Metal Soap Greases - Progress in Organic and Physical Chemistry: Structures and Mechanisms - page 64

forms such as fine fibers, ribbons, twisted fibers, rods, and flat platelets depending on
crystallization conditions and the type and mixture of soap molecules involved.
FIGURE 2 Simplified schematic T-x phase diagram of the aqueous soap system. L 1 , micellar
solution, H 1 , hexagonal phase, L Į , lamellar phase, S, solid phase, T K , Krafft boundary, dotted
line, CMC curve, dashed line, and molecular solubility curve for solid phase [23].
6.6 GREASES WITH DIFFERENT BASE OILS: MINERAL OIL AND
VEGETABLE SOYBEAN OIL
Recent environmental awareness has forced consideration of the use of biodegrad-
able fluids such as vegetable oils and certain synthetic fluids in grease formulations.
The higher cost of synthetic greases limits their use only in aerospace, computer, and
medical applications. The soybean oil as lubricating base oil is rapidly biodegradable
and the thickeners such as lithium soaps are not harmful in the environment, however
vegetable oil based greases have poor thermo-oxidative stability resulting from the
highly unsaturated nature of vegetable oils and thus cannot be used at high tempera-
tures. Typical grease formulation is outlined in Figure 3 and typical grease recipies are
shown in Table 1.