Plasma technology its application in textile wet processing

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Plasma technology its application in textile wet processing

Transcript Of Plasma technology its application in textile wet processing

International Journal of Engineering Research & Technology (IJERT) Vol. 1IISsSsuNe: 52,2J7u8l-y0-1821012

PLASMA TECHNOLOGY & ITS APPLICATION IN TEXTILE WET PROCESSING
S. K. Chinta*, S. M. Landage and Sathish Kumar. M
D.K.T.E.Society‟s, Textile & Engineering Institute, Ichalkaranji, Maharashtra, India
Abstract
Plasma treatments are gaining popularity in the textile industry due to their numerous advantages over conventional wet processing techniques. The plasma treatment does not alter the bulk property. Plasma surface treatments show distinct advantages, because they are able to modify the surface properties of inert materials, sometimes with environment friendly devices. Application of “Plasma Technology” in chemical processing of textiles is one of the revolutionary ways to enhance the textile wet processing right from pretreatments to finishing. This paper deals with application of plasma technology for cotton pretreatment and finishing.
Key words: Cotton, Dyeing, Finishing, Pretreatments, Plasma Technology
1. Introduction
Textiles have undergone chemical processing since time immemorial. The textile industry is searching for innovative production techniques to improve the product quality, as well as society requires new
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finishing techniques working in environmental respect. Over recent years, physicochemical techniques have become more commercially attractive and have begun to overcome conventional wet chemical methods for property modification. The importance of surface modification of textile materials extends over a wide range of alterations or embedded selective additions, to provide desired single or multi features for various applications. It is a highly focused area of research in which alterations to physical and/or chemical properties lead to new textile products that provide new applications or satisfy specific needs. These processes, however, can involve numerous chemicals, some of which are toxic to humans and hazardous to the environment. Additional problems also arise due to degradation and/or weakening of the treated material. Alternative techniques have been investigated over the past two decades to decrease or eliminate dependency on chemical treatments. One recent alternative, involving non-aqueous processing, is plasma treatment of textile materials. Appropriate choice of gas and control of plasma operation conditions provide a variety of effects on textiles (improvement of dyeability, printability and colour fastness, improvement of adhesion properties of coated fabrics, increase in hydrophobicity and water resistance, etc.). Surface modification via plasma treatment not only eliminates the need for wet processing, but also yields unique surface characteristics. Several modifications include, but are not limited to: hydrophilicity/ hydrophobicity alterations, surface roughening, grafting, flame retardant, antimicrobial, insect repellant, stain resistant, and single or multiple surface functionalisation. An ideal plasma treatment for textile applications is a plasma system that can be

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Vol. 1IISsSsuNe: 52,2J7u8l-y0-1821012
introduced into the production line without major changes or system interruption, allowing for high speed and continuous processing.
“Plasma” derived from the Greek and referring to “something molded or fabricated”. A literature review of plasma technology reveals considerable interest of the scientific community in this field since the fifties. Several studies proved that surface properties of different polymeric materials can be easily modified with high energy irradiating sources. Plasma can be considered as a gaseous condition that contains several excited species such ions, free electrons and a large amount of visible, UV and IR radiations. The plasma state can be generated by:
Electrical energy Nuclear energy Thermal energy Mechanical energy Radiant energy
The differentiation between plasmas can be made based on his main characteristics, namely by the charged particle density, temperature, pressure and the presence/absence of electrical and/or magnetic fields.

1.1 Types of Plasma
Plasma is generally classified as thermal or nonthermal. In thermal plasma, temperature of several thousand degrees is reached which is of a destructive

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nature and no material can stand their action. Contrary to thermal plasmas, non-thermal plasmas are „cold‟ plasmas where the chemically active environment is achieved at nearly room temperature and this one is used for surface modification of textiles. There are two types of cold 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. The table below gives an idea of the working pressures of vacuum and atmospheric plasmas.
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.
The coupling of electromagnetic power into a process gas volume generates the plasma medium comprising a dynamic mix of ions, electrons, neutrons, photons, free radicals, meta-stable excited species and molecular and polymeric fragments, the system overall being at room temperature. This allows the surface functionalisation of fibres and textiles without affecting their bulk properties. These species move under electromagnetic fields, diffusion
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Vol. 1IISsSsuNe: 52,2J7u8l-y0-1821012
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. In all these processes a highly surface specific region of the material (<1000 A) is given new, desirable properties without negatively affecting the bulk properties of the constituent fibres.
Plasmas are acknowledged to be uniquely effective surface engineering tools due to:
Their unparalleled physical, chemical and thermal range, allowing the tailoring of surface properties to extraordinary precision. Their low temperature, thus avoiding sample destruction. Their non-equilibrium nature, offering new material and new research areas. Their dry, environmentally friendly nature.
1.2 Plasma reactors
Different types of power supply to generate the plasma are:
Low-frequency (LF, 50–450 kHz) Radio-frequency (RF, 13.56 or 27.12 MHz) Microwave (MW, 915 MHz or 2.45 GHz)

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The power required ranges from 10 to 5000 watts, depending on the size of the reactor and the desired treatment.
1.3 Effect of plasma on fibers and polymers
Textile materials subjected to plasma treatments undergo major 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. Plasmas create a high density of free radicals by disassociating molecules through electron collisions and photochemical processes. This causes disruption of the chemical bonds in the fibre polymer surface which results in formation of new chemical species. Both the surface chemistry and surface topography are affected and the specific surface area of fibres is significantly increased. Plasma treatment on fibre and polymer surfaces results in the formation of new functional groups such as -OH, -COOH which affect fabric wettability as well as facilitate graft polymerization which, in turn, affects liquid repellence of treated textiles and nonwovens.
In the plasma treatment of fibres and polymers, energetic particles and photons generated in the plasma interact strongly with the substrate surface, usually via free-radical chemistry. Four major effects on surfaces are normally observed. Each is always present to some degree, but one may be favored over the others, depending on the substrate and the gas chemistry, the reactor design, and the operating parameters. The four major effects are surface cleaning, ablation or etching, cross-linking of nearsurface molecules and modification of surfacechemical structure.
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International Journal of Engineering Research & Technology (IJERT) Vol. 1IISsSsuNe: 52,2J7u8l-y0-1821012

