Since the introduction of plasma technology in the 1960s, the industrial applications of low-pressure and low-temperature plasma were mainly in microelectronic etching. In the 1980s, plasma technology also applied to other material surface treatment, especially in metals and chemical polymers. Due to high restriction in the control of chemical finishing on textile materials, the new and innovative textile treatments are demanded. In this regard, plasma technology shows distinct merits due to its environmental friendly and better treatment results. Presently, research institutions are applying plasma technology in textile processing.
The plasma is an ionized gas with equal density of positive and negative charges which exist over an extremely wide range of temperature and pressure. The plasma consists of free electrons, ions, radicals UV-radiation and other particles depending upon the gas used. The plasma gas particles etch on the fabric surface in nano scale so as to modify the functional properties of the fabric.
Unlike conventional wet processes, which penetrate deeply into fibres, plasma only react with the fabric surface that will not affect the internal structure of the fibres. Plasma technology is to modify the chemical structure as well as the topography of the textile material surface. In conclusion, plasma can modify the surface properties of textile materials, deposit chemical materials (plasma polymerization) to add up functionality, or remove substances (plasma etching) from the textile materials.
There are different methodologies to induce the ionization of plasma gas for textile treatment:
- Glow-discharge method- plasma gas is produced at reduced pressure. The methodology applies direct electric current, low frequency over a pair of electrodes.
- Corona discharge method - plasma gas is produced at atmospheric pressure by applying a low frequency or pulsed high voltage over an electrode pair.
- Dielectric barrier discharge method - plasma gas is produced by applying a pulsed voltage over an electrode pair of which at least one is covered by a dielectric material.
Low-temperature plasma technology including both low glow discharge under reduced pressure as well as dielectric barrier discharge under normal pressure have been well established in different industrial applications. The applications on textiles include desizing of woven fabric, adding functionality and modification of surface properties of textile materials.
The functionality of textile materials can be improved by the plasma technology such as:
- Wettability- there are a lot of investigations on plasma treatment of some textile fibres for changing their wettability properties. For examples, polyester, polypropylene, wool that plasma treatment can improve the ability of these fibres to retain moisture or water droplets on their surface.
- Hydrophobic finishing- the treatment of cotton fibre with identified plasma gas such as hexamethyldisiloxane (HMDSO) leads to a smooth surface with increased contact angle of water. The treatment gives strong effect of hydrophobization of treated cotton fibre.
- Adhesion- plasma technology can increase adhesion of chemical coating and enhance dye affinity of textile materials.
- Product quality- Felting is an essential issue of wool garment due to the fibre scales. Conventional anti-felting gives negative effects on hand feel and environmental issues. Oxygen plasma gives anti-felting effect on wool fibre without incurring traditional issues.
- Functionality- different kinds of plasma gases provide special functionality to textile materials such as UV-protection, anti-bacteria, medical function, bleaching, flame retardancy, etc.