3.4. Plasma Application on Textile Substrate:

3.4.1. Pretreatment of Textile Substrate: ⁶

The application of sizing agent to warp yarns prior to weaving is essential for high weaving efficiency in the production of most fabrics. Starch-based products carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) are most frequently used sizes for cotton yarns. It is very important that these sizes should be removed by wet processing prior to the dyeing and finishing of the woven fabrics. Because of the resulting desizing waste there has recently been great interest in physico-chemicals methods.

The weight loss for plasma-treated fabric increased dramatically with the exposure time of less than 5 min. in the plasma chamber, however, it increased slowly after the plasma treatment time exceeded 5 min. The effect of plasma treatment on the removal of PVA was studied. The effect of varying plasma treatment time on the PVA removal was apparent. Even treatment duration of 0.5 minute removed 3.48% PVA on cotton.

3.4.2. Plasma Application for Dyeing of Textile Substrate:

3.4.2.1 Dyeability of Cotton Substrate: ^{7, 8}

It has been reported that plasma treatment on cotton in presence of air or argon gas increases its water absorbency. This report was concerned with the effect of air and oxygen plasma on the rate and extent of dye uptake of Chloramine Fast Red K on cotton print cloth. The effect of plasma treatment in two different gas atmospheres (air and oxygen) for different treatment times was studied by applying 2% of Chloramine Fast Red K.

The effect of plasma treatment in air and oxygen appears to increase both the rate of dyeing and the direct dye uptake in the absence of electrolyte in the dye bath. Oxygen treatment is more effective than air plasma treatment. This shows that the increase in the rate and extent of dye uptake for the direct dye studied depends more on the oxygen component of the air than on the nitrogen component, which supports an oxidative mechanism of attack on the cotton.

The contributory factors leading to this increase in dye uptake can be:

• The change of the fabric surface area per unit volume due to the surface erosion.
• The etching effect of the plasma effect on the fibred mages the fiber surface and also removes surface fiber impurities (e.g. cotton wax or any remaining warp size, etc.)
• The chemical changes in the cotton fiber surface (leading to carbonyl and carboxyl groups in the fiber.
• The possibility of the formation of free radicals on the cellulosic chains of cotton.
• Thus the action of oxygen and air plasma treatments modifies the surface properties of cotton and leads to an increase in the rate and extent of uptake of direct dye.

3.4.3. Dyeability of Synthetic Fibres: ¹⁰

In the synthetic fibres, plasma causes etching of the fibre and the introduction of polar groups. In this case, in situ polymerization of acrylic acid has been applied to polyester, polyamide and polypropylene fabrics in order to evaluate the improvement in dyeability of basic dyes. This procedure could later be extended by using different monomers to improve the affinity of these fibers for other types of dyes. The surface modification induced by grafting of polyacrylic acid has been investigated by scanning electron microscopy and Fourier transform spectroscopy.

3.4.3.1. Microdenier Polyester: ¹¹

Plasma-induced surface modification of microdenier polyester produces cationic dyeable polyester fiber.SiCl4, silicone tetrachloride (ST) and radiofrequency generated (RF) generated plasma are used to create a polysiloxane type surface in polyester and provide sites for basic dyes. The researchers believe that the possibility of using basic dyes. On polyester could lead to a continuous flow system, low energy consumption, and more environmentally friendly consumption, low temperature dyeing technology on polyester substrates.