Ficus sycomorus as a Sustainable Source of Leather Dyeing Material: An Ecofriendly Approach

Natural colorants play a vital role in the production of eco-leather by substituting environmentally hazardous and toxic synthetic dyestufs. In this study, a natural dye is extracted and optimized from the bark of Ficus sycomorus , a plant species locally known as shola, by designing diferent combinations of concentration, temperature, and time parameters. A dye extracted from 120g/l concentration at a temperature of 1000 ° C for 60minutes showed the highest absorbance value, and it has been used for further dyeing processes with and without mordant. Properties such as color strength (k/s), L ∗ a ∗ b ∗ values, and color fastness of a dyed leather specimen were measured and analyzed. Oxalic acid mordant-dyed leather samples mordanted with the postmordanting method have revealed the highest k/s value among other experimental samples. Moreover, better color fastness properties were obtained from a leather sample mordanted with oxalic acid. Consequently, a dye extracted from the bark of Ficus sycomorus can be used as a leather dyeing material.


Introduction
Being a fexible, hygienic, and durable biomass material, leather is obtained from the by-products of animals through a series of processes, in which various chemicals are employed [1]. Leather processing involves pretanning, tanning, wet fnishing, and fnishing processes [2]. Imparting and improving the mechanical and sensory properties of tanned leathers are some of the central roles of post-tanning operations [3]. Leather dyeing is one of the crucial processes after tanning, where the color of the leather matrix is built [4]. Dyes can be either natural or synthetic based on their source. While synthetic dyes are derived from petroleum and coal-tar sources [5], natural colorants are obtained from natural sources like plants and invertebrates [6]. Besides, leather dyes are among the critical chemical pollutants of industrial origin. It is estimated that during the dyeing process, around 10-35% of the dye is lost in the efuent [7]. According to Saravanan and Chandramohan, currently around ten million tons of synthetic dyestufs are consumed annually [8].
Tis is a serious cause of health and environmental hazards during its application by releasing signifcant amounts of waste and unfxed dyestufs [9,10]. On the other hand, due to the high level of biodegradability of natural dyes, wastewater can degrade organic substances without the need for physical and chemical processes. Hence, the demand for eco-friendly natural colorants has increased in the past few decades [11]. In an attempt to dye a leather matrix with sustainably sourced dying materials, a number of natural dyes have been reported. According to research [12], the leather matrix can be efciently dyed using walnut bark, tea leaves, turmeric rhizomes, eucalyptus bark, and tea leaves. In another study, it was discovered that four distinct fower species, including Tagetes erecta, Lantana camara, Celosia cristata, and Rosa damascena, could color wet-blue goat leather [10]. Generally, beetroot [13], fungal pigment [14], Mucuna pruriens [15], and Garcinia mangostana Linn peels [16] were some of the sources from which natural colorants were sourced in the leather dyeing process so far. Te fastness properties of leather efects in the dyeing process can be enhanced by using mordants such as chitosan [17].
Ficus sycomorus is a fairly hardy, medium to a large spreading fg tree with a distinctive yellow stem that is often seen along riverbanks. Despite having its origins in Africa, it is now found in practically all tropical nations [1]. According to [18], the phytochemical analysis of Ficus sycomorus revealed that its bark extract contains phenols, tannins, favonoids, coumarins, quninol, alkaloids, steroids, and saponins. Also, traditionally, its bark was used as a source of dyeing material for coloring fabrics in Ethiopian Orthodox Tewahedo Church monasteries. Hence, in this study, an attempt was made to optimize conditions for the extraction of dye from the bark of Ficus sycomorus plant species and the application of the dye extract onto leather samples. Afterward, the fastness properties of experimentally dyed leather samples were analyzed along with their color strength and color diferences.

Materials and Methods
Sheep crust leather (0.3 kg based on shaved weight) was chosen as experimental leather and sourced from Bahir Dar tannery, Bahir Dar, Ethiopia. Te barks of Ficus sycomorus extract were collected from Bahir Dar district of the Amhara regional state, Ethiopia. Moreover, a concentration of 1 M oxalic acid and aluminum sulfate (KAl(SO) 2 .12H 2 O) were used for the mordanting method.

Dye Extraction Process.
Te bark of Ficus sycomorus was collected and dried at room temperature. Te dried bark extract was then grinded and sieved using a 0.9 mm sieve. Te dye was extracted from the sieved powder by varying concentration, temperature, and time. A concentration of 100 g/l, 80 g/l, and 120 g/l at a temperature of 60°C, 80°C, and 100°C for about 45 minutes, 60 minutes, and 75 minutes was used to optimize the best condition for the extraction process.

Determination of Total Phenolic Content.
Te total phenolic content (TPC) of F. sycomorus extract was measured with the Folin-Ciocalteu reagent by the method employed by [19] using a UV-Visible spectrometer at 760 nm, and the result was expressed as mg of gallic acid equivalent per gram of sample (GAE/g) plus standard deviations using gallic acid as the reference.

