Diffusion Behavior Of Reactive Blue 194 In Cellulose Fibers

The study on the diffusion of reactive dyes in cellulose fibers during the dyeing process has guiding significance for comprehension of dyeing behavior and formulating appropriate dyeing process of reactive dyes.In this paper,a new method to study the diffusion behavior of dye molecules in fibers was established by confocal Raman technology.Purified Reactive Blue 194 was used as the target substance diffusing into the center of viscose fibers under the condition without salt and alkali.Characteristic peaks of the dyes and the fibers belong to dyed fibers were obtained by Raman real-time spectroscopy.The distribution of the dyes on the cross section of viscose fibers was observed by Raman depth mapping.The effects of dyeing time,initial dye concentration and dyeing temperature on the dye diffusion process were analyzed.The results of Raman depth mapping of the dyed fibers at different dyeing time depicted that at the initial dyeing time（from 30 s to 120 s）,the dye content on the fibers was small and mainly distributed on the surface of the fibers,appearing the state of cyclic dyeing.The dye content on the cross section of the fiber gradually decreased from the outside to the inside.The diffusion of dye molecules to the inside of the fiber was drove by the concentration difference.With the increase of dyeing time,dye diffused to the interior of the fiber,which made itself evenly distributed in the inside of the fiber gradually.Finally,the dynamic equilibrium was achieved.All of these were consistent with the diffusion model of reactive dyes,which demonstrated the feasibility of using confocal Raman technology to study the dye diffusion behavior in the fibers.In addition,the results of Raman real-time spectroscopy and Raman depth mapping of the dyed fibers at different initial dye concentration illustrated that with the enhancement of initial dye concentration（from 1 g/L to 20 g/L）,the dye content in the fibers gradually increased.When the initial dye concentration was low,the dye content on the same location of the fibers was linearly dependent on had a linear the initial dye concentration.Nevertheless,the variation of dye Raman intensity diverged from the linear function which was original fitted when the initial dye concentration was higher than 10 g/L.Combined with hill’s formula,the values of diffusion coefficient of Reactive Blue 194 in the different depths of viscose fibers in cross section under the conditions of the initial dye concentration was 5 g/L and the dyeing temperature was 60°C were calculated.The results showed that the diffusion coefficient reduced with the enlargement of dyeing time and the fiber depth.When dye time was 30 s,the diffusion coefficient on the surface of the fiber was the largest(D=2.01×10^-9 cm²/s).The dye diffusion rate was also accelerated by raising the dyeing temperature.At the beginning of dyeing（from 30 s to 120 s）,the influence of dyeing temperature on dye diffusion was not conspicuous.As the dyeing time lengthened（from150 s to 300 s）,the acceleration of dye diffusion was caused by the elevation of the dyeing temperature.However,the effects of the temperature elevation on dye diffusion were not evident when the dyeing temperature was higher than 60°C.