July 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
the sulfoxylate formula. During 30 days of heat-aging a t 140" F. gel formation occurred with the polymers from the high iron formula, but was negligible in the polymers from the iron-free or low iron formulas. Generally, polymers made with soaps of rosin acid are more stable (longer induction periods) than those made with fatty acid. Those with mixed soaps more nearly resemble those made with rosin than with fatty acids. The rate of breakdown, but not the ultimate amount, was higher for the polymers with fatty acid than for those with rosin acid. The induction period that polymers made according to the iron-free amine formula undergo prior to breakdown during heataging can be eliminated in the oil masterbatches or reduced in the base polymer by adding iron to the latex. The rate of breakdown is increased, and the level to which breakdown occurs is decreased by the same means. An increase in the rate of gel formation and the amount formed accompanied the addition of iron. The salt-acid-coagulated Polymers are more susceptible to breakdown than those coagulated with zinc sulfate and alum-
1225
coagulated polymers are somewhat more stable than those coagulated with zinc sulfate as far as stability, rate, and amount of breakdown are concerned. Alum-coagulated polymers seemed to cross link more than did the zinc salt-coagulated polymers and very much more than did the salt-acid-coagulated polymers. LITERATURE CITED
(1) Albert, H. E., others, IND.ESG. CHEM.40, 482-7 (1948). (2) Chambers, V. S.,others CR-2181 (Oct. 7,1949); CR-2349 (April 20,1950).
(3) D'Ianni, J. D., others, IND. ENC.CHEM.41, 2270-2 (1944). (4) Mitchell, J. M., Embree, W. H., MacFarlane, R. B., Ibid., 48, 345 (1956). ( 5 ) Rao, N.V. C., Winn, H., Shelton, J. R., Ibid., 44, 576-80 (1952). (6) Taft, W. K., Snyder, A . D., Duke, J., Mooney, H. R.,Ibid., 48, 336 (1956).
RECEIVED for review November 15, 1955. ACCEPTED February 15, 1956. Division of Rubber Chemistry, ACS Meeting, Philadelphia, Pa., November 1955. Work performed as part of the government synthetic rubber program sponsored by the National Science Foundation.
Oil-Polymer Masterbatching v
J
CORRELATION OF POLYMER BREAKDOWN WITH ABSORBANCY INDEX W. K. TAFT', JUNE DUKE', DOROTHY PREM', AND A. D. SNYDER' Government Laboratories, University of Akron, Akron, Ohio
P
REVIOUS work has indicated correlation between breakdown a t 140" F. of polymer in oil-polymer masterbatches and the aromaticity of the oils used in masterbatching (10). The heat breakdown of vacuum-dried polymer has been shown to follow an exponential equation (14). With the use of this equation, a means of calculating the initial rate of breakdown is available, and this rate can be regarded as a measure of the tendency of an oil to cause breakdown. As the breakdown of the polymer is affected by the oil, then the various factors involved can be expressed by a mathematical equation. The Rostler method of analysis, which was adopted by the Office of Synthetic Rubber for characterizing oils, has provided an indication OF the relative reactivity of oils, with respect to heat breakdown of polymers. The first acidaffins were found to to be more reactive than the second acidaffins, and the nitrogen bases were the most reactive of all ( 1 2 ) . The paraffins showed evidence of being stabilizers which diminished the influence of the other components (12). However, no mathematical correlation with breakdown was found with any one component. These generalizations applied to the breakdown of air-dried pilot plant polymers when further heated a t 140' F., and probably to storage stability and to Banbury treatment. Oxygen (11, 18) has been shown to act as a stabilizing factor, and also to enter into the breakdown ( I O ) . Reactive hydrocarbons ( I S ) has also been demonstrated to be a factor. These results led the authors to attempt correlating breakdown and the oxygen absorption of the oil. A qualitative correlation was found, and it was observed that those oils which most readily absorbed oxygen caused the most polymer breakdown. Hersh (4) and Adams ( I ) , among others, have used ultraviolet absorption spectra for analyzing petroleum products and their components. This means of attempting to obtain a quantitative measure of the degree of reactivity of the aromatic portion seemed to offer the possibility of a quantitative solution of the problem. Kurtz (6)reports the presence of chemically aromatic-type materials in the aromatic fraction of various petroleum oils. These types of materials have maxima a t wave lengths a t about 260 mp, Present address, O h Mathieson Chemical Corp., Aviation Division, Niagara Falls, N Y . 1
