2.1 Materials and chemicals

The Portulaca oleracea L. plant grows in Anhui Province, China. Wool fabric was purchased from Jiangsu Lugang Wool Textile Printing and Dyeing Co., Ltd. with the following specifications: Warp and weft: 17.2 × 17.2 tex; warp density: 216 threads per 10 cm; weft density: 184 threads per 10 cm, and weight: 224 g/m². Fresh Musa basjoo leaves were produced in Deqing County, Guangdong Province.

Staphylococcus aureus CMCC (b) 26,003 and E. coli CMCC (B) 44,102 were provided by the National Center for Medical Culture Collections. The nutritional broth was purchased from Beijing Aoboxing Biotechnology Co. Ltd.

Synthetic dyes including cerulein golden CE-01, cerulein blue 3G, cerulein red 6G were provided by Tianjin Sanhuan Chemical Co., Ltd. 1,1-diphenyl-2-trinitrophenylhydrazine was purchased from Fuzhou Feijing Biotechnology Co., Ltd. Acetic acid (HAC) was used for pH adjustment. The analytical reagents including anhydrous sodium carbonate (Na₂CO₃), anhydrous ethanol (C₂H₅OH), ammonium sulfate ((NH₄)₂SO₄), were obtained from Tianjin Yongda Chemical Reagent Co. Ltd., China.

2.2 Methodology

2.2.5

2.2.5 Dyeing WF with synthetic dyes

The synthetic dyes are used to compare the dyeing strength and functional properties of fabrics with that of natural dyed fabrics to evaluate the advantages of eco-dyeing and functional finishing of Portulaca oleracea L. as natural dyes. In order to obtain the same color as NF and MF, synthetic dye (Sd) baths were prepared with 1.28% CE-01, 0.17% CE-blue 3G and 0.23% CE-6G, and WF was dyed based on the process shown in Fig. 2 to obtain synthetic dyed fabric (SF) samples. The assistant comprised two drops of ring coeven B, 2% ammonium sulfate, and 0.15 mL HAc.

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Fig. 2

Dyeing process flow chart of WF with synthetic dyes.

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2.3 Characterization

The visible spectrophotometer (V-5600, Shanghai Yuanshi Instrument Co., Ltd., China) was used for spectral scanning of Nd at a wavelength range of 320–400 nm. The chemical groups of extracted Nd were analyzed using the Infrared-Raman spectrometer (Nicolet 6700/FT-Raman modules, Thermo Fisher, USA); the infrared spectra of WF, NF, and MF were collected at the wavelength range of 600 cm⁻¹–4000 cm⁻¹ by Thermo Nicolet Is10 Fourier transform infrared spectrometer. Transmission electron microscopy (FEI Talos F200s, USA) was used to observe the size and shape of Nd particles. The surface morphology of WF, NF, and MF and the distributed elements on the surface was recorded using an electron microscope analyzer (Bruker nano Berlin, Germany) equipped with XFlash 6T|30 detectors. The K/S and L*, a*, b*, c*, h^o values of wool fabrics at 340 nm wavelength under different dyeing processes were measured by computer color matching instrument (Color i 5D, American Datacolor). The wash fastness of dyed woolen yarn samples was measured in Digi wash SSTM (Launder-o-meter) as per the ISO 105-C06:1994 (2010) specifications. The wet and dry rubbing fastness were tested based on ISO 105-X16-2002. The colorfastness to sunlight was rated according to ISO 105-B02-2013. The ultraviolet protection factor (UPF) and ultraviolet transmittance (UVA and UVB) were measured on the textile ultraviolet protection performance tester (YG909-III, Wenzhou Fangyuan Instrument Co., Ltd.).

