Textiles Dyeing with Pomegranate (Punica granatum) Peel Extract Using Natural Mordant

ABSTRACT

Agricultural waste represents a potential source of raw materials as natural dyes. The peel from pomegranate (Punica granatum) is a waste product, it is used in the textiles industry as dye. The objective of the study is to improve dyeing properties of pomegranate peel dyed silk fabric. We analyzed the pigment composition of pomegranate peel extract through ultraviolet-visible and Fourier-transform infrared (FTIR) spectroscopy; evaluated natural mordants and metallic mordants on fabrics dyed with pomegranate peel extracts by testing the K/S value, color characteristics, and color fastness; examined the morphology of dyed fabrics before and after color fixing treatment by scanning electron microscopy. The major pigment component in pomegranate peel is ellagic acid. An orthogonal array experiment revealed that the optimum dyeing conditions were pH 9, 60°C 60 min for silk fibers. Under the natural mordant, the K/S value of dyed fabric could acquire maximum (8.70). Moreover, the K/S value and color fastness of dyed fabrics could be further enhanced to 11.74 and level 5 by color-fixing treatment of natural gum rosin. Overall, the dyed silk samples with pomegranate peel represented good dyeing properties with natural mordant and natural color-fixing agent of gum rosin.

摘要

农业废弃物是作为天然染料的原料的潜在来源. 石榴皮是一种废物，在纺织工业中用作染料. 本研究旨在改善石榴皮染色丝绸织物的染色性能. 通过紫外-可见光谱和傅立叶变换红外光谱对石榴皮提取物的色素成分进行了分析; 通过测试K/S值、颜色特性和色牢度，评估石榴皮提取物染色织物的天然媒染剂和金属媒染剂; 用扫描电镜观察染色织物固色剂处理前后的形态变化. 石榴皮中的主要色素成分是鞣花酸. 正交试验表明，丝绸纤维的最佳染色条件为pH值9，60°C的60 min. 在天然媒染剂作用下，织物的K/S值达到最大值（8.70）. 天然松香固色处理可使织物的K/S值和色牢度进一步提高到11.74和5级. 总体而言，石榴皮染色丝绸样品在天然媒染剂和天然固色剂松香的作用下表现出良好的染色性能.

KEYWORDS:

• Plant dye
• pomegranate peel
• natural mordants
• dye-fixing agent
• silk fabric
• color properties

关键字:

• 植物染料
• 石榴皮
• 天然媒染剂
• 染料固色剂
• 丝绸面料
• 颜色属性

Introduction

Wastewater contaminated with synthetic dyes from the textile industry pollutes the environment and affects human health (Hole and Hole 2019). Natural dyes would be a safer alternative for the textile industry, as they are environmentally friendly and biodegradable, and have therefore attracted attention (Hou et al. 2013). However, natural dyes also have disadvantages for textile dyeing, such as low color fastness and single-color effect. These issues have been addressed using chemical fixing agents and metallic mordants. While natural dyeing can be improved using fixing agents, most of which are synthetic (Zhou et al. 2006), when metallic mordants and natural dyes react, they form coordinate bonds (Mongkholrattanasit, Jirikrystufek, and Vikova 2011). The alum, copper sulfate and ferric sulfate have been the most widely used as metallic mordants in natural dyeing since ancient times (Vuthiganond, Nakpathom, and Mongkholrattanasit 2018). These metallic mordants are within the limits of NODS standard (Baliarsingh et al. 2012). And alum is brightening mordants, while copper sulfate and ferric sulfate are dulling mordants (Samanta and Konar 2011). Alum and ferrous sulfate are considered the safest of the metallic mordants, whereas copper sulfate can be used within limits in GOTS standard (Karadag 2023; Savvidis et al. 2013; Zarkogianni et al. 2011). Because metallic mordants and chemical fixing agents can be toxic to the environment and harm human health (Özlenen, Leyla, and Esen 2015), it is important to identify alternative natural fixing agents and mordants to develop cleaner dyeing procedures. One such natural fixing agent, gum rosin, is fast drying and forms a film in organic solvents (Li, Cui, and Shi 2014). Natural mordants involve tannin, tannic acid, tartaric acid, metal containing plants, biowastes and by-products (İ̇şmal 2017). The color yields of natural mordants can be equal to metallic mordants, and even surpass in some cases (İ̇şmal 2017). Because the chemical structure, quantity and type of metal ions of the natural mordants determine the effect of the mordanting. And various changes of color and fastness are depended on the different interactions between the metal ions of natural mordants, natural dye molecules and fibers (İ̇şmal 2017). Some natural mordants include extracts form Chinese quince (Chaenomeles speciosa [Sweet] Nakai) (Yan et al. 2021), rare earth (Zheng, Hong, and Liu 2011), and mineral salts (Yang 2013). And the rare earth accord with NODS standard, but the C. speciosa and mineral salt as new natural mordants, which haven’t been regulated in NODS standard (Karadag 2023). Natural dyes are expensive, and their supplies are often limited. Agricultural crop waste is a potential source of natural dyes (Da Silva et al. 2018), and their use in the textile industry will increase the value of these remnant materials.

