Plasma Technology For Textile Fibres Biology Essay

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The aim of the study is to provide an insight into plasma treatment for textile fiber assemblies. This study has undertaken to shed light on research being conducted across the world and does provide an overview of the methodology behind surface modification and fictionalizations of materials with plasma. Also, the review addresses the tremendous potential of the technology to develop processes which can limit the environmental impact of textile processing and contribute towards sustainable development.

This approach requires the contribution of researchers of different disciplines, with a theoretical or practical background, and cannot be successful without an input from the textile industry. It is hoped that this paper will be inspirational to such a generic and multidisciplinary research effort.

Plasma is an ionized form of gas. It contains electrons, ions and neutral atoms and molecules. Its application area is huge and diverse, it finds its application area in niche applications in many industrial areas including, polymers, paper, metals, ceramics and in-organics, biomaterials (Shishoo, 2007), electronic equipments. And now plasma technology is finding its promising position in textile as well.

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Now the study of surface physico-chemical properties of atmospheric air-plasma-treatment on material surface is emerging. To-date there are only few papers

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The potential of plasma technology for the treatment of textiles is enormous. This is shown in the numerous scientific, technical and review papers published in the course of the last four decades. Some of the possible effects are improved hydrophilic properties [1], an increased chemical reactivity of the fiber surface [2], an improved adhesion to coatings [3] and to polymer matrices [4], plasma induced hydrophobic properties [5], fiber surface cleaning [6], etc.

The segmented applications to textiles are surface modification without changing the bulk properties of substrate control hydrophobicity, hydrophilicity.

Plasma also used as a precursor to other surface modification techniques (John & Anandjiwala, 2009).

In recent times, some companies have also started to offer commercial systems for atmospheric-pressure plasma processing of textiles, both in-line and on-line. Despite all the significant benefits demonstrated in the laboratory and industrial prototypes, plasma processing on an industrial scale has been slow to make an impact in the textile industry. The factors may behind such a slow progress are slow development of suitable industrial plasma systems, late focus on developing in-line atmospheric pressure plasma systems and less public transparency regarding the successes and failures of industrial trials (Shishoo, 2007).

The principle

A 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 nature of the breakdown and the voltage at which this occurs varies with the gas species, gas pressure, gas flow rate, the materials and the nature, geometry and separation of the surfaces across which the voltage is sustained, the separation distance of the electrodes, the nature of the high voltage supply (e.g. dc, ac, radiofrequency or microwave) and the actual electrical circuitry. (Bryant, 2007)

The coupling of electromagnetic power into a process gas volume generates the plasma medium which comprises a dynamic mix of ions, electrons, neutrons, photons, free radicals, meta-stable excited species and molecular and polymeric fragments, rather affecting their bulk properties. These species move under electromagnetic fields, diffusion gradients, etc. on the textile substrates placed in or passed through the plasma. This enables a variety of generic surface processes including surface activation by bond breaking to create reactive sites, grafting of chemical moieties and functional groups, material volatilization and removal (etching), dissociation of surface contaminants/layers (cleaning/ scouring) and deposition of conformal coatings (Shishoo, 2007)

Types of Plasma

Though there are many types of plasma, the route to textile applicable plasma is illustrated in figure below:

Thermal Plasma

It is a type of plasma that is found in the universe in the form of sufficiently high temperature. That is, temperature of several thousand degrees. If the gas density is sufficiently high, the frequency of collisions between electrons, ions, and neutral species composing the plasma is such that an efficient energy exchange is possible. It can be observed in nature as Northern Lights, stars and other celestial bodies. It can also be seen on earth as flash lightening, Since, no material can withstand against such intrinsic destructive nature, particularly if addressing Textile. Thus, it is not the topic of our discussion.

Low Temperature Plasma (Cold Plasma)

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There are two types of plasma which can be used for application on textiles, namely vacuum pressure and atmospheric pressure. 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. Many authors, however, choose to classify vacuum pressure plasmas into sub categories of low and medium pressures (Li & Hsueh, 2005); (Einagar, Kh.; et al, 2006); (De Geyter, Morent, & Leys, 2006). The table below gives an idea of the working pressures of vacuum and atmospheric plasmas.

