Soil removal, microemulsions

The importance of a surfactant - rich phase, particularly a lamellar one, to detergency performance was noted for liquid soils such as C16 and mineral oil (3.6). Videomicroscopy experiments indicated that middle phase microemulsion formation for C12E04 and Cjg was enhanced at 30 °C, while at 18 °C, oil - in - water, and at 40 °C, water - in - oil microemulsions were found to form at the oil - bath interface (3.6). A strong temperature dependence of liquid soil removal by lamellar liquid crystals, attributed to viscosity effects, has been noted for surfactant - soil systems where a middle - phase microemulsion was not formed (10). 

A recent review [32] describes several cases in which the maximum soil removal occurs when the soil is incorporated into an intermediate phase, such as a microemulsion or lamellar liquid crystals. These intermediate phases form at the interface between the soil and the washing bath. The phases grow up to a point and then, as a result of agitation, break off into the bath, where they are emulsified into the aqueous solution. 

A significant number of patents on LDLDs have been issued in the U.S., Europe, and Japan in recent years. Listed in Table 7.10 are examples of LDLD patents formulating for effective soil removal/cleaning. The technology utilized in these patents ranges from special surfactants, surfactant mixtures, salts, and microemulsion to the use of special additives such as lemon juice and abrasives. 

Liquid-crystalline phase or microemulsion formation between surfactant, water, and oily soil accompanies oily soil removal from hydrophobic fabrics such as polyester (Raney, 1987 Yatagai, 1990). It has been suggested (Miller, 1993) that maximum soil removal occurs not by solubilization into ordinary micelles, but into the liquid-crystal phases or microemulsions that develop above the cloud point of the POE nonionic. 

Figure 8.13 Soil removal (5) by a surfactant phase microemulsion (ME) and by a 1 wt.% aqueous liquid detergent solution (L. Det) from different fabrics. (From Ref. [81 ], reprinted with permission of Taylor Francis.)...

At temperatures significantly below the PIT (e.g., in the Winsor I phase region), the microemulsion can solubilize much less hydrocarbon (see Figure 4.25). The rate of solubilization is also slower (Miller and Raney, 1993) and interfacial tension is higher. As a result, soil removal is considerably lower, as may be seen from Figure 4.32. Well below the cloud point temperature, no... 

Liquid detergent formulation A light-duty microemulsion liquid detergent composition, useful for removing greasy soils from surfaces with both concentrated and diluted forms, has been reported. It consists of the following components ... 

The cleaning composition may be used in concentrated or diluted form for cleaning soil from glass and metal parts, among others. This microemulsion shows that, by combining water and oil, metal surfaces can be cleaned effectively. This becomes possible because both oil- and water-soluble dirt is removed by the microemulsion. 

Although the contacting experiments were performed with surfactant systems typical of those used in enhanced oil recovery, application of the results to detergency processes may be possible. For example, the growth of oil-rich intermediate phases is sometimes a means for removing oily soils from fabrics. Diffusion path theory predicts that oil is consumed fastest in the oil-soluble end of the three-phase regime where an oil-rich intermediate microemulsion phase forms. 

Liquid soil is usually removed by roll-up, emulsification, direct solubilization, and possibly formation of microemulsion or liquid crystalline phases. The oil emulsification capability of the surfactant solution and the oil-water interfacial tension are relevant physicochemical parameters. 

Kinscherf Colgate-Palmolive Thickened microemulsion cleaning compositions comprising xanthum gum Superior cling to a vertical surface and effective in the removal of oily and greasy soil... 

Unlike the experiments carried out below the cloud point temperature, appreciable solubilisation of oil was observed in the time frame of the study, as indicated by upward movement of the oil-microemulsion interface. Similar phenomena were observed with both tetradecane and hexadecane as the oil phases. When the temperature of the system was raised to just below the PITs of the hydrocarbons with C12E5 (45°C for tetradecane and 50°C for hexadecane), two intermediate phases formed when the initial dispersion of Li drops in the water contacted the oil. One was the lamellar liquid crystalline phase La (probably containing some dispersed water). Above it was a middle-phase microemulsion. In contrast to the studies below the cloud point temperature, there was appreciable solubilisation of hydrocarbon into the two intermediate phases. A similar progression of phases was found at 35°C using n-decane as the hydrocarbon. At this temperature, which is near the PIT of the water/decane/C Es system, the existence of a two-phase dispersion of La and water below the middle-phase microemulsion was clearly evident. These results can be utilised to optimise surfactant systems in cleaners, and in particular to improve the removal of oily soils. The formation of microemulsions is also described in the context of the pre-treatment of oil-stained textiles with a mixture of water, surfactants and co-surfactants. 

Surfactants and microemulsion systems can be used for ex situ treatment of contaminated soil or in situ soil decontamination. In situ remediation is usually preferred if excavation of the contaminated soil is not possible or expensive, e.g. beneath buildings or for contaminations at great depth. Often bioremediation or natural attenuation is used for decontamination. In most cases, these techniques only permit the effective degradation of contaminants in the plume formed by dissolved pollutants which may be very large. However, for the remediation of a contaminated site, it is also necessary to remove the source where the pollutants maybe adsorbed in large quantities or may be present as solid or liquid phases. The latter are called NAPL (non-aqueous phase liquids) and a differentiation is made between LNAPL (light non-aqueous phase liquids) with a lower density than water and DNAPL (dense non-aqueous phase liquids) with a higher density than water (see Fig. 10.1). 

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