Sustainable Dyeing of Cotton Fibers Using Aqueous Extract of Citrullus Colocynthis Leaves: Chemical Characterization, and Dyeing Optimization Process Using Response Surface Methodology

ABSTRACT Owing to their advantageous characteristics, natural dyes are highly needed to replace hazardous synthetic colored molecules. In this work, an aqueous extract of Citrullus colocynthis leaves was prepared, analyzed using Fourier Transform Infrared (FT-IR) spectroscopy and High-Pressure Liquid Chromatography/Mass Spectrometry (LC-MS/MS), and further used to dye cotton fibers. FT-IR results suggested that the studied Citrullus colocynthis leaf is possibly rich in phenolic and flavonoid constituents. The dyeing experiments were carried out at various experimental conditions: dyeing duration (30–60 min), temperature (60–100°C), and pH (5–9). Response surface methodology (RSM), with the help of Minitab 17.1.0, was used to optimize the dyeing process. The optimum obtained dyeing conditions were time = 30 min, temperature = 91°C, and pH = 7. The cationization of cotton fabric with polyethyleneimine and a co-polymer of dimethyl diallyl ammonium chloride and diallylamin, and the pre-biomordanting with pomegranate peel and date palm pits significantly improved the color strength (K/S) results. Overall, the dyed cotton samples exhibited good fastness characteristics.


Introduction
Dyeing with natural products has today become a principal area of interest in the search for healthy substitutes.The identification and analysis of natural molecules is becoming one of the most important goals for scientists.Natural dyes are becoming increasingly popular as an alternative to synthetic dyes in textile dyeing (Fitz-binder and Bechtold 2019;Jiang et al. 2019;Ltaief et al. 2021;Manian, Paul, and Bechtold 2016).Literature exhibited the potential for a wide-scale utilization of natural dyes in textile dyeing and finishing due to their high economic value and waste management efficiency (Ltaief et al. 2020;Shahid, Mohammad, and Mohammad 2013).
In spite of plentiful availability of various well-known plants as sources of natural dyes, researchers had continued their efforts to search for new sources of natural dye molecules.As examples of recently published investigations, Mahery Andriamanantena (Andriamanantena et al. 2021) explored red dyes with high stability and antimicrobial properties from Acridocarpus excelsus, Ceriops tagal, Rhizophora mucronata, Woodfordia fruticosa, and Xylocarpus granatum.Hosam El-Sayed and Nagla El-Shemy used Malus domestica peel extract to color wool fabric in the presence of mordants (El-Sayed and El-Shemy 2021).Linan Wang et al. investigated a natural dyestuff from Sargentodoxa cuneata giving an ultraviolet resistance to silk fabrics (Wang et al. 2021).Nimra Nawaz et al. extracted a natural dye from Dalbergia sissoo leaves to dye wool fabric (Nawaz et al. 2021).Hossain et al. extracted a new natural dye from the leaves of date palm using a simple aqueous extraction process to dye cotton and silk fabrics in the presence of different mordants (Hossain et al. 2021).Zhu et al. developed a recyclable and environmentally friendly dyeing method using colored residues of Dalbergia cochinchinensis to improve anti-UV property of the dyed wood (Zhu et al. 2021).In this regard, we have investigated the dyeing of cellulosic fibers using aqueous extracts of Pistacia vera hulls (Ltaief et al. 2020), Cynomorium Coccineum peels (Sebeia et al. 2019), and Limoniastrum Monopetalum leaves (Ltaief et al. 2021) Citrullus colocynthis is a perennial herbaceous plant belonging to Cucurbitaceae family.Basically, it looks like a common watermelon vine, with small, hard fruits and a bitter pulp.Following literature, only biological and medicinal characteristics of Citrullus colocynthis were reported (Chen et al. 2019;Hamdan, Jwad, and Jasim 2021;Perveen et al. 2021;Saeed et al. 2019).Citrullus colocynthis leaf has not yet been used to dye textiles.Based on reasons of chemical content, functional groups, and other diverse groups, Citrullus colocynthis leaf could be checked for dyeing experiments.In the present study, an aqueous Citrullus colocynthis leaf extract was prepared and analyzed using FT-IR spectroscopy and LC-MS/MS analyses.The dyeing process of cotton fibers with the aqueous extract of Citrullus colocynthis leaves was carried out under the change of dyeing duration (30-60 min), temperature (60-100°C), and pH (5-9).Colored cotton samples are morphologically characterized using Scanning Electron Microscope (SEM).Response surface methodology is used to optimize the dyeing data.The color strength values are measured for cellulosic fabrics modified with polyethyleneimine and a copolymer of dimethyl diallyl ammonium chloride and diallylamin in the presence of the bio-mordants: pomegranate peel and date palm pits.The fastness properties of the colored cotton samples are assessed.