Pomegranate (Punica granatum L.) is a traditional fruit crop grown in China (Figure 1). This crop originated from Iran and the Himalayan region and is widely distributed in Mediterranean countries such as Egypt, China, and India (Dhinesh and Ramasamy 2016). The cultivation area of pomegranate was 300,000 ha in 2019, with an annual production of 3 million metric tons worldwide (Venkitasamy et al. 2019). The cultivation area of pomegranate in China was 117,800 ha in 2019, making China the largest producer in the world (Yu and Sheng 2019). More than 100,000 tons of fresh pomegranates and more than 5,000 tons of pomegranate juice are produced in China each year, with approximately 95% of these products used for export (Zhao and Jing 2019). This agricultural waste product could be used to make natural dyes (Tutak, Acar, and Akman 2014), which would equate to the recycling of 20,000–30,000 tons of pomegranate peel waste each year in China alone.

Figure 1. Pomegranate (punica granatum L.).

Punica granatum is containing flavogallol, ellagitannins, punicalin, 2-O-galloylpunicalin, punicalin, punicacorteins (Mo et al. 2022). Pomegranate peel is rich in polyphenols, including phenolic acids, tannins, flavonoids and anthocyanins (Ain et al. 2023). The major chemical component of aqueous pomegranate peel extract is tannins (Chen and Zhou 2019). Tannins are classified into two categories: hydrolyzable tannins and condensed tannins. Hydrolyzable tannins, which are found in pomegranate peels, are further divided into ellagic tannins and gallate tannins (Chen and Zhou 2019). The tannin pigments in pomegranate peel include amphiregulin, ellagic acid, pomegranate pithin A, pomegranate pithin B, and mucoepidene (Kasiri and Safapour 2014; Željka et al. 2020), the main compound being ellagic acid (Figure 1) (Lee et al. 2013). These compounds have high water solubility but low affinity for fibers (Chen and Zhou 2019), prompting the need for mordants and fixing agents to increase the color fastness of the dye.

So far, no studies have evaluated the dyeing properties of pomegranate peel extract using natural mordants and fixing agents. The aim of this study was to explore the feasibility of using natural mordants and natural fixing agents to dye silk fabrics with pomegranate peel extract.

Materials & methods

Materials

Pomegranate (Punica granatum L.) peels were collected from local fresh fruit juice sellers in Kunming City, Yunnan, China, in September 2020. Chinese quince (Chaenomeles speciosa) fruits and gum rosin were purchased from a local market in Heqing County, Dali Bai Autonomous Prefecture of China. Mineral salts were obtained from Chaka Town, Wulan County, Qinghai Province, China. Rare earth was purchased from Nanchang City, Jiangxi Province, China. Ethanol (EtOH), sodium hydroxide (NaOH), and hydrochloric acid (HCl) were of analytical reagent grade. Distilled water was used throughout the study. Bleached silk (weight 16.0 g m⁻², plain weave) fabrics were provided by Esquel Enterprises Ltd.

