Introduction
Plasma
is a state of matter in which an ionized
gaseous substance becomes highly electrically conductive to
the point that long-range electric and
magnetic fields dominate the behavior of the matter. The plasma condition may be
contrasted with the other states: solid, liquid,
and gas.
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| Plasma treatment |
Plasma
is an electrically neutral medium of untied positive and negative particles.
Although these particles are infinite, they are not "free" in terms
of not giving the force experience. Moving charged particles generate an
electric current within a magnetic field, and any movement of a charged plasma
particle affects and is affected by the fields created by the other charges. In
turn, this governs collective behavior with many degrees of variation.
Three factors define a plasma-
a. The plasma approximation: The
plasma parameter is applied when the number of charge carriers in a sphere
surrounding a given charged particle is large enough to protect the electronic
effect of the particle outside the sphere.
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| Plasma factor |
b.
Bulk interactions: The Debye screening length (defined above) is short compared
to the physical size of the plasma. This criterion means that interactions in
most parts of the plasma are more important than their edges where boundary
effects can occur. When this criterion is fulfilled, the plasma is
quasineutral.
c.
Plasma frequency: The electron plasma frequency is large compared to the
electron-neutral collision frequency. When this condition is valid,
electrostatic interactions predominate over the processes of general gas
dynamics.
The environmental benefits of plasma treatment were-
1.
Reduced amount of
chemicals needed in conventional
processing,
2.
Better exhaustion of chemicals from the bath,
3.
Reduced BOD/COD of effluents,
4. Shortening of the
wet processing time,
5.
A decrease in needed wet processing temperature and
6.
Energy savings.
The
comparative cost analysis of conventional chlorination and plasma processing of
wool was worked out and they demonstrated that energy costs for chlorination
are 7 kWh/kg wool whereas for
low-pressure plasma treatment only 0.3-0.6
kWh/kg wool. The application of low-pressure plasma for the modification
of 120 t/year of wool can save 27000 m of water, 44 t of sodium hypochlorite,
16 t of sodium bisulfite, and 11 t of sulphuric acid, and 685 MWh of electrical
energy.
Conclusion
Plasma
processing is a dry and environmentally friendly practice. It does not require
immense supplies of water, heating, and drying, and only infinitesimal amounts
of chemicals are necessary to reach the preferred functionality. Because the
desired material behavior is accomplished by modifying only the surface of
fibers, bulk characteristics of the
material, such as its mechanical
strength, are unchanged.
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