Absorption of N-Cetylpyridinium Chloride on Leacril Fibers: Kinetics and Thermodynamics

Abstract

Data are presented on the kinetics and thermodynamics of absorption of N-cetylpyridinium chloride (N-CP-Cl) by Leacril fibers at different temperatures. The increased temperature of the system increases the surfactant content of the fibers. The experimental time-sorption isotherms are represented by the exponential kinetic equation, M_t = M_eq (1 – e^−kt ), where M_t and M_eq refer to the amounts of surfactant taken up by Leacril at time t and equilibrium, respectively, and k refers to the rate constant. The empirical rate constant decreases with temperature. Values of half-absorption time at different temperatures are presented. Sorption equilibria of N-CP-Cl by Leacril are described by a Freundlich isotherm equation. Changes of enthalpy and entropy related to the process of absorption are calculated from the Clausius-Clapeyron equation. Isosteric heats of absorption are positive, between 20 and 120 kJ/mol. The global change of entropy is positive, between 126 and 500 J/mol K. The best thermodynamic conditions for surfactant uptake by Leacril appear at the highest temperatures, when the standard free energy of absorption takes the most negative values. From the results, we find that the absorption of N-CP-Cl by Leacril in the temperature interval investigated takes place wim establishment of chemical bonds, although physical contributions of an electrostatic nature between the cation of the surfactant and the sulphonate and sulfate end-groups of Leacril are the most important.