The dyeing rate in the early stages and the penetration coefficient of dye were studied on the dyeing of heat set (at a constant length), drawn polyethylene terephthalate fibres with a disperse dye, C. I. Disperse Red 1 in relation to the fine structure of the fibres.
Two sets of fibres with draw ratios of 3.3 and 4.0 were used after heat treatment under various conditions.
The findings are as follows:
Monotonic increases with the temperature of heat treatment have been observed for the penetration coefficient on both sets of fibres and for the dyeing rate on the fibres with a draw ratio of 3.3 However, the dyeing rate on the fibres with a draw ratio of 4.0 showed a minimum in the fiber heatset at 200°C. The penetration coefficient increased linearly while the dyeing rate decreased linearly with the logarithm of the time of heat treatment. Both penetration coefficient and dyeing rate were much higher for the fibres with a draw ratio of 3.3 than for those with a draw ratio of 4.0 heat-treated under the same conditions.
The density and the peak height of the small angle X-ray scattering increased, while the gauche content of the ethylenedioxy linkages in amorphous region decreased with the increase of the temperature or time of heat treatment. All of the above three quantities were linearly dependent on the logarithm of the time of heat treatment. Under the same annealing conditions, the fibres of draw ratio 3.3 showed higher value of the peak height of X-ray small angle scattering and the gauche content, compared to the fibres with draw ratio of 4.0.
The dependence of the dyeing rate on the heat setting conditions was discussed by using the following equation, where
Ct is the amount of dye absorbed in the fibres at time
t and will come up to
C∞ at equilibrium,
r is the radius of the fibres, and
D the diffusion coefficient of the dye which is proportional to the penetration coefficient.
The penetration coefficient is a function of two structural parameters: the intensity of the X-ray small angle scattering, and the gauche content of ethylenedioxy linkages in the amorphous region. The relation between the above parameters and the morphology of the fibre were discussed with particular stress on the mobility of the polymer chain segments.
View full abstract