Abstract
Background
Natural colorants from renewable biological resources are increasingly being explored as sustainable alternatives to synthetic textile dyes. In this study, the freshwater green algae Zygnema stellinum was investigated as a natural dye source for cotton, with emphasis on extraction, dyeing optimization, bio-mordanting, and fastness performance.
Methods
Colorants were extracted from dried algal powder using aqueous and alkaline media. Cotton dyeing conditions were optimized by varying alkali concentration, dyeing time, temperature, salt concentration, and dye liquor ratio. Bio-mordanting was performed using onion peel, turmeric, and neem bark in both pre- and post-mordanting approaches. Dyed samples were evaluated for color strength, fastness properties, and functional groups by Fourier transform infrared spectroscopy.
Results
Alkaline extraction gave better color yield than aqueous extraction, with 4% sodium hydroxide producing the highest color strength. The optimum dyeing conditions were 30 min dyeing time, 50 °C dyeing temperature, 5% sodium chloride, and 45 mL dye-to-liquor ratio. Bio-mordanting improved color depth and generated a range of shades. In pre-mordanting, 4% onion peel and 3% turmeric or neem bark gave the best results, while in post-mordanting, 3% of each bio-mordant produced the highest color strength. Mordanted samples also showed good to excellent light, washing, and rubbing fastness. Fourier transform infrared spectroscopy indicated the presence of phenolic constituents, which likely contributed to dye-fiber interaction.
Conclusion
Zygnema stellinum is a promising sustainable natural colorant for cotton dyeing, and bio-mordanting offers an eco-friendly route to improve shade development and fastness properties.
1. Introduction
Environmental pollution has become a major issue around the world due to the intensification of industrialization and anthropogenic activities. 1 Day by day, it is going to be increasing at an alarming rate, posing adverse effects on human health and disrupting eco-balance.2,3 Nowadays, the textile industry is also considered one of the major pollutant sources of water pollution. 4 Textile industries largely use synthetic dyes and release thousands of tons of toxic chemicals, such as dyes, effluents that are toxic, carcinogenic, and non-biodegradable. 5 Toxic chemical dyes pose severe health issues including respiratory disorders and skin diseases. Due to these severe health and environmental concern, people are more attracting towards eco-friendly natural colorant. 6 While natural dyes are biodegradable, non-toxic, and obtained from natural sources like fauna, plants, minerals, microbes, insects, lichens, and algae7-11 having excellent antimicrobial properties.12,13 One of the key advantages of natural dyes is that they are typically derived from renewable sources, reducing dependence on petrochemical sources of colorant and minimize the resultant pollution associated with chemical dyes. 14 Recent advances in natural dyes are on-going. Researchers are using different advance techniques including nanotechnology, enzymatic treatment and eco-friendly colorant fixation techniques to improve fastness properties and dye uptake ability of natural colorants. 15 Every year tons of plant waste material becomes problematic to farmers and causes environmental pollution. Recently, conversion of bio waste into valuable products is one of the emerging field. 16 In this regards, natural dyes are best option for replacing of chemical dyes. 17 By utilizing natural dyes, we can promote an eco-friendly approach to combating pollution and potential health hazards.18-20
Plant-based natural dyes are an environmentally friendly alternative to toxic dyes, however, overuse of plants are detrimental to plant biodiversity.21-23 Consequently, there is a dire need to find out an eco-friendly option that does not harm the flora of the world. 24 Keeping in view the statement above, the production of natural dyes from microorganisms could also be a good option for textile dyeing. 25 Algae are excellent photosynthetic organisms and rich source of different secondary metabolites, which have greater economic importance and has excellent antioxidant, anti-microbial as well as anti-cancerous properties. Algae also used as food, fodder, fertilizer, for the preparation of commercial products, pharmaceuticals, sewage disposal, and to maintain aquatic life.26,27 Algae are also rich sources of coloring pigments such as betalains, carotenoids, phenolics, flavonoids, and chlorophylls. 28 Due to the abundance occurrence of phytochemicals and color shades of algae, these are used as natural dyes.25,29 Literature studies also showed that some of the green and brown algal species have been explored as natural colorant sources for fabric dyeing.30-33
Among algae, Zygnema stellinum, a fresh water green algae abundantly found worldwide, including in various parts of Pakistan, holds significant importance for ecological balance. 34 It is a potent source of different secondary metabolites including alkaloids, steroids, saponins, flavonoids, phenolics, and terpenoids that are biologically active and possess significant antimicrobial properties.35,36 It has been widely utilized in the production of commercial products such as food, medicines, shampoo, creams, shower gels, and masks. 36 Therefore, in this study, Zygnema was selected as a sustainable dye source for cotton dyeing.
