HENRY M. TRAMUTT and ERVIN G. ANDERSON Gates Rubber Co., Denver, Colo.
FRITZ S. ROSTLER and RICHARD M. WHITE Golden Bear Oil Co., Oildale, Calif.
Influence of Petroleum Oils on Staining and Discoloration of Elastomeric Compounds Preliminary studies demonstrate the influence of oil composition on staining and discoloration of elastomeric compounds and show the usefulness of quantitative reflectance determinations in measuring these effects
COLOR
in elastomers is employed either for sales appeal or distinction. White side wall or colored tires and molded automotive parts for interiors are examples of color for sales appeal; colored wire insulation, for distinction or identification. The existing favorable economic conditions and the increasing complexity of instrumentation with its wiring requirements are two reasons for the current interest of compounders in stocks which are white, light colored, or designed to be in contact with such stocks. The work reported here was prompted by this steadily increasing interest in color retention. As a number of petroleum oils are used as plasticizers or extenders for all widely used polymers, the investigation was designed to establish generally valid facts regarding the influence of oil composition on color phenomena. Oils representative of currently used petroleum oil compositions and compounds based on natural rubber, GR-S, Butyl rubber, nitrile rubber, neoprene, Hypalon, and poly(viny1 chloride), containing the various oils were tested as to pigmentation (coloration imparted by the color of the oil), discoloration (coloration imparted by exposure to light), and staining (coloration imparted by migration). Discolor-
ation was induced by exposure to sun lamp aging and roof aging. Two commercial white side wall compounds were used as a reference material. The work has been planned as an extensive investigation. The findings presented here are a report of the first phase of this study, which is a preliminary orientation. The second part of the investigation is in progress. Background of Investigation
Several investigations dealing with color and color retention of elastomeric compounds are recorded in the literature, but only a few deal with plasticizers and extenders-products extensively used in modern compounding. Haworth and Pryer (9) reported a study of the effects caused by a variety of ingredients on color of compounds of pale crepe, smoked sheets, GR-S (staining), Perbunan, Hycar OR-15, Butyl, Neoprene GN, and Vulcaprene A, a poly(esteramide). The work reported by Haworth and Pryer is comprehensive and informative. The discussion of softeners is, however, limited in products and amounts investigated (570 maximum), The authors consequently found that softeners as a rule do not contribute to staining or discoloration.
Figure 1 . Oils of listed in Table I
In an investigation of oil types used in oil-extended rubber, Taft, Feldon, Duke. Laundrie, and Prem (22) found nitrogen bases in petroleum oils are responsible to a large extent for pigmentation, staining, and discoloring. The first published report of an extensive investigation of influence of extender composition on staining is a paper by Provost, Borg, Paige, White, and Howland (77), which concludes that a threshold level of 30 to “aromatics,” as determined by the Watson analysis (24), is the maximum permissible -to assure nonstaining characteristics of an oil used as extender. Some general observations regarding pigmentation, discoloring, and staining of petroleum oils as caused by components of the oil as defined in the present investigation have been made in a paper dealing with the chemical nature of oil extenders for GR-S (20). Previous Investigations
Assessment of Color Phenomena. Haworth and Pryer (9) employed exposure to ultraviolet light and to ordinary daylight and defined the color changes observed by common color names and terms, suchas yellow, brown, dark brown, pink, slight, very heavy, and nil. Hunter,
A
group
Upper. Before exposure to sun lamp Middle. After 1 -week exposure Bottom. After 3-week exposure
Figure 2. Oils of listed in Table I Upper. lower.
group
B
Before exposure to sun lamp After 3-week exposure
VOL. 49, NO. 8
v
AUGUST 1957
1283
Table I.
