Optimization of Process Conditions of Cotton Fabric Dyeing with Nettle Leaf Extract for Antibacterial Application Using Central Composite Design

ABSTRACT

In this study, all conditions of the natural dyeing process of cotton fabric with antibacterial efficiency, extracted from the leaves of the nettle were optimized using a central composite design. The optimized dyeing conditions are: concentration of 16.943 g, temperature of 50 °C, time of 40 min, and the color strength obtained at optimum condition was 1.53. The Nettle natural dye is applied to cotton fabrics by the Pad-Dry-Cure method for imparting antibacterial properties to the textile product for apparel applications. Biomordants were applied on scoured cotton fabric in the pre-mordanting process of dyeing. Color characteristics of the dyed fabrics were measured by CIE L*a*b* value using a spectrophotometer. Gram-positive (S. aureus) and gram-negative (E. coli) bacterial assessments were performed quantitatively using the AATCC-100 test method. The results provided evidence that the treated fabric exhibits higher antibacterial efficiency of gram-positive and gram-negative bacteria by 96.5–98% reduction compared to the control samples, respectively. The one having the highest antibacterial activity was washed 15 times under the same conditions and samples were taken after 1, 5, 10, and 15 washes. They retained nearly 91% S. aureus and 94% E. coli activity up to 10 launderings against the two bacteria.

摘要

在本研究中，采用中心复合设计对从荨麻叶中提取的具有抗菌效果的棉织物的天然染色工艺的所有条件进行了优化. 最佳染色条件为: 浓度16.943 g，温度50°C，染色时间40 min，最佳染色条件下的显色强度为1.53. 荨麻天然染料通过垫干固化法应用于棉织物，以赋予服装应用的纺织品抗菌性能. 在纯棉织物的预媒染染色过程中，应用了生物絮凝剂。使用分光光度计通过CIE L*a*b*值测量染色织物的颜色特性. 使用AATCC-100测试方法对革兰氏阳性（金黄色葡萄球菌）和革兰氏阴性（大肠杆菌）细菌进行定量评估. 结果证明，与对照样品相比，经处理的织物对革兰氏阳性菌和革兰氏阴性菌的抗菌效率分别降低了96.5-98%. 具有最高抗菌活性的一种在相同条件下洗涤15次，并在洗涤1次、5次、10次和15次后取样. 经过10次洗涤，它们保留了近91%的金黄色葡萄球菌和94%的大肠杆菌活性.

KEYWORDS:

• Nettle leaf
• Natural dye
• Cotton fabric
• Pad-Dry-Cure
• Staphylococcus aureus
• Escherichia coli

关键词:

• 荨麻叶
• 天然染料
• 棉布
• 衬垫干固化
• 金黄色葡萄球菌
• 大肠杆菌

Introduction

A substantial amount of various synthetic dyes are manufactured for textile fabric dyeing purposes. Most textile and garment industries used synthetic dyes. The use of synthetic dyes hurts all types of life. The harmful effects of synthetic dyes used in a massive textile industry on the environment and causing allergies have made some researchers fascinated by this subject. The textile processing industry is one of the major environmental polluters as the effluent from these industries contains a heavy load of chemicals including dyes used during textile processing (Sheikh, Singh, and Pinjari 2021).

Eco-friendly products are always growing throughout the world. Natural dyes contain colorants that are obtained from animals and different plant parts with no chemical processing. Natural dyes are increasing attention to reducing water pollution, increasing the sustainability of textile raw materials and products, biodegradability, and the environment. Natural dyes are eco-friendly and harmless compared to synthetic dyes in handling and use because of their non-carcinogenic and biodegradable nature. For the extraction of natural dyes, different plant parts are used like seeds, flowers, leaves, bark, and fruits (Chattopadhyay et al. 2013; Samanta and Agarwal 2009). Mordants are metal salts that produce affinity between dyes and fabrics. Some bio-mordants including tannic acid, pine cone, lemon peel, Myrobalan, and sodium alginate, as well as metal mordants such as iron(II) sulfate, copper sulfate, zinc sulfate, and aluminum potassium sulfate were investigated based on three conventional mordanting procedures (pre-, meta-, and after-mordanting) (Ghaheh, Moghaddam, and Tehrani 2021). Natural dyes are used to develop color on fabrics with the help of synthetic mordants. However, in the present work, natural dyes extracted from Nettle leaves were applied with two biomordants, sodium alginate, and Myrobalan.

