I
11.
Table
Composition of Parts by Weight
Butyl A,
OFRICTION
d5
(Cure time, I hour a t 140" C.) GRI, 100 Zinc oxide, 5 Stearic acid, 3 Sulfur, 2 Tuads, 1 Captax, 0.5
the correct value for G. There is considerable deformation of the material surrounding the indention [similar to shallowing in the case of metals (SO)] and this leads to a depth of penetration o which may be as much as four times that given by Equations 4 or 5 . Moreover, as stated by Hertz, the mathematical representation of the deformation outside the contact area can be somewhat complicated (IS). A more correct value of 1, and hence, also d, within the contact area, may be obtained by coating the elastomer surface with an indicator (Dykem Hi-Spot Blue) and observing the average track widths produced by the three balls during rolliig. Doing this for butyl A at a series of loads, a straight line is obtained on plotting Equation 5 which has a much lower slope than obtained when measured values of d are used. Calculation then yields a value for G of 4.7 X 106 dynes per sq. cm. a t 25" C. The appropriate correction factor when applied to Equation 4 allows that equation to be used for subsequent determinations of G at temperatures other than 25' C. The working expression which results from the above procedure resembles closely that proposed by Scott for measuring rubber modulus by penetration with a hard sphere (25). The results of both modulus and rolling friction measurements for butyl A are given in Figure 8. The modulus
I
-12
2'
- 4O . TEMPERATURE,
'C
Figure 8. Dynamic modulus and rolling friction for butyl elastomer A Load = 538 grams per ball
drops most sharply in the vicinity of the friction peak as would be expected on the basis of the previously found correlation between X and tan 6. If measurements were extended to still lower temperatures, the modulus would be increased by at least another factor of 10. ACKNOWLEDGMENT
The author thanks A. M. Bueche for many helpful discussions and suggestions during the course of this work. LITERATURE CITED
(1) Alfrey, T., Jr., ''Mechanical Behavior of High Polymers," p. 176, Interscience, New York, 1948. (2) Atack, D., Tabor, D., Proc. Roy. Soc. (London) A246, 539 (1958). (3) Bueche, A. M., unpublished data, September 1959. (4) Bueche, A. M., Flom, D. G., Wear 2, 168 (1959). (5) Bulgin, D., Hubbard, G. D., Trans. Inst. Rubber Ind. 34, 201 (1958).
(6) Drutowski, R. C., Annual Meeting e e r i e a n Society of Mechanical Engineers, New York, November 30 to December 5, 1958. (7) Evans, I., Brit. J. A p p l . Phys. 5, 187 (1954). (8) Flom, D. G., J . A p p l . Phys. 31, 306 (1960). (9) Flom, D. G., Ibid., submitted for publication. (10) Flom, D. G., Bueche, A. M., Zbid., 30, 1725 (1959). (11) Gehman, S. D., Rubber Reviews for 1957 30, No. 5, 1202 (1957). (12) Greenwood, J. A,, Tabor, D., Proc. Phys. SOC.(London) 71, 989 (1958). (13) Hertz, H., J . reane angew. Math. 92, 156 (1881). (14) Jenckel, E., Herwig, H. U., Kolloid-Z. 148, 57 (1956). (15) Kline, D. E., Sauer, J. A., Woodward, A. E., J. Polymer Sci. 22, 458 (1956). (16) hlcCrum, N. G., Zbid., 34,355 (1959). (17) Maxwell, B., Princeton Plastics Laboratory Technical Rept. 46C, August 15, 1957. (18) May, W. .D., Morris, E. L., Atack, D., J . A p p l . Phys 30, 1713 (1959). (19) Nielsen, L. E., Buchdahl, R , Levresult, R., Ibid., 21, 607 (1950). (20) Nolle, A. W., Ibzd., 19, 753 (1948). (21) Nowick, A. S., "Progress in Metal Physics," Vol. 4, p. 1, Interscience. New York, 1953. (22) Schaevitz Engineering Bull. AA-1, Caniden, N. J., 1955. (23) Schmieder, K., Wolf, K., Kolloid-2. 127, 65 (1952). (24) Zbid., 134, 149 (1953). (25) Scott, J. R., Rubber Chem. Tech. 28, 1071 (1955). (26) Tabor, D., Brit. J. A p p l . Phys. 6, 79 (1955). (27) Tabor, D., Lubrication Eng. 12, 379 (1956). (28) Tabor, D., Phil. Mag. 43, 1055 (1952). (29) Tabor, D., Proc. Roy. SOC.(London) A229, 198 (1955). (30) Tab:;, D., 'The Hardness of Metals, p. 84, Clarendon Press, Oxford, 1951. (31) Wolf, K., Schmieder, K., International Symposium on Macromolecular Chemistry, Torino, Italy, Septemher 26 to October 2, 1954. RECEIVEDfor review April 15, 1960 Accepted August ,18, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
Spectrophotometric Determination of Flexzone and Other p-Phenylenediamine Derivatives
