Use of N-methylformanilide as swelling agent for meta-aramid fibers dyeing: kinetics and equilibrium adsorption of Basic Blue 41

The present study focuses on the use of N-methylformanilide as swelling agent in the dyeing process of meta-aramid fibers. Fiber dyeability with a cationic dye (C.I. Basic Blue 41) has been examined at three different N-methylformanilide concentrations: in particular, adsorption isotherms, dyeing kinetics and fastness to washing and rubbing have been investigated. The experiments have been carried out in a batch system to optimize initial dyestuff concentration, swelling agent concentration and dyeing time. Langmuir, Freundlich and Temkin adsorption isotherms have been used to model equilibrium data. It was found that Freundlich model agreed very well with experimental data: the correlation coefficients ranged from 0.97 to 0.99. The adsorption kinetics has been discussed in view of two kinetics models, i.e. the first-order Lagergren's model and a pseudo-second order model. The pseudo-first order kinetics model describes Basic Blue 41 adsorption on meta-aramid fiber very well. From the technological point of view, 5% on weight fiber (o.w.f.) of Basic Blue 41 and 60% o.w.f. of N-methylformanilide has been found to be adequate to obtain a deep and uniform hue. All dyeing conditions provide satisfactory fastness properties.