Materials and reagents
Woven cotton was provided as a twill weave at 264 g/m 2 , a thickness of 0.5 mm, and warp and weft densities of 20 yarns/cm and 36 yarns/cm, respectively.Dyeing experiments were carried out using aqueous extracts of powdered Citrullus colocynthis leaves which were collected from the Sidi Bouzid region (Tunisia) during the month of August.In order to guarantee the homogeneity of the material, all the used quantities were gathered in a similar area and period.It was ground and mixed in a standard medium (T = 20°C, RH = 65%) over 1 day before being stored in a dry holder sheltered from light.In order to check the effect of the cationization on dyeing properties, cotton fabric was treated with different amounts of polyethyleneimine solution (average M n ~60,000, average M w ~750,000, 50 wt.% in H 2 O), and a copolymer of dimethyl diallyl ammonium chloride and diallylamin (purchased from Sigma Aldrich company).Pomegranate peel and date pits were provided from a local market (Monastir-Tunisia) and used as bio-mordants.All other used chemical reagents were of laboratory grade.Distilled water was used to prepare colored solutions.

Preparation of aqueous extract of Citrullus colocynthis leaves
A weighted mass of powdered Citrullus colocynthis leaves (2 g) was mixed with 100 mL of distilled water for 45 min.The temperature was set at 70°C to avoid the degradation of the extracted coloring matter using a thermo-regulated water bath (Ltaief et al. 2020).After which, the resulting solution was filtered using a Whatman filter paper to yield liquid dye extract.Figure 1 gives photographs of dyed samples after treatment with dimethyl diallyl ammonium chloride and diallylamin, polyethyleneimine, pomegranate peel, and date pits.

Characterization techniques
A Perkin Elmer Spectrum Two ATR-FTIR using UATR-unit was used to study the chemical structure of the studied samples.FT-IR spectra were studied on 32 scans from 400 to 4000 cm −1 at a resolution of 4 cm −1 .
The LC-MS/MS analyses were performed using a Bruker system consisting of an Elute UHPLC chain coupled to a Q-TOF IMPACT II mass spectrometer (Mulhouse, France).
The morphological characteristics of cotton samples were examined with a JEOL JSM-5400 Scanning Electron Microscope.The samples were covered with gold utilizing a vacuum sputtercoater to improve their conductivity and image quality.The acceleration voltage was measured at 20 kV.

Dyeing procedure and design of experiment
Dyeing experiments were carried out in a laboratory dyeing machine (AHIBA Datacolor International, USA).Cotton fabrics were incubated into the bath and treated at different durations (30-60 min), temperatures (60-100°C), and pH (5-9).At the end, the dyed fabric is removed, rinsed with water, and air-dried.To optimize the cotton dyeing process with the extracted dye, MINITAB 17 was used to study the interactions between the various parameters and their effects on the dyeing process.The evaluation is done based on the dye strength K/S and the bath exhaustion E (%) values.The studied parameters are the dyeing temperature (T), the pH of the dye bath (pH), and the dyeing time (t).The evaluation of K/S was performed by means of a spectrocolorimeter (Data Color 650®, USA).
The dye bath exhaustion [E(%)] was determined using the following equation: Abs0 and Absf denote the amounts of absorbance of the starting and the remaining dye baths, respectively.

Cationization of cotton fabric and mordanting
Two cationic reagents, polyethyleneimine, and a copolymer of dimethyl diallyl ammonium chloride and diallylamin were used, at different amounts, to impart amino groups onto cotton fabric surface.
The cationization was carried out during 60 min at 50°C.Afterwards, the cationized samples were airdried and further dyed.Two bio-mordants, pomegranate peel and date palm pits, were used to study the influence of mordanting on the quality of cotton dyeing with Citrullus colocynthis leaves extract.
During the mordanting process, different quantities of bio-mordants were applied before dyeing for 45 min at 60°C followed by a simple rinse with cold water.

Fastness properties
In order to evaluate the dyeing fastnesses of the dyed samples, the ISO 105-C06 standard was used to estimate fastnesses for washing.The ISO 105-X12 standard is employed to evaluate the fastnesses to rubbing, and the ISO 105-B02 standard is adopted to elucidate the fastness to light (105-B02 1994; 105-X12 1993).

