The Cleaning Process

While most detergent-related applications are carried out in aqueous systems, the important nonaqueous dry cleaning systems also fulfill the foregoing requirements for detergency. In the following discussion, however, all references are to water as the solvent unless noted otherwise. 

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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... 

All glassware should be scrupulously clean and, for most purposes, dry before being employed in preparative work in the laboratory. It is well to develop the habit of cleaning all glass apparatus immediately after use the nature of the dirt will, in general, be known at the time, and, furthermore, the cleaning process becomes more difficult if the dirty apparatus is allowed to stand for any considerable period, particularly if volatile solvents have evaporated in the meantime. 

Another quaHty control problem of multipurpose plants is the clean out for a product change. A test for residual cleaning solvents in the ppm level is a necessity. The best vaHdation of the cleaning process is to develop an analytical method that is able to find the previous product in the new product at a level of not more than 1 ppm. Tests should be mn on at least the first three batches. 

Fig. 4. Process flow diagram for aluminum enameling showing (a) enamel preparation and application, and (b) metal preparation, where the cleaning processes A, B, and C represent primarily sheet D, primarily castings and E, aluminized steel (11).

Particulate matter contributes to the soiling of fabrics. The increased frequency of washing to remove dirt results in more wear on the fabric, causing it to deteriorate in the cleaning process. 

In the past, air washers were used for air cleaning today, however, more efficient methods are available for the cleaning process. 

This can be a real problem for baghouses that rely on automatic timers to control cleaning frequency. The use of a timing function to control cleaning frequency is not recommended unless the dust load is known to be consistent. A better approach is to use differential-pressure gages to physically measure the pressure drop across the filter media to trigger the cleaning process based on preset limits. 

In general, the cleanup of oiled shorelines has been by mechanical, labor-intensive means. The use of surfactants to deterge and lift the oil from the surface results in more complete and rapid cleaning. Not only is the cleaning process more efficient, but it can also be less environmentally damaging because potentially less human intrusion and stress on the biologic community occurs and because the chemicals can make the washing more effective at a lower temperature. 

After the cleaning process, other techniques are used to prepare the surface of the substrate for coating. Some techniques include drying, surface etching, and chemical surface preparation. Examples of chemical surface preparation include the formation of an oxide layer or the monolayer assembly of an adhesion promoter on the surface. These processes modify the surface of the substrates so as to facilitate the subsequent deposition process. In surface preparation, frequently, the hydrophilic/hydrophobic character of the surface is controlled to match the coating solution properties. For example, Van Driessche et al.19 reported on improving the wettability of Ni-4at%W tapes... 

Washing and cleansing are processes that involve many interfacial effects, which is why a fundamental description of detergency has to be very complex. If we cluster the different processes involved, we can distinguish the following main steps in the cleaning process ... 

We often clean away the grime and dirt in a kitchen with bleach, the active ingredient of which is the hypochlorite ion CIO-. The cleaning process we see by eye ( the bleaching reaction ) occurs between an aqueous solution of CIO- ion and coloured species stuck to the kitchen surfaces, which explains why the dirt or grease, etc., appears to vanish during the reaction. The reaction proceeds concurrently with colour loss in this example. 

The cleaning process usually washes out the CaS04 originally present as binder. Therefore, the silica gel thus obtained by purification may be reused to prepare TLC-plates with other appropriate binders like gypsum, starch etc. 

In order to soften the sludge, which was estimated to have a depth of 14 in (34 cm), steam was applied to the bottom heating element. Advice was given not to exceed 194°F (90°C). Employees started the clean-out operation using a metal rake. The material was tar-like and had liquid entrained in it. Approximately one hour into the cleaning process, a longer rake was used to reach further into the still. 

We arbitrarily considered a maximum acceptable material removal during the cleaning process of 5 nm, which corresponds for an industrial 10-min process time to a 0.5 nm/min etching rate. Different oxidant-free mixtures able to remove particles by underetching mechanisms and covering the whole pH range were adjusted to remove—in 10 min — 5nm of PECD... 

We must ensure that the etching steps performed during the cleaning processes are sufficient to remove the damaged layer as well. 

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