Green Sustainable Textile Supercritical Dyeing Process Using CO₂ Madder (Rubia tinctorum L.) Extract

ABSTRACT

Waterless or reduced water consumption dyeing methods based on supercritical technologies are of interest to fabric manufacturers. The study was aimed at developing a dyeing method for natural fibers, in particular linen and silk, by pressure supercritical impregnation using madder alizarin (R. tinctorum) coloring compound produced by supercritical extraction method as an ecological alternative to conventional dyeing methods. A comparative test of fabric dyeing using supercritical and conventional methods was also carried out. In these dyeing technologies, the pre-treatment process plays an important role in the color intensity. The tests were performed using fabrics without and with mordants, and the results were compared using the color analysis method. The colors of the dyed samples obtained in the supercritical technology are more in shades of carmine, and in the traditional method in duller reds. The proposed modern and ecological dyeing technology guarantees a good resistance to washing and light. Antibacterial activity tests were also performed using supercritical and ethanol extracts. Dyed fabrics play health-promoting and protective roles for their users. Linen fabrics showed antimicrobial activity and positive effects on the skin, which was more moisturized. Waterless technologies should be developed in conjunction with user and environmental impact studies.

摘要

基于超临界技术的无水或降低耗水量的染色方法引起了织物制造商的兴趣. 本研究旨在开发一种天然纤维，特别是亚麻和丝绸的染色方法，采用超临界萃取法生产的茜素（R.tinctorum）着色化合物作为传统染色方法的生态替代品，通过压力超临界浸渍进行染色. 并对超临界法和常规法染色织物进行了对比试验. 在这些染色技术中，预处理过程对颜色强度起着重要作用. 使用不含媒染剂和有媒染剂的织物进行测试，并使用颜色分析方法对结果进行比较. 在超临界技术中获得的染色样品的颜色更多地是胭脂红色调，而在传统方法中是暗红色. 所提出的现代生态染色技术保证了良好的耐洗性和耐光性. 还使用超临界和乙醇提取物进行了抗菌活性测试. 染色织物对使用者起到促进健康和保护作用. 亚麻织物具有抗菌活性，对皮肤有积极作用，使皮肤更加滋润. 应结合用户和环境影响研究开发无水技术.

KEYWORDS:

• Waterless dyeing
• supercritical carbon dioxide
• madder
• silk
• linen
• cleaner production

关键词:

• 无水染色，超临界二氧化碳，很生气,亚麻布
• 清洁生产
• 丝

Introduction

The textile industry is one of the largest water users, which is caused by its production system, and consumes huge amounts of water during all processing operations. The challenge for the industry is to adopt more water-friendly technologies of pre-treatment, dyeing, printing, and finishing operations (Choudhury and Roy 2017; Lakshmanan and Raghavendran 2017). In the conventional dyeing process, water is one of the key ingredients and is used as a solvent in pre-treatment and finishing processes. According to the World Bank (Kant 2012), textile dyeing and cleaning are the source of 17–20% of the industrial water pollution.

Water is still used in dyeing technology, but new technologies have emerged that completely eliminate or significantly reduce its use. New dyeing techniques and new dyes have been developed for polyester fabrics due to their simpler chemical structure (Zhang et al. 2022). A careful analysis showed that the color was increased by 31.1%.

Experimental studies have been conducted on using liquid solvents to leach alizarin from madder roots (Rubia tinctorum). It was found that methanol at a temperature of 25°C is able to extract not only free alizarin but also its glycosidic forms, which gives a total alizarin extraction yield of 2.9 ± 0.1 g kg⁻¹ of dried material (De Santis and Moresi 2007). Alizarin was used to dye samples of raw cotton and wool using the liquid method.

The use of disperse fluorescent dyes in supercritical carbon dioxide to dye polyester fabrics was discussed The implementation of synchronous synthesis and dyeing of fabrics with fluorescent dyes in supercritical carbon dioxide was rated as an effective way to prevent the environmental pollution caused by dyeing processes. A method for the synthesis of series of nitrothiazole dye derivatives using readily available substrates, which were used to dye cotton fabrics using supercritical carbon dioxide, was discussed. In recent years, the use of supercritical fluids, especially supercritical carbon dioxide, in the textile industry as a substitute for water-based dyeing has been of interest to researchers due to its far-reaching implications both in terms of technology and environmental protection (De Oliveira et al. forthcoming; Elmaaty et al. 2022).

