Surface properties and sub-surface aggregate assimilation of rhamnolipid surfactants in different aqueous systems.

Tensioactive properties of rhamnolipids produced by a Pseudomonas aeruginosa strain were investigated in the presence or absence of Sr(2+) or Pb(2+). Surface and interfacial properties, and aggregate forming properties and morphologies were studied by various techniques including scanning electron microscopy. When the pH of a rhamnolipid aqueous solution (40 mg/l) was increased from 5 to 8, irregular vesicles gradually took the shape of oligo-vesicles, then regular vesicles and finally smaller spherical vesicles. Addition of metal ions controlled the aggregates' morphology and stability, and influenced the surface and interfacial behavior of rhamnolipid solutions.

Production of rhamnolipid surfactant and its application in bioscouring of cotton fabric.

In the present study, a biosurfactant was synthesized by using a bacterial strain of Pseudomonas aeruginosa in minimal media provided with n-heptadecane as sole carbon source under shake-flask conditions. The biosurfactant was isolated (by acid precipitation, solvent extraction, and rotary evaporation), purified (by column chromatography and TLC), identified (by FAB-MS, FTIR, and 1D-(1)H NMR), and chemo-physical characterized (by tensiometry). Two principal rhamnolipid congeners were identified as dirhamnolipid RRC10C10 and monorhamnolipid RC10C10 with a CMC of 50mg/L. The biosurfactant, hence produced, was applied in sole and in combination with pectinase in scouring of cotton fabric in contrast to conventional scouring agents of NaOH and anionic surfactant SDS. The scoured cotton fabric was investigated for its weight loss, residual oil and grease, wettability, whiteness, and tensile strength. The results were compared both for conventional and biological approaches. The scouring with biosurfactant plus pectinase was equivalent to or better in efficiency than conventional alkaline scouring. The former process is additionally environmentally friendly and bio-compatible. Scanning electron microscopy of cotton fabric showed that the alkaline scouring deteriorates the fabric texture whereas bioscouring with biosurfactant plus pectinase gently removes hydrophobic impurities from the cotton fabric.