LLASTOMERS-Ozone
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(11) Buist, J. M., and Welding, 0. N., Trans. Inst. Rubber Ind., 21, 49 (1945). (12) Coleman, C., U. S. Patents 2,246,932; 2,306,779 (1942). (13) Crabtree, J., and Kemp, A. R., IND. ENG. CHEM.,38, 278 (1946). (14) Dekker,’P., Kautschuk, 15, NO. 11, 179 (1939) [Rubber Chem. and Technol., 13, 431 (194O)l. (16) Dobson, G. B. M., Proc. Roy. SOC. (London), 110, 660 (1926); 114, 621 (1927); 122, 456 (1929). (16) Dufraisse, C., and Viellefasse, R., Rubber Chem. and TechnoZ., 7, 213 (1934). (17) Eaton, B. J., d g r . Bull. Federated M a l a y States, 1, 17 (1912). (18) Fickenday, E., KolEoid-Z., 9 , 81 (1911). (19) Fielding, J. H., India Rubber World, 115, 802 (1947). (20) Fol, J. G., and de Visser, W., Bull. Rubber Grower’s dssoc., 10, No. 2, 124 (1928) [Rubber Chem. and Technol., 1 , 2 8 8 (1928) 1. (21) Freundlioh, H., and Talaly, J., Kautschuk, 9, 34, 49 (1933) [Rubber Chem. and Technol., 6, 378 (1933)l. (22) Georgi, Malayan Agr. J., 16, 204 (1928). (23) Gluckauf, Quart. J. Rou. Met. SOC.,70, 13 (1944). (24) Harrison, D. N., Nature, 124, 58 (1929). (25) Hastings & Rhodes, J . Rubber Inst. Malaya, 6, 42 (1935). (26) Jones, P. C., and Craig, D., IND.ENG. CHEM.,23, 23 (1931) [Rubber Chem. and Technol., 4, 108 (1931)l. L27) Xirchhot, F., Kautschuk, 3, 256 (1927). (28) Ibid., 7, 26 (1931). (29) Kreusler and Budde, Ger. Patent 18,740 (Bug. 26, 1881). 20.0 give the same approximate ozone resistNatural whiting 75 225 2 4.0 ance as castor oil. hlethylacetyl ri60 200 10 3.0 cinoleate gives less resistance, and a 50 22.5 10 2,540 430 Broke in stretching 2.ID processed type of castor oil is relatively Natural whiting/clay, 50/50 75 550 11/2 ineffective. All compounds tested con60 600 6 50 675 10 tained 40 volumes of NT carbon black 40 S25 10 and 20 volumes of oil per 100 volumes Natural whiting/clay, 7 5 / 2 5 1 of neoprene. 3 8 Several commonly used softeners, ex10 tenders, and tackifiers were tested usHard clay A 3 B 3 ing the same amount and same base C 3 formula just described. Factices includCoated precipitated calcium 60 525 1 carbonate 10.5 ing white, amber, and brown varieties 60 250 Barytes 10 derived from soybean, rapeseed, and 60 950 Calcium silicate 10 castor oils; mineral rubber; coumarone60 775 3 Ashestene indene resins of different melting points; 60 950 3 Magnesium carbonate and butadiene-styrene resins ivere tested. Little if any effects on ozone resistance were noted. This type of material is commonly used in compounding elastoinch) and ozone resistance. It therefore is concluded that the mers for ozone resistance. They are known to produce vuladverse effects of increased amounts and particle sizes of canizates having a high degree of stress relaxation. The tebt loading material on ozone resistance are independent of their procedure used in this investigation permitted only 30 minutes' effects on the stress-strain characteristics of the vulcanizate. time to elapse between stretching the samples and exposure to Plasticizers, Softeners, Extenders, and Tackifiers. Liquid ozone. This was apparently too short a period to allow a signifiplasticizers vary greatly in their effect on the ozone resistance of neoprene vulcanizates. I n general, the petroleum base types produce a slight though measurable impairment. A number of Table 11. Effect of Liquid plasticizers commercially available types were tested in a neoprene compound Type of tesr. Constant strain Constant load containing 40 volumes of M T carbon black and 20 volumes of the Ozone concentrarion High Low Low Exposure time 30 Min. 7 Hours oil per 100 volumes of neoprene. Except for one brand, known to Rating Rating Hours t o Failure contain incompatible fractions, which bloomed forming a protecNone 4 2 > 24 tive surface film, all were found to produce slightly less ozoneDibutyl phthalate 6 3 9.5 11.4 Diootyl phthalate 5 3 resistant vulcanizates