gnk first phase

8/8/2019 GNK First Phase

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G.NALANKILLIBannari Amman Institute of Technology


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This enables a variety of generic surface processesincluding Surface activation by bond breaking to create reactive

sites Grafting of chemical moieties and functional groups Material volatilisation and removal (etching) Dissociation of surface contaminants/layers (cleaning/

scouring) and Deposition of conformal coatings.

In all these processes a highly surface speci c region of thematerial (


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Plasma

Highly Reactive & Energetic

+ve, -ve Charges,Radicals,

Electrons,Excited molecules, atoms.

Electrically neutralElectrically neutral


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S unS un

FireFireHydrogen BombHydrogen Bomb


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Potential Difference > Dielectric Strength , 13.56MHz RF Power


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Wha t is Pl asm a?y Matter within the universe is most commonly found in the

form of plasma rather than as a solid, liquid or gas.y Plasma is partially-ioniz ed gas normally generated by an

electrical discharge at near-ambient temperatures.y Plasma, often considered as the fourth state of matter, is

composed of an ioniz ed gas containing a mixture of ions,electron, neutral and excited molecule, and photons.

y This state of matter was first identified by Sir WilliamCrookes in 1879, and named 'plasma' by Irving Langmuir in1928.


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Wha t pl asm a consists of ? The coupling of electromagnetic power into a process gas volume generates the plasma medium comprising adynamic mix of ions, electrons, neutrons, photons, free

radicals, meta-stable excited species and molecular andpolymeric fragments, the system overall being at roomtemperature. A plasma is an ionised gas, i.e. it contains electrons, ionsand neutral atoms and/or moleculesThis allows the surface functionalisation of bres andtextiles without affecting their bulk properties. Thesespecies move under electromagnetic elds, diffusiongradients, etc. on the textile substrates placed in or passedthrough the plasma.


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Definitiony A commonly accepted de nition of plasma is: a

partially ionised gas composed of highly excitedatomic, molecular, ionic and radical species, as well as

photons and electronsF rom 60s to 80s

y In the 1960s, the main industrial applications of (low-pressure) plasmas have been in the micro-electronicindustries.

y In the 1980s their uses broadened to include many other surface treatments, especially in the elds of

metals and polymers.


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How d

ept h it acts ?y All these phenomena are limited to the most external

layer of the substrate. Normally, the effects do notinvolve layers deeper than 10 100 nm.H owever, it mustbe noticed also that ultraviolet (UV) or vacuumultraviolet (VUV) radiation (with wavelength 10 nm) depending on the absorption coef cient of the substrate


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y Cleaning or etching : For such a phenomenon to occur, inertgases (Ar,H e, etc.), nitrogen or oxygen plasmas are typically used. The bombardment of the substrate with the plasma speciescauses the breakdown of covalent bonds. As a consequence,detachment of low molecular weight species (ablation) takesplace. In this way, contaminants or even thin layers of thesubstrate are removed, producing extremely clean surfaces,modifications in the surface area, or controlled reduction of weight of the exposed substrate.

y The removal of bulk substrate material, occurs when theinteraction between the solid surface and the plasma generatesgas-state byproducts, which include atoms or molecules, fromthe substrate. These desorbs from the surface and are carriedaway from the substrate, thus removing bulk material.

y Cleaning, the removal of contamination, is a form of etching but with very high selectivity. Essentially, only the unwanted surfacecontaminant is volatiliz ed and removed while the substrateremains untouched by the process.

G e ne ric Surf ace Engg. Proc e ss


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y Activ a tion : Interaction with plasma may induce theformation of active sites on the polymer surface (radicals or other active groups, such as hydroxyl, carboxyl, carbonyl,amine groups), which can give rise to chemical reactions,not typical of the untreated material, with substances brought

in contact with the material after plasma processing. Activation, enhancement of the surface energy, is thegeneration of chemically reactive sites on a previouslyuncreative surface resulting in a rise in surface tension.

y C o a ting, deposition of a functional thin lm, occurs if theplasma solid surface interaction creates a solid phasematerial. This remains on the surface and agglomerates over time, e.g. micro-seconds, to generate a conformal film. Thisprocess is sometimes called Plasma Enhanced Chemical

Vapor Deposition (PECVD) or plasma polymerization


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y

Gr afting : Radical species present in the plasma may bedirectly grafted onto the polymer surface.

y Po lyme r izati o n : by using specific molecules, a processknown as plasma enhanced chemical vapour deposition(PECVD) may occur. These molecules, activated in theplasma, may react with themselves forming a polymerdirectly on the surface of the substrate. Depending on thedifferent experimental conditions, chemically unique,nanometric polymeric coatings are obtained and chemical,permeation, adhesion and other properties of the startingmaterial can be dramatically modi ed.


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Effect of plasma on bres and polymers

Textile materials subjected to plasma treatments undergomajor chemical and physical transformations including(i) chemical changes in surface layers,

(ii) changes in surface layer structure, and(iii) changes in physical properties of surface layers.Plasma treatment on bre and polymer surfaces resultsin the formation of new functional groups such as

OH

, C=O, COOH

which affect fabric wettability as well as facilitate graft polymerisation which, in turn,affect liquid repellence of treated textiles andnonwovens.