Summary of Data on Oils Tested
Composition of Oils Oil Designation Group Group Group -A B C
I1 111
IV
IV
V VI VI1 VI11
IX 1 2 3 4
1 3
5 6
6
6a
6b 6c
7 8 9
___
Watson Rostler (19) - _ . analysis _ Analvsis ~ 1st 2nd OSR (24)I acidacidPararoma- Nomengen affins bases affins tics affins clatureb 0.0 0.8 5.9 93.3 6.7 P 0.0 44.0 2.8 46.8 N 53.2 0.0 87.0 4.8 H 13.0 -.82.2 __ 0.6 9.9 41.6 52.1 47.9 N 1.3 12.7 32.3 46.3 N 53.7 1.3 14.7 70.5 86.5 13.5 H 14.1 2.6 24.6 58.7 86.9 H 47.8 19.4 11.2 21.6 88.8 H ~
0.0 0.0 0.0 1.2 0.1 0.2 1.0 1.9 2.8
7
0.7
9
17.0 15.3 __
7.8 -
12.6 17.4 17.0 17.4 21.2 21.1 20.9 20.8 -.24.3 18.8 20.1
66.0 64.9 63.7 64.6 65.3 64.5 63.9 63.4 62.7 62.2 53.0 51.4
26.2 22.5 18.9 17.2 17.2 14.1 14.0 13.8 13.7 12.8 11.2 13.2
~
73.8 77.5 81.1 82.8 82.8 85.9 86.0 86.2 86.3 87.2 88.8 86.8
A A A A A H H H H H H H
Staininn. L?, Reflectance" Pale Crepe Stocks Laminated with Stocks Containlng Oilsd Color Stability of O h , S P A Colors 24rhr. Change, Sun Lamp Exposure, D a 5 . L Stored sun reflect0 2 4 7 10 14 18 21 1 year lampe ance 1- 1 l ' / z l ' / z 1 1 / 2 1',* 1 1 / 2 11/* 58 55 -3 1 I'/z 2 3l/2 4 5 6 6 59 -6 53 -6 52 I1/z 1't'z I'/z l'/z 2 2 2112 3 58 S+ 55 50 3'12 3'/2 4 4112 6 -5 4 5 7 8 + 52 52 0 51 -3 4 4 4 4l/2 5 5 6 6 54 5 7 8 8 __ + 59 55 -4 8+ 14 12 -- 2 -
-
1 I'/z 2 2'/2 2 3
1 ll/n I'/z I'/z I'/z 11/2 2'/z 2l/z 2 2 2'/n 3 4l/2 5 6 6
2 2
2 3 2 3 1l/p 2 2 2'/2 3'/2 4 21/* 3 4 3 3l/2 4 5 5 6 7 7 7
5 6 8 7 8 8 1 8+ 6 7 8+ 4l/2 4l/2 5 5 6
3112 4
3112 4 3 31/2 4 41/2 4 4'/2 4 4112 6 6 7 8
-_
7
8
8
60 60 60 62 58 58 62 62 59 60 29 50
59 59 58 58
55 56
55 56 52 50 21 20
-1 -1 -2 .- 4 -3 -2 -7 -6 -7 - 10 -8 - 30
Control (no oil)
-4 62 58 Welch instrument, dark blue filter. p = paraffinic, N = naphthenic, -4= aromatic, H = highly aromatic, by 0 3 R nomenclature based on percentage of paraffinic hydrocarbons; P = >56%, N = 48-56%, A = 15-32"',, H = 5-15%, paraffins ( 2 2 ) . R-Slamp, Golden Bear Method. Test formulation B , Table 11. e General Electric 5-1 sun lamp, Gates method. a
Table II. A" B" Base polymer GR-S 1006 Pale crepe Polymer (as indicated) 100 100 Sulfur 1.80 3.00 Zinc oxide 70 60 Titanium dioxide 50 20 Hard clay Magnesium oxide SRF black Oild 20 20 Stearic acid 1.5 3.5 Helizone 1.0 2.5 MBTS 1.00 0.75 DOTG 0.20 DPG Ethyl Tuads Paraffin Retarder W Staybelite resin Tetrone A Dioctyl phthalate Dyphos Dythal a Press condition, 45 minutes at 300' F. Press condition, 45 minutes at 280' F.
... ... ...
... ... ... ... ... ... ... ...
...
1 284
C" Butyl NS 365 100 2.00 10 100
... ...