The antibacterial properties of WF, NF, MF, and SF samples were tested using S. aureus and E. coli as test strains following the GB/T 20944.3–2008 “textile antibacterial performance evaluation method”. The bacteriostatic rate was calculated based on Formula (3):

In vitro, antioxidant activity was evaluated by the DPPH radical scavenging assay based on Ivan Best with modifications. Briefly, 50 μL of Nd, mordant dye, synthetic dyes extract was mixed with 950 μL DPPH (65 μmol/L in ethanol), then shaken for 10 min to completely dissolve DPPH. The wool fabric was placed in the mixture and reacted in dark for 30 min. Then, a small amount of DPPH ethanol solution was transferred into a 10 mm colorimetric dish (Ren et al., 2021). The absorbance was measured by a UV spectrophotometer at 517 nm. The free radical scavenging efficacy of DPPH was calculated using Formula (4) (Iba et al., 2020):

3.1 Chemical composition of Nd powder

The major active components in Portulaca oleracea L. include α-linolenic acid, quercetin, p-coumaric acid, catechin, and tannic acid. Generally, quercetin (flavonols) is largely gray-yellow. In the quercetin molecules, the introduction of —OH and —OCH₃ and other auxochromes at the 7-site and 4-site promotes electron transfer and rearrangement, resulting in the darker color of the compound as brownish-yellow (Fig. 3) (Yang et al., 2021). Fig. 3 shows the FT-IR infrared spectra of Nd in the range of 4000–500 cm⁻¹, where 3418.6 cm⁻¹ and 2969.8 cm⁻¹ are broad absorption peaks with moderate intensity. The —OH stretching vibration of tannin molecules contained in phenolic aldehyde and aliphatic structure is at 3418.6 cm⁻¹, and the small peak at 2969.8 cm⁻¹ originated from the —CH stretching vibration in aromatic methoxy and the side chain of methyl and methylene (Chupin et al., 2013). The carbonyl absorption peak is in the region of 1900–1600 cm⁻¹. Due to the stretching vibration of C⚌O and the influence of hydrogen bond, the C⚌O absorption in carboxyl group moves to a low wave. The peaks at 1621.8 cm⁻¹ and 1384.6 cm⁻¹ are attributed to C⚌C stretching vibration of α-linolenic acid, —C—OH stretching vibration of phenolic acid, C⚌O stretching vibration of carboxyl group and —CH deformation in flavonoid aromatic ring system. The peak at 1318.5 cm⁻¹ was attributed to the out-of-plane bending vibration of C-H of olefin compounds. The peak at 1075.1 cm⁻¹ and 619.5 cm⁻¹ corresponded to the stretching vibration of —CO and the plane bending vibration of the C—O bond of tannins (Ricci et al., 2015).

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Fig. 3

FT-IR spectra of Nd powder.

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3.2 Extract processes of Nd colorant

The parameters such as temperature, time, and bath ratio of wool fabric were optimized by a single factor experiment and the results are shown in Fig. 4. As shown, the absorbance increased with increasing temperature, and reached the maximum value at extraction temperature of 90 °C, however, it decreased with further increasing temperature. This is because the α-linolenic acid molecules primarily comprising ω-3 in Portulaca oleracea L. are easy to decompose under high temperature, which potentially disrupts the conjugated system of Nd and absorbance, thereby producing a deepening effect. Nonetheless, if the temperature was too high, it would destroy the structure of Portulaca oleracea L. and reduce absorbance (Ye et al., 2021). Therefore, the extraction temperature can be defined as 90 °C.

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Fig. 4

UV–vis spectral analysis for the absorbance of Nd extracted by the conditions: (a) different temperatures under 1 h and 1:30; (b) different times under 1 h and 90 °C; (c) different bath ratios under 1 h and 90 °C. (d) Stability of extracted Nd solution under acidic conditions.

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The absorbance increased with the extension of extract time within 1 h, whereas decreased with a further prolonged time. When the time is within 1 h and the time is short, the extraction of Portulaca oleracea L. is not sufficient. If the time exceeds 1 h, it may cause the decomposition of colorant, which is not conducive to the extraction. The time should be controlled within a certain range. Under this condition, it is more appropriate to select the extraction time of about 1 h. The absorbance of Nd at a bath ratio of 1:20–1:30 was higher than that of a large bath ratio due to the higher Nd and more tannins obtained per unit mass of deionized water at a low bath ratio.

