Definition
In metalworking and industrial fluid applications, an emulsifier is a surfactant additive that stabilizes oil-water emulsions by reducing interfacial tension between the two immiscible phases. Emulsifiers allow oil and water to form stable dispersions that resist separation.
Types of metalworking fluid emulsifiers:
- Anionic surfactants — petroleum sulfonates, fatty acid soaps; most common; negatively charged, effective in hard water if paired with correct countercation
- Nonionic surfactants — ethoxylated alcohols, sorbitan esters (e.g., PIBSA-based); less sensitive to water hardness; good compatibility with biocides
- Cationic surfactants — rare in MWF; antimicrobial properties but incompatible with many additives
PIBSA (polyisobutenyl succinic anhydride) derivatives are widely used as emulsifiers in both soluble cutting fluids and emulsion explosives. HLB (Hydrophilic-Lipophilic Balance) value guides emulsifier selection for oil-in-water vs water-in-oil systems.