3C
C. L. HILTON Research Center,
U. S.
Rubber Co., Wayne, N. J.
b Derivatives of p-phenylenediamine have been used extensively 0 s antiozonants in rubber products. The newest, and perhaps the most effective, of these chemicals is Fiexzone 3C (N-isopropyl N' phenyl - p phenylenediamine), manufactured by the Naugatuck Chemical Division of the U.S. Rubber Co.
-
1554
0
-
-
ANALYTICAL CHEMISTRY
The present paper describes the identification and estimation of these by oxidation to the corre-
spending Wcrster
and coiori" metric analysis of the resulting SdUtions. Accuracy and precision are better than &370 relative.
A
p-phenylenediamine derivatives absorb rather strongly in the ukraviolet region, their absorption spectra are usually masked by those of other compounding ingredients to such an extent t,hzit identification and estimation are not possible by this methud. Elution (3, 4 ) or paper (7-9) c,hronictLTHOC'GH
ographic techniques have been utilized, but these are tedious and time consuming. The diazotized p-nitroaniline color reaction, which served for the determination of 31 commercial amine antioxidants (8), cannot be applied to derivatives of p-phenylenediamine. Colorimetric methods using benzoyl peroxide (I, 7-9) yielded unsatisfactory results when applied to ethyl alcohol extracts of rubber samples. Waters (6) found that N,N'-diphenyl-p-phenylenediamine is readily oxidized by mild oxidizing agents to produce Wurster salts. Lane ( 5 ) used this reaction for the determination of Spergon (tetrachloro-1,4-benzoquinone) residues on food crops. Here, of course, the oxidizing agent was present in small quantities compared with the reagent. When this reaction was tried for the determination of the antiozonants, the presence of th'e excess oxidizing agent caused the reaction to proceed beyond the Wurster salt stage and the color disappeared. Other oxidizing agent,s were tried. Under the conditions utilized in this investigation] the best reagent was found to be cupric acetate in a potassium chloride-hydrochloric acid buffer. The oxidizing agents and buffer systems studied will be discussed later. EXPERIMENTAL
Apparatus. T h e instrument used was a Beckman Model D K - 2 recording spectrophotometer &-ith a temperature-regulated cell holder. T h e instrument settings were as follows: scanning timr 5 ; scale expanded l X , time constant 0.1, sensitivity 50. The lead sulfide cell was used. At this sensitivity, the nominal slit widths obtained were: Wave Length, hlr
750 700 650 600
550
500
450 400
Slit Width, Mm. 0.075 0.083 0,096
0.104 0.158 0.220 0.360 0.5tiu
Reagents. Ethyl alcohol, 95%, and reagent grade cupric acetate monohydrate, qotassium chloride, and hydrochloric acid. U.5N HCI, 4.27 ml. of concentrated acid diluted to I liter with distilled c-ater. 0.!25Ar HCl, 250 ml. of 0.6N acid diluted t'o 1 liter with 955%ethyl alcohol. Oxidizing agent, 0.500 grnni of cupric acetate nionohydratr, 4.66 grams of potassium chloride, 10 mi. of 0.5X HCl, and 2.50 ml. of disti!l.(! water diluted to 1 iiier uii.h 95S)'&_eth:;: :i:-ohol. Procedure. I Jie :,ample t o be an-
Table 1.
