Detergency is the process of cleaning without solvents. A detergent removes contaminants from a surface by solubilizing, suspending, or emulsifing them.

The detergency process is surprisingly complex. Good detergency requires the synergism of many simultaneous processes. Surfactants in a detergent or cleaning formulation must cause the cleaning solution to wet both the surface to be cleaned and the contaminant to be removed. The contaminant must then be suspended, solubilized or emulsified by the cleaning formulation, so that it does not become redeposited on the surface. The surfactant must, therefore, not be too water soluble, or it will not have good adsorption on the contaminant. It must also not be too close to a phase boundary, or it may precipitate or form a coacervate.

While surfactants are generally the primary active agents in water based cleaning formulations, modern cleaning systems include numerous other additives to optimize the cleaning. For example, builders are added to reduce the activity of multivalent counterions that otherwise might precipitate the surfactant. Enzymes are often added to assist in solubilizing heavy oil or fats, or even to remove loose fibrils from the fabric that cause it to look grey.

For all of these reasons, a fundamental understanding of detergency requires a good grounding in all aspects of surfactant science, including micelle formation, surfactant precipitation and phase separation, wetting, adsorption, emulsification, microemulsions, dispersion and suspension of particulates, and foaming.

In our short course, detergency is placed at the end of our coverage of these other phenomena, allowing us to cover a great deal of cleaning science in a short time, because of the foundation laid in the first part of the course.

Articles

• Microemulsion Formation and Detergency with Oily Soils: I. Phase Behavior and Interfacial Tension

  The ultimate objective of the project was to investigate the relationship between mlcroemulsion phase behavior and detergency for oily soils. In this study. surfactant phase behavior was evaluated for hexadecane and motor oil as model oiiy soils. Producing microamulsions with these oils is particularly chalenging because ot their large hydrophobic character. To produce the desired phase behavior we included three surfactants with a wide range of hydrophilic/lipophilic character: alkyl diphenyl oxide disullonate (highly hydrophilic). dioctyi sodum sulfosuccinate (intermediate character), and sorbitan monooleata (hydrophobic). This mixed surfactant was able to bridge the hydrophilidlipophilic gap between the water and the oil phases, producing mlcroernulsions with substantial solubilisation and ultralow interfacial tension. The effects of surfactant composition, temperature, and salinity on system performance were investigated. The transition of microemulsion phases could be observed for both systems with hexadecane and motor oil. ln addition, the use of surfactant mixtures containing both anionic and nonionic surfactants leads to systems that are robust with respect to temperature compared to single-surfactant systems. Under conditions corresponding to “supereolubilization,“ the solubilization parameters and oil/microemulslon interfacial tensions are not substantially worse than at optimal condition for a middle-phase system, so a middle-phase rnicroernulsion is not necessary to attain quite low interfacial tensions. A potential drawbadt ol the formulations developed here is the fairly high salinity (e.g., 5 wt% NaCl) needed to attain optimal middle-phase systems. The correlation between interfacial tension and solubillzetion follow the trend predicted by the Chun-Huh equation. Paper no. S1361 in JSD 6. 191-213 (July 2003).

• 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) on alkyl diphenyl oxide disulfonate (ADPODS) and sorbitan monooleate (SpanSO) was shown to form Winsor type I and type III microemulsions with hexadecane and motor oil. In addition, high solubilization and low inter facial tension were obtained between the oils and surfactant solutions, both in the super solubilization 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 the middle-phase regions (type III), much better detergency performance was found for both hexadecane and motoroil 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.

Recommended Reading

• Detergency of Specialty Surfactants, , F. E. Friedli, Marcel Dekker, New York, NY (2001)

• Formulating Detergents and Personal Care Products: A Guide to Product Developmen, , L.H.T. Tai, AOCS Press, Champaign, Illinois (1999)

• Powdered Detergents, , M.S. Showell, Ed., Marcel Dekker, New York (1998)

• Enzymes in Detergency, , J.H. van Ee, O. Misset, and E.J. Baas, Eds., Marcel Dekker (1997)

• Liquid Detergents, , K-Y. Lai, Ed., Marcel Dekker, New York (1997)

• Detergents and Cleaners: A Handbook for Formulators, , K. R. Lange, Hanser, Munich, 1994

• Surfactants in Consumer Products, Theory, Technology and Application, , J. Falbe, Ed., Springer-Verlag, Berlin, 1987, Chapters 5 and 11

• Detergents and Textile Washing, , G. Jakobi and A. Lohr, Eds., VCH, Weinheim, Germany, 1987

• Detergency, , W. G. Cutler and R. C. Davis, Eds., Marcel Dekker, New York, Parts I - III, 1973-1981

• Kirk-Othmer Encyclopedia of Chemical Technology, 4th Edition, , Lynn, J. L. Wiley, New York, Vol. 7, p. 1012 (1993)

• Advanced Cleaning Product Formulations: Household, Industrial, Automotive, , E. W. Flick, Noyes Publications, Park Ridge, NJ, 1989

• Advanced Cleaning Product Formulations, Volume 2, , E. W. Flick, Noyes Publications, Park Ridge, NJ, 1994

• Cationic Surfactants: Physical Chemistry, , D. N. Rubingh and P. M. Holland, Eds., Marcel Dekker, New York, 1990, Chapters 9 and 10

• Soap Technology for the 1990’s, , L. Spitz (Ed.), American Oil Chemists’ Society, Champaign, Illinois, 1990

• Kirk-Othmer Encyclopedia of Chemical Technology 4th Edition, , Farr, J. P., Smith, W. L., and Steichen, D. S. New York Vol. 4, 27 (1992)

• The Role of Oil Detachment Mechanisms in Determining Optimum Detergency Conditions, , Thompson, L., J. Colloid Interface Sci., 163, 61 (1994). [NOTE: an excellent paper with a good literature survey on the topic.]

• The Science of Hair Care, , Zviak, C., Ed., Marcel Dekker, New York (1986)

• Handbook of Detergents, Part A: Properties, , G. Broze, Ed., Marcel Dekker, New York, 1999

• Industrial Cleaning Technology, , J. Harrington, Ed., Kluwer Academic Publishers, London, UK (2001)