Plasma Treatment as Green Technology for Dyeing of Textile Fabrics

Textile sector is facing an increased global competition in current decade owing to changing market conditions. The utilization of novel technical skills is thus forced for fabricating textile products for high quality performances [1]. This aspect is further accelerated to employ such technologies due to high level of hazardous chemicals in large quantities and volume of waste water textile effluents. Thus extra purification methods are needed to purify these effluents. As alternative to conventional chemical treatments, radiation has potential to tailor surface characteristics of polymeric, micro and nanostructures [2]. Among all available surface treatment methods, Plasma irradiation is observed a remarkable significance. This is a green, dry, worker friendly and ecofriendly method that can alter surface properties without major change in bulk performance of textile materials. Owing to heat sensitive nature of textile polymeric materials, non-thermal plasma is particularly suitable [3,4].


Introduction
Textile sector is facing an increased global competition in current decade owing to changing market conditions. The utilization of novel technical skills is thus forced for fabricating textile products for high quality performances [1]. This aspect is further accelerated to employ such technologies due to high level of hazardous chemicals in large quantities and volume of waste water textile effluents. Thus extra purification methods are needed to purify these effluents. As alternative to conventional chemical treatments, radiation has potential to tailor surface characteristics of polymeric, micro and nanostructures [2]. Among all available surface treatment methods, Plasma irradiation is observed a remarkable significance. This is a green, dry, worker friendly and ecofriendly method that can alter surface properties without major change in bulk performance of textile materials. Owing to heat sensitive nature of textile polymeric materials, non-thermal plasma is particularly suitable [3,4].

Plasma treatment Vs chemical modification
Surface morphology of fiber greatly influences the choice of processing method for it. For example, a fiber having scales on its surface may exploit unwanted phenomenon like barrier of diffusion or felting. Therefore, many fiber degradation effects as well as environmental issues are concerned by using chemical treatment for modification of such fibers [5,6]. Thus a number of green processes have focused due to ecological and economical awareness to deal these issues.
As comparison, low yield of dyeing and more than 50% dye lost in waste water effluent, some esthetic and environmental issues can minimized by plasma treatment before, during dyeing or finishing processes. Advantageously, this technology can operate at ambient conditions with lesser of no chemical auxiliaries are needed. Thus, this technology is attributed green textile technology.

Plasma treatment
Various characteristics have developed for textiles e.g., high level of shrink resistance [7-10] wet ability [11,12]. Low temperature plasma (LTP) treatment has shown significant plasmapolymer surface interactions to tailor process and performance characteristics of dyeing wool fiber including improved dye uptake, lesser felting dispute, increased electro negativity on fiber surface [7,[13][14][15][16]. In this way, penetration of dye become more penetrated in treated fiber and ultimately enhance coloration achieved. Exocutile A-layer of wool fiber is expected to under gone cytokine oxidation under exposure of sputtering results of plasma. Ultimately, partial swelling of A-layer at fiber surface occurred owing to decrease in cross-linkages and improved fiber-dye affinity. Comparatively, Acetone/argon plasma is favored in place of helium/argon plasma to improve dyeing ability of wool at room temperature towards acid dyes [14]. Furthermore, coupling enzymatic treatment along with low temperature plasma pre-treatment is significant to further increase dyeing rate of cotton and wool fabrics toward milling acid dye [17]. This performance achieved by simultaneous effect of enzymatic and plasma treatments which attack in interior and exterior of fiber respectively. Nature of plasma gas also contribute its significant effect for modifying fiber surface. For example, chrome dyeing of wool fabric is favored to use nitrogen plasma in place of oxygen plasma [18]. Thus, mordant treatment of wool fabric in textile processing can be substituted with plasma sputtering of which gives better performance characteristics of fabric and enhanced antibacterial properties advantageously [19]. Different schematic view of plasma sputtering setup for fabric is depicted in Figure 1. The performance of air plasma pre-treated fabrics is dependent to optimized process parameters [20,21]. Unwanted results may achieved at prolonged plasma exposure of fibe r such as change in appearance of fabric and heavier weight loss.  In place of natural fibers, plasma technology is shown extraordinary results for synthetic fibers as well. PET fabric treated by cold plasma exhibit enhanced dyeing performance owing to enhanced surface area and surface roughness induced by plasma treatment [22,23]. Enhanced dye exhaustion is also may be due to greater affinity and enhanced water swelling ability of PET fiber towards polar parts of dyes during dyeing process of treated PET fabric [24]. Anti-reflective coating of PET with better coloration is achieved by plasma sputter etching of organo-silicon compounds on surface of PET [25]. Corona plasma is able to remove unwanted matter substance from surface of acrylic [26] and polyamide [27] fibers as depicted in Figure [52], polypropylene [53][54][55], polyester [22, [56][57][58][59][60], polyamide [61][62][63][64], ramie [65] and viscose fibers [66].

Conclusion
This article is an attempt to exploit and summarize potential aspects of plasma technology for textile dyeing to be employed in textile sector. Plasma treatment is a dry and clean technique operates at ambient temperature which is able to improve coloration and to develop characteristic functionalities on surface of textile fabric without altering the performance of bulk fiber. Furthermore, plasma treatment can couple with other natural treatment methods which further improve the performance of treated fabric. This results insignificant reduction of toxic chemicals and auxiliaries in effluent load which diminish energy usage and cost and environmental impact.