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Plasmas are acknowledged to be uniquely effective surface engineering tools due to:

Their unparalleled physical, chemical and thermalrange, allowing the tailoring of surface properties toextraordinary precision.

Their low temperature, thus avoiding sampledestruction.

Their non-equilibrium nature, offering newmaterial and new research areas.

Their dry, environmentally friendly nature.


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C lassifica tion of Pl asm a(i) On the basis of pressure in plasma chamber--

Atmospheric Pressure and low pressure plasma.(ii) On the basis of degree of ioniz ation and the

temperature of electrons and ions-H ot and cold plasma.(iii) On the basis of frequency of the power supply- DC and

AC plasma(RF, Microwave, GHz Plasma).(iv) Depending upon the electron affinity of the process

gases used-Electropositive and electronegative gasplasma.

y Any plasma reactor will be a combination of all of theabove, e.g. one atmosphere glow discharge cold plasma is

based on cold, AC and atmospheric pressure plasma.


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Atmospheric Pressure Plasmay Traditional sources include transferred arcs, plasma torches,

corona discharges and dielectric barrier discharges.y In arcs and torches, the electron and neutral temperatures exceed

3000C and the densities of charge species range from 1016cm-3 to

1019

cm-3

.y Due to the high gas temperature, this plasma is used primarily inmetallurgy.

y Corona and dielectric barrier discharges produce non-equilibriumplasma with gas temperatures between 50C and 400C.H igher voltages are required for gas breakdown at 760 torr and oftenarcing occurs between the electrodes.

y H owever, to prevent arcing and lower the gas temperature, severalschemes have been devised, such as the use of pointed electrodesin corona discharges and insulating inserts in dielectric barrierdischarges


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A dvant age s and D isadvant age s of A PPy The advantages of atmospheric pressure plasma are:

(i) continuous treatment can be given, and(ii) it is cost effective process.

y On the other hand, the disadvantages of atmosphericpressure plasma are:(i) difficulty of sustaining of glow discharge,

(ii) higher voltages are required for gas breakdown, and(iii) difficult to form uniform plasma through out the

reactor volume.y Different types of atmospheric pressure plasma used are:corona discharge, dielectric barrier discharge and plasma

jet.


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C orona Discharge


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Corona discharge is characteriz ed by bright filaments extendingfrom a sharp, high-voltageelectrode towards the substrate.

Corona treatment is the longest established and most widely usedplasma process; it has the advantage of operating at atmosphericpressure, the reagent gas usually being the ambient air.This is obtained at atmospheric pressure by applying D.C., lowfrequency or pulsed high voltage between two electrodes of very different siz es. The corona consists of a series of rapid, non-uniform,non-arcing discharges. Plasma density drops off rapidly with

increasing distance from the electrode.

Corona treatment


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Dielectric Barrier Discharge


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Dielectric barrier discharge(Silent discharge )y This is an atmospheric-pressure plasma source.

In this case a pulsed high voltage power rangingfrom low frequency AC to 100 kHz is appliedbetween electrodes, one or both of which iscovered by a dielectric layer. The purpose of thedielectric layer is to terminate rapidly the arcsthat form in the region between electrodes. Thedischarge consists of series of rapid microdischarges


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Plasma Jet


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Low Pressure Plasmay Low pressure plasma has found wide applications in

materials processing and play a key role in manufacturingsemiconductor devices.

y They generate high concentrations of reactive species thatcan etch and deposit thin films at the rates up to 10 m/miny The temperature of the gas is usually below 1500C, so that

the thermally sensitive substrates are not damaged.y The ions produced in the plasma can be accelerated toward

a substrate to cause directional etch at submicron level.y In addition, a uniform glow discharge can be generated, so

that the materials processing proceeds at the same rate overlarge substrate areas.


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Low-pr e ssur e plasm as

Low-pressure plasmas are a highly mature technology developed for the microelectronics industry.H owever, the requirements of microelectronics

fabrication are not, in detail, compatible with textileprocessing

Vacuum vessel is pumped down to a pressure in therange of 10-3 to 10 mbar with the use of high vacuumpumps. The gas which is then introduced in the vessel is ionised with the help of a high frequency generator. The advantage of the low-pressure plasmamethod is that it is a well controlled and

reproducible technique.


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y In a weakly ioniz ed gas at low pressure, the electron density ranges between 108cm-3and 1013cm-3. Under theseconditions, the collision rate between electrons and neutralmolecule, insufficient to bring about thermal equilibrium


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A dvant age s & D isadvant age s of lowpr e ssur e plasm a

y Advantages:(i) the generate high concentrations of reactive specie that can etch

and deposit thin films;(ii) uniform glows is obtained;(iii) the temperature of the gas is usually below 1500C, so that thethermally sensitive substrates are not damaged;(iv) low breakdown voltages; and

(v) a stable operating window between spark ignition and arcing.y Disadvantages:

(i) vacuum systems are expensive and have high maintenance cost, and(ii) Siz e -of the object to be treated is limited by the siz e of the vacuumchamber


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H ot Plasmay Production in Universe is of hot plasma.H ot plasma

occurs when the temperature of electrons and atomicand molecular species are extremely high. Ninety nine

per cent of the matter in the universe is in the plasmastate.y H ot plasma is nearly fully ioniz ed which is actually

known as the fourth-state of matter. The Sun and the

stars in the universe consist entirely of hot plasma, andthe space within the stars of a galaxy is filled withplasma.