than the control containing no oil. The 14.2 2 Diallvl ohthalate 7 effects of commonly used process oils are so slight, however, that 10.7 Dicapry'l phthalate 6 2'/2 12.2 Tricresyl phosphste 6 21/2 they may be used a t least up to the amount tested in most neol5,3 Tributoxyethyl phosphate 8 11/2 6 4 7.6 Dibutyl sebacate prene compounds without concern as to their effect on the ozone 12.8 6 3 Dioctyl sebacate TP-Q LRa resistance. "_ 7 3 6.9 Plasticizer SCh 7.2 6 3 Several esters and a number of other types of plasticizers com7 6 Flexol 3GOC 3 12.4 Flexol TOFC 2 monly used in compounding neoprene for low temperature per15.2 3 Arneel TODJ 6 formance were tested in t h e same manner as the petroleum oils. Supplied by Thiokol Corp. b Supplied by E. F. Drew 6: Co. Results are shown in Table I1 for tests conducted under constant C Supplied by Carbide 6 :Carbon Chemicals Corp. strain a t the t w o ozone concentrations and for tests under cond Supplied by Armour & Co. stant load a t the low ozone concentration. Although there is Table I.
Effect of Fillers on Ozone Resistance of Neoprene Vulcanizates
I
P.-
-
__
s
Q
854
INDUSTRIAL AND ENGINEERING CHEMISTRY
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4LASTOMERS-Oeone cant degree of relaxation to occur. It is concluded, therefore, that if materials of this type provid'e ozone resistance, it only results from the stress relaxation they produce in the vulcanizate. Unlike the other ingredients of this type, wood rosin provided a degree of resistance to ozone sufficient t o warrant its selection in preference to the other materials. Antioxidants. Anumber of antioxidants known to protect neoprene vulcanizates effectively against deterioration by oxidation as measured by oxygen pressure or ovenaging tests were evaluated for their effects on ozone resistance. Some were found to provide excellent protection from attack by ozone, especially in the case of compounds designed for dynamic service where protective wax film is destroyed and where vulcanizates having high permanent set may not be used. Others showed only moderate ozone resistance and some even had a deleterious effect. The concentration Figure 9. Effect of of ozone during exposure and the Vegetable Oil amount of antioxidant used had a A. Linseed pronounced bearing on the relative B. Tung C. Castor efficiency of the different antioxiD. Cottonseed E. Control dants on ozone resistance. For F. Coconut this reason, conclusions pertaining to comparative effectiveness under one set of conditions will be misleading if applied to another set of conditions.
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loaded compounds. One part of each was added to base stocks containing 40 volumes of M T carbon black, EPC carbon black, and hard clay, respectively. Tests conducted at both ozone concentrations generally showed effects similar t o those noted in the gum stocks. The adverse effect of fillers on ozone resistance increased the difficulty of determining the relative efficiency of the less effective antioxidants, even in the tests conducted a t the low ozone concentration. This was especially the case in stocks containing clay and EPC carbon black. EFFECT O F ANTIOXIDANT CONCENTRATION
The effect of antioxidant concentration on ozone resistance was studied. Gum neoprene compounds containing 1, 2, 5, and 10 parts, respectively, of all the antioxidants previously studied were compared at the high ozone concentration. I n most cases, as the amount of antioxidant was increased, differences in the degree of their effects on ozone resistance were accentuated markedly. It will be noted by reference to the footnotes uhder Table 111 that certain antioxidants, which were relatively ineffective when only 1%was used, became highly effective when used in larger amounts. Those which increased only moderately in effectiveness when their concentration was increased also are identified. Thd antioxidants listed in Group V became more injurious to ozone resistance as A
