The effect of surfactants, enzymes and temperature on soils investigated using electrochemical and crystallisation techniques for detergency applications

Abstract

The behaviour of surfactant at an oil-water interface is of fundamental importance across a range of application, one of which is detergency. For the characterisation of various anionic and non-ionic surfactants, which make up commercial detergent solution, at the aqueous-organic interface, electrochemical methods combined with conductivity, electrocapillary curves and optical microscopy were employed. The findings have revealed that the adsorption and partitioning of the anionic surface active ions at the interface between two immiscible electrolyte solutions can cause reproducible chaotic effects at the region of transfer potentials of the surfactant ions. Factors such as the Marangoni effect and spontaneous emulsification at the phase boundary, as well as the presence of micelles, micellar emulsification and transfer of emulsion droplets across the interface have been found to contribute to these chaotic currents at the organic-water interface. By applying cyclic voltammetry and chronoamperometry techniques, it was established that the irregular oscillations became more pronounced as the concentration of sodium dodecylbenzene sulphonate (SDBS) was increased from 1.5 mM -13.4 mM and the current spikes dissipated as the concentration of triton- x- 114 was increased from 8.6 mM - 114 mM in the aqueous phase consisting of 13.4 mM of SDBS. Similar results were obtained using P&G’s Y and N surfactants. The rise in current instability due to enhanced concentration of the SDBS, which was used as the standard surfactant, was confirmed using chronoamperometry, conductivity measurements and electrocapillary curves. The interfacial instability was prominent in the presence of electrolytes at the aqueous-1,2-DCE/oil phase boundaries which was visually evident in the optical microscopic images obtained. Furthermore, needle-like crystals were identified at the aqueous-1,2-DCE interface with electrolytes, with and without the addition of anionic/non-ionic surfactants. This suggests that a crystallisation process was initiated by the presence of dehydrated salt ions at the phase boundary, which is likely to be promoted by the surfactant ions.
Lard has been used as the fat ‘model’ for washing experiments since it is composed of more problematic high melting point components compared to other sources of fat. Lard was deposited onto fabrics and left to age over a period of 4 hours at 20 oC and also, at the temperatures of -10 oC, 10 oC, 20 oC and 30 oC for 5 days. These samples, when analysed using the small angle X-ray scattering (SAXS) technique, revealed peaks at 2