Mechanisms of the Cleaning Process

Surfactants and Interfacial Phenomena, Third Edition. Milton J. Rosen ISBN 0-471-47818-0 2004 John Wiley Sons, Inc. 

In general, cleaning consists essentially of two processes (1) removal of the soil from the substrate and (2) suspension of the soil in the bath and prevention of its redeposition. This second process is just as important as the first, since it prevents redeposition of the soil onto another part of the substrate. 

---

Liquefiable Soil The first stage in the removal of this type of soil is believed to be liquefaction of the soil (Cox, 1986). Penetration of the soil by surfactant (and associated water molecules) from the cleaning bath with resulting liquefaction may be a key process in the removal of this type of soil (Cox, 1984). In cases where penetration of the solid soil by surfactants or other additives does not occur, an increase in the temperature of the cleaning process may result in its liquefaction. The liquefied soil is then removed by the roll-back mechanism described above (Cox, 1987). 

The common point of the different cleaning mechanisms (roll-up, solubilization, emulsification) is the wetting of the surface by an aqueous solution of one or several surfac-tant(s). To clearly understand this essential step of the cleaning process, it is important to get good information on how the surfactant system interacts at the water-solid grease (soil) and water-substrate (clean surface) interfaces. 

All metal parts exposed to the room are made of stainless steel and motors and transmissions are IP 65 to withstand the eflfect of the cleaning agents. The design also takes into account the special considerations necessary for food processing machinery with regards to easy accessibility to all parts and the lack of corners, edges, pockets or other food traps , so that the mechanical system can be easily cleaned. 

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 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. 

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... 

The concept of preassembly as a requirement for substitution may throw light upon the vexed question of the mechanism of the base hydrolysis reaction. It has long been known that complexes of the type, [Co en2 A X]+n can react rapidly with hydroxide in aqueous solution. The kinetic form is cleanly second-order even at high hydroxide concentrations, provided that the ionic strength is held constant. Hydroxide is unique in this respect for these complexes. Two mechanisms have been suggested. The first is a bimolecular process the second is a base-catalyzed dissociative solvolysis in which the base removes a proton from the nitrogen in preequilibrium to form a dissociatively labile amido species (5, 19, 30). 

Nitration is widely applicable, can be carried out under a variety of conditions, can usually be stopped cleanly after mononitration, is usually effected by the nitronium ion, can take place on a neutral molecule or a cation, and in many cases can be considered as the standard aromatic electrophilic substitution. However, this last point must be treated with caution. Depending on the reaction conditions and reagents, the mechanism of the reaction does vary, and accompanying reactions such as oxidation (due to the oxidative action of nitric acid), acetoxylation (by acetyl nitrate), and migration of nitro groups following ipso attack (80MI1) can occur. Ipso nitration processes have been extensively studied by Fischer and co-workers. 

Yamanaka, T. (2002). Growth mechanism of the ammonia fungi—Experimental myco-logical studies on cleaning processes in the sites after decomposition of dead-bodies and excrement of animals. Ph.D. diss., Kyoto University (in Japanese). 

---