Introduction

An increased interest in the use of natural dyes in textile and food coloration industries has been growing since the last few decades. Introduction of natural dyes into modern dye industries is a very promising concept which should be encouraged more and more to reduce the dependency of protein fabric dyeing on some toxic, expensive, more polluted and non-biodegradable synthetic dyes like Azo and Benzedrine dyes. Therefore, the demand and need for the availability of natural dye yielding plants for fulfilling the purpose of ecological coloration has increased at a fast rate. Recently discovered properties of natural color extracts such as insect repellents [1], deodorizing [2],flame retardants [3], UV protection property [4], fluorescence [5,6,7,8], besides being biocompatible, biodegradable, renewable, and non-toxic, have revolutionized all coloring sectors, especially textile industries for producing more aesthetic and highly functional value-added textiles [9]. This is a result of ecological concerns with the use of 118 of the Azo and Benzedrine synthetic dyes with 24 carcinogenic aromatic amines as their primary photolytic degradation products resulting in motivation of researchers toward exploring new eco-friendly substitutes for minimizing their negative environmental impacts [10]. In the application of natural dyes, different dyeing techniques in combination with different mordanting techniques are used to improve color fastness properties. As a result, optimization of the dyeing conditions for dyeing with regard to the type of natural dye is quite common and a broad set of variations in the dyeing recipes is given in the literature available for natural dyeing of textiles [11]. Fashion industry changes every day, therefore the rapid changes in trends and the demand for good fastness properties on different substrates requires a basic database describing possible applications of natural dyes for reduction in parallel optimization work to be done by each dye house. But lower light fastness, poor shade reproducibility, non-standardization of raw material and complexity of extraction processes involved in natural dyeing restrict their use in textile dyeing and finishing applications, besides many advancements have been taken into consideration for modifying color characteristics of dyed textile materials [12]. Mordants play a vital role in natural dyeing processes in terms of achieving broad spectrum of colors of various shades and special performance characteristics on a wide range of natural as well as synthetic textile materials [13]. Chemical nature of mordants and fiber–mordant–dye interactions highly modifies the color characteristics of dyed textiles. The most common mordants in natural dyeing are used to alter the colorimetric parameters and fastness properties of dyed textile materials. These are aluminum, potassium dichromate, copper sulfate, ferrous sulfate and stannous chloride [14]. Use of some earth metals has been successfully employed in textile dyeing as mordants for increasing dyeing behavior of ramie fabrics [15]. Significant amounts of metal ions remain unexhausted in residual mordant baths during dyeing which then are discharged into wastewater, which possess ecological concerns and negative impact on public health [16]. The amount of metal ion discharged from textile industries has been limited strictly beyond a certain limit [17].The rise of new advancements in mordanting processes and selecting new, safe and eco-friendly mordants to replace traditional heavy metal ions have been an important part in the development of natural dyeing processes [18]. The textile industry consumes the biggest amount of water, so extensive data about the effluent production have been collected and are available from the literature [19]. Hence, the use of natural mordants (bio-mordants) in place of metallic salt mordants has been advised by researchers as an effective and safe alternative of textile natural dyeing by considering environmental aspects of pollution and their biodegradable nature [20, 21]. Recently, a lot of research work has been done for the use of bio-mordants as an alternative and safe substitute to metal mordants, and encouraging results have been achieved [22]. Some plants and plant parts with high tannin or metal content may impart mordanting effect to various extents depending on their chemical structure and amount of metal ions present in them [23]. Mordants from natural origins like myrobalan (Terminalia chebula), pomegranate rinds (Punica granatum), tannin, tannic acid, tartaric acid, guava and banana leaves ash have been used for mordanting purposes [5]. Carica papaya (papaya) is a tree-like herbaceous plant and a member of the small family Caricaceae which is widely cultivated for its edible fruits. It originates in the low lands of all tropical countries and many subtropical regions of the world. The present study was undertaken in order to explore dyeing properties of Carica papaya L. leaf powder extract dye alone (control dyeing) and in conjunction with small amounts of metal mordants and alternative bio-mordants. Additionally, comparison between metal mordanted and bio-mordanted protein fabrics samples was also made with the aim of making this research a viable alternative for non-biodegradable metal mordants with eco-friendly, biodegradable and non-toxic bio-mordants.

