3.4.3.2. Dyeability of Polyamide: ¹²

Polyamide (nylon6) fabrics have been treated with tetrafluoromethane low temperature plasma and then dyed with commercially available acid and dispersed dyes. The morphology of the treated surfaces was examined by scanning electron microscopy and chemical surface charges characterized by X-ray photoelectron spectroscopy. Dyeing results showed that the plasma treatment slows down the rate of exhaustion but does not reduce the amount of absorption of acid dyes. The dyeing properties of disperse dyes on plasma treated nylon fabric charged markedly when compared with untreated fabric. A slight improvement in colorfastness was seen with the treated sample. The dyeing process had only a minor effect on the water-resistant surface, indicating that a stable surface has been achieved by the plasma treatment.

3.5. Future Growth and Developments: ¹³

Plasma will play many important roles in the future manufacturing of non-woven and textile products. The first of these will be meeting the need to custom-design products and develop highly technical products, by which the manufacturer must distinguish himself from the competition. Another will be by providing a solution to increasing regulation in the use of process water and in energy consumption. A third in meeting the need of environment ally friendly processes, as well as for a safe operator environment. The fact that new products cab be designed, that quality can be improved and costs can be decreased, will give a further impetus to plasma growth.

4. Supercritical Carbon dioxide (CO2) - the dyeing technique of future: ¹⁵

Water is a valuable raw material which is not unlimitedly available. It must be protected by appropriate legal measures. Usage of water as solvent for chemicals is mostly because of its abundant availability and low cost. Problems associated with usage of water are effluent generation and additional step is needed to dry the fabrics after each step. The amount of energy spent to remove the water is also huge adding to the woes of processors, making processing the weakest link among the entire textile chain. The unspent dyestuffs remain in liquor, thus polluting the effluent. It leads to additional pollution of waste water.

To eliminate the disadvantages it is proposed that certain gases can replace water as solvating medium. High pressure and temperature are needed to dissolve the dyes. Of all the gases being possible of converted into super critical fluids, CO2 is the most versatile and prominently used. Because of their high diffusion rates and low viscosities that allow the dye to penetrate into the fiber. Moreover, by reducing the pressure at the end of the process, dye and CO2 can be recycled.

4.1. Supercritical CO2:

Prominent substances exhibiting super critical phases are CO2, H2O and Propane, of which CO2 is the second most abundant and second least costly solvent. Low temperature and pressure are needed to convert carbon dioxide gas into super critical fluid. In the supercritical state CO2 exhibits very low viscosity and surface tension properties. Supercritical CO2 is one of the most popular fluids currently used in manufacturing processes.

4.1.1. Why only CO2:

1. Abundantly available
2. Recovery and reuse is easier
3. Easily Handel able and environment friendly
4. Non toxic, non hazardous and low cost.
5. No waste generation
6. Chemically inert.

4.2. Supercritical Dye system:

It represents the presence of three components the textile substrate, dye stuff and the super critical fluid. The dyestuff is dissolved in the supercritical fluid, transferred to, absorbed by and diffused into the fiber.