Through single factor experiment, SPSS was designed for the factors that have a great impact on Portulaca oleracea L. pigment, namely extraction temperature, extraction time and solid–liquid ratio. The test scheme is shown in Table 1.

Through single factor experiment, the better three levels under each factor were selected for three factor and three level SPSS design to screen the best extraction conditions of Portulaca oleracea L. The extraction effect is analyzed according to the value of each factor, as shown in Table 2. The results show that the best extraction conditions are: temperature 100 °C, time 1.5 h and bath ratio 1:20.

Fig. 4(d) is mainly used to test the acid resistance stability of the extracted oleracea L. solution. The initial pH value of nature dye solution was recorded as 7. First of all, the absorption wavelength of the solution does not change with the change of pH, but always maintains the same position. Second, at the λ_max of 340 nm, the absorbance corresponding to each pH fluctuates regularly, and the absorbance value fluctuates around 1. It indicate that the acid resistance stability of the solution is very good and shows that acidic medium will not change the chemical composition and chromogenic group of Portulaca oleracea L., but promote the increase of release by improving the permeability of solvent and damage to plant tissue (Shelembe et al., 2014).

3.3 Dyeing conditions and exhaustion rate

As shown in Fig. 5(a) and Table 3, the color intensity of wool fabric decreasedwith increased pH value when the pH of the dyeing bath was below the isoelectric point of wool of 4.2–4.8 due to the existing coulomb force and Van der Waals force. In contrast, the dye uptake decreased with a further increased pH value when the pH was higher than 4.8 (Zhou et al., 2020). As shown in Fig. 5(b), the maximum exhaustion rate was 35.67% at 90 °C. The increase in temperature promotes the swelling of the wool fiber; this is conducive to the further diffusion of Nd into the wool fiber. When the temperature exceeds 60 °C, the disulfide bond in the macromolecular structure of wool begins to open, and the reaction activity between the colorant and wool fabric is simultaneously enhanced. A reasonable increase in dyeing time would help in the increase of Nd exhaustion rate (Fig. 5(c)); the dyeing rate cannot significantly increase when the dyeing time is higher than 75 min. Fig. 5(d) shows that the increase of bath ratio would increase the number of Nd molecules in dye solution, which will improve the binding rate with wool fabric. When the liquor ratio is 1:35, the dye exhaustion rate reaches the maximum. Nevertheless, the adsorbed capacity of remaining Nd in dye solution would decrease after adequate adsorption on the surface of wool fabric. Therefore, if continue to increase the bath ratio and dye content, the adsorption capacity of the wool fabric will decrease instead.

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Fig. 5

The effect of conditions on dye exhaustion rate:(a) pH values with other conditions: 90 °C, 1 h and 1:20; (b) Temperatures with other conditions: pH 2, 1 h and 1:20; (c) Times with other conditions: pH 2, 90 °C and 1:20; (d) Bath ratio with other conditions: pH 2, 90 °C, 75 min.

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Through single factor experiment, the factors that have great influence on dyeing were designed, namely dyeing pH, temperature, time and solid–liquid ratio. The test scheme is shown in Table 4.

The dyeing effect was analyzed based on the value of each factor, and SPSS design was applied (Table 5). The findings show the optimum dyeing process of pH = 2, temperature 100 °C, time 1.5 h, solid–liquid bath ratio 1:35, and the dye uptake of up to 43.79%.

3.4 Adsorption dynamics

Based on the single factor experimental results of natural dye dyeing, a suitable adsorption system was selected, and the temperatures were regulated at 80 °C, 90 °C, and 100 °C. Fig. 6(a) reveals that the adsorption capacity of the wool fabric significantly increases within the first 40 min. After dyeing for 40 min, the adsorption rate decreased from 1.3205 kg/g/min to 7.828 × 10⁻² kg/g/min, and the equilibrium time was about 120 min. To comprehensively understand the adsorption kinetics, the adsorption kinetics equation, pseudo-first-order, and pseudo-second-order models were utilized to further analyze the adsorption features and influencing factors (Shen et al., 2014).