The textile substrate is one of the important vectors for microbial growth, which leads to discoloration, odor, and allergic response in the wearer (Boominathan and Balakrishnan 2020). The physical and chemical structure of the fabric and the chemical processes may bring the growth of microorganisms. Infestation by microbes causes cross-infection by pathogens and the development of odors where the fabric is worn next to the skin, surface changes, discoloration of the fabric, and associated unpleasant odors. Antimicrobial finishing agents currently on the market are made of synthetic polymers showing good antibacterial power and durability but the toxic nature of synthetic agents, and their non-degradability in the environment (Montazer and Afjeh 2007). Eco-friendly antimicrobial textile products continue to increase in popularity for skin friendliness, smell, and high-performance fabrics (Dastjerdi and Montazer 2010).

Nettle has dark green leaves, roots, stems, and serrations with small and green flowers. It could give flowers from June to October. Huda Jasim Al-Tameme and Hameed (2015). Nettle leaf has been used in medicine, cosmetic, food, and dye industries (Eser and Onal 2015). The availability of different phytochemical ingredients in nettle leaves, noticeable activity against Gram-positive and Gram-negative bacterial activities (Dorota, Pawlikowska, and Antolak 2018).

The previous research paper was explaining the optimum dyeing conditions for wool and cotton fabrics using nettle (Urtica dioica L.) Leaf extracts (Eser and Onal 2015). However, it did not assess the dyed fabric imparted with antibacterial properties. This research aimed to optimize the conditions of the extracted process using nettle plant leaf as raw material for natural dye and antibacterial activity using Central composite design (CCD). Nettle leaf plant extracts as colorants in dyeing as well as impart antibacterial activity to the cotton fabric.

Materials and methods

Materials

One hundred percent Scoured cotton fabric (100%) with 22 picks/inch, 24 ends/inch, warp, and weft count of 37 Ne, a density of 138 g/m². Chemicals like citric acid, aluminum sulfate, and distilled water were used for extraction. The following apparatus was used in the study: FT-IR, photo spectrometer (L1600400, UK), pneumatic Padding mangle, Shaker extractor, Oven-dry, and RE-5A rotary evaporator.

Methods

Sample preparation and optimization of extraction

Only healthy leaf was collected in March and April from Addis Ababa City, Ethiopia, washed to remove any external impurities, air dried the leaf for 7 days to evaporate water and grind up to 0.710 μm particle size for better penetration of extraction solvents. The Shaker extraction process was optimized using a central composite design with distilled water at a low and high range of extraction time and material-to-liquor ratio. After extraction, the solvent was concentrated using a rotary evaporator machine. The amount of the concentrated ingredient extracted was stored in air-tight glass bottles in a refrigerator until further use.

The number of extraction runs was done by the central composite design method and the model significance was checked by ANOVA Analysis (Farmoudeh, Shokoohi, and Ebrahimnejad 2021). The parameters or factors needed for the extraction were two, which were concentration and time. After the extraction process, the extraction efficiency or yield value at different extraction conditions is calculated using Equation (1)(1) $Yield\left(\mathrm{\%}\right)=\frac{W_0-W_1}{W_0}\times 100$(1) (Ben Fadhel et al. 2012).

(1) $Yield\left(\mathrm{\%}\right)=\frac{W_0-W_1}{W_0}\times 100$(1)

Where W₀ is the weight of dry nettle leaves before extraction and W₁ is the weight of dry extracted powder after extraction.