Procedure for Various Antiozonants
Composition
Procedure
50% N-Phenyl-%naphthylamine (PBNA) 25% p-Ieopropoxydiphenylamine 2570 Diphenyl-pphenylenediamine (DPPD) 65% PBNA, 3570 DPPD Di-%naphthyl-pphen ylenediamine 65% N-Phenyl-1-naphthylamine 35% DPPD 6570 PBNA, 35% DPPD Mixture of diarylamine ketone and DPPD N-N '-Dimethyl-pphenylenediamine N-N '-Diphenyl-p-phenylenediamine N-N '-Di-2-octyl-p-phenylenediamine N-N'-Di-3-( 5-methylhepty1)-p-phenylene-
A
Antiozonant Agerite Hipar
Agerite H P Agerite White Akroflex C Akroflex CD BLE Powder Dimethyl-p-phenylenediamine DPPD Eastozone 30 Eastozone 31
Flexzone 6H Nonox ZA Perflectol p-Phenylenediamine Santoflex BX Santoflex H P Santoflex 75 Santowhite CI Tenamene-2 Thermoglex A UOP 88 UOP 288 Variamine Blue B hydrochloride Wingstny 100
A A A A B A B
B
A or B
Eastozone 32 Flexamine Flexzone 3C
A
% Diaiylamine ketone, 35% DPPE N-Phen yl-N '-isopropyl-pphenylenediamine N-Phenyl-N '-cyclohexyi-p-phen ylenediamine N-Phenyl-N '-isopropyl-p-phenylenediamine Polymerized trimethyldihydroquinoline and DPPD D-Phenvlenediamine
A A
A A
A A A
A A decylquinoline 7570 DPPD D i-2-napht hy 1-pphenylenediamine Di-( 1-methylpropy1)-p-phenylenediamine Same as Agerite Hipar Dioctyl-pphenylenediamine Dioctyl-pphenylenediamine
N-( pMethoxypheny1)-p-phenylenediamine Diaryl-p-p hen ylenediamine
with extraction cloth which has been previously extracted to remove sizing, etc. The sample is placed in an Underviriters' extraction cup and extracted for 16 hours with 95% ethanol or methanol. The alcohol extract is transferred to a 100-ml. volunietric flask, coo!ed to room temperature, and brought to the mark ivitli the extraction solvent. A 5-m1. aliquot is transferred to a 25-ml. volumetric flask. If the antiozonant is qualitatively known, the procedure to be followed from this point is indicated in Table I. PROCEDURE A. 2 ml. of oxidizing agent are added to a 5-ml. aliquot of the sample. If a red to pink color is not olitained, the solution is brought to the mark with oxidizing agent, PROCEDURE B. If a red to pink color is obtained when the 2 nil. of oxidizing agent arc added, the antiozonant is a di- or tetraalkyl derivative of p pheny1cnediair:ine. The procedure for these compounds is to add 2 ml. of 0.12Siz' HC1 and bring to the mark with 0570 ethyl alcohol. Determine the absorption spectrum froin 750 to 400 mP using a Beckman 1 : d e l DE(-2 spectrophotometer. The c,i)lor formation is complet,e by the time t l i , . solution is brought, t o the ma.rk. 1 : I C coior is stnhle for a t least, hour.
Ethyl alcohol is used in the reference cell unless the alcohol extract is strongly colored. I n this case, the reference solvent is taken to be a 5 m l . aliquot of the ethyl alcohol extract diluted t o 25 ml. with ethyl alcohol. The absorbance readings are plotted on Keuffel and Esser semilogarithmic graph paper No. 358-63, 2 cycles x 10'12 inch. The resulting spectrum is compared with Figure 1 for identification of the antioxidant. The per cent antioxidant is calculated using the equation developed for the antioxidant concerned. I n Figure 1, the log absorbance scale has been intentionally eliminatcd since the curves have been displaced vertically for better presentation of the curves. The color formation is illustrated by the following example :
f
r,.,
VOL. 32, NO. 12, NOVEMBER 1960
e
1555
A. Eastozone 30 Eastozone 31
A. N,N'-dimethyl p-phenylenediamine 8. Flexzone 3 C Flexzone 6 H
A. Agerite white Sontowhite C.I.
U . 0 . P 288 E. Variaminc Blue 8 HCI
E. DPPD Wingstay 100 C. Eastozone 32
I
\
\
~
450
550
650
450
550
Millimicrons
Figure 1.
