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Advanced Technologies

Introduction: Laser / Plasma Technologies

Laser and Plasma technologies are being explored as processing options for the textiles industry. Currently this technology is implemented to treat substrates in the electronics and engineering sectors but the technology is relatively new in the textiles field.

The advantages are cleaner processing and improved environmental impact due to a reduced amount of water, chemicals and resultant effluent. Energy use is lower due to the elimination of the need for drying or curing.

The Textile Innovation Project is exploring using laser plasma technology as a finishing technology to impact properties such as flame retardancy, anti microbial and hydrophobicity/hydrophilicity. 

For further information contact: enquiries@textilehouse.co.uk

Laserplasmalanding

Basic Principles

In elementary physics reference is often made to the three states of matter: Solid, Liquid and Gas. However, there is a fourth state: Plasma. See Fig.1

Fig.1 The Four States of Matter

Fig 1

To convert a solid to a liquid energy is imparted to the solid, usually in the form of heat; similarly to convert a liquid to a gas. It is not therefore surprising that to convert a gas to a plasma, energy also needs to be imparted to the gas. The energy disassociates electrons from the gas atoms through atomic particle collisions. This occurs randomly, which means the energised gas is a mixture of ions, freed electrons, photons and neutral atoms (those yet to lose electrons). If a solid or liquid substance is introduced into the plasma, the high energy gas particles of the plasma will penetrate and collide with atoms or molecules several nanometres into the solid or liquid, disassociating those electrons and bringing those atoms or molecules to an excited state to be part of the plasma. This means that the high energy particles of the plasma will continuously etch away a several nanometre layer of a solid or liquid substrate for as long as the material is in contact with the energised gas.

Since there is an equal number of dissociated species (ions /electrons, etc) in the gas volume, the gas remains electrically neutral. Thus, any ionised gas that is composed of nearly equal numbers of negative and positive ions may be called a plasma.

Definition

 A plasma is a partially ionised gas, composed of neutral species (atoms/molecules) and UV/visible radiation and an equal number of positive ions, and freed electrons in an excited/energetic state.

Irving Langmuir first used the term plasma in 1926 to describe the inner region of an electrical discharge.  However, the atmospheres of most stars, the gas within the glass tubing of neon advertising signs, and the gases of the upper atmosphere of the earth are examples of plasmas. On the earth, plasmas occur naturally in the form of lightning bolts and in parts of flames. See Fig.2

Fig.2 Four Categories of Plasma

Fig 2

The ionisation of a gas to form a plasma is achieved by the introduction of large concentrations of energy, which can be in the form of bombardment with fast external electrons resulting from an applied high energy electric field, or by irradiation with high energy laser light, or by heating the gas to very high temperatures. The type of gas being considered,the amount of energy given to that gas, and the pressure under which that gas is held will determine the level of excitation, i.e. the amount or degree of ionisation, and therefore the type of plasma. 

The degree of ionisation is quantified by the number of freed electrons per cm3; this is called the “Plasma Density”, and from Fig.2 it can be seen that, corresponding to particular sections of  the range of plasma densities, there are mainly four categories of plasma: dark plasma, where the gas temperature is low and no visible light is emitted; cold plasma where the temperature is also relatively low but a visible glow of light is emitted (the plasma may be called glow discharge plasma); thermal plasma, where the temperature is high and a strong visible light is emitted; and, hot plasma, where the temperature is very high and a emitted light is intense. With dark and cold plasma the gas pressures are low: near vacuum to atmospheric pressure. Thermal and hot plasmas are produced at much high pressures > 10kPa.  In general the colour of the emitted light is dependent on the type of gas or gases involved.

For the surface modification of textiles the interest is in cold plasmas of the type generated by applying an electric field to the contained gas.  See Fig.3 The electric field may be generated with DC or AC, RF (40 kHz, 13.56 MHz) voltage or microwave (GHz) power supply. In practice most are RF generated.

Venugopalan, M., Ch. 1: The plasma state, Reactions Under Plasma Conditions, Venugopalan, M., Ed., Vol.I,John Wiley, New York,1-72 (1971.)

Cold plasmas are suitable for surface treatment of textiles because the ionised gas can be kept close to room temperature. This is due to the fact that the energy of the plasma is mainly confined to the energy of the low mass electrons. As the electrons are extremely light, they move quickly and have almost no heat capacity. Ionisation is maintained by the impact of electrons with neutral species. Cold plasma is better to use than dark plasma, because of the higher plasma densities; having more electrons equates to faster treatment times.

