Solubilization-emulsification mechanisms of detergency

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202 C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 phase, whose films are known to be slightly lipophilic, cannot persist, and the lamellar phase forms as myelinic figures. Since the triolein-rich drop does not dissolve, it may well be that the system enters a four-phase region at the time the myelinic figures develop. For a drop containing 75% oleyl alcohol behavior was more complex. Two intermediate liquid phases formed at various times during the experiment and greater solubilization was observed [61]. Ultimately, the liquid crystalline phase was seen as well. When the drop is pure oleyl alcohol, no D' phase is seen, and the first intermediate phase is the lamellar liquid crystal. It develops as many short myelinic figures, the appearance being more similar to that of Fig. 35 for hydrocarbon-oleyl alcohol drops than to that of Fig. 33 for the C 12E 5-water-oleyl alcohol system. 8. Fabric detergency test methods Laboratory evaluations of laundry detergency can range from use of an actual washing machine with a capacity of several gallons to use of a Terg-O-Tometer mini-laundry machine. The Terg-0-Tometer is a washing machine which replicates on a small scale the cleaning action of an agitatortype washing machine [77]. The capacity of a single Terg-O-Tometer pot is approximately 11. The temperature can be controlled quite accurately through the use of a water bath surrounding a bank of four or six pots. The small size of a Terg-O-Tometer allows rapid comparative studies of detergent formulations under the same washing conditions. Also, formulations containing expensive ingredients, e.g. pure alcohol ethoxylates, or experimental surfactants of limited quantity, can be evaluated at reasonable costs. For these reasons, the use of Terg-O-Tometer machines in detergent research laboratories has become quite common. The measurement of soil removal from fabrics can be performed in several ways [78]. The most straightforward technique involves visual inspection for determination of cleanliness. More sophisticated techniques involve the use of spectrophotometry, chemical analyses, and radiotracer methods. As with visual inspection, the measurement of light reflectance from fabric does not quantify actual soil removal but depends on factors such as the distribution of soil on the fabric, and the particle sizes. Analyses of weight gain or loss through the chemical extraction of soils from the fabric as well as radiotracer methods both yield measurements of actual soil removal and do not depend on the change of appearance of the fabric. Although not representative of real-world visualization of cleanliness, both techniques provide complementary information to reflectance measurements and are more useful for mechanistic studies. Specific advantages of the radiotracer detergency method are given elsewhere [79,80]. This method makes use of mildly radiolabeled soils for highly sensitive quantitative determination of soil removal by simple radiochernical techniques. Several radioisotopes may be used as labels. Generally, polar oily soils such as alcohols and acids are tagged with small amounts of carbon-14 labeled material. The use of two labels in a soil such as artificial sebum, which contains both polar and non-polar components, allows the removal of both types of soil to be monitored simultaneously. The recipe for such a labeled artificial sebum has been given elsewhere [80]. Radiolabelled particulate and protein soils have also been developed and utilized [80]. The Shell Development Company has utilized a radiotracer detergency method for many years to evaluate laundry detergents and to study the fundamental nature of oily soil removal [81,82]. In the case of oily soils, a 4-in square fabric swatch is soiled with 28 mg of radiolabeled oil. The soil is applied to the fabric in a toluene solution, which is allowed to air dry. The swatch is washed under controlled conditions in a Terg-0-Tometer. Aliquots of wash water are removed for radioactive counting, with the level of soil remaining on the swatch determined by difference. In addition to the sebum oil described above, oily soils which have been commonly utilized include tritium-labelled hexadecane (cetane), 1/1 hexadecane-squalane
C.A. Miller and K.H. Raney/Colloids Surfaces A: Physicochem. Eng. Aspects 74 (1993) 169-215 203 (a C 30 branched hydrocarbon) and triolein. Also, hydrocarbon-fatty acid (or alcohol) soils of varying composition have been studied in which both carbon- 14 and tritium labels are utilized to allow the discrimination of removal of both components. The following are results of fundamental detergency studies using some of these soils, which were performed to allow correlation to the phase behavior and dynamic contacting studies described above. 9. Fabric detergency - non-polar hydrocarbon soils Results of radiotracer detergency studies of removal of hexadecane from 65/35 permanent press polyester-cotton fabric are shown in Fig. 37 [18]. This soil can be considered a model for non-polar hydrocarbon-based soils such as lubricating oils. The washing solutions contained 0.05 wt.% surfactant, resulting in a fabric-to-soil weight ratio of Fig. 37. Removal of n-hexadecane from 65/35 polyester-cotton fabric using 0.05 wt.% aqueous solutions of C 12E 4 and C 12E 5 [18]. The arrows show the cloud point temperatures of the surfactants. Reprinted with permission of Academic Press. 40/1 and a surfactant-to-soil ratio of 9/1. Triethanolamine (50 ppm) was included as a buffer, and no water hardness was present. The washing time in the Terg-0-Tometer was 10 min. Of particular interest in these studies was the effect of temperature and non-ionic alcohol ethoxylate surfactant structure on the levels of soil removal. As shown in Fig. 37, a strong dependence on temperature was observed with the highest levels of soil removal occurring almost 200C above the cloud point of the washing solution, a temperature regime in which the washing solution structure is a liquid crystalline dispersion. In fact, the optimum detergency temperature (ODT) in each case occurred very near the PIT of the water-surfactant-hexadecane system. Although not shown in Fig. 37, very poor detergency occurred in the temperature range of interest with C 12E 3 as the surfactant. Also, when a 1/1 by weight mixture of hexadecane and squalane was used as the soil, a similar peak in performance was found for each surfactant near its PIT for the mixed soil. These PITs were approximately 7ºC higher than the corresponding values for hexadecane alone, i.e. 37 and 58ºC versus 30 and 52ºC. The equivalence of the PIT and ODT in this type of detergency system has been confirmed by the work of Schambil and Schwuger [22] as well as Solans et al. [83]. Also, the same correspondence has been found for the removal of hydrocarbon by the same surfactant from 100% polyester fabric [84]. The high levels of soil removed near the PIT can be attributed to the ultralow interfacial tensions achieved near that temperature, and to the high rates of oily soil solubilization into middle-phase microemulsions, as was visualized in the dynamic contacting studies described previously. When the detergent properties of mixtures of C 12E 5 with the hydrophobic additives C 12E 3 and n-dodecanol (C 12E 0) were studied, optimum detergency was found at temperatures lower than the ODT for C 12E 5 alone but somewhat higher than the ODT for C12E4. Detergency data for the two additive systems, which exhibited the same cloud point as C 12E 4, are
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Solubilization-emulsification mechanisms of detergency

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