Fundamental interactions of ultrasound with cotton fibers and vat dyes

Ultrasound has been shown, by earlier researchers, to improve the dyeing process by increasing the dye uptake of the substrate and reducing the time and energy required to obtain a desired color. How this improvement takes place has never been completely defined. Several hypotheses have been put forth in the literature though few if any have been explored in great detail. This work takes two of these hypotheses and explores them in great detail to determine whether they are the mechanisms responsible for the reported improvements in the dyeing process attributed to ultrasound. For this exploration, cotton fibers and vat dyes were chosen as a continuation of the work begun by another researcher at North Carolina State University. The first hypothesis: ultrasound increases the swelling of the fiber thereby making it easier for dyes to penetrate into the interior of the yarn bundle. The second hypothesis: ultrasound reduces the size of dye aggregates in the dyebath which would allow the smaller particles to penetrate into the interior of the fabric and yarn bundle more easily. From this work it was found that ultrasound does cause an increase in fiber swelling over that of swelling in water alone. The increase in swelling was independent of the order of treatment of the fiber and the measurement method used to measure the fiber diameter. Ultrasound was also found to reduce the average particle size of vat dyes suspended in water. Ultrasound's greatest effect was eliminating particles larger than 2 {dollar}mu{dollar}m and shifting the particle size distribution toward smaller particles.