Methods

Pomegranate peel extraction

The pomegranate peels were rinsed with water, dried at room temperature (20–25°C), and ground into a powder. To create pomegranate peel extract with a mass fraction of 6%, the ground peel was extracted in distilled water at a liquor ratio of 1:30 in a water bath at 100°C for 30 min. The solution was cooled and filtered for use as natural dye.

Preparation of natural fixing agent

Gum rosin was pounded into a powder and used to create 15 g/L natural fixing agent solution at the mixture of 800 mL ethyl alcohol and 200 mL distilled water at room temperature. The mixture was stirred continuously until the gum rosin powder had dissolved and was then used as a natural fixing agent.

Fourier transform-infrared and ultraviolet-visible spectroscopy

The FT-IR spectra of pomegranate peel extract were obtained by Fourier transform infrared spectrometry (Nicolet iS10, Thermo Fisher Scientific), with 16 scans at a 4 cm⁻¹ resolution in a spectral range of 4000–400 cm⁻¹. The KBr pellet method was used to obtain spectral data.

UV-visible spectroscopy of pomegranate peel extract was conducted by scanning from 190 nm to 600 nm using a UV-5500PC spectrophotometer (Shanghai Metash Instruments Co., Ltd.).

Experimental design to examine the properties of pomegranate peel dye

An orthogonal design was used to determine the optimum conditions for dyeing silk fabrics with pomegranate peel extract. Three factors (temperature [A], time [B], and pH [C]) were selected, and their dyeing levels (1, 2, and 3) were controlled experimentally. The three levels of each factor used in the orthogonal experiment are listed in Table 1. Based on orthogonal experimental design L₉ (3³), nine experiments each were implemented using silk fabrics, as shown in Table 2.

Table 1. Factors and levels selected for the orthogonal array experiment for dyeing fabrics with pomegranate peel extract.

Level	Factors
	A. Temperature (℃)	B. Time (minutes)	C. pH
1	40	30	5
2	60	60	7
3	80	90	9

Table 2. Orthogonal array design used for the nine dyeing experiments based on design L₉ (3^3.).

No.	A (Temperature)	B (Time)	C (pH)
1	A^1	B1	C^1
2	A^1	B2	C^2
3	A^1	B3	C^3
4	A^2	B1	C^2
5	A^2	B2	C^3
6	A^2	B3	C^1
7	A^3	B1	C^3
8	A^3	B2	C^1
9	A^3	B3	C^2

Dyeing

The pomegranate peel extract with a mass fraction of 6% was used to dye silk fabric samples at a liquor ratio of 30:1. Parameters tested included temperature (40, 60, or 80°C), time (30, 60, or 90 min), and the pH value (5, 7, or 9) of the dye (Sadeghi-Kiakhani et al. 2019). The dyed fabrics were rinsed with distilled water and dried at room temperature.

Mordanting methods

Pre, simultaneous, and post-mordanting methods were conducted at 80°C for 30 min at a liquor ratio of 30:1 by three natural mordants (20 g/L C. speciosa, 10 g/L mineral salts, and 5 g/L rare earth) (Yang et al. 2021; Zheng, Hong, and Liu 2011).

Color fixing treatment

The dyed fabrics were placed in gum rosin dye-fixing agent to fix the color at a liquor ratio of 30:1 at 70°C for 30 min, with constant stirring. After treatment, the dyed fabrics were dried, rinsed with distilled water, and redried at room temperature. Three methods were utilized for dyeing and color fixation: First, Natural mordant, then Dye, then Dye-fixing agent; Second, Natural mordant + Dye, then Dye-fixing agent; Third, Dye, then Natural mordant, then Dye-fixing agent.

Color measurements

The color characteristics of the dyed samples, including lightness (L*), redness-greenness (a*), and blueness-yellowness (b*), were measured with a benchtop spectrophotometer (Shenzhen ThreeNH Technology Co., Ltd.) using an Illuminant D65 and 10° standard observer. The standard samples were from undyed fabrics. K/S was calculated by the Kubelka-Munk equation:

K/S = (1 - R) ²/2R

where R is the reflectance of the dyed fabric, K is the absorption coefficient, and S is the scattering coefficient.

