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Polymer-thickened hydraulic fluids and lubricants undergo a permanent viscosity loss with use in hydraulic and automotive equipment. Four high-energy sources, including high-temperature levels, ultrasonic irradiation, flow through a sharp-edged orifice, and gamma irradiation, have been used to produce permanent viscosity loss experimentally with fluids containing polyisobutylene, polymethacrylate, or polyester thickeners. The relative severity of these high-energy sources in producing viscosity decreases with the various polymer types is compared. Thermally induced viscosity decrease appears to differ in mechanism and relative order of severity from viscosity changes due to the other high-energy sources studied. Good correlation has been shown for the effects of mechanical shear, sonic irradiation, and gamma radiation on the relative values of viscosity loss for two polymethacrylate-thickened fluids. However, these three energy sources do not show good correlation for the polymers of different chemical structures. The possibilities of short-time mechanical shear tests are illustrated. The overall study tends to emphasize the importance of tailoring the laboratory and specification shear stability test to the severity level and type of shear involved in the end-use application.
Klaus, E. E.
Associate research professor of petroleum chemistry, College of Engineering, Pennsylvania State University, University Park, Pa.
Tewksbury, E. J.
Research associate in chemical engineering, College of Engineering, Pennsylvania State University, University Park, Pa.
Jolie, R. M.
Supervisor, Socony Mobil Oil Co., Paulsboro, N. J.
Lloyd, W. A.
Research director, Cannon Instrument Co., State College, Pa.
Manning, R. E.
Personal Members, ASTM, Technical director, Cannon Instrument Co., State College, Pa.