Untitled

68
dramatically increased rinsing times and high-rinse water consumption. The
formation of foam also can affect level control equipment and can cause severe
damage by cavitation in centrifugal pumps.
Foam is created either by foaming surfactants, production residues, or from
the reaction between cleaner and soil. Defoamers could be used to alleviate the
problem. They are predominantly hydrophobic substances and work at the
interfacial areas of the cleaning solution, preventing the formation offoam.
However, ironically, their disadvantage is their hydrophobia for they are not
water soluble, difficult to integrate into cleaner formulations, and aproblem to
rinse. Typical substances used as defoamers are paraffin oil, silicones, fatty acids,
and fatty alcohols with very short EO or PO chains, etc.
However, the last substance class offers a solution to the problem. By
combining longer hydrophilic molecules with relatively short EO-chains or by
introducing PO into the EO-chain, it is possible to produce surfactants that reach
their insolubility (so-called “cloud point” because the clear solution becomes
cloudy at this temperature) at a temperature far below the intended
cleaning temperature.
For example, asurfactant with acloud point at 308 Cwill become increasingly
hydrophobic at temperatures above 308 C. This effect produces foam-controlling
properties and the surfactant does not foam anymore. Even more, it acts increasingly
as adefoamer for all other substances that might be present and cause
foaming. When finally rinsing with cold water ( ! 308 C), the substance becomes
increasingly more soluble thus facilitating its removal from surfaces (Fig. 27).
Oxidizing Agents
Oxidizing agents, such as peroxides and hypochlorites, assist in decomposing
carbonized residues and insoluble high-molecular compounds. They also can
destroy dyes or discoloring agents providing ableaching effect. When considering
the use of such chemicals as cleaning boosters added to acleaning solution, it is
essential to be aware of the risk of chemical attack.
Although hypochlorites are extremely efficient, they are also highly corrosive
towards certain materials and can cause pitting corrosion on stainless steel as well
as attacking such sealing materials as rubber and plastics. Oxidizing agents based
on hydrogen peroxide show agood efficacy, but they are less likely to attack
equipment.
FIGURE 27 The cloud point of anonionic surfactant.
Rosner