Solubilization-emulsification mechanisms of detergency

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204 C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 Fig. 38. Removal of n-hexadecane from 65/35 polyester-cotton fabric using 0.05 wt.% aqueous solutions of a 90/10 blend of C 12E 5 and n-dodecanol [30]. Reprinted with permission of Academic Press. shown in Figs. 38 and 39 [30]. The optimum temperatures correspond quite closely to the phase inversion temperatures extrapolated to the low soil-to-surfactant ratios used in the detergency studies. In this regard, C 12E 3 was somewhat more effective than dodecanol in lowering the optimum detergency temperature. Of interest here is that the detergency results Fig. 39. Removal of n-hexadecane from 65/35 polyester-cotton fabric using 0.05 wt.% aqueous solutions of a 60/40 blend of C 12E 5 and C 12E 3 [30]. Reprinted with permission of Academic Press. differed from the behavior observed in the verticalcontacting studies in which, as discussed above, somewhat higher temperatures were required for fastest oil solubilization due to partitioning of the additive into the oil. Practical detergency applications utilize commercial alcohol ethoxylate surfactants which contain a broad range of species having varying hydrophobe lengths and levels of ethylene oxide, Detergency studies were performed in the manner described above for the single ethoxylate and ethoxylate-additive systems using commercial ethoxylates based on a blend of predominantly normal C 12-C 13 alcohols and containing an average of 3, 4 and 5 mol of ethylene oxide, respectively [85]. These materials are denoted N23-3, N23-4 and N23-5. Table 2 compares the ODTs for these systems to those of the corresponding specific alcohol ethoxylate systems having the same average structure. The ODTs of the commercial materials and their molar-average equivalents are the same in all three cases. The ODTs of the commercial systems, in fact, match the PITs for those systems with hexadecane extrapolated to very low levels of oil. The PIT data are shown in Fig. 40. Shown for comparison are the PIT vs. soil-surfactant ratio plots for C 12E 4 and C 12E 5. These are flat, indicative of the fact that the PITs for ternary specific alcohol ethoxylatewater-hydrocarbon systems are independent of the oil-surfactant ratio. Bercovici and Krussman Table 2 Correlation of PIT to optimum detergency temperature ODT Surfactant PIT (ºC) ODT (ºC) Specific ethoxylate C 12E 5 52 50 C 12E 4 31 30 C 12E 3 < 20 < 20 Broad-range Ethoxylate N23-5 51 a 50 N23-4 26 a 30 N23-3 < 20 a < 20 The data shown are for cetane removal from 65/35 polyester-cotton with 0.05% surfactant [85]. a Evaluated at cetane-surfactant ratio → 0.
C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 205 Fig. 40. PIT as a function of n-hexadecane(cetane)surfactant weight ratio for commercial (broad-range) and specific alcohol ethoxylates [85]. [86] have shown that the addition of long-chain alcohols to commercial alcohol ethoxylates, as described above for the specific ethoxylate C 12E 5, reduces the PIT and optimum detergency temperature for nonpolar soil removal by those surfactants. As with the specific ethoxylate and surfactant- additive systems, optimum soil removal with commercial nonionic surfactants occurs near the extrapolated PIT because the balanced surfactant system provides high rates of oil solubilization and low interfacial tensions. The effects of the addition of anionic surfactants to non-ionics on the relationship of soil removal to washing temperature have also been investigated [87]. In this case, the same commercial sodium alcohol ethoxysulfate mentioned in the phase behavior section (Neodol 23-3S) and the sodium salt of C 12 linear alkylbenzenesulfonate (denoted C 12LAS) were used as the anionic surfactants. As noted previously, C 12E 3 itself is not effective at removing hexadecane from 65/35 polyestercotton at temperatures between 20 and 70ºC. This result can be attributed to C 12E 3 being too hydrophobic. However, the addition of appropriate amounts of hydrophilic anionic surfactant was found to improve its performance in a 1% NaCl solution, as shown in Figs. 41 and 42. The total surfactant concentration in the Fig. 41. Removal of n-hexadecane (cetane) by C 12E 3-N23-3S blends [87]. Reprinted with permission of the American Oil Chemists' Society. Fig. 42. Removal of n-hexadecane by C 12E 3-C 12LAS blends [87]. Reprinted with permission of the American Oil Chemists' Society. washing solution in these experiments was 0.05% by weight, the same as in the non-ionic surfactant studies discussed above. Optimum detergency temperatures were increased to approximately 30ºC by the substitution for C 12E 3 of 22% and 24% N23-3S and LAS, respectively, and to approximately 50ºC by the substitution of 33% and 38% N23-3S and LAS. Consistent with these results was the finding of optimum detergency at 35ºC with a 76.5/23.5 mixture of C 12E 3 and N23-3S [24]. Thus, in contrast to the hydrophobic
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Solubilization-emulsification mechanisms of detergency

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