Total phenolic and flavonoid contents

The amount of total phenol content in the extracted dye was determined by the Folin-Ciocalteau reagent using Gallic acid as the standard. The absorbance was taken at 765 nm, and the data were used to estimate the total phenolic content using a standard calibration curve obtained from various diluted concentrations of gallic acid (Akinseye, Morayo, and Olawumi 2017).

The total flavonoid was calculated using quercetin as a standard curve. The absorbance of each reaction mixture was subsequently measured at 510 nm (Akinseye, Morayo, and Olawumi 2017). The total flavonoid content of the samples was determined twice and the result was expressed as mg quercetin equivalent per gram of the sample.

Dyeing

The wetting/pre-soaking time of the samples in the dye solution were 40, 55, and 70 min at 50 °C, 65°C, and 80°C. Pre-soaking treatment was done in a bath containing 10, 20, and 30 g/L of dye powder, 4 g/L aluminum sulfate (metallic mordant), 5% owf bio mordants (sodium alginate, and Myrobalan), and 0.5 g/L of an anionic wetting agent with the material-to-liquor ratio (MLR) of 1:20 (Adeel et al. 2023). Subsequently, the wetted sample were padded between two rollers at 85% wet pick-up and then dried at 105°C for 5 min.

Colour measurement

The color strength of the dyed cotton fabric has been measured in terms of CIE LAB values (L*, a*, b*, c*) using a standard illuminated at D65 and 10° observers. The K/S value of different naturally dyed cotton fabrics was measured by the light reflectance technique using the Kubelka–Munk (K/S) Equation (2)(2) $\frac{K}{\hspace{0.17em}S}=\frac{\left(1-R\right)2}{2R}$(2) (Endris and Govindan 2020; Zavareh, Hamadani, and Tavanai 2010).

(2) $\frac{K}{\hspace{0.17em}S}=\frac{\left(1-R\right)2}{2R}$(2)

where K is the coefficient of absorption; S is the coefficient of scattering and R is the reflectance. The color difference of dyed cotton samples was obtained using the following relationships.

L, a*, and b* correspond, respectively: L to the brightness (100 = ideal white, 0 = ideal black); a* to the red/green coordinate (positive sign = red, negative sign = green); b* to the yellow/blue coordinate (positive sign = yellow, negative sign = blue) (Mansour, Ezzili, and Farouk 2017).

Fastness testing

The dyed samples are evaluated by washing, rubbing, and the light was measured according to ISO and AATCC standard methods: ISO 105-A02- 1995, AATCC Test Method 8–2007, AATCC Test Method 16–2004 in a launder-O-meter, Crock meter, and Xenon light solar box.

The antibacterial testing method

The antibacterial testing was done by AATCC test method 100:2004 for the quantitative assessment of the antibacterial effectiveness of the antimicrobial agents against Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). Percentage reduction (R %) of bacterial growth, i.e., CFU in treated samples was calculated in comparison with untreated fabric according to the following relationship in Equation (3)(3) $R\left(\mathrm{\%}\right)=\frac{B-A}{B}\times 100$(3) .

(3) $R\left(\mathrm{\%}\right)=\frac{B-A}{B}\times 100$(3)

where “B” is the number of bacteria CFU recovered from the inoculated untreated cotton test specimen swatches in the jar incubated over the desired contact period, and “A” is the number of bacteria CFU recovered from the inoculated treated test specimen swatches in the jar incubated over the desired contact period (Montazer and Afjeh 2007).

Results and discussion

Statistical analysis

Central composite design (CCD) shows very helpfully to study and analyze the effects of factors that influence the yield through variation in the factor combinations simultaneously. The amount of yield (percent) values of extracted dyes from nettle plant leaves at different extraction conditions are given in Table 1. A higher value of yield indicates thus better dye extraction efficiency.

Table 1. The amount of natural dye from nettle leaf at different extraction conditions.

