependence of OFEXTRUSIONTIME OF UKcure time varied from about 65 minutes for the stock containextrusion time on loading CURED TREADSTOCKox ing dry black to 55 minutes for the stock containing black for a carbon black-rubber MOISTURECOXTEST OF CARBOX BLACK of the highest water content used (11.7 per cent). As shown master batch is as follows, in the top graph of Figure 4, the tensile strengths of the unwhere the carbon black aged stocks showed no trend with increasing moisture concontained 0.69 per cent moisture: tent. The actual values of the unaged tensiles for the samples reported in the bottom graph of Figure 4 nvre within the Extruaioii Time, Loading, 7*by Wt. Carbon limits 4300 * 120 pounds. Seconds Black in Master Batch ~
~
39 40
41
14.8
13.8 15.0
It mas thought possible that the large change in extiusion time might be accounted for by the effect of moisture content on the completeness of dispersion of the carbon black. However, under the conditions of our experiments no differences in the dispersion could be detected by comparing the sheen ( 1 ) of freshly torn surfaces of the various stocks. Furthermore, if changes in degree of dispersion mere the cause of these large changes in extrusion, it would be logical to expect corresponding changes in tensile and modulus As shown below, this is not the case. Schoenfeld and Allen ( 5 ) published results which indicate that the degree of dispersion of carbon black reaches a maximum when the black contains about 1 to 2 per cent water. This apparent disagreement with the present observations is probably due to the more intense mixing which our stocks received. The degree of dispersion produced by a 12-inch laboratory mill is so nearly perfect that differences in dispersibility produced by moisture changes are too small tc detect. I n any case, the extrusion-moisture content curves show no relation to the dispersibility-moisture curve of Schoenfeld and Allen. Properties of Cured Rubber I n Figure 4 the effect of moisture content of the carbon black on tensile strength, modulus a t 400 per cent, abrasion loss, and aged tensile strength is shown. The data in all cases are for the optimum cure. I n the three upper graphs, results for only one series of experiments are given; however, three check experiments gave essentially the same results. Tensile strength at break point shows no trend within the limits of accuracy of the experiment. I n some of the check experiments a tendency for the tensile measurements to scatter, particularly at higher moisture contents, was observed. Curve A shows that modulus a t 400 per cent elongation decreases slightly with increasing moisture content. Again, more scattering was noticeable in some of the other experiments than in the one shotvn. However, the downward trend was present in all cases. If a correction is applied for the change in loading, corrected curve. B , increases slowly with the moisture content. This increase is probably within the limits of error involved.
OF MOISTURE CONFIGURE 4. EFFECT TENT OF CARBON BLACK ON PROPERTIES OF CUREDRCBBER
It is worth noting that aging data taken at a definite curee. g. 60 minutes-instead of a t the optimum cure make the variation with moisture content more marked than is shown in the figure.
Conclusions The moisture content of carbon black should be kept approximately constant if maximum accuracy in rubber testing is to be attained. I n this laboratory we have found it convenient to equilibrate blacks at about 30 per cent humidity, under which condition most rubber channel blacks adsorb 1.5 to 2.0 per cent water. I n the case of most of the properties of
September, 1941
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
tread stocks, this precaution decreases the average deviation from the mean value in any series of experiments. I n the case of extrusion tests, the effect of adsorbed moisture is so great that the use of a standard moisture content, or a t least the determination of moisture content a t the same time as the black is milled for extrusion, is necessary if reproducible results are to be expected.
Acknowledgment We gratefully acknowledge the assistance of B. S. Phillips and other members of Continental Carbon Company’s tech-
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nical staff for carrying out various tests in connection with the experiments.
Literature Cited (1) Allen, R. P., and Schoenfeld, F. K., IND. ENG.CHEM.,25, 994 (1933). (2) Amon, F.H., and Estelow, R. K., Ibid., 2 4 , 5 7 9 (1932). (3) Dewey, C. S.,and Lefforge, P. K., Ibid.,24, 1045 (1932). (4) Johnson, C.R., Ibid., 20, 904 (1928). (5) Schoenfeld, F. K., and Allen, R. P., Ibid., 25, 1102 (1933).
PRESENTED before the Division of Rubber Chemistry at the lOlst Meeting of the Amerioan Chemiral Society, St. Louis, Ma.
Effect of Cupric Oxychloride Cement on Microorganisms M. A. FARRELL AND R. T. WOLFF The Pennsylvania State College, State College, Penna.
This study reports the action of cupric oxychloride cement, “Hubbellite”, on the growth of eight mold and eighteen bacterial cultures representing microorganisms associated with various skin infections, such as athlete’s foot, ringworm, etc., as well as bacteria of different chemical compositions. Cupric oxychloride cement brings about a marked reduction in the number of bacterial cells within a 15-minute interval, and the growth of all the mold cultures was completely inhibited within this period. Covering the cement with dirt or washing with water for 6 hours did not diminish the antiseptic properties. Similar results were obtained with this cement under actual service conditions over a 6-month test period. Throughout the study cupric oxychloride cement had a marked antiseptic effect on the mold cultures, while the growth of bacteria was influenced to a less marked degree. S A RESULT of investigations to overcome certain of the disadvantages of magnesium oxychloride cements, Hubbell (3) developed a new material, “Hubbellite”, by the incorporation of finely powdered copper. During and for long periods following the initial hardening, the metal powder reacts to form a new phase in the cement composition which has been identified (4) as a cupric oxychloride, closely resembling the natural mineral atacamite. This new cementing material was found to possess an unusual combination of
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properties of advantage for a variety of applications-for example, in the use of the cement as a floor surfacing. The known bactericidal and fungicidal properties of certain of the copper compounds suggested that the new cupric oxychloride cement might possess inhibitory or destructive powers against microorganisms. Preliminary studies by Emig ( 2 ) gave definite indications that this was the case. The present study mas undertaken to obtain further quantitative data on the influence of this cement on the growth of microorganisms; such an influence may be significant in connection with practical uses for the cement which inhibitory or destructive powers suggest, such as floor surfacing in locker rooms and showers, around swimming pools, in certain food industries, and in similar places where sanitation is of paramount importance.
Experimental Procedure The microorganisms selected for this $project included eight mold and eighteen bacterial cultures. Table I shows the microorganisms employed and the environment with which they are usually associated. The types of bacteria listed contain representative species of microorganisms of different chemical composition as evidenced by their reaction t o a differential stain; certain species grow in the absence of air while others do not, and certain forms possess protoplasm which is more resistant to destruction by chemical agents. These microorganisms were grown by the generally accepted methods on different substrates. I n studies dealing with the influence of the environment on the growth of microorganisms, numerous factors play important roles. As a preliminary t o this investigation, rather extensive exploratory studies were conducted, including (a) the influence of temperature on the rate of destruction of microorganisms in the presence of Hubbellite, (b) the influence of various media adjusted to different p H values on the survival of microorganisms, (c) the influence of different temperatures of incubation in demonstrating the presence of living cells, and (d) the effect of the type of surface on the