...
50
...
e . .
20 1.0
... ...
... ... ... ... ... ... ... ... ...
1.25 2.0
... ... ... ... ...
...
. I .
Barnhart, and Provost ( 7 7 ) used a General Electric sun lamp (24-hour exposure) and defined the phenomena observed as nil, slight, moderate, or severe. Taft (22) employed sun lamp exposure and used a Photovolt reflectance meter equipped with a green tristimulus filter. Provost (77) employed sun lamp exposure following in general the method of Moses and Rodde
Composition of Test Compound Compound Designation D" E" Paracril B J Seoprene W 100 100 1.75 5 5 20 100 15 60 4
...
... ...
15
1.0
...
1.50
... ...
0.10
... ... e . .
... ... ...
* a .
...
15 3.0
... ...
F" Hypaloii 20 100
... *..
...
100 2.00 3
...
20
...
10
13
35 20 1.0
...
... ... ...
... ...
2.0 2.00
...
...
...
Hh GR-S 1006
25 50 20
... ... ...
... ... ... ...
Ga Opalon 300 100
... ...
2.50 1.00
... ...
...
...
... ... ... ... ...
... . . a
27c 3 2
... 1.00
0.25
... ... ... ... ...
40 parts in control without oil. Oils as given in Table I.
( 7 6 ) , which is fundamentally the same as given in the ASTM procedure D 1148-55 (71, and rated phenomena observed by assigning them values between 0 and 10, which are relative within each series of tests. Harrison, Labbe, and Clibourn (8) determined pigmentation, staining, and discoloration quantitatively by measuring with a Photovolt instrument equipped with
I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
a green filter the light reflectance of white compounds, unexposed and ultraviolet exposed ; the degree of reproducibility attainable and the sensitivity of the method are described. Assessment of Oil Composition. Two basic approaches permit assessment of oil composition in terms of components which can be chemically identified, isolated, and individually tested. One
ELASTOMERIC C O M P O U N D S D I S C O L O R A T I O N
h
P
(i
approach is based on adsorption and elution of fractions; the other on stepwise precipitation. The three methods most widely used based on the chromatographic approach are the methods of Watson (24),Eby ( 5 ) , and Glasgow and Termini (7). The method of ‘Watson separates oil into two fractions, “aromatics” and “saturates,” by elution from silica gel; the saturates are eluted with n-heptane and the aromatics with benzene, followed by a wash with ethyl alcohol. This method is described as rapid and superior to the method of Lipkin, Hoffecker, Martin, and Ledley (75). The method of Eby separates petroleum oils into “nonaromatics,” “aromatics,” and “oxy” fractions (the latter includes sulfur- and nitrogen-containing compounds). The method employs silica gel as adsorbent and n-heptane, benzene, and pyridine as eluents. The method of Glasgow and Termini employs pentane, benzene, carbon tetrachloride, and ethyl alcohol successively as eluents. Assessing petroleum oils on the basis of stepwise precipitation was used by the Office of Synthetic Rubber to define extender oils in the synthetic rubber program (78, 79). This method employs n-pentane; dry hydrogen chloride; 85% sulfuric acid; 98’3. sulfuric acid; fuming sulfuric acid; and an adsorbent used in successive steps. The petroleum oils are defined by percentage asphaltenes; nitrogen bases, Group I ; nitrogen bases, Group 11; first acidaffins; second acidaffins; and paraffins. Using the value AnDSH, the paraffinic fraction can be further defined as paraffinic, predominantly paraffinic, predominantly naphthenic, and naphthenic (27). Both elution and precipitation give results which can be correlated and mutually interpreted, and numerical values obtained in one method can, to some extent, be converted to those of the other. Provost and others (77) presented analytical data by both methods (79, 24) and for some oils calculated composition in terms of one method with the figures obtained by the other. The degree of correlation obtainable has been shown by Dunkel, Ford, and McAteer (2) and by Taft, Feldon, Duke, Laundrie, and Prem (22). Linnig and Stewart (74) have shown on the basis of spectroscopic data that fractions obtained by one of the elution methods (7) and by the precipitation method (79) are identical as to those fractions which represent the bulk of the total oil. The only major differences appear to be in the fraction labeled by the precipitation method “nitrogen bases, Group 11,” particularly when the so-called “highly aromatic oils” are used as test samples. However, the