Table , Operating pressures of vacuum and atmospheric plasmas

Atmosphere

Pressure

kPa

Torr (mmHg)

(atm)

Bar

Low

0 - 0.29

0 - 2.175

0 ­0.003

0 ­0.0029

Vacuum

Medium

0.3 - 7

2.25 - 52.5

0.003 ­0.069

0.003 ­0.07

Atmospheric

101.3

760

1

1.103

This text, due to very little difference between the sub classes of vacuum plasma will not differentiate between the two forms and discuss two main classes of plasma which are (near) vacuum pressure plasmas and atmospheric pressure plasmas.

Both these forms are suitable for application on textiles and progress continues to determine their effect on textiles. More work has, however, been documented on characterization of vacuum pressure plasmas as compared to atmospheric pressure plasmas (M. G. McCord et al,, 2002)

Figure 2.2 (Roth, 2001) provides an idea of the variation in the existence of plasma as the current is increased. The regions marked as dark and glow discharge are normally suitable for surface modification. The corona region of dark discharges is used in atmospheric plasmas while vacuum pressure plasmas usually lie in the glow discharge region. Arc discharges, due to heavy bombardment of the cathode at high currents attain temperatures which are too high for safe surface modification techniques (Reichel, 2001). This section will thus discuss vacuum and atmospheric plasmas which have been realized as suitable for application on textile substrate.

Figure , Voltage current characteristics of the classical DC intermediate pressure electrical discharge tube (Roth, 2001)

Vacuum pressure plasmas

If a voltage is applied across a nearly evacuated gas chamber, under appropriate conditions, a plasma will ignite (Reichel, 2001). Changes in these conditions vary the effect and appearance of the plasma.

Vacuum pressure treatments are generally used to achieve varying outcomes of textile substrate. These plasmas will either etch or form radicals on the surface of the processed material. Each of these terms is explained in more detail in section 3.

Vacuum pressure plasma systems have certain limitations adhered with them in terms of commercial application. The vacuum creating equipment adds to the cost of treatment and is expensive to run. Also, the operating pressure range allows only for batch processing of material to be possible.

There are certain advantages in terms of application such as etching and coating which can be performed better under low pressure plasmas. These advantages are discussed in more detail in section 3.

Atmospheric pressure plasmas

As the name suggests, these systems process materials at atmospheric pressures thereby increasing the processing capabilities of the machine while reducing processing costs and loading times.

Different types of cold plasma can be described: (Marcandalli & Riccardi, 2007)

Glow discharge

This is obtained at low pressures, typically less than 10 mbar. The plasma is generated by antennas, fed with electromagnetic fields at frequencies of 40 kHz or 13.56 MHz or microwaves (2.45 GHz).

Figure Glow discharge plasma (Mathews, 2005)

Corona discharge

This is obtained at atmospheric pressure by applying D.C., low frequency or pulsed high voltage between two electrodes of very different sizes. The corona consists of a series of rapid, non-uniform, non-arcing discharges. Plasma density drops off rapidly with increasing distance from the electrode.

Figure Schematic diagram of Corona Discharge (Mathews, 2005)

It has one limitation in corona systems that it affects only in loose fibers and cannot penetrate deeply into yarn or woven fabric so that their effects on textiles are limited and short-lived. Essentially, the corona plasma type is too weak. Corona systems also rely upon very small inter-electrode spacing (-1 mm) and accurate web positioning, which are incompatible with 'thick' materials and rapid, uniform treatment (Shishoo, 2007)

Dielectric barrier discharge

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This is an atmospheric-pressure plasma source. In this case a pulsed high voltage is applied between electrodes, one or both of which is covered by a dielectric layer. The purpose of 284 Plasma technologies for textiles the dielectric layer is to terminate rapidly the arcs that form in the region between electrodes. The discharge consists of series of rapid microdischarges.