Determination of Flavonoid Content.
Te total favonoid content (TFC) of F. sycomorus extract was estimated according to the procedure outlined by [20] using a UV-Visible spectrometer at a wavelength of 425 nm. Quercetin was used as standard and the result was presented as mg quercetin equivalent per gram of sample (QE/g) plus standard deviations.

UV-Visible Spectroscopy and Fourier-Transform
Infrared Spectroscopy (FTIR). A UV-Vis spectrophotometer was used to examine the optimum absorption of the dye extract. On the other hand, the functional groups present in F. sycomorus colorant were investigated using Fouriertransform infrared spectroscopy (FTIR) with a resolution of 4 cm −1 over the range of 4000−500 cm −1 .

Leather Dyeing Process with and without Mordant.
Ten pieces of sheep crust leather were taken from Bahir Dar Tannery Ltd. for dyeing with and without mordant. Te dyeing condition was optimized by varying the dyeing temperature and time to 40°C, 50°C, 60°C, and 45 minutes, 55 minutes, and 65 minutes, respectively. Oxalic acid (2.5%) and aluminum sulphate (KAl(SO) 2 .12H 2 O) (2.5%) based on the shaved weight were applied both in premordanting and postmordanting methods onto Ficus sycomorus extract dyed leather specimen.

Color Fastness Properties.
Dyed leather samples were cut from experimentally dyed leather samples after conditioning them at a temperature of 20 ± 2°C and 65 ± 2% relative humidity for about 48 hours.

Dry and Wet Rub Color
Fastness. Dyed leather samples were cut and tested for dry and wet rub fastness to assess their resistance to color fading using a grey scale according to EN ISO 105-A02 by following the standard procedure. Te rating scales were from 1 to 5, with 1 being the worst rating and 5 being the best rating.

Color Fastness to Light.
Te resistance to change in color of dyed leather samples to the action of a standard artifcial light source (a Xenon Lamp) was also assessed using EN ISO 105-B02 under controlled conditions by following the standard guidelines. Te fastness of dyed sample leather was then assessed by comparing the color fading of dyed samples with standards of blue scale from 1 to 8. Blue scale 1 indicates that the light fastness property of the dyed leather sample is low, and 8 implied that the light fastness property of the dyed leather sample is best.

Color Fastness to
Washing. Te resistance to change in color of a dyed leather specimen and the staining of a dye substrate onto cotton and wool were assessed by following IUF 453. Dyed leather samples in contact with cotton and wool were agitated in a standard wash detergent solution for 30 minutes at 400 C. Ten, the change in color of a leather sample was compared with the original leather specimen. Similarly, the staining on cotton and wool was assessed with a standard grey scale.

Color Fastness to Perspiration.
Te resistance of a dyed leather sample to the prolonged action of an artifcial perspiration solution was assessed using the IUF 426 standard procedure. Te change in color of a dyed leather sample was then compared with the original leather sample. Te staining of cotton and wool textiles was also assessed by using standard grey scales.

K/S Values and Color Diference.
To measure the color depth of a sample at the surface, the surface refectance of dyed leather samples was measured using a Macbeth color eye 3100 refectance spectrophotometer using the Kubelka-Munk equation.
where K is the light absorption coefcient, S is the light scattering coefcient, and Rλmax is the light refectance value of a dyed surface of leather samples at a wavelength of maximum absorption. Moreover, the color diference of dyed leather samples was measured to evaluate their lightness-darkness (L * ), greenness-redness (a * ), and blueness-yellowness (b * ).

Condition Optimization for Extraction and Dyeing
Process. Temperature, time, and concentration of the dye extract were variables considered for extracting dye from Ficus sycomorus plant species. Te experimental designs were done by using the Taguchi orthogonal array method with three-level experimental designs by Minitab 17 software [21]. Nine experimental conditions were organized by the software for optimizing the best conditions for extraction. Finally, the best combinations of variable conditions that yield the highest concentration of dye (highest absorption indicates the highest dye concentration) were used to color a leather sample for further process.
Te duration of dyeing a leather sample and temperature were optimized to obtain the best condition of variable combination for the dyeing process. A temperature of 40°C, 50°C, and 60°C, for a dyeing duration of 45 minutes, 55 minutes, and 65 minutes were used to optimize the best match of conditions as presented in Table 1 above. Te efects of dyed leather samples were also analyzed by dyeing the sample with and without the application of mordant. Oxalic acid and aluminum sulfate (KAl(SO) 2 .12H 2 O), both 2.5% based on the shaved weight of a leather sample were used for premordant and postmordant dyeing at a temperature of 60°C and a dyeing duration of 1 hour. A comparison for K/S values, color diference, and fastness properties were then made between leather samples dyed with and without the application of mordant.