450
Millimicrons
Millimicrons
Absorptivity values, a, w-ere determined for 24 commercial p-phenylenediamine-type antiozonants and three related compounds. The absorptivities were obtained with one batch of the antiozonant. Since the absorptivity of an antiozonant will vary from batch to batch, a new absorptivity must be calculated each time a different batch is used. Absorptivity equals A/bc
where A is the absorbance of the solution, b is the path length in centimeters, and e is the concentration in grams per liter. Pertinent information about the 27 compounds studied is given in Table 11. The equations for the quantitative determination of the antiozonants are as fOllO\\ 3 : a (solution) 9; antiozonant = a100 (antiozonant) ( 1 ) Since a = A / b e , this equation can be changed to
Table II. Spectrographic Characterisiics of Compounds Studied
Rave Length Maximum, Antiozonant Absorptivity Mp Agerite Hipar 9 . 51 432 Agerite HP 6 . 84 432 Agerite White 3 5 .7 478 Akroflex C 11 .o 432 9.77 436 Akroflex CD BLE Powder 12.8 430 Dimethyl-pphenylenediamine 69.2 558 33.8 435 DPPD Eastozone 30 37.6 550 Eastozone 31 41.7 552 59.2 614 Eastozone 32 Flexamine 12.3 430 22.8 495 Flexzone 3C Flexzone 6H 20.4 495 2 3 . 9 495 Nonox ZA Perflectol 10.0 430
o/c antiozonant
=
100 A 1 .OOO X concn. in grams per liter X a (antiozonant)
(2)
Table I11 shows the results obtained by direct ultraviolet absorption analysis and by the colorimetric method. These
Table 111.
U.V.
Stocks containing Flexzone 3C
0.52 1.03
Stocks containing Flexzone 6H
0.35 0.49
diamine Santoflex BX Santoflex HP Santoflex 75 Santowhite CI Tenamene-2 Thermoflex A
0.85 1.90
Stocks containing Ringstay 100
UOP 88 UOP 288
49.6 23.8
ANALYTICAL CHEMISTRY
555 440
stocks were raw styrene-butadiene rubbers containing no interfering materials. DISCUSSION
The method is applicable to raw and cured polymers whether natural or synthetic. Compounding ingredients other than p-phenylenediamine do not interfere with the exception of dithiocarbamate or thiuram sulfide aecelerators which form colored compounds with cupric ions. In cured stocks, quantitative recovery of the antiozonant is not always possible. This is usually due to oxidation or other reaction of the antiozonant. The determination of unreacted antiozonant, however, is quantitative. Although the absorptivities of commercial antiozonants vary from batch to batch, no gross error is to be expected in either qualitative or quanti-
Results Obtained by the Different Methods
p-Phenylene-
1556
1
650
Absorbance spectra of various p-phenylenediamine derivatives commonly used as antiozonants
RESULTS
Variamine Blue B Hydrochloride \Vingstay 100
\
550
0 56
Amount Found Colorimetric 0.51 0.52 1 .oo 1.02 0.34 0.34 0.46 0.52 0.84 0.85 1.86 1.91
1 22
0 55 0 55 1 20 1 20
2 02
1 98 2 05
% Difference, Relative
2.00 0.00 2.91 0.97 Av. 1.47% 2.86 286 6 12 6.12 1.18 0.00 2.11 0 53 Av. 2 7270 1 79 1 79 1 64 1 64 1 98 1 49
tative analysis because of buch variations. Since the method is based upon partial oxidation of the antiozonant, the method is not applicable to highly oxidized samples. Identification of mixtures of antiozonants is usually not possible. Howcver, quantitative analysis can he arcomplished with mixtures when the components are qualitatively known. This is done by the use of simultaneous equations. In the case of strongly colored alcohol extracts, an aliquot of the extract diluted without the addition of oxidizing agent is used in the reference cell and the differential absorption curve is obtained. Since the Wurster salts are rcported to be stablc only in the pH range of 3.5 to 6.0 ( 6 ) ,a buffer solution in this range \yas sclected. The apparent pH of the final solution was 4.2 in the case of Procedure A. Table IV shows the effect of pH on the absorptivity for DPPD. With the alkyl derivatives of pphenylenediamine, double peaks were observed in the region from 500 to 600 mp. A gradual increase in absorptivity was noticed using Procedure A. For these compounds the cupric ion concentration must be lowered and the acid contrnt must be raised. The result is Procedure 13. The apparent pH of the final solution in this case was 1.8. I n Procedure 13, there was no change in absorptivity or stability over the pH range of 1.5 to 2.5. Other oxidizing agents which were
Table IV.