Figure Dielectric barrier discharge (Mathews, 2005)

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Dielectric barrier discharges (DBDs) or "silent" discharges are widely studied for the treatment of polymer films and textiles [5, 6, 19-22]. These discharges demonstrate great flexibility with respect to their geometric shape, working gas composition and operational parameters (input power, frequency of the applied voltage, pressure, gas flow, substrate exposure time, etc.) [23]. A DBD is obtained between two electrodes, at least one of which is covered with a dielectric, when an AC high voltage is applied between the electrodes. The most interesting property of DBDs is that in most gases the breakdown starts at many points, followed by the development of independent current filaments (named micro-discharges). These microdischarges are of nanosecond duration and are uniformly distributed over the dielectric surface [24-27].

Atmospheric pressure plasma jet (APPJ)

This technology enables plasma to be applied to textile fabrics in the in-situ mode in which the fabric is passed through the plasma generation region between electrodes (Herbert, 2007)

Figure (Herbert, 2007)

Plasma substrate interaction - Surface modification

In the plasma bulk, reactive species (positive and negative ions, atoms, neutrals, meta-stables and free radicals) are generated by ionization, fragmentation, and excitation. These species lead to chemical and physical interactions between the plasma and the substrate surface depending on plasma conditions such as gas, power, pressure, frequency, and exposure time. The depth of interaction and modification, however, is independent of gas type and is limited to 5mm. (Mathews, 2005) (Rakowski, Okoneiwski, Bartos, & Zawadzki, 1982)

In this case, a medium of particular interest is weakly ionized highly dissociated oxidative plasma that can be sustained in high frequency discharges in oxygen, air, carbon dioxide, water vapor, and mixtures of these gases with a noble gas.

Plasma is used in no. of ways to synthesis and modifications the substrate surface as, removal of thin films of organic impurities (Radetić, et al., 2008) (Köchler & Fritzshe, 2007), selective etching of composites (Wang, Ren, & Qiu, 2007) (Akishev, Grushin, Monich, Napartovich, & Trushkin, 2003), sterilization (Negulescu, et al., 2000), passivation of metals (Costa, Feitor, Alves, & Freire, 2006), ashing of biological materials (Park, 2008), etching of photo-resists (A., Raffaele-Addamo;, 2006), functionalization of polymers (Vesel, 2008), and conditioning of tokamaks with carbon walls (Makabe, 2006). The choice of discharge parameters is determined by the requirements of each particular application.

Though there are number of opportunities exist for plasma treatment besides only few have been graphically modeled. However, in principle, plasma surface interaction i.e. surface modification of the surface can be divided in two major routes

Physical surface modification (Etching)

Chemical surface modification (Radial formation)

Surface graft polymerization

Incorporation of Functional group

Figure Mechanisms of Plasma-Substrate Interaction (Mathews, 2005)

Figure A typical graphical model of possible plasma-substrate interaction (Selwyn, Herrmann, Park, & Henins, 1999-2000)

Questioned:

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The previously mentioned aspects lead to the conclusion that the treatment of a textile fiber surface is, in fact, the treatment of a large number of surfaces in a range of accessibilities to the plasma created reactive species and whose chemistry ranges from pure fiber polymer to pure processing chemical. As a consequence, in the assessment of a plasma treatment effect on the complete textile structure, results from surface selective techniques, such as scanning probe microscopy or X-ray photoelectron spectroscopy, require (a) an indication of the depth into the textile structure from which the fiber was extracted and (b) the analysis of a sufficient number of separate fibers.

In the end, the aim of a plasma treatment and of any other chemical treatment of a textile is to change the properties of the textile, rather than of each fiber individually. Thus, apart from analyzing individual fibers (through e.g. AFM) and the textiles' surface (through e.g. X-ray Photoelectron spectroscopy (XPS)), it is not only useful, but also necessary to analyze the textile in its entirety. Unfortunately, the fiber surface related characterization of complete textile structures, for instance through wicking properties, often results in data expressed in units other than SI-units. In view of plasma treatment inhomogeneity, it is also clear that those results are an average within the range of values for the individual fibers. Still, when resulting from e.g. depth profiling experiments, those results can lead to the understanding of what actually happens inside a textile product during its plasma treatment and can be a valuable basis for the creation of a general mathematical model.

