Liquid Oily Soil

Solubilization Solubilization has long been known to be a major factor in the removal of oily soil and its retention by the bath. This is based upon the observation (Ginn, 1961 Mankowich, 1961) that oily soil removal from both hard and textile surfaces becomes significant only above the CMC for nonionics and even for some anionics having low CMCs, and reaches its maximum only at several times the CMC. A considerable amount of research has been devoted to the removal of 

Liquid-crystalline phase or microemulsion formation between surfactant, water, and oily soil accompanies oily soil removal from hydrophobic fabrics such as polyester (Raney, 1987 Yatagai, 1990). It has been suggested (Miller, 1993) that maximum soil removal occurs not by solubilization into ordinary micelles, but into the liquid-crystal phases or microemulsions that develop above the cloud point of the POE nonionic. 

The extent of solubilization of the oily soil depends on the chemical structure of the surfactant, its concentration in the bath, and the temperature (Chapter 4, Section IB). At low bath concentrations only a relatively small amount of oily soil can be solubilized, whereas at high surfactant concentrations (10-100 times the CMC), solubilization is more similar to microemulsion formation (Chapter 8, Section II) and the high concentration of surfactant can accommodate a much larger amount of oily matter (Schwartz, 1972). With ionic surfactants, the use concentration is generally not much above the CMC consequently, solubilization is almost always insufficient to suspend all the oily soil. When insufficient surfactant is present to solubilize all the oily soil, the remainder is probably suspended in the bath by macroemulsification Antiredeposition agents, such as the POE terephthate polyesters mentioped in Section 1 above, help prevent redeposition of suspended oily soil particles. 

Macroemulsification For macroemulsification to be important, it is imperative that the interfacial tension between oily soil droplets and bath be low, so that emulsification can be accomplished with very little mechanical work. Here adsorption of surfactants at the oily soil-bath interface, with consequent lowering of the interfacial tensions, may play an important role. Emulsification was found to become a major factor when alkaline builders were added to a cleaning bath containing POE nonionic surfactant and the soil was mineral oil containing 5% oleic acid (Dillan, 1979). It is also involved in the suspension of liquefiable solid soil (Cox, 1987). 

The ability of the bath to emulsify the oily soil is, however, in itself insufficient to keep all the soil from redepositing on the substrate (Schwartz, 1972). When the emulsified oil droplets impinge on the substrate, some of them may adhere to it in part, with the adhering portion tending to assume the equilibrium contact angle, unless the latter is 180° (i.e., unless complete oily soil removal by roll-back has been attained). This is in contrast to solubilization, which can result in complete removal of the oily soil from the substrate. 

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The removal of liquid oily soils from surfaces is generally understood in terms of three basic mechanisms the roll - back of droplets of oily soil, the surfaces of which are modified by the presence of an adsorbed layer of surfactant direct emulsification of macroscopic droplets of soil and the direct solubilization of the oily soil into surfactant micelles or other interfacial phases formed (1-3). 

Removal of Liquid Soil Removal of liquid (oily) soil by aqueous baths is accomplished mainly by a roll-back or roll-up mechanism in which the contact angle that the liquid soil makes with the substrate is increased by adsorption of surfactant from the cleaning bath. 

Figure 6-3 illustrates the situation of a liquid soil adhering to a substrate in the presence of air. The reversible work to remove the liquid oily soil O from the substrate, the work of adhesion Wa (equations 6.12 and 6.13) is given by the expressions... 

Although soil retardants reduce soiling, the deposition of soil onto a textile cannot be entirely prevented. If the textile can be washed, soil-release finishes can facilitate the removal of soil considerably. The term soil release suggests a separation of soil from a fabric immersed in water, but such a spontaneous separation is possible only with liquid oily soils. Solid soils cannot separate spontaneously and require mechanical action for their removal. 

The phenomena at the liquid/liquid interface are of outstanding importance for the removal of oily soil from the surface. The interfacial tension is one of the decisive parameters in the rolling-up process. This parameter vary considerably, de-... 

We also describe the spreading of a thin surfactant laden aqueous film on a hydrophilic solid, i.e., one in which the dynamic contact angle is small. In such a case, the osmotic pressure gradient generated by the nonuniform distribution of surfactant micelles in the liquid film can drive fhe spreading process. The mofivation for this study comes from the need to understand the detergent action involved in the removal of an oily soil from a soiled surface. This paper presents an overview of our recent work. 

The surface tensions of materials prepared with are some of the lowest attainable with the reagents commonly available, which is why many carpet and textile repellents are based on the chemistry of perfluoroalkyl chains. For example, a nylon-6,6 carpet would be wetted by oily soils, which, according to Eq. (4), would be difficult to remove. The presence of a FA coating on die fiber lowers its surface tension and repels the oil contaminant. In general, a liquid dial has a high surface tension will not wet a solid with low surface tension (e.g., water on PTFE). The converse is also true. A low-surface-tension liquid will wet a high surface tension solid (e.g., hexadecane on nylon-6,6). 

Figure 3.12 Two liquids A (detergent) and B (oily soil) on a solid surface (a) separated and (b) in contact, yA and yB = wetting tensions, yAB = interfacial tension, R = interfacial wetting tension [3].

Derivatives of nonylphenol up to about the 12-mol ethoxylate are liquid at ambient temperature and do not require heated storage. They are used for reducing oil-water interfacial tension and are excellent for removing oily soils. The major drawback is the biodegradation resistance of the benzene ring, which limits the use to industrial applications in which waste can be treated before any discharge to waterways. However, their relative cheapness has maintained their use in some formulations destined for the household market in certain parts of the world. 

