Document 06g7KxDp0Eqq5gL3eXKLReVVx

, :|ceiled fro** Ot'ck 6 jxi ) **' kh irejj of Mow Cfre^tmi 4~> D ooi/ 't'kerv^ ` f^i M -Ourh]Je SOCIETY OF AUTOMOTIVE ENGINEERS. INC. Two Pennsylvania Plaza, New York, N. Y. 10001 \ The Effect of Ethylene Glycol and Methoxypropanol-Based Coolants on Elastomers James E. Miller Technical Service and Development, The Dow Chemical Co. Turner Alfrey, Jr. Plastics Department Research Laboratory, The Dow Chemical Co. SOCIETY OF AUTOMOTIVE ENGINEERS Mid-Year Meeting Detroit, Mich. May 20-24,1968 680496 VPD-81-0001673 DANA-191 680496 The Effect of Ethylene Glycol and Methoxypropanol-Based Coolants on Elastomers James E. Miller Technical Service and Development, The Dow Chemical Co. Turner Alfrey, Jr. Plastics Department Research Laboratory, The Dow Chemical Co. SEALING THE COOLANT PASSAGES in a liquid-cooled in ternal combustion engine is becoming more and more diffi cult as coolant temperatures and pressures increase and as the expected service life from all engine components is ex tended. This paper attempts to explain what happens when different coolants contact nonmetallic components of the cooling system and how this relates to field performance. Of particular concern in this paper is the effect of alter nate exposure of elastomers to water and to antifreeze/cool ant solutions. Year-around use of an antifreeze /coolant is the exception rather than the rule in heavy-duty equipment such as trucks, buses, and off-highway vehicles, so this al ternate exposure must be considered. In 1965 an antifreeze/coolant based on methoxypropanol rather than the traditional ethylene glycol or methanol was introduced for use in heavy-duty equipment under the name Dowtherm* 209 coolant. During the development of Dowtherm 209 coolant, the effect of solutions of methoxypro panol on commonly used hose and seal materials was thor oughly studied. This investigation has continued and was expanded recently to include a re-evaluation of ethylene glycol - based antifreeze products with respect to the al ternate use of water in warm weather and antifreeze/coolant in cold weather. THEORY BEHIND "RUBBER SWELL' NONPOLAR ELASTOMERS - The simplest case is that of a nonpolar elastomer, such as natural rubber or GR-S, in contact with an organic liquid. The equilibrium swelling depends upon the degree of cross-linking of die rubber and upon the thermodynamic affinity of the liquid for the hydro carbon chains. The latter factor can be simply related to the solvent cohesive-energy-density (CED) or its square root, die "solu bility parameter (SP)." AE AH -RT CED =_______________________________ Molar volume Molar volume SP = (CED)1^2 `Registered trademark. The best swelling agents for a given (nonpolar) elastomer are those which match the polymer in CED and hence in SP. ABSTRACT The effect of different coolants on common hose and seal formulations currently in use in heavy-duty engines has been studied. Water, ethylene glycol, and methoxy propanol coolants have been studied in contact with seven different types of elastomers. A brief discussion of the theory behind rubber swell is presented, as are laboratory and field test data. The data indicate that seasonal failure of hoses and seals may be caused by a sudden change in the com position of the coolant. 2 Swelling power decreases with increasing mismatch in SP has been suggested to provide the necessary multiple char between elastomer and liquid. With a given liquid, the de acterization of a given liquid (2, 3,4). gree of swelling decreases with increasing cross-linking of In particular, Beerbower, et al. relate the swelling of the elastomer. This dependency is particularly pronounced with powerful swelling agents, which have unlimited mis various elastomers to the solubility parameter, the dipole moment, and the hydrogen-bonding power of the liquid in cibility with the unvulcanized elastomer. For poor swelling question. agents, which are nonsolvents for the unvulcanized elastomer, Every hydrogen bond involves a "Lewis acid" (that is, the variation in equilibrium swelling resulting from differ electron acceptor) and a "Lewis base" (electron donor). ences in cross-link density is less pronounced, but still pie- Some molecules can play die role of "base" in hydrogen sent. These effects ate indicated schematically