Inspire of tremendous benefits of natural dyes, having still some challenges. 37 During the dyeing process, mordant is commonly used, a substance that aids in the dye’s adhesion to the fabric and helps to develop different shades. 38 Mostly, chemical and herbal mordants are being used. 39 Chemical mordant is most commonly used as a mordant in textile dyeing processes, but it causes environmental health hazards.40,41 In contrast, herbal mordants, which are obtained from natural sources, are renewable and bio-degradable, with a smaller ecological footprint.42-44 They offer a safe, more sustainable option for mordanting with a reduced impact on the environment. Although algae-based colorants have recently gained attention as sustainable alternatives for textile dyeing, most available studies have focused on selected algal species such as Cladophora glomerata, mixed marine algal sources, and Chlorella vulgaris.29-33 These studies indicate the potential of algal pigments for textile coloration; however, the dyeing behavior of Zygnema stellinum on cotton fabric has not been sufficiently explored. Unlike many plant-derived dyes, algae are fast-growing, renewable, and less dependent on seasonal biomass availability, making them promising candidates for sustainable colorant production. Therefore, the novelty of the present study lies in the use of freshwater green algae Zygnema stellinum as a natural colorant source for cotton dyeing, together with dyeing-parameter optimization and bio-mordanting using onion peel, turmeric, and neem bark to improve shade development and fastness properties.
The main objectives of the current work are conversion of algal material into useful product, to explore the colorant potential of Zygnema and use it for cotton dyeing, as well as to find out the impact of bio mordants in the production of color shades. Current study presents a novel approach by exploring algal-based Zygnema natural dye and by using eco-friendly bio mordants instead of toxic chemical mordants to achieve variety of shades that leads to environmentally alternative of toxic dyes.
2. Materials and Methods
2.1. Sample Collection
Freshwater green algae, Zygnema stellinum (Vaucher) C.A. Agardh was obtained from the shallow water regions of head Saifan from Mailsi, Pakistan. The identification of the Zygnema samples took place under the compound microscope at the Botany Lab, Department of Botany, University of Education Lahore, Vehari Campus (Figure 1). The algal samples were carefully separated, washed, and dried in sunlight for four days. Finally, the dried samples were ground into a powder and used as natural colorant. Sodium hydroxide NaOH (1g-10g Merck Germany) was used for extraction purpose. Bio mordants including Turmeric (Curcuma longa L.), Neem bark (Azadirachta indica), and onion peel (Allium cepa L.) were purchased from local herbal store in Vehari, Pakistan. All bio mordants were washed, dried and grinded into find powder. Freshly collected Zygnema stellinum studied under compound microscope
2.2. Dye Extraction
The natural colorant was extracted using two extraction media. 1) Aqueous medium: Distilled water 2) Alkaline medium: Sodium hydroxide, NaOH (1-10%)
Dye extract was made by boiling 4g of algal powder in 100 mL of the above-mentioned extraction media. Dye extracts were employed for fabric coloration at 60°C for 40 minutes on a hot plate.
