Introduction
The
use of plasma in textile modification represents a great outlook for the
improvement of older, energetically demanding, slow, and environment-polluting
treatment technologies. The application of plasma is eco-friendly and reduces
production costs due to energy savings and the reduction of processing times.
Moreover, plasma treatment offers the possibility to obtain textile finishes
without changing the key textile properties. The present review attempts to
give an overview of plasmas for textile treatment from a broad perspective.
Plasmas are ionized gases and gas is normally an electric insulator. However,
when a sufficiently large voltage is applied across a gap containing a gas or
gas mixture, it will break down and conduct electricity. The reason is that the
electrically neutral atoms or molecules of the gas have been ionized, i.e.
split into negatively charged electrons and positively charged ions. The
resulting ionized gas is often called a discharge or plasma. The interaction, neutral gas, and contact of
the electrically charged particles with each other produce the unique physical
and chemical properties of the surface plasma environment. This environment is
different from those found in solids, liquids, or gases; so plasmas are
sometimes called the fourth state of matter.
What is plasma?
Plasma
is a state of matter where an ionized gaseous substance becomes so highly
electrically conductive that the electrical and magnetic fields at a distance
dominate the behavior of the substance. Plasma states are seen in contrast to
other states: solid, liquid, and gas.
Plasma
is an electrically neutral medium that is unbound positive and negative
particles. Although these particles are infinite, they are not "free"
in terms of not giving experience to the forces. The stored charged particles
create an electric current within the magnetic field and any movement of the
charged plasma particles is affected by the fields created by other charges.
Instead, it manages joint behavior with a variety of different levels.
Three factors define a
plasma-
A. Plasma Estimation: When the plasma parameter represents
the number of charge carriers in a sphere surrounding a given charged particle,
the plasma estimation is applied when the particle outside the sphere is sufficient
to withstand the electrical effect.
B. Bulk Interaction: The length of screening (as defined
above) is much shorter than 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. If this criterion is satisfied, then
the plasma is quasineutral.
C. Plasma Frequency: Electronic plasma frequency is larger
than electron-neutral collision frequency When this condition is valid,
electrostatic interactions predominate over the processes of general gas
dynamics.
There
are many ways to induce the ionization of gases. Such as-
a.
Glow discharge,
b.
Corona discharge,
c.
Dielectric Barrier discharge,
d.
atmospheric pressure plasma technique.
a. Glow discharge:
The oldest type of plasma technique is glow discharge and it is produced at reduced
pressure (low-pressure plasma technique) and provides the highest possible
uniformity and flexibility of any plasma treatment.
b. Corona discharge:
Corona
Discharge is made at atmospheric pressure by applying a low frequency or pulsed
high voltage over an electrode pair, the configuration of that can be one of
many types.
c. Dielectric Barrier
Discharge:
The
dielectric-barrier discharge is created by applying a vibrating voltage over an electrical joint that is covered by at least one dielectric element.
d. Atmospheric pressure
plasma technique:
The
atmospheric pressure has better stability, control, and reproducibility. Since
plasma cannot be generated in a complete vacuum the name vacuum pressure is
somewhat misleading and only refers to the low working pressures of such systems.
However,
choose to classify vacuum pressure plasmas into subcategories of low and medium
pressures. Both these forms are suitable for application on textiles and
progress continues to determine their effect on textiles.
Importance of low-temperature Plasmas in Textile Treatment
Low-temperature
plasma (LTP) or cold plasma is produced almost exclusively in glow discharges
in a gaseous environment. A key property of this type of plasma is the lack of
equilibrium between the temperature of the electrons and the energy of the
unionized gas particles. This allows the creation of conditions in which the
temperature of the plasma gas remains close to that of the environment, while
the energy of the electrons is sufficient to break intermolecular and covalent
bonds. This property of LTP makes it useful for initiating modifications in
polymers that are not resistant to high temperatures, that is, of almost all
fiber-forming polymers. Very high plasma
densities can only exist with very high gas temperatures (Thermal Plasma). This
extremely high level of plasma concentration is unsuitable for textile
treatment because the energy of plasma will burn almost any material. For
textile processing, plasma needs to work at room temperature, hence the name
‘cold plasma’. Another advantage of cold plasma is that it chemically treats
fabric and other substrates without subjecting them to damaging high
temperatures.
