Cold water detergency studies using radiolabeled soils

The effects of single and multiple washing and of resoiling-rewashing of cotton and synthetic fabrics have been studied in Tergotometer tests at various levels of temperature, detergent concentration and water hardness. The soiling mixture consisted of a seven component sebum tagged with tritium and carbon-14; in some tests gammaray emitting Kaolinite clay was also used. Linear primary alcohol ethoxylate (LAEO) and linear alkylbenzene sulfonate (LAS) were used for surfactant type comparisons. In single wash tests in both hot and cold water, LAEO was generally more effective than LAS in removing sebum. This was particularly noticeable at low product concentration where insufficient sodium tripolyphosphate was present to sequester the water hardness. A 1/1 blend of the two surfactants approached LAEO in performance. The nonpolar sebum fraction was more readily removed from Dacron or nylon in cold water; otherwise, detergency was generally better at high temperatures. In rewash tests, using labeled lube oil, cholesterol and clay, a progressive increase in soil removal was found during five wash cycles. The nonpolar lube oil component was the most difficult to remove from permanent press Dacron-cotton (PP), but was more readily removed from cotton. The more polar cholesterol and especially the clay were more easily removed from PP. LAEO gave better detergency both hot and cold than LAS, especially in hard water. On cotton swatches resoiled with sebum after each wash the residual sebum content was still increasing after five cycles. With PP in soft water, a steady state was reached after three to five cycles. Soil buildup was greater as hardness increased and as wash temperature and active matter concentration decreased, and was generally greater on cotton than on PP. LAEO allowed appreciably less soil buildup than did LAS especially at low concentration in hard water, indicating a reduced requirement for sodium tripolyphosphate. Presented before the AOCS Meeting, New Orleans, April 1970.     

Microemulsion formation and detergency with oily soils: II. Detergency formulation and performance

In part I of this series (J. Surfact. Deterg. 6, 191–203, 2003), the mixed surfactant system of sodium dioctyl sulfosuccinate (AOT), alkyl diphenyl oxide disulfonate (ADPODS) and sorbitan monooleate (Span 80) was shown to form Winsor type I and type III microemulsions with hexadecane and motor oil. In addition, high solubilization and low interfacial tension were obtained between the oils and surfactant solutions both in the supersolubilization region (Winsor type I system close to type III system) and at optimal conditions in a type III system. In the present study, this mixed surfactant system was applied to remove oily soil from fabric (a polyester/cotton blend), and detergency results were correlated to phase behavior. Dynamic interfacial tensions were also measured between the oils and washing solutions. In the supersolubilization and in the middle-phase regions (type III), much better detergency performance was found for both hexadecane and motor oil removal than that with a commercial liquid detergent product. In addition, the detergency performance of our system at low temperature (25°C) was close to that obtained at high temperature (55°C), consistent with the temperature robustness of the microemulsion phase behavior of this system.     

Cold Water Detergency of Triacylglycerol Semisolid Soils: The Effect of Salinity,Alcohol Type,and Surfactant Systems

Cold water detergency of triacylglycerol semisolid soils is much more challenging than liquid vegetable oils due to poorer interaction between surfactants and semisolid soil. This research seeks to improve the removal efficiency of semisolid soils below their melting points using surfactant-based formulations containing different alcohol additives. To this end, cold water detergency of solid coconut oil and solid palm kernel oil was investigated in various surfactant/alcohol systems, including single anionic extended surfactants, single nonionic alcohol ethoxylate surfactants, and a mixture of anionic surfactants. A series of alcohols (2-butanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol) were added to the surfactant formulations to investigate cold water detergency improvement. While cold water detergency using surfactants alone was poor, it was considerably improved when optimum salinity (S*) and 1-heptanol, 1-octanol, or 1-nonanol were introduced to the studied surfactant formulations. The maximum detergency of solid coconut oil exceeded 90% removal in the 0.1 w/v% C_14-15-8PO-SO₄Na/0.2 w/v% 1-octanol/4 w/v% NaCl system (a final optimized surfactant system) at a washing temperature of 10°C versus 22.9 ± 2.2% in the surfactant alone (not at optimum salinity and no additive). Further analysis showed that improved cold water detergency using surfactant/intermediate-chain alcohols/NaCl could be correlated with high wettability (low contact angle) as well as favorable surfactant system-soil interaction as observed by lower interfacial tension values. In contrast, the improved cold water detergency was observed to be independent of dispersion stability. This work thus demonstrates that surfactant system design, including additives, can improve cold water detergency of semisolid soils and should be further explored in future research.     