B
Group
I
I1 111 IV
COMPARISON OF VARIOUS ANTIOXIDANTS
Antioxidants were compared first in gum stocks. One per cent of antioxidant was used, based on the neoprene, and vulcanizates were exposed t o ozone at high concentration, 100 p.p.m., and a t low concentration, 1 to 3 p.p.m. Tests a t the high concentration reveal& differences among the more protective types which could not be detected a t the low ozone concentration, Tests at the low ozone concentration permitted differentiation among the less protective antioxidants not possible when testing a t the high ozone concentration. Results obtained a t both ozone concentrations permitted classification of the antioxidants into the five groups shown in Table 111. Those haying different classifications a t the two ozone concentrations are so indicated. The antioxidants in Group I provided the highest degree of ozone resistance. These were diphenyl-p-phenylenediamineand di-p-methoxydiphenylamine, The former is superior by a slight margin. Commercially prepared mixtures of these with other antioxidants are likewise excellent ozone-resisting agents. Group I1 lists certain ketone-amines which were found to provide good ozone resistance, and Group I11 shows several antioxidants which provided moderate ozone resistance. Antioxidants classified in Group I V were found t o be relatively ineffective when used only to the extent of 1 part; however, as will be discussed later, certain of these-notably phenyl-1-naphthylamine, phenyl-2-naphthylamine, diphenylethylenediamine, and butyraldehyde-anilinewere found to be extremely efficient when more than 2y0 was used. Antioxidants which produced vulcanizates having less oaone resistance than the control are shown in Group V. Within each group, relative effectiveness was difficult t o establish; so the order in which antioxidants are listed in a given group is not necessarily significant. Figure 10 shows a representative of each of these groupings after exposure for 30 minutes at the high ozone concentration and after 48 hours a t the low ozone concentration. Certain of these antioxidants were selected for testing in
April 1952
Contro
V
Figure 10.
Effect of l q ~Antioxidant
A. Low ozone concentration B. High ozone concentration
Table 111. Effect of Antioxidants on Ozone Resistance of Neoprene Vulcanizates
Group
I I1 I11
IV
Chemical Name Diphenyl-p-phenylenediaminea Di-p-methoxydiphenylaminea Diphenylamine-acetonea Phenyl-2-naphthylamine-acetone" Acetone-anilineb Acetone-p-aminodi henyl" Polymerized trimetRyldihydroquinolinea Symmetrical di-2-naphthyl-p-phenylenediaminecrd p-(p-Tolylsulfonylamido)diphenylaminea~e Butyraldehyde-anilinea Dialkylphenol sulfideb Diphenylethylenediaminea Phenyl-l-naphthylaminea Phenyl-2-naphthyleminea Diphenylamine Heptylated diphenylamineb
V
Common or Trade Name DPPD Thermoflex BLE, Aminox Betanox Flectol H Santofleli B Agerite Resin D Agerite White Aranox Antox Smtowhite Crystals Stabilite Neozone A P B N , .Neozone D, Agerite Powder Agerite Stalite
2,5-Di-tert-butylhydroquinonef 2 ,a'-Methylenebis (4-methyl-6-te~t-butyl-
Antioxidant 2246 Parazone p-#k%$~henoll Agerite Alba Hydroquinone monobenzyl ether/ Very effective when used in greater amounts than l%,based on the neoprene. b Increases somewhat in effectiveness when used in greater amounts than
INDUSTRIAL AND ENGINEERING CHEMISTRY
855
-ELASTOMERS-Ozone
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A
Parts
Table IV.
Solubility of Antioxidants in Neoprene Vulcanizates Per Cent
Thermoflex DPPD Neozone D Agerite White Stabilite BLE Aranox Agerite Alba 2 5-di-tert-butvlhydroquinone Antioxidant 2546 Santowhite Crystals Parazone
5 2 10
10 5 10 5 2 2 10 5
2
neoprene in the indicated amounts. The others shown in Table I11 apparently were soluble t o the extent of 10%. Figure 1 1 .
Effect of Antioxidant Concentration A. B.
