Plasma is so called fourth state of matter, the other three ordinary states being solid, liquid and gaseous and by scientists as the ‘ionized state’. Thus plasma state of matter was used by the industry for almost one century before being christened.
What is plasma?
Any matter in its gaseous, liquid or solid state can be transformed into its plasma state by applying an external stimulus, if it is held within a suitable container.
The electrons in the outermost orbit of the atoms making up the gas, liquid or solid matter gets knocked off and thus a mixture of electrons and ions or the atomic nuclei exists. The ordinary atoms of matter do not have any electrical charge nor do they conduct electrical currents. The ability to conduct electricity is one fundamental difference between an ordinary state of matter and the plasma state.
Electrical energy initiated cold plasma states arise when free electrons of a low pressure gas or gaseous mixture are accelerated by electrical or electromagnetic fields to a kinetic energy level at which ionization, excitation and molecular fragmentation processes are generated by an electromagnetic radiation. This state of the matter is characterized y the simultaneous presence of electrons, ions and either polarity, neutral atoms and gas molecules. It also can be noticed that the 0-5eV energy spectrum of cold plasmas are intense enough to cleave almost all chemical bonds involved in organic structure and to create active molecular fragments. (e.g., free radicals). Relatively higher energies are required only by the dissociation of double bonds and by the formation of corrosponding free radicals. As a consequence, all organic and elemental organic derivatives can easily be modified and converted into macromolecular structures which limit the plasma states through the recombination of plasma generation active molecular fragments. It also can be understood why higher energies of active species of plasmas will generate macromolecular structures based on unsaturated bonds and three dimensional networks. (Cross linked structures).
The modification of the chemical structure reactivity and bonding characteristics of polymer surfaces has considerable technological importance in the areas of metallization, composite fabrication and biomedical compatibility. Plasma treatment is one type of surface modification that is commonly used. A unique feature of plasma modification is that the surface structure of the polymer can be selectively modified for a specific application while the bulk properties of the polymer are unaffected. The surface specificity of plasma modification makes it difficult to elucidate the nature of the chemical changes with conventional techniques. Also the complexity of the plasma itself makes it difficult to unravel the mechanism responsible for the surface modifications.
Low temperature plasma treatment is a useful technique to modify a polymer surface and leads to polymerization, grafting, cross linking of chemical incorporation. Free radicals generated in the treatment play an important role in these reactions and it is likely that some of unstable free radicals combine rapidly and some of stable free radicals remain in the polymer matrix as living radicals.
The treatment of cloth containing PVA size with low temperature plasma has been suggested as a pretreatment to desizing. The PVA was degraded by the O2 in the air to carbon dioxide and water during plasma exposure. Adverse effects on fabric properties were not observed. Upto 95% of the PVA can be oxidized in this manner. Costs of the process are not available and no useful products can be recovered.
Water repellency and surface modification of PET
PET fabrics have also been successfully treated with O2 or CF4 plasma under different power pressure and time conditions. Oxygen plasma treatment improved both water uptake and surface disability while CF4 plasma treatment improves water repellency along with improved surface dyeability.
Effects of plasma
Induced chemical reactivity of fibre surface
Induced hydrophobic properties
Fibre surface cleaning
No water required
Small amount of chemical needed
No waste production
Confined to fibre surface
Special textile properties can only be obtained via plasma processing