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Cold Plasmay Cold plasma occurs when the atomic and molecular

species are at ambient temperature, whereas theelectrons are at high temperatures. A small fraction of thegas molecules (e.g. 1 %) is ioniz ed. It has already found

uses in a variety of manufacturing processes. Forexample, flat-screen televisions use cold plasma toradiate light and create images.

y Cold plasma can be used to treat surfaces (e.g. oxidation,functionaliz ation) or to deposit specific coatings ontoorganic and inorganic substrates. Cold plasma canproduce oz one as its secondary offspring. Mostimportant, cold plasma is used to finely etch channels onintegrated circuits - the chips inside our desktop andlaptop computers that made the computer and internetage possible


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Cold pl asm a y Contrary to thermal plasmas, non-thermal plasmas are

cold plasmas and are produced at room temperature or alittle above room temperature. In this case, electronsacquire higher energies than ions and molecules, theirenergies ranging from 0.1 to some electron volts, and, dueto the low density of the gas, collisions with the otherspecies are relatively rare and thermal equilibrium is notreached: the bulk temperature of the gas is comparable toroom temperature.

y Electron collisions with neutral species produce additionalelectrons and ions. Thanks to the low operatingtemperatures, cold plasmas can be put in contact with any material, even delicate textiles, without problems.


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DC & AC Plasmay AC discharges are preferred over DC-driven discharges in

plasma systems for a number of reasons.y First, as the frequency of AC increases, the energy transfer

into the discharge becomes more efficient, especially atfrequencies between ~100 kHz and 1GHz , the RF regime.

y Also, in a DC discharge, charged particles from the plasmacan accumulate on the substrate surface causing unwantedcharging effects. By alternating the direction of the currentflow sufficiently rapidly, these charging effects can bereduced.

y At RF frequencies, this alternation is sufficiently rapid toalmost completely eliminate charging effects.


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Electropositive andElectronegative Gas Plasma

y Most of the etching plasma used in the semiconductorindustry is formed from gases which readily form negativeions, i.e. electronegative gases. Plasma is usually classifiedinto two different types depending upon the electronaffinity of the process gases used. Process gases can bearranged roughly in the following order of increasing

electronegativity: Ar


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lectropositive (EP) Plasmay These are discharges consisting mainly of spices which

do not form negative ions easily. Examples are allnoble gases, such as Ar,H e and some unreactive gaseslike N2. In this plasma, the number of positive ions isalmost exactly equal to the number of electrons,although both are still much smaller than the numberof neutrals.


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Eleclronegative (EN) Plasmay By contrast, EN plasma contains a significant number of species

which have a positive electron affinity. In these cases, the numberof free electrons is significantly reduced as a result of capture by EN species to form negative ions. A typical reactions might be:

e + CCl4 CCl4 CCl3 + Cl-

y In CCl4 plasma, the number of electrons can be up to 100 timesless than the number of positive ions, with overall chargeneutrality being maintained by large numbers of negative ions.EN plasma requires higher power to sustain and is difficult toinitiate. This make EN plasma unstable and often non-uniform.The electron temperature is also much higher than in EP plasma.


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Glow D ischarge Plasmay It is an ioniz ed gas consisting of equal concentrations of

positive and negative charges and a large number of neutral species.

y In the simplest case, it is formed by applying a potentialdifference (of a few 100 V to a few kV) between twoelectrodes that are inserted on a cell (or that form the walls of the cell).

y The cell is filled with a gas (an inert gas or a reactive gas)at a pressure ranging from a few mTorr to atmosphericpressure.y This is obtained at low pressures, typically less than10 mbar. The plasma is generated by antennas, fed withelectromagnetic fields at frequencies of 40 kHz or 13.56MHz or microwaves (2.45 GHz ).


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Glow D ischarge Plasma .y Due to the potential difference, electrons that are emitted from the

cathode by the omnipresent cosmic radiation are accelerated away fromthe cathode, and give rise to collisions with the gas atoms or molecules.

y As a result of this excitation, the ioniz ation and dissociation take

place. The excitation collisions give rise to excited species, which candecay to lower levels by the emission of light.y This process is responsible for the characteristic name of the "glow"

discharge.y Gl ow discharge is characterised as a uniform, homogeneous and stable

discharge usually generated in helium or argon (and some in nitrogen). Atmospheric Pressure Glow Discharge (APGD) offers an alternativehomogeneous cold-plasma source, which has many of the bene ts of the vacuum, cold-plasma method, while operating at atmosphericpressure.