Materials and Methods

Four protein fabrics, i.e., wool, silk, soya and milk, were used for the present study. Soya and milk fabrics were sourced from Champs Agro unit, Thane, India, and wool and silk fabrics were purchased from Khadi Gram Udyog, Bhiwani, India. Carica papaya leaves were plucked from a garden in Bhiwani. They were further dried in shadow and converted to dry powder using a grinder. Natural mordants used in study, such as orange peel, pomegranate peel, amla powder and harda powder, were procured from the local market. Other laboratory-grade chemicals used in study such as alum, sodium hydroxide, acetic acid, ferrous sulfate, copper and sulfate were of Hi-Media (Table 1).

Table 1 Specifications of fabrics
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Fabric Pre-treatment

All fabrics were ready for dyeing when purchased, but still they were washed thoroughly with 0.5 g/l wetting agent for 1 h MLR as 1:20 at 70 °C for removal of any dust and dirt particles present in the sourced fabrics to insure even dyeing of fabrics.

Preparation of Dye Solution and Dyeing

Using optimized conditions of extraction, i.e., MLR 1:30, pH 3, time 60 min at 100 °C, the dye was extracted from Carica papaya. All fabrics were cut into 20 × 20 cm size samples and dyed for optimizing different dyeing parameters, i.e., MLR, pH, and temperature of the dye bath and time of dyeing for obtaining maximum K/S value. As shown in Table 2, Box and Behnken experimental design was used for considering all variables. Further, the dyed fabrics by optimized dyeing recipe were mordanted with four natural mordants such as amla powder, harda powder, orange peel powder and pomegranate powder to improve dyeing fastness properties. Dyed fabrics with optimized dye recipe were also mordanted with three chemical mordants, i.e., alum, copper sulfate and ferrous sulfate, to compare their fastness behavior with natural mordants.

Table 2 Box and Behnken experimental design for variables
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Further, the dyed fabrics were mordanted with four natural mordants such as pomegranate powder, orange peel powder, harda powder and amla powder by optimized dyeing recipe to improve dyeing fastness properties. Further, all dyed fabrics were also mordanted with three chemical mordants, i.e., ferrous sulfate, alum and copper sulfate to compare their fastness behavior with natural mordants.

Characterization of Dye Extract

Anti-oxidant Property

Anti-Diphenyl-2-picryl-hydrazyl (DPPH) assay was used to measure anti-oxidant testing of dye extract was carried out by to calculate the free radical scavenging activity (RSA). Anti-oxidant property is a measure of capacity of its extracts to scavenge the stable free radicals of DPPH, and to measure that property, samples of 0.20 ml volumes were added to 3.8 ml of 0.1 mM DPPH solution in ethanol as reported [24]. Samples were put in dark for 30 min afterward to complete the reaction at room temperature for decolorizing the solution. Further, de-colorization was checked on spectrophotometer at 517 nm wavelength and RSA percentage was calculated using formula (1):

$$ {\text{Radical}}\,{\text{Scavenging}}\,{\text{Activity}}\,\left( \% \right) = 1 - \frac{{{\text{Absorbance}}_{{\left( {\text{sample}} \right)}} }}{{{\text{Absorbance}}_{{\left( {\text{control}} \right)}} }} \times \, 100 $$
(1)

where Absorbance(sample) refers to the absorbance of the solution having dye extract and Absorbance(control) refers to the absorbance of the solution having the de-ionized water.

Tannin Content

The Carica papaya extract was assessed for qualitative analysis by treating 0.5% solution of extract with various reagents such as aqueous ferric chloride, gelatine, lead acetate and copper sulfate solution. After the addition of reagent, the color change was observed to measure total tannin content of the Carica papaya extract [25, 26].

