Model metalworking fluids, characterized by phase separation of functional
components at elevated temperatures, were studied. Results of membrane filt
ration experiments with three oils of differing chemical nature confirm the
feasibility of specific removal of finely dispersed contaminant oils witho
ut the simultaneous loss of active components from adequately formulated fl
uids. Prerequisites are that membrane materials and pore sizes be suitably
chosen and that operating temperatures be kept below the cloud point of the
least soluble component. The most suitable filter in the present study was
a hydrophilic regenerated cellulose membrane with a NMWL of 100,000 dalton
. Complete oil removal was attained if membrane pore sizes did not exceed 0
.1 mu m It was also found that intrinsically water-soluble boundary lubrica
nts of the polyglycol ether type are retained by membranes in the presence
of PPG-1800, which serves as a precipitation promoter above the cloud point
. This is of considerable practical importance since it offers the possibil
ity of designing water-soluble boundary lubrication and extreme pressure ad
ditives which are activated by the presence of a inversely soluble componen
t above its cloud point. The latter compound also acts as the principal hyd
rodynamic lubricant of the present model formulations. The usefulness of a
new analytical tool for the rapid acquisition and imaging of data pertinent
to changes in molecular aggregation and phase conditions was demonstrated.