Document 7EVZ2yX1d1KLXv969nK4nmnj

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.