The study of actual plasma-textile interactions is a very complex matter, as indicated by the small number of papers on this topic. When industrialists or researchers have the ambition to have thorough control over the result of the plasma treatment of a textile product resp. to acquire fundamental knowledge on plasma-textile interactions, the aforementioned typical textile properties are best taken into account. Due to the complexity of the plasma state and of a textile structure in their own right and the large variation in types of plasma and textile, the development of a general mathematical model describing and predicting plasma-textile interactions - including effect penetration - is a huge task to accomplish.

Conclusion:

A number of steps can be proposed:

• The further development of means to observe the textile during plasma treatment and means to characterize plasma-induced changes throughout the textile structure.

• The development of substrates that can serve as a structural and surface chemical model for (industrial) textiles.

• The qualitative description of what is observed and the formulation of empiric rules after systematic experimentation in which textile parameters are varied.

• Comparison of the experimental results with results from the treatment of non-porous polymer surfaces and with models for such treatment.

First, it is possible that a desired textile property cannot be optimized to an industrially acceptable level, for a given combination of textile structure, fiber surface condition, plasma source and required productivity. Secondly, in the description of plasma-induced textile modifications, it is possible that systematic data relevant to the increase of fundamental knowledge are acquired rather

plasma treatment, as well as their scientifically sound characterization particularly challenging: (a) a large specific surface, (b) a three-dimensional porous structure and (c) the presence of impurities at the fiber surface, as well as in the fiber structure. In order to obtain insight into the fundamentals of plasma-textile interactions, which would enable research and the industry to steer away from the current plasma treatment by trial-and-error, a generic approach to the plasma treatment of textiles - dubbed "plasma-for-textiles" - is proposed, in which the above properties are taken into account. It is expected that the study of effect penetration will play an important role in this matter. This approach requires the contribution of researchers of different disciplines, with a theoretical or practical background, and cannot be successful without an input from the textile industry. It is hoped that this paper will be inspirational to such a generic and multidisciplinary research effort.

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Another problem related to the surface modification using plasma technology is the fact that plasma-treated textile materials may not be stable after treatment [15]. There are often changes in the surface wettability and surface chemistry as a function of storage time after treatment [16-18]. Treatment parameters must be optimized in order to achieve the desirable surface modifications without causing physical degradation and in order to achieve a small ageing effect.

Overcome:

Nowadays, the surface treatment of textiles using DBDs is mostly studied at atmospheric pressure (Borcia, 2003) (Shenton M. J.-H., 2001), since the textile industry requires a plasma technology that can be integrated in a continuous production or finishing line. Therefore, low and medium pressure technologies are regarded as being non-competitive. However, plasma treatment at medium pressure has some advantages over atmospheric plasma systems. A large plasma volume, available for surface treatment, can be easier obtained at medium pressure than at atmospheric pressure. This can result in a higher overall productivity at medium pressure. Furthermore, at medium pressure the pumping equipment is relatively inexpensive. However, until now, only little research (De Geyter N. M., Surface Modification of a Polyester Non-woven with a Dielectric Barrier Discharge in Air at Medium Pressure, 2006) (De Geyter N. M., Penetration of a Dielectric Barrier Discharge Plasma into Textile Structures at Medium Pressure, 2006) has been done on medium pressure plasma treatment of textiles.

Etching / Adhession

Etching is more or less a physical process. Plasma etching is the key process for the removal of surface material from a given substrate. This process relies on the chemical combination of the solid surface being etched and the active gaseous species produced in the discharge. The resulting etched material will have a lower molecular weight and the topmost layer will be stripped. In previous methods, such as chemical wet processing, plasma has shown much more controllability and a much finer resolution (Mathews, 2005) (Chapman, 1980) the treatment requires physical and chemical etching process conditions that change the frictional properties of fibers. The mechanical properties change via an increase in tensile strength, bursting strength and wear resistance (Morent, 2008).

The four basic plasma processes commonly used for surface removal are shown in Figure

Figure The Four Basic Plasma Etching Processes: (a) sputtering, (b) pure chemical etching, (c) reactive ion etching, and (d) ion inhibitor etching. (Mathews, 2005)

The first process, sputtering, is a purely physical, unselective process. Energetic ions crossing the sheath transfer large amounts of energy to the substrate, resulting in the ejection of surface material. This mechanical process is sensitive only to the magnitude of bonding forces and structure of the surface, rather than its chemical nature (Tsai, 2005).