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O ne Atmosphere Uniform Glow D ischarge

Plasma ( O AUGD P)y The OAUGDP is produced by applying a kilohertz electric field

between two parallel plates.y The electric field required to initiate the OAUGDP is 8.5 kV/cm for

air, well below the DC electric field for sparking.y Both electrodes may be covered with quartz , pyrex alumina or glass

insulating plates, the thickness of which is between 1mm and 3mm.y The exposed samples are placed on the lower electrode. The working

gas is entered from one side and flows out through the other side.y OAUGDP reactor is uniform without filamentary microdischarge if

the proper combination of gap distance, RF driving frequency andrms voltage is selected to maintain ion trapping.

y The OAUGDP technology is simple, cost effective and suitable foronline treatment of fabrics and films.


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D iff e re nt A PP & SURFAC E MOD IF ICAT IONS


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Why plasma processes at atmospheric pressureare advantageous for the textile industry ?

y The typical working width of textile machines is between 1.5 and 10 meters. Textile-suited plasma modules need to be scalable up to these dimensions, which is easierfor atmospheric-pressure techniques.

y Textiles have large speci c surfaces compared to foils, piece goods or bulk solids.Even with strong pumps, the reduced pressure which is necessary for low pressureplasma will only be reached slowly due to the desorption of adsorbed gases.

y Depending on the bre material, textiles can adsorb and absorb relatively largeamounts of water. To reduce the chamber pressure below the vapor pressure of water (23.4 mbar at 20 C), a drying process is necessary. This is time consumingbecause diffusion processes within the ber and the cooling due to evaporation of the water slow down the drying (vapour pressure of ice: 4.02 mbar at -5 C). Theevaporation time can be shortened by heating the substrate.

y Atmospheric-pressure processes can be combined with spraying or aqueousaerosols.

y Atmospheric-pressure processes are in-line capable, in contrast to batch low-pressure plasma processes.

y Investment and maintenance costs for atmospheric-pressure plasma modules aremoderate


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Wha t gas plasm a, do e s w ha t?y H elium/oxygen plasma treatment of PP introduces oxidised functional groups

onto the surface, which may include alcohol, ketone, carboxy, ether, ester orhydroperoxide. The introduction of polar groups onto the PP bres allowschemical bonding with, for example, dye molecules, in contrast to the untreatedPP molecular chains which are non-polar giving a hydrophobic surface.

y Oxygen and oxygen-containing plasmas impart functional groups such as C-O,C=O, O-C=O and C O O, as well as surface etching of bres, all enhancing wettability and adhesion characteristics.

y Fluorine and uorine containing gases (CF4, C2F6) result in the incorporation of uorine into the surface, resulting in hydrophobicity.

y Nitrogen and ammonia plasmas introduce amino ( NH 2) and other nitrogen

containing functionalities onto natural and synthetic bres. On wool, these aredye sites increasing dye absorption.y Treatment of PTFE with hydrogen-containing plasmas such as forming gas

(N2/H 2::95%/5%) and ammonia results in large increase in surface energy due toa high de uorination rate resulting in the formation of C C, CH and C=Cbonds and cross-links, and to nitrogen and oxygen species grafted onto the

treated surface


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B reakdown Voltagey To ignite plasma, the breakdown voltage for the gas must be exceeded.

This voltage depends on the electrode spacingd and the pressure p asfollows:

where A and B are the constants found experimentally; and , thesecondary electron emission coefficient of the cathode. Breakdown voltage (V b) increases rapidly with pressure at constant electrode

spacing. For example, the breakdown voltage for argon is estimated tobe 2500 V at 760 torr and with a 5 mm gap distance. A narrow gap isnecessary to achieve a reasonable breakdown voltage at atmosphericpressure.

? A ? A scb In Ind p A In

d p BV K /11.

.!


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Effect of Frequencyy The electric fields in the one atmosphere glow discharge

plasma reactor are only a few kilovolts per centimeter; values are usually too low to electrically break down the

background gas.y The most desirable uniform one atmosphere glow

discharge plasma is therefore created when the appliedfrequency of the electric field is high enough to trap theions between the two parallel plates, but not so high thatthe electrons are also trapped


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Effect of Frequencyy If the frequency is so low that both the ions and the electrons can

reach the boundaries and recombine, the plasma will either notinitiate or form a few coarse filamentary discharges between theplates.

y If the applied frequency is in a narrow band in which the ionsoscillate between the two plates, they do not have time to reacheither boundary during a half period of oscillation.

y If the more mobile electrons are still able to leave the plasma volume and impinge on the boundary surfaces, then the desirableuniform plasma is produced.

y If the applied frequency is still higher so that both electrons( e) andions ( i) are trapped in the discharge, the discharge forms thefilamentary plasma.