Fig.3 Mechanism of Cold Plasma Creation by Electric Field

fig 3

There are various differing cold plasma systems, but the two which that have attracted most attention for textile applications are 1) low pressure plasma (i.e. near vacuum plasma) and 2) atmospheric plasma. Fig.4 illustrates the principles of the two systems.

Fig.4 Low Pressure and Atmospheric Pressure Plasma

Fig 4

The low pressure gas plasma is formed by first evacuating a chamber and introducing low flow of the required gas through the chamber at pressures of the order of 2-4mTorrs (0.3 – 0.5Pa). The textile substrate is placed close to the ground electrode as the high voltage RF is applied to the opposite electrode to initiate and maintain the plasma.

  • T Wakida, S Tokino, S Niu, H Kawamura, Y Sato, M Lee, H; Uchiyama and H Inagaki, Text. Res. J, 63 (1993) 433.

Fig.5 shows (a) woven fabric prior to being placed in a vacuum chamber for low pressure air plasma treatment and (b) the glow of the air plasma during treatment of the fabric.

A dielectric barrier discharge (DBD) arrangement can be used to produce cold plasmas at atmospheric pressure. Atmospheric plasmas provide the highest possible plasma density (in the range of 1 to 5 x 1012 electrons cm-3). See Fig.3.  The DBD arrangement involves applying a pulsed voltage over an electrode pair of which at least one is covered by a dielectric material. The purpose of the dielectric material is to prevent electrical arcing between the two electrodes (corona discharge) that may take place at atmospheric pressure.

Fig.5 Low Pressure Plasma Glow Discharge

  • Fig 5Atmospheric pressure plasma of dielectric barrier discharges,  Chirokov, A. Gutsol‡, and A. Fridman, Pur Appl. Chem. Vol 77, No.2 p487-495 2005
  • Penetration of a dielectric barrier discharge plasma into textile structures at medium pressure N De Geyter, R Morent and C Leys INSTITUTE OF PHYSICS PUBLISHING PLASMA SOURCES SCIENCE AND TECHNOLOGY Plasma Sources Sci. Technol. 15 (2006) 78–84

As  Fig 4 illustrates, the various ionised species will interact with the textile substrate to give different surface treatments.

Plasma- substrate surface interaction

i)        ion bombardment

The combined action of chemically reactive and accelerated ions results in sputtering and etching of the substrate surface. (Reactive Ion Etching)

ii)      UV radiation with wavelengths of less than 178 nm

Photo-ionization will cause dissociation of molecular bonds, yielding free radicals and may excite specific groups. Chain scissions can occur leading to rearrangements or even elimination of the original specific functional group (e.g. by Norrish’s type reactions).  The radicals created on the substrate surface can in the absence of oxygen cause cross linking; react with species from the plasma gas;  or can react with oxygen to form peroxides.

iii)    Electrons

The electrons are substantially retarded as they penetrate nanometre depths of the substrate and impact with atoms of the substrate to release more ionised particles.

Radicals in the plasma gas can be deposited and  incorporated at the substrate surface (ie radical-radical recombination); or can abstract atoms from the substrate surface; or can induce polymerization and/or cross linking at the surface.

iv)     Neutral species

If unsaturated, these may polymerise at a radical containing surface. During each plasma process  etching (sputtering or chemical etching) and (re)deposition are occurring.

During each plasma process the above interactions are occurring, i.e. sputtering & chemical etching,  (re)deposition, and polymerisation. The net effect depends on the gases used and the plasma conditions, i.e.  the type of gas or gases used, the energy density, etc. Generally,

Gas Type:

·        oxidising gases [O2, CO2,H2O]  will give  etching & functionalising, i.e functional groups will be boned to the substrate surface

·        noble gases will largely produce etching  of the substrate surface

·       hydrocarbon containing gases  will give plasma polymerisation reactions

This means that depositing or non-depositing plasmas may be created.

-         Depositing Plasmas – may use saturated or unsaturated gases e.g  fluro-and hydro-carbons or vapours(monomers) such as acetone, methanol, allyamine and acrylic acid.

-         Non-depositing gases can be reactive etching gases (Ar, He, O2, N2, F2) or non-polymerisable gases (H2O, NH3)

Plasma treatments can therefore decrease the surface hydrophobicity ( by using Ar or O2) or increase the hydrophobicity (by using CF4, NF3, SiF4 or BF3). Only outermost surface layers (25-100 Å) of the substrate are modified by plasma treatments.

