Nonylphenols are water-soluble surfactants that are used extensively in industry and are found in many consumer products. Nonylphenol polyoxyethylene ether (known commercially as TX-100), which is one of the most popular members of this family, has a detrimental effect oil the environment. Adding chitosan to a solution of TX-100 reduces the amount of surfactant required While maintaining its surface activity. We evaluated the interfacial properties, including the surface tension, contact angle, and particle size, as well as the fluorescence and Fourier transform infrared spectra of various test solutions prepared from three stock solutions: (1) chitosan dissolved in dilute acetic acid, (2) TX-100 dis solved in deionized water, and (3) a mixed chitosan/TX-100 solution. Previous results revealed that low concentrations of TX-100 are relatively harmless to the environment; in this study, we found that its surface activity at a higher concentration vas equal to that of its chemical mixture with chitosan. In addition, we found that the Presence Of chitosan improved the stability of emulsions of TX-100. The micellar particles were small, and the stability of the emulsion was maximized at a TX-100 to chitosan ratio of 7 : 3. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2227-2233, 2010