Soil removal

The low-energy micelle formed must be sufficiently stable to permit its removal in the laundering process. Mineral soils, being partially hydrophilic in nature, undeigo a more complex process in soil removal. The soil mixes with the surfactant to form a liquid crystal. Additional surfactant forms a complex micelle which includes myel inic tubes to provide sufficient surface area to remove and stabilize the solubilized soil. 

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Fig. XIII-14. Surface tensional relationships in soil removal.

Solid Soil Type and Size. Different soHd soils differ greatly in ease of removal and redeposition behavior. These differences can be traced to particle size and soil—substrate bonding. The effect of particle size variation on detergency has been studied with soil removal and redeposition techniques. 

As with the case of energy input, detergency generally reaches a plateau after a certain wash time as would be expected from a kinetic analysis. In a practical system, each of its numerous components has a different rate constant, hence its rate behavior generally does not exhibit any simple pattern. Many attempts have been made to fit soil removal (50) rates in practical systems to the usual rate equations of physical chemistry. The rate of soil removal in the Launder-Ometer could be reasonably well described by the equation of a first-order chemical reaction, ie, the rate was proportional to the amount of removable soil remaining on the fabric (51,52). In a study of soil removal rates from artificially soiled fabrics in the Terg-O-Tometer, the percent soil removal increased linearly with the log of cumulative wash time. 

In detailed studies with a number of different artificial test cloths, first-order kinetics were obtained for soil removal during the first 6—20 min of the cycle (53). 

Adsorption of bath components is a necessary and possibly the most important and fundamental detergency effect. Adsorption (qv) is the mechanism whereby the interfacial free energy values between the bath and the soHd components (sofld soil and substrate) of the system are lowered, thereby increasing the tendency of the bath to separate the soHd components from one another. Furthermore, the soHd components acquire electrical charges that tend to keep them separated, or acquire a layer of strongly solvated radicals that have the same effect. If it were possible to foUow the adsorption effects in a detersive system, in all their complex ramifications and interactions, the molecular picture of soil removal would be greatly clarified. 

Colloidal Stabilization. Surfactant adsorption reduces soil—substrate interactions and faciUtates soil removal. For a better understanding of these interactions, a consideration of coUoidal forces is required. 

Furthermore, in a series of polyoxyethylene nonylphenol nonionic surfactants, the value of varied linearly with the HLB number of the surfactant. The value of K2 varied linearly with the log of the interfacial tension measured at the surfactant concentration that gives 90% soil removal. Carrying the correlations still further, it was found that from the detergency equation of a single surfactant with three different polar sods, was a function of the sod s dipole moment and a function of the sod s surface tension (81). 

Combiaatioa soak-and-electrocleaner products are touted for use whea aormal soak cleaner is too much and a normal electrocleaner is too Htfle. These combination cleaners are often electrocleaners with additional surfactants. The results are often hard-to-tinse electrocleaner or a low capacity soak. The term heavy-duty, often used to describe cleaners, can refer to high caustic content or to good soil-removing, high soH-load capacity. 

Four means of soil removal have been proposed mechanical action ... 

In summary, directly hydrolyzed IOS has good n-hexadecane solubilizing kinetics. This class of compounds then is attractive for detergent formulations where the kinetics of apolar soil removal is imperative. Also, it is observed that shifting the ionic head group toward the middle of the alkyl chain results in an... 

In principle, the soil removal for the a-ester sulfonates increases appreciably in soft water as chain length increases. In hard water the results for C16 and C18 ester sulfonates are nearly the same with and without zeolite A, a builder for complexing Ca2+ ions (Fig. 8) [58]. 

The effects of the removal of organic matter and iron oxides on Zn adsorption on soils are also influenced by Zn concentration. At low concentrations (5-10 mg L initial concentration), both treated soils (removed organic matter and iron oxides) behaved similarly. At high Zn concentration, however, treated soils behaved differently. When the initial Zn concentration was between 5 and 10 mg kg-1, adsorption of Zn by soils without organic matter and without both organic matter and iron oxides were 2-2.5 times that of the untreated soil. With an increase in initial Zn concentration, the soil without both iron oxides and organic matter adsorbed more Zn than the soil without organic matter. This indicates that the available sites for Zn decrease with increases in the initial Zn concentration. 

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