FT-IR spectroscopy analysis
The FT-IR spectrum of powdered Citrullus colocynthis leaves is shown in Figure 2. The absorption peak observed at 3335 cm −1 confirms the presence of O-H stretching vibrations of benzene rings in polyphenolic structures (Sanjay et al. 2018).The absorption peaks observed at 2904 and 2851 cm −1 are due to the asymmetric and symmetric vibrational modes corresponding to the -CH stretching vibrations of methyl and methylene groups, respectively (Sanjay et al. 2018).The peak at 1715 cm −1 is assigned to -C=O stretch.The peaks observed at 1410 and 1338 cm −1 are attributed to the vibrations of aromatic C=C bond and -CH bending, respectively (Güzel et al. 2018).The sharp peak observed at 1019 cm −1 is assigned to the C-O stretching mode vibration of ester acetate.The peak around 722 cm −1 is attributed to the bending vibration of aromatic C-H.As globally observed, FT-IR results showed that the studied powdered Citrullus colocynthis leaf is possibly rich in phenolic and flavonoid constituents.These compounds have many reactive groups and therefore could react with cellulosic fibers chemically modified using polyethyleneimine and copolymer of dimethyl diallyl ammonium chloride and diallylamin through hydrogen bonding and/or electrostatic interactions.

LC-MS/MS analyses
Negative ESI results indicated that no compound possessing the diagnostic fragment ions of gallic or ellagic tannins is detectable in the studied extract (Figure S1, S2).At the wavelength of 350 nm, the negative peaks for registered signals (Figure S3) prove that many flavonoid or coumarin derivatives do not absorb but emit light.Some compounds could ionize only in positive mode; therefore, positive ESI analyses were also carried out (Figure S4).The number of peaks detected by MS demonstrated that integrating the peaks of the chromatograms is complex.For example, after extraction, the MS analysis in negative ESI gave nearly 400 different compounds (Figure S5).Some compounds showed the same MS/MS spectrum at different retention times.At the beginning of the chromatogram, the compound was very polar.In the middle, the molecules are less rich in oxygenated or nitrogenous groups.Finally, the molecules are rich in carbon and very weakly or not glycosylated.Indeed, the ions can be identified as being mainly  All the buckets representing the molecules detected through the identified ions are then subjected to the calculation of gross formulas from the m/z of each of the ions.The parameters of this calculation are as follows: only C, H, and O atoms are present in the molecular compositions, the error on the mass m/z is identified as being very low if it is less than 1 ppm, correct if it is between 1 and 5 ppm, bad if it is greater than 5 ppm.The value of mSigma, which represents the quality of the isotopic mass of the gross formula calculated with respect to that of the measured isotopic mass, is considered to be excellent if less than 150, good between 150 and 500 and bad if greater than 500.Only 174 molecules thus received a raw formula with more or less error on the measurement and on the mSigma (Figure S6).Subsequently, for each bucket, databases are queried: Analyte DB (Bruker), ChEBI, Chem Sipder, PubChem, in order to identify the different molecules by comparison of the raw formula and the MS/ MS spectrum.The structures of the main compounds that could be detected in the studied aqueous extract are given in Figure S7.

Morphological characteristics of cotton fabrics
SEM images of untreated cotton, cotton treated with amino reagents and bio-mordants, and dyed samples are shown in Figure 4.The images revealed that the untreated samples are characterized by a comparatively smooth, twisted, and undisturbed surface texture.In contrast, all treated fabrics exhibited a less smooth surface that could be attributed to the action of the various reagents and biomordants used during the treatment.This evolution is particularly evident in the case of cotton treated with polyethyleneimine and the copolymers of dimethyl diallyl ammonium chloride and diallylamin.The treated samples are also much less cylindrical than the untreated samples because of the damage caused by the application of cationic reagents and bio-mordants.After dyeing, the samples become brighter.

