FLOCCULATION OF PIGMENT IN
CARBON
BLACKRUBBER MIXTURES c. R. PARK A N D P A m P . M
& W '
The Firestone TiFe & Rubber Company. A h o n , Ohio
UhlEROUS references occur in the literature as to the cause of so-called scorching or burning in rubber-pigment mixes containing no vulcanizing agent. It was suggested (6') that this stiffening effect may he caused by flocculation of the pigment particles.
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x
100
x
500
FIQUREI. SUCCESSIVE STAGESOF FLOCCULATION OF A SAMPLE OF CHANNEL BLACK-RWBER MIXTU~E DUWG HEATING AT 135" C. Cornpoeition: rubber 100. ohemel carbon black 8 pmb by volume. The are88 marked by oir& (in h to Dl are shown at higher rnsgnifioation in E to H .
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Green (8) demonstrated a relation between the stiffness and flocculating tendency of pigments in paint mixtures, s n d Depew and Ruby (4)and Green (7) suggested that the phenomenon of flocculation may have some relation to the properties of cured rubber mixes which contain pigments, espccially carbon black pigments. Grenguist (9) re ported that carbon black exists in a more or less flocculated condition in vulcanized rnhber, and some evidence was presented by Park and Morris ( 1 1 ) that mill-scorched batches which exhibit abnormal stiffness possess a structure which suggests that the black has been flocculated. The increase in stiffuess of unvulcanized rubber-carbon black mixes upon standing ior periods of several days w ~mentioned s by Stainberger (19). Busse and Davies (2) presented data showing the effect of heat upon the stiffness of .such mixes and mentioned the possible relation between flocculation and increase in stiffness. In order to throw more light upon the behavior of carbon black in the stiffening of rnbber, a series of experiments w&s L
Present sddiesa. American Cyanamid Corn-
y a w . Stamford. Conn.
JUNE, 1938
INDUSTRIAL AND ENGIXEEHING CHEMISTRY
planned following the general methods of Busse and Davies, which include heating the sample for various periods of time and attempting to follow the changes in gross physical p r o p erties and in the minute structure of the mix.
Stiffening Effect of Heat on Master Batches To determine quantitatively the effect of heat on the plasticity of master batches, a number of batches containing varying concentrations of rubber channel black were made up and heated in nitrogen for 8 hours a t 132" C . The plasticities of these stock8 were then determined on the extrusion plastometer (6). Table I shows, in agreement with the results of Busse and Davies that, with the exception of pure gum rubber, all of the samples were markedly stiffened by heating. Such stiffening action of heat on master batches is not confined to channel black batches but may also be obtained on master batches of much coarser black. An example is the ac-
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TABLEI. AVERAGE EFFLWX RATE At 3260 Lb./Ba. In. (230 Kx./Sq. Cm.)
Carbon Bleok per 100 Vel. Rubber
PrSnSUre
Volrrmea 0
Before heating cc./min. 242
4 8 12
134 103 63.5
2
6
169
After heatingo cc./min. 268 1io 60.5
At8120 Lb S In Carbon (570 Kg./d.%m.j Black PW8.uIB per 100 Vol. Before After Rubber heating heatingvolumea cc./mi*. co./nin. 30 7.6 0.4 40 1.0 0.6337
12.3 5.0
16 2s 2.8 20 8.4 0.4 25 2.3 0.1 In nitrogen 8 hours at 132' C .
tion of heat on a Gastex master batch. When a master batch containing 67 parts of Gastex (the product of a free Aame process) per 100 parts of rubber wm heated under the same conditions as were used for channel black, the stiffening was
13 l"i"
A study has been made of the effect of heat upon the properties and structure of carbon black-rubber mixtures. Progressive stiffening is shown to accompany heating. Photomicrographs present in detail the progress of flocculation after successive periods of heating. The theories of Depew and Ruby and of Green regarding the effect of carbon black flocculation upon stiffening are indicated to be in agreement with these observations.
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100
x
500
FIGURE 2. SUCCESEIVE STAGES OF FLOCCULATIOX OF A MIXTURE OF GASClRBoN BLACK AND RUBBER DURING HEAT~NQ AT 135" c. Cornpasition: rubber, 1 0 0 ; Gaster, 8 perk by volume. T h e are- marked by the drcles on A to C) are shown at higher magnifiostion in D to F.
FIGURE3. P~L~SRE SECTION D OF NORMALLY M U ~ E DMASTERBATCH CONTA~NING 40 PER CENT CARBON & BLACKB Y WEIQHT
IhDlJSTRIAL AUD ENCINf.:ERl?IG CHEMISTRY
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to cause it to flow out and become trauslucent. Figure I D represents the same sample after heing heated at 135" C. in an oven for 1 hour; C arid D show tlre inme sample heated for 6 and 12 hours, rapectively . The increasing Aocculation is evident in these plrotographs a t It@ "0 (Iiameters, hut a rnagnificatim of 500 shows the details mnch more clearly. Figitre IE rrliows the sarnple after the prelimiiiary heating, and P, 0, and H represent the p r ~ g r eof~ floect~latioi~ ~ at periods (if I , 6, and 12 hours, respectively. Floccolnti~~ir may tn! followed similarly in a Gastex master batch. Figure 2:i shows a t 100 magnifications an 8-volume stock aft.er heing heated lor 15minutes in the squeezing chainher; U and C represent the smnc sitmpie after being heated 1.5 and 3 hours, respectively. Figures 21), E , and P show this same sample a t 500 I125 magnifications. Rere also the formation $ i f flocciiles is plainly evident. As has been mentioned, this ctrangc in structure brought about by the heat treatment is accompanied hy aii increase in stiffness of the material, making it itifficult or, in some cases, impossible t o obtain a smooth homoeeneous mixture Gntreated rribrtor batoh Treated mmter. batch upon iurt,her mastication of the hatch. FIGURE4. APPE.IKAUrocess. The data liere
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INDUSTRIAL AND ENGINEERING CHEMlSTRY
given furnish reasonably substantial evidence for the views of Depew and Ruby and of Green regarding the relation of flocculation to the reinforcing effect of carbon black in vulcanized rubber.