Std	Run	Time (Hr.)	M:L (g/L)	Efficiency (Yield (%))
12	1	36	20	36
1	2	24	10	24
6	3	53	20	48
7	4	36	6	24
9	5	36	20	36
8	6	36	34	40
10	7	36	20	40
13	8	36	20	38
11	9	36	20	36
2	10	48	10	42
3	11	24	30	26
4	12	48	30	44
5	13	19	20	20

Analysis of variance (ANOVA)

As shown in Table 2, the extraction time and the material-to-liquor ratio are significantly affecting the amount of yield value of the extracted dye, within the range of values experimented in this study.

Table 2. Analysis of Variance (ANOVA) for the amount of dye for different dye extraction variables.

Source	Sum of Squares	Df	Mean Square	F-value	p-value
Model	802.44	2	401.22	37.68	<.0001	significant
A-Time	714.44	1	714.44	67.09	<.0001
B-Material to Liquor ration	88.00	1	88.00	8.26	.0165
Residual	106.48	10	10.65
Lack of Fit	93.68	6	15.61	4.88	.0734	not significant
Pure Error	12.80	4	3.20
Cor Total	908.92	12

The optimized extraction conditions are: concentration of dry powder of 10 g, extraction time of 34.636 min, and the extracted yield obtained at optimum condition was 30.517%.

Total phenolic and flavonoid contents

The total phenolic content in distilled water extract of nettle leaves is high (28.4969 ± 1.0533 mg GAE/g dry extract), whereas the content of total flavonoids is lower (12.2476 ± 1.7934 mg QUE/g of dry extract). The total phenolic content that is considerably higher than one gram of nettle powder has been reported is 12.9 GAE/g dry weight (Kregiel, Pawlikowska, and Antolak 2018). On the other hand, the values of total phenolic components in distilled water nettle leaf extract were lower than the values found by Soxhlet extraction with ethanol extract from nettle leaf was 208.37 ± 4.39 (Kukrica et al. 2012). The aromatic structure of the phenolic compounds is reasonable for dyeing.

Accordingly, the content of total flavonoids in distilled water nettle extract is significantly higher than that in ethyl acetate extract (10.2 mg QUE/g dry extract). Phenol and flavonoid content results vary from different research papers. This may be due to the chemical composition of nettle plants being affected by climate, soil, extraction method, and solvent type (Kukric et al. 2012).

Optimization of dyeing conditions

The K/S values of samples that are dyed by dyeing time, temperature, and dye concentration factors that affect the dyeing performance. In CIE Lab color measurements, the Db value obtained in our study shows that the dyed samples are on the yellow side in Table 3.

Table 3. Colour strength values in different parameter combinations.

Run	Presoak (min.)	Temp. (^℃)	Conc. (g/L)	DL	Da	Db	dE	K/S
1	55	65	20	−7.35	1.19	8.17	11.05	0.9952
2	40	80	10	−6.06	0.06	8.59	10.51	0.4283
3	55	65	20	−7.16	1.27	8.33	11.06	1.1129
4	55	86	20	−11.04	1.73	8.97	14.33	1.0636
5	55	65	20	−7.15	1.03	8.81	11.39	1.1234
6	34	65	20	−6.51	0.94	8.23	10.54	1.0205
7	55	44	20	−6.58	0.92	8.82	11.04	0.8893
8	70	80	30	−5.97	0.47	8.11	10.08	1.6021
9	55	65	20	−7.77	1.02	8.83	11.81	1.0486
10	70	50	30	−8.32	1.43	8.78	11.91	1.5825
11	55	86	20	−10.1	1.46	8.72	13.42	1.0861
12	76	65	20	−7.14	1.06	7.89	10.69	0.9648
13	55	65	6	−4.79	0.22	7.31	8.74	0.0328
14	55	65	34	−7.9	1.02	10.36	13.07	1.8893
15	55	65	34	−7.77	0.83	10.5	13.09	1.9893
16	70	80	10	−2.17	0.19	2.54	3.35	0.4083
17	40	50	30	−6.68	0.71	6.4	9.28	1.6525
18	40	50	10	−1.27	0.37	0.83	1.56	0.4927
19	76	65	20	−7.53	1.15	8.09	11.11	1.0152
20	55	43	20	−5.35	0.7	8.38	9.97	0.8849
21	55	65	20	−8.25	1.38	9.42	12.6	1.0173
22	34	65	20	−7.68	1.19	8.9	11.82	0.9803
23	40	80	30	−4.82	0.39	5.95	7.67	1.6701
24	55	65	20	−7.24	1.11	8.93	11.55	0.9304
25	70	50	10	−3.14	0.57	2.79	4.24	0.4219
26	55	65	6	−7.06	0.6	7.84	10.57	0.0344