Microemulsion Formation and Detergency with Oily Soil: V. Effects of Water Hardness and Builder

In this study, the impact of water hardness and builder on the phase diagrams of motor oil microemulsions and the detergency of oil removal from a polyester/cotton blend was investigated. Water hardness and builder were found to have insignificant effects on the microemulsion phase diagram with motor oil. A mixed surfactant system of two parts C_14–15(PO)₃SO₄Na, and 98 parts C_12–14H_25–29O(EO)₅H of the total actives at 4% salinity was used to study the effect of water hardness and builders sodium tripolyphosphate (STPP) or ethylenediaminetetraacetic acid (EDTA) on detergency at 30 °C at a total active concentration of 0.3%. This formulation is in the Winsor Type III microemulsion regime. The microemulsion-based formulation resulted in better detergency than a leading commercial liquid laundry detergent at all concentrations up to 0.5% actives. The microemulsion-based formulation showed a plateau in detergency at >80% oil removal above 0.1% actives. The total oil removal decreased with increasing water hardness while the interfacial tension increased. When hard water was used in laundering, the total oil removal improved with increasing concentrations of STPP or EDTA up to stoichiometric levels, with STPP being slightly more effective than EDTA on a molar basis. Even high builder concentration could not improve hard water detergency to that of soft water. A significant fraction of oil removal occurred in the rinse steps vs. the wash step. Increasing water hardness reduced this fractional oil removal in the rinse steps, but it was still over half of total oil removal at 1,000 ppm water hardness.

Surfactants and protocols to induce spontaneous emulsification and enhance detergency

In this study the presence of an oil-soluble nonionic surfactant, Brij 30 (polyoxyethylene-4 lauryl ether), in an oil stain, or its addition to the stain through an oil-based solution or water-based mixture is shown to enhance, to a great extent, the spontaneous removal of the stain from a polyester fabric by inducing rollback and spontaneous emulsification phenomena. These findings lead to potential applications of Brij 30 as laundry pre-spotters for enhancement of the removal of tough stains. The effect of three key factors, namely, the surfactant type, the surfactant concentration, and the surfactant application protocol, on the effectiveness of spontaneous detergency was analyzed via ultraviolet-visible spectroscopy. The test fabrics were soiled with a stain composed of mineral oil plus orange OT dye [1-(o-tolylazo)-2-naphthol]. The results showed that all three factors were important for effective detergency. Brij 30 removed more than 80% w/w of the stain, whereas sodium dodecyl sulfate removed less than 24% w/w, and Brij 35 (polyoxyethylene-23 lauryl ether) was ineffective, removing less than 1% w/w. It was also observed that a low threshold concentration of Brij 30, approximately 0.2 mM, was required to spontaneously remove the oil stain, and that higher concentrations did not cause a significant enhancement of the effectiveness of soil removal. Brij 30 completed the detergency effect in less than 1 min, which may have beneficial implications regarding reduced energy consumption. Video microscopy studies revealed that at low Brij 30 surfactant concentrations, the mechanism for spontaneous oil removal proceeded predominantly via a rollback mechanism and that at higher concentrations, a spontaneous emulsification mechanism became progressively more important.     

Microemulsion-Based Vegetable Oil Detergency Using an Extended Surfactant

This work examined the use of a single extended surfactant in the microemulsion-based detergency of vegetable oils. The results showed that good canola oil detergency (>80%) was achieved at 25 °C using a single extended surfactant (C_14,15–8PO–SO₄Na) at concentrations as low as 125 ppm, i.e., significantly lower than the surfactant concentration range of 500–2,500 ppm reported in other microemulsion-based detergency work. It was found that the maximum detergency (95%) was achieved in the type II microemulsion region. These results demonstrate that the microemulsion-based extended surfactant formulation is a promising approach for vegetable oil detergency at low temperature.     