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B reakdown voltages and densities of charge

species in the plasma discharges

Source Breakdown

voltage (V b),kV

Plasma

density cm-3

Low pressuredischarge

0.2-0.8 10 8 -10 13

Arc and plasma torch 10-50 10 16 -10 19

Corona 10-50 10 9 -10 13

Dielectric barrier discharge

5-25 10 12 -10 15

Plasma jet 0.05-0.2 10 11 -10 12


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M echanism of Surface M odificationy Both vacuum and atmospheric pressure plasma achieve

their surface treatment effects as a result of the interactionof one or more active species from the plasma with thesurface of interest. These active species are more chemically reactive and more energetic than the species associated with conventional chemical processing. Such species may include

y Ultraviolet photons which are capable of breaking chemical

bonds, and photons in the visible parts of the spectrum which can produce a positive surface charge by thephotoelectric.


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Mechanism of Surface

Modification

y Charges particles are a second major class of active species fromplasma; they include electron that either recombine on the surface orbuild up a surface charge; ions that may be produced by ioniz ationevents, attachment or charge exchange in the plasma; and free radicalsor other charge molecular fragments such as OH resulting from plasmachemical reactions.

y A third major class of active species is neutral particles which caninclude very reactive atoms such as monoatomic fluorine, oxygen orother atomic fragments; atoms or molecule in excited atomic states;

and highly reactive molecular fragments, including monomersproduced in the plasma. Most of these active species are rarely presentor much less dense in ordinary chemical reactors, and their highenergy levels make possible surface treatment effects that can beachieved only with difficulty, if at all, with conventional chemicalprocessing.


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Surface M odifications Using Inert gas plasma

y Ablation / etching The ability of plasma processing tobreak down weak covalent bonds in a polymer throughbombardment with high-energy particles is known asablation. This affects the outermost molecular layers of thesubstrate exposed to the plasma which evaporated as small volatile fragments. Desiz ing of cotton and antifelting of wool are some examples.

y Surface cross-linking Cross-linking is the setting up of multiple chemical links between the molecular chains of polymers. Plasma processing with inert gases can be usedto crosslink polymers and produce a stronger and hardersubstrate microsurface.


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Surface M odification using Reactive Gases & M olecules

y The replacement of surface polymer groups with chemicalgroups from the plasma is called activation.

y During activation, the plasma breaks down weak bonds inthe polymer and converts them to highly functional groupssuch as carboxyl, hydroxyl, etc. in the presence of activespecies such as reactive gases and other small organic

compounds.


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S urface Modification using Polymerizable Monomers

y In this case, a thin polymer layer may be formed on thesubstrate surface through polymeriz ation of a monomer.

y The monomer is directly polymeriz ed on the surfaceactivated by plasma treatment. This is known as graftingthrough plasma.

y Grafting can be carried out insitu, where the monomer gasis introduced within the plasmaz one or carried outsubsequently, where the activated Surface is exposed topolymeriz ation conditions in the presence of a reactivemonomer such as vinyl monomer after the plasmatreatment.

y Depending on the selection of the gas, monomer andprocess parameters, these thin coatings can be deposited/grafted with various properties or physical characteristics


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Ageing of Plasma-treated Surfaces

y

Concentration of functional groups may change as afunction of time


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Plasma M odification of Textiley Some of the effects or characteristics that have been shown by cold

plasma treatment on textile substrates include crease-resistantfinishes, reduced felting of wool, antistatic finishes, improvement of wetting, enhancement of dyeability or printability enhancement of UV-protection, flame-retardant finishes, hydrophilic and hydrophobicfinishes, cleaning of surfaces such as desiz ing, scouring and bleaching

y In natural fibers, such as wool and cotton, the hydrophobic layer on thesurface is oxidiz ed and partially removed (desiz ing). The specificsurface area is increased during plasma treatment, which is clearly demonstrated by means of atomic force microscopy. Again, due to thesurface-directed activity of the plasma, the tenacity of the fibers ishardly influenced. The chemical and physical surface modificationresults in decreased shrinkage behaviour of wool top.

y Specific surface area of cotton also increases with oxygen plasmatreatment. In hydrophobic materials such as polypropylene, plasmatreatment significantly increases the hydrophilicity of the surface andsurface modifications are sustained for a long time.


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Surface modification with reactive gasesand molecules in plasma

Plasma Treatment EffectsAtmospheric pressure glow plasma; gas; air; onn lon and PU melt blown and electrospun fibres.

he surface energ increased to > 70 d nes / cm b5 s of plasma e x posure; did not degradesignificantl up to 120 s treatment.

Vaccum plasma; gases; dichloromethane; on cottonand P fabrics.

Moisture content and d eabilit were enhancedwithout affecting other properties.

Vaccum; 70 W; gas; o xgen; on PBO, Ke vlar andcarbon fibres.

otal surface free energ of PBO increased from43.3 mJm -2 to 61.1 mJm -2 (b 41%) with treatmentfor 5 min and the interfacial shear strength of amodel PBO/epo xy composite increased from 34.7MPa to 44.7MPa (or 29%). Similar results for other fibres.

Vacuum; gas; o xygen; on wool subtrate.

Level of shrink resistance could be significantl y

enhanced on application of pol ymers to wool fabricafter a 2 min treatment.

