Sorption isotherms and behaviour of direct dyes on lyocell fibres

Lyocell fibres, new solvent spun cellulosic polymers. have some advantages over conventional viscose fibres: less pollution produced during the manufacturing process and improved mechanical properties in particular high modulus and tenacity when wet. The aim of this work was centred, on the characterisation of the main influencing parameters in the yield of dyeing with the C.I, Direct Blue I dye through the study of equilibrium isotherms. In order to establish a quantitative analysis, some known dyeing sorption isotherms: Nernst, Freundlich and Langmuir, were compared to the experimental isotherm obtained, The free internal volume has been calculated for lyocell fibre. Also, the dyeing characteristic thermodynamic magnitudes were determined: standard affinity, entropy and enthalpy. This will allow for comparison between different operational parameters in order to evaluate the whole process of dyeing lyocell fibres with the dye used. (C) 2002 Elsevier Science Ltd. All rights reserved.