Plasma cleaning and etching means a removal of material (impurities or substrate material) from the exposed surface. Plasma activation consists of the introduction of new functional groups onto the treated surface. Properties of the surface then depend on the nature of the chemical groups. Plasma-assisted grafting is a two-step process in which the plasma activation is followed by the exposure to a liquid or gaseous precursor, e.g. a monomer. The monomer then undergoes a conventional free radical polymerization on the activated surface. In plasma polymerization, a monomer is introduced directly into the plasma and the polymerization occurs in the plasma itself.
1.4 Environmental benefits
The complexity of textile processing environmental impact starts with high water and energy consumption, high oxygen demand of several input materials being used as well as a generation of huge amounts of effluents with high chemical oxygen demand (COD), excessive colour, pH and toxicity. In general, desizing, dyeing, washing and finishing are the main sources of effluent pollution. The main advantage of plasma processing is that it is a dry treatment. Additionally, it is a very energy efficient and clean process. In general, the environmental benefits of plasma treatment can be summarized as:
Reduced amount of chemicals needed in conventional processing

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Better exhaustion of chemicals from the bath reduced BOD/COD of effluents shortening of the wet processing time Decrease in needed wet processing temperature Energy savings.
2. Application of Plasma in Textile Processing
2.1 Desizing
Atmospheric pressure plasma treatment on cotton grey fabric (sized by standard sizing recipe containing starch) with air and He gas mixture alters the surface morphology, gave rise to desizing effect and enhance the wettability and wicking action. The hitting of ions gave rise to loosening of the surfaces that were removed in subsequent process of washing. The surface roughness as well as formation of (-C=O, -OH or C-N) bonds created functional groups are responsible for improved hydrophilic properties. The loss of weight in desizing process was more for plasma treated fabric that too in initial part of treatment. These higher rates of desizing plasma pre treated fabric can save time, energy and water. [1]
Atmospheric plasma treatments are applied to Desizing the cotton (PVA were used for sizing) using air/He and air/He/O2 combinations. These treatments removed some PVA film and significantly improved PDR (percent desizing ratio) by washing, especially by cold water washing. The tensile strengths of cotton fabrics treated with atmospheric pressure plasma were the same as for the unsized fabric. Results of the plasma treated PVA films revealed surface chemical changes such as chain scission and formation of polar groups, which promoted the

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solubility of PVA in cold water. Air/He/O2 plasma is more effective than air/He plasma on PVA desizing (because of oxidation is more for Air/He/O2 plasma) [2].
2.2 Scouring
Low temperature plasma treatment modified the surface of cotton fabrics. The contact angles between the liquid (scouring bath) and the low temperature plasma treated cotton fabric surfaces decreased significantly. Furthermore, the O2 plasma treatment by changing the surface properties dramatically increased the wicking rate of cotton fabrics, making them more absorbent. The results for scourability revealed that low temperature plasma treatment increased the scouring rate of cotton fabrics. O2 plasma caused changes in the oil, fat, and wax contents by etching where the topmost of the layer of the substrate is stripped off. This increased rate means that a shorter time have been chosen for scouring, the process was more environmentally friendly, and energy consumption decreased because less time was needed to reach the desirable state. For the scouring process, 25 minutes have been used for plasma treated instead of 40 minutes needed for scouring cotton fabrics [3].
2.3 Dyeing
The O2 plasma treatment dramatically increases the wicking rate of cotton fabrics, making them more absorbent hence increase the dyeing rate of cotton fabrics. Holes were visible on the O2 plasma treated cotton fabric surfaces, which were caused by the ablation effect of this nonpolymerizing reactive plasma gas. These holes provided a new pathway for
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the dye to enter the fiber and hence increased the dyeing rate. For the dyeing process 50 minutes have been chosen after plasma treatment instead of 90 minutes needed for dyeing untreated cotton fabrics. [3]
The Modification of the Cuticle and Primary Wall of Cotton by Corona Treatment was studied in which the effects of corona treatment were limited to the cuticle and primary wall of cotton, although one or two experiments (radiation sensitivity, bundle strength) suggested possibility for deeper penetration through to the secondary wall. Some disturbance of the wax on cotton was indicated in air chlorine corona treatments, and both the wax and cellulose reacted with chlorine in an air chlorine corona to produce C-Cl covalent bonds. Air-chlorine corona treatments have greater effect than the air corona treatments and air-chlorine corona treated fabrics are more wettable. A possible practical application of these results was to reduce the scouring or kier boiling required achieving a given dyeing level or dyeing uniformity [4].
The effect of low pressure plasma treatment on bleached and mercerized cotton fabrics was investigated with water vapour as working gas. Though bleached and mercerized cotton fabrics were hydrophilic, the change in hydrophilicity after plasma treatment has been tested and higher concentration of oxygen was founded on the surface of water vapour plasma treated surface. These higher oxygen concentrated surfaces gained higher hydrophilic properties. An increase in hydrophilicity revealed deeper dyeability of plasma treated fabrics [5].
2.4 Finishing
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