as shown by Freidel and others (3). Since infrared analysis of the acidaffins by Linnig ( 7 ) reveals peaks characteristic of aromatics, polar groups, and double bonds, it appeared promising to investigate the possibility of correlating optical measurements with those of the chemical analysis, and to develop a mathematical expression based on both methods of approach. This article presents how this correlation has been achieved and thus provides mutual support for both approaches, which are identification of reactivity by optical means and by Rostler's precipitation method. PRQCEDURE
The oils used and their analyses are given in Table I. Some of the oils are representative of the three types of oils established by the Office of Synthetic Rubber; Dutrex 20 is representative of the highly aromatic oil type, SPX-97 and Sundex-53 of the aromatic type, and Circosol-2XH and Cyclolube of the naphthenic oil type. The other oils have been included to broaden the basis of the investigation. A latex made according to the iron-pyrophosphate formula was coprecipitated with the oils, and the polymers were vacuum dried. A smaller group selected from the same oils was also used with latex that had been made by a similar iron-pyrophosphate formula. Portions of this latex were also treated with 0.97 part per 100 parts of rubber of Versene Fe-3 (technical tetrasodium ethylenediamine tetraacetate mixed with other chelating agents) before coprecipitation with the oils. Also used were fresh latices made according to the sulfoxylate formula using rosin or fatty acid soaps, as well as an equal mixture of the two soaps. The amount of oil used in all cases was 37.5 parts per 100 parts of rubber. These formulas and the procedures are shown in a previous paper (9). The various polymers and masterbatches were heat aged a t 140" F. for 30 days, and the dilute solution viscosity of the polymers determined. The parameters for each polymer were calculated using the equation V A = Bc-a(t-x)
-
where V = dilute solution viscosity (DSV) t = time in days x = induction period in days
INDUSTRIAL AND ENGINEERING CHEMISTRY
1226 A , B , and a are constants.
Vol. 48, No, 1
901
A plus B is equal to the dilute solution viscosity of thc original contained polymer. e is the base of the natural logarithm. The results arc given in Table 11. Ultraviolet absorbancy index spectra were determined for 10 oils (Table 11). These spectra covered a range from 215 to 250 mp, determined a t 1-mp intervals, and from 240 to 320 mp) determined a t 2-mp intervals. For the 215- to 250-mp range the solvent was n-heptane, and for the 240- to 320-mp range, 85y0 methylcpclohexane t o 15% ethanol by volume was used. At 10mp intervals, absorbancies were determined using four different concentrations. These absorbancies were then plotted us concentration, and tlieee results indicated that in this range (215 to 320 mp) and with these solvents, the absorption properties of the 10 oils obey Beer's law. The absorbancies of the solutions were determined a t the specified wave lengths, using a Beckman Model DU spectrophotometer The absorbancy indices were then calculated:
i
i *\ i
70 X
SOLVENTS 220-250mp-n-HEPTANE 250-2701r$-85/15% METHYLGYGLOHEXANE/ ETHANOL
DUTREX 2 0
301
k' = A -.
C
where K
absorbancy indes (specific extinction coefficient) A = absorbancy (optical density) C = concentration, grams per liter =
The absorbancy indices mere then plotted against wave length,
Cltraviolet absorbancy indices of four of the oils, plotted against the rravc length, are shown in Figure 1. These are typical of the results obtained. The values a t 260 mp, where most of the oils have an absorbancy index peak, have been used for expressing the aromatic content of the oils. The slope of each breakdown curve was calculated from the developed exponential equation for the first 10 oil-polymer masterbatches and base polymers shoTm in Table I1 (Latcs I). The slope was taken at, a point 0.1 day after the induction period so that an initial rate of breakdom was obtained. This rate can be considered to be essentially the breakdown activation of the polymer rcsulbing from the oil, and comparison of this mt,e wit,h the knox-n variables in the oil may explain the functions and relative importance of these variables. I n Figure 2, these rates, 17-hichrepresent relative amounts of brealrdown in dilute solution viscosity units per unit of time in days, have been plotted against the ultraviolet absorbancy index a t 260 mi.l for each of the 10 oils. The general trend of an equation expressing this relationship is represented by the line. With the esception of Gulf SE-C, the rat,e of breakdown increased up to an absorbancy index of about 35. At about this point, the rate of breakdown increased a t a much higher rate. It was suspected that Gulf NE-C might contain vanadium.