discrepancies concern relatively small amounts of the total and appear to have little influence on compounding properties such as tensile strength, abrasion, hardness, and cure rate. Taft and others (22) have shown that the influence of the components as determined by the method in question (79) is specific when tested in the form of concentrates and that their effect is additive when tested in the form of blends. This might, however, not be the case in studying color phenomena, where traces of components not identified by the analysis might have a considesable bearing. The differences detected in the spectroscopic studies (74) point to this as a probability. Scope of Investigation The present investigation had primarily two aims: to establish in a preliminary study whether or not a general relationship exists between composition of oils and their influence on color and to select testing procedures giving data that can be recorded and referred to later. In view of the literature reported above, it was decided to use both sun lamp and daylight exposure (roof aging) to induce color changes; to use the precipitation method (79) for assessment of oil composition; and to measure the color changes in terms of reflectance. The experimental program was designed to be an orientation study of suitable instruments as well as of the influence of oils on color of elastomeric compounds containing them. This program was carried out in two laboratories. Oils Tested. A multitude of petroleum-base products are sold under proprietary names such as Califlux, Dutrex, Philrich, and Paraflux; by functional designation such as lubricating oils, process oils, and neutral oils; or under some general designations denoting the origin or manufacturing procedure such as distillates, extracts, and raffinates. T o include all these products in the program or a selection of products from the various groups of these designations would neither be feasible nor definitive for the products investigated. Therefore, a limited number of commercially available petroleum products were selected, complemented by laboratorymade blends such that a sufficiently great variety of compositions was tested to represent all currently used petroleumbased plasticizers and extenders. The blends were made from concentrates of the individual components prepared as described (20). Table I lists the oils investigated and their analytical data. The first series of oils tested, group A, represented a wide range of compositions. Group B was designed to test the influence of composition within narrower limits of nitrogen bases
Figure 3. Method C
Sun
lamp
cabinet
for
and acidaffins. Group C was selected from the first two series of oils tested in GR-S and natural rubber for testing in the other polymers. The last three columns of Table I show some of the results of the staining tests discussed later. The oils (with the exception of oil 9) are listed in the order of increasing color, as can be seen in the first column under the heading “Color Stability of Oils.” Figures 1 and 2 are photographs of the oils, before and after sun lamp exposure. The analyses given in Table I are sufficiently definitive to be usable as specifications, if the products tested are to be bought on the open market. All the oils have viscosities of 10 to 20 cp. at 99’ C. and initial boiling points higher than 160’ C. at 10 mm. of mercury. Polymers Tested. Because petroleum-based plasticizers and extenders are used in practically all widely employed elastomers, representatives of all these elastomers were included in this study. Examples of the most used elastomer types were chosen : GR-S 1006 (as a butadiene styrene copolymer), pale crepe (as natural rubber). Butyl NS 365 (as a polybutene). Paracril BJ (as
Figure 4. Paper gage for measuring reflectance b y visual matching with
sample VOL. 49, NO. 8
AUGUST 1957
1285
Table 111. Description of Filters Filters in Welch reflectance unit Dot on filter wheel. Clear Red White Yellow Green Light blue Dark blue
Filter used for illumination of reflectance gage
Figure 5. Rotating table for sun lamp exposure of oils
a butadienc-acr ) lonitrile copolymer), Seoprene W (as a polychloroprene), Hypalon 20 (as chlorosulfonated polyethylene), and Opalon 300 [as poly (vinyl chloride)]. The selection of these polymers to represent the types was more or less accidental, and other products could equally well have been used. However. the polymers selected and the compounding ingredients used in this study are generally considered suitable for the production of light colored articles. Methods Employed
Compounding. All compounds were prepared by regular ASTM procedures. Composition of the compounds is shown in Table 11. Light Aging. The color phenomena investigated were induced by three different methods. Exposure times Icere as indicated in each test series. GATES METHOD.Exposure to General Electric S-1 sun lamp for 24 hours, following ASTM Procedure D 1148-55 (7). ROOFAGIKG. Exposure to natural light for u p to 30 days; location, Denver, Colo., date, between Mal- and August 1955. GOLDEN BEARMETHOD. Eaposure io a Type R-S 275-watt sun lamp in a N F A COLOR WOlLS
Filter used in Photovolt instrument
Color"
Illuminations Used
Manufacturer
Designation
...