Color fastness tests

The color fastness of the dyed samples was tested according to Chinese Textiles Test Specification based on ISO international standards. The color fastness to washing, perspiration, and rubbing was measured according to standards GB/T3921–2008, GB/T3922–2013, and GB/T3920–2008, respectively (National Standard of the People’s Republic of China 2008a, 2008b, 2013).

Scanning electron microscopy analysis

The surface morphology of dyed fabric fibers was characterized by scanning electron microscopy (SEM; ZEISS EVO LS10) before and after the color fixing treatment. The surface morphological features of dyed fabric fibers were observed and analyzed.

Results & discussion

Fourier-transform infrared and UV-visible spectroscopy

Fourier-transform infrared (FT-IR) analysis revealed the functional groups in the aqueous pomegranate peel extract, as shown in Figure 2. The spectrum had a broad peak corresponding to phenolic -OH groups stretching at 3379 cm⁻¹, C-H bonds on the aromatic ring telescopically vibrating at 2932 cm⁻¹, carbonyl groups in lactones stretching at 1722 cm⁻¹, and aromatic ring skeletons vibrating at 1613 cm⁻¹. Moreover, there was an OH deformation and C-O stretch combination (phenols) at 1344 cm⁻¹, a C-O-C anti-symmetric stretch at 1071 cm⁻¹, and an out-of-plane CH undergoing twisted vibrations at 868, 813, and 773 cm⁻¹. These spectral data were highly similar to the infrared (IR) data for ellagic acid, indicating that the pomegranate peel extract likely contains ellagic acid (Cui et al. 2002; Lee et al. 2013).

Figure 2. FT-IR spectrum of the aqueous pomegranate peel extract.

The UV-visible absorption spectrum of the aqueous pomegranate peel extract is shown in Figure 3. The maximum absorption of this extract occurred at wavelengths of 207 (0.548) nm, 272 nm (0.256), and 377 (0.050) nm. Absorption at 207 nm and 272 nm is characteristic of benzene. We attributed the absorption band at 207 nm to the E₂ absorption band, while the absorption band at 272 nm was attributed to the B absorption band. These absorption signals were identical to the UV absorption bands of ellagic acid (Cui et al. 2002; Lee et al. 2013). These results indicate that the main component in the aqueous pomegranate peel extract is ellagic acid.

Figure 3. UV – visible spectrum of the aqueous pomegranate peel extract.

Evaluation of color properties

Optimum dyeing procedure using pomegranate peel extract

The nine experiments were performed based on an orthogonal array design. The color characteristics and K/S values (which reflects the color strength of dyed fabric) of the dyed fabrics are shown in Table 3. The R and k values calculated for each factor using range analysis are listed in Table 4. kij represents the average of the sum of the L*, a*, b*, and K/S values in Table 4 at three levels i (i = 1, 2, 3) for the three factors j (j = A, B, C) tested here. Rj represents the difference between the maximum kij and minimum kij for the same j value. In general, a larger Rj value indicates that a factor is more important. kij and Rj were calculated as follows: kij = (Σ(h)ij)/3 (h = L, a, b, K/S; i = 1, 2, 3; j = A, B, C); Rj = max(kij) − min(kij) (when the j value is the same) (i = 1, 2, 3; j = A, B, C)

Table 3. K/S values and colorimetric data of dyed silk fabrics for the orthogonal array of nine dyeing experiments.

No.	A	B	C	L*	a*	b*	K/S
1	1	1	1	62.65	−4.65	19.90	2.66
2	1	2	2	62.50	−1.93	15.95	5.34
3	1	3	3	60.43	−1.74	12.57	5.71
4	2	1	2	59.18	−2.75	17.25	5.11
5	2	2	3	60.29	−1.79	13.17	5.53
6	2	3	1	59.61	−2.15	17.76	3.63
7	3	1	3	69.43	−1.34	21.63	5.48
8	3	2	1	59.53	−1.85	16.37	3.89
9	3	3	2	57.46	−1.59	16.00	4.16

Table 4. Range analysis of the orthogonal array for dyed silk fabrics using three experimental factors (A, B, and C).

