Textile materials possess desirable inherent qualities, such as flexibility, low specific weight, strength, a high surface-to-volume ratio, a pleasant "touch and feel" effect, and softness. Because of this, they readily adopt additional qualities, such as hydrophobic, oleophobic, or antibacterial ones. It is well knowledge that traditional wet techniques for applying these finishes need enormous quantities of chemicals, water, and energy. Plasma processing and PVD coating of textiles are a dry method that facilitates the reduction of all three materials indicated. Let see how we can use plasma in the textile industry, what plasma can do on textile materials, and the present state of plasma integration in textile processes.
Consider the possible influence that plasma might have on the textile finishing business.
Prior to that, we will see why the present chemical methods for textile processing are not good for environment and the sustainable earth.
Through impregnation, mixing with molten polymer prior to spinning, or impregnation with resin and thermal fixing, conventional additives are commonly included into textiles to impart desired properties. All these conventional procedures generate pollutants, cost significant amounts of energy, and alter the physical qualities of the materials.
As a result of the commercialization of industrial plasma equipment, plasma processing offers an intriguing alternative to conventional aqueous procedures for textiles, most of whose qualities are dependent on the surface rather than the bulk.
Conventional aqueous process is a wet chemical process, while plasma-based treatments and coatings are dry and non-chemical processes.
Large volumes of water are required for textile finishing processes that employ chemical agents. Typically, 330 liters of water are required to create 1 kilogram of wool and 380 liters for 1 kilogram of cotton. Due to the continually rising costs of providing water and purifying effluents, as well as the high energy costs caused by the after-treatment drying, limiting, or eliminating water usage during finishing is economically justifiable. Environmental protection and safer working conditions also justify the textile industry's interest in innovative dry processes. From a legal standpoint, the pollution caused by textile finishing is a significant issue that must be resolved soon, as law becomes more stringent. In France, for instance, over 200 kt of textiles are treated annually, generating approximately 250 kt of oxidative materials as per the French Ministry of Economy. On top of this, one must add the employed harmful substances.
The standard cotton processing involves washing, mercerizing, dyeing, impregnation, rinsing, finishing and that requires about 400 liters of water for 1kg of cotton cloth. While the wool requires 350 liters of water for the processing involving chlorination, anti-chlorination, neutralization, rinsing, resin, and softening process. This makes the case, why we need to go for plasma processing of coating of textiles, while leaving behind the conventional wet chemical processing.
The plasma technology has the ability to enhance or replace the majority of finishing treatments and offers a cost-effective solution to environmental issues by conserving water and energy and reducing the number of effluents that must be treated. Plasma technology can replace or even enhance most of the finishing processes listed below. In addition, it provides a competitive solution to environmental and economic issues associated with water and energy consumption, and it reduces the number of effluents that must be treated.
In general, a vast array of plasma treatments for textiles are conceivable. A great deal of research has been conducted and published on this topic. The most typical treatments consist of:
• conferring hydrophilic characteristics • boosting adhesion • improving printability and colorability • modifying electrical conductance • imparting hydrophobic and oleophobic qualities • antibacterial agent application • use of fire retardants • treatment of wool to prevent shrinkage
• sterilization
• de-sizing of cotton.
In addition to the desired functionalization, the plasma treatment of textiles is frequently subject to other standards and specifications. Actually, the therapy was applicable:
• must impart the necessary functionality;
• must not interfere with potential activities of finishing effect
• should not generally alter the intrinsic features of fibers (touch, behavior, texture, etc.).
• must withstand maintenance procedures such as, removing the stain, washing, drying, hot ironing, drying machine, dry cleaning etc.
It is crucial to understand that certain surface alterations generated by plasma therapy are not permanent. Instead, ageing occurs, meaning that the impact of the plasma therapy diminishes over time. Usually, a portion of the impact will persist, and a stable state will be attained after a few weeks.
Plasma therapies that are especially susceptible to ageing must be distinguished from those that are not. For processes like as etching and coating, ageing is not a significant concern. In the first scenario, material is removed permanently, but in the second scenario, material is added permanently. Regarding surface functionalization, ageing might be problematic. Plasma therapy is a surface effect; only the surface's uppermost layers are affected. For functionalization, grafted chemical groups can reorient themselves, or additives or smaller molecules can migrate to the surface from within the bulk.
Typically, both effects occur under the influence of thermal energy. They also have the same result: less of the grafted chemical substance is available at the surface, reducing the functionalization's effectiveness.
The preceding logic applies especially to surface activation involving oxygen-based groups that can reorient themselves relatively easily. Consequently, the typical activation process by corona is performed in-line, immediately prior to the intended finishing step.
Dye exhaustion decreases with age, indicating a decrease in the coating's hydrophilicity. The best recovery of wettability by water immersion was discovered to be when water vapour was added to the discharge.
Plasma chemistry generally considers ageing to be an undesirable side effect. In contrast, ageing may be considered advantageous in SiClx coatings, for instance. Hydrolysis will be induced by atmospheric water vapour, resulting in a hydrophilic Si(OH)x coating. In addition to hydrolysis and the creation of oxygen bonds, the imprisoned radicals undergo reorientation of their surface groups.
Let's investigate the textile manufacturing process and provide references to the employment of plasma throughout this production chain, that is, during the preparation of natural fibers, extrusion, spinning, treatment of fibers, textiles, non-woven, and garment treatment.
The textile sector may also utilize plasma therapy for effluent treatment. This application will not be evaluated since it is not considered a direct textile treatment.
From the raw material, natural fibers or filaments can be extracted or extruded. Natural fibers are turned into a sliver or top before being produced into yarn during the spinning process. By mixing extruded filaments, yarns can also be produced. A single filament may also be used as such; in this case, it is referred to as a monofilament, and it may undergo additional finishing.
Furthermore, fibers can be treated directly into non-woven structures. The majority of the time, however, yarns are created that are further processed using traditional textile techniques such as weaving, knitting, or braiding to create, for example, textiles, ropes, or plaits. Often, these items undergo additional finishing and tailoring processes before becoming completed textiles.
In theory, a plasma treatment might be implemented between any two subsequent manufacturing processes. However, certain places in the manufacturing chain will be considerably more convenient than others. Considered here are essentially five positions where plasma treatment is more prevalent:
• fiber level
• filament level
• yarn level
• fabric level
• intermediate/complete textile products.