2.3. Optimization of Varying Dyeing Levels
Dyeing levels were optimized to find the best condition for cotton dyeing. • Dyeing time: 10, 20, 30, 40, and 50 minutes. • Varying dyeing temperature: 30, 40, 50, 60, 70, and 80°C. • Varying salt concentrations: 1, 3, 5, 7, and 9 % • Dye to liquor ratio: 15, 25, 35, 45, and 55mL.
2.4. Bio-Mordanting Process
To develop a variety of shades, bio-mordants like Turmeric (Curcuma longa L.), Neem bark (Azadirachta indica), and onion peel (Allium cepa L.) in different levels (1-5%) were applied as pre and post mordant. 45 All bio mordants powder 1-5 % were separately boiled in 100 mL distilled water for 30 min separately. Then filtrate was used as the bio-mordant solution.
2.5. Determination of Color Strength Characteristics and Fastness Attributes
Color strength characteristics of the dyed as well as bio-mordanted fabrics were determined using a Spectraflash SF600 (Datacolor, USA) Spectrophotometer at the Department of Chemistry, G C University Faisalabad. Color strength represent by K/S and it is determined by K/S (Kubelka–Munk value) using the equation 1.
To assess color fastness features of the mordanted samples, ISO105-B02 was utilized for light fastness testing, ISO 105-CO6 for washing fastness, as well as ISO 105-X12 for dry rubbing fastness properties.
2.6. Statistical Test
One way ANOVA completely randomized test was employed to determine the statistically best result.
3. Results
Current experimentation results show that aqueous and alkaline NaOH (1-10%) media have been used to isolate algal colorant components. Results (Figure 2) showed that algal components were partially soluble in an aqueous medium, and as a result, the dyed cotton sample gave the lowest color strength value. While algal colorant has maximum solubility in alkaline media and produced satisfactory results. The statistical data showed that the use of 4% NaOH is highly significant and gave maximum solubility of colorant in an alkaline medium, Hence, extraction of natural colorant in 4% NaOH is optimal for obtaining a higher colorant yield (Table 1). While more than optimal level of alkali produced minimum color strength value onto Zygnema dyed fabric. Effect of aqueous and alkali extraction media on the K/S value of dyed sample in Zygnema stellinum algal dye extract (key to 1: aqueous (100% water), 2: 1% NaOH, 3: 2% NaOH, 4: 3% NaOH, 5: 4% NaOH, 6: 5% NaOH, 7: 6% NaOH, 8: 7% NaOH, 9: 8% NaOH, 10: 9% NaOH, 11: 10% NaOH Mean Square Values From ANOVA Table Representing the Impact of Extraction Media Used to Extract Natural Colorant From Zygnema stellinum
Natural dyeing mainly depends on time duration. Given results (Figure 3A), indicated the impact of different time intervals on the cotton dyeing with Zygnema dye extract. Results show that dyeing of fabric below 30 min reveals lower color strength value. However, 30 min dyeing time was efficient in achieving maximum color strength value on the algal dyed sample (Figure 3A). Effect of varying dyeing levels (A) different dyeing time (B) different dyeing temperature (C) different salt concentration (D) different mL ratio on the K/S value of Zygnema stellinum dyed cotton fabric
Temperature has vital role in fabric coloration. Experimentation data (Figure 3B) showed the role of different heating levels on the K/S features of Zygnema dyed fabric. Among the various dyeing temperature regimes (30-80°C), 50°C was proved to be an optimal heating condition for attaining the maximum color strength output on the Zygnema dyed fabric.
Salt is an important exhausting agent in natural dyeing. Results (Figure 3C) showed the impact of different salt concentrations (1-9%) on dyed cotton samples. It has been observed that 5% NaCl proved to be an economical and optimum level for attaining higher color strength value on Zygnema dyed fabric. Given data (Figure 3D) showed the effect of varying (15-55mL) dye extract levels on the K/S properties of algal dyed samples. Results suggested that a small concentration of dye extract ratio tends towards minimum colorant sorption, while an increase in dye extract level up to 45 mL gives maximum colorant sorption onto dyed fabric. Hence, 45 mL of dye extract proved to be the best level by forming strong dye fabric interaction and tending towards higher color strength value on the Zygnema dyed sample.
