Extender Oils for Nonstaining Rubber R. L. PROVOST, E. L. BORG, J. L. PAIGE, W. W. WHITE,
AND
L. H . HOWLAND
'Vaugatuck Chemical Division, Z'. S . Rubber Co., Xaugatuck, Conn.
S
INCE the introduction of oil-extended GR-S in early 1951,
consumption has increased rapidly until, in 1954, more than 260,000,000 pounds of net GR-S were produced as oil masterhatch--approximately 25% of total GR-Sproduction for the year. The largest proportion of the oil masterbatches hafi been used in the tire industry, where processing considerations have dictated employment of oils of relatively high aromatic content. Oil-extended polymers containing a relatively naphthenic oil have been produced and have been used in applications l\-here processing is not of prime importance. Oils containing 48 to 56% saturated hydrocarbons have been classified as naphthenic in the synthetic rubber iridustry. Some of the riaphtheriic oilextended products have been stabilized with nonstaining antioxidants ( I ) , in which case satisfactory reception Kas enjoyed only in end products where freedom from staining and discoloration is not critical. T h e naphthenic oil was found t o cause an appreciable degree of staining and discoloration in white or lightcolored vulcanizates upon exposure t o light. T h e nonstaining antioxidants usually employed (alkylated aryl phosphite and styrenated phenol) afford maximum protection against staining, so that the deficiency must be attributed t o the oil. Thus, the naphthenic oil-extended rubbers are not acceptable to a large portion of the potential market for nonstaining GR-S. Taft and others confirm t h a t naphthenic oil causes staining (6). It was known that, in some segments of the rubber industry, expensive "white" (paraffinic) oils were being incorporated in rubber compounds on the mill or in the Banbury miser ivith success, and that these oils were considered adequate from t h e standpoint of staining and discoloration resistance. Accordingly, the present investigators initiated a n experimental program with two major objectives: to discover which component(s) of the rubber processing oils are responsible for staining and discoloration, and t o find inexpensive, commercially availnble oils which could be satisfactorily employed in applications where staining and discoloration are critical. EXPERIRIENTAL PROCEDURE
I n general, the procedure followed throughout the investigation was t o request samples of oils from various suppliers and then screen these oils in a nonstaining GR-S composition using the method of lloses and Rodde (4).
Table I. Unless otherwise noted, the oil loading \vas 37.5 parts per 100 parts of GR-S. The oil-latex mixture was stabilized by adding 1.25 partP of Polygard (alkylated aryl phosphite, U. S. Rubber Co.) antioxidant based on the dry rubber hydrocarbon content and the niistiire was coagulated with salt-sulfuric acid. Polygard was employed in order t o give maximum protection against oxidative changes during drying and thus ensure exhibition of the msximuni inherent physical characteristics (3). The m t crumb obtained was dried in a circulating air oven a t 170" F. T h e numerical values assigned t o the various stocks t o designate ratings on pigmentation, staining, and discoloration are relative within any series reported and do not carry over from table to table for the same oil. RESULTS
The first series of oils was tested a t a loading of 40 parts of oil using GR-S 1503 type latex. A second series i v a s tePted at a
Table I.
Formulations for Latices [:sed in Oil I)Iasterbatching GR-P 1503
Ingredients Water Butadiene (100% basis) Styrene (100% baais) F a t t y acid soapa Rosin soap b Potassium chloride Trisodium phosphate. 1 2 H i 0 tert-Ci? mercaptan Diisopropylbenzene monoli).droperoxide Diethylenetriamine Ferrous sulfate 7H20 Potassium pj-rophosphate Tamol NC
200 75 25 4.7
0.4
The more promising samples were then more fully evaluated by compounding in a tread recipe and obtaining data on stressstrain and abrasion resistance. I n pertinent cases compositional analyses of the oils were made b y combining the methods of Rostler ( 6 )and Watson (7). T h e oils were incorporated into GR-S latex by first emulsifying the oil using the folloving recipe: Oil Water Sodium oleate
...
...
4.7
0.08 0.125
0.08
...
...
0.4 0 . I O (approx.)
...
0.10 0.10
,..
0.05
0.05
Shortstop Potassium dimetliyl dithiocarbamate 0 . 1 5 0.15 Conversion, 53 60 60 Polymerization temperature, F. 41 41 Ilooney viscosity (ML-4) 130 130 Potash soap of hydrogenated tallow (OSR) acids. b Potash soap of disproportionated rosin acids. Sodium salt of naphthalene sulfonic acids condensed with formaldehyde.
Table 11.