The dye concentration affects the color strength value of the dyed material. As shown in Table 3, when the dye concentration increases for the same dyeing time, and temperature, the K/S value also increases. Because the amount of dye concentration available in the dye bath to diffuse from the dye bath to the fiber increases. Therefore, the higher dye exhaustion causes increasing the dye amount on and inside the fiber, enabling a larger amount of dye to get fixed. The treatment time does not influence the color strength value of the treated sample. It means the dyeing time and dyeing temperature do not have significant effects on the color value of the fabric. The optimized dyeing conditions are: concentration of extracted dye 16.943 g, temperature of 50 °C, time of 40 min, and color strength obtained at optimum condition was 1.53.

Analysis of variance (ANOVA) for K/S response

A Linear Model of the dye color value (response) and the independent dyeing parameters were chosen by the CCD, and the linear equation as given in Equation (4)(4) $\mathrm{K}/\mathrm{S}=-0.335\mathrm{A}+0.002\mathrm{B}+0.06\mathrm{C}$(4) .

(4) $\mathrm{K}/\mathrm{S}=-0.335\mathrm{A}+0.002\mathrm{B}+0.06\mathrm{C}$(4)

The dyed cotton fabric was explained using an analysis of Variance (ANOVA). The significance of the model can be determined by the P-value (Table 4). In this case, C (concentration of the dye) is a significant model term. Pre-soak time and dyeing temperature values are greater than 0.05, an insignificant effect in the experimental design. It means the dyeing time and dyeing temperature are not important for the color value of the fabric.

Table 4. Analysis of Variance (ANOVA) for K/S value.

Source	Sum of squares	df	Mean square	F-value	p-value
Model	6.45	3	2.15	455.76	<.0001	significant
A-presoak	0.0042	1	0.0042	0.8904	.3556
B-temperature	0.0152	1	0.0152	3.22	.0865
C-powder	6.43	1	6.4300	1363.17	<.0001
Residual	0.1038	22	0.0047
Lack of Fit	0.0696	12	0.0058	1.70	.2052	not significant
Pure Error	0.0342	10	0.0034
Cor Total	6.55	25

Functional group analysis

The extracted dye obtained from nettle leaves showed strong absorption peaks at 2989.20 cm⁻¹, 1550.38 cm⁻¹, 1410.12 cm⁻¹, and 1076.96 cm⁻¹. The broad peak between 3650 cm⁻¹ and 3200 cm⁻¹ corresponds to a strong O – H stretch vibration, which indicates the presence of hydroxyl groups in the extracted dye. As shown in Figure 1, it has been found that the spectrum of both dyed with sodium alginate mordant and dyed without mordant cotton fabric are alike and show almost similar curves. However, in the case of mordant dyed fabric, the peaks having strong intensity between 3550 cm⁻¹ and 3200 cm⁻¹ region indicating the presence of OH group. The spectrum of sodium alginate mordant dyed fabric of Figure 1 shows the peaks at 1000–1400 cm⁻¹ C=C stretching bond indicates the presence of conjugated aromatic compounds, and peaks at 1775 cm⁻¹ denote the presence of C-O stretch which signify the formation of a covalent bond between mordant dye fabric and the cellulose of cotton fiber.

Figure 1. FT-IR spectra of the extracted dye, dyed sample with sodium alginate mordant, and without mordant, respectively.