Flavonoid Content

Carica total flavonoid content was calculated by measuring the absorbance and taking quercetin as a standard sample. Totally, 25 mg of aqueous water extract was dissolved in 25 ml of methanol, diluted till 300 ppm concentration, and 2 ml of this solution was added with 0.1 ml of AlCl3 following the addition of 0.1 ml of sodium acetate and 2.8 ml of distilled water. Total flavonoid content of the solution was measured using formula (2) after assessing absorbance at 750 nm wavelength using UV spectrophotometer (make: Systronics).

$$ {\text{Total}}\,{\text{flavonoid}}\,{\text{content}} = \frac{{x.V.{\text{DF}}}}{w} $$
(2)

where x = concentration (ppm) of extract, V = volume of sample solution (extract) (ml); DF = dilution factor of sample solution, w = sample weight (g) [27].

Phenolic Content

Carica papaya extract’s total phenolic content (TPC) was measured by Folin–Ciocalteu method [28]. Totally, 0.1 ml of Carica papaya leaf extract 200 µg/ml was kept in a test tube after the addition of 0.1 ml solutions of 50% Folin–Ciocalteu reagent further followed by vortexing for 1 min. After the addition of 2 ml of 2% sodium carbonate (Na2CO3), this mixture was kept for the chemical reaction in a dark room for 30 min. Afterward, the absorbance of the extract solution was read at 750 nm wavelengths with the UV–Vis spectrophotometer, and using formula (3) total phenolic content was calculated.

$$ {\text{Total}}\,{\text{phenolic}}\,{\text{content}} = \frac{{x.V.{\text{DF}}}}{w} $$
(3)

where x = concentration (ppm) of extract, V = volume of sample solution (extract) (ml), DF = dilution factor of sample solution, w = sample weight (g).

Analysis of Color Co-ordinates of Dyed Fabrics

All the dyed samples were assessed for measuring color co-ordinates (L, a, b and K/S) using Premier Colorscan computer color matching system at D65 illuminant/100 observer.

Evaluation of Fastness Properties of Dyed Fabrics

The light fastness, rubbing fastness (wet and dry) and washing fastness of the dyed fabric samples were evaluated as per ISO 105-BO2:2002, ISO-105-X12 and IS: 3361:79 methods, respectively.

FTIR and UV–visible Spectrophotometer Analysis of Dye and Dyed Fabric Samples

Carica papaya dye extract and dyed fabrics were assessed for FTIR analysis using a double-beam FTIR spectrophotometer in attenuated total reflectance (ATR) mode attachment (Bruker, model: Alpha) using OPUS software at M.D. U, Rohtak. Extract was also analyzed through UV–visible spectrophotometer by scanning from 200 to 800 nm wavelength using UV-2450 spectrophotometer (Shimadzu) at IIT, Delhi.

Ultraviolet Protection Factor (UPF) Evaluation of Dyed Fabrics

All the dyed fabric samples were tested for their UPF values with UV-2600 series in the range of 280–400 nm, Model UV-2600 (A11665101436), from the total spectral transmittance based on AS/NZS 4399:2017 method [29]. As per Eq. (4), UPF is defined as the ratio of average effective UVR irradiance of unprotected skin to the average effective UVR irradiance of dyed fabric protected skin.

$$ {\text{UPF}} = \frac{{\mathop \sum \nolimits_{\lambda = 280}^{400} E\lambda . S\lambda .\Delta \lambda }}{{\mathop \sum \nolimits_{\lambda = 280}^{400} E\lambda . S\lambda .T\lambda .\Delta \lambda }} $$
(4)

where Eλ: erythemal spectral effectiveness, Sλ: solar spectral irradiance in Wm−2 nm−1, Tλ: spectral transmittance of fabric (%), ∆λ: the bandwidth in nm (5 nm), λ: the wavelength in nm (290–400 nm). As per standard, textile fabrics having UPF of 25–39 are categorized as “Very Good” with 96–97.4% of UVR blocked, UPF of 40 or above as “Excellent” with ≥ 97.5% of UVR blocked and UPF rating of 15–24 are categorized as “Good” with 93.3–95.9% of UVR blocked [30, 31].

Anti-microbial Behavior Evaluation of Dye and Dyed Fabrics

Extracted dye and dyed fabrics were evaluated for anti-microbial behavior using AATCC-100 method using gram-positive (S. aureus) and gram-negative (E. coli) bacteria at IIT, Delhi.