Artificial plasmas-
Most
artificial plasmas are generated by the application of electric or magnetic
fields through a gas. The plasma produced for a laboratory setting and
industrial use can generally be classified as:
The
type of power source used to generate the plasma—DC, AC (typically with radio
frequency (RF)), and microwave
The pressure they operate at—vacuum pressure (< 10 m Torr or 1 Pa), moderate
pressure (≈1 Torr or 100 Pa), atmospheric pressure (760 Torr or 100 kPa)
The
degree of ionization
Within
the plasma—fully, partially, or weakly ionized
The
temperature relationships within the plasma—thermal plasma (Te = Ti = Tgas ),
non-thermal or "cold" plasma (Te greater than Ti = Tgas)
The electrode configuration used to generate the plasma
The
magnetization of the particles within the plasma—magnetized (both ion and
electrons are trapped in Larmor orbits by the magnetic field), partially
magnetized (the electrons but not the ions are trapped by the magnetic field),
non-magnetized (the magnetic field is too weak to trap the particles in orbits
but may generate Lorentz forces)
Effect of plasma treatment on different types of fabric
Effect of plasma treatment on Cotton
Cotton
is the most widely used natural fiber and has gone through quite a bit of
experimentation in terms of plasma treatment.
Atmospheric plasma has been used to remove PVA-sizing material from
cotton fibers. It has been noted that in contrast with conventional treatment
which requires hot water for effective removal of size, plasma-treated cotton
could be completely rid of PVA sizing material with a simple cold water
wash. The scouring and dyeing behavior
has been shown to improve with O2 plasma treatment under low-pressure
conditions. Sun et al, investigated the effect of low-pressure plasma treatment
on the dyeing of cotton fabrics.
Effect of plasma treatment on Wool
In
wool, the surface character of plasma treatment is limited to a small part of
the fiber, in relation both to its mass and volume. Physical properties such as
the fiber friction coefficient, dye
diffusion, etc. depend on the highly networked layer known as the epicuticle.
Modifying this layer, without causing changes in the wool cortex, facilitates
and accelerates some technological processes, including the dyeing of
fibers. Dorota BiniaÅ› worked on the
effect of LTP on the dyeing process of woolen fabrics and found that
LTP-treated samples proved to have bound the dye better than the unmodified
sample. In addition, LTP damages an ultra-thin hydrophobic layer on the
protective surface of the fiber. This process occurs only on the surface and
does not damage the inner structure of keratin. Wool fibers were treated
with LTP
with different gases, namely
oxygen, nitrogen, and a mixture of gases (25%
hydrogen, 75% nitrogen), and it was shown that the surface
composition of the LTP-treated wool fiber was found to vary differently with different plasma gases. The results have been similar to the previous
reports, in which it was explained that the concentration of the functional
groups influences the properties of the wool fiber.
The
effects of using either radiofrequency or microwave power sources on the
generation of plasma, different plasma
gases, and treatment times on the surface of wool fabrics and fibers were
analyzed by means of SEM. Ar, O2, and air plasma drastically improved the
wettability of wool-knitted fabric.
Additionally, plasma treatment brought about enhanced swelling of wool
fibers. The swelling was the most pronounced in the case of oxygen plasma,
whereas air plasma performed a swelling degree of the same order as a
conventionally chlorinated sample.
Improved wettability and swelling of wool are attributed to plasma
modification of the layer of covalently bound fatty acids known as the F-layer,
which is mostly responsible for the natural hydrophobicity of the wool fiber
surface. The dye fastness of the wool fabrics was improved significantly after
plasma treatment.
