When a sufficiently large voltage is applied across a gap containing a gas or a gaseous mixture, it will break down and conduct electricity. The electrically neutral atoms or molecules of the gas split into negatively charged electrons and positively charged ions. The nature of the break down and the voltage at which this occurs varies with the gaseous species, gas pressure, gas flow rate, nature of the materials, separation distance of the electrodes, voltage supply and electrical circuitry. The resulting ionized gas is often called a discharge or plasma. Plasma used in textiles processing vary considerably but are usually only partially ionized gases containing electrons, ions and neutral atoms and or molecules. The inter-actions of the electrically charged particles with each other, with the neutral gas and with contact surfaces produce the unique physical and chemical properties of the plasma environment. The environment is distinct from that found in solids, liquids or gases; hence plasmas are sometimes called the fourth state of matter. A gas becomes plasma when the kinetic energy of the gas particles rises to equal the ionization energy of the gas. When this level is reached collisions of the gas particles cause a rapid cascading ionization resulting in plasma. When the neutral molecules of a gas are energized e.g. by exposing to high electric field, to a point when some electrons become free and the gas turns into a mixture of electrons, ionized atoms and molecules, photons and residual neutral species. In this state it behaves as a chemically active species and there is likelihood of surface interaction with organic substrates.

Atmospheric pressure plasma (APP) treatment of a textile surface can be employed to impart    functional properties to the textile surface. Plasma treatment with non-polymerizing gases     results in better wettability, hydrophilicity and adhesion. Some of the Polypropylene (4   varieties) and Polyester (Polyethylene terephthalate – 4 varieties) were treated with air,             oxygen             and helium – APP. The plasma treated fabrics were observed under the SEM to            gauge the              effect of plasma treatment. It was found that oxygen-APP did not show significant surface          modifications. Hence all the fabrics were given air and helium – APP treatment. This initial        plasma treatment was carried out at WRA on small samples (20 cm x 15 cm). After the     Continuous Plasma Treatment machine was installed at MANTRA, 2 varieties each    of PP    and PET were given air-APP treatment to continuous length of fabric (10m). The time    duration of plasma treatment was varied (5 min, 10 min and 15 min).  

Maximum effective plasma treatment was observed for continuous air-APP for 15 min (SEM images).

The air APP and helium-APP treated samples were tested for certain properties to evaluate the effect of plasma treatment. These properties indicate the changes in surface properties such as wettability, hydrophilicity, adhesion. APP treatment affects not only the mechanical properties but also the air permeability, thermal properties and water vapor permeability of PP and PET fabrics.

The contact angle values of PP and PET fabrics decreased after plasma treatment while the capillary rise (LAC, Liquid absorption) also increased. This is an indicator of increased hydrophilicity of PP and PET fabrics. There is a slight decrease in air permeability of the APP treated samples which means that plasma treated fabrics have poorer air permeability as compared to untreated             

The atmospheric pressure plasma treatment (air) given to polypropylene and polyester fabrics has resulted in changes in surface morphology which has also affected, some comfort related fabric properties. The changes in liquid absorption and transfer properties (increased liquid absorption) will definitely enhance comfort properties. Continuous Air APP treatment at 3-5 kV for 15 mins gives optimum results with respect to liquid transfer properties. The decreased air permeability of plasma treated fabrics and        thermal insulation clo-values indicate that the plasma treated fabrics have good insulation properties. Air plasma treatment reduces the contact angle which also gives improves wettability of the treated fabrics.

Printing properties of APP treated fabrics were studied and it was found that plasma treatment improves the uptake of colour of printed fabrics. The uptake of colour in the dyeing process is not significantly affected by plasma treatment. Visual observation and comparison of the printed shades (plasma treated and untreated) shows the significant difference in uptake of colour. This is supported by K/S data.

Cost economic study of plasma treatment process also shows its viability for industrial application i.e. from initial investment, operational costs are at par with other textile processes. This makes it a viable option for large-scale application to improve fabric functional properties.

Plasma treatment of textile fabrics is a clean, green process which does not involve the use of chemicals and water. Plasma treatment thus has great potential for application to textiles.