in Fig. 1. bonding, but not that of "acid," for example, pyridine, or Table 1 lists the values of CED and SP for several typical more weakly, ethers and ketones. Other molecules can act solvents and elastomers. A more complete tabulation is as "Lewis acids." And some molecules (for example, water, available in the literature (1)*. OIL RESISTANT ELASTOMERS - Some synthetic elasto alcohols, primary amines, amides) possess both an "acidic" and a "basic" atom and thus can hydrogen bond to their own mers contain polar groups. This reduces their swelling by species. In terms of this terminology, an elastomer which low SP liquids, such as hydrocarbons, but increases their possesses Lewis acid groups will exhibit a particularly strong swelling by many polar liquids. affinity for solvents which contain Lewis base groups, and The swelling behavior of a polar elastomer differs from vice versa- that of a nonpolar elastomer in two important ways: Styrene-butadiene rubber, for example, has a rather low 1 It has a higher value of SP. SP, and no tendency for hydrogen bonding: the most powerful 2. Solubility parameter alone does not provide a satis swelling agents are liquids with solubility parameters in die factory means of quantitatively explaining or predicting the range of 8.0-10.0. degree of swelling by a wide variety of liquids. Neoprene rubber is somewhat more polar than SBR; and The swelling of a polar polymer by a polar solvent in volves specific interaction between polar groups - - not nitrile rubber still more polar. Nitrile rubber acts both as a Lewis acid and as a Lewis base, and is strongly swelled by merely an overall match in SP. A number of approaches intermediate SP liquids, particularly those containing "base" or "acid" groups. Viton rubber (a fluorine-containing elas tomer) acts as a Lewis acid and, consequently, is preferen Number in parentheses designates References at end of paper. tially swelled by intermediate SP liquids which possess Lewis base groups. SPECIAL ROLE OF WATER - Compared with all these elastomers, water has a very high cohesive energy density and, on the basis of the above discussion, would be expected Table 1 - Cohesive Energy Density (CED) and Solubility Parameter (SP) for Typical Liquids and Elastomers Substance CED SP n-Octane n-Decane Cyclohexane Propylbenzene Toluene Ethyl Propionate Dioxane Butanol Ethanol Methanol Ethylene-Propylene Rubber Styrene-Butadiene Rubber Neoprene 75/25 Butadiene/Acrylonitrile 70/30 Butadiene/Acrylonitrile 58 61 67 76 81 81 94 117 170 210 64 69-74 77 88 92 7.6 . 7.8 8.2 8.7 9.0 9.0 9.7 10.8 13.0 14.5 8.0 8.3-8.6 8.8 9.4 9.6 VPD-81-0001675 3 to exhibit a very low swelling power. And yet many elas tomers in contact with liquid water for long periods of time, particularly at high temperatures, can absorb very large amounts. The explanation of this apparent anomaly lies in the fact that typical vulcanizates contain small amounts of extremely hydrophilic materials. Water can be imbibed to form a colloidal dispersion of droplets, which also contain hydrophilic impurities. The osmotic action of these hydro philic materials within the water droplets provides the driv ing force for entry of more water. The elastic properties of the elastomer matrix provide some resistance to continued enlargement of the droplets. Different elastomers vary widely in their tendency to imbibe water by this two-phase mechanism (5). LEAKAGE PROBLEM Ever since ethylene glycol was first used as an antifreeze/ coolant for internal combustion engines about 40 years ago, the problem of "glycol creep" has been a major concern to engine operators. "Glycol creep" may be defined as die common tendency of coolant leaks to appear in a seemingly "tight" cooling system shortly after die installation of ethyl ene glycol-based antifreeze. - External coolant leakage resulting from "glycol creep" is at best a costly nuisance, resulting in high coolant make up and requiring tightening or replacement of hose clamps. Since external leakage of glycol antifreeze can often go undetected by the operator for long periods of time, there is a very serious danger that coolant loss will continue until there is insufficient coolant in the engine and severe over heating occurs with resulting engine damage. Internal leakage of glycol-based coolant can be