Synthetic Grease Formulated Using PAO-6 and mPAO-65 Paul A. Bessette, * and Ked Hope** *Triboscience & Engineering, Inc., Fall River, MA 02742 ** Chevron Phillips Chemical Co., LP, The Woodlands, TX 77380
Introduction:
Synthetic lubricants are superior to petroleum based products in terms of thermooxidative stability and low temperature performance. Numerous automotive requirements demand that lubricating grease function at -40ºC while military specification may demand serviceability to -54ºC. MIL PRF 32014 describes a lithium 12-hydroxystearate thickened blend of polyalphaolefins. The viscosity requirements of the specification can be achieved by blending PAO 6 and PAO 40. This paper describes a grease formulated with PAO 6 and mPAO 65. The high viscosity component was synthesized using a metallocene catalyst. The metallocene catalyzed PAO’s differ from conventionally PAO’s in that their pendent groups, the side chains, represent have a comblike structure with a chiral center at the branch carbon. The chirality provides for a random distribution of branch stereoregularity and isomer distribution to yield excellent low temperature properties. The kinematic viscosity requirements for the base oil in the grease are quite specific. At 40ºC, the maximum viscosity is 140 centistokes while at 100ºC the minimum viscosity is 16 centistokes. The specified viscosity requirements have been achieved for typical greases by blending PAO 6 and PAO 40. However, the military specification requires that the low temperature torque as determined by ASTM D1478 not exceed 14,000 g/cm for the starting torque and should not exceed 2800 g/cm for the running torque. We show that decene based PAO 40 is a viable blending component to achieve the viscometrics demanded by the specification while mixedmonomer fluids can be problematical. However, our work suggests that blends using mPAO 65 can produce stellar results in terms of low temperature torque requirements at -54ºC. Typical Structures of PAO and mPAO materials:
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