Cyclosiloxane-in-Water Emulsion Stabilized by Lipopeptide Biosurfactant, Surfactin

摘要

Surface and emulsifying properties of lipopeptide biosurfactant, surfactin (SF) were studied. Surfactin sodium salt (SFNa) shows remarkable surface activities as well as an excellent emulsifying activities against cyclosiloxane oils such as octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) which are regarded as causative agents for pollution from silicon sealants. The interfacial tensions of D5/water were measured by the pendant drop method, revealing that SFNa shows an excellent interfacial tension-lowering activities. Addition of excess amount of D4 to a SFNa solution provided a stable emulsion which was confirmed by turbidity measurements with emulsification index (E_(24)) and decay constants (K_d). Since SFNa shows considerably low critical micelle concentration (CMC), the emulsions were formed at low concentration of SFNa. Proton nuclear magnetic resonance (~1H NMR) spectroscopy of D4 in the presence of SFNa in D_2O solution shows a sharp peak at -0.10 ppm corresponding OSiMe protons, indicating D4 is solubilized in micellar phase. Generally, removing cyclosiloxanes is troublesome due to their super-hydrophobic characters and it has been required more powerful surfactants to cleaning them up. Thus, our results suggest that SFNa would contribute to application for the environmentally friendly surfactant for silicon wastes in industry.