EFFECT OF' PETROLEUM PRODUCTS ON NEOPRENE VULCANIZATES Effect of Lubricating Oils DONALD F. FRASER Organic Chemicals Department, Rubber Chemicals Division, E. I. du Pont de Nemours & Company, Inc., Wilmington. Del.
tioii in individual glass test tubes. The test tubes were plaeed in glycerol bath maintsioed a t 100" C. (212' F.). The volume was determined hv a dolly spring balance after immersion periods
When immersed in commercial lubricating oils, neoprene vulcanizates reach equilibria with respect to swelling or volume increase. The time necessary to reach equilibrium depends upon the immersion temperature and the chemical characteristics of the oil. It is shown that the volume increase of a neoprene compound inlubricating oils is a logarithmic function of the viscositygravity constants (or a direct function of the gravity indices). The volume increase appears to he independent of the refractive and viscosity indices of the oils.
.~ ~
~~
the various Gmperatures.
Time
LO Reach
Equilibrium
The curves indicate that after immersion for a short time the neoprene vulcanisate sbows a maximum swelling in each oil, and that the oil-neoprene system attains a sweUing equilibrium. Equilibria are reached more rapidly in the case of those oils having the least swelling effect on neoprene at a given temperature; with all the oils the length of time before equilibrium is reached is decreased when the temperature of immersion is increased. As might bo expected, the swelling of the neoprene in the oil increases as the temperature of immersion is increased. Obviously, in order to increase ita practical)ility, a volume increase specification should specify a time of immersion sufficiently prolonged so that the neoprene conipouiid may attain equilibrium in the particular oil and at the particular temperature used. The fact that neoprene compounds attain equilibria with petroleum derivatives ROcounts for the successful use of neoprene products where resistance to swelling in petroleum derivatives is important. Rubber products, on the other hand, are progressively swollen by oils, the swelling increasing until the swelling pressure exceeds the strength of the vulcanizate, a t which point the rubber vulcanizate disintegrates. Figure 1 also discloses the fact that in a variety of oils the swelling of the neoprene compound is independent of the SAE numbers of the oils. Therefore, in writing a volume increase
N WRITIXG control specifications for fabricated neoprene parts, a volume increase test after immersion in a lubricab ing oil is frequently made part of the requirements. Since the choice of neoprene in preference to rubber is frequently dictated by its superior oil resistance (as well as it8 superior age, heat, and sunlight resistance), the use of such a test is logical provided the conditions are intelligently chosen. This paper is devoted to a discusion of the various factors iduencing the volume increase test and tlre method of choosing representative oils so that the oil samples may be duplicated with respect to their swelling effect on neoprene wlcanizates.
I
Neoprene and Oils Used The neoprene compound used in this investigation was: 100 4 28.8
2
5
Gesta. w'88 wed.
This compound contains 20 volumes of carbon black r 100 volumes of neoprene. The compound included a relativecsmall amount of loading in order to show more clearly the andl differences in the results and is to be considered aa a test formula rather than a commercial compound. slabs of the compound, 3 X 6 X 0.085 inch, were vulcanized in a mold in a hydraulic press for 80 minutes at 141.7" C. (287" F.). For the volume IRc r w e test, specimens 2 x 0.5 inch were died out from the vulcanized slabs. The per sent volume increase of the specimen wm determined by the volume dis lacement method according to the procedure of the Amerioan &oiety for Testing Materials (Designation D47!-37T). The oils investigated were oommercid lubricating oils purchased on the open market as various SAX grsxles. The source, treatment, and physical inspection dats. of these oils are given in Table I. After the original volumes of duplicate test specimens were obtained, the specimens were immersed in the oil under examina
RESILIENT PSTVNASD VALVES RESIST OIL A s a n s ~ A o N~D DETERIORATION IN OIL-FIESD SLUSH PUMPS
320
MARCH, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
321
TABLEI. SUMMARY O F DATAON LUBRICATING OILS Sample
No. 1 2 3 4 5 6 7 8 9
10 11 12 13
Source Coastal Mid-continent Mid-continent Mid-continent Pennsylvania Mid-continent Pennsylvania Pennsylvania Mid-continent Pennsylvania Coaatal Mid-continent Coastal mid-continent
+
/ I 1
I
A. P. I. SAE Gravity Treatment No. (60' F.) 10 21.5 Acid-treated 26.5 10 Acid-treated 10 26.9 Acid-treated 20 23.8 Acid-treated 30.8 20 Filtered 29.0 Solvent-extd. 20 29.2 Solvent-extd. 20 20 29.6 Filtered 28.9 Solvent-extd. 20 31.2 Solvent-extd. 20 22.0 40 Acid-treated 26.9 40 Acid-treated 17.3 50 Acid-treated
I
I OIL SAMPLE NO.
I
Sp. Gr. (60' F.) 0.7249 0.8955 0.8933 0.9112 0.8719 0.8816 0.8805 0.8784 0.8822 0.8697 0.9218 0.8933 0.9510
VISCOSITY SAE NO.