Table I.
N-Bases 22.3 26.2 8.9 8.7 5.6 6.8 8 0
1.8 0 5 Si1
220
Figure 1.
RESULTS AND DISCUSSION
Oil Dutres 20 Califlux 550 Gulf NE-C Sundex 170 SPX-97 Sundex 53 Roxtone 180 Circosol-2XH Cyclolube Necton 60
.-._.
*4.U..*-.-.-.-...-.-
0
Rostler Analysis ( 8 ) , yo First Second llcidaffins Acidaffins 18.4 53.4 18.8 45.1 13.3 63.3 13.6 60.7 17.3 51.4 12.3 59.3 12.2 38.6 6.2 41.9 7.8 35.4 26.7 0.6
NECTON 60
240 260 WAVE LENGTH, m g
280
Ultraviolet absorption of oils
Analysis shoived trace amounts of this metal werc present in Roxtone 180 (indicating the greatest quantity), Gnlf KE-C, and Dutrex 20 and Sundex 53 (the latter two shoving only negligible amounts). S o vanadium was found in the remaining five oils of this series. Johnson (5) and others discuss the presence of vnnadium in the bottoms as well as in the distillates of cert,ain oils due to entrainment in the latt'er. Previous experience had indicated salts of this mat'erial to be oxidative catalysts. To demonstrate that they would increase the rate of breakdown, 0.007 part of vanadium pentoside per 100 parts of rubber was added to a latex. This latex and the untreated control were latex-masterbatched i\-ith 37.5 parts per 100 parts of rubhcr of Sundex 170, dried, and heat softened as described. The rate of breakdom a t 0.1 day was increased by this addition from 0.66 to 0.89. Ten times this amount of the oxide increased the rate to 1.64. The ultraviolet examination of the Gulf KE-C indicated the paraffinic fraction u-as markedly different from that of the other oils in that it r a s much more absorptive throughout the ultraviolet spectrum covered. Therefore, the values for the Gulf KE-C have not been considered, since it contained a catalytic material and the paraffinic fraction was not that of usual types of est,cnder oils.
Analyses of Oils
Paraffins 5.9 9.9 14.5 17.0 25.7 21.6 41.2 50.1 56.3 72.7
Mole of N Bases 0.064 0 058 0,025 0,020 0.016 0,019 0.018 0.04 OIO0l 0
Eby Method (Z), yo xonAromatic Polar aromatic 11.2 83.7 5.1 77.2 11.7 11.1 10.2 69.3 20.5 6.9 72.3 20.8 68.9 6.3 24.8 67.5 7.2 25.3 47.8 4.2 48.0 54.8 40.7 4.7 1.7 60.8 37.5 0.0 21.1 78.9
Ahsorbaney Index, Peak a t 260 mp 61.0 48.7 23.2 35.3 35.5 31.8 17.2 10.7 5.4 2.3
July 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
Considering the variables discussed in the procedure, i t seemed that the increase in polymer breakdown rate with increase in absorbancy index might be related to the amount of nitrogen bases, but calculations, based on moles of nitrogen bases, indicated a more rapid increase in rate than was found experimentally. Further calculations included the per cent paraffins to lower the rate of increasc in the slope. The following general equation was found to express thc rate of breakdown, -R,
-R = Ki ( A I )
+
Ka X Moles N bases yo Paraffins
)
S
C
where AI = absorbancy index of the whole oil a t 260 mp, moles of nitrogen bases and per cent paraffins are determined by the Rostler method, c = the rate of breakdown of the base polymer, and K , and Kn are constants.