Atmosphere glow plasma; gases; He, Ar, air, carbondio xide and other gases; on PP melt blown. Increase in wettabilit y.

DBD plasma; gas; he xafluoroeth ylene/H 2; on nome xfibres.

Plasma is used to appl y a diffusion barrier la yer tothe surface to impro ve the resistance to 85% H 2SO 4(20 h at room temperature)


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Vacuum plasma; gases; o xygen andhexafluoroethane; on cotton fabric

Provide an effecti ve barrier to aqueouscontamination.

Atmospheric pressure glow discharge anddielectric barrier discharge plasma; gas; air; onP F.

he atmospheric pressure glow dischargeresults in .more uniform and effecti ve thandielectric barrier discharge.

Atmospheric pressure; gases; Ar/fluorocarbonmixtures; on technical te xtiles.

A small percentage admi xture of h ydrogen toAr/C 3F8 resulted in increased deposition rate.Plasma-post-treatment in etching gases can beused to decrease the surface tension.-

Atmospheric pressure; gas; N 2 &vinyltrietho xysilane; on P substrate.

Hy brid organic-inorganic precursor resulted in better barrier properties against o xygen gas incomparison to an organic precursor due toorganic and inorganic networks formation.

Atmospheric pressure; gases; helium / argon or acetone/argon; on wool and P fabric andfilm.

Wettabilit y increased with increased treatmenttime. he helium/argon plasma treatment moreeffecti ve than the acetone/ argon plasma.

Atmospheric pressure; gas: air; on N ylon- ,film.

urface contact angle decreased rapidl y from83.5 to 3 5.

Atmospheric pressure: gases; N 2, H 2, NH 3 andmixtures; on H P and PP plates.

Increase in surface energ y was obser ved. Fromthe XP anal ysis, the bonds C-H, C-C, C-N, C-

-C and C- -H were found in the surfaces of the treated samples.

Plasma Treatment Effects


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Surface modification with polymerizable monomers

Plasma Treatment EffectsVacuum plasma; gas: Ar monomer: acr ylonitrile;on PP fabric.

PPAN (plasma pol ymerized acr ylonitri]e)surface grafted PP fabrics e xhibit impro ve water absorption and d yeing properties.

Vacuum of 0.2 mbar; gas: Ar; monomer:Perflouroacr ylate; on cotton/P fabrics.

reatment for 1 min ga ve water repellent properties.

Vacuum; gas: Ar; monomer: acr ylic acid; onP fabric.

Increase in wettabilit y, soiling resistance andcolour strength of pol yester fabric was better b yargon post-plasma pol ymerization of acr ylic acidcompared to in s itu polymerization

Atmospheric pressure; gases: He/O 2; monomer;organosilicone; on P fabric.

Antireflection la yer causes increase in colour intensit y of the pol ymerized P surfaces.

Vacuum; gas: Ar; monomer: fluoroacr ylate in presence of vinyl crosslinking agents; on N ylon-6.

Fire-retardant coating; 50% decrease in peak value of rate of heat release.

Vacuum; pretreatment with Ar/O 2 followed graft pol ymerization b y acr ylamide, acr ylic acids andacr ylates; on cellulosics, acetates, and acr ylicsubstrates.

Grafting yield varied depending upon the parameters and monomers used; breakingstrength decreased36 due to etching in the order:cotton> acetate> acr ylic


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Atmospheric pressure; on P for 10 s.Direct grafting of perfluoroalk yltrichlorosilanes. onacti vated P occurs much more readil y comparedto monochloro-substituted silanes.

Vacuum; gases: Ar, 0 2,N2 and organic sol vents;monomers: gl ycid yl methacr ylate, 2,2-diphen yl-l-picr ylhydraz yl; on cotton fabric for 60-300 s.

Plasma induced grafting yield with different gasesand their mi xture is compared.

Vacuum; gases: air, Ar and O 2; monomer: acr ylicacid;on P and pol yamide fabric for 1-90 min.

In s itu plasma pol ymerization of acr ylic acidresulted in impro ved wettabilit y, dyeabilit y and soilresistance.

Vacuum; gases: air, Ar and O 2; monomers: acr ylatecontaining phosphorus; on PAN fabric for 15 min.

he LOI value of PAN (18.5) increases b y 4-8 unitswhen treated with the flame retardant phosphate

and phosphonate monomers.Vacuum; gas: Ar; monomer: 1,1,2,2, etrahydroperfluoro dec yl acr ylate; on PAN fabric for 10 min.

Graft-pol ymerization of monomer in direct contactwith the substrate surface required much smaller amounts of fluorinated reactant to achie ve water and oil repellenc y.

Vacuum; gas: O 2; monomer: 1.1.3.3-tetrameth yldisilo xane acr ylate; on N-6 film for 20min.

Rate of heat release decreased b y 30%. Man ydifferent properties such as flame retardanc y,damping , film deposition or hindering of additi vediffusion out of the host matri x can be achie vedusing this in a single stage, treatment.

Vacuum; gas: Ar; monomer: acr ylic acid; on P for 1-4 min.