Acknowledgment The writers wish to thank the Firestone Tire & Rubber Company for kind permission to publish this work.
Literature Cited (1) Allen, R. P., IND.ENQ.CHEM.,Anal. Ed., 2, 311 (1930). (2) Busse, W . F., and Davies, J. M., paper presented before Div. of Rubber Chemistry at 86th Meeting of Am. Chem. SOC.. Chicago, Ill., Sept. 10 to 15, 1933.
VOL. 30, NO. 6
(3) Dannenberg, H., Kautschuk, 2, 276 (1926). (4) Depew, H. A., and Ruby, I. R., J. IND. ENQ.CHEM.,12, 1156 (1920). (5) Dillon, J. H., Physics, 4, 225-35 (1933). (6) Goodwin, N., and Park, C. R., IND. ENQ.CHEM.,20, 621 (1928). (7) Green, H., Chem. & Met. Eng., 28, 53 (1923). ( 8 ) Green, H., IND. ENQ.CHEM.,15, 122 (1923). (9) Grenguist, E. A., Ibid., 20, 1073 (1928); 21, 665 (1929). (10) Menadue, F. B., I n d i a Rubber J.,85, 689,717; 8 6 , 2 3 , 5 3 (1933). (11) Park, C. R., and Morris, V. N., IND. ENO.CHEM.,27,582 (1935). (12) Roninger, F. H., IND. ENQ.CHEM.,Anal. Ed., 5, 251 (1933). (13) Stamberger, P., “Colloid Chemistry of Rubber,” Oxford Univ. Press, 1929. RECEIVED April 2, 1938. Presented before the meeting of the Division of Rubber Chemistry of the American Chemioal Soeiety, Detroit. Mich., March 28 and 29, 1938.
FILTRATION Accuracy of Prediction of Plant Operation from Test Data E. L. McMILLEN AND H. A. WEBBER Iowa State College, Ames, Iowa
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URING the past three years a rather comprehensive investigation of the accuracy with which large-scale filter operations may be predicted from test filtration data by means of the new Ruth filtration equations (8) has been carried out in the chemical engineering laboratories of Iowa State College. Predictions of larger scale operation secured previous to this time when utilizing the Lewis equations (14) were not satisfactory. Likewise, Irvin (6‘) in 1934 stated: “Mathematical theory can be employed only to a limited extent in explaining or predicting the results obtained”; Badger and McCabe (2) in 1931 stated that “in spite of much careful investigation, complete answers to these questions (amount of filtration to be expected in a definite time, rate, and efficiency of washings) cannot be given.” This situation was due to the variety of equations suggested by Lewis for different conditions, some of which neglected septum resistance, and to the various methods used for plotting test filtration data. The confusion which resulted is best illustrated by Badger and McCabe’s use (3) of the logarithmic plot intended for nonhomogeneous sludges for data secured upon a homogeneous sludge of chromium hydroxide (1). I n addition, the use of fractional exponents, three of which may occur in the same equation, renders the calculations needlessly difficult by means of the Lewis equations. The Ruth constant-pressure filtration equation (9) is similar to that proposed by Sperry (IS)in 1916, but a more tangible meaning has been given to the constants employed than was the case in the Sperry equation. A single parabolic equation is applicable to constant-pressure filtration of any type of sludge (homogeneous or nonhomogeneous, compressible or noncompressible):
- (v+ cp = K (e + e,)
(1)
The differential form of Equation 1, when plotted as inverted rate of flow, dO/dV, against quantity of filtrate, V , yields a
means of evaluating the two constants, K and C, since i t is a straight line of slope 2 / K and negative intercept upon the V axis of C:
The slope, 2 / K , is a measure of filter cake resistance; intercept C is a measure of filter cloth resistance during the filtration under the conditions that the cloth is used. Probably the chief contribution of Ruth to constant-pressure filtration is this new method of analyzing test filtration data to show its parabolic nature and readily yield constants representing cake and cloth resistance. Consequently it is not surprising to find that the authors of the recent (1937) edition of “Principles of Chemical Engineering” (16)have entirely discarded their earlier methods of plotting test fltration data in order to adopt a method essentially similar to Ruth’s inverted rate plot. The similarity between the newer Lewis plot and the Ruth plot is brought out in Figure 1 for the parabola, 1 1 2 = lo(e e,)
(v+
+
for the condition that P and A are unity. Provided time measurement and filtrate collection begin simultaneously, the plotting of this rearranged Lewis equation does yield a measure of both filter cake and cloth resistance, which was not accomplished by their earlier methods of plotting data. When filtrate collection is delayed until the filtrate outlet pipes become full, the Lewis plot is no longer a straight line as is shown in b, Figure 1, while the Ruth plot, d, remains a straight line; the latter is displaced parallel to itself sufficiently to make intercept C larger by the amount of filtrate necessary to fill outlet pipes. The newer Lewis equations retain the scouring coefficient, t, as applied to nonhomogeneous sludges, in spite of the admission (16) that “the available laboratory data on the filtration
