Soil removal, detergent type

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. 

On the basis of the degree and type of soiling, conservators can choose between localized or complete treatment of the item. Stain removal with solvents with or without additives is the method of choice if soils are localized and the general appearance of the rest of the textile is satisfactory. A systematic overview of methods of stain removal is given in the literature (4). The present discussion focuses on the method of complete immersion in the cleaning medium and on the principles of soil removal associated with this technique. Excellent summaries (5) on detergency in aqueous media exist, but detergency in nonaqueous media is not as well documented. 

Enzymes catalyze destruction and removal of stubborn proteinaceous stains and specific types of soils by detergent. Chocolate and starch-based food stains as well as greasy stains that are difficult to remove in low-temperature washing, are eliminated by detergent-enzymes [1-4]. 

The strong adverse influence of calcium ions on the stability of lyophobic suspensions is predicted by DLVO theory, and has been demonstrated with many types of simple soils. That calcium ions have an overwhelming effect on the redeposition of carbon soil onto cotton tends to support the idea that DLVO theory is a principal key in explaining detersive action. The redeposition of carbon onto cotton has been correlated quantitatively with the calcium ion content of the system, both in the presence and absence of surfactant (95). The adverse effect of calcium ions on wet soil removal in practical washing has also been well established (96). The effect of calcium in detergency cannot be explained solely, however, by its shrinking of... 

When a surfactant-water or surfactant-brine mixture is carefully contacted with oil in the absence of flow, bulk diffusion and, in some cases, adsorption-desorption or phase transformation kinetics dictate the way in which the equilibrium state is approached and the time required to reach it. Nonequilibrium behavior in such systems is of interest in connection with certain enhanced oil recovery processes where surfactant-brine mixtures are injected into underground formations to diplace globules of oil trapped in the porous rock structure. Indications exist that recovery efficiency can be affected by the extent of equilibration between phases and by the type of nonequilibrium phenomena which occur (J ). In detergency also, the rate and manner of oily soil removal by solubilization and "complexing" or "emulsification" mechanisms are controlled by diffusion and phase transformation kinetics (2-2). 

Because of the importance of solubilization in the removal of oily soil by detergents and in the preparation of pharmaceutical, cosmetic, insecticide, and other types of formulations, a good deal of work has been done on elucidating the factors that determine the amount of solubilizate that can be solubilized by various types of surfactants. The situation is complicated by the existence of the different sites for the solubilization of different types of materials. 

Nonionics have been shown also to be more effective than ionics in the removal of oily soil from relatively nonpolar substrates (polyester, nylon). On cotton, however, a relatively hydrophilic fiber, anionics can outperform nonionics in detergency, and both of these are superior to cationics (Fort, 1968). The effects here may be due to differences in the orientation of adsorption of the different types of surfactants on the different substrates. On nonpolar substrates and soils, POE nonionics are adsorbed (Chapter 2) from aqueous solution via dispersion forces or hydrophobic bonding with their hydrophobic POE groups oriented toward the adsorbent and their hydrophilic POE groups toward the bath. Adsorption of the surfactant in this fashion on the substrate lowers the substrate-bath interfacial tension jSB and facilitates soil removal (equation 10.3) adsorption in this fashion on both substrate and soil produces a steric barrier that inhibits soil redeposition. 

In the cleaning process the soil is removed by either batch or bath operation. These operations differ in solvent circulation, moisture content, detergent type, and length of wash time. The batch operation uses a fixed quantity of solvent for one operation. The solvent is not circulated during the wash cycle, while it is in the bath method. The bath operation is also known as the charged system. In the bath system, 1% to 4% concentrations of detergent and water are added into the wash tank. 

In general, there are two types of soil encountered in detergency simations liquid, oily substances, and solid particulate material. Many stains on textiles such as blood, wine, mustard, catsup, and the like involve proteins, carbohydrates, and relatively high-molecular-weight pigmentlike materials that pose special problems in terms of the interfacial interactions involved. The interactions of each class of soil or stain with the solid substrate can be quite complex, and the mechanisms of soil removal may be correspondingly complex. 

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. 

Again, the optimum nonionic of choice for this application will depend upon the type of soil to be removed in the laundry process. For example, Figure 3 shows the optimum nonionic for removing typical sebum soil (body oil) in a nonbuilt heavy duty liquid. This figure shows that the optimum lies in the circle between and C., alcohol at an ethylene oxide level of 60 to oO percent. The peak of this optimum would be in the vicinity of a alcohol with 70 percent EO. This is considerably higher in EO content than the ethylene oxide optimum found for powdered laundry detergents. 

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