100.0 10.0 10.0 2.0 1.5
Type
200 75 25
0. IO' '(approx.)
Screening of Various Oils
Compounding Recipe, Parts Oil-extended polymer TiOr (reagent grade) ZnO ( S B S grade) Sulfur ( X BS) Benzothiazyl disulfide (NBS)
GR-S 1500
Type
Oil
Producer
Pigmentation First Series
Primol D Tech. Primol D Necton 60 Coprol B Circosol 2XH
Esso Std. Oil Esso Std. Oil Esso Std. Oil Atlantic Ref. Sun Oil
0 0 0 1
1
Ratings_ _ _ ~ ~ _ _ _ ~ _ Staining Discoloration Total
1
I
1
1
1 3 2
1 3
2
2 2 2 7 5
0
0
0
2
2
Second Series Texas C o . 0 Esso Std. Oil 0 Esso Std. Oil 1 P a n Anierican Ref. c-293 C. P. Hall Lopor 70 Esso Std. Oil Plasticizer 14 Atlantic Ref. Circosol 2XH Sun Oil Acme I1 Atlantic Ref. Coray 230 Esso Std. Oil WS 2430 Esso Std. Oil a Lowest number denotes best stock. Texas white oil Necton 60 Diol 70 Panaflex BK-I
100.0 100.0 3.0
T h e latices used mwe of either the GR-S 1503 or GR-S 1500 type and Kere prepared according t o the formulations given in 455
1
2
3
5
4
5
8 8
9 11 12 15
voi. 48, N ~ 3.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
456
Table 111. Physical Teats on Oil Masterbatches
Table IV.
(NB-100; Philblxck 0. 50; zinc oxide, 2 ; stearic acid, 1.5; sulfur, 1. RlBTS, 1.25)
Texas White Oil
Type of oil Parts of oil in RIB" Mooney viscosity (RIL-4) Raw Compounded
Necton 00
Diol
70
Clrcmol 2XH
33.0
35.0
37 5
3G 0
81 75
76 71
76 F7
8% 08
hlin. Cured a t 292O F. 300% modulus, lb./sq. inch Tensile, Ib./sq. inch Elongation,
4
25 50 100
1270 1940 2490
1210 1840 2370
1030 1600 2150
1090 1740 2400
25 50 100
3310 3090 2870
3240 3210 2680
$810 -720 2710
3230 3340 2900
25 50 100
5 80 420 340
620 450 330 104
600 430 360 112
660 500 350 100
Abrasion rating
107
37.5 parts masterbatched with high RIL-4 GR-S 1500 latex; parts given are by analysis (ETA extract). a
Screening of Various Oils
(37.5 parts of oil in GR-9 1500) Ratings Staining Discoloration ~
Oil Circosol Extra Circolight Sunvis 99 G B light process oil Necton 60
Producer Sun Oil Sun Oil Sun Oil
Pigmentation
Golden Bear Esso Std. Oil
2 2 2
Total
0 0 0
2
1
3
0
8
0
1
2
3
3
>
4 5 4
the treated aromatic oil showed considerably darker stain than the treated naphthenic. However, the treated naphthenic oil exhibited a significant degree of staining. A systematic study was then undertaken in a n effort to determine the effects of viscosity and degree of refinement of oils on staining and discoloration. Solvent-refined lubricating oils of 100 Saybolt seconds viscosity were selected for the initial tests (Table V). A, B, and C for the oils identify raffinates, while X identifies the extracts. It is apparent t h a t the extracts cause excessive staining. The masterbatches prepared with the A and B oils exhibit inferior tensile strengths, although in the case of the 1OOB oil masterbatch this could have been partly a result of the low Mooney viscosity. Staining and discoloration characteristics of all the raffinates are excellent. A silica gel analysis of the lOOC oil gave an aromatic content of 23%. Oils of 200 and 350 Saybolt seconds viscosity were then teated in the same manner, giving the results listed in Table VI. Again t,he physical properties of the experiniental inasterbatches are equivalent to those of the control. Staining and discoloration characteristics are excellent and equivalent to those of the m-hite oil xvhich was included as a secondary control in this seriep. Solvent-refined lubricating oils from a different supplier were evaluated (Table VII). These datn confirm the superiority of this class of oils where staining and discoloration must be minimized. The analytical characterization for several of the oils tectetl is given in Tahle VIII. I n general, although the data are limited, mithin the lubricating oil class, the aromatic content, incrcaees
loading of 37.5 parts, using GR-S 1500 type latex. TWOof the oils included in the first series were retested in the second spt. T h e staining and discoloration data are given in Table 11. T h e staining and discoloration results indicated that, :is CXpected, t,he white oil was significantly superior to any other of the oils tested up to this point. This product, with three others selected from Table 11, second series, &*asevaluated further blcompounding the masterbatch in a tread recipe and deteriniiiing sh-ess-strain and abrasion characteristics. The abrasion test was conducted by the method of Howland, White, arid LIeeser (3,. Table I11 shows that the physical characteristics of the espcrimental oil inasterbatches are almost fully equivalent to those of the naphthenic oil (Circosol 2XH) masterbatch, except for a slightly low tensile strength for the Diol 70 masterbatch. Of particular significance are the abrasion dat,a, which indicate somen-hat superior resist'ance for the experimental stocks. According- to information from suppliers as to the coniposition of the oils, i t was smpectcd t h a t nitrogen bases (Rostler terminology) might inTable V. Testing of Solvent-Refined Lubricating Oils fluence staining and discolor,ation characteristics of a n oil. .kccordinply, in the nest series icreened, an aromatic oil free of nitrogen hases and asphaltenes (Golden Bear light procw s oil) n a s included. Table IS' shows that the absence of asphaltenes and nitrogen bases docs not ensure that the oil will not stain and t h a t aromatics in high enough proportion will cause staining. This was confirmed by chemically treating a naphthenic and a highly aromatic oil in the laboratory so as t o remove asphaltenes and nitrogen bases and then determining the staining and discoloration characteristics of the treated oils by preparing GR-S masterbatches and testing a white vulcanizate. I n each case a reduced tendency to stain, compared with untreated samples, was noted;
(GR-S 1500 latex)
Parts of oil Staining and discoloration ratings Pigmentation Staining Discoloration Total
100.4 37.1
lO0X 36.4
1 0 0 1
2 2 2 6
Procoila IOOB lOOBX 36.1 37.2
0 0 0 0
5 4 4 13
lO0C 39.4
0 0 0 0
l0OCX 40.0 4 3 3 10
Circosol 2XH 35.5 3 1 1 5
Compounding Recipe Parts Polymer Philblack 0 Zinc oxide Physical tests hIooney viscosity Raw Compounded
Stearic acid NBTS Sulfur
5:
(ML-4)
3007, modulus, lb./sq. inch Tensile, lb./sq. inch Elongation, 5 Abrasion rating (I
100
Cities Service Oil Co.
