EFFECT OF EXTENSION ON THE RATE OF DIFFUSION OF A DISPERSE DYE IN POLYETHYLENETEREPHTHALATE FIBER

Abstract

The dye penetration coefficient of C. I. Disperse Red 15 in PET fiber was measured as a function of extension given to the fiber in dyeing, and the following results were obtained; The penetration coefficient remarkably increased with increasing extension. In order to explain the effect of the extension on the rate of diffusion of dye, the density and the intensity of small angle x-ray diffraction were also measured as a function of the extension. The changes of both of them strongly suggest that the density of the amorphous region decreased by extension, implying that the remarkable increase in the rate of diffusion of dye may be due to the increase in the free volume with extension. The change in the specific volume with the extension was calculated from the changes in the density and the small angle x-ray intensity. Specific volume calculated from the intensity was greater than that from the density. The increase in the specific volume thus estimated from the density was reduced into the temperature increase by use of the thermal expansion coefficient of the fiber. The penetration coefficient assumed from the temperature thus estimated, by use of W. L. F. relation for the temperature dependence of diffusion of the dye in the fiber, was much larger than that actually observed. From these results it was concluded that the remarkable increase in the rate of dye diffusion is attributable to the increase in free volume by extension, although the increase in the free volume effective for diffusion of dye seems smaller than that expected from the increase in the specific volume of the fiber.