(:Nofilter)
1. R 1. r Br Y G 1. B d. B d. R
G
Predominant Wave Lengths, A .
Eastman Kodak Eastman Kodak Eastman Kodak Eastman Kodak Eastman Kodak Eastman Kodak Klett Mfg. Co.
Wratten A25b Wratten 106* Wratten 16b Wratten B58* Wratten 38Ab Wratten 47Bb No. 66
(4000-7000) 6000-70OOc 5500-70OOc 5300-70OOc 5000-57OOc 4000--56OOc 4000-47OOc 6400-7000
Corning Glass Works
CS No. 4-98
4900-6000
s * .
Light used with v Beckman Instruments, Photoelectric 4250 Beckman instruInc. spectrophotometer ment Model DU Names and abbreviations listed follow National Bureau of Standards recommendations (13) ' B = blue G = green 0 = orange R = red b = bluish g = greenish 01 = olive r = reddish Br = brown Gy = gray p. = pale s. = strong br = brownish gy. = grayish P = purple v. = very or vivicl brill. = brilliant 1. = light p = purplish T' = violet d. = dark m. = moderate P k = pink Y = yellow med. = medium pk = pinkish y = yellowish Identifications obtained from Welch Manufacturing Co. (10). Eastman Kodak Wratten filters (4).
cabinet shown in Figure 3 ; distance between sun lamp and specimen adjusted to give a reading of 40 to 45 on General Electric sun lamp tester No. 87 (scale reading X 0.291 = E in vitons per sq. cm.); diameter of the rotating table, 18 inches; rotation, 6 r.p.m. Compound samples were located 3 to 6 inches from center; measurements on the exposed samples were made in center of exposed area.
ber industry. I t would be beyond the scope of this paper to go into the question of color measurements further than concerns this particular investigation, but a brief resume of the considerations leading to the selection of instruments and methods appears in order. As this was a preliminary screening. it appeared necessary to select a method of reporting the findings in terms and values useful as records for future reference and having meaning in communication between different laboratories. Units of measurements had to be selected which are, to the largest possible extent, absolute values. Everyday language was followed whenever possible, for simplicity and clarity. T o establish uniformity regarding color names throughout the investigation and to establish some relation to color names
Measurement of Color Phenomena. A great deal of difficulty is inherent in all investigations dealing with color. Test methods, nomenclature, and even spelling differ from publication to publication, and values reported are: as a rule, pertinent to only one series of tests. Some of the industries concerned to a large extent with color of their products have agreed on certain standards for terms and measurements. Little in this respect has been done in the rubSTAINING OF RUBBER IN PER CENT REFLECTAWE
to1VIPOSITION OF
OILS
CONTROL (NO OIL1 I
N P A COLOR OF OiLS
STAINING OF RUBBEQ lh PER CENT REiLECTAhCE
m
2 3 IV
4
v
5
VI
VI1 VI11
IX 100
50-
0-50
100
I -PARAFFINS -2ND ACIDAFFINS IST ACIDAFFINS
-NITROGEN
Figure 6.
1286
BASES
-ORiGlNAi
ORIG'NAL
AFTER 7 DAYS
AFTER 24 HRS.
Summary of data on oils, Group A
INDUSTRIAL AND ENGINEERING CHEMISTRY
6 60
6b 6c
7
8 9
U PARAFFINS -2ND I ST
NeB
4ad38W.
ORIGINAL
ACIDAiiINS ACIDAFFINS
NITROGEN BASES
Figure 7.