Considerable increase in surface free energ y andwettabilit y was obser ve within 1 min of plasmatreatment.

Vacuum; gas: o xygen; monomer: acr ylic acid; onPP.

tching + plasma pol ymer coating pro videdenhanced electrochemical properties.


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Pot e nti a l use of pl asm a tr e a tm e nts of br e s,

ya rns and f abrics Anti-felting/shrink-resistance of woollen fabrics.H ydrophilic enhancement for improving wetting and dyeing.H ydrophilic enhancement for improving adhesive bonding.H ydrophobic enhancement of water and oil-repellent textiles.Facilitating the removal of siz ing agents.Removing the surface hairiness in yarn.Scouring of cotton, viscose, polyester and nylon fabrics.

Anti-bacterial fabrics by deposition of silver particles in the presence of plasma.

Room-temperature sterilisationof medical textiles.Improved adhesion between textiles and rubber.Plasma-treated fabrics with high hydrophilic stability when stored inalkaline media.Graft plasma polymerisation for producing fabrics with laundry-durable oleophobic, hydrophobic and stain-resistant nishes.


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Pot e nti a l use of pl asm a tr e a tm e nts of fibr e s,

ya rns and f abricsy Atmospheric plasma-based graft polymerisation of textiles and nonwovens

having different surface functional properties on the face and back side of thefabric.

y A fabric which is coated with siz ing agent inactive to plasma on one side and onthe other side left as hydrophobic or hydrophilic after siz e removal, the resultantfabric having different functionality on its two sides.

y Flame-retardant coating using monomer vapour (halogen and/or phosphorus)in combination with nitrogen and/or silicone.

y Silicone coating of air-bag fabrics using crosslinked silicone(polyorganosiloxanes).

y Scouring of cotton, rayon, polyester fabrics using a non-polymerisable gas(nitrogen, argon, ammonia, helium), followed by wet treatment for removing theimpurities.

y Prevention of readily-occurring colour variation in textiles.y Durable antistatic properties using PU-resin and plasma processing.y Shrink resistance of animal hair textiles using urethane-based resin and plasma

processing.y Electro-conductivity of textile yarns by surface plasma deposition.


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y Optical coatingsy Ultraviolet protective textiles block UV radiationy Far infrared textiles fabric absorbs radiation and re-

radiates at lower wavelength to aid body warmthy Conductive coatingsy Electromagnetic shielding textiles for medical

devices, safety and general uniforms, electronics,assembly equipment, aprons, maternity wear, general wear

Pot e nti a l use of pl asm a tr e a tm e nts of fibr e s,

ya rns and f abrics


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Pot e nti a l use of pl asm a tr e a tm e nts

of fibr e s, ya rns and f abrics ..y H ydrophobic or oleophobic nishing of Nomex fabricsy H ydrorepellent nishing for polyamide fabrics for skiweary

Antibacterial nishing for micro bre lining of shoesy Flame-retardant nishing for home textilesy coupling of polyester fabrics and polymeric membranes for

surgical Weary

coupling of polyester fabrics and polymers for industrialtapes


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C ha ract e risa tiony The techniques for surface analysis described are divided

into two main categories those that assess physical andtopographical properties and those that assess chemicalproperties.

y The physical and topographical properties are measured by scanning electron microscopy (SEM), transmissionelectronic microscope (TEM) and atomic force microscopy (AMF) techniques and the chemical properties aremeasured using Fourier transform infrared (FTIR)

technique.y Other techniques such as X-ray photoelectron spectroscopy

(XPS) and the future possibilities of nanoindentation and X-ray absorption spectroscopy (XAS).


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Q ua li e r crit e ria for n e w t ex tile te chnologi e sy Safet y and handling: he new technolog y must be operated

safel y, predominantl y needing onl y the e xisting skill set of thetextile mills

y Operating speed: Line speeds need to be as fast as or faster thanexisting technologies to a void bottlenecks

y Production e xibilit y: Fast switching between fabric t y pes andeffects must be a vailable to allow for rapid adaptations in productand process

y

Investment: he technolog y should offer a return on in vestmentin under 5 years and maintain or impro ve the protabilit y of themill

y nvironmental: he technolog y should compl y with e xistinglegislation and impro ve compatibilit y with anticipated law


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Major P a ram e te rs


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Plasma reactors

Different types of power supply to generate theplasma are

y Low-frequency (LF, 50 450 kHz )y Radio-frequency (RF, 13.56 or 27.12 MHz )y Microwave (MW, 915 MHz or 2.45 GHz )

The power required ranges from 10 to 5000 watts,depending on the siz e of the reactor and the desiredtreatment.


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Co

ld plasmas can be used f o r

vario

us treatments:y plasma polymersation (gaseous monomers)

y Graftingy deposition of polymers, chemicals and metal particles by

suitable selection of gas and process parametersy plasma liquid deposition in vaporised form.

G ases c o mm o nly used f o r plasma t r eatments :y

Chemically inert (e.g. helium and argon).y Reactive and non-polymerisable (e.g. ammonia, air, andnitrogen).

y Reactive and polymerisable (e.g. tetra uoroethylene,hexamethyldisiloxane).