The energy density of a plasma can be increased by:

·       Increasing the frequency of the electric field,

·       Confining the plasma with a magnetic field,

·       Decreasing the plasma volume (by varying the place, positions, shape and surface ratio of the electrodes)

·       Increasing the input power.

The final chemical composition of the surface is influenced by:

·       the substrate used (e.g. fibre type)

·       the gases used (etching or deposition)

·       the energy density of the plasma,

·        the bias voltage,

·       substrate temperature (>Tg etching rate increases)

·       increasing  flow rate for a set power. This increases etching or the deposition 

Applications

Low-temperature, low-pressure plasma (LTLPP) is already used industrially for the treatment of certain metals, semiconductors and polymer materials. For example, in chemical, pharmaceutical, biological and medical equipment low-pressure plasma is used to treat plastic surfaces, such as mouldings from polyethylene for bottles, pipes and containers. LTLPP is also used for the treatment of polymer surfaces in the packing industry. There have not, however, been many applications for the treatment of fibre and textile materials, mainly for the reason that LTLPP systems have to be vacuum based which is expensive and such systems are only suitable for batch processing, although some attempts have been made at developing continuous low pressure plasma machines.

For plasma processing methods to be used in the textile industry, they need to based on atmospheric pressure, low temperature plasma (APLTP) and a number of such systems are now being developed commercially. [see section on manufacturers] Nevertheless, most of the research studies that have identified the potential plasma surface treatment offers, have been undertaken with LTLPP; the technology transfer to APLTP is seen as mainly a matter of modification to process conditions.  The following is, therefore,  a summary of the findings from LTLPP treatments of various textile structures and fibre types.

LTLPP technology has been widely investigated for the surface modification of textiles and an overview of such plasma treatments has been published by Morent et al.  Many of the improvements to fabrics of various fibre types largely depended on the gas employed. See Table 1 

·       Non-thermal Plasma Treatment of Textiles, Morent, R., De Geyter, N., Verschuren, J., De Clerck, K., Kiekens, P., and Leys, C., Surf. Coating. Tech., 202, 3427–3449 (2008).

Table 1 Effect of Gas Type on Plasma Application

APPLICATION

MATERIAL

TREATMENT

Hydrophilic? finish

PP, PET, PE

Oxygen plasma, Air plasma

Hydrophobic finish

Cotton, P-C blend

Siloxane plasma

Antistatic finish

Rayon, PET

Plasma consisting of dimethyl silane

Reduced felting

Wool

Oxygen plasma

Crease resistance

Wool, cotton

Nitrogen plasma

Improved capillarity

Wool, cotton

Oxygen plasma

Improved dyeing

PET

SiCl4 plasma

Improved depth of shed

Polyamide

Air plasma

Bleaching

Wool

Oxygen plasma

UV protection

Cotton/PET

HMDSO plasma

Flame retardancy

PAN, Cotton, Rayon

Plasma containing phosphorus

 
There have been examples of surface modification of materials, for  wettability of synthetic materials for enhanced adhesion of subsequent coatings. 

·       Strategies to Improve the Adhesion of Rubbers to Adhesives by Means of Plasma Surface

Modification, Eur.Martı´n-Martı´nez, J.M. and Romero-Sa´nchez, M.D. (2006)., Phys. J. Appl. Phys., 34: 125–138.

Desizing and Improved wettability of cotton and most synthetic fabrics (PP, PET, PA, PE) were related to plasma gases of nitrogen(N2), air and oxygen(O2), and the operating parameters of power and exposure time. The plasma caused etching of the fibre surface and the bonding of polar groups.

·       F.Ferro, Polymer Testing, 22(2003) 571

·       Effect of Atmospheric Plasma Treatment on Desizing of PVA on Cotton.

ZAISHENG CAI AND YIPING Qiu CHUYANG ZHANG, YOON-JIONG HWANG, AND MARIAN MCCORD,Textile Research Journal 73(8) 670-674 2003

For example, it was found that oxygen plasma treatment can be used to remove contaminants, finishing and sizing agents from cotton fabrics, while at the same time increasing the specific surface area of cotton fibre, thereby improving dye uptake. Desizing of polyester fabrics that used polyvinyl alcohol as the sizing agents can also be achieved with oxygen plasma treatment. The wetability of polyester fabrics also increases significantly.

