Solubilization-emulsification mechanisms of detergency

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208 C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 decane was consistently higher than that of triolein at all temperatures. The regions of optimum detergency occur near the PITs of the surfactants with the oil blend. The preferential removal of hexadecane can be attributed to the higher solubility of hexadecane in the middle-phase microemulsion D (see Table 1). The removal of blends of hexadecane with oleyl alcohol and oleic acid by 0.05% solutions of alcohol ethoxylates has also been studied [12]. These binary soil mixtures are models of sebum-like soils containing both non-polar and polar fractions. In general, somewhat more hydrophilic surfactants are required to obtain high removal of these soils compared to the optimum surfactants for nonpolar hexadecane removal. Results for the removal of hexadecane from 9/1 and 3/1 blends of hexadecane and oleyl alcohol are shown in Figs. 47 and 48. N25-9 is a broad-range commercial ethoxylate based on a predominantly linear C 12-C 15 alcohol and containing an average of nine ethylene oxide (EO) units. In the case of the 9/1 soil at 20ºC, detergency was found to increase with decreasing EO content of the pure non-ionic surfactants, while the reverse trend was true at the higher temperatures. For both soils, optimum detergency occurred over a temperature range below the cloud points of the surfactants, behavior which contrasts markedly Fig. 47. Removal of n-hexadecane for mixed 9/1 n-hexadecane-oleyl alcohol soil [12]. Reprinted with permission of the American Oil Chemists' Society. Fig. 48. Removal of n-hexadecane for mixed 3/1 n-hexadecane-oleyl alcohol soil [12]. Reprinted with permission of American Oil Chemists' Society. markedly with the results discussed above for hydrocarbon and triolein soils. The cleaning efficiency of the commercial broad-range ethoxylate is almost identical at all temperatures to that of the specific ethoxylate (C 12E 8) having nearly the same cloud point temperature, indicating, once again, that surfactant partitioning effects in the detergency studies are negligible. The effect of the soil composition on soil removal can be seen more clearly in Fig. 49. While the detergency peaks near 80ºC with the pure hexadecane soil, good detergency is obtained at much lower temperature with the Fig. 49. Effect of oleyl alcohol content on n-hexadecane removal [12]. Reprinted with permission of the American Oil Chemists' Society.
C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 209 mixed soils. Maximum detergency is reached near 40ºC with 10% oleyl alcohol in the soil while high levels of cetane removal are attained down to 20ºC with 25% oleyl alcohol present. The temperatures at the lower limit of the plateaus in detergency are the respective phase inversion temperatures. For C 12E 7, PIT values can be obtained from the curves in Fig. 15. Above the PIT, soil removal remains at a high level until the cloud point of the surfactant is reached. As implied in the oil drop-contacting section, the formation of an intermediate liquid crystalline phase plays the key role in the soilremoval process in the plateau regime. The relative amount of polar soil also affects the rate of soil removal. Despite being removed at a comparable level to that of the 3/1 cetane-oleyl alcohol soil after 10 min at 50ºC, the 9/1 soil is actually removed much more quickly, as indicated in Fig. 50. This very fast removal can be attributed to that soil having a PIT of approximately 50ºC with C 12E 7. A 1/1 cetane-oleyl alcohol soil is removed very slowly at 50ºC, although a high level of removal is ultimately attained. Removal of the hexadecane soil reaches a plateau at a lower level since the washing temperature is well below the optimum detergency temperature for its removal by C 12E 7, i.e. approximately 80ºC. Fig. 50. Kinetics of n-hexadecane removal for mixed n-hexadecane-oleyl alcohol blends [12]. Reprinted with permission of the American Oil Chemists' Society. Similar results to those described for hexadecane-oleyl alcohol soils were obtained for hexadecane-oleic acid soils having the same ratio of nonpolar and polar constituents. These studies were performed in the absence of triethanolarnine to insure that the oleic acid was in the non-ionized state. Also, the oleic acid was tagged with 14C-labeled material to allow measurement of its removal as well as that of hexadecane. The results for 3/1 cetane-oleic acid soil are shown in Fig. 51. High levels of soil removal were found over a wide temperature range from 20ºC to the cloud point of the surfactant. As with the oleyl alcoholcontaining soils, optimum removal was found between the PIT and cloud point temperature. Interestingly, the data show that the removal of oleic acid paralleled that of cetane, although at levels 10-20% higher. This behavior results from the higher ratio of oleic acid to hexadecane found in the intermediate liquid crystalline phase compared to that in the original soil. Presumably, preferential removal of oleyl alcohol would have been found in the hexadecane-oleyl alcohol experiments if the alcohol had been radioactively tagged. 11. Discussion As shown above, maximum removal of liquid hydrocarbon soil from synthetic fabrics in non- Fig. 51. Oil removal for mixed 3/1 n-hexadecaneoleic acid soil [12]. Reprinted with permission of the American Oil Chemists' Society.
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Solubilization-emulsification mechanisms of detergency

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