By maintaining varying optimized dyeing conditions, bio-mordanting treatment has been performed to develop an array of shades on Zygnema dyed fabrics. In pre-mordanting the herbal mordant binds to the cotton fabric before algal dyeing, while in case of post-mordanting treatment, bio mordant interacts with the algal dye already fixed on the cotton fabric and approaches to difference in complex formation and color strength values. Current experiments indicated the impact of different bio-mordants in varying levels (1-5%) on pre-mordanting and post-mordanting of Zygnema dyed cotton fabrics (Figure 4A and B). In the case of pre-mordanting (Figure 4A), 4% onion peel, 3% of turmeric, and 3% of neem bark produce darker shade with a higher K/S value. In post-mordanting (Figures 4B and 3% of all bio mordant (onion peel, turmeric, neem bark) levels develops a variety of shade with a higher K/S value than other post-mordant levels. Statistical analysis (Table 2) indicated that among all bio mordant 4% onion peel in pre mordanting and 3% onion peel in post mordanting gave highly significant results in term of darker shade with higher K/S strength value. Impact of (A) bio pre-mordants (B) bio post mordants on the K/S value of Zygnema stellinum dyed fabric Mean Square Values From ANOVA Table for Bio Mordanting of Zygnema Dyed Cotton Fabrics
Mechanism (Figure 5) behind the bio-mordanting is close interaction of OH groups in biomolecules (quercetin in onions, curcumin in turmeric, and tannins in neem bark) that form strong H-bonds with the OH group of the Zygnema bio colorant (phenolics) and with the OH group of cotton fabric in results that approach a darker shade with a maximum K/S value. Mechanism of action of algal natural colorant (phenolics) with bio-mordants and with cotton fabric
FTIR analysis of the Zygnema stellinum extract showed several characteristic absorption peaks, indicating the presence of functional groups associated with algal phytochemicals and natural colorant compounds (Figure 6). The broad absorption band observed at 3449.7 cm-1 was assigned to O–H stretching vibrations, suggesting the presence of hydroxyl-containing compounds such as phenolics, alcohols, and flavonoids. The peak at 1653.1 cm-1 was attributed to C=C stretching vibrations of aromatic or unsaturated structures, which may be associated with phenolic and pigment-related constituents. In addition, the absorption band at 1176.0 cm-1 corresponded to C–O stretching vibrations, further supporting the presence of phenolic or alcohol-based functional groups. These functional groups, particularly hydroxyl and C–O groups, may contribute to dye–fiber interaction through hydrogen bonding with the hydroxyl groups of cotton cellulose. Therefore, the FTIR results support the presence of phenolic-type colorant components in Zygnema stellinum, which may play an important role in cotton coloration and shade development. Fourier transform infrared spectroscopy (FTIR) analysis of Zygnema extract
Determination of Colorfastness Properties of Dyed Samples With Zygnema stellinum Dye Extract
Here, LF=Light fastness, WF= Washing fastness, DRF= Dry rubbing fastness, WRF= Wet rubbing fastness.
Color Shade of Un-mordanted and Biomordanted Fabrics Dyed With Zygnema stellinum Extract
4. Discussion
Aqueous and alkaline extraction media have used to extract colorant potential of Zygnema. Overall, current extraction results and statistical analysis indicated that among all alkali levels (1-10%), a small concentration of alkali (NaOH) 4% proved to be an economical and gave maximum solubility of algal pigments by resolving its cell wall in results, leading to a higher colorant output on the dyed fabric.45,46 While >4% of alkali showed negative impact in term of degradation of bio colorant and fabric and in return produced lower color strength results. Previous literature studies also revealed that small level of alkali proved to be effective in attaining higher color strength value onto naturally dyed fabric.30,31 In current experimentation, small amount of NaOH (4%) minimizes environmental impact and improve the sustainability. 47 Overall, algal colorant should be extracted in alkaline medium to get maximum colorant output.