1227
Table 11. Parameters of Equation for Masterbatches of Various Oils Made with I ~ i t i c E1 ~ om s V:wious I’olyinwization Formulas Polymerization Slope a t Latex Formula Oil A B u .r U.lday(--J) 1 Iron 4-pyrophosphate, Dutrex 20 1 18 2.33 1.41 0 2.61 0.02 part Fea (mixed Califlux 550 1.24 2.06 0.69 0 1.33 soaps) Gulf NE-C 1.21 2 . 1 0 0 0.49 0.97 Rundex 170 1.21 2.10 0.41 0 0 83 SPX-97 1.21 2.10 0.24 0 0.69 1 21 2 . 1 0 Sundex 53 0 49 0.34 0 Roxtone 180 J .31 2.00 0.16 0 0 32 Circosol-2XHh 1 54 1.56 0.17 2 . 5 0.26 1 51 1 . 8 0 Cyclolube 0.06 0 0,11 1.81 1 50 Necton 60b 0.13 0.09 3 Base (Nonea) 0.06 3 2 51 0 . 7 3 0 04 2 1.22 0.95 soaps) Sundex 53 0.70 Circosol-2x1s 0.32 0.07 0.10 3 Iron-pyi ophosphate, Dutiex 20 133238 020 0 5 0 47 (same latex as X o 2) SPX-97 1 29 2 46 0.22 1 5 0 53 plus 0.97 part Verseiic. Sundex 53 203167 006 2 5 0 10 Fe-3 C I ~ C O S O I - ~ X 2H 85 0 86 0 08 9 0 0 07 Necton 60 N o breakdown 0 Basc(i\;one) 3 49 0 23 hlatex No. 3. The osidntion of the latex seem2 t o inlply lhnt ferrous iron accelcrates the effect of the nitroycn bases, but ferric iron does not,.
jC
60
(1) hdains, Norman G., Richardson, Dorothy 31., Anal. CItem. 23, 129-33 (1951). (2) Eby, L. T., Ibid., 25, 1057 (1953). (3) Froidel, Robert d.,Orchin, Alilton, "Ultra Violet Spectra of Aromatic C'ompounds," Wiley, K e w York, 1951. (4) Hersh, R. E., Fenske, El. R., Uatson, H. J., Koch, E. F.,Booser, E. R., Braun, W.G., Anal. Chena. 20, 434-44 (1948). (5) Johnson, Paul H., Afiller, K. L . , Jr., Benedict, B. C., IKD. EXG.CHEW47, 1578 (1955). (6) Kurtz. S. F., Jr., Nartin, C . C . , India Rubher World 126, 495 (1952). (7) Linnig, Frederick 3.. private caoinmunication. (8) Nostler, F'.S.,White, R. R I . , IND.ENG.CHEM. 41,598 (1949). (9) Taft, Mi. K., Duke, J., Larchsr, T. B., Sr., Hitzmiller, W. G.. Feldon, SI.,Ibid., 48, 1220 (1956). (10) Taft, W. K., Duke, June, Lauridrie, It. W., Snyder, A. D., Prem, D. C., hlooney, Howard, I b i d . , 46, 396-412 (11) Taft, W. K., Duke, J., Snyder R. W., R u b b e r Aye (N. Y.) 75, Xo. 1, (1954). (12) Taft, W. K., E'eldon, Milton, Duke, June,
RECEIVEDio!. review November 16, 1956. ACCEPTEDFebruary 13, 1956. l\leeting, Pa., L)ivision of Rubber Chemistry, I , ~ , . 1955. Work performed as p a r t of the government synthetic rubber
Design Equations for Continuous Stirred-Tank Reactors 1)EAIt S1R:
The authow of this article [Acton, F. S.,Lapidus, I,., Isu. ICNG. CHFM.47, 706 (1955)] ( 1 ) made t v o mistakes, which some\rh:*f \yeaken their treatment,. The basic points in the folloxing discussion are taken from some unpublished lectuw riotcs (111 liomogeneous reactors. ('onqicier the irreversible second-orc1c.r r t w c l ion
A f B (in excese) -+ products
(11
which occurs in the cont,inuous stirred-tank reactor, then the material lsalance for A4on the nth tank in the form is
- a,
=
da, dT
+ Ka,b,
(2)