cata strophic. The glycol reacts with lubricating oil to form sludge and varnish which increase oil viscosity, plug oil pas sages, cause piston rings and pins to "freeze," and, in many cases, cause seizure of the engine. While it is certainly true that seals and sealing systems have been vastly improved in recent years, the problem of coolant leakage remains a serious one, particularly for die operator of heavy-duty equipment. For example, a 1966 survey conducted by the Regular Common Carrier Conference (RCCC) showed 74% of the truck operators surveyed con sidered internal leakage of coolant to be a serious mainte nance problem in their operation. This internal leakage problem appears to occur in all types of diesel engines. Leakage is most common past cylinder head seals, injector tubes, and cylinder liners. In the past few years, methoxypropanol-based antifreeze coolant has replaced glycol-based antifreeze in many truck and off-the-road fleet operations. Methoxypropanol has been shown to minimize the progressive engine damage associated with internal leakage of glycol-based coolant. Also, the distinctive odor of methoxypropanol makes detec tion of external leaks much easier. While the movement from glycol to methoxypropanol coolant in heavy-duty equipment means less severe results VPD-81-0001676 of leakage past seals and hose clamps, leakage still poses a problem and must be minimized. "CYCLING" EFFECT Published data usually show the effect of a single immer sion of a given elastomer in a solution of antifreeze. In actual practice many operators of heavy-duty equipment I use inhibited water in the summer and antifreeze/coolant only in die winter or, at best, the concentration of antifreeze is allowed to vary significantly during the year. Thus, it was felt to be more realistic to measure the effect of alter nate exposure of the same sample of elastomer to the anti freeze/coolant and to plain water. ' EFFECT ON O-RINGS - Fig. 2 shows die per cent volume swell of a buna-N "O" ring after 300 hr at 200 F in a 50% solution of antifreeze, followed by 100 hr at 200 F in water, followed by an additional 100 hr at 200 F in a 50% solution of antifreeze. Curve 1 on Fig. 2 shows die data obtained with ethylene glycol antifreeze and curve 2 shows data ob tained with methoxypropanol antifreeze. Note the very pronounced "saw tooth" pattern which in dicates a substantial reduction in volume when moving from water to glycol or from methoxypropanol to water. This, of course, corresponds to shrinkage of the rubber part in the "fall" with glycol and in die "spring" with methoxypropanol. In contrast, curve 3 in Fig. 2 shows the per cent volume swell resulting from immersion of die seal in water only. The slow, smooth increase shown in curve 3 on Fig. 2 should help keep the seal pressed against the metal surfaces, extending the effective life of die seal. The sudden reduc tion of volume experienced when changing types of coolant, however, may cause the seal to fail if it has become hard ened and lost its ability to conform to the new conditions. Fig. 3 shows data obtained with buna-N "O' rings used by another engine manufacturer. The pattern is similar to the previous tests. Fig. 4 shows the same "cycling" pattern obtained with neoprene "O" rings. In this case, water alone results in more swelling than either type of antifreeze, but the swelling is uniform in contrast to die saw-tooth pattern obtained when the antifreeze/coolant is alternated with water. Fig. 5 shows data obtained with ethylene-propylene (EPT) "O" rings. The saw-tooth pattern is the same as for buna-N and neoprene although the absolute volume changes are different. Silicone "O" ring formulations used by several different engine manufacturers were also tested. The volume change caused by immersion in any of the coolants tested was so slight, however, that no meaningful pattern was detectable. EFFECT ON HOSES - The same testing was done on seven different types of cooling system hoses. The tests were car ried out with transverse sections cut from commercially available heater hoses. The types of hose tested were butyl, neoprene, Hypalon rubber (chlorosulfonated polyethylene), ethylenepropylene 4 VPD-81-0001677 5 Fig. 8 - Section of heater hose made of Hypalon Fig. 7 - Neoprene heater hose section Fig. 9 - EPT