The second process, chemical etching, involves gas-phase etchant atoms or molecules formed through collisions between energetic free electrons and gas molecules, which stimulate dissociation and reaction of the feed gas. These etchants chemically react with the surface to form volatile products (Tsai, 2005). This process is invariably isotropic or non-directional, since the gas-phase etchants arrive at the substrate with near uniform angular distribution. The etch rate for pure chemical etching can be quite large due to a high flux of etchants to the substrate (Ferreira, 2007).

The third is the combine process of both first and second process. Thus, have greater effect on the substrate. Reactive ion etching, is characterized by a combination of physical sputtering and chemical activity of reactive species. In most situations, the chemistry in this process is provided by the neutral species. A basic reactive ion etch system proceeds by (1) generation active species in the plasma, (2) transport of reactive intermediates from the plasma bulk to the substrate surface, (3) absorption of reactive radicals and "active site" formation, concluding with (4) chemical reaction and desorption of volatile reaction products (Drenik, 2005).

The fourth technique involves an inhibitor as a precursor molecules that absorb or deposit on the substrate.

The polymer-forming inhibitor species may originate from the feed gas, feed gas additives, sputtered reactor material, or a resist mask. During this process, the plasma chemistry initiates the formation of a thin film on the sidewalls of the etched feature, which prevents chemical attacks. The bombarding vertical ion flux keeps horizontal surfaces clear of this inhibitor film. A highly anisotropic etch with vertical side walls is formed, and a volatile etch product is released […38, …53, …54].

However, in this process, the etched material (volatile or non volatile) might revert back to substrate surface, known as redeposition or backscattering. It depends on the volatility of the etched material.

 

Chemical

 

 

 

 

 

 Plasma treatment also increases the hydrophilic character of PET fibers [13-27], and has positive effects on dyeing properties [21- 25, 28, 29].

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Gorjanc, et al. studied the The influence of water vapor plasma on chemical, morphological and mechanical properties of bleached and mercerized cotton fabric

 Induce hydrophobicity in cotton

Sen'I gakkaishi studies the effect of plasma treatment methods, which were ordinary plasma treatment and pulsed plasma treatment, he revealed the following three points:

Oxygen plasma treatment enhance he adhesive strength at Cu\PEEK interfaces.

O plasma treatment introduce O functional group n produce an etching action at the interfaces. This etching action certainly contributed to the adhesive strength among these actions.

Introduction of o functional groups might also produce a synergetic effect with an etching action and this might turnout in stringer adhesion of the two interfaces. (Gakkaishi, 2009)

Polyester

Recently (Píchal & Klenko, 2009) czech technical university conducted an experimental on PES sheets. They study on the dielectric barrier discharge sustaining in air at atmospheric pressure and ambient temperature for synchronous treatment of several sheets of fabric. Effectiveness of the modification process was determined with hydrophilicity measurements evaluated by means of the drop test. Hydrophilicity of individual sheets of fabric has distinctly increased after plasma treatment. Important aspect for practical application of the plasma treatment is the modification effect time-stability, i.e. time stability of acquired surface changes of the fabric. However the analytical tests showed the recovery of hydrophobicity was fastest in first days after treatment, later gradually diminished until reached almost original untreated state.

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Morent et. Al studied PET and PP non-wovens using DBD in air, helium and argon at medium pressure. The study showed the non-wovens, modified in air, helium and argon, points toward a significant increase in liquid absorptive capacity due to the incorporation of oxygen-containing groups, such as C-O, O-C=O and C=O. It was shown that an air plasma was more efficient in incorporating oxygen functionalities than an argon plasma, which was more efficient than a helium plasma.

(c)

(b)

(a)

Figure SEM image of (a) the untreated PET non-woven, (b) the PET non-woven after plasma treatment in air (energy density = 230 mJ/cm2) and (c) the PET non-woven after plasma treatment in air (energy density = 1.13 J/cm2).

Conclusion

Development are ongoing, more versatilities are being brought to execute the processe, such as replacing of the precursor gases with the ones which are readily mre available to drive the this technolgyon the real pragmatic side.