Microemulsion Formation and Detergency with Oily Soil: IV. Effect of Rinse Cycle Design

The objective of this work was to apply a microemulsion-based formulation for the removal of motor oil in laundry detergency at low salinity. To produce the desired phase behavior, three surfactants were used: alkyl diphenyl oxide disulfonate (ADPODS), sodium dioctyl sulfosuccinate (AOT) and sorbitan monooleate (Span 80). The mixed surfactant system of 1.5% ADPODS, 5% AOT and 5% Span 80 (13 parts ADPODS, 43.5 parts AOT, and 43.5 parts Span 80 of the total actives) was found to form a middle phase microemulsion (Type III) at a relatively low salinity of 2.83% NaCl. When this formulation was diluted, detergency performance increased with increasing total surfactant concentration and leveled off above about 0.1% total actives on the three types of fabrics studied (pure cotton, 65/35 polyester/cotton blend, and pure polyester). Detergency was found to improve with increasing hydrophilicity of the fabric with cotton being cleanest after washing and polyester the most difficult to clean. To achieve a specified oil removal, less rinse water can be used if a higher number of lower-volume rinses are employed. An interesting characteristic of microemulsion-based formulations is that a substantial fraction of oil removal occurs during the rinse cycle. In this work, this removal is shown to be due to the low oil/water interfacial tension during initial rinsing and is therefore strongly correlated to residual surfactant concentration in the rinse steps. As a result, the number of rinses and the volume of water per rinse can profoundly affect detergency in these systems.

Optimized Microemulsion Systems for Detergency of Vegetable Oils at Low Surfactant Concentration and Bath Temperature

Triglycerides and vegetable oils are amongst the most difficult oils to remove from fabrics due to their highly hydrophobic nature; this is all the more challenging as cold water detergency is pursued in the interest of energy efficiency. Recently, extended surfactants have produced very encouraging detergency performance at ambient temperature, especially at low surfactant concentration. However, the salinity requirement for extended surfactants was excessive (4–14%) and there is limited research on extended‐surfactant‐based microemulsions for cold water detergency (below 25 °C). Therefore, extended‐surfactant‐based microemulsions are introduced in this study for cold temperature detergency of vegetable oils with promising salinity and surfactant concentration. The overall goal of this study is to explore the optimized microemulsion formulations with low surfactant and salt concentration using extended surfactant for canola oil detergency at both 25 and 10 °C. It was found that microemulsion systems achieved good performances (higher than those of commercial detergents) corresponding to IFT value 0.1–1 mN/m with the surfactant concentration as low as 10 ppm and 4% NaCl at 25 °C, and as low as 250 ppm and 0.1% (1000 ppm) NaCl at 10 °C. In addition, microemulsion systems were investigated with a different salt (CaCl₂, or water hardness, versus NaCl) at 10 °C, demonstrating that 0.025% CaCl₂ (250 ppm) can produce good detergency; this is in the hardness range of natural water. These results provide qualitative guidance for microemulsion formulations of vegetable oil detergency and for future design of energy‐efficient microemulsion systems.     

Radiotracer detergency testing in a horizontal-axis washing machine

Proposed regulations by the U.S. Department of Energy have spurred development of energy-efficient washing machines that utilize less water and operate with lower energy requirements than conventional machines. As a result, major changes in washing machine design are required. Among expected changes are increased use of a horizontal-axis wash tub, an increase in fabric-to-wash liquor ratio, greater surfactant concentration in the wash water, and reduced average washing temperatures. As a result, surfactants used in future detergent formulations will be required to clean effectively in this new regime while producing minimal foam. Detergency test methods utilizing radiotracer techniques have been developed to study the detergency process in energy-efficient washing machines. Detergency and redeposition of radiolabeled oily soils can be determined in a full-size horizontal-axis washing machine through scintillation counting of wash and rinse water samples. Measurements can be made after each wash process step and combined to determine total cycle detergency. This is a distinct advantage over conventional reflectance detergency methods where only total detergency at the end of the entire washing and rinsing process can be conveniently measured. Also, in contrast to indirect reflectance methods, measurements of absolute soil removal are obtained with the radiotracer method. In this study, soil redeposition was determined by measuring residual radioactivity on fabric swatches and then performing a material balance on the oily soil.     