The extraction method of alizarin from madder roots (Rubia tinctorum L.) using supercritical CO₂ with the addition of a co-solvent (0–50%), temperature (45–95°C), pressure (150–250 bar), extraction time (15–120 min), and flow rate (5–9 mL/min). The alizarin extraction yield and its content in the extract of R. tinctorum (MR) were determined to be 1.34 g kg⁻¹ of roots and 6.42%; it was discussed respectively (Elmaaty et al. 2023). The extract was used for the conventional dyeing of wool fabric. A theoretical basis for the process and the solubility of dyes in supercritical carbon dioxide, dye distribution, and mass transfer phenomena between textile fibers and carbon dioxide were discussed, highlighting the challenges and limitations of supercritical carbon dioxide dyeing and offering suggestions for solving these problems (Amenaghawon et al. 2019). The dyeing of cotton previously modified by reaction with benzoyl chloride was discussed (Özcan et al. 1998). Dyeing was performed with dispersion dyes in supercritical carbon dioxide at a temperature of 100°C and a pressure of 300 bar and compared with polyester dyeing under the same conditions. The color performance of the fibers was assessed by pre- and post-wash measurements to test the quality of dyeing in this environment. Good color intensity was obtained. The results of research on dyeing wool in supercritical carbon dioxide were presented (Zheng et al. 2017; 2018). A model of the mechanism of yak wool fiber breakage was proposed, based on Bernoulli’s law and Boyle’s law in a supercritical carbon dioxide environment. The method of synthesis and the use of special dispersion reactive dyes in the waterless dyeing of wool with supercritical carbon dioxide were discussed (Zhang, Wei, and Long 2016). The researchers pointed out the limitations in the use of the technology of dyeing fabrics using supercritical carbon dioxide due to the lack of special dyes for this anhydrous technology, especially due to the lack of dispersion reactive dyes useful for natural fibers. The obtained results indicate that the developed method is useful for the development of special dispersion reactive dyes with safe and environmentally friendly properties, especially for the waterless dyeing of wool with supercritical carbon dioxide.

The novelty is the simultaneous production of a supercritical madder extract and dyeing of the fabric by impregnation with the extract. The influence of mordants on the quality and stability of colors obtained by supercritical and conventional methods was tested. The developed method of dyeing natural origin fabrics does not generate any waste.

MW-microwave, US-ultrasound, UV-ultraviolet, gamma rays-assisted dyeing

The conventional textile dyeing requires the dye to be dissolved in an aqueous solution or a different liquid solvent. The mixture of dye and liquid solvent is then pumped into a vat containing textiles. The dyeing process usually involves the vigorous agitation or recirculation of the dye/solvent mixture through the fabric, which takes place several times.

The use of supercritical CO₂ for dyeing textiles is a competitive method in comparison to solvent methods and constitutes an environmentally friendly and sustainable alternative. Instead of using an aqueous solution or other liquid dye solvents, supercritical CO₂ was used. The process is the same as the conventional method, except that at the end of the dyeing process, the supercritical CO₂/dye mixture is depressurized to ambient pressure and gaseous CO₂ is released into the atmosphere.

The use of microwave radiation – MW, ultra sound radiation – US, ultraviolet radiation – UV, gamma radiation-Gamma methods in the dyeing process is possible in both cases, i.e. both in the solvent method (using water or a different solvent) and supercritical CO₂. In these cases, the action of radiation changes the surface structure of the dyed material, which results in easier and more durable deposition of the dye on the dyed surface (Adeel, Rehman and Khosa et al. 2021; Adeel, Habib and Batool et al. 2021; Arshad et al. 2020; Jabar, Owokotomo, and Ogunsade 2022; Muneer et al. 2020; Rehman et al. 2022).

Microwave (MW), ultrasonic (US), ultraviolet (UV), or gamma (Gamma) assisted processes are also used in the extraction of dye from plant materials. In this case, the radiation energy damages the structure of the cells in which the dyeing extract is placed, which makes it easier to dissolve it in the solvent and transport the mixture of solvent and dye to the fabrics to be dyed. Both in the case of dyeing fabrics with various methods and in the case of the production of dyes from plant or other materials, the mentioned physical radiation methods always accelerate significantly the speed of the process.

Materials and methods

Madder roots (Rubia tinctorum L.)

Madder (Rubia tinctorium L.), belonging to the family Rubiaceae, has a high commercial, economical, and medicinal importance. The roots of this plant contain the pigment alizarin and purpurin, lucidin, pseudo purpurin, rubiadin, and the glucosides (Cardon 2007, 109). Each of these components is important in the dyeing process. Purpurin produces oranges and yellows, alizarin – clear, strong red. The compounds contained in madder roots have many applications in medicine. Rubiadin has anti-inflammatory (Chien et al. 2015), anti-oxidant (Malik and Müller 2016), anti-bacterial (Fosso et al. 2012), anti-malarial (Winter et al. 1996) anti-fungal, anti-viral, and other properties (Ahmed, Nassar, and El-Shishtawy 2020).

Madder roots (Rubia tinctorum L.) were obtained from an experimental plantation in Pętkowo after the third year of cultivation by the Institute of Natural Fibers and Medicinal Plants – National Research Institute in 2021, Figure 1. This scientific organization cultivates crops in accordance with global standards (Ozdemir and Karadag 2023).