Saybolt Universal Viscosity, Sec. 100' F. 210' F. 223.2 44.8 221.1 46.4 235.5 47.7 324.7 50.7 362.5 57.0 267.4 51.0 263.7 52.8 359.9 57.2 334.3 54.7 391.7 60.0 764.4 63.1 672.6 72.6 1631.0 77.4
Viscosity Index 50.8 77.8 85.4 67.8 103.7 102.3 117.6 105.7 100.0 109.5 32.0 93.5 0.0
VischsityGravity Constant 0.8806 0,8480 0.8390 0.8576 0.8035 0.8217 0.8206 0.8123 0.8185 0.7993 0.8600 0.8219 0.8925
Refractive Index 1.5109 1.4978 1.4940 1.5032 1.4898 1.4890 1.4887 1.4868 1.4855 1.4807 1.5120 1.4962 1.5308
Gravity Index 17.6 71.2 81.0 59.3 109.4 96.4 97.3 103.4 99.0 111.8 55.8 96.3 -5.5
test compound after immersion in the oils for 14 days a t 100" C. This time period was chosen so that the oil-neoprene systems were at or had almost attained equilibria. The viscosity-gravity constants were calculated by the method of Hill and Coates (5') according to the equation: 10G
a =
where a G V
- 1.0752log (V - 38) 10
- log (V
- 38)
= viscosity-gravity constant = s ecific gravity at 60' F. = &bolt Universal viscosity
at 100" F., sec.
The shape of the curve in Figure 3 indicates that a t swelling equilibrium the per cent volume increase is a logarithmic function of the viscosity-gravity constants. This function for the Neoprene Type G compound used in the investigation is. log V where V
I1 4
a 2
\;
1
10
I 01 2
7
I 14 TIME OF IMMERSION (IN DAYS)
=
10.34a - 7.09
=
yovolume increase of neoprene compound at swell-
ing equilibrium viscosity-gravity constant of oil
After the viscosity-gravity constant was determined, the gravity index was calculated as proposed by McCluer and Fenske (4) who assigned gravity index figures to the range
3
7
=
I I
I
t
I
-O!,L ----
I SAMPLE N?, I 2
TEMPERATURE OF IMMERSION
I 2s
FIGURE1. TIME-SWELLING CURVES OF NEOPRENE COMPOUND IN VARIOUSOILSAT 100" C. specification, it is not sufficient merely to indicate the SAE rating of the oil to be used, because the swelling power of the oil depends upon the chemical components and these are governed by the source and/or treatment of the crude. It has been found that neoprene is resistant to members of the paraffin series, whereas naphthenes cause a severe swelling and aromatics a very severe swelling. Consequently the specification for the oil must include some factor that will specify or indicate these components of the oil. A search of the literature (6) reveals that the "average" chemical constitution or the predominating constituents of mineral oils may be classified or characterized by several of the data presented in Table I.
Effect of Physical Properties of Oils I n Figure 3 the viscosity-gravity constants of the oils are plotted against the per cent volume increase of the neoprene
>
------------------I2
7
14 T I M OF IMMERSION (IN DAYS)
-15.C.
1
28
FIGURE2. TIME-SWELLING CURVESOF NEOPRENE COMPOUND IN OILS1 AND 2 AT SEVERALTEMPERATURES
VOL. 32, NO. 3
IKDUSTRIAL AND ENGINEERING CHEMISTRY
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tested at 100" C., provided that softeners or other extraetable materials are not present in the composition. When these materials are present in normal amounts, the equation will approximate the true results. It is implied that these relations refer only to compositions urhich are vulcanized in a basic compound, similar to the one described previously, to an optimum technical cure as judged by stress-strain data. The relations are: log V = (5.43e - 3.723) log N and V = (1.460 - 0.0117g) N where V = Tovolume increase of neoprene coming position equilibrium at swelliy =