Enhanced triolein removal using microemulsions formulated with mixed surfactants

In previous work, a microemulsion-based formulation approach yielded excellent laundry detergency with hydrophobic oily soils hexadecane and motor oil. In this work, the same approach is used in detergency of triolein, which is a model triglyceride, some of the most difficult oils to be removed from fabric. The linker concept was applied in formulation of the microemulsion system. Three different surfactants were used: (i) dihexyl sulfosuccinate, an ionic surfactant with a moderate hydrophile-lipophile balance (HLB); (ii) secondary alcohol ethoxylate, a lipophilic nonionic surfactant with a very low HLB; and (iii) alkyl diphenyl oxide disulfonate (ADPODS), a hydrophilic anionic surfactant with a very high HLB. The phase behavior and interfacial tension (IFT) of the surfactant systems were determined with different concentrations of ADPODS. The results indicate that as the HLB of the system increases, a higher salinity is required to shift the phase transition from Winsor Type I to Type III to Type II. The three formulations at different salinities were used in detergency experiments to remove triolein from polyester/cotton sample fabric. The results showed that there were two peaks of maximum detergency in the range of salinity from 0.1% to 10% NaCl. The higher the hydrophilicity of the system, the higher the salinity required for maximum detergency. The results of the dynamic IFT and the detergency performance from two rinsing methods lead to the hypothesis that one of these maxima in detergency results from a spreading or wetting effect. The other maximum in detergency is believed to be related to ultralow IFT associated with oil/water middle-phase microemulsion formation. Triolein removal exceeding 80% was attained, validating the microemulsion approach to detergency.     

Effect of Surfactant Systems,Alcohol Types,and Salinity on Cold-Water Detergency of Triacylglycerol Semisolid Soil. Part II

Our prior work found that detergency of coconut oil was relatively poor using C_14-15-8PO-SO₄Na alone but showed promising improvement with the presence of linear intermediate-chain alcohols (C7–C9 alcohols) in the surfactant formulation. The maximum detergency exceeded 90% removal using 0.1 w/v% C_14-15-8PO-SO₄Na/0.2 w/v% 1-octanol/4 w/v% NaCl (final optimized surfactant system) at 10 °C. The current work thus seeks to further investigate surfactant formulations capable of providing improved detergency performance. Different 50% linear anionic extended surfactant structures (LC_14-15-8PO-SO₄Na, LC_14-15-8PO-3EO-SO₄Na, and LC_14-15-8PO-7EO-SO₄Na) were compared with the branched C_14-15-8PO-SO₄Na previously studied. Detergency of coconut oil using C_14-15-8PO-SO₄Na at 8 w/v% NaCl (S*) still performed more effectively than these new surfactant systems. The addition of octanol as a detergency additive was further studied, and it showed that S* reduced from 8 w/v% NaCl to 4 w/v% NaCl for 1-octanol and to 2 w/v% NaCl for 2-octanol and 2-ethyl-hexanol in the C_14-15-8PO-SO₄Na surfactant formulation. Coconut oil removal significantly improved detergency from roughly 49% for no alcohol with 8 w/v% NaCl, to 83% for 2-ethyl-hexanol with 2 w/v% NaCl, to 95% for 1-octanol with 4 w/v% NaCl, and to 98% for 2-octanol with 2 w/v% NaCl. Further studies on octanol concentration showed that decreasing 1-octanol from 1.2% (90 mM) to 0.2% (15.3 mM) and 2-octanol from 1.2% (90 mM) to 0.5% (38.5 mM) still maintained detergency over 90% removal. In this work, cold-water detergency was found to correlate with low interfacial tension above the melting point, improved wetting of the semisolid soil, and oil solubilization in surfactant micelles.     

Design of Experiments to Evaluate the Detergency of Surfactants on Fatty Soils in a Continuous-Flow Device

Detersive processes are complex systems involving a great number of variables. To determine the effect of these variables on the washing of hard surfaces and fatty soils is the object of this work. The statistical design of experiments has been used to evaluate the influence of factors such as temperature, soil concentration and surfactant concentration on detergency. The experimental trials have been made in a continuous-flow device where the soiling agent is confined in a column filled with borosilicate glass spheres. Solutions of the commercial surfactant Berol^© LFG61 (a mixture of alkylpolyglucosides and fatty-alcohol ethoxylates) have been employed as the wash bath. Both the design of experiments and the continuous experimental system used proved to be an effective tool for detecting the key variables in the cleaning process. Expressions were developed to simulate detergency levels as a function of the variables assayed, always inside the experimental domain. In the trials with oleic acid as the soiling agent, it was found that the temperature and soil concentration were the most important variables to take into account, while the surfactant concentration was not a significant variable. When a semi-solid mixture of different fatty acids was employed, all the variables assayed proved significant, with high detergency values being reached by combining temperature and surfactant concentrations. Results clearly show that the effectiveness of the surfactant used is influenced by the type and concentration of the soil and thus the intended application of the product being developed should be taken into account when designing detergent formulas.     