Figure 1. Madder root from Institute plantation, after 3 years of cultivation.

The roots were washed with distilled water and dried at room temperature. The dried roots were then ground using a Retsch SM100 cutting mill. A sieve with trapezoid holes of 0.5 mm was installed in the mill.

Fabrics

For the purpose of the experimental research, 100% linen fabric KT1579 and 100% silk fabrics were used. Further research focused on the linen fabrics certified by Oeko Tex® standard 100 and REACH (Linen Partner s c 2023). Linen fabric has rare bacteriological properties. Resistant to fungi and bacteria, it has been found to be an effective barrier to certain diseases and is useful in the treatment of many allergic diseases. Linen fibers are characterized by the antioxidant activity; apart from their main components as cellulose, hemicellulose, pectin, lignin, fats, and waxes, they contain in their chemical composition phenolic acids, which are natural antioxidants (Mustata and Mustata 2013; Zimniewska 2015; Zimniewska and Romanowska 2022). The standard (OEKO-TEX) was developed by the International Association for Research and Testing in the Field of Textile and Leather Ecology to address the growing concerns about the presence of harmful chemicals in textile products (Karadag 2023; OEKO-TEX® 2023).

Silk fabrics were also used for preliminary tests. Fabrics of 100% natural silk purchased from a manufacturer in China. Unfortunately, it is unknown if the fabrics are certified. The purpose of the dyeing tests was to evaluate the new madder extract for further research and projects.

Linen and silk samples dyed with a supercritical carbon dioxide extract SLm and with the conventional dyeing method – labeling:

The samples before dyeing:

Lu -linen unmordanted. Lm- linen-mordanted

Sm-silk-unmordanted, Sm-silk-mordanted

S-supercritical dyeing: SLu-linen-unmordanted, SLm – linen mordanted, SSu – silk unmordanted, SSm – silk mordanted

C-conventional dyeing: CLu- linen-unmordanted, CLm – linen mordanted.

CSu unmordanted, CSu

Mordants

In the latest research, scientists, out of concern for the environment, are looking for ecological, safe dyeing methods and sustainable products such as natural dyes and mordants.

The compounds contained in the above-mentioned natural sources have therapeutic properties, both in extracts and in dyed fabrics; they increase skin hydration and help in dermatological diseases (Habib et al. 2021). Some of plant species containing tannins are Oak galls (50–70%), Treripod (65%), Myrobalan (30–35%), Tara (43–51%), and Chest Nut (30%) (Prabhu and Bhute 2012).

Oak galls and alum were used as the mordants. Oak galls are used to provide bioactive constituents, such as phenolic acids, including gallic acids (GA), tannic acids (TA), and ellagic acids along with flavonoids, such as quercetin with main constituents of TA and GA in the oak galls (Rahman et al. 2015). The tannin compounds contained in oak galls contribute to a better bonding of the dye with the fabric. Different colors derive from different mordants when combined with the same dye.

Alum refers to potassium alum, with the formula AlK(SO₄)₂*12 H₂0

12 H₂0 and is used as a mordant for protein (animal) and cellulose (plant) fibers and fabrics. It improves light and wash fastness of all natural dyes and keeps colors clear.

Preparation of the fabrics for dyeing – pretreatment

Before the mordanting, a fabric should be washed to remove dust, dirt, and grease. Linen is washed for about 15 min in water at a temperature of about 40°C, which is then heated to 60°C. Then, linen fabrics are subjected to pre-mordanting. This process makes it easier to dye the fabric.

Linen pre-mordanting method

11 g of alum AlK(SO₄)₂ *12 H₂0

15 g of oak galls

100 g of linen fabric

3000 mL of water

Oak galls was soaked in water and heated for 60 min to 90°C. Then, 11 g of alum was added to this solution. Later, wet linen fabrics were added to this solution. The treated fabric was then thoroughly rinsed with water and air-dried.

Silk pre-mordanting method

7 g of alum AlK(SO₄)₂ *12 H₂0

100 g of silk fabric

3000 mL of water

Alum was dissolved in a small amount of warm water and added to the Ugolini dyeing machine. Silk was heated with the temperature of 60°C for 90 min. After drying, the fabrics were dyed.

Analytics

A gas chromatograph coupled with a mass spectrometer (GC-MS/MS), with a triple quadrupole (Agilent 7890) and the Mass Hunter operating system (ver. C.01.03) and the NIST 2011 MS library, with a DB-EUPAH capillary column was used for the chromatographic analysis (60 m × 250 μm; 0.25 μm). The duration of the analysis was 82 min, the temperature of the dispenser was 300°C. Detector settings: ionization − 70 eV in EI mode, scanning mode in the range of 40–650 amu, ion source temperature − 230°C. Carrier gas: helium, flow rate: 2 mL/min. The method of analysis of alizarin in the raw material and extract was developed on the basis of the paper by Boldizsár et al. (2006), Table 1.