Generally polyester fibres have very hydrophobic surfaces because their surfaces are made up of ether oxygen (C-O-C) linkages while the Hydrophilic? ester oxygen (C=O) is facing towards the core of the fibre. When fibre surfaces are treated by the plasma, C-O-C linkages get broken through etching and the C=O linkages come closer to the fibre surface, in addition new C=O bonds are formed with oxygen ions. The result is increased capillary sorption of aqueous solutions. The etching of the PET is readily seen from scanning electron microscopic images. See Fig.6,

 PP is a very hydrophobic material with extreme low Surface Tension?, but it is used in a large number of technical applications where an improved wetability or adhesion properties are advantageous; for example, technical textile applications such as filters, medical and hygiene products.  By using oxidative plasma important improvements in Surface Tension? can be obtained. Air or oxygen  plasma treatment of polypropylene significantly increases the hydrophilicity of the fibre surface, the Contact Angle? of water being decreased from 90° to 55°. Although aging (the decrease in wettability with time) is a recognised problem, a sustained effect was observed even after two weeks, the Contact Angle? with water being 60°.  

The uptake of oxygen at polypropylene fibre surfaces was even more significantly demonstrated when maleic acid anhydride (MAH) was used as an assisting reagent. The incorporation of oxygen became permanent and a Contact Angle? with water of 42° was achieved.

Fig.6 Etching of PET Fibre Surface with Air Plasma

Fig 6

 

Plasma treatment of natural fibres can improve not only improve wettability, coloration, ( for example Table 1 shows the improvement in  reflectance(%R) and K/S value of dyed untreated and dyed plasma treated Angora fibres)  with enhanced colourfastness, but with suitably chosen plasma gases these materials can be made highly hydrophobic.

 

Table 1 Reflectance and K/S values for Dyed Angora Fabrics after Plasma Treatment

Sample specification

% R

K/S

Untreated

2.03

23.6176

He+air plasma treated(for 10 min)

1.80

26.8366

 
The treatment of cotton with a hexamethyldisiloxane (HMDSO) or a silicone-based plasma gives a smooth surface with increased water Contact Angle? of up to 130°.  See Fig.7. Thus, a strong effect of hydrophobisation is achieved. Similarly, when a hexafluoroethane plasma was used instead of an HMDSO plasma, the surface composition of the cotton fibres clearly indicated the presence of fluorine and the cotton fabrics were highly hydrophobic. However, water vapour transmission was not compromised by the hydrophobisation. Hydrophobisation in conjunction with increased specific surface area results in an effect generally known as Lotus effect: dirt particles are easily removed from the surface by water droplets (Figure 8).
 
Fig.7 Cotton Fabric Plasma Treated for Hydrophobicity
Fig 7

Fig. 8 Plasma induced Lotus Effect

Fig 8

Lower temperature plasma treatment of wool has emerged as one of the environmentally friendly surface modification method for wool fabrics. The efficiency of the plasma treatment is governed by several operational parameters like the type of gas used, the system pressure, the discharge power and the duration of treatment.

 Plasma treatment can impart an  anti-felting effect (by etching of the scales – see Fig.9) , degreasing, improved dyestuff absorption and increasing wetting properties.

The fatty matter content in wool is reduced by about 1/3 by plasma treatment.

 Plasma treatment etching of the wool scales considerably reduces the felting potential of  wool fabrics, similar to chlorinated treatments, but the plasma process has environmental benefits of being a clean, dry process. The reduction in the content of covalently bound highly hydrophobic methylicosanoic acid and the increase in oxidised sulfur spaces give significant improvement of dyeing and shrink resistance of plasma treated wool. Silicon resins applied to plasma treated wool further will improve the anti-felting character and shrink resistance during laundering. The original surface shrinkage of 57 % (according TM 31) can be reduced below 10% after plasma treatment, offering "Super-wash" quality to the treated fabric. 

Fig. 9 Plasma Treatment of Wool Fibres

Fig 9

It is now widely acknowledged that plasma technology has the potential advantages of improving the surface properties of polymeric materials without changing the bulk properties to give enhanced wettability, water repellency, anti-soiling/soil release, printing, dyeing and other finishing processes of textile fibres and fabrics. However, the main possible advantages of plasma treatments are a shortened processing time, the non-existence of water in the process, no hazardous chemicals and therefore non-polluting. The consumption of chemicals as precursors is very low and, being a dry process, less energy and time are required for fabric treatments.