Time duration has a significant role in fabric coloration. 45 Varying dyeing time (10-50 min) have been optimized to get maximum color strength value. Maximum color strength value has attained at 30 min dyeing time. Whereas, time durations above 30 min. Induce the higher desorption of colorant molecules and decreased the color strength characteristics of Zygnema dyed cotton. Similarly, literature studies showed that dyeing for a prolong duration caused desorption of colorant onto fabric due to disturbance in dyeing bath equilibrium. 48 Different heating levels (30-80°C) have been optimized to find out one of the best heating conditions. Among all heating levels, 50°C was found to be an optimal heating level in achieving higher color strength value due to maximum kinetic energy of dye molecules Meanwhile, overheating causes the deterioration of algal colorant molecules and cotton fabrics, in result yields lower K/S value on the dyed sample.49,50 Hence, dyeing at 50°C for 30 min has given best result. Salt act as an exhausting agent in natural dyeing. In current optimization experimentation varying salt levels (1-9%) have been used. It has been observed that initially low amount of salt (NaCl) did not maximize the colorant exhaustion, while slowly increasing its level up to 5%., it neutralized the negative charge on fabric in result approaches to enhance dye fabric interaction and gave maximum color strength value on the dyed fabric. 50 While, >5% of salt leads to over exhaustion of algal colorant and form clusters in dyeing bath that was failed to penetrate into the cotton fabric in result produced low K/S value. Dye extract volume are of significant importance in attaining best results in term of maximum K/S value. 51 Varying (15-55mL) dye extract levels have been optimized. Among all applied dye extract levels, 45 mL gave excellent results in term of higher color strength value. It has been observed that in case of using excess level of dye extract, form aggregation on the cotton fabric in dyeing bath, that leads to unevenness in dyed cotton fabric. 52
From a mechanistic perspective, the changes in color strength with dyeing time, temperature, salt concentration, and dye extract volume may be associated with the balance between colorant adsorption, diffusion, and desorption from the cotton surface. 48 During the initial dyeing stage, algal colorant molecules can gradually diffuse toward the cotton surface and interact with accessible hydroxyl groups of cellulose, resulting in increased K/S value. After the optimum dyeing time, the dyeing system may approach equilibrium, and prolonged treatment may promote partial desorption or redistribution of weakly attached colorant molecules, reducing color strength. Similarly, moderate temperature can improve molecular mobility and dye–fiber contact, whereas excessive heating may disturb weak hydrogen bonding or degrade heat-sensitive algal phytochemicals. The use of salt may improve dye exhaustion by reducing repulsion between cotton and colorant species; however, excess salt can promote pigment aggregation in the dye bath, limiting effective diffusion and uniform adsorption. Although the present study explains these trends based on dyeing equilibrium and adsorption–desorption behavior, adsorption isotherms, diffusion coefficients, and thermodynamic parameters were not determined. Therefore, future studies should include adsorption kinetic modeling, isotherm analysis, and thermodynamic evaluation to better confirm the physicochemical mechanism of Zygnema stellinum colorant adsorption onto cotton.
