Development of environmentally friendly dyeing technology for textiles: DBD plasma management and green tea leaf extracts toward multifunctional cotton fabric

2.1. Material

Cotton (100%): This exquisite fabric, crafted from 100% pure cotton and weighing 130 g/m², is produced by the esteemed Misr-Helwan for Spinning and Weaving Company (Egypt). It has undergone meticulous processes of bleaching, mercerization, and finishing to meet the highest mill standards. Before any further treatments, the sample was gently cleansed with a non-ionic detergent and allowed to air dry naturally, preserving its integrity. The innovative NPs utilized in this process were sourced from Orchid Pharmaceutical Company, located in the vibrant city of Obour, Egypt. Additionally, laboratory-grade non-ionic detergent, urea, and ammonium persulfate ((NH₄)₂S₂O₈), which serve as essential thermal initiators, were carefully selected. Thermal curing binders and thickeners, known for their exceptional quality, were sourced from Sigma Aldrich. To add a touch of nature’s beauty, dyestuffs derived from green tea were procured from the local market, enriching the fabric with vibrant and organic hues.

2.2. Method

2.2.2. Plasma set up

The textile fabrics were immersed in an innovative low-temperature plasma, generated by a DBD system operating under atmospheric pressure with a stream of oxygen gas. A schematic diagram of this cutting-edge experimental setup has been illustrated in Figure 1. The DBD cell featured two elegantly designed stainless-steel disc electrodes, each boasting a thickness of 2 mm and a diameter of 25.5 cm. The lower electrode was securely anchored to a Perspex base, measuring 30 cm in diameter and 2 cm thick, which provided a stable grounding. Elevating the experiment further, the upper electrode was paired with a high-voltage AC power source, delivering a frequency of 50 Hz and a variable voltage range from 0 to 20 kV. A sleek 1.7 mm thick glass dielectric was affixed to the upper electrode, creating a precise gap distance (d) of 3 mm between it and the lower electrode. To ensure accurate monitoring, discharge voltage and current were captured using a sophisticated two-channel digital storage oscilloscope (HM-407). The discharge voltage was connected through a 2000:1 resistive potential divider, while the discharge current was gauged as a voltage drop across a 1 kΩ resistor linked in series with the ground. The entire DBD system was meticulously encased in an airtight Plexiglass box, allowing for a controlled environment as oxygen gas was elegantly injected through the inlet of the electrode chamber. This meticulous design not only ensured precision but also fostered an atmosphere ripe for exploration and discovery in the realm of textile treatment.

Close

Figure 1.

Diagram representing the plasma discharge cell.

Export to PPT

2.2.3. Dye extraction

The extraction of natural colorants from tea leaves Figure 2 was performed following the method with slight adaptations. The combination was incubated in a water bath at 95°C for 1 h with deionized water and for 15 min with hexane or ethanol. After incubation, the mixtures were allowed to stand for 15 min before being filtered. The resulting filtrate was then used for dyeing.

Close

Figure 2.

(a) Theaflavins and (b) Thearubigins - coloring component of tea (Camellia sinensis).

Export to PPT

2.3. Measurements

3.1. Wettability

We measured the wetting times for cotton textiles that had been treated with ZnO NPs, O₂ plasma, and a mixture of O₂ plasma / ZnO NPs. Figure 3 presents the data that were acquired. Figure 3 shows that all treated samples had shorter wetting times, indicating that applying this treatment increased the wettability of cotton fabric. It is possible to conclude that cotton treated with ZnO NPs or a combination of O₂ plasma and ZnO NPs may exhibit improved hydrophilicity. The presence of ZnO NPs or the combined treatment can enhance the fabric’s ability to absorb and interact with water, leading to better hydrophilic properties compared to untreated cotton. The O₂ plasma treatment can indeed create OH and COOH groups on the surface of cotton, which in turn increases the surface free energy of the material [54,55]. This can lead to improved properties such as better adhesion, wettability, and overall performance of the cotton fabric. Wetting time for the untreated sample was approximately 22 s, but after treatment with O₂ plasma / ZnO NPs at a concentration of 1.5 g/100g fiber and applying 17.35 W of plasma power for 20 min, it was almost a fourth of this value (7.5s). In Figure 3, the other two curves represent fabrics treated with NPs but not with plasma. These samples exhibit longer wetting times because the NPs reduce the surface’s wettability, making it more resistant to liquid absorption.