heater hose section VPD-81-0001678 Fig. 10 - Buna-S heater hose section 6 (EPT), buna-S, buna-N. and relaim stock. The data obtained from these tests are shown in Figs. 6-12. It should be emphasized that all the materials tested with the cycling pattern of coolant were commercially available materials, representative of what is being used today in all types of heavy-duty equipment. FIELD FAILURE PATTERNS Tests by leading hose, seal, and engine manufacturers as well as customer experience have shown no significant dif ferences in the service life of commonly used nonmetallic materials whether methoxypropanol or glycol-based anti freeze is used. The data presented in Figs- 2-12, however, suggest that seals are more likely to fail at the time of re placement of water with glycol or replacement of methoxy propanol with water. That is, if the hose or seal is nearing die end of its useful life, die sudden "shock" caused by changing the coolant may cause failure to occur at the time of changing the coolant. Limited field data tends to confirm that most seal failures occur when switching to glycol from water or to water from methoxypropanol. That is, in the fall if glycol antifreeze is used and in the spring if methoxypropanol is used. Fig. 13 shows a typical distribution of seal failures when glycol anti freeze is used. Also shown on Fig. 13 is the distribution of seal failures for one over-the-road carrier using Dowtherm 209 coolant (methoxypropanol base). The peaks occurred soon after the coolant was changed to or from water. VPD-81-0001679 7 Fig. 13 - Typical seal failure pattern It should be made cleat that both cases described by Fig. 13 are extreme and the average user of either type of anti freeze does not experience this severe seasonal failure rate. However, whenever seasonality of seal failures occurs, it imposes an additional burden on die equipment operator due to loss of availability of many units at one time. When ever seasonality is severe, it appears to be coincident with: 1. `A large number of units with a similar high mileage (and hence seals which are nearing the end of their normal lifespan). 2. A sudden change from antifreeze/cdolant to plain water or vice-versa. Some operators have found that year -around use of methoxypropanol coolant helps to reduce the seasonality of seal fail ures . Others simply allow the concentration to decrease slowly by the addition of water as make-up once the danger of freezing is past. Likewise, year-aiound use of glycol anti freeze should minimize the seasonal pattern of seal failures, and result in a more uniform rate of leakage throughout the year. SUMMARY AND CONCLUSIONS 1. Different types of elastomers are affected differently by different types of coolant. The general effect can often be estimated by an examination of various chemical and thermodynamic properties of both the elastomer and coolant. 2. Changing the composition of the coolant in contact with a given elastomer causes corresponding changes in the volume of the elastomer. 3. Limited field data indicate that seasonal failure of hoses and seals may be due to a sudden change in the com position of the coolant. 4. From the data presented, it may be reasonably con cluded that seasonal failure of nonmetallic components of the cooling system can be minimized by avoiding sudden changes in the composition of the coolant. REFERENCES 1. C. J. Sheehan and A. L. Bisio, Rubber Chem. and Tech., Vol. 39 (1963), p, 621. 2. H. Burrell and B. Immergut, Polymer Handbook, p. IV311. 3- W. Gordy, J. Chem. Phys., Vol. 9 (1941), p. 204. 4- A. Beerbower, L. A. Kaye, and D. A. Patterson, Chem. Eng., Dec. 18, 1967, p. 118. 5. G. J. Briggs, D. C. Edwards, and E. B. Storey, Rubber Chem. and Tech., Vol. 36 (1963), p. 621. This paper is subject to revision. Statements and opinions advanced in papers or discussion are the author's and are his responsibility, not the Society's; however, the paper has Society of Automotive Engineers, Inc. J. A. ULRICH JUN 27 1968 OEPT. 35 MATLS- DEVEl. LAB. been edited by SAB for uniform styling and format. Discussion will be printed with the paper if it is published in SAE Transactions. For permission to publish this papet in full ot in pan. contact the SAE Publications Division and the authors. 8 page booklet, Printed in U. S. A. VPD-81-0001680