Microemulsion formation and detergency with oily soils: III. Performance and mechanisms

The objective of this study was to investigate the correlation between oily soil removal efficiency and low oil-water interfacial tension (IFT) generated by microemulsion formation. A mixture of sodium dioctyl sulfosuccinate, alkyl diphenyl oxide disulfonate, and sorbitan monooleate was selected as a detergent formulation to evaluate detergency performance for two highly hydrophobic oils: hexadecane and motor oil. The maximum detergency corresponds to formation of a Winsor Type III microemulsion as well as to the supersolubilization region, which is a Winsor Type I microemulsion close to the Winsor Type III region. In addition, the oil removal in the rinse step is almost as high as that in the wash step for both regions. We propose the following mechanism to explain these results: During the wash step, the contact angle of the oil on the fabric surface is progressively increased, resulting in the detachment of the oil droplets. However, owing to the very low IFT, the spreading effect is dominant, thereby causing incomplete oil removal. During the subsequent rinse step, the IFT increases, passing through a composition at which the rollup mechanism causes additional oil removal. These results demonstrate that microemulsion formation and the resulting IFT reduction are important mechanisms in oily soil detergency.     

Measuring detergency of oily soils in the vicinity of phase inversion temperatures of commercial nonionic surfactants using an oil-soluble dye

We have used a simple technique to measure the detergency of model oily soil from 63∶35 blended polyester/cotton fabrics using solutions of commercial linear lauryl alcohol ethoxylates in the vicinity of their phase inversion temperatures (PIT). The method involves incorporation of an oil-soluble dye in the oily soil, and measurement of reflectance at an appropriate wavelength directly on the fabric before and after wash. This technique was validated for our systems, and it provides an additional visual cue for the efficiency of soil removal. Hexadecane, which represents the linear hydrocarbon part of sebum (typical soil encountered in detergency) and has been widely studied in the literature, was used as the model oily soil. Maximal detergency occurs as a function of washing temperature at approximately 35, 62, and 80°C for ethoxylates with four, five, and six moles of ethylene oxide (C₁₂EO₄, C₁₂EO₅, and C₁₂EO₆), respectively. The oil/water interfacial tension, measured using the spinning drop method, exhibits corresponding minima and complements the detergency results. Addition of sodium carbonate, a salting-out electrolyte, decreases the optimal detergency temperature (ODT) of C₁₂EO₅, shifting its behavior toward C₁₂FO₄ whereas addition of anionic surfactant increases the ODT of C₁₂FO₅, mimicking the behavior of a higher ethoxylate.     

Are theoretical surface chemistry measurements really practical?

The principles and concepts of surface chemistry can be of enormous aid in the application of surfactant chemicals to practical cleaning and foaming problems. The use of surfactants for foam stability was seen to be dependent on rheological properties of the foam (bulk and surface viscosity) and to the energetics of the adsorbed surfactant monolayer (area/surfactant molecule, monolayer clasticity modulus, rate of monolayer spreading and rate of surfactant adsorption into the interface). From these principles, an equation predicting foam volume in the presence or absence of soil was derived and found to be in good agreement with experiment. In detergency, the performance was dictated by the thermodynamic work of adhesion between the soil and substrate. The adhesion was a function of surface properties (soil/water interfacial tension and soil/water/substrate). The role of agitation in detergency was shown to be that energy which was needed to overcome the adhesive bond between soil and substrate. The implicit form of the agitation term was discussed (dependent on substrate configuration, agitator system geometry and mechanics) but not explicitly deduced. The role of interfacial tension was discussed in relation to foam stability and detergency. In both applications, low interfacial tension is beneficial to performance. However, because other surface chemical effects play a role in performance in detergency and foam stability, it was noted that interfacial tension is not the sole correlating parameter with performance. The situations in which low interfacial tension is not sufficient to give improved detergency and foam stability performance were delineated. A possible new method of aiding in optimizing oil/surfactant performance also was discussed. Finally, the role of micelles in detergency was examined in light of very recent experimental work which suggests that micelles may be detrimental to detergency and foam stability performance. This study suggests that surfactants which form mesomorphic phases with soil give better performance. Micelles, instead of solubilizing soil in their hydrophobic cores, are said to be competing with the mesomorphic phase formation process, thereby hindering detergency performance. It is suggested by the sheer weight of new theoretical and innovative approaches to surface chemistry applied to detergency and foam stability performance that “theoretical surface chemistry measurements really (are) practical!”     