NeozoneA Parazone
their concentration xas increased. TWO outstanding examples are shown in Figure 11. One per cent of Neozone A (chemical name listed in Table 111) afforded no measurable protection after exposure for 60 minutes to the high ozone, hut when 5% or more n-as used, no cracking was induced after a 24-hour exposure. Contrarily the compounds containing Parazone under the same test conditions became progressively a-orse as the antioxidant concentration was increased. I n a number of cases the comparative position of antioxidants relative to ozone resistance was reversed by changing the concentration of antioxidant and concentrations of ozone, An example is shown in Figure 12 in which gum neoprene compounds containing 1 and 5 parts of Antox and Agerite White, respectively, are compared. At a concentration of 1 yo,the stock containing Agerite White is superior to the stock containing Antox after a 48-hour exposure a t the low ozone concentration, After a 1-hour exposure at the high ozone concentration the two stocks are essentially equal. A comparison of the two antioxidants a t the &part level when tested a t the low ozone concentration shows them to be equivalent. At the high ozone concentration, however, the stock containing 5 parts of Antox is vastly superior to the one containing 5 parts of Agerite IThite, the latter showing flo improvement in effectiveness as its concentration is increased. Because the effectiveness of some antioxidants changes, depending upon the amount of antioxidant and the ozone concentration, conclusions based on one set of test conditions will be misleading if applied to another. Certain of the antioxidants studied were not soluble in neoprene vulcanizates up to the maximum limit-10 parts-at which they were tested. What effect this may have had on ozone resistance is not knovn. The antioxidante shonn in Table IV produced a visible bloom on gum vulcanizates \The11 added to the A
B
1 part Antox
5 parts Antox *
Figure 12. Effect of Varying Concentration of Ozone and Antioxidant A. B.
856
All of the antioxidants used in this investigation also v w e tested in compounds containing R-ax in order to determine T+ hether the protection offered by wax would obscure the benefits deiived from the antioxidants. Tests mere conducted using 2, 5, and 10 parts of the antioxidants in gum neoprene stocks containing 3 parts of Heliozone. Because of the additional protection piovided by the Heliozone, it was necessary t o use longer exposuie periods at the high ozone concentration to induce cracking. The results show that in the presence of the wax, the differences in degree of ozone resistance conferred by the antioxidant were wen more pronounced than in its absence. I n compounding neoprene for the ultimate in ozone resistance it is advisable t o use the maximum quantity of the most protective types of antioxidants The solubility limits generally must be recognized in order t o avoid bloom. If the application permits the use of waxes, the film formed by them x-ill mask the antioxidant bloom. If it is not desired to exceed the solubility level, a blend of antioxidants is in order. A typical neopiene cable-jacket compound having the following formula was tested:
a
Low ozone concentration
High ozone congentration
Neoprene Type G N - 4 Phenyl-%naphthylamine Di-p-methoxj-diphenylamine Diphenyl-p-phenylenediamine P henyl-1-naph thylamine Stearic acid M a nesia E P 8 carbon black Hard clay Heliosone Light process oil Zinc oxide Permalux 5 parts of "The1inoflex -4" neie used
100.0 2.5a 1.25a 1.25"
5.0 0.5
'
4.0 25
50 5 10 10
0 5
The solubility limit of none of the anti'oxidants used v a s cxceeded. This compound had exceptional ozone resistance, xithstanding exposure a t the high ozone concentration for 144 houis, after which time it was removed without having cracked. LITERATURE CITED (1) Best and Xoakes, Trans. I n s t . Rubber Ind., 27, No. 2, 103-26
(1951). (2) Bridgwater, IND.ENG.CHEM.,26, 33 (1934). (3) Cosler. I n d i a Rubber World. 93. 31 (1935). (4) Crabtree and Kemp, IND.ENG. CHEM.,k w a L . , ED., 18, No. 12, 769-74 (1946). (5) Haushalter, Jones, and Sohade, IND. ENG.CHEM.,20, No. 3, 300 (1928) [Rubber Chem. and Technol., 1, 120 (1928)l. (6) Kearsley, Rubber Age, 27, No. 12 (1930) [Rubber Chem. and Technol., 4, 13 (1931)l. (7) Morris, Hollister, Barrett, and Werkinthin, Rubber Age Y.), 55, 45 (1944). ( 8 ) Morris, James, and Werlrinthin, Ibid., 51, 205 (1942) [Rubbe,. Chem. and Technol., 16, 209 (194311. (9) Newton, Rubber Chem. and Technol., 18, 504-56 (1945). (10) Xortham, E. I. du Pont de Nemours & Co., Rept. 38-2 (1938). (11) Thompson and Catton, IND. ENG.CHEM.,42, 892-5 (1950). (12) Winkelmann, Rubber Age ( N . Y , ) , 69, 325 (1951). I
1 part Agerite White
5 parts Agerite White
EFFECT OF ANTIOXIDANTS PLUS WAXES
,
.
,
I
I
RECEIVED for review September 17, 1951. ACCEPTED January 17, 1952. Contribution 86, Rubber Laboratory, E. I. du Pont de Nemours & Co., Ino., Wilmington, Del.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 44, No. 4