Close

Figure 3.

Wettability of cotton fabrics cured with oxygen plasma only and O₂ plasma/ZnO NPs.

Export to PPT

3.2. Tensile strength

Table 1 elegantly illustrates the tensile strength for the cotton samples, which underwent O₂ plasma exposure at power settings of 15.5 and 17.35 W for varying durations. The cotton samples were enriched with a 3% concentration of ZnO (on a weight-of-fabric basis) using the innovative padding technique, applied both independently and in synergy with O₂ plasma and ZnO NPs. From the insights provided in Table 1, it is remarkable to note that the tensile strength and elongation percentage for the O₂ plasma-treated samples exhibit a modest yet noteworthy increase, highlighting the efficacy of this treatment method. O₂ plasma treatment can modify the material’s surface properties, potentially leading to enhancements in tensile strength and elongation characteristics. These improvements may be observed in the treated sample compared to the untreated samples. This may be because Oxygen plasma treatment can cause etching of the material surface, which involves the removal of surface layers through chemical reactions. This etching process can remove contaminants, impurities, and weak surface layers, resulting in a cleaner and more uniform surface. As a result, the treated material may exhibit improved tensile strength because the removed layers could have contained defects or weak bonds that could compromise mechanical properties regardless of their specific conditions, resulted in either a slight improvement or no change in tensile strength compared to untreated cotton, the combination of O₂ plasma and ZnO NPs proved most effective in enhancing this mechanical property. This aligns with previous research [56,57], which reported that treating cotton with NPs improves tensile properties and crease recovery angle without compromising its mechanical integrity.

3.3. UPF of treated cotton

The untreated cotton samples give low UPF (3.8) as shown in Table 2, which is below the protection UPF value. So, treatment is required to provide skin protection against ultraviolet rays. Treating cotton with O₂ plasma alone significantly improves its UPF to 15.6, offering excellent protection against UV rays. However, when combined with O₂ plasma treatment and ZnO NPs on cotton fabrics, it improves the UPF by about 25.8 by enhancing the fabric’s ability to block UV rays. O₂ plasma curing alters the surface properties of the fabric, creating a rougher surface that enhances its ability to scatter and reflect UV radiation. The addition of ZnO NPs further enhances UV protection by increasing the uniform distribution of NPs on the fabric, which aids in reflecting and scattering UV rays [58-62]. This combined treatment effectively boosts the UPF value of cotton fabrics, providing improved protection against harmful UV radiation. The mechanism behind this improvement likely involves the reflection and scattering of UV rays by the ZnO NPs, further enhancing the fabric’s UV protection.

3.4. Color strength

Applying Dielectric Barrier Discharge (DBD) air plasma treatment to cotton fabric, followed by coating with nano ZnO, can significantly enhance the printability of the fabric, especially when using eco-friendly dyes like green tea. In Table 3, the untreated printed cotton fabric has the lowest k/s value (1.71), indicating poor color strength. Treatment with ZnO NPs improves this to 2.56. But when using oxygen plasma treatment, we show that at 15.5 W, the color strength significantly increases with longer plasma treatment times, peaking at 8.21 for 20 min before slightly decreasing at 30 min (7.50). At 17.35 W, higher discharge power results in even greater k/s values, with the maximum at 10.78 for 20 min, suggesting more effective dye uptake compared to the lower power treatment. The combination of oxygen plasma and ZnO NPs consistently yields higher k/s values than plasma treatment alone, enhancing the color strength further. Overall, both oxygen plasma treatment and the addition of ZnO NPs significantly enhance the color strength of printed fabrics, with increased plasma curing time and higher discharge power contributing to better results [36,43,44,63].

