Clinical surface modification process using the nitrogen plasma and its anti-bacterial efficiency

1 Introduction

Synthetic dyestuffs and pigments are toxic. They are not bio-degradable and ecological. The use of natural dye has begun to increase for their better properties as being bio-degradable, non-toxic, origination no problem to human health and waste water contaminant [1]. Natural dyes are classified into three categories: vegetable, mineral and animal origin. Turmeric is a natural dye with vegetable bases. Turmeric classified as yellow color dyes which produce dull deep shade. Turmeric is the roots of the plant. Some of the natural dyes based on plants exhibit antimicrobial, anti-carcinogenic and antioxidant, which make them ideal to be used in the textile and other industries [2]. So, natural pigments could contribute towards sustainability of the textile industry greatly and so many researchers work on natural dyeing of textiles and many studies are currently underway all around the world [3–7]. The study conducted by Ashis Kumar Samanta in 2011 [8] concluded that without the use of mordants, natural dyes had no tendency on cellulose or other textile fibers. To create an affinity between the fiber and dye, natural dyes need a mordanting chemical. Metallic mordants anchored to any fiber, chemically combine with certain mordantable functional groups present in the natural dyes and bound by secondary bonds [8]. The major disadvantage of natural dye is metal mordants such as Fe, Al, Cu, Pb, Sn that are used in order to increase dye uptake, improve the fastnesses and obtain different color effects. These metal mordants in large scales in factories are not suitable. They create many ecological problems on fabric and in waste water [9].

Many techniques such as color isolation on fabrics, bio polishing, bio scouring of fabrics, cationization, mercerization of fabric, ultrasonic treatments, enzyme treatment, chitosan treatment, UV exposures and etc. are being used to improve dyeing behavior of natural dyes to get good shades and fastness properties and modified fabric by improving extraction process or enhancing dye uptake activity of fabric. In addition, to improve the absorption of natural dyes to textiles, plasma treatment is used as a pretreatment [10–16]. Plasma is a source of ions, chemically reactive atoms, photons and molecular radicals. Surface modification of textile materials by plasma treatment, in recent years, has opened up new possibilities in textile industries. Plasma treatments for textiles and fabrics are growing rapidly due to their effect is limited to the uppermost layers of a material surface and does not affecting their bulk properties. Also, amount of toxic by-products is low compared to finishing processes based on wet chemistry [17–18]. Textiles are sensitive to microbial attack. They have a large surface area and absorb moisture and can improve microbial growth. Natural fibers allow bacterial growth, by providing basic requirements such as nutrients (in the form of protein or cellulose), appropriate conditions of oxygen and temperature and moisture. Textiles are treated with various compounds such as organic and inorganic compounds for antimicrobial functionality.

Many of these chemicals are toxic to humans and are difficult to degrade naturally. As a result, researchers are interested to derived natural antimicrobials [19]. There has been much interest in the development of natural fibers for use in textile industry, apparently due to strong consumer demand for ‘green’ products based on renewables. Cotton fiber is the most widely used natural fiber in textile industry today; it is most often spun into yarn or thread and used to make a soft, breathable textile. Nowadays, cotton is the principal raw material for use in textile industry [3]. In this study, turmeric as a natural dye was applied to both untreated and nitrogen plasma treated cotton fabric by using an exhaustion process. Some parts of samples were treated with silver nitrate as a mordant before dyeing. Effect of plasma and silver nitrate on both dyeability and antibacterial activity of cotton was compared. Use of plasma treatment for more absorption of turmeric and better antibacterial efficiency on cotton fabric is the main goal of this research.

2 Experimental setup

The 100% plain weave cotton fabric (a woven, with a fabric weight of 204.44 g/m²) used as the substrate in this study was supplied by Baft Azadi Co., Tehran. The fabric was weaved by 18.8 tex warp and 56.88 tex weft yarns. To remove any residual impurities from fabric, before treating the samples with low temperature plasma, fabrics were washed with an aqueous solution containing 1 g/L non-ionic detergent and then dried in a laboratory oven. Turmeric was acquired from a local market in Iran in the powder form. Silver nitrate was also, purchased from Merck. A direct-current (DC) magnetron sputtering device was used for plasma treatment. The description of the experimental setup was described in previous research work [20].

Next, nitrogen was used as working gas in the study. An aluminum (Al) post cathode was used because of its lower sputtering rate. Fabric samples were put on the anode in the plasma reactor. The chamber was pumped down to 2×10^-3 torr using a rotary pump, and nitrogen was admitted into it up to a pressure of 5×10^-2 torr. Voltage and current of the system were kept constant at 1000 V and 200 mA. Time of exposure was 5 minutes. Some parts of both untreated and plasma treated samples were treated for 45 minutes at 80°C in a 0.01 M solution of AgNO₃, protected from light. The materials were then rinsed three times with deionized water and dried at room temperature. All prepared samples (untreated, plasma treated, silver nitrate treated one and plasma/silver nitrate treated) dyed with turmeric as a natural dye by use of conventional dyeing method with 1 : 100 liquor ratio (L:R). Samples were dyed at boiling temperature for 45 minutes. And these processes, the samples were rinsed with cold water and left to dry.