Quantitative Assessment of Anti-microbial Behavior

The stock solution of Carica papaya Leaf extract was tested to check the degree of antibacterial activity using AATCC 100 method. Testing was followed by taking 20 g/1000 ml of Luria broth for preparing the liquid culture media, and the test specimens of different concentrations (1% and 2%) ranging from 5 ppm to 200 ppm were further dispersed in 10 ml of Luria broth. Afterward, test organism having volume 106 cfu/ml count of 20 μl was incubated at 200 rpm at 37 °C for 24 h. As control, water similar to that of test specimens was used after incubation with Luria broth. In a test tube containing 9 ml distilled water, 1000 μl solution was transferred and shaker was used to shake it. Again, the same amount taken in micropipette was further diluted with 9.9 ml distilled water in the other test tube. Repetition of process was done as per bacterial growth in each flask. From the last diluted test tube, 20 μl of inoculums was taken and spread on agar plates. Agar plates were incubated for 24 h at 37 °C, and grown visible bacterial colonies were counted.

Anti-microbial activity of dyed fabrics was assessed by cutting samples into 2 in. × 1 in. swatches and further exposed to 20 μl of bacterial inoculums containing 108 cfu/ml of bacteria. Undyed fabric swatches were used as control. All dyed and undyed swatches were placed for 24-h incubation in a 50-ml sterilized flask containing 10 ml sterilized distilled water. All the incubated flasks were shaken for 1 h at 200 rpm to remove bacteria from fabric swatches. Afterward, sterilized water serial dilutions up to 106 were prepared. Agar plates were prepared by using the diluted liquor (20 μl) followed by incubation for 24 h at 37 °C. Equation (5) is used to calculate bacterial reduction percentage.

$$ {\text{Bacterium}}\,{\text{reduction}}\,\left( \% \right) \, = \, \left( {A - B} \right)/A \times 100 $$
(5)

where A represents bacterial colonies for the control after 24-h incubation time; B represents bacterial colonies for sample after 24-h incubation time.

Results and Discussion

K/S was taken as the optimized criteria for different variables for dyeing with required dye volume and optimized dyeing, as shown in Table 3.

Table 3 Optimized dyeing conditions for protein fabrics
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It is quite clear from Table 3 that all Carica papaya extract-dyed protein fabrics have maximum K/S values in acidic medium, while other variables like time and temperature vary as per fabric that may be due to maximum saturation achieved at those conditions.

Anti-oxidant Activity of the Carica papaya Extract

All natural species of plants have rich phenolics, carotenoids, flavonoids and secondary metabolites in their chemical structure which are contributing factors for the anti-oxidant behavior of these species. Carica papaya leaf extract was tested for anti-oxidant activity against the free radicals by DPPH because its chemical reaction is very easy to perform [32, 33]. The findings of the study are as follows:

Ascorbic acid calibration curve equation:

$$ y = - 0.4892x + 0.7801 $$

where y is absorbance value and x is amount of ascorbic acid, absorbance of Carica papaya leaf extract = 0.523

$$ {\text{Therefore}}\,{\text{Anti-oxidant}}\,{\text{Assay }}\left( {\text{AOA}} \right) \, = \, 0.525\,{\text{equivalent}}\,{\text{to}}\,{\text{ascorbic}}\,{\text{acid}} $$

It can be seen that the Carica papaya leaf extract has good anti-oxidant potential so can be used in cosmetics and finishing of facial wipes, etc. for textile application as reported by Thakare et al. [34].

Tannin Content of the Carica papaya Extract

Tannins are the natural polyphenol with molecular weight of 500–3000 g/mol with very good water solubility and found in plants, herbs, fruits, etc. These are widely used in different foods, cosmetic, pharmaceutical industries and functional textiles like facial wipes, etc. Their applications as color stabilizers and balancing fining agents in wines are contributing factors for their increased applications. Therefore, to assess the amount of tannin content in natural extracts is very important to specify its anti-oxidative properties [35, 36].

The tannin content of the Carica papaya leaf was calculated to be 85.06 mg/g dry matter which can be utilized in dyeing and finishing of textile with the above-said beneficial properties.

