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Evaluation of Physico-Chemical Interactions between Linear Alkylbenzene Sulfonate (LAS) and Alcohol Ethoxylates

Bewertung der physikalisch-chemischen Beziehungen zwischen linearem Alkylbenzensulfonat (LAS) und Alkoholethoxylaten
F. B. Malihi, A. Khaani, N. Changizi and B. Adeeb


Linear alkylbenzene sulfonate (LAS) is the most widely used surfactant in household products. The dominance of LAS is particularly apparent in laundry detergents, dishwashing liquids, household cleaners, and institutional/industrial cleaners, where it accounts for over 3 million tons per year worldwide consumption. However, detergency performance of LAS is decreased in hard water due to lower solubility and surfactant loss in the presence of calcium and magnesium ions. In this study behavior of an aqueous binary surfactant mixture composed LAS and nonionic surfactants was investigated. Ethoxylated alcohols (C12–C14) with 7 EO and 2 EO units were mixed with LAS in laundry detergent formulations, and performance factors including detergency, solubility, and efficiency and effectiveness of surface tension reduction were examined. Analysis of surface tension data indicated strong molecular interaction between LAS and nonionic surfactant. The results indicated that the addition of low amounts of the nonionic surfactant lowers significantly CMC of the mixed surfactant system, and causes the formation of mixed micelles containing predominantly nonionic molecules which provide water hardness protection for LAS. The overall improvement in detergency appears to be due to: lower CMC of the mixed surfactant system which improves soil solubilization, solubilization of Ca(LAS)2, and reduction of free calcium ions which frees up soluble LAS in solution to adsorb at fabric-soil interfaces for enhanced soil removal.


Lineares Alkylbenzolsulfonat (LAS) ist das am häufigsten in Haushaltsprodukten eingesetzte Tensid. Die Dominanz von LAS ist besonders deutlich in Waschmitteln, Geschirrreinigern, Haushaltsreinigern und gewerblichen Reinigern. Dafür werden weltweit jährlich mehr als 3 Millionen Tonnen verbraucht. Die Waschleistung von LAS nimmt ab in hartem Wasser aufgrund der verringerten Löslichkeit und des Tensidverlusts in Gegenwart von Calcium- und Magnesiumionen. In dieser Studie wurde das Verhalten einer binären Tensidmischung aus LAS und nichtionischen Tensiden untersucht. Ethoxylierte Alkohole (C12–C14) mit 7 EO und 2 EO-Einheiten wurden mit LAS in Waschmittelformulierungen gemischt. Die Wirkung der Mischungen auf das Waschvermögen, die Löslichkeit, die Effizienz und Wirksamkeit bei der Reduktion der Oberflächenspannung wurde untersucht. Die Analyse der Daten für die Oberflächenspannung zeigte eine starke molekulare Wechselwirkung zwischen LAS und dem nichtionischen Tensid. Die Ergebnisse zeigen, dass die Zugabe von geringen Mengen an nichtionischem Tensid die CMC des Mischsystems deutlich verringert und die Entstehung von Mischmizellen verursacht, die vorwiegend nichtionische Moleküle enthalten. Diese sorgen für den Schutz des LAS vor der Wasserhärte. Die Gesamtverbesserung der Waschleistung zeigt sich einmal wegen der reduzierten CMC des Mischtensidsystems, die die Schmutzlöslichkeit und die Löslichkeit von Ca(LAS)2 verbessert und zum anderen aufgrund der Verminderung der freien Calciumionen, wodurch mehr freies LAS in Lösung ist, das an der Grenzfläche zwischen Textilien und Schmutz adsorbieren kann und die Schmutzentfernung verstärkt.

Dr. Farrokh Malihi, Fargol Group, 19 Sahba St., Eskandari St., Tehran, P.O. Box 14665-169 Tehran – 14665, Tel.: (9821)88063036, Fax: (9821)88063036. E-Mail:

Farrokh B. Malihi has over 25 years of experience in petrochemical industry, and consumer products. He is founder and managing director of Fargol Group, an international consulting firm specializing in product design and development, research, and professional training. Prior to his consulting experience he was a section manager for household product development at Colgate-Palmolive Technology Center, Piscataway, New Jersey. His professional experience also includes four years as senior scientist at Glidden Coatings & Resins, Division of ICI Chemicals, Strongsville, Ohio. He completed his graduate studies in Polymers & Surface Sciences at Carnegie-Mellon University, Pittsburgh, Pennsylvania. He received a M.Sc. in Chemical Engineering from Carnegie-Mellon University, and a B.Sc. in Electrical Engineering from Sharif University of Technology. Farrokh Malihi is holder of two U.S. patents, and three international patents on detergent formulation and processing. He has published over thirty technical papers in the field of polymers, detergents, and surfactant technology, and has been a frequent speaker at major international conferences., Email:

Azam Khaani is a research chemist at analytical laboratory of Behdash Chemical Company. She joined Behdash Company in 2006, and has responsibility for developing instrumental analysis methods for characterization of raw materials and cleaning products for detergent industry. She received her M.Sc. in chemistry from Ghazvin University in Iran.

Niloofar Changizi worked on this project as her thesis research for completion of her M.Sc. degree in applied chemistry from Azad University in Tehran.


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Received: 2009-08-23
Published Online: 2013-04-11
Published in Print: 2011-09-01

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