Tuning the polydispersity of alcohol ethoxylates for enhanced oily soil removal

Commercially available alkyl alcohol ethoxylates have a broad distribution of ethylene oxide (EO) units and also a somewhat narrower distribution of alkyl chain length. Generally, the purer the surfactant sample (narrower distribution), the better is its detergency performance, and detergency peaks at the phase inversion temperature (PIT) for a given oil. However, in real detergency processes this may not hold true since soils are typically mixtures of several oily components, and temperature variations are significant. Therefore, if a polydispersity index (PDI) of ethoxylates is defined as the ratio of weight average EO moles to number average EO moles in the sample, then it is conceivable that an optimal PDI might be obtained. We compared the detergency of hexadecane for pentaethylene glycol monododecyl alcohol (C₁₂EO₅) samples in a broad PDI range, using an oil-soluble dye. While detergency at 55°C (PIT of hexadecane with C₁₂EO₅) decreases monotonically with increasing creasing PDI, average detergency over a 20°C temperature range around the PIT tends to show a maximum at PDI of ca. 1.1 (narrow-range ethoxylate). Similarly, for a mixture of undecane/hexadecane/tetracosane (30∶50∶20 w/w/w) for which the average PIT is approximately the same as that of hexadecane detergency at 55°C shows a maximum as a function of PDI at a value of ∼1.37 (broad-range ethoxylate). All detergency results are in general agreement with the reverse trends in oil/water interfacial tension and suggest that, having decided the optimal EO moles for a given application based on PIT, one can further improve the performance of alcohol ethoxylates in real detergency processes by tuning their polydispersity.     

Microemulsion phase behavior of anionic-cationic surfactant mixtures: Effect of tail branching

This research evaluated middle-phase microemulsion formation by varying the mole ratio of anionic and cationic surfactants in mixtures with four different oils (trichloroethylene, n-hexane, limonene, and n-hexadecane). Mixtures of a double-tailed anionic surfactant (sodium dihexyl sulfosuccinate, SDHS) and an unbalanced-tail (i.e., doubletailed with tails of different length) cationic surfactant (benzethonium chloride, BCl) were able to form microemulsions without alcohol addition. The amount of NaCl required to form the middle-phase microemulsion decreased dramatically as an equimolar anionic-cationic surfactant mixture was approached. Although the mixture of anionic and cationic surfactants demonstrated a higher critical microemulsion concentration (cμc) compared to the anionic surfactant alone, the Winsor Type IV single-phase microemulsion started at lower surfactant concentrations for the anionic-cationic mixture than for the anionic surfactant alone. Under optimum middlephase microemulsion conditions, mixed anionic-cationic surfactant systems solubilized more oil than the anionic surfactant alone. Pretreatment detergency studies were conducted to test the capacity of these mixed surfactant systems to remove oil form fabrics. It was found that anionic-rich mixed surfactant formulations yielded the largest oil removal, followed by cationic-rich systems.     