Table 1. Temperature program implemented by the chromatograph.

Temperature buildup, ℃/min	Oven temperature, ℃	Holding time, min
Initial value	50	1
5	260	6
3	300	20

Supercritical extraction and dyeing equipment

Due to the polar nature of the alizarin, before starting the dyeing process, the ground raw material was moistened with distilled water to a moisture content of 30%, mixed well and left until constant humidity was established in the entire volume of the charge for 4 h. Then, the raw material was loaded into the extractor (A), and the samples for dyeing were placed on the upper surface of the charge (B).

The solvent used for extracting the dye from the madder root was CO₂ with a purity of 99.8%, supplied by the domestic supplier of technical gases ZAP, Pulawy, Poland.

Material for dyeing – samples of silk and linen fabrics were used – weight 110 g/m², in accordance with the EU safety standard (http://www.reach-info.pl/13, rozporzadzanie_reach.html), provided by a domestic supplier.

Distilled water produced by Merck’s Water Purification Systems was used to moisten the batch before extraction.

For dye extraction and dyeing silk and linen fabrics with the supercritical method, a pressure extraction equipment was used. The equipment consisted of an extractor, two separators S1 and S2, carbon dioxide pump P, heat exchangers E1, E2, E3, and E4 and carbon dioxide tank V1. Maximum working parameters of the pressure system: working pressure − 40 MPa, working temperature − 100°C, extractor volume − 40 dm³, CO₂ flowrate − 140 kg/h.

The dyeing of fabric samples was carried out in one apparatus with the use of madder dye produced on an ongoing basis by the supercritical method in the lower part of the extractor A, and then the obtained extract was directed to the impregnation of fabric samples placed on the surface of the madder charge B. The madder extract, flowing with carbon dioxide through the fabrics, was adsorbed on the surface of the pores of the fabric samples intended for dyeing. The extract not adsorbed by the dyed fabrics was recovered in separator S1, Figure 2. The process parameters are presented in Table 2.

Figure 2. Flow diagram of the plant for dyeing fabrics with the supercritical method.

Figure 3. Supercritical CO₂ extract – MR and linen unmordanted and mordanted fabrics.

Figure 4. Madder extract-MR.

Table 2. Parameters of the supercritical carbon dioxide extraction process.

Extraction		Separation, S1		Separation, S2		Extraction yield, %	CO2 consumption, kg/kg of charge
P, bar	T, °C	P, bar	T, °C	P, bar	T, °C
300	60	65	50	50	20	2.2	190

Ground madder root mass of 14.2 kg was moistened with water before extraction to the level of about 30% for about 4 h in a closed vessel, and then the prepared batch was put into an extractor with a capacity of 40 dm³. Wetting the batch with water was aimed at changing the pH of the solvent and improving the extraction efficiency of alizarin from madder, without using harmful co-solvents, e.g. methanol, due to poor solubility of alizarin in supercritical CO₂. The extraction was carried out under a pressure of 300 bar and a temperature of 60°C. The first separation stage S1 was at a pressure of 56 bar and a temperature of 60°C. The second separation stage S2 was at a pressure of 50 bar and a temperature of 20°C. CO₂ consumption was 190 kg/kg of dry madder. The average extraction yield was 2.2% w/w, and the content of alizarin in the extract was 7.85%. At the outlet of the extractor, samples of prepared silk and linen fabrics were placed, marked: unmordanted samples Su (silk) and Lu (linen), and mordanted samples – Sm – silk and Lm – linen. These samples were dyed by pressure impregnation with an online produced madder extract. After the process of madder extraction and dyeing was completed, the CO₂ pressure in the extractor was reduced and the fabric samples were sent for evaluation in terms of color quality and fastness as well as uniformity of application on fabrics. The excess extract MR was used to test the dyeing of silk and linen fabric samples using the conventional water method, Figure 4. Fabric samples for water dyeing with the use of supercritical extract were prepared similarly to pressure dyeing, i.e. unmordanted (marking Su and Lu) and mordanted (marking Sm and Lm). The obtained samples of dyed fabrics were subjected to standard tests for the quality of dyeing. The test results confirmed the high quality of the fabrics dyed with the supercritical method.

Conventional methods of dyeing

The dyeing process was carried out in the Ugolini Redkrome dyeing apparatus.

Linen and silk fabrics were used for dyeing (unmordanted and mordanted). Different dyeing programs were used for linen and silk. Important information is that no mordants were used in the dyeing solution.