When cotton fabric is exposed to DBD air plasma, it creates reactive species that modify the surface properties of the fabric. This treatment increases surface energy, leading to improved wettability, printability, and adhesion properties. The enhanced surface roughness promotes better dye absorption. Increased functional groups (-OH and -COOH) on the fabric surface improve dye and dye bonding. Eco-friendly process with minimal chemical usage. The fabric is coated with nano ZnO particles after plasma treatment. The nano ZnO provides antibacterial properties and can enhance UV protection, printability, due to ZnO coating aids in even distribution and fixation of the green tea dye. We have shown enhanced durability of prints due to better adhesion. Utilizing green tea as a natural dye promotes sustainability [33,45,57].

By combining DBD oxygen plasma treatment, nano ZnO coating, and green tea dyeing, you create a fabric that is not only esthetically pleasing and printable but also environmentally friendly and functional. This approach enhances the textile’s performance and opens up new avenues for sustainable textile applications.

3.5. Fastness properties

The study demonstrates that DBD oxygen plasma treatment, only or combined with ZnO NPs, significantly enhances K/S and colorfastness properties of printed cotton fabrics, as results show in Tables 4 and 5. All fastness properties (washing, rubbing, perspiration, and light) show marked improvements with treatment, indicating that this method effectively enhances the durability of the fabric. Shows low washing fastness (3-4), indicating color fading upon washing. The treatment with ZnO NPs improves washing fastness to 4, and combined treatments with O₂ plasma show further enhancements, especially at longer exposure times (up to 5). The untreated fabric has a rubbing fastness of 4. Treatments with ZnO and O₂ plasma significantly enhance this property, with values reaching 6-7, particularly at the higher plasma power and longer exposure times. The treated fabrics show consistent improvements in both acid and alkali perspiration fastness compared to untreated samples. Most treated samples reach levels of 4-5, indicating good resistance to color fading from perspiration. The light fastness ratings for untreated cotton are moderate (5-6), but treatments increase this significantly, with the best results showing values of 7. This indicates excellent resistance to fading from light exposure. Higher plasma power and longer exposure times yield better results, suggesting a synergistic effect between the treatments. These enhanced properties make the treated fabrics suitable for various applications, particularly in the textile industry, where durability and color retention are crucial.

3.6. Antibacterial activity

To assess the antimicrobial efficacy of treated fabrics, both quantitative and qualitative analyses were conducted against E. coli and S. aureus. Based on optimized conditions, untreated and 20-min, 17.35-W O₂ plasma-treated samples were selected. Figure 4 illustrates that O₂ plasma/ZnO NPs-treated fabrics, subsequently coated with green tea leaf extract, exhibited a significantly higher bacterial reduction percentage compared to untreated fabrics. Table 6 further supports this observation, showing bacterial reductions of 92% and 86% for E. coli and S. aureus, respectively, on plasma-treated fabrics, a trend mirrored in green tea extract-finished fabrics. This improved antimicrobial performance can be attributed to several factors:

Close

Figure 4.

Antimicrobial activity of (un)treated samples with O₂ plasma/ZnO NPs post-coating with green tea leaf extracts.

Export to PPT

Plasma treatment: O₂ plasma treatment enhances fabric hydrophilicity, facilitating better absorption of the antimicrobial coating and thus increasing bacterial reduction.

ZnO NPs: ZnO NPs release ions that inhibit bacterial growth, further enhancing antibacterial properties.

Green tea extract: Rich in antioxidants and bioactive compounds like flavonoids, terpenoids, polyphenols, and tannins, green tea extract contributes significantly to antimicrobial activity. Catechin, a key component, disrupts bacterial cell membranes, leading to altered permeability and cell lysis. Additionally, these bioactive compounds may inhibit the act of specific bacterial enzymes, ultimately resulting in cell death.

This combined treatment approach, O₂ plasma/ZnO NPs followed by extract coating, effectively imparts potent antibacterial properties to cotton fabric. This makes it a promising candidate for applications where hygiene, longevity, and cleanliness are paramount.