Effect of plasma treatment on Flax and Hemp
The
observed increase in water retention and wetting rate of flax is attributed to
better susceptibility of fiber to water molecules as a result of plasma etching
and plasma oxidation i.e. the formation of new carboxyl groups. The effect of low-temperature plasma (LTP) on
hemp has been studied. Radetic studied the influence of low-temperature air
plasma and enzymatic treatment on the dyeing properties of hemp. In addition to
determining color dynamics, color yield, and color, SEM analysis was performed
on weight loss assessments, water retention, and degree of whiteness, as well
as samples treated differently. Low-temperature plasma treatment of hemp fabric
caused an increase in the dyeing rate, final dye exhaustion, and color yield of
dyed samples. The positive effect of
plasma treatment was explained by plasma etching and oxidation effect on the
hemp fiber surface. This could be attributed to the more pronounced digestion of
the amorphous areas of the fiber that became considerably more accessible to
enzymes after plasma etching. It is likely that plasma etching increased fiber
porosity and induced minor topographical changes that make hemp fiber more
susceptible to dye and water molecules. Easier diffusion of dye into the fiber
caused by plasma treatment is not sufficient for an increase in dye exhaustion
as it is also considerably influenced by the structure, molecular weight, and state
of dye in the dyeing bath.
Effect of plasma treatment on Synthetic Fabrics/Fibers
Atmospheric
pressure has been used to control water retention and pigmentation of DBD
surfaces and to improve the capillary of synthetic fabrics. Polyester fabric is
a system of micro and macro-perforated. Plasma contains various active particles
(e.g. electrons, radicals, ions, photons, etc.). These species may attach to or
react with the polyester (PES) surface, altering the nature of the functional
group present, capillary-porous structure, and, consequently, surface
properties as high-performance fibers; Unfortunately, they are prone to
hydrolysis. Thus, the application of an isolated barrier to the surface should
reduce the tendency to hydrolyze in the corresponding media.
Hexafluoroethane/hydrogen plasma is highly suitable for applying this type of
expansion-barrier layer on the surface. Resistance to 85% H2SO4 results in
fibers remaining completely intact when conventional fluorocarbons terminate
within a given condition resulting in significant shrinkage of the fibers in
association with property loss.
When
polyethylene terephthalate (PET) fibers are used as the application material
for polyethylene (PE) matrix, the hydrophobization of PET fibers using ethylene
plasma is quite impressive, as the adhesive strength can be increased from 1 to
2.5 N / mm. The fracture morphology of these composite materials clearly shows
the tight adherence of the fiber matrix.
Polyester-cotton
blended fabrics are treated with oxygen plasma. The effect of plasma treatment
on the water absorption behavior of polyester-cotton blended fabrics was
analyzed and the results indicate that the water absorption behavior was
significantly improved.
Instead
of the angle of contact of water, the oxygen/carbon ratio of the atomic
composition of the surface can be used to follow the effect of plasma
treatment, especially for layered-structured polypropylene burns. The
oxygen/carbon ratio is highest for the first layer; however, a significant
effect is also observed in the tenth level. To build soil resistance and
improve pigmentation, poly (ethylene terephthalate) (PET) and polyamide (PAM)
fabrics are treated in low-temperature plasmas. Five separate modification
types were applied. Fabrics are treated directly with acrylic acid, water, air,
and 2, and argon plasma. All types of plasma polymerization improve wettability
and therefore soil color and soil resistance.
Effect of plasma treatment on Nonwovens
In
experiments at the UTK (the University of Tennessee at Knoxville's ) Plasma
Sciences Laboratory on the surface energy, wettability,
and wick ability of melt-blown polymeric fabrics exposed to inert gas
OAUGDP (One Atmosphere
Uniform Glow Discharge Plasma)
plasmas (helium and argon), it was found that durations ranging from 30
seconds to 5 minutes were required to
produce significant improvements to these characteristics. The nonwoven fabric
Sentara, commonly used for surgical gowns, is treated with antimicrobial
finishes and plasma containing fluorocarbon gas. Treated samples are
evaluated for changes in physical and functional characteristics. Plasma
treatment does not change weight, density, stiffness, air permeability, breaking strength, and elongation.
