Fundamental Investigation of Ultrasonic Effects in Textile Wet Processing

The use of ultrasound in textile wet processing offers many potential advantages. Previous work has shown that the use of ultrasonics in dyeing provides the following benefits: (1) energy savings and reduced processing times, (2) environmental improvements, (3) process enhancement, and (4) lower overall processing costs. A fundamental understanding of the operative processes are needed so that meaningful application of ultrasonics in textile processing may be made. This project is directed at determining the phenomena responsible for the effects of ultrasound in textile wet processing and the relative importance of phenomena occurring in the bulk solution and in the fiber. Our studies show that ultrasound increases the swelling of both unmercerized and mercerized cotton. Although the beneficial effects of ultrasound are also observed to occur in polyester, no effect of ultrasound on the glass transition temperature was observed. An experimental approach has been developed that will enable a direct determination of the effect of ultrasound on the diffusion coefficient of the dye within polyester. Research including modeling is being conducted to determine the effect of ultrasound on the partition coefficient and enhancement of dye transport to the fiber surface by reducing the boundary layer thickness. The effect of ultrasound on the particle size of insoluble dyes is being studied. Ultrasound C95g-13 2 reduces the average particle size of vat dyes in their insoluble form suspended in water and eliminates the larger particles. Introduction There are many potential advantages offered by the use of ultrasound in textile wet processing. The following benefits due to the use of ultrasonics in dyeing were shown by previous researchers [1-4]: (1) energy savings by dyeing at lower temperatures and reduced processing times, (2) environmental improvements by reduced consumption of auxiliary chemicals, (3) process enhancement by allowing real-time control of color shade, and (4) lower overall processing costs, thereby increasing industry competitiveness. A fundamental understanding of the relative operative processes is needed so that meaningful application of ultrasonics in textile wet processing can be made. Although several fundamental studies [5-9] on the effects of ultrasound in various physicochemical processes have been conducted, the mechanisms responsible for the effects of ultrasound on textile processes have not been established. This project is directed at determining the phenomena responsible for the effects of ultrasound in textile wet processing and establishing the relative importance of phenomena occurring in the bulk solution and in the fiber. The mechanisms under investigation include: (1) increasing swelling in water, (2) reducing glass transition temperature of the fiber (dilation of amorphous regions), (3) increasing the diffusion coefficient of dye in the polymer, (4) increasing the fiber/dye bath partition coefficient, (5) enhancing transport of the dye to the fiber surface by reducing the boundary layer thickness, and (6) breaking up of micelles and high molecular weight aggregates into uniform dispersions in the dye bath. Cotton Fiber Swelling (G. Mock, R. McCall, D. Klutz) The swelling of both mercerized and unmercerized cotton fibers with water alone and with ultrasound has been studied. Ultrasound causes significant fiber swelling compared to water alone. Since cotton fibers are very nonuniform and hard to measure, the tests were repeated numerous times and the results averaged. Several methods of measurement were used to confirm the results. C95g-13 3 For unmercerized cotton, the swelling with water alone ranges from 10% to 20%, but with ultrasound the range is from 25% to almost 50%. For mercerized cotton, the swelling with water alone is only about 3% but with ultrasound is about 35%. Remember, the mercerization process causes permanent swelling of the cotton fiber. Of interest here is that ultrasound still causes additional swelling. The fiber swelling is observed for at least an hour after the removal of the ultrasound, as long as the fiber remains in water. When removed from water and allowed to dry, the fiber returned to its original diameter. Dye Particle Size (G. Mock, R. McCall, D. Klutz) Vat dyes were examined in their insoluble unreduced form suspended in water to determine if ultrasound changed the dye particle size. Five different vat dyes of known structure were examined, most of which had previously been used in ultrasound dyeing trials. A 5-g/L solution of each dye was prepared, then divided in half to give two samples for each dye. One sample of each dye was treated with 20 kHz ultrasound at 25C for 60 minutes; the other sample was used as a control untreated sample. The dye samples were measured with a Honeywell Microtrac Particle Size Analyzer. This instrument measures each sample twice and averages the results to produce an average particle size and a particle size distribution. The results of the particle size analysis are shown in Table 1. Vat Violet 1 was effected most by ultrasound. The particle size distribution was initially bimodal, but when treated with ultrasound, became unimodal (Figure 1). The large particles were reduced in size, and the smallest particles were increased in size. Table 1. The Average Particle Size Of Vat Dyes Dye Manufacturer Without Ultrasound (microns) With Ultrasound (microns) Avg. Size Decrease (microns) Vat Violet 1 Catawba Charlab 2.447 0.606 1.841 Vat Black 25 Catawba Charlab 0.462 0.405 0.057 Vat Black 25 Sunbelt 0.516 0.514 0.002 Vat Green 3 (Dyeing) Catawba Charlab 0.941 0.268 0.673 Vat Green 3 (Printing) Catawba Charlab 1.434 0.292 1.142 Vat Green 1 Catawba Charlab 0.454 0.392 0.062 Vat Violet 13 Sunbelt 0.444 0.431 0.011