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Fig. 6

(a) Kinetic curves of dyeing wool fabric with Nd at different temperatures; (b) pseudo-second-order fitting line; (c) Comparison of wool fabrics dyed with different methods.

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For pseudo-first-order dynamics, the linearized rate equation was calculated using the Formula (5):

In the equation, K₂ (kg/g/min) is the equilibrium rate constant of the pseudo-second-order process. The linear changes of ln (q_e-q_t) and $\raisebox{1ex}{$t$}\!\left/ \!\raisebox{-1ex}{$q_t$}\right.$ verses t (min) was analyzed by nonlinear least square regression, which confirms the applicability and fitting of the above two dynamic models. The rate constant (k₂) and equilibrium adsorption capacity (q_e) were calculated using the slope and intercept of the linearized Equation (Kayodé et al., 2012). In addition, the adsorption rate and half-staining time (t_1/2) are calculated using Formulas (7) and (8):

Generally, the pseudo-first-order kinetic model is suitable for describing the initial stage of adsorption, while the pseudo-second-order kinetic model describes the whole adsorption process. Table 5 demonstrates that the R² of the pseudo-second-order kinetic model is above 0.997, indicating that the adsorption process of Nd on WF is increasingly in line with the pseudo-second-order kinetic adsorption model. Besides, it illustrates that the adsorption process is primarily regulated by chemical adsorption accompanied by electrostatic force, hydrogen bond, and ion–dipole interaction (Zhang et al., 2017). As shown in Table 6, when the temperature is further increased from 90 °C to 100 °C, the adsorption capacity increases from 25.991 g/kg to 44.067 g/kg, suggesting that the equilibrium is immediately attained at 100 °C compared to 80 °C and 90 °C. The initial adsorption rate r_i (g/kg/min) increases with increasing temperature, resulting in the decrease of t_1/2 (min).

As shown in Table 7, the sequence of color intensity (K/S value) of different dyeing methods is MF > NF > SF > WF. According to the literature, the use of mordant improves the combination of dye and fiber; the fiber can attain a stable color (Vankar et al., 2008). The higher K/S value and darker color of the sample are attained after dyeing with natural mordant as shown in Fig. 6(c).

3.5 Chemical analysis of fabrics

The FT-IR spectrums of WF, NF, and MF were significantly similar (Fig. 7(a)), indicating that the overall structure of wool fabric dyed with Nd and Md remained undamaged. Notably, near 3280 cm⁻¹ in the infrared spectrum is the coupling of - NH stretching vibration and amide stretching vibration, which is related to the change of force caused by hydrogen bond breaking between molecular chains. When the hydrogen bond between molecular chains breaks, the electron cloud density of C in C—H decreases, causing a shift in the stretching vibration band of C—H. To highlight the small differences that are difficult to detect, NF and MF infrared spectra were subtracted from WF infrared spectra, respectively (Fig. 7(b)) to eliminate the interference of background spectra and similar conditions. In the difference spectrum, COO^– and —OH in natural dyes are combined with —NH₂ or —CO—NH on protein fibers to enhance the hydrogen bond between natural dyes and wool. Among them, 1631 cm⁻¹ and 1647 cm⁻¹ are carboxyl stretching vibration regions, and 3750–3000 cm⁻¹ are O—H and N—H stretching vibration regions. Therefore, the corresponding characteristics of the absorption peak are gradually enhanced (Yrab et al., 2019).

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Fig. 7

(a) Infrared spectrum of three dyed fabric samples; (b) Infrared difference spectrum of MF and NF; (c) and (d): TEM images of Nd solution.

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The dye colorants exist in black spot-like aggregates with a diameter of 100 nm–150 nm (Fig. 7b). Unlike other natural dyes with the particle size of 2–4 μm (Lbkma et al., 2021; Li et al., 2021; Zhang et al., 2019), the dye aggregates comprise dozens to hundreds of nanoscale particles and the particle size of about 2.98 ± 0.54 nm (Fig. 7(c)); this is similar to the size of quantum dots. Thus, the colorant particles could be effectively and evenly dispersed in water and diffused into the wool fabric to attain a high exhaustion rate and color intensity (K/S).