error, no attempt has been made to make the identification more specific. Those antiozonants in Table I which are shown to be mixtures of D P P D and one or more nonabsorbing materials yield the same spectrum as that for DPPD. I n this ease, the presence of a mixed antiozonant can be ascertained by resorting to the coupling procedure for amine antioxidants (2).
Effect of pH on Absorptivity for DPPD
-4pparent pH Absorptivity 2.6 2.8 3.0 3.2 3.4 3.6
28.6 29.4 31,5 31 . 5 32.6 33.0
3.8 4.0 4.1 4 2 4.3 4.4
33.4 33.4 33.7 33 8 33.6 35.2
Notes Fading rapidly Fading rapidly Fading rapidly Fading rapidly Fading rapidly Fading moderatelv Fad& slightly Stable Stable Stable Stable Fading
ACKNOWLEDGMENT
The author gratefully acknowledges the work of D. N. Pregler who carried out much of the experimental work described herein. LITERATURE CITED
investigated but which proved unsatisfactory for the analysis include Spergon (tctrachloro-1,4-benzoquinone) Phygon (2,3-dichloro-1,4-naphthoquinone), quinone, quinhydrone, 2,6dibronioquinonechlorimide, the sodium salt of 1,2-naphthoquinone-4-sulfonic acid, iodine, bromine, sodium periodate, ammonium vanadate, sodium hypochlorite, CdfZ, Nif2, Fef3, and Cof2 The method does not distinguish between two antiozonants with essentially the same structure-e.g., Eastozone 30 and Eastozone 31. Thus, in Figure 1, one spectrum is given for several antiozonants where the structures are too biniilar to be distinguished. Since identification of an antiozonant as Eastozone 30 instead of Eastozone 31 would not be a serious ~
( 1 ) Biirchfield, H. P., Judy, J. N., ANAL. CHEM.19, 786 (1947). (2) Hilton, C. L., Rubber Age 84, 263 (1958). (3) Hively, R. A., Cole, J. O., Parks,
C. R., Field, J. E., Fink, Raymond, ANAL.CHEM.27, 100-3 (1955). (4) Kawaguchi, T., Ueda, K., Koga, A., Ueda, T., J SOC.Rubber Ind. Japan 29,
8-13 (1956). (5) Lane, J. R., J. Agr. Food Chem. 6 , 667-9 (1958). (6). Waterc, W. A., “Chemistry of Free Radicals,” pp. 75-6, Clarendon Press, Oxford, England, 1946. ( 7 ) Zijp, J. W. H., Kautschuk u. Gummi IO, WT 14-16 (1957). (81 . , Z i h J. W. H.. Rec. trau. chirn. 75. 1126r36 (1956). ’ (9) Zbid., 76, 317-20 (1957).
RECEIVED for review April 11, 19M. Accepted July 21, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
END OF SYMPOSIUM
VOL. 32.
NO
1 2 , NOVEMBER 1960
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