Natural dyeing and antibacterial activity of atmospheric-plasma-treated nylon 6 fabric Aminoddin Haji, a, * Ahmad Mousavi Shoushtari b and Maryam Mirafshar b a Textile Engineering Department, Birjand Branch, Islamic Azad University, Birjand, Iran Email: Ahaji@iaubir.ac.ir b Textile Engineering Department, Amirkabir University of Technology, Tehran, Iran Received: 28 October 2012; Accepted: 8 May 2013 Atmospheric plasma treatment as an environmentally friendly method was employed to modify the surface properties and improve the absorption of natural cationic dye on to nylon 6 fabric. Nylon fabric was treated in atmospheric air plasma, and the surface characteristics of the fabric were evaluated using attenuated total reflection Fourier Transform-infrared analysis, scanning electron microscopy, and a wicking test. The effects of plasma treatment and mordanting with copper sulfate on the dye uptake of the samples were investigated. Plasma-treated and mordanted samples showed the highest colour strength when dyed. The antibacterial activity of samples was evaluated according to AATCC test method 100-2004. Premordanting with copper sulfate showed a synergistic effect on the antibacterial properties of the dyed fabric. The plasma-treated and copper-sulfate-mordanted sample showed acceptable antibacterial activity against both gram-negative and gram-positive bacteria when dyed with an extract from Berberis vulgaris, berberine. Coloration Technology Society of Dyers and Colourists Introduction The most outstanding characteristic of nylon fibre in the textile industry is its versatility. Nylon is used both alone and in blends with other fibres, where its chief contribu- tions are strength and abrasion resistance. Nylon washes easily, dries quickly, needs little pressing, and holds its shape well, as it neither shrinks nor stretches [1]. The presence and growth of microorganisms are an environmental concern to the public owing to increasing cross-transmission of diseases in hospitals and working areas [2]. Textile materials are suitable media for the growth of microorganisms. Textiles have been widely used in medical and surgical applications. So, they may be treated with antibacterial and fluid-repellent finishes [3]. The increasing demand for multifunctional fabrics requires strong multidisciplinary approaches as well as the fusion of traditional scientific disciplines [4]. Nylon textiles are used in hospitals and medical appli- cations [5]. Several studies have been carried out on the antibacterial treatment of nylon fibres. Quaternary ammo- nium salts have been used to impart durable antibacterial properties to nylon textiles [2,6–8]. The antibacterial effect for gram-positive and gram-negative bacteria on polyamide fabrics was studied by deposition of silver nanoparticles from colloids [9–12]. Also, nylon 6/nanosilver nanocom- posite multifilament yarns prepared by melt spinning showed acceptable antibacterial activity [13]. Nylon fabrics grafted with chitosan after plasma treatment of the substrate showed good antibacterial activity [5]. Metal salts, includ- ing copper sulfate, nickel sulfate, and silver nitrate, induced antibacterial activity to atmospheric-plasma-treated nylon fabric [3]. Berberine as a natural dye and antibacterial agent has been used on wool and nylon fabrics and exhibited excellent antibacterial activity [1,14–17]. Plasma treatment of textiles is being investigated as an alternative to wet chemical fabric treatment and pretreatment processes. It may result in desirable surface modifications (about 10 nm in depth), including but not limited to surface etching, activation, crosslinking, chain scission, decrystalli- sation, and oxidation [18]. Atmospheric pressure plasma techniques are gaining popularity owing to the ease of incorporating them in textile finishing operations [3]. In this study, berberine natural cationic dye, with antibacterial properties, was used to dye nylon 6 fibres and simultaneously impart antibacterial activity. Atmo- spheric air plasma treatment was used as an environmen- tally friendly pretreatment to improve the adsorption of the dye on to the fibres. The synergistic behaviour of copper with this natural dye was analysed to increase the dyeabil- ity, fastness, and antibacterial activity of the dyed samples. Materials and Methods Materials Polyamide 6 knitted-fabric, 210 denier/35 filament yarns were supplied by a local mill. To remove any impurities, the fabric was soaped with 2 g l 1 of Ultravon GPN (anionic surfactant; Ciba, Switzerland) at 60 °C for 30 min, thor- oughly washed, and air dried at room temperature. Sodium carbonate, acetic acid, and copper sulfate were analytical- grade reagents obtained from Merck (Germany). To extract the berberine colorant (Natural Yellow 18), Berberis vulgaris roots were first washed and dried and then chopped and powdered. To prepare the original solution of the dye, each 100 g of the powder was added to 1 l of distilled water and boiled for 2 h. Then, the volume of the solution was adjusted to the initial amount by adding distilled water, and filtered. The concentration of the resultant solution was 10% (w/v). The UV-vis spectrum of the resultant solution was recorded using a Jenway (UK) 6850 UV-vis spectrophotometer (Figure 1), which is in agreement with the literature [1,15]. Methods Plasma treatment The samples were treated in atmospheric pressure plasma equipment (corona system) composed of a rotating silicone- © 2013 The Authors. Coloration Technology © 2013 Society of Dyers and Colourists, Color. Technol., 130, 37–42 37 doi: 10.1111/cote.12060