Dyeing linen

The process of dyeing was conducted in the Ugolini dyeing machine. Six dye cups were used in this process. The solution of 500 mL H₂O containing 0.5 g of dissolved supercritical madder extract was poured into each cup. Next, 5 g of linen fabric was added.

The dyeing was conducted in a temperature of 95°C (gradient 1°C/1 min) for 30 min, followed by a slow cooling process to 50°C (gradient 2°C/1 min).

Dyeing silk

The process of dyeing was conducted in the Ugolini dyeing machine. Six dye cups were used in this process. The solution of 500 mL H₂O containing 0.5 g of dissolved supercritical madder extract was poured into each cup. Next, 5 g of silk fabric was added.

The dyeing liquid was heated to a temperature of 80°C (gradient 1°C/1 min), which was maintained for 30 min. Then, the solution of dissolved supercritical Madder extract MR with silk fabric was cooled to 50°C (gradient 2°C/1 min).

No mordants were used in these two dyeing processes. The differences in color result from the preparation of fabrics before dyeing – the process of mordanting linen in oak galls and alum and silk with alum before dyeing.

Color measurements

The color measurements of the dyed fabrics were made using the RM200QC spectrophotometer. The coordinates of the CIEL*a*b* color evaluation system (CIE L *, a *, b *) are presented in the tables assigned to the individual raw materials with which the fabrics were dyed. (CIELAB) is a color space specified by the International Commission on Illumination. This CIE L*a*b* system describes all the colors visible to the human eye and was created to serve as a device-independent model to be used as a reference. The parameters are colorfulness, saturation, lightness, and brightness (Kamucki et al. 2011; Kazimierska 2014) L* - lightness, a* - redness, b* - yellowness, C* - chroma, hº - hue angle

The equation describing the color difference between any dyed samples was calculated as the square root of the squares of the corresponding L*, a* and b* differences, as follows:

(1) $\mathrm{\Delta }{E}^{\ast }=\sqrt{{\left(L_2^{\ast }-L_1^{\ast }\right)}^2+{\left(a_2^{\ast }-a_1^{\ast }\right)}^2+{\left(b_2^{\ast }-b_1^{\ast }\right)}^2}$(1)

The color of the samples was compared with the standards of the color identification system developed by Pantone according to the sampler – Pantone (Color) Matching System (PMS).

Testing the antibacterial activity of madder extract against Staphylococcus aureus ATCC 6538P

The research was aimed at determining the antibacterial effect of Rubia tinctorum madder extract. The experiment included three samples of extracts obtained from madder.

ME – Ethanol extract of madder rhizome

MN – Ethanol extract of madder rhizome – fortified

MR – Supercritical extract of madder rhizome

ME and MN extracts were purchased from a French manufacturer – Coloures de Plantes. Organic cotton and linen knitted fabrics were used for dyeing fabrics on an industrial scale. The MR extract was made in Puławy. This extract is presented in Table 3 and 4

Table 3. Antibacterial activity of the tested extracts from dye plants.

Sample number	Name of extract	MIC, mg/mL	MBC, mg/mL	JA/g
1.	ME	1.50	5.0	670
2.	MN	0.75	2.5	1330
3.	MR	0.25	0.5	4000

Table 4. Spectrophotometric and pantone measurements of color – linen and silk samples dyed with an extract produced by supercritical carbon dioxide extraction method.

Sample	Spectophotometric analysis results					Color	PANTONE®
	L*	a*	b*	c*	h*
SLu	78.9 ± 0.9	13.9 ± 0.3	0.3 ± 0.1	13.9 ± 0.6	1.2 ± 0.3	pale pink	14–1513 TCX
SLm	44.2 ± 0.5	42.2 ± 0.6	14.2 ± 0.2	14.9 ± 0.5	19.5 ± 0.8	Pink-red. cranbery	13–2805 TCX
SSu	48.8 ± 0.7	29.0 ± 0.5	32.7 ± 0.7	42.1 ± 0.7	48.5 ± 1.2	dark peach	16–1532 TCX
SSm	48.7 ± 0.4	44.8 ± 0.3	44.9 ± 0.4	18.0 ± 0.5	48.4 ± 0.9	rasberry	18–1624

The excess supercritical MR extract collected in the S1 separator and subjected to lyophilization was used for antibacterial activity tests.

The tested samples were weighed in the amount of 100 mg and dissolved in 1 mL of DMSO, and then diluted with a liquid bacteriological medium (CASO Broth, Merck) in the concentration range from 0.1 to 5 mg/mL. 0.1 mL of the culture of the standard strain of Staphylococcus aureus ATCC 6538P with the number of cells 105/mL was added to the test tubes containing the solutions of the tested samples with a volume of 1 mL. The samples were then incubated for 18 h at 37°C and after that time, the lowest concentration of madder extract inhibiting the growth of the standard strain (MIC – Minimal Inhibitory Concentration) was determined. All dilutions of the tested samples were inoculated on an agar medium (CASO Agar, Merck) and after 24 h of incubation of the samples at 37°C, the lowest bactericidal concentration of the extract from dyeing plants (MBC – Minimal Bactericidal Concentration) was read.