Flavonoid Content of the Carica papaya Extract

Flavonoid is a polyphenolic compound with a number of hydroxyl groups attached to aromatic ring structures which is ubiquitous in nature [37]. Anti-oxidants are also found in the form of flavonoids [38, 39].

Standard calibration curve of Rutin was used to measure the flavonoid content of Carica papaya leaf extract [40], and findings are as follows:

  • Absorbance of Papaya leave extract = 0.594,

  • So its flavonoid content = 12.77 mg equivalent to Rutin.

Thus, Carica papaya leaf extract flavonoids contents justify the significant anti-oxidant properties and its potential as a dyeing agent for textiles.

Phenolic Content of the Carica papaya Extract

The presence of abundant phenolic (–OH) groups in the natural dyes and mordants is responsible for its coloring behavior [41]. Gallic acid is used to estimate the amount of phenol content of any natural substrate [42]. After calibrating the values, the obtained phenolic content of Carica papaya leaf extract was 62.36 mg GAE/g dry (supplementary information). As reported toward hindering the influence of free radicals and ROS, phenolics have been reported as strong anti-oxidants which are the basis of several chronic human infections [37].

Crude Dye Extraction from Carica papaya Leaf Powder and Dyeing of Protein Fabrics

In the present study, water-soluble Carica papaya extract was applied to protein fabrics to check its coloring behavior and the colorant obtained as yield was 37.5% which is better than the reported amount in natural extracts [43]. After extraction, the leaves become slightly brown in color showing maximum removal of auxochromes and chromophore from the skin [44]. After color extraction, four protein fabrics, i.e., wool, silk, soya and milk, were dyed and showed very good affinity toward the extract. Tannin present in Carica papaya leaf is in very good amount in extract bonds with fabrics either a covalent bond or ionic bond which are also enriched with amino and carboxylic groups. Dyeing of textile substrate without any mordant with Carica papaya extract is totally an ecological approach. Mordanting was carried out using natural as well as chemical mordants to produce a broad spectrum of shades obtained followed by all three mordanting processes, i.e., pre-mordanting, meta-mordanting and post-mordanting.

Color Measurement Using Computer Color Matching System

As shown in Table 4, all dyed samples with different mordants exhibit different shades as per mordant color. As alum does not have much effect on color, ferrous sulfate again gives tones of gray, and copper sulfate changes shades into a greenish tone. Pomegranate peel has a large amount of tannins, hence highlights its own shades in combination with Carica papaya extract. Harda powder along with Carica papaya modifies the shades of dyed fabrics up to a little extent, while orange peel and amla powder do not affect the actual shade obtained with true extract. Wool being coarse absorbs large quantity of dye resulting in brilliant shades obtained followed by milk, soya and silk fabrics being low in GSM or fabric density [45].

Table 4 Color strength and shades of Carica papaya leaf extract-dyed wool, silk, soya and milk fabrics
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Table 4 shows color spectrum and K/S values for dyed fabrics, and it is clear from Table 4 that a particular trend was not followed by all mordants in different mordanting techniques.

Color Fastness Analysis

Tables 5, 6, 7 and 8 show results of color fastness of the dyed fabric with Carica papaya leaf extract, and values of the tables clearly indicate that all fabrics possess very-good-to-excellent wash and rubbing fastness. Chemical mordants form H-bond or coordinate bonds with dye and fabric resulting in very-good-to-excellent fastness properties. Natural mordants also perform very well and possess very good rubbing and wash fastness which may be the result of tannin present in them. Light fastness shows different trends in all four dyed fabrics, somewhere no change in shade or little change in shade, somewhere it is darker, which may be the reason for different oxidation behaviors of fabrics with different mordants [46]. Hence, the overall findings of all color fastness of Carica papaya extract-dyed fabric exhibit very good potential of application as a colorant for dyeing of textiles in an eco-friendly way.

