Plasma Technology in Textile: A step towards the green environment (Part-4)

Plasma Technology in Textile: A step towards the green environment (Part-4)

Arpita Kothari
M. Tech. Scholar
Department of Textile Technology,
NIT Jalandhar, India
Cell: +91- 7837-696041

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4.3. Textile finishing:
Unlike wet finishing processes, which penetrate deep into the fibres, plasma treatment is restricted to surface reaction and limited to a surface layer of around 100 Ao. Because of this various functionality and properties can be imparted to both natural fibres and polymers, as well as to non-woven fabrics, without having any adverse effect on their internal structures.

This leads to produce various types of functional textiles. Various finishing applications of plasma in textiles are given in table-1.

Table 1: Various application of plasma in textile finishing

Hydrophilic finish
Oxygen plasma, Air plasma
Hydrophobic finish
Cotton, P-C blend
Siloxane plasma
Antistatic finish
Rayon, PET
Plasma consisting of dimethyl silane
Reduced felting
Oxygen plasma
Crease resistance
Wool, cotton
Nitrogen plasma
Improved capillarity
Wool, cotton
Oxygen plasma
UV protection
HMDSO plasma
Flame retardancy
PAN, Cotton, Rayon
Plasma containing phosphorus

Plasma can be used for grafting molecules on the fibre surface to impart special functionality to textiles. Hydrophobic character to lightweight cotton fabric can be done by polymerization using microwave plasma. A polymer layer of about 100 Ao thick is deposited on the cotton fibre surface as a result of this plasma assisted grafting and polymerization. Europlasma, CD Roll 1100/600, CD Roll 1800/600 are some machines based on plasma system tailored for textile surface finishing, developed in Belgium14. The costs of these devices are very high, If the cost factor is eliminated, this technology will be very important for textile finishing industry.

4.4. Bio-Medical Applications:
New medical products, materials and surgical procedures keep improving current health-care practices. Plasma surface modification can improve biocompatibility and bio functionality. The use of synthetic materials in biomedical applications has increased dramatically during the past few decades. Although most synthetic biomaterials have the physical properties that meet Surface Modification Methods. Modifying the surface of a material can improve its biocompatibility without changing its bulk properties.

Several methodologies have been considered and developed for alter the interactions of biomaterials with their biological environments; plasma surface modification is one of these methodologies. The Process In the plasma surface modification process, a glow discharge plasma is created by evacuating a vessel, usually quartz because of its inertness, and then refilling it with a low-pressure gas,. The gas is then energized using techniques such as radiofrequency energy, microwaves, alternating current of direct current. The energetic species in a gas plasma include ions, electrons, radicals, meta stables, and photons in the short-wave ultraviolet (UV) range. Surfaces in contact with gas plasmas are bombarded by these energetic species and their energy is transferred from the plasma to the solid,. These energy transfers are dissipated within the solid by a variety of chemical and physical processes as schematically to result in the surface modification.

4.5. Antifelting of wool:

Felting is an essential issue of wool garment due to the fibre scales. Conventional anti-felting gives negative effects on hand feel and environmental issues. Oxygen plasma gives anti-felting effect on wool fibre without incurring traditional issues.

4.6. Water repellent fabric:
Cotton or hemp fabric usually absorbs water immediately. Applying a low-pressure plasma process, the fibre’s surface can be altered to make it repel water. After the treatment, drops run freely over the surface while mechanical properties, the visual appearance, and the permeability for water vapour remain unchanged. The surface modification is limited to a very thin layer. A treatment as short as 2 seconds can be sufficient to achieve this effect in a batch process. Continuous treatments with a speed of more than 20 m/min are conceivable. The stability of the modification can be seen in intermitted washing cycles of fluorocarbon treated cotton fabric. After an initial drop, the finishing remains stable for at least two hours at 95°C. The quality of the repellent effect is evaluated by putting water drops to the fabric surface. A value of 1 means that the drops run freely over the surface and do not penetrate into the material while at a value of 3 the water does not penetrate but it needs vibrations to move the drop. Obviously this evaluation depends also on the nature of the fabric.
Figure 7: Water repellence of fabric
4.7. Adhesion improvement in laminates and composites:
In oxygen plasma the number of functional groups at the surface can be increased which can improve the adhesion to other material. The results are stronger laminates and better composite materials.
Adhesion improvement in laminates
4.8. Flame retardant fabric:
Currently, halogen-containing flame retardants are being banned for ecological reasons. The new kinds of flame-retardant chemistry, e.g. based on organic phosphonate derivatives, are much more expensive. Therefore, their usage should be limited to the absolute minimum. It has been shown that, in the case of plasma-activated fabrics consisting of both natural fibres and polymers, the concentration of flame-retardant chemicals can be reduced considerably without influencing the flame-retardant properties of the treated web. This again leads to considerable cost savings.

4.9. Hydrophobation of nonwovens for filtration applications:
It is mainly plasma polymerisation for coating deposition that has found its way into the filtration industry. A first example of plasma coating can be found in air filter media both for respirator masks and for filters used in HVAC systems. Such filters consist of several layers of meltblown nonwoven PP, which are electrically charged (electrets). Filtration efficiency for oily particles can be greatly improved by applying a hydrophobic/oleophobic coating prior to electrical charging.
Hydrophobation of nonwovens for filtration applications
4.10. Hydrophilic coatings on nonwoven PP for battery separators :
NiMhydride rechargeable batteries normally use a nonwoven meltblown PP separator web. In order to improve wetting with the electrolyte, some manufacturers are using gamma rays to increase surface energy, but this is an expensive and even hazardous type of treatment. By applying a permanently hydrophilic type of coating out of gaseous pre-cursors, one can increase wetting behaviour of the battery separator considerably.

For a 1 min wicking of a plasma-coated material, values between 22 and 25 mm were obtained immediately after plasma coating, whereas the uncoated reference material gave 0 mm (no wicking at all). Commercial reference materials on the market, which were not plasma coated, showed wicking values of only 5 to 10 mm. The samples from the wicking test performed 21 days after plasma coating were immersed in a beaker with 30% KOH solution. The beaker was covered with aluminium foil and was then put in an oven at 70 ÂșC for 7 full days. After this, the samples were rinsed in demineralised water and air dried. Then the wicking test was repeated, showing wicking values of 16–18 mm. Wash resistance of permanently hydrophilic coatings is better than for hydrophobic/oleophobic coatings but is still limited to about 7 wash cycles. Again, in the battery separator application, this is not important. 

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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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