Statistical analysis

An Excel program version MS-Office 2021 was used to analyze the data obtained from this study. The statistical analysis of variance was used to compare all the samples. The standard deviation (SD) was calculated, and significant variations among all means were analyzed using Student test at p = .05. A sample of each color was statistically analyzed three times.

Results and discussion

As a result of the extraction of the moistened madder charge, the extract and the water were collected. In the first separator S1, mainly the madder extract was collected. In the second separator S2, mainly water coming from the wetted charge was collected. Due to the increased polarity of CO₂ with the addition of water, the dominant chemical compound extracted was alizarin. The extraction content of alizarin in dry raw material was 1.73 g/kg. The extraction yield of alizarin was 2.2%. The concentration of alizarin in the extract after lyophilization was 7.85%, and it was the highest content of the produced extract component.

As a result of the dyeing process combined with dye extraction, colored fabric samples were obtained Slu and SSu – linen and silk, both samples unmordanted and samples SLm and SSm mordanted and an additional unused dye extract which was collected in separator S1.

The color analysis – supercritical dyeing and conventional dyeing

Table 4 presents the spectrophotometric results of dyed samples of linen SLu – raw linen sample, SLm- linen treated alum and galas and silk – SSu raw silk and SSm – silk treated alum silk. The presented samples were dyed in a supercritical carbon dioxide atmosphere.

SLu – linen; SSu – silk – unmordanted – linen and silk fabrics; SLm (gall oak and alum); SSm mordanted silk (alum) – samples dyed in a supercritical carbon dioxide, p = .05

For the dyed linen samples – SLu and SLm, the L* coordinate values ranged from 44.2 to 78.9. L* is the colorimetric coordinate of lightness, which indicates the lightness or transparency point where all shades are located. For pure black L* = 0 and for pure white L* = 100

The color difference of the linen samples SLu and SLm - ΔE* is 46.8, which means that the obtained colors are completely different. In the case of the a* and b* coordinates, positive values were obtained, which means the saturation of the samples in yellow and red.

For silk fabrics SSu and SSm - L* coordinates were obtained − 32.7–44.9. In the case of the a* and b* coordinates, positive values were obtained, which means the saturation of the samples in yellow and red. The color difference between the samples - ΔE* is 20, which means that completely different colors were obtained.

CLu – linen; CSu – silk – unmordanted – linen and silk fabrics; CLm (gall oak and alum); CSm mordanted silk (alum) – samples dyed in a supercritical carbon dioxide, p = .05.

Table 5 presents the spectrophotometric results of dyed samples of linen (CLu – linen, CLm – linen treated with alum and galas) and silk (CSu – raw silk and CSm – treated with alum). Supercritical extract Madder was used in the conventional dyeing process.

Table 5. Spectrophotometric and pantone measurements of color – linen and silk samples dyed with madder MR extract using the conventional method.

Sample	Spectophotometric analysis results					Color	PANTONE®
	L*	a*	b*	c*	h*
CLu	78.7 ± 0.4	11.5 ± 0.3	11.2 ± 0.2	16.1 ± 0.4	44.2 ± 0.8	Light peach skin	14–1907 TCX
CLm	47.5 ± 0.4	34.4 ± 0.2	15.0 ± 0.3	37.5 ± 0.2	23.6 ± 1.2	Mineral red	17–1537 TCX
CSu	70.0 ± 0.5	16.3 ± 0.3	34.9 ± 0.4	38.6 ± 0.8	5.0 ± 0.1	Peach	13–1027 TCX
CSm	31.6 ± 0.3	40.3 ± 0.2	24.0 ± 0.3	46.9 ± 0.7	30.7 ± 0.5	light burgundy	19–1655 TCX

For linen samples, the L* coordinate values ranged from 47.5 to 78.7. The color difference ΔE* between the CLu and CLm samples is 38.8, which means that the obtained colors are completely different. In the case of the a* and b* coordinates, positive values were obtained, which means the saturation of the samples in red and yellow.

For silk fabrics, L* coordinate values ranged from 31.3 to 70. The color difference between the ΔE * samples is 46.6, which means that completely different colors are obtained. In the case of coordinates a* and b* positive values were obtained, which means the saturation of samples in red and yellow.

Differences in the colors of the samples are shown in Figures 5 and 6.

Figure 5. Linen and silk fabrics dyed with supercritical extract MR.

Figure 6. Linen and silk fabrics dyed with supercritical extract MR – conventional method.