Table 5 Color fastness results of Carica papaya leaf extract-dyed wool fabric
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Table 6 Color fastness results of Carica papaya leaf extract-dyed silk fabric
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Table 7 Color fastness results of Carica papaya leaf extract-dyed soya fabric
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Table 8 Color fastness results of Carica papaya leaf extract-dyed milk fabric
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FTIR and UV–visible Analysis

The FTIR spectrum was performed for Carica papaya leaf extract to identify the functional groups of the active components present in the extract based on the peak values in the region of IR radiation. As shown in Fig. 1, the broad peaks at different wavenumbers showed the presence of different functional groups like 654.59 cm−1 for C=C, 784.96 cm−1 for C=C, 861.97 cm−1 for C–H, 1028.26 cm−1 for C–F, 1394.35 cm−1 for O–H, 1593.40 cm−1 for N–H, 1922.16 cm−1 for C=C=C, 2357.95 cm−1 for O=C=O, 2899.14 cm−1 for N–H, 3170.60 cm−1 for C–H, 3633.60 cm−1 for –OH, 3731.41 cm−1 for –OH, 3822.17 cm−1 for –OH and 3915.94 cm−1 for –OH [47]. This can be clearly seen from the obtained peaks that papaya leaf extract has maximum –OH, N–H, C=C, C–H and other functional groups present in the extract which may be responsible for their functionality toward textile substrates [48].

Fig. 1
figure 1

FTIR spectra of Carica papaya leaf water extract

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As shown in Fig. 2, the UV–visible spectrum of Carica papaya leaf extract in water, 20% w/v has maximum absorbance of 1.58 at 206 nm wavelength which is dependent on specific acylation configuration and sugar conjugation [49].

Fig. 2
figure 2

UV spectra of Carica papaya leaf water extract

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Ultraviolet Protection Factor (UPF) Analysis

Ultraviolet protection factor is defined as the extent of the ability of the textile to protect UV radiation, and it is strongly dependent on the concentration of dye in fabric as well as dye–fiber interactions fiber properties, yarn and fabric construction. Hence, different UPF values can be obtained from the same extract depending upon fabric construction such as PPI, EPI, type of weave thickness, porosity and moisture content [50].The UPF values of wool, silk, soya and milk fabrics dyed with Carica papaya water extract, as shown in Table 9, were determined from the total spectral transmittance based on AS/NZS 4399:1996.

Table 9 UPF results of Carica papaya leaf water extract-dyed and undyed fabrics
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It can be clearly observed from Table 9 that among the four undyed fabrics, wool has the highest UPF due to its compact and dense structure, while milk, soya and silk fabrics possess low UPF due to their light and shear fabric structure. After dyeing, the same trend was followed and wool showed significantly improved UPF than the other three protein fabrics. Improved UPF values may be due to absorption of significant amount of Carica papaya leaf-extracted particles by wool fabric. However, improvement was observed in the other three fabrics also, but very less UPF values were obtained again due to less absorption of natural extracted particles inside the fabric because of the structure of these fabrics being lighter [45].

Anti-microbial Property

The Carica papaya leaf extract and the extract-dyed protein fabrics showed very good anti-microbial property against E. coli (gram −) and S. aureus (gram  +) bacteria. As mentioned in Table 10, Carica papaya leaf extract has very good bacterial reduction percentage. Therefore, the extract and dyed fabrics have wide potential in medical textile applications.

Table 10 Bacterial reduction % of Carica papaya leaf dye extract and dyed fabric samples
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Conclusion

In the present study of dyeing of protein fabrics with Carica papaya leaf extract, the findings are as follows. Carica papaya leaf extract has a very good amount of tannin, phenolic content and flavonoids that make it effective for finishing and coloring of textiles. The plant is available in abundance in nature and has a number of medicinal applications. Dyeing behavior showed very good affinity toward all four protein fabrics with a brilliant and wide color spectrum obtained after mordanting. All natural mordants showed very-good-to-excellent color fastness properties along with chemical mordants providing an eco-friendly alternative to chemical mordants. FTIR spectra showed a number of functional groups present in extract showing its application in finishing and coloration of textiles. UPF values are very good, and all dyed fabrics possess very high bacterial reduction percentage; and these can be the leading factors for application in medical and functional textiles.

In summary, natural mordanting followed by treatment with Carica papaya leaf-extracted dye using environmentally friendly solvents can significantly enhance UPF, anti-microbial property, color strength and fastness of dyed substrates offering directions for manufacturing textiles with good appearance and health benefits but without environmental hazards.