		A	B	C
K/S	k1	4.57	4.42	3.39
	k2	4.76	4.92	4.87
	k3	4.51	4.50	5.57
	R	0.25	0.50	2.18
	Optimum factors		C3B2A2
L*	k1	61.86	63.75	60.60
	k2	59.69	60.77	59.71
	k3	62.14	59.17	63.38
	R	2.45	4.58	3.67
	Optimum factors		B1C3A3
a*	k1	−2.77	−2.91	−2.88
	k2	−2.23	−1.86	−2.09
	k3	−1.59	−1.83	−1.62
	R	1.18	1.08	1.26
	Optimum factors		C3A3B3
b*	k1	16.14	19.59	18.01
	k2	16.06	15.16	16.40
	k3	18.00	15.44	15.79
	R	1.94	4.43	2.22
	Optimum factors		B1C1A3

Taking the K/S value and the first factor (A) in silk fabrics as examples, k_1A = (Σ(K/S)_1A)/3 = (2.66 + 5.34 + 5.71)/3 = 4.57; k_2A = (Σ(K/S)_2A)/3 = (5.11 + 5.53 + 3.63)/3 = 4.76; k_3A = (Σ(K/S)_3A)/3 = (5.48 + 3.89 + 4.16)/3 = 4.51; R_A = max(k_iA) − min(k_iA) = k_2A − k_3A = 4.76 − 4.51 = 0.25. As shown in Table 4, the level of influence of these three factors on the K/S value was in the order C > B > A. This result indicated that the pH of the pomegranate peel extract has the greatest influence on the K/S value, followed by duration of dyeing, while temperature had the least influence on the dyeing of silk fabrics with pomegranate peel extract. The K/S value was highest when the dyeing conditions were C₃B₂A₂, and the L*, a*, and b* values were optimal under the dyeing conditions B₁C₃A₃, C₃A₃B₃, and B₁C₁A₃, respectively (Table 5). Since the K/S value reflects the color strength of dyed fabric, it is also used as the main indicator of color properties (Yan et al. 2021). The ideal dyeing conditions for pomegranate peel extract were pH 9, 60 min, and 60°C for silk fabrics.

Table 5. K/S values and colorimetric data for silk fabrics dyed with pomegranate peel extract.

Mordant	Mordanting methods	L*	a*	b*	K/S	Sample
None		60.43	−1.74	12.57	5.71
KAl(SO4)2	Pre-mord.	74.11	0.29	16.90	4.76
	Simult. mord.	58.70	−2.66	22.02	4.70
	Post-mord.	59.74	−2.38	13.94	5.49
FeSO4	Pre-mord.	59.18	−4.30	17.79	3.43
	Simult. mord.	41.19	−1.24	2.39	3.87
	Post-mord.	40.43	−1.54	1.37	3.68
SnCl2	Pre-mord.	46.52	1.46	8.93	3.54
	Simult. mord.	69.25	1.19	40.16	3.94
	Post-mord.	58.36	−2.99	19.63	5.44
Rare earth	Pre-mord.	70.05	6.28	23.87	6.55
	Simult. mord.	72.13	1.18	18.16	8.70
	Post-mord.	70.51	6.72	24.42	6.60
Mineral salts	Pre-mord.	75.45	2.85	28.66	6.17
	Simult. mord.	75.80	2.58	28.93	6.21
	Post-mord.	59.27	1.80	13.37	7.65
C. speciosa	Pre-mord.	60.73	−1.56	12.73	7.05
	Simult. mord.	61.25	−2.2	13.56	6.14
	Post-mord.	69.50	6.07	22.73	7.06

Color characters of natural mordants

The K/S values of dyed fabrics can be improved using natural (Table 5). Specifically, the K/S values of dyed silk were markedly improved using C. speciosa in pre-mordanting (7.05 for silk), rare earth in simultaneous mordanting (8.70 for silk), and mineral salts in post-mordanting (7.65 for silk) methods. These results indicate that the natural mordants are effective to enhance K/S values of silk fabrics. In addition, the color characteristics (L*, a*, b*) values of dyed fabrics differed depending on the fabric, mordant, and mordanting method.

