Detergency and Soil Removal

Detergency is unquestionably a surface and colloidal phenomenon reflecting the physicochemical behavior of matter at interfaces. Since the field is concerned principally with the removal of complex mixtures of soils and oily mixtures from equally complex soUd substrates, it is not surprising that such systems do not lend themselves readily to analysis by the more fundamental theories of surface and colloid science. A rigorous treatment of the current status of detergency theory would constitute a book itself. This section summarizes some of the most important aspects of detergency and illustrates how the chemical structure of the surfactants and other components in a formulation can affect overall performance. 

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The mechanisms underlying the detergency and soil removal process have been reviewed by many authors [164-172], This section briefly summarizes the test methods used to characterize the performance of liquid laundry detergents. There are typically three stages of testing during product development (1) laboratory evaluation, (2) practical evaluation, and (3) consumer tests. 

The maintenance of a textile product after purchase is of prime interest to the consumer and to commercial fabric care operations. The major factor to be eonsidered is cleaning and soil removal of the textile during continued use. In order to have a fuller understanding of the cleaning process, one must examine the nature of textile soils, detergency, and soil removal, and the wet (laundering) or dry (solvent) cleaning processes used. 

In the USA, this surfactant is a well established product used in many household and industrial formulations. In particular, in light-duty liquid detergents the water solubility and soil removal ability of a-olefinesulfonates are excellent. In addition, o -olefinesulfonates are compatible with many other surfactants on the market, including alkyl sulfates, alkylbenzene sulfonates and alcohol ethoxylates. Therefore, o -olefinesulfonates can be used to obtain synergistic effects in binary or ternary mixtures. 

Quaternary ammonium compounds have been utilized for a number of purposes in laundry detergents. The performance characteristics where benefits are seen include fabric softening and soil removal. Laundry detergents that also provide fabric softening can utilize relatively simple quaternary ammonium compounds of structures such as alkyldimethylammonium quaternaries with an alkyl chain length of 12 to 18 carbon atoms. 

One-step clean-and-shine products have become popular in the household market. These products are appHed to the floor with a sponge mop and their detergent action removes and suspends soil, which coUects on the mop and is removed when the mop is rinsed with water. The formulation, which remains on the floor, dries to a poHsh film. An earlier product of this type was dispensed from an aerosol as a foam. Formulas as of this writing (ca 1995) are appHed as Hquids (29,30). In one product, the dried film obtained from the formulation is soluble in the formulation, which includes low molecular weight, high acid polymers and a fairly large amount of ammonia (31). Repeated use does not contribute to a buildup of poHsh. 

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. 

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. 

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). 

Detergency, or the power of a detergent product to remove soil, depends on the ability of surfactants to lower the interfacial tension between different phases. This can be explained for a typical case where removal of liquid soil is aided by surfactant adsorption onto the soil and substrate surfaces from the cleaning bath (Figure 2) using Young s equation,... 

Correlation Plot of Cohesive Energy Ratio for LAS Homolog Detergency of Mineral and the Experimental Soil Removal. 

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