% neoprene (by volume) in the comuosition
article: Gr. Indcr
V. C. C .
Cr. Index
Y. G . C .
Gr. Indcr
V. G . C .
In Figure 4 the calculated gravity indices (Table I) arc plotted against the same volume increase results BS were used before. Figure 4 shows that there is a direct relation between per cent volume increase at the swelling equilibrium and tho gravity indices of the oils. The specific gravity, refractive index (determined with an Ahhe split prism refractometer at 20" C.), and viscosity index (determined according to the method of Davis, Lapeyrouse, and Dean, 2 ) were also plotted against tho same per cent volume incream results, hut none of them showed any evident simple correlation with the volome increase. It is evident, therefore, that in specifying oils to be used for testing neoprene compositions, it is necessary t o specify the gravity index or the viscosity-gravity constant in order to obtain samples of oils which mill he duplicable in so far as their effects on the neoprene compositions are concerned. I n fact, if the gravity index of the oil or the viscosity gravity constant is known, it is possible to predict the equilibrium swelling of the neoprene compound. Thus, as can he calculated from Figure 4, the equilibrium volume increase of the Neoprene Type G compound used in these tests at 100' C. will be: V = 117.0
With commercial neoprene vulcanieates the maximum swelling may he followed by a shrinkage in volume due to extraction of oily or waxy materials from the neoprene compound by the oil under test. These materials are present in practically all commercial compounds and are used for their softening and lubricating effect on the neoprene during compounding and processing. Unpublished results indicate that those oils having the greatest swelling effect on vulcanized neoprene compounds are tho most soluble in unwlcanized
- 0.935g
where V = % volume increase of neoprene compound a t swelling equilibrium g = gravity index of oil
A previous paper (I) shomed that the swelling of neoprene compositions in a given petroleum derivative is dependent on the dilution of the neoprene by the other ingredients in the compound. In other words, V = NC where V = % volume increase N = % neoprene (by volume) C = a constant Consequently the relations established in this paper may be restated to include any Neoprene Type G composition when
FIGURE 3. EFFECTOF VISCOSITY-GRAVITY CONSTANT ON V o ~ n mINCP.EAP.E OF NEOPRENE COISP~DNU IN VARIQV~ OILS
MARCH, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
neoprene and consequently may be used in larger amounts during compounding without the appearance of an oil "bloom" on the vulcanized product. The time-swelling cumes shown in Figure 1may he used to calculate the amount of oil that is soluble in the neoprene vulcanizate under test at 100' C. I n the case of oil sample 10 the maximum volume increase caused by this oil is 13.8 per cent. If this particular oil is added to the unvulcanized neoprene compound in an amount sufficient to increase the volume after vulcanization to 113.8 (when the volume of the compound without the oil is loo), then this new compound should show a nero swelling when immersed in this partioular oil at 100" C. I n other words, to obtain a zero swelling compound i t is necessary to add oil to the unvulcanized compound in an amount equal to the volume of the same oil which the vulcanized compound would otherwise absorb during the swelling test or service life. Upon calculation it was found that theitquired amount of this particular oil was 11.96 parts by weight. Accordingly the following formula was compounded: Neoprene Type.0 Extra iight calcined ms neeia Semireinforoing oarbon %bok
Phenyl-8-naphthylamine
100 4
Zinc88mpIe Oil oxide 10
28.8
PITM~FRE?TE-LINED SXOOTH-RORE DOCK HOSESPEEDS DrLIYLRY OF THE Pnonwm AND Tirus REDUCES TIMEAT THE DQCR
2
The efficiency of this type of hose n,ould be seriously limited if the smooth inner tube of neoprene swelled excessivcly.
12 5
This conipound was vulcanized and tested as described before; the volume increase results after immersion in oil sample 10 at 100" C . were: ?& voi. Inoreas* in Oil S*mple 10 'rime*i immersion Compou,nd with Compound without loo* c., Days d Oil 1
2
0.8 0.7
11.8 12.0
...
13:s
soluble in the neoprene and the hloom will disappear when the compound is raised t,o tlie chosen operating temperature (1000C . ) . As mentioned previously, the compound used in this study is a test formula rather than a commercial formula. Beoaose it carries a small amount of ioadine.,(carbon black>. , ,, it shows greater swelling in tlie oils blian woiild more heavily loaded commercial eolnpoul,ds,
0.7
6
7
323
Consequently it is possible to obtain a compound having practically no swellinr in a aarticular oil at a narticular
Conelusions
~
Neoprene vulcanizates reach equilibria with respect to swelling or volume increase when immersed in lubricating oils. The time necessary to attain oquilihriuni is dependent upon the temperature of the test and the chemical components of the oil. I n any specification involving a volume increase test for neoprene products, the time should be sufficiently long so that equilibrium is attained in the particular oil a t the particular temperature under investigation. Furthermore, in order to ensure duplicability of oil samples with respect to the swelling effects on neoprene compositions, it is essential that tho specification for the oil include a dest designed to indicate the chemical characteristics of that oil. It has been shown that the gravity index or the viscosity-gravlty constant may be used as such a test. ~
2
i
BO-
Y
c
g
" 4 =
3
-
% 3 30-
"
Acknowledgment Acknowledgment is made of the helpful collab+ ration with A. B. Hoe1 of the Sun Oil Company, C. C. Morrison of the Gulf Oil Corporation, and M. A. Dewey and J. R. Sabina of the Petroleum Chemicals Testing Laboratory, E. I. du Pont de Nemours & Company, Znc.
>
$ zc-
Literature Cited
B
( 1 ) Criton, Io-
-10
.
FIG"'1CS
I
1
I
0
lo
20
I so
REFER
I 40
TO OiL SIIUPLE
31, 956 (1938). (2) Davis. G. H . U., Ilapeyrouse, M., and
NUUBERS
I
I
I
I
I
I
00
bo WDEX
TO
80
90
(00
CR6YITI
FIGURE 4. EFFECTOF GR~VZTY INDEX
N. L.,and Fraser, D. F., IND.ENU.Caex..
1 ,,o
ON VOLUME INCKSAGE of NEoPKSNE COMPOUND IN VARIOUS OILs
Dean, E. W.,
Oil Gas J., 30, 92 (1932). ( 3 ) Hili, J. R.. and Coatas, H . B., IXD.Eno. CXEM.,20, 641 (19%). (4) BleCluei. W. R.. atid Fenske, M. E., I b X , 24. 1371 (1932) (8) Rossini, 1'. I>., Oil Gas J.. 36, 183 (1937).
