Liquid oily soils, removal from

Figure 6-3 illustrates the situation of a liquid soil adhering to a substrate in the presence of air. The reversible work to remove the liquid oily soil O from the substrate, the work of adhesion Wa (equations 6.12 and 6.13) is given by the expressions... 

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. 

The removal of liquid oily soils from surfaces is generally understood in terms of three basic mechanisms the roll - back of droplets of oily soil, the surfaces of which are modified by the presence of an adsorbed layer of surfactant direct emulsification of macroscopic droplets of soil and the direct solubilization of the oily soil into surfactant micelles or other interfacial phases formed (1-3). 

Removal of Liquid Soil Removal of liquid (oily) soil by aqueous baths is accomplished mainly by a roll-back or roll-up mechanism in which the contact angle that the liquid soil makes with the substrate is increased by adsorption of surfactant from the cleaning bath. 

When surfactants of the proper structure are present in the bath, they will adsorb at the substrate-bath (SB) and liquid soil-bath (OB) interfaces in such a fashion (i.e., with the hydrophilic group oriented toward the aqueous bath) as to reduce jSB and Job, with consequent reduction in the work to remove the soil from the substrate. Reduction in ySB will also cause a decrease in cos 0 and an increase in 0, resulting in the observed roll-back of the liquid soil. Many investigators of oily soil removal,... 

Although soil retardants reduce soiling, the deposition of soil onto a textile cannot be entirely prevented. If the textile can be washed, soil-release finishes can facilitate the removal of soil considerably. The term soil release suggests a separation of soil from a fabric immersed in water, but such a spontaneous separation is possible only with liquid oily soils. Solid soils cannot separate spontaneously and require mechanical action for their removal. 

The phenomena at the liquid/liquid interface are of outstanding importance for the removal of oily soil from the surface. The interfacial tension is one of the decisive parameters in the rolling-up process. This parameter vary considerably, de-... 

We also describe the spreading of a thin surfactant laden aqueous film on a hydrophilic solid, i.e., one in which the dynamic contact angle is small. In such a case, the osmotic pressure gradient generated by the nonuniform distribution of surfactant micelles in the liquid film can drive fhe spreading process. The mofivation for this study comes from the need to understand the detergent action involved in the removal of an oily soil from a soiled surface. This paper presents an overview of our recent work. 

Oily soils containing amphiphilic species, such as fatty acids or fatty alcohols, can also be removed from substrates as a result of the formation of liquid crystal or mesomorphic phases between the amphiphile and a detergent. The liquid crystals are then broken up by subsequent osmotic penetration by water [140-142], Removal of solid soils by mesophase formation can be accelerated by increasing the temperature. This has been reported for stearyl alcohol [143] and for lauric, palmitic, and stearic acids [128, 129] and is likely due at least in part to the increased penetration of the soils at higher temperatures [128,129,143],... 

On the other hand, if the surfactant has appreciable solubility in both liquids, then very different factors may determine the value of the interfacial tension. Although low liquid-liquid interfacial tension is important in promoting emulsification (Chapter 8) and in the removal of oily soil by detergents (Chapter 10), advances in our knowledge of the factors governing the reduction at that interface stem from the intense interest in enhanced oil recovery by use of surfactant solutions. 

If the contact angle is 180°, the bath will spontaneously completely displace the liquid soil from the substrate if the contact angle is less than 180° but more than 90°, the soil will not be displaced spontaneously but can be removed by hydraulic currents in the bath (Figure 10-2) (Schwartz, 1972). When the contact angle is less than 90°, at least part of the oily soil will remain attached to the substrate, even when it is subjected to the hydraulic currents of the bath (Figure 10-3) (Schwartz, 1971, 1972), and mechanical work or some other mechanism (e.g., solubilization, see below) is required to remove the residual soil from the substrate. 

The most frequently discussed topic in washing is the role of solubilisation processes. Many investigators [76] attract attention to the fact that the surfactant concentration in a washing solution is much lower than CMC, and in this connection, solubilisation of oils is principally excluded due to absence of surfactant micelles. At the same time, the review of recent works [85, 86] show that solubilisation can play a dominant role both in washing fabrics and in the removal of soils from solid surfaces. These views are based on the following mechanisms. Surfactants adsorb at w/o interfaces under formation of densely packed adsorption layers which leads to a high local surfactant concentration as compared with the rather low concentration in the washing solution. After that, noticeable penetration of water into the oily soil is possible, under formation of liquid-crystal phases. Then, mesomorphic phases are swelled and destroyed under the formation of emulsion droplets. 

Fundamental principles leading to the removal of oily soil from the solid substrate by the so-called roll-up mechanism, in which liquid oil is displaced from the surface by the washing solution in the form of dispersed tiny droplets [60], are essentially the same as those evoked in the attachment of air bubbles onto a mineral surface. 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

In 1980, Syntex, Inc., utilized a process based on photolysis to destroy approximately 13 pounds of 2,3,7,8-TCDD contained in 4300 gallons of oily trichlorophenol still-bottom residues ( ). In 1984, EPA began to use a transportable rotary kiln incinerator to detoxify solid and liquid waste which were contaminated with 2,3,7,8-TCDD (i6). Concurrent with the incineration activities, EPA began removing soils and other contaminated materials from a number of sites including a mobile home park near Grays Summit, Missouri. These activities required the application of extensive compositing techniques and statistical treatment of the data to assure the removal of... 

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