DIFFUSION OF DYE ACID IN POLYAMIDE

The diffusion of dye acid in polyamides (nylon 6 and nylon 12) was investigated by means of the cylindrical film roll method. The dye acids of C. I. Acid Orange 7, Blue 25 (monobasic), C. I. Food Yellow 3, C. I. Acid Blue 45 (dibasic) and C. I. Acid Red 18 (tribasic) were used. The diffusions of the dye acids in polyamides were determined at the dye acid concentrations between 1×10-3 and 1×10-4 mol/l, and at 90°C using infinite dye bath condition.The diffusion profiles of dye acid in polyamide were assumed as mixed type which is consisted of Type F (Fickian diffusion) and Type I (box-like diffusion without ion-exchange). The profiles of the mixed type were analyzed to divide into the Type F and the Type I parts by modified McGregor's method.2)The results are as follows:1. The diffusion coefficient (DF) for the Type F part was concentration independent.2. The surface concentration (CI0) for the Type I part corresponded to the terminal amino group content for the polyamide. The diffusion coefficient (DI) for the Type I showed a constant value at Cnylon 12 were approximately one-tenth of that in the nylon 6.It may be concluded that the diffusion of dye acid in polyamide occurs by two mechanisms, one of which is Fickian diffusion, the other is box-like diffusion without ion-exchange. These two mechanisms can operate independently but simultaneously. The contribution of the two diffusion mechanisms was discussed.