The surface of the untreated, plasma treated, AgNO₃ treated and dyed cotton samples were investigated using a Scanning Electron Microscope (SEM, Philips, XL30, and Made in Netherland). The surface of each sample was first coated with a thin layer of gold (10 nm) by Physical Vapor Deposition using a sputter coater (SCDOOS, BAL-TEC, Swiss made). By using a UV–Vis–NIR reflective spectrophotometer in the range of 200–800 nm, color intensities of the samples were measured and the reflection factor (R) was obtained. Effect of plasma and silver nitrate treatment on dye ability of cotton with turmeric was studied. Luria-Bertani media (LB) broth in the bacteria counting test, was used as the growing medium for Staphylococcus aureus. Bacteria were dripped into 10 mL of LB broth to reach a cell concentration of 10⁸ (CFU)/mL. Then this was diluted to a cell concentration of 10⁶ (CFU)/mL. The 1 cm×1 cm fabric samples were put into a 1 mL bacteria suspension, and all samples were incubated for 24 h at 37°C. Then from each incubated sample, 100μL of solution was taken and distributed over an agar plate. All plates were incubated again for 24 h, and the numbers of colonies were counted [21].

3 Results and discussions

Rashidi et al. in 2013 [22] reported that, after nitrogen plasma treatment, some functional groups such as NH, NH₂ and nitril bands were produced on the fabric by the reaction between the active species induced by the plasma in the gas phase and the fabric surface atoms. By nitrogen plasma treatment, cotton fabric converted to a cationic material successfully. Silver particles absorption by cotton fabrics can be increased with nitrogen plasma treatment cause of reduction in the zeta potential on the surface of cotton fabrics after N₂ plasma treatment. The morphology of the untreated samples, plasma treated, plasma treated/dyed and AgNO₃ treated samples were analyzed using scanning electron microscopy. The SEM images related to untreated and plasma treated samples with different magnifications are shown in Fig. 1. After nitrogen plasma treatment, ripple-like patterns oriented along the fiber axis developed. Surface of plasma treated cotton fabric is not smooth and nanometric etching can be observed on the surface.

By AgNO₃ treatment of fabric, the surface of cotton fabric is covered by silver and the results can be seen in Fig. 2. Amounts of AgNO₃ particles on the surface of plasma treated fabric in more than untreated fabrics and this is cause of functional group on the surface and the etched surface of plasma treated fabrics, which can absorb more amounts of AgNO₃.

SEM images of untreated cotton and plasma treated cotton which dyed with turmeric are shown in Fig. 3. From the results, it can be concluded that the plasma treated sample absorbs more amount of dyes and more amounts of turmeric can be absorb on the surface of plasma treated samples.

The results in Fig. 4 demonstrated that, after plasma/silver nitrate treatment, more amounts of turmeric can be absorbed on the surface of cotton as compare with untreated/silver nitrate treatment.

Existence of more silver on the surface of plasma treated cotton, causes absorption of more turmeric. The reflection spectrophotometry results related to both untreated and plasma treated cotton after immersion in silver nitrate is shown in Fig. 5. As it can be seen in Fig. 5, the reflection factor of AgNO₃/plasma treated samples were less than AgNO₃ untreated sample. Results also show that N₂ plasma treatment is effective in increasing the absorption of AgNO₃ and more amount of Ag can be absorbed on the plasma treated samples and samples seem darker. In the other hand, in previous research it was concluded that, after N₂ plasma treatment, the magnitude of the reflection factor decreased and the sample appeared yellower.

In addition, spectrophotometry results of dyed samples are shown in Fig. 6. From the results, it can be concluded that the nitrogen plasma treated samples can absorb more amounts of turmeric dye as compare with untreated cotton. The reflection factor is reduced and samples seem darker. Results showed that N₂ plasma treatment can be effective for improving the natural dyeability of cotton fabric. The dyeability of mordant treated cotton is more and the reflection factor is less as compared with dyed untreated cotton. The reflection curves for both dyed untreated/AgNo3 and plasma/AgNO3 treated cotton are overlapping. However, in some wavelength in range of 300–350 nm, the reflection factor for plasma/AgNO3- turmeric sample is less and it shows that this sample is darker as compare with the others.

Antibacterial activity of untreated, turmeric dyed, AgNO₃/dyed and plasma treated/dyed samples were tested. Results are shown in Fig. 7. The results of the antibacterial test show more reduction of survival of bacteria in the case of dyed sample, in compare with untreated one. It can be concluded that, dyeing with turmeric is effective for antibacterial efficiency and turmeric as a natural dye has antibacterial activity on fabric. By plasma treatment as a dry and eco-friendly technology, more amounts of turmeric can be absorbed on the surface of cotton fabric and in plasma treated/dyed treated fabric, antibacterial activity has been developed. It means that by plasma treatment and then dyeing cotton samples, some of bacteria colonies were killed. But in case of AgNO₃ treatment, no bacteria can spread over the agar plate. Silver is an inorganic antibacterial agent. Plasma has a synergic role on antibacterial activity of turmeric on cotton samples.

4 Conclusions

Using natural products and natural dyes on textiles is a very promising prospect for future textile industry. Natural dyes are safe in processes and do not contain toxic and do not have allergic problems or damage the ecological balance. In this research work, turmeric as a natural dye was applied to untreated, nitrogen plasma treated, AgNO₃ treated and plasma/AgNO₃ treated cotton fabric by using an exhaustion process. From the SEM results, it can be concluded that plasma treated samples can absorb more amounts of turmeric in compare with raw material. But more amounts of dyes can be observed on the surface of AgNO₃ treated samples. From reflective spectrophotometry test, it can be concluded that AgNO₃ treated samples can absorb more amount of turmeric dyes, in compare with untreated and plasma treated cotton fabrics. By plasma treatment of fabrics, more amounts of turmeric can be absorbed on the surface of cotton fabric and antibacterial activity has been developed. Also, by AgNO₃ treatment, no bacteria can spread over the agar plate and 100% antibacterial cotton fabric is achieved.