The SEM images in Fig. 8(a-c) show the surface morphology of different wool fabrics without an apparent difference, suggesting that the dyeing process would not alter the surface morphology of the fabrics. The smooth fiber with a clear scale layer structure is shown on the surface of WF (Fig. 8(d)). However, the images in Fig. 8(e) and (f) show that the scale layer of wool fiber is destroyed, which would promote the diffusion of dye molecules into the fiber and significantly improve the efficiency of dyeing. Fig. 8(g-i) shows the cross-sectional of WF, NF, and MF. Of note, the material is solid and will not lose its capillary structure in the fiber due to expansion. These capillary structures ensure satisfactory diffusion characteristics.

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Fig. 8

SEM images of fabric samples :(a) WF × 2 K; (b) NF × 2 K; (c) MF × 2 K; (d) WF × 10 K; (e) NF × 10 K; (f) MF × 10 K; (g), (h) and (i): Cross section electron microscope of wool WF, NF and MF.

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Fig. 9 shows the distribution of elements in undyed and dyed WFs. Because of the presence of Se in Portulaca oleracea L., K in Musa basjoo leaves, Se and K appearing in Fig. 9(b) and (c) further verifies that natural dyes and mordants have been successfully dyed on WFs. The carbon–oxygen ratios (C/O) of WF, NF, and MF are 2.49, 2.67, and 2.85, respectively. MF samples have higher C/O and higher color intensity. The weight percentage of carbon and oxygen confirms the presence of hydroxylated flavonoids and catechin derivatives, which in turn verifies that the natural mordants rich in tannins cause the adsorption of fibers and dyes, and the excellent C/O improves the bioactivity of dyed fabrics (Hosseinzadeh et al., 2021; Rather et al., 2021).

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Fig. 9

EDS analysis of fabrics: (a) WF; (b) NF; (c) MF.

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3.6 UV protection and antioxidant properties

Due to the presence of quercetin, the number of functional groups including phenolic groups on the surface of fabric increased after Nd dyeing, thereby enabling NF and MF samples to have a better antioxidant capacity (Lu et al., 2018; Diao et al., 2021). The transmittance of UVA and UVB radiation depends on the type and degree of chemical interaction between wool fabric and natural dyes. As shown in Table 8, the UPF of WF is 153.29; this is classified as excellent. The dyed fabrics demonstrated lower transmittance (blocking ultraviolet radiation) and higher UPF values than that of the control samples, hence determining the superior UV resistance (Shabbir et al., 2018).

3.7 Antibacterial properties

S. aureus and E. coli colonies in the dyed fabric were lower than that in the blank control group; S. aureus was significantly reduced on the MF in Table 9. This is because α-linolenic acid, quercetin, coumarin, catechin, and other components exhibit certain antibacterial abilities. Quercetin inhibits DNA and RNA synthesis in bacterial cells and interferes with cell membrane activity (Yl et al., 2021). Coumarinic acid exhibits effective antibacterial activity against E. coli and S. aureus; it inhibits cell proliferation resulting in apoptosis (Lu et al., 2018; Ren et al., 2021). The phenolic hydroxyl groups in the catechins molecule are combined with peptide bonds, amino and carboxyl groups in bacterial cell membrane proteins, resulting in membrane protein denaturation and further bacterial death (Ben et al., 2015; Ren et al., 2016). The antibacterial rate of wool fabric increased after mordant dyeing, specifically for S. aureus (71.3%); this confirms that the chemical reaction of Nd has a significant effect on its antibacterial activity.

Table 9 Antibacterial activity of fabrics against S. aureus and E. coli.

S. No.	S. aureus	E. coli	Antibacterial rates against S. aureus / E. coli	Error
WF			–/–	–/–
NF			47.8%/12.5%	6.8%/4.5%
MF			71.3%/37.0%	5.6%/3.9%
SF			25.2%/11.8%	7.2%/4%