-0
xi E R 4 O W S O ORIGINAL
AFTER 24 HRS.
SUYLAMP EXPOSURE
SUNLAMP EXPWJRE
Summary of data on oils, Growp
B
ELASTOMERIC COMPOUNDS D I S C O L O R A T I O N Figure 8 (Sop).
Specimens from stoining tests of group A oils
Top halves of 011 samples expaed 24 h o w to 5 1 sun lamp hp. Uncured block GR-S stocks containing dh, with *le lacquer h n d row. Bbck OR-S staks containing olb, Iamnhoted to whim pale u e p e stock Third row. Urnred white pole crepe stocks containing oils, with white IOcqu*, BottM. WhHe polecrepe rtpcb Containing Oils, laminated to whitepqle crepe
Figure 9 (Bottom). Specimensfrom staining tests of group 8 oils Top.
Block GR-S stocks containlng oils, laminated to w h l h pale u e p e *k.
lop h k a d samples e x p o d 24 hours to 5 1 sun I m p S
d row.
Block OR-S &ks
cmhhing olb, lamhaled to white pals u e p e
skd. Enlire samples exposed 30 days on mof Rid row. U h e d bbck GR-5 stocks containing ollr, wHh whHe lacquer. k4mm h m h a d samples srp-d 24 hn to 5 1 sun lamp WmS pale u e p e S Mcontaining S oils, blnlnoted lo w h i i pale cnpe rtodL lop h a k n of wmphs exposed 24 h u m to 5 1 sun lamp Ib(t0n. Whih pale crepe &b rmtoinlnp 011%laminatedto white pale crepe skd. Enlire samples e r p a s d 30 days on mof
FMlrM row.
used by o h ,the designations suggested by Kelly and Judd (73) were used (Table 111, footnote a). Pigmentation, discoloration, and staimng are defined a t the w i gof thispaper. Rdcctance values reported here were mcasured (as indicated in the tables) with either of four instruments:
DU Type Be&nan spectrometer employing a violet light bcam (425 -). F'hotovolt photoelectric retiection meter, Model 610, equipped with Model 610-Ys e d unit and green tristimaus Klter, as deswibcd by'Harrison, Labbe, and Cliboum (8). Welch Densichron No. 3830A coupled with a Welch Densichron reflection -unit No. 3832A equipped with a.Klter wheel providing several colored lighe of relatively wide spectral bands. (A detailed dcsaiptibn of the light KlterJ is given in Table 111.) .Simple rdlection gage (a gray scale printed on a papu wheel approximately 3 inches in d i h e t e r ) supplied by El+ tric Testing Laboratories, Inc., New York. Thh gage (Figure 4) .was used by viewing and matching the sample to be tested with the gage,under light produced by a spot light equipped with a ark red light Kltcr (Table 111). A la& mask with a I-square-inch openwas placed over the sample and the of the gage. The wheel was'then ed back and forth until the sample a portion of the reflection gage n the viewing area matched. '
Of the instrumen@ used, the Welch instrument using the darkblue (d.3)Klter wasfoundmastpractical. The dection gage reading8 are presented primarily to demonstrate that it &.pOarible to obtain and report, although not very acakately, g e n d y Galid and repmduc'ible values without acquiring costly
insgumene. The ,color changes in the oils investigatkd were induced by using the sun lamp aging, method (Golden Bear method). Bent test.tubcs were used to permit placing the tubes on @e horiVOL. 49, NO.
A W U I T 1957
1287
Table IV. Discoloration of stock tested (containing oil) Sun lamp exposureg
Control, no oil Oil I1
Laminated White Pale Crepe StockC White Lacquerd White Pale Black GR-S White Pale Black GR-S Crepe (Cured)e (Cured) f Crepe (Uncured)e (Uncured)' None 24Hr. None 24Hr. None 24Hr. Xone 24Hr. 62 58 6537) 6 6 5 6 ) 58 55 6857) 6938) 59 6555) 60 (64) 52 58 7 1 3 6 ) 65765) 55 50 5835) 59762) 52 52 66