As shown in Table 5, the dyed samples with mordant show comparatively good wash, fastness, rubbing, and light properties. Thus, sodium alginate shows a marked effect on the light fastness of dyed cotton samples. The result clearly shows that the treated fabric has a good relation with biomordant fabric.

Table 5. Values of light, washing, and rubbing fastness of cotton fabrics dyed by the pre-mordanting method.

	Wash fastness
		Staining on white		Rubbing Fastness
Dyed samples	Change in color	Cotton	Polyester	Dry	wet	Light fastness
Without mordant	1–2	2	4–5	3–4	1–2	3
aluminum sulfate	3–4	4	4–5	3–4	3–4	4
Myrobalan	3–4	5	4–5	4	4	4–5
Sodium alginate	4	5	4–5	5	4–5	5

The above dyeing process is done with a combination of natural dyes extracted from nettle leaves and biomordants. The dye extract was taken in dyeing process as nettle leaves with the two biomordants as sodium alginate, and Myrobalan compare with metalic salt as Alum. The bio-mordants used the same as metal salt, increased the color fastness on the dyed cotton fabrics and produced excellent light fastness (rating of 4 to 5), wash fastness (rating of 4 to 5), and dry/wet rub fastness (rating of 3 to 5). The result shows the six shades of natural color obtained on cotton fabric. After dyeing with biomordants Myrobalan, and Sodium alginate viz. Alum. Sodium alginate showed light yellow coloration. The evaluation of color fastness to washing of dyed samples was tested by standard methods. The sample treated with Sodium alginate showed excellent washing fastness. Myrobalan-treated samples exhibit good to excellent fastness.

Anti-bacterial finish

The samples at optimized conditions of concentration, time, and temperature of the dyed fabric have been taken for evaluation of the efficacy of the antibacterial finish (Table 6). In the control sample, both gram-negative (E. coli) and gram-positive (S. aureus) develop fully on the fabric, i.e., 200 colonies or 200,000 CFU/ml (colony-forming unit), respectively, as shown in Figure 2. The reason for the development of the bacteria is due to the non-presence of any chemical that repels or kills the bacteria hence the bacteria use the fabric as their food source and grow on the fabric and destroy the fabric. Therefore, the control sample shows 0% bacterial reduction for both E. coli and S. aureus.

Figure 2. Bacterial growth conditions on the control fabric.

Table 6. Bacterial reduction test results for the treated fabric.

Run	Presoak (Min.)	Temp. (^OC)	Conc. (g/L)	Antibacterial reduction
				S. aureus E. coli
1	55	65	20	88	92
2	40	80	10	73	73
3	55	65	20	88	91
4	55	86	20	86	89
5	55	65	20	87.6	90.2
6	34	65	20	87	89.8
7	55	44	20	89	90.4
8	70	80	30	89	89
9	55	65	20	89	89.7
10	70	50	30	92	92
11	55	86	20	80	80
12	76	65	20	83	83.8
13	55	65	6	48	52.2
14	55	65	34	96.5	98
15	55	65	34	96.5	98
16	70	80	10	72.8	76
17	40	50	30	93.1	94
18	40	50	10	76	77.5
19	76	65	20	84	84
20	55	43	20	80.3	81.6
21	55	65	20	87	86
22	34	65	20	78	79.6
23	40	80	30	93	93.5
24	55	65	20	86	86
25	70	50	10	68	70
26	55	65	6	46	50

The most important parameter checked after-treatment of the cotton fabric was bacteria reduction. The efficiency of S. aureus bacteria resistance of the dyed cotton fabric was explained using analysis of Variance (ANOVA). In this research, proving the response surfaces as three-dimensional (3D) plots determined the importance of three independent factors of treatment time, dyeing temperature, amount of dye concentration, and the response value of the S. aureus bacterial reduction for the treated fabric (Figure 3).

Figure 3. 3D response surface plots for the effects of extracted powder concentration, temperature, and pre-soak time on S. aureus after cotton fabric dyeing.