The samples of fabrics dyed with the innovative technology obtained more saturated colors, with a predominance of carmine color in the fabrics before the treatment. The colors of linen and silk fabrics dyed with supercritical and conventional methods were different (see Table 4, 5 and 6 and Figures 3, 5 and 6).

CC: color change; CS: Color staining; SLu – linen samples; SLm – linen samples mordanted alum/gall oak; - SSu – silk; SSm – silk mordanted alum.

Table 7 presents the results of evaluating the fastness to light, washing, rub, and perspiration. The results of the tests are good or very good. The light fastness in blue scale (1–8) rating 5 is quite a good result. Also, other results show that all the samples mordanted as well as unmordanted have a good result (5, 4–5). It is a good test for the textile industry. The results of the analyses are good or very good. The color is stable and the supercritical Madder – MR dye fabrics have antibacterial properties.

Table 6. Fastness properties for dyed linen and silk fabrics in a supercritical carbon method technology.

					Rub fastness			Perspiration fastness
			Wash fastness		Dry		Wet	Alkaline		Acidic
Samples	CO2	Light fastness	CC	CS	CC	CS	CC	CC	CS	CC	CS
SLu SLm SSu SSm	CO2 CO2 CO2 CO2	5 5 4 5	4–5 4–5 3–4 4–5	5 5 5 5	4–5 4–5 4–5 4–5	3– 4 4–5 3–4 4–5	5 5 5 5	4 4 4 4–5	5 5 5 5	4 4 4 4	5 5 5 5

Table 7. Fastness properties for dyed linen and silk fabric by conventional methods – extract Madder MR.

					Rub fastness			Perspiration fastness
			Wash fastness		Dry		Wet	Alkaline		Acidic
Samples	Mordants	Light fastness	CC	CS	CC	CS	CC	CC	CS	CC	CS
CLu CLm CSu CSm	– alum/Oak galls – alum	4 4 3 4	4–5 4 3–4 4	4 4 4 4	4–5 4–5 3–4 4	4–4 4–5 3–4 3–4	4 4 4 4	4 4 4 4	5 4 4 4	4 4 4 4	5 5 5 4

The color difference ΔE* between the linen fabrics unmordanted SLu and mordanted SLm samples dyed by the supercritical method calculated on the basis of equation (1)(1) $\mathrm{\Delta }{E}^{\ast }=\sqrt{{\left(L_2^{\ast }-L_1^{\ast }\right)}^2+{\left(a_2^{\ast }-a_1^{\ast }\right)}^2+{\left(b_2^{\ast }-b_1^{\ast }\right)}^2}$(1) was 46.9, while the color difference between the unmordanted SSu and mordanted SSm silk samples was 22.3.

The color difference ΔE* between the sample of linen fabrics unmordanted CLu and mordanted CLm, dyed using the conventional method calculated on the basis of equation (1)(1) $\mathrm{\Delta }{E}^{\ast }=\sqrt{{\left(L_2^{\ast }-L_1^{\ast }\right)}^2+{\left(a_2^{\ast }-a_1^{\ast }\right)}^2+{\left(b_2^{\ast }-b_1^{\ast }\right)}^2}$(1) , was 38.9, while the color difference between the sample of silk unmordanted CSu and mordanted CSm was 79.9.

CC: color change; CS: color staining; CLu – raw linen samples; CLm – linen samples mordanted alum/gall oak; CSu – raw silk; CSm – silk mordanted alum

The fastness of dyeing samples in the conventional method using Madder R extract is slightly worse – shown in Table 7.

The light fastness of samples was analyzed with using Atlas Alfa 150 S test instrument according to EN ISO 105-B02.

The washing fastness of samples was determined according to PN-EN ISO 105-E01:2013 standard in Ugolini Redkrome wash fastness tester.

The rubbing fastness of samples (dry and wet standard) was determined according to

James H. Heal 255 crockmeter according to ISO 105-X12:2016(E).

The perspiration fastness of samples was determined according to PN-EN ISO 105 E04:2013 standard in Perspiration tester KitTF416B.

The antibacterial activity of madder extract against Staphylococcus aureus ATCC 6538P

A research on extracts which was conducted earlier at the Institute fully proved that the majority of plant natural dyes are the bioactive compounds contained in them: glycosides, tannins, essential oils, mucus, and others (Prabhu, Teli, and Waghmare 2011). Plant extracts used in the fabric dyeing process, depending on the content of active substances and their valuable ingredients, may have the following properties: compounds contained in plants have a great effect on skin hydration, smoothing, healing wounds; compounds have anti-inflammatory, regenerating, antiviral, antifungal, and antioxidant properties (Adeel et al. 2021; Kamboj, Jose, and Singh 2022; Khan et al. 2014; Pizzicato et al. 2023).