48.0 43.0 Min. Cured a t 292' 25 50 100 25 50 100 25 50 100
43.0 43.0
29.0 36.0
1.5 2 2 47.5 48.0
48.5 53.0
45.0 51.0
51.0 53.0
F. 1210 2040 2140 2240 2240 2140 420 320 280 106
1440 1870 2290 2780 2700 2610
1320 1710
490 400 340 105
390 330 280 101
...
1960 1900 1930
1330 1830 2170 2880 2760 2630 580 430 370 97.5
1840 1840 2420 2620 2300 2420 400 360 300 101
1280 1880 2240 2710 2790 2240 540 420 300 97.5
1390 1850 2250 2790 2830 2760 550 430 360 100
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1956 rvith viscosity, the C oils having t h e highest aromatic content. Some oils which exhibit excellent staining and discoloration characteristics have as much 3s 1.0% nitrogen bases present.
Table VI.
457
Testing of Solvent-Refined Lubricating Oils (GR-S 1500 latex)
Oil P a r t s of oil Staining and discoloration ratings Pigmentation Staining Discoloration Total
CONCLUSIONS
Below a threshold value of 30 t o 407, aromatic content, solvent-refined lubricating oils, free of asphaltenes, exhibit a remarkable degree of freedom from staining and discoloration in a white- or light-colored compound prepared from their GR-S masterbatches. As t h e requirements in a nonst,aining oil-extended synthet,ic rubber vary .;videly, depending on specific end product and processing techniques, it m a y not he possible t o satisfy all requirements xvith a single product. Holyever, a majority of users would favor a product conhining a n oil with very good staining and discoloration resistance a t the highest possible aromatic content. Recent information indicates t h a t differences in staining and discolomtion in oils of aromatic contents below 307, can be discerned in some t j p e s of lightr colored compounds. I n these special cases masterbatches cont,aining paraffinic Tyhite oils woiild provide maximum resistance t o discoloration.
Procoil 200.4 41.8
Procoila 41.8
Procoil 360.4 37.5
Procoil 350C 42.9
Circosol
?XI1
39.2
0
0
0
1
0
0
0 0
0 0
0 0
0 0
0
0
1 1 3
100
1060 1420 2030
1030 1520 1960
1010 1480 1930
920 1500 1910
980 1500 1990
Tensile, lb /sq. inch
50 100
2680 2390
2540 2330
2540 2390
2350 2600
2670 2760
Elongation, 70
50 100
480 340
440 360 109
470 360
420 390
470 390
106
100
100
0
300'7, modulus, lb./sq. inch
25
50
Abrasion rating a White oil from 100B.
107
Table VII.
Testing of Other Solvent-Refined Lubricating Oils (37.5 parts of oil in GR-5 1603)
Oil ?.Iooney viscosity (ML-4) Raw Compounded
Circosol 2XH
Procoil 350C
69.0 70.0
70.0 78.0
Process Oil No. 4a
Process Oil No. lja
64.0 63.0
62.0 59.0
hlin. Cured at 292" F.
300% modulus, lb./sq. inch
25 60
1410 2120 2410
1380 2060 2400
25 50 100
3130 2810
2860
2860 2880 2640
25 50 100
570 390 3 70 100
100
Tensile, lb./sq. inch Elongation, $Zc
Abrasion rating Staining and discoloration ratings Staining Discoloration Pigmentation Total a
1
2 1 4
1510 2140 2450
510 400 330
1520 2100 2480 2830 2550 2650 490 340 320
99
108
108
0 0
0 0 0 0
0 0
0
0
2940 2610 2510 490 3:0 310
0 0
Sooony-Vacuum
LITERATURE CITED
Rodde. 1.L.. India Rubber T o d d 119, 201 (1048). ( 5 ) Rostler, F.S.,ISD. E s o . CHEAI.41, 598 ( 1 9 4 9 ) . (6) Taft, ITr. I