Color fastness of fabrics dyed with pomegranate peel extract

The color fastness values of silk dyed with pomegranate peel extract are shown in Table 6. The natural mordants improved the color fastness of the dyed fabrics. For color fastness to rubbing of dyed fabrics, it was observed that a great improvement with natural mordants, achieving levels between 4 and 5 (The rating scale was as follows: 1, very poor; 2, poor; 3, moderate; 4, good; 5, excellent). The color fastness to dry rubbing of dyed silk fabrics with natural mordants was higher than wet rubbing, except for the dyed silk fabrics using rare earth in post mordanting method. And the color fastness of dyed fabrics following dry rubbing was enhanced with C. speciosa and mineral salt, reaching level 5, whereas only levels of 4–5 were reached in wet rubbing. Similarly, for the color fastness of dyed fabrics to washing and perspiration, it achieved levels between 4 and 5 with the natural mordants. The color staining fastness of dyed fabrics with natural mordants to washing and perspiration was higher than color change fastness. When using C. speciosa in simultaneous mordanting method, the color staining fastness to washing and perspiration of dyed samples could reach level 4–5, but the color change fastness just attained level 3.

Table 6. Color fastness of silk fabrics dyed with pomegranate peel extract.

Mordants	Mordanting methods	Washing fastness		Rubbing fastness		Perspiration fastness
						Acidic		Alkaline
		CC	CS	Dry	Wet	CC	CS	CC	CS
Without		2	4	4	3–4	2	3	2	3
C. speciosa	Pre-mord.	3	4–5	5	4–5	3	4–5	3	4–5
	Simult. mord.	3	5	5	4–5	3	4–5	3	4–5
	Post-mord.	2–3	4–5	5	4–5	4–5	4–5	4	4–5
Mineral salt	Pre-mord.	2–3	5	5	4–5	2–3	4	2–3	4–5
	Simult. mord.	2–3	5	5	4–5	2–3	5	3	5
	Post-mord.	4	4–5	5	4–5	3	4	3	4–5
Rare earth	Pre-mord.	3	5	4–5	4	2–3	4	2–3	4–5
	Simult. mord.	2–3	4–5	5	4	2–3	4	2–3	5
	Post-mord.	2–3	5	4–5	4–5	3–4	5	3–4	4–5

CC: Color change, CS: Color staining, 1: very poor, 2: poor, 3: moderate, 4: good, 5: excellent..

Evaluation of the color-fixing effects of gum rosin

Dyeing properties of treated and untreated fabric

Based on previous findings, when silk fabrics were dyed with C. speciosa used in pre-mordanting, rare earth used in simultaneous mordanting, and mineral salts used in post-mordanting, better color fixing and improved K/S values were achieved using gum rosin as the dye-fixing agent (Table 7). The K/S values of dyed silk fabrics treated with mineral salts in the post-mordanting method were sharply enhanced by the color fixing treatment, increasing from 7.65 to 11.74.

Table 7. K/S values and colorimetric data of dyed silk fabrics with and without color fixation treatment.

Mordanting method	Mordant	Color fixation	L*	a*	b*	K/S	Sample
Pre-mord.	C. speciosa	Before	60.73	−1.56	12.73	7.05
		After	80.23	3.04	23.02	9.19
Simult. mord.	Rare earth	Before	72.13	1.18	18.16	8.70
		After	64.72	−0.28	10.48	9.15
Post-mord.	Mineral salts	Before	59.27	1.80	13.37	7.65
		After	72.39	1.22	14.21	11.74

The color-fixing treatment substantially improved the color fastness of dyed fabrics (Table 8). The color-fixing treatment greatly improved the color fastness to washing, perspiration, and wet rubbing of dyed fabrics, whereas the color fastness to dry rubbing of dyed fabrics was the same before and after the color-fixing treatment (level 5). For instance, the color fastness to perspiration of dyed silk fabrics treated with mineral salts in the post-mordanting method increased from level 3 to 5 after the color-fixing treatment.

Table 8. Color fastness of color-fixing-treated and color-fixing-untreated fabrics.