According to a previous research (Alkan, Torgan, and Karadag 2017; Pargai, Jahan, and Gahlot 2020), alizarine functional group contained in madder in reaction with alum and tannic acid from oak galls increases the antibacterial properties of the fabric. In madder, a component responsible for antimicrobial properties is di- and trihydroxyanthraquinones.

The madder extracts have been tested for antibacterial activity at the Institute of Natural Fibers and Medicinal Plants in Poznań. Ethanol extracts ME, MN from madder rhizome and supercritical extract MR were tested for the antibacterial activity against Staphylococcus aureus ATCC 6538P. MIC, MBC, and activity JA indicators were determined. Table 4 shows the results. The supercritical extract was found to be the most active agent against ATCC 6538P.

The results obtained were also expressed in the form of antibiotic units (JA), assuming that the MIC value corresponds to 1 JA. The conducted research has demonstrated that all the madder extracts had antibacterial activity. Among them, madder R extract, 4000 JA/g of extract, had the greatest antibacterial activity. The remaining extracts tested showed slightly lower antibacterial activity ranging from 670 to 1330 JA/g of extract.

Conclusion

The conducted research has proved the possibility of dyeing fabrics produced on the basis of linen or silk fabrics using the supercritical dye impregnation method. The dyeing process can be combined with the simultaneous extraction of the dye from the raw material and carried out in the same pressure vessel. The produced extract can be used as a dye source. In both cases, the extraction and dyeing process can be carried out using the high-pressure method. The use of supercritical carbon dioxide with water as a cosolvent enabled the extraction of polar raw materials from the group of natural anthraquinone. The water collected from the separator S2 during the extraction and dyeing process can be used to moisten the next batch of material to be extracted.

The colors of the dyed samples obtained in the supercritical technology are more in shades of carmine, and in the traditional method in duller reds. In these two different dyeing technologies, the pre-treatment process plays an important role in the color intensity. The proposed modern and ecological dyeing technology guarantees a better resistance to sweat, washing, and light. Fabrics dyed with a madder are an excellent offer for the textile industry. Some examples of the linen collection dyed by supercritical extract of madder MR in conventional methods of dyeing are presented below – Figures 7–9.

Figure 7. Children linen collection – fabrics – unmordanted.

Figure 8. Children linen collection – fabrics – mordanted (alum and galas).

Figure 9. Woman linen collection.

In order to use natural dyes for dyeing fabrics, the extensive research on the biological activity of dyes and their impact on users should be conducted. Dyed fabrics should additionally play health-promoting and protective roles for their users. Linen fabrics showed antimicrobial activity and positive effects on the skin, which was more moisturized and very well protected against the UV radiation (Arora, Agarwal, and Gupta 2017; Schmidt-Przewozna and Zajaczek 2022).

Waterless technologies should be developed in conjunction with user and environmental impact studies.

Advantages of natural dyes and future trends

Natural dyes produce an extraordinary diversity of rich and complex colors that complement each other. Dye extracts may seem a little expensive at first, but they are very economical when their concentration is taken to account. A lot of work has already been done on most of natural dyes. The need for newer dye sources has emerged to keep alive the use of these dyes. Recently, many researchers have done a lot of work in the field of refining natural dyes, and this period can be considered as the rebirth of natural dyes. Increasing knowledge about natural dyes that provide beautiful colors expands the range of shades of various fabrics. New techniques enabling the waterless dyeing of natural fabrics are particularly interesting. This group includes pressure methods of dyeing fabrics in supercritical conditions. New methods of design mordanting dyeing materials are expected to be developed to improve color control and color fastness. It is also expected to improve the antibacterial effectiveness of fabric dyes, the protection against the UV radiation and insects.

Highlights

• A polar dye extraction method using charge moistening has been developed, which allowed applying the produced extract in fabric dyeing.

• A simultaneous extraction method of the dye from madder and the dyeing of fabrics from linen and silk by impregnating the dye with supercritical carbon dioxide have been developed.

• The preliminary studies on the biological activity of three extracts were conducted, out of which the supercritical extract (MR) had the highest antibacterial activity

• Samples dyed with the supercritical method have unique shades.

• The process of supercritical dyeing can be repeated using the same dyeing equipment.

Ethical approval statement

We confirm that all the research meets ethical guidelines and adheres to the legal requirements of the study country. The research does not involve any human or animal welfare related ethical matters.

Acknowledgments

The Institute of Natural Fibres and Medicinal Plants implemented the topic: Technology for the production of innovative, naturally colored, functional textile products, financed from the state budget by the Ministry of Agriculture and Rural Development, Warsaw.

Research Multiannual Program title: “Reconstruction and sustainable development of production and processing of natural fibrous raw materials for the needs of agriculture and economy”

Disclosure statement

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

Additional information

Funding

details: This research was supported by the Polish Ministry of Agriculture and Rural Development, Resolution of the Council of Ministers 171/2017/20