Plasma-treated
and water-repellent Sentara samples show higher blood and water resistance
compared to other treatments. Plasma-treated samples also show a zone of
inhibition for Staphylococcus aureus, thus providing a barrier against
microbes. There is no zone of inhibition for the water-repellent Sentara,
untreated, and wet control samples. This suggests that nonwoven fabrics treated
with plasma may provide a better barrier against germs than commonly available
surgical gown fabrics with a fluorocarbon finish.
Effect of plasma treatment on Silk
The
properties, integration structure, and properties of Bombyx mori silk treated
by low-temperature oxygen plasma were studied. The weight of B-Mori silk yarn
decreased after low-temperature oxygen plasma treatment and decreased further
as treatment time increased. It was a result of an etching by oxygen plasma.
Slight flutes appeared on the surface of the treated fiber and fibrillary units
became more evident in the section of treated fiber. The β-sheet conformation
increased and crystallinity decreased after plasma treatment. Demura et al.
studied the Bombyx mori silk fibroin fabrics treated with low-temperature
plasma using various gases. After a short period of plasma treatment, the
strength of the silk yarn changed somewhat. Plasma treatment for the improvement
of the hydrophobic of the silk fabrics was investigated by Shen Li and Dai
Jinjin and the results showed much improved hydrophobic properties.
Effect of plasma treatment on Denim Finishing
Recently,
low-pressure plasma and corona treatments for obtaining a worn look effect on
denim fabrics are proposed. In a study by Radetic et al., the CIE Lab colorimetric
system was used for the determination of the color difference between untreated
and plasma-treated denim fabrics. The lightness difference between untreated
and corona and low-pressure argon plasma-treated denim fabrics is
demonstrated. Apparently, the higher the power and number of passes in the case
of corona treatment, the higher the lightness.
Similarly, in the case of argon plasma treatment, the prolongation of
treatment time and increase in power brought about an increase in fabric
lightness. In both cases, under severe treatment conditions samples became more
yellow, but yellowness disappeared after washing. The mechanical properties of
the material were not changed after the plasma treatments. The decolorization
of denim fabrics after plasma treatment in oxygen or argon was studied by
Ghoranneviss et al. The results showed a better-decolorized output for Ar than
O2 after a 15 min treatment. However, after washing the treated denim, the O2-treated samples looked well than those treated by Ar.
Environmental Impact of Plasma treatment
Plasma
treatment became a negligible part of many industrial processes. Despite the
obvious intrinsic effects and an environmentally friendly approach, it is still
claimed as a potential or promising plasma treatment in the textile industry. It might
be due to the too traditional and rigid textile industry, which finds an excuse
in expansive vacuum pumps required for plasma processing at low pressures.
However, treatments at atmospheric pressures are available as well. The substantial shortcoming of plasma treatment in the textile industry is that it cannot
replace all wet processes, but it can be a viable pretreatment, which provides
plenty of environmental and economic benefits. Therefore, the textile industry
should consider the concept of higher initial investments in equipment that
will be paid off quickly with respect to environment-related savings and the
profit of the sale of high-added-value products.
The
environmental benefits of plasma treatment were-
a.
the reduced amount of chemicals needed in conventional processing,
b.
better exhaustion of chemicals from the bath,
c.
reduced BOD/COD of effluents,
d.
shortening of the wet processing time,
e.
the decrease in needed wet processing temperature, and
f.
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, 11t 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, the bulk characteristics of the material, such as its mechanical
strength, are unchanged. Further, plasma treatment allows for achieving surface characteristics
that are ahead of the reach in the field of textiles.
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