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Plasm a tr e a tm e nt vs. Tradition a l tex tile proc e ssing


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y Examples of functional coatings that could be achieved by APP liquidprecursor coating include:

y H ydrophobic coatings for durable, breathable, water repellence, waterroll-off and inhibition of capillary ow; dry process for the waterproofing of polyaramid bres with no loss of bre strength, e.g.for bulletproof vests.

y H ydrophilic response for water wicking for moisture transferring andquick-drying textiles, e.g. sport, military; extra absorbance, e.g. easy capillary ow; anti-fog; easy take-up and good coverage for painting,coating, dyeing, etc.

y Oleophobic coatings with high oil, solvent, blood, etc. repellence anddurability to boiling water and solvent washes

y Low friction coatings with coef cient of friction comparable to PTFEy

Reactive coatings, e.g. chemically reactive and reagent-speci cltrationfabricsy Non-stick/release low release force; stain release, e.g. anti-dirt, easy

clean workwear, automotive upholstery y Adhesion promotion coatings for outstanding bondability, coating and

laminationy Bioactive coatings


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Anti-bacterial nishes for both general and medical use inhibit bacterialgrowth, achieve reduction in bacteria, e.g. anti-bacterial face masks Antifungal nish inhibit growth of fungi on textilesSelective biological tethering sites bio-receptors/bio-af nity,biofunctional wound dressingsGrafting of enz ymes, proteins, cells

y Copolymersy Multifunctional surfaces, e.g. dual function NH 2 with COOH groupsy Smart/responsive surfaces, e.g. F + PEG in air, stain-repellent F on

surface, in water, stain removing PEG on surfacey Trapped active coatings The coating matrix encapsulates sophisticated

active molecules that can be released in a controlled manner over time orthrough applied stimulus. Potential actives include anti-microbials,enz ymes and bio-molecules, pharmaceutical agents, cosmeceuticals,fragrances, agro-chemicals, anti-oxidants, ame retardants, catalysts andphotochromic agents.


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y Substrate surfaces can be modi ed homogeneously in shortprocessing times without any change in bulk properties.

y A huge range of surface modi cations are possible by choosing appropriate plasma types, equipment, and gas or

liquid precursors.y Chemical consumption is low and the process is safer and

much more environmentally friendly.y Above all, APP processing, particularly liquid precursor

coating treatments, offers the textile industry extensivepotential for innovation and more exible manufacturingcapabilities.


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H ot/ Th e rm a l Plasm ay Plasmas are generally classi ed as thermal or non-

thermal. Thermal ( hot ) plasmas are characterised by a condition of thermal equilibrium between all thedifferent species contained in the gas.

y In fact, if the gas density is sufficiently high, thefrequency of collisions between electrons, ions, andneutral species composing the plasma is such that anefficient energy exchange is possible. In thermalplasmas, temperatures of several thousands degreesare reached.


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Re sults obt a ine d on Tex tile Ma te ria lsy E nhancement of both h ydrophi l ic and h ydrophobic properties .

This is one of the most widely studied plasma applications.Oxygen, ammonia air, nitrogen, etc. plasmas have been used toincrease the wettability of synthetic polymers (PA, PE, PP, PET,PTFE, etc.), while hydrophobic or oleophobic nishing of natural

bres (cotton, wool, silk, etc.) has been obtained by usingsiloxanes, per uorocarbons, SF6, acrylates, etc.

y Adhesion promotion . Good adhesion between bres and matrixis essential in the production of composites and laminates.Plasma treatments can increase markedly the surface energy of synthetic bres, improving the mechanical characteristics of the

nal products.


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Re

sults obt a ine

d onTex

tile

Ma te

ria ls (C

ontd.)y D yeing and printing . Several studies have shown that dyeability or

printability of textiles can be markedly improved by plasmatreatments. This effect can be obtained on both synthetic and natural bres. Capillarity improvement, enhancement of surface area, reductionof external crystallinity, creation of reactive sites on the bres andmany other actions can contribute to the nal effect depending on theoperative conditions. Also production of colours on bres exploitingdiffraction effects has been attempted.

y E l ectrica l properties . Antistatic properties have been conferred to articial or synthetic polymers. Moreover, studies have been carried out forthe creation of fabrics with very high conductive properties, suitable forintegrating electronic devices into fabrics.


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Re sults obt a ine d on Tex tile Ma te ria ls (C ontd.)

y I nte ll igent l tration properties . Filtration of gases or liquids is one of the most common technical applications of bres, fabrics or nonwovens. Appropriate surface functionalisation can enhance chemicalselectivity of traditional lters based on more conventionaladsorption/absorption or physical separation processes.

y Other properties . The extreme versatility of the plasma processes isshown by a very large number of investigations concerned with a widerange of different properties of great importance for textiles, such as

ame retardancy, crease resistance, antimicrobic, antimicotic,biological compatibility, antifelting for wool, UV-protection, as well as

hand modi cation, softening and antipilling.


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