Adsorption of a nonionic surfactant by cotton

Abstract

The adsorption and desorption of polyoxyethylated 1-dodecanol containing an average of 14 ethylene oxide (EO) units on cotton was studied over a concentration range of two decades in distilled water at 25°C. The method consisted in equilibrating cotton fabric or chopped fiber with surfactant solutions and determining the equilibrium surfactant concentration by surface tension or by the cobalt blue colorimetric analysis. Surface tension is more affected by surfactant molecules of few EO units, whereas the colorimetric method emphasizes the more highly polyoxyethylated surfactant molecules; the observed discrepancy between the two methods (10%–30%) was caused by preferential adsorption of surfactant of shorter EO chain length onto cotton. The adsorption was almost completely reversible. The adsorption isotherm leveled off at 35 mg. surfactant/100 g. cotton near the critical micelle concentration. In view of the specific surface area of cotton, this level of adsorbed surfactant is of the order of the amount required to cover the cotton completely with a close-packed monolayer of surfactant molecules lying flat against the substrate.