3.7. Fourier-transform infrared spectrophotometer

The ATR-FTIR spectroscopy was employed to investigate the changes in surface functionality induced by plasma treatment. As depicted in Figure 5, the FTIR spectra of plasma-cured samples exhibited an increase in peak intensity, suggesting an enhancement in the number of functional groups on the fabric’s surface. Specifically, Figure 5 reveals broad bands at 3859, 3744, and 3677 cm⁻¹, characteristic of -CH- stretching vibrations. Additionally, peaks observed at 3565 and 3248 cm⁻¹ are attributed to H-bonded -OH- stretching, typically associated with aromatic compounds and primary alcohols. A sharp peak at 1743 cm⁻¹, closely aligned with the peak at 1748 cm⁻¹, is indicative of -C=O- stretching in carboxylic acids present within the cellulosic fabric. Plasma treatment significantly enhanced the carbonyl peak intensity on the cellulosic fabric surface, a key factor in improving its hydrophilicity. The presence of prominent peaks at 1691 and 1629 cm⁻¹ indicates the formation of asymmetric carboxylate stretches (-COO⁻). It is suggested that plasma ions interact with carboxylic substituents, converting them into aldehyde substituents. Furthermore, the FTIR spectrum revealed several characteristic peaks. 1149 cm⁻¹ is assigned to the C-H region and CH wagging (-CH₂-X) in glucosides, indicative of cyclic ether structures. The peaks at 1219, 1149, and 1037 cm⁻¹ are associated with CH wagging (-CH₂-X) in glucosides, confirming the existence of cyclic ether structures. The C-H flapping vibration, typically observed in the 1020-1250 cm⁻¹ range, further supports this finding. The 703 cm⁻¹ peak corresponds to the out-of-plane C-O-C structure, a characteristic feature of polysaccharides.

Close

Figure 5.

FTIR spectra of (a) untreated cotton fabric. (b) treated cotton with oxygen plasma (c) treated cotton ZnO NPs (d) treated cotton with O₂ plasma/ZnO NPs.

Export to PPT

3.8. Scanning electron microscope

Among the most prominent tools for topographical imaging, SEM analysis finds broad application across various fields. Figure 6 presents SEM micrographs of cotton fabrics that have undergone various treatments: 20 min of oxygen plasma treatment, oxygen plasma combined with ZnO NPs, ZnO NPs only, and untreated cotton fabrics. Both untreated and plasma-treated cotton fabrics have shown a relatively smooth surface as shown in Figure 6a-b. This baseline provides a reference point, demonstrating the natural texture and morphology of cotton fibers before any treatment. The lack of modifications suggests limited interaction with antimicrobial agents. At 20 min oxygen plasma-treated cotton fabric in Figure 6(c) appearance the micrograph would reveal increased surface roughness and potential changes in fiber morphology, such as etching or the formation of microstructures. The oxygen plasma treatment enhances the surface area and reactivity of the cotton fibers, promoting better interaction with subsequent treatments (e.g., ZnO NPs and green tea extracts). This modification is essential for improving the fabric’s ability to absorb and retain antimicrobial agents. When oxygen plasma combined with ZnO NPs as Figure 6(d) shown the SEM image may display a more textured surface with ZnO nanoparticles visibly adhered to the fibers, indicating successful deposition. This treatment combines the benefits of both oxygen plasma and ZnO NPs, leading to a rougher, more porous surface [20,22,33,47]. The presence of ZnO NPs suggests enhanced antimicrobial properties due to the nanoparticles’ known effectiveness against bacteria and fungi. In Figure 6(b) show ZnO NPs Only, the micrograph could show ZnO nanoparticles either aggregated or well-dispersed on the cotton surface, depending on the application method. While this treatment introduces antimicrobial properties, the lack of plasma treatment may limit the interaction and bonding between the nanoparticles and the cotton fibers, potentially reducing overall effectiveness compared to the combined treatment. Surface modifications, each treatment alters the surface morphology of the cotton fabric, impacting its properties and potential for antimicrobial efficacy. Enhanced interaction, the combination of oxygen plasma and ZnO NPs results in a more reactive surface, promoting better adhesion and retention of antimicrobial agents. The SEM micrographs visually demonstrate the efficacy of the treatment methods, showing how modifications enhance the performance of cotton fabrics in terms of antimicrobial activity.

Close

Figure 6.

SEM spectra of (a) untreated fabric. (b) treated cotton with oxygen plasma (c) treated cotton ZnO NPs (d) treated cotton with O₂ plasma/ZnO NPs.

Export to PPT