Bio-mordanting is of greater importance in the shade development of fabric coloration.38,53 In bio pre and bio post mordanting different bio mordants levels (1-5%) have been used to produce different color shade on dyed cotton fabrics. In pre-mordanting, 4% of quercetin from onion peel, 3% of curcumin from turmeric, and 3% of tannins from neem bark produce darker shade with a higher K/S value in comparison to other pre-mordant concentrations. While, in case of post-mordanting treatment, 3% of all bio mordant (onion peel, turmeric, neem bark) levels were found to be cost-effective, economical concentration, and produce a broad range of shade with a maximum K/S value than other post-mordant concentrations. Overall, Statistical analysis (Table 2) revealed that 4% onion peel as pre mordant in pre mordanting and 3% onion peel as post mordant in post mordanting gave highly significant results with darker shade along with higher color strength value. Excellent results of bio-mordanting might be due to the presence of OH groups in quercetin, in curcumin and in tannins that form firm H-bonds with the OH group of the phenolics (colorant) and with the OH group of cotton fabric in results leads to a darker shade with color strength value.54,55 Our results regarding the improvement in color strength of fabric by using bio-mordants are consistent with the previous literature studies. 43 FTIR analysis confirm the phenolics coloring group in Zygnema. Our results are similar with the previous studies 30 represent that current green algal sample is rich source of phenolics. Comparatively post-mordanting develops a darker shade than pre-mordanting (Table. 4). Overall, Zygnema dye proved to be an excellent dye source for cotton coloration. The variety of shade develops by bio mordanting has been presented (Table. 4). Meanwhile, bio post mordanting produce darker shade.
4.1. Limitations of the Study
Although the present study demonstrates the potential of Zygnema stellinum as a sustainable natural colorant for cotton dyeing, some limitations should be acknowledged. The study mainly focused on extraction optimization, dyeing conditions, bio-mordanting, color strength, fastness properties, and FTIR-based functional group identification. However, detailed phytochemical profiling of the algal extract, adsorption isotherms, dyeing kinetics, diffusion behavior, and thermodynamic parameters were not investigated. In addition, the study was limited to cotton fabric and selected bio-mordants, while other textile substrates, functional properties such as antibacterial or UV-protective performance, and industrial-scale environmental assessment were not evaluated. Therefore, future studies should focus on advanced pigment identification, physicochemical dyeing mechanism, application to different fibers, functional textile performance, dye-bath effluent characterization, cost analysis, and pilot-scale validation.
5. Conclusion
Zygnema stellinum is considered an excellent source of natural colorant. FTIR analysis confirm the presence of phenolics in Zygnema. It produced a darker shade on cotton fabric dyed with Zygnema dye extract. Alkaline extraction (4% NaOH) media proved to be excellent for obtaining maximum algal colorant. Optimized dyeing conditions are 30 minutes of dyeing time, 50 °C heating level, 5% salt, and 45 mL dye extract volume for fabric coloration in Zygnema dye extract. Bio-mordanted fabrics with onion peel, neem bark, and turmeric gave variety of shades with higher color strength values. Statistical data showed that 4% onion peel as pre mordant and 3% onion peel as post mordant gave highly significant result with darker shade. Hence, bio-mordanting treatment is an eco-friendly approach to produce excellent results by improving fastness properties. In the future, Zygnema could be the best and cost-effective source of natural colorant for the textile industry. Meanwhile, algal colorants are sustainable and eco-friendly alternatives to toxic chemical dyes in textile sector offering additional functional properties and favour to the greener industrial progress.
Footnotes
Acknowledgment
The authors are thankful to the Eco-friendly Textile Lab at Department of Applied Chemistry Government College University Faisalabad, Pakistan for supporting this work by providing facilities for the evaluation of the dyed fabrics.
Ethical Considerations
We approve that this manuscript is part of MS Studies.
Consent for Publication
We give consent to publish our work of MS studies and is jointly contributed by all authors.
Authors Contributions
This paper is an outcome of the research work conducted by Mr. Muhammad Owais under the supervision of Dr. Fatima Batool. Dr. Shahid Adeel provided technical guidance for the smooth execution of the experiments and assisted in data analysis. Muhammad Hussaan and Mr. Rony Mia contributed to the bio-mordanting process, data curation, formal analysis, and manuscript writing and editing.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data Availability Statement
The work is from MS studies.
Statement of Human and Animal Rights
This article does not contain any studies on human or animal subjects.