Mordanting method	Mordant	Color fixing treatment	Washing fastness		Rubbing fastness		Perspiration fastness
							Acidic		Alkaline
			CC	CS	Dry	Wet	CC	CS	CC	CS
Pre-mord.	C. speciosa	Before	3	4–5	5	4–5	3	4–5	3	4–5
		After	4	5	5	5	4	5	4	5
Simult. mord.	Rare earth	Before	2–3	4–5	5	4	2–3	4	2–3	4–5
		After	3–4	5	5	5	3	4–5	3–4	5
Post – mord.	Mineral salts	Before	4	4–5	5	4–5	3	4	3	4–5
		After	5	5	5	5	5	5	5	5

CC: Color change, CS: Color staining, 1: very poor, 2: poor, 3: moderate, 4: good, 5: excellent..

Morphological analysis of treated vs. untreated fabrics

SEM images of color-fixing-treated and color-fixing-untreated silk fabrics are shown in Figure 4. The surface morphology of color-fixing-untreated silk fibers Figure 4(a–f) was smooth. By contrast, following the color-fixing treatment, the dyed silk fibers Figure 4(a–f) appeared granular, with a thin film on the surface of the fiber. These observations confirmed the finding that gum rosin forms a physical film on the surfaces of fabric fibers to fix the color and reduce the loss of dye (Li, Cui, and Shi 2014). The surfaces of fabric fibers appeared granular due to reactions between the gum rosin fixing agent and the pigments, fibers, and natural mordants. Furthermore, the formation of coordinate bonds could promote joining of fibers and pigments (Li 2014).

Figure 4. SEM images of silk fibers. Color-fixing-untreated fibers (a – c) and fibers treated with gum rosin (d – f). (a) color-fixing-untreated silk fabric treated with C. speciosa in the pre-mordanting method; (b) color-fixing-untreated silk fabric treated with rare earth in the simultaneous mordanting method; (c) color-fixing-untreated silk fabric treated with mineral salt in the post-mordanting method; (d) color-fixing-treated silk fabric treated with C. speciosa in the pre-mordanting method; (e) color-fixing-treated silk fabric treated with rare earth in the simultaneous mordanting method; (f) color-fixing-treated silk fabric treated with mineral salt in the post-mordanting method.

Conclusion

This study highlights the potential of using pomegranate peel extract as a dye for silk fabrics. Experimental result determined that ellagic acid as the major pigment in pomegranate peels. Meanwhile, the optimum conditions of dyed silk fabrics with pomegranate peel were pH 9, 60 min, and 60°C for by orthogonal experiment. And the natural mordants could be potential to strengthen the color properties of dyed silk fabrics through the evaluation of dyeing properties of silk fabrics. Moreover, the color properties of dyed fabrics could be further improved under post-treatment with gum rosin which fixed color by forming a physical film on dyed fibers and by undergoing chemical reactions with the dye, fiber, and natural mordants through SEM analysis. Therefore, pomegranate peels are an agricultural waste product that could be used to create dye along with natural mordants and dye-fixing agents, to facilitate the recycling of agricultural by-products.

As a prospect, the industrial application of pomegranate peel dye in the textile field needs to consider the functional characteristics (such as: anti-ultraviolet, antibacterial, antioxidant) and color of the fabric endowed by dye, so as to carry out purposefully development and utilization of related products. Furthermore, the research on the dyeing potential of other agricultural wastes, the dyeing mechanism of natural mordants and environmental dyeing methods will be the focus of future research to promote the sustainable development of natural dyes.

Highlights

• Dyeing silk fabrics with a natural colorant from Pomegranate (Punica granatum) peel.

• Evaluated the effect of natural mordants under different mordanting methods.

• Improved the dyeing properties of dyed silk fabrics with natural mordants and natural fixing agent.

• Provided a case study is to explore natural dyes for textile industry through agricultural waste recycling.

Acknowledgments

The authors would like to acknowledge the support of Minzu University of China and Kunming Institute of Botany for this project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the National Nature Science Foundation of China (project ID: 31670340 and 31970357), the Strategic Priority Research Program of Chinese Academy of Sciences (project ID: XDA20050204, XDA19050301, and XDA19050303) and Yunnan Province Science and Technology Department of building Science and Technology Innovation Center for South Asia and Southeast Asia (No. 202203AP140007).