The efficiency of E. coli bacteria resistance of the dyed cotton fabric was explained using analysis of Variance (ANOVA). During E. coli bacteria, the reduction efficiency of the treated fabric, dyeing time, and dyeing temperature were not important or did not affect the reduction efficiency of the bacteria (Figure 4).

Figure 4. Response surface plots for the effects of extracted powder concentration, temperature, and presoak time on E. coli after cotton fabric dyeing.

The optimized S. aureus bacteria reduction conditions are: concentration of extracted powder 14.477 g, temperature 50°C, time of 40 min, and the extracted yield obtained at optimum condition was 77.92%. However, the optimized E. coli bacteria reduction conditions are: concentration of extracted powder 14.714 g, temperature 50°C, time of 40 min, and the extracted yield obtained at optimum condition was 80.139%.

Nettle leaf essential oil-treated samples killed and removed both gram-negative (E. coli) and gram-positive (S. aureus) bacteria. The sample contains phytoconstituents, alkaloids, saponins, tannins, flavonoids, steroids, terpenoids, glycosides, phenols, and other chemical constituents that are responsible for reducing and blocking bacterial growth (Ghaima, Hashim, and Ali 2013). The treated sample gives 96.5% and 98% bacterial reduction for both E. coli and S. aureus bacteria as shown in Figure 5. The treated fabric, subject to several wash cycles (1, 5, 10, and 15), showed a gradual decrease in antibacterial properties with a 96.5–80% reduction in the bacterial count for Staphylococcus aureus and 98–84% reduction in the bacterial count for Escherichia coli. The bacterial reduction percentage for all wash durability tested samples is presented in Table 7. Figures 6–7 show the effect of after-wash on the treated sample against bacterial growth protection. The treated sample after 10 washes showed better repellency and resistance with both gram-negative (E. coli) and gram-positive (S. aureus) bacteria.

Figure 5. Gram-negative and Gram-positive bacteria growth conditions on the treated cotton fabric.

Figure 6. Bacterial growing conditions for both E. coli and S. aureus on the treated sample after one and five washes, respectively.

Figure 7. Bacterial growing conditions for both E. coli, and S. aureus on the treated sample after 10 and 15 washes, respectively.

Table 7. Bacterial reduction (%) test results of wash durability for the treated fabrics.

			Sample
Bacteria	Control	Treated fabric	After 1 wash	After 10 wash	After 10 wash	After 15 wash
S. aureus	0	96.5	96.5	91	85	80
E. coli	0	98	98	94	90	84

Conclusion

The current study successfully confirms the possible use of natural dyes extracted from nettle plant leaves to impart antibacterial activity to cotton fabric. The optimum condition for dye extract from the nettle plant was successful by using a central composite design and regression analysis. The optimized extraction conditions are: concentration of dry powder of 10 g, and extraction time of 34.636 min, and the extracted yield obtained at optimum condition was 30.517%. The total phenolic content is 28.4969 ± 1.0533 mg GAE/g dry weight, and the total flavonoid content is 12.2476 ± 1.7934 mg QUE/g of extracted dye from a nettle plant leaf. The dyed fabrics displayed moderate to efficient antibacterial activity against S. aureus and E. coli as gram-positive and gram-negative bacteria, respectively. The use of sodium alginate as bio-mordents in the dyeing of the cotton fabric could be, therefore, recommended due to the biocompatibility and non-toxicity of biomordants, along with excellent color fastness and appropriate antibacterial properties.

Highlights

• The nettle plant leaf is used as raw material for naturally dyed cotton fabric.

• The optimum dye extraction time does not exceed 53 minutes.

• The color value and antibacterial activity property were studied on cotton fabric.

• The dyed fabric shows superior antibacterial activity against S. aureus and E. coli.

Acknowledgements

The authors are thankful to Dire Dawa University Institute of Technology, Dire Dawa, Ethiopia, for continuous encouragement and support for this work.

Disclosure statement

No potential conflict of interest was reported by the authors.