Optimization of the dyeing process
Dyeing was examined in terms of the color strength of dyed fabrics (K/S) and dye bath exhaustion E (%).The experimental design adopted in this investigation is outlined in Table 1.
Based on the findings of the experiments, the regression model equations relating the color strength and exhaustion yield to the relevant process variables were further detailed and are given in the following equations: Color The squared multiple-correlation coefficient R (%), otherwise referred to as the proportion of variance clarified by the model, is used to estimate the uncertainty between the real model and the hypothetical one.Indeed, a model with an outstanding consistency would have an R 2 = 100% and a model with no consistency would have an R 2 = 0.In the case of the regression model for K/S, it is concluded that the resulting model is highly predictable (R2 = 97.00%).In the case of the regression model for the exhaustion yield E (%), it is concluded that the resulting model is predictable (R2 = 91.00%).
The obtained outcomes could indicate the significance of any experimental variable in the response regardless of the remaining variables.The main effects diagram demonstrates the behavior of the response across the various changes in the inputs.As Figure 5a reveals, the response conduct changes from one reaction to another, but it is clear that the pH parameter has the most important effect on the color strength and the dyeing bath exhaustion.
The interaction between the various operating parameters and their impact on the color strength of the dyed samples and the dyeing bath exhaustion has been plotted in Figure 5b.Based on the obtained results, we observe a strong interaction of the parameters temperature and pH, a strong interaction of time and temperature, and a weak interaction of time and pH.To predict the response values of the experimental parameters, the contour plots in the adopted design of experiments are interesting.The response surface is represented by a contour plot with a two-dimensional view in which all items with identical responses provide contour rows of continuous responses.Figure 6 illustrates the contour graphs obtained for K/S and E (%).The zones showing the best values for both the color strength and the dyeing bath exhaustion are shown in dark green.For the color strength K/S, this area occurs in the center of the graphic and it occurs in the upper right corner of the graphic for the dyeing bath exhaustion E (%).The response optimizer plots indicated that a dyeing temperature of about 91°C, pH of about 7, and a dyeing duration of about 30 min are the optimal levels of the studied variables.For the optimal conditions, the obtained responses are E (%) = 65.90 and K/S = 4.61.An experimental confirmation of the obtained optimal results was carried out, and the values of E (%) and K/S are 64.82 and 4.17, respectively.

Effect of cationization and pre-mordanting on the dyeing quality
The impact of cationization on the color strength of cotton fabrics is displayed in Figure 7.The results showed that the unmodified cotton had a restricted affinity to the extract (K/S = 0.4) compared to treated samples.Indeed, after cationization with polyethyleneimine and the copolymer of dimethyl diallyl ammonium chloride and diallylamin, K/S values are highly significant and reached 2.39 and 3.55, respectively.This result proves that the amino groups of the amino reagents were introduced into cellulose structure, which considerably improves the affinity of the cationized cotton fabrics toward the biological extract.Polyethyleneimine and the copolymer of dimethyl diallyl ammonium chloride and diallylamin are rich in amino groups, which favor electrostatic attraction through functional groups present in each structure.It is also shown that the color strength increases significantly with the change of the concentration of the bio-mordant.After which an optimum amount is required to reach maximum (20 g/L for both bio-mordants).The maximum color strength values using pomegranate peel and date palm pits were 1.56 and 1.19, respectively.This slight change in K/S value is related to the variation in the composition of the used bio-mordants.

Fastness results
Table 2 shows the results of fastness tests for fabrics dyed at optimal dyeing conditions.Different shades (photographs given in Figure 1) have been obtained with the different used reagents and biomordants.Depending on the nature of the bio-mordant, the shade of the colored fabric changes.Overall, the colored fabrics exhibited good fastness properties and the best results were achieved when treating cotton with polyethyleneimine.This was explained by the strong interaction between amino groups imparted onto cellulose and functional groups present in Citrullus colocynthis extract.

Conclusion
In conclusion, an extract of Citrullus colocynthis leaves was used as a source of color to dye cotton fibers.Colored cotton samples were morphologically characterized using Scanning Electron Microscope.All treated fabrics exhibited a less smooth surface compared to untreated samples.This trend proved the action of the amino reagents and bio-mordants used during chemical treatment.Dyeing experiments were carried out at dyeing duration (30-60 min), temperature (60-100°C), and pH (5-9).The dyeing process was optimized using a response surface methodology with the help of Minitab 17.1.0.The optimum dyeing conditions were found to be; time = 30 min, temperature = 91°C, and pH = 7.The cationization of cotton fabric with polyethyleneimine, a co-polymer of dimethyl diallyl ammonium chloride and diallylamin, and the pre-biomordanting with pomegranate peel and date palm pits significantly improved the color strength and exhaustion results.Regarding the fastness properties, it was observed that the shade of the colored fabric depended on the nature of the used biomordant.The colored fabrics displayed good fastness characteristics and the best results were reached when cotton was treated with polyethyleneimine.Further study will be extended for the evaluation of the biological activities of the dyed cotton fabrics.

Highlights
• Aqueous extract of Citrullus colocynthis leaves was used to dye cotton fibers.
• Dyeing experiments were optimized using Response Surface Methodology.
• The dyed cotton samples exhibited good fastness characteristics.

Figure 1 .
Figure 1.Preparation of aqueous extract of Citrullus colocynthis leaves and photographs of dyed cotton samples.

Figure 3 .
Figure 3. 3D representation of ion detection during LC-MS/MS analysis (each point represents an ion detected and fragmented with its retention time in minutes on the abscissa and its mass m/z on the ordinate, the larger the circle, the greater the intensity of the ion).

Figure 7 .
Figure 7. Effect of cationisation and mordanting on the color strength of dyed cotton.

Table 1 .
Presentation of the experiments considered in the optimization of the dyeing process.