DIFFUSION OF DISPERSE DYES INTO SUPERMICROFIBRES

Abstract

All dyers share the common goal of achieving the correct shade as early as the first dyeing. But the dyeing process is very complex, being characterised by the diffusion-controlled sorption of dyes that depends on several physicochemical parameters. Moreover, the dyeing properties relating to microfibres and conventional fibres are caused by different properties such as the exposed surface area and the crystallinity index. Wilson and Hill developed equations describing the uptake rate of disperse dyes by a cylindrical fibre model as a function of the diffusion coefficient and the nature of the dyebath. The inverse of Shibusawa’s polynomial approximation of Hill’s and Wilson’s equation is used to compute the diffusion coefficient, which depends on the initial dye concentration, the time and the fibre count at a fixed temperature. In this paper, the sorption isotherms, the diffusion coefficient, the dye concentration evolution into the fibres and the dyeing uptake rate are computed from experimental results for conventional fibres, microfibres and supermicrofibres. The sorption isotherms and the diffusion coefficient evolutions as a function of time, initial dye concentration and temperature for supermicrofibres are discussed by considering the surface area and the diffusional boundary layer’s influence. Important differences in the dyeing properties are observed, depending on the fibre count, which should be useful in the optimisation of the supermicrofibre dyeing process. The aim is to provide a tool for dyeing practitioners to increase dyeing reproducibility and to improve the performance of ‘right-first-time’ production.