Formulation, characterization and treatment of metalworking oil-in-water emulsions

The performance of colloidal dispersion systems such as emulsions and suspensions depends greatly on their formulation. A proper characterization of the system oil–water–surfactant for emulsions used in metalworking operations may extend emulsion life and lower process costs. The behavior of an oil-in-water (O/W) emulsion formulated in our laboratory is described in this study. The base oil was selected from a list of mineral, synthetic, animal and vegetable oils according to their tribological properties. Three different surfactants (anionic, cationic and non-ionic) were used to stabilize the emulsion for subsequent O/W emulsion formulation. The effect of concentration of the three emulsifiers on the interfacial properties and emulsion stability is reported. It has been found that the type and concentration of emulsifier are key parameters with respect to O/W emulsion performance. Elastohydrodynamic film thickness measurements and extreme pressure tests were also conducted in order to determine how the O/W emulsion formulation affects its lubricating properties. The disposal of waste O/W emulsions has increasingly become an expensive challenge to industry and their treatment is described in this work using several techniques, such as coagulation, centrifugation, ultrafiltration and vacuum evaporation.