Nature of the soil Oily soil or particulate soil, hydrophobic or hydrophilic, liquid or solid... 

A low interfacial tension between the oil and the wash liquid will favour oily soil release. 

Since the 1990s enzyme mixtures have been commonly used in heavy-duty liquids. Most products contain a minimum of a protease for removal of proteinaceous soils and an amylase to facilitate starchy food-based soil removal. Some products contain lipases for degrading fatty or oily soils and cellulases to improve fabric appearance by cleaving the pills or fuzz formed on cotton and synthetic blends. 

When insufficient surfactant is present to solubilize all of the oily soil, the remainder can be suspended in the bath by emulsification. An emulsion is a thermodynamically unstable suspension of liquid particles in a second liquid phase. Emulsion particles are much larger than micelles, about 500 nm or greater. The fact that emulsions are not thermodynamically stable is irrelevant since the dirty suspension is drained down the sink and the dishes are rinsed. 

FIG. 8.24 Clay/oily soil redeposition of typical HDLDs. A, B, C, and D represent commercial liquid detergents, ranging from low-cost to premium brands, with and without the addition of a low-molecular-weight polyacrylate (pAA) homopolymer. 

The soil found on hair can be classified into two types solid particulate and liquid or oily soil. Solid soils can come from hair care products or from the environment. Examples of the former might be polymeric resins or antidandruff agents, while the latter includes airborne particles carried by air currents, dust, carbon particles in the form of soot or clays, or rubber abraded from automobile tires [113-116],... 

Oily soils containing amphiphilic species, such as fatty acids or fatty alcohols, can also be removed from substrates as a result of the formation of liquid crystal or mesomorphic phases between the amphiphile and a detergent. The liquid crystals are then broken up by subsequent osmotic penetration by water [140-142], Removal of solid soils by mesophase formation can be accelerated by increasing the temperature. This has been reported for stearyl alcohol [143] and for lauric, palmitic, and stearic acids [128, 129] and is likely due at least in part to the increased penetration of the soils at higher temperatures [128,129,143],... 

On the other hand, if the surfactant has appreciable solubility in both liquids, then very different factors may determine the value of the interfacial tension. Although low liquid-liquid interfacial tension is important in promoting emulsification (Chapter 8) and in the removal of oily soil by detergents (Chapter 10), advances in our knowledge of the factors governing the reduction at that interface stem from the intense interest in enhanced oil recovery by use of surfactant solutions. 

When surfactants of the proper structure are present in the bath, they will adsorb at the substrate-bath (SB) and liquid soil-bath (OB) interfaces in such a fashion (i.e., with the hydrophilic group oriented toward the aqueous bath) as to reduce jSB and Job, with consequent reduction in the work to remove the soil from the substrate. Reduction in ySB will also cause a decrease in cos 0 and an increase in 0, resulting in the observed roll-back of the liquid soil. Many investigators of oily soil removal,... 

If the contact angle is 180°, the bath will spontaneously completely displace the liquid soil from the substrate if the contact angle is less than 180° but more than 90°, the soil will not be displaced spontaneously but can be removed by hydraulic currents in the bath (Figure 10-2) (Schwartz, 1972). When the contact angle is less than 90°, at least part of the oily soil will remain attached to the substrate, even when it is subjected to the hydraulic currents of the bath (Figure 10-3) (Schwartz, 1971, 1972), and mechanical work or some other mechanism (e.g., solubilization, see below) is required to remove the residual soil from the substrate. 

Unlike the experiments carried out below the cloud point temperature, appreciable solubilisation of oil was observed in the time frame of the study, as indicated by upward movement of the oil-microemulsion interface. Similar phenomena were observed with both tetradecane and hexadecane as the oil phases. When the temperature of the system was raised to just below the PITs of the hydrocarbons with C12E5 (45°C for tetradecane and 50°C for hexadecane), two intermediate phases formed when the initial dispersion of Li drops in the water contacted the oil. One was the lamellar liquid crystalline phase La (probably containing some dispersed water). Above it was a middle-phase microemulsion. In contrast to the studies below the cloud point temperature, there was appreciable solubilisation of hydrocarbon into the two intermediate phases. A similar progression of phases was found at 35°C using n-decane as the hydrocarbon. At this temperature, which is near the PIT of the water/decane/C Es system, the existence of a two-phase dispersion of La and water below the middle-phase microemulsion was clearly evident. These results can be utilised to optimise surfactant systems in cleaners, and in particular to improve the removal of oily soils. The formation of microemulsions is also described in the context of the pre-treatment of oil-stained textiles with a mixture of water, surfactants and co-surfactants. 

The most frequently discussed topic in washing is the role of solubilisation processes. Many investigators [76] attract attention to the fact that the surfactant concentration in a washing solution is much lower than CMC, and in this connection, solubilisation of oils is principally excluded due to absence of surfactant micelles. At the same time, the review of recent works [85, 86] show that solubilisation can play a dominant role both in washing fabrics and in the removal of soils from solid surfaces. These views are based on the following mechanisms. Surfactants adsorb at w/o interfaces under formation of densely packed adsorption layers which leads to a high local surfactant concentration as compared with the rather low concentration in the washing solution. After that, noticeable penetration of water into the oily soil is possible, under formation of liquid-crystal phases. Then, mesomorphic phases are swelled and destroyed under the formation of emulsion droplets. 

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