The environmental aspect is without doubt one of the most attractive potential advantages of plasma technology. Plasma processing is a clean, simple and multifunctional process which should enable textile finishing procedures to meet the growing restrictive economic and ecological demands

Machinery Manufacturers

http://www.arioli.biz/en/plasma-inglese/85-plasma-production-unit-inglese

http://www.htpunitex.com/HTP%20Unitex%20-%20EN.html

http://www.tantec.com/

http://www.sigmalabs.com/atmospheric-plasma-treatment/

http://sigmalabs.squarespace.com/storage/publications-and-resources/SIGMA%20APT%20Brochure.pdf

http://tri-star-technologies.com/catalog/plasma.php

Spraying?.aspx">http://www.bodycotemetallurgicalcoatings.com/technologies/plasma-Spraying?.aspx

http://www.enerconind.com/treating/library/technology-spotlights/plasma-treatment-industry-applications.aspx

http://www.apjet.com/technology.html

http://www.europlasma.be/pageview.aspx

Publications

GAS FLOW AROUND AND THROUGH TEXTILE STRUCTURES DURING

  • PLASMA TREATMENT, J. Verschuren, P. Kiekens
  • AUTEX Research Journal, Vol. 5, No3, September 2005 © AUTEX

Modification of polyester fabrics by in situ plasma or post-plasma polymerisation of acrylic acid

Room-temperature atmospheric pressure plasma plume for biomedical applications

A new approach for dyeability of cotton fabrics by different plasma polymerisation Methods.

  • E Özdogan,a R Saber,b H Ayhanb and N Seventekin,a,Color. Technol., 118 (2002) p100 -103

Acrylic Fabrics Treated with Plasma Outdoor Applications

  • S. PANE,  R. TEDESCO and R. GREGER.JOURNAL OF INDUSTRIAL TEXTILES, Vol. 31, No. 2—October 2001 135 -145

Dynamic (de)wetting properties of superhydrophobic plasma-treated polyethylene surfaces

  • J. Fresnais, L. Benyahia and F. Poncin-Epaillard: SURFACE AND INTERFACE ANALYSIS Surf. Interface Anal. 2006; 38: 144–149

The Effect of Plasma Treatment on Some Properties of Cotton

  • Reza M.A. Malek1 and Ian Holme: Iranian Polymer Journal, 12 (4), 2003, 271-280

SURFACE CHARACTERISATION OF LOW-TEMPERATURE PLASMA TREATED WOOL FIBRE

  • Kan Chi-wai*, Chan Kwong and Marcus Yuen Chun-wah: AUTEX Research Journal, Vol. 3, No4, December 2003

Investigating the Plasma Modification of Natural Fiber Fabrics–The Effect on Fabric Surface and Mechanical Properties

  • D. SUN1 AND G. K. STYLIOS, Textile Res. J. 75(9), 639–644 (2005)

Pore Structures and Anti-bacterial Properties of Cotton Fabrics Treated with DMDHEU-AA by Plasma Processes, Meng-Shung Yen1, Jui-Chin Chen and Po-Da Hong

  • Textile Research Journal Vol 76(3): 208–215

Surface characterization of plasma-treated polypropylene fibers

  • Q.F. Wei. Materials Characterization 52 (2004) 231– 235

Dyeing Transition Temperature of Wools Treated with Low Temperature Plasma, Liquid Ammonia, and High-Pressure Steam in Dyeing with Acid and Disperse Dyes

  • MUNCHEUL LEE,1 TOMIJI WAKIDA,2 MYUNG SUN LEE,1 PYONG KI PAK,3 JIERONG CHEN4
  • Journal of Applied Polymer Science, Vol. 80, 1058–1062 (2001)

 Selected Properties of Wool Treated by Low-Temperature Plasma

  •  Dorota Biniaś, Andrzej Włochowicz, Włodzimierz Biniaś,
  •  FIBRES & TEXTILES in Eastern Europe April / June 2004, Vol. 12, No. 2 (46)

Plasma treatment of textile fibers, Hartwig Höcker

  • Pure Appl. Chem., Vol. 74, No. 3, pp. 423–427, 2002.

Reactive Physical Vapour Deposition of TixAlyN: Integrated Plasma-surface Modelling Characterization,. Zhang, D. and Schaeffer, J.K.

  • Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 22(2): 264–271. (2004).

Radiofrequency-generated

  • Glow Discharge Treatment: Potential Benefits for Polyester Ligaments Richard, J., Rowland, J., Tsukazaki, S., Kikuchi, T., Fujikawa, K., Kearney, J.,Lomas, R., Wood, E. and Seedhom, B.B.., Journal of Orthopaedic Science, 8(2): 198–206. (2003).