A Effect of Soil and Substrate

Oily Soil Nonpolar soil has been found to be removed from hydrophobic substrates (e.g., polyester) more effectively by POE nonionics than by anionics (Fort, 1968 McGuire, 1975), and investigations of this type of soil removal have concentrated on the use of POE nonionics. POE nonionics have also been found (Rutkowski, 1971) to remove oily soils and prevent their redeposition at lower bath concentrations than anionics (i.e., nonionic surfactants are more efficient for these purposes than anionics). The greater efficiency of nonionics in soil removal is presumably due to their lower CMCs in the prevention of soil redeposition it is probably due to their greater surface coverage per molecule when adsorbed on substrate and soil. 

AS mentioned previously, the term detergency as used here refers to the power of the surfactant to enhance the cleaning power of the bath liquid. Except for dry cleaning (Section IVD below), the bath liquid referred to in this discussion is water. 

As mentioned above, maximum oily soil removal from polyester substrates by POE nonionics is obtained when the PIT of the surfactant in the presence of that soil is close to the wash temperature. Since the PIT decreases with decrease in the EO content of the POE nonionic surfactant, it is to be expected that as the wash temperature is decreased, the EO content of the surfactant showing optimum oily soil removal will decrease. Thus, for single homogeneous surfactants, C12H25 (OC2H4)vOH, maximum cetane detergency at 30°C was shown by the 4EO compound (PIT = 30°C), at 50°C by the 5EO compound (PIT = 52°C), and at 65°C by the 6EO compound (Benson, 1986). The detergency of the 5EO compound at 30°C could be increased by additives that decreased its cloud point (and PIT). 

In addition, as the wash temperature decreases, the chain length of the hydro-phobic group for optimum oily soil removal appears to decrease. Thus, for oily soil removal from polyester/cotton by blends of homogeneous 3EO and 8EO nonionics having similar cloud points, the order of maximum oil removal at 70° was Ci4 = Ci2 Cio, at 38°C it was Cio = Ci2 Ci4, and at 24°C it was Ci0 Cn C 14. The difference has been ascribed to the rate of solubilization of the soil, since the rate for these surfactant blends decreases with increase in the length of the hydrophobe (Benson, 1982). 

For commercial POE nonionics with different types of hydrophobic groups of approximately equivalent chain length and the same degree of oxyethylenation (9 mol EO), the order of decreasing nonpolar soil removal from polyester/ cotton was nonylphenol adduct secondary Cn — C15 alcohol adduct linear primary C12 — C15 alcohol adduct. This was the order of decreased effectiveness of equilibrium jow reduction and of reduced rate of yow reduction (Dillan, 1984). 

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