Factors affecting oil/water interfacial tension in detergent systems: Nonionic surfactants and nonpolar oils

Because earlier model detergency studies have shown that oil/water interfacial tension is critically important in oil removal processes, factors affecting the interfacial tension between detergent-range nonionic surfactant solutions and paraffin oil have been examined. For a given hydrophobe, equilibrium interfacial tension values increase with the length of the ethylene oxide chain in the hydrophile, because of the attendant decrease in overall surface activity. For a given degree of ethoxylation, commercial nonlphenol ethoxylates reduce interfacial tension more effectively than their secondary alcohol-based counterparts, and these in turn are more effective than commercial primary alcohol ethoxylates. Furthermore, monodisperse primary alcohol ethoxylates reduce interfacial tension more effectively than broad-range ethoxylates with similar cloud points. This observed order of effectiveness is attributed in part to variations in the extent of fractionation that occur as nonionic surfactants divide between the oil and water phases. Equilibrium interfacial tension values produced by commercial nonionic surfactants are significantly more dependent on concentration and temperature than those obtained with monodisperse ethoxylates. However, the time-course for lowering interfacial tension exhibited by monodisperse ethoxylates varies with concentration and temperature to a greater extent than that displayed by commercial products. These findings are accounted for by the combined effects of the changes in relative surface activity and partitioning that occur as the concentration and temperature are varied. An imidazoline-based quaternary fabric softener markedly increases the interfacial tension immediately following phase contact, whereas equilibrium values are only slightly higher in the presence of the softener. Appatently, preferential adsorption of the softener occurs at the interface, followed by adsorption of the nonionic surfactant at the new softener/water interface. Builders and electrolytes have no significant effect on the interfacial tension between aqueous nonionic surfactant solutions and paraffin oil. Terg-O-Tometer results demonstrate the correlation between oil/water interfacial tension and detergency.     

Phase behavior and detergency study of lauryl alcohol ethoxylates with high ethylene oxide content

Nonionic surfactants such as fatty alcohol ethoxylates have been extensively used in many detergent applications, because of their high calcium ion tolerance, low critical micelle concentrations, and mildness. Although ethoxylates containing high ethylene oxide (EO) content (EO>10 moles) score higher than their low-FO counterparts on many of these desired properties, they have not been studied adequately in the context of detergency, primarily because their cloud points (CP) are higher than normal wash temperatures, typically >100°C, and thus cannot be measured. However, once the CP are manipulated appropriately using salting-out electrolytes, these surfactants can offer certain distinct advantages in terms of their molecular and phase structure. We have studied the phase structure and clouding behavior of tetradecyl ethylene-oxide mono dodecyl alcohol (C₁₂EO₁₄), a broad-range ethoxylate, as a function of the concentrations of various electrolytes. We found that, beyond a certain critical concentration, the CP decreases monotonically with increasing salt concentration. For sodium salts of various anions, the CP depression is inversely proportional to the lyotropic number of the anion. Similarly, for chloride salts of various cations, CP depression is inversely proporitional to the lyotropic number of the cation However, the effect of changing anion is stronger than that of changing cation. A micrograph of a water penetration scan at room temperature indicates the presence of isotropic L₁; hexagonal, isotropic L₂; and solid phases with increasing surfactant concentration. As is the case with low-FO nonionics, a maximum in detergency of model oily soils was found to correlate well with the minimum in oil/water interfacial tension when plotted vs. temperature. Ross Miles foam height increases with increasing concentration of salt.     

Laundry Detergency of Solid Non-particulate Soil or Waxy Solids: Part I. Relation to Oily Soil Removal Above the Melting Point

In this work, methyl palmitate or palmitic acid methyl ester, a monoglyceride, was used as both a model solid fat below the melting point and as an oily soil above the melting point. An anionic extended surfactant [branched alcohol propoxylate sulfate sodium salt (C₁₂₃‐(PO)₄‐SO₄Na)] was used to remove methyl palmitate from cotton and from polyester. Above the melting point (~30 °C) of methyl palmitate, the maximum oily soil removal was found to correspond to the lowest dynamic interfacial tension, as is common with liquid soils. Below the melting point, the lower the contact angle of the wash solution against the soil (indicating higher wettability), the higher the solid fat soil detergency. The removed methyl palmitate was found to be mostly in unsolubilized droplets or particles with a small fraction of micellar solubilization for both solid and liquid forms. The presence of surfactant can prevent the agglomeration of detached methyl palmitate particles in both liquid and solid forms, reducing redeposition and enhancing detergency. Below the melting point, the surfactant aids the solution wetting the surfaces, then penetrating the waxy solid, causing detachment as small particles, and dispersion of these particles. Unlike particulate soil detergency, electrostatic forces are not the dominant factor in fatty soil detergency.