Total Phenolic and Total Flavonoid Content of F. sycomorus Dye Extract.
Te results of the quantitative determination of the total phenolic content of Ficus sycomorus stem bark dye extract revealed 171.849 ± 0.251 mg GAE/g polyphenols, as shown in Table 2 underneath. On the other hand, the total favonoid content of F. sycomorus stem bark dye extract was found to be (19.727 ± 0.638 mg QE/g) which is in agreement with the study conducted by [19].
Here, according to the TPC and TFC results of F. sycomorus, it can be noted that polyphenols are the major constituents of the dye extract.

UV-Visible Spectrometer and Fourier Transform
Spectroscopy. Te absorption spectra of aqueous F. sycomorus bark extract revealed a maximum absorption wavelength at 492 nm (Figure 1(a)). On the other hand, the FTIR spectrum of the dye showed infuential absorption peaks at 3383.6370, 2942.7473, 1706.9902, and 1632.8439 cm −1 neglecting the fngerprint region (Figure 1(b)). Due to the presence of chemicals like favonoids and other phytochemicals within the crude extract, the bands signify stretched vibration bands [22]. Te broad, medium absorbance at 3383.6370 is similar to an O-H stretching vibration. Weak C-H stretching of an aldehyde or an alkane's hydroxyl group was noted at 2942.7473, and FTIR spectrogram observations made around 1632.8439 indicates C�C stretching of an alkene, or C�O stretch of the amides identifed in alkaloids lying within the given range [23]. Te peak at 1706.9902 cm −1 corresponds to the color intensity present in the extract [24].

Conditions Optimized for Extraction.
Te process of dye extraction from Ficus sycomorus was carried out with an experimental design for parameters illustrated in Table 3 to identify the best match of conditions from those parameters, the maximum absorbance of a dye extracted from Ficus sycomorus was measured using an instrument called a UV-Visible spectrophotometer. Te maximum absorbances measured were diluted with a ratio of 1 : 5 [21], and the outcome is presented in Table 3 underneath. A dye that has a maximum value of absorbency has a maximum dye concentration, as stated by Abera and Negassi [21].
A dyed leather sample with a concentration of 120 g/l at a temperature of 100°C for 60 minutes duration has revealed the highest absorbance among other experimental test conditions performed with a diferent arrangement of parameters. Consequently, further dyeing processes were undertaken with a dye extracted with this set/arrangement of variables.

Mordant-Free Dyeing.
Mordant-free dyeing of a leather sample was undertaken with a dye extract optimized based on conditions of parameters designed and presented in Table 4, and both K/S and CIE Lab values of Ficus sycomorus extract dyed leather samples were measured with color eye 3100 spectrophotometer by following a standard procedure. Te results obtained from K/S of a dyed leather sample were used to judge the best-optimized matches of parameters for dyeing with mordants. Accordingly, test number eight dyed at a temperature of 60°C for 55 minutes duration was found to give the highest K/S value and was considered to be the best condition optimized for dyeing with mordant using oxalic acid and aluminum sulfate.

Dyeing with Mordant.
Oxalic acid and aluminum sulfate (both 2.5% based on sample shaved weight) were used for mordant dyeing with a condition of variables optimized in Table 5, dyed samples were then measured for color strength to identify a mordant that yield the highest K/S value. Te Table 1: Condition optimization for extraction and dyeing process.

Test#
Dye concentration (g/L) Extraction process Dyeing process Temperature (°C) Time (minute) Temperature (°C) Time (minute)  1  80  60  45  40  45  2  80  80  60  40  55  3  80  100  70  40  65  4  100  60  60  50  45  5  100  80  70  50  55  6  100  100  45  50  65  7  120  60  70  60  45  8  120  80  45  60  55  9 120 100 60 60 65    color diferences of those mordant dyed samples were also measured to assess the lightness-darkness, rednessgreenness, and blueness-yellowness of the samples. Te K/ S values of dyed leather samples become optimum at a wavelength of around 490 nm, as stated in Figure 2 below. As stated by Negassi and Abera, dyeability is directly proportional to the color strength of a dyed leather sample [21]. In this study, an oxalic acid mordant dyed leather sample has revealed a K/S value of 6.626 and 7.982 in premordanting and postmordanting techniques signifying its increased dyeability. Tis was a bit higher when compared with a K/S value of a leather sample dyed with alum mordant. Similarly, the K/S value of alum mordant dyed leather samples were 5.403 and 5.927 in premordanting and postmordanting techniques which were greater than the controlled (a sample dyed without mordant) leather sample having a K/S value of 4.585. All the dyed leather samples have been presented in Figure 3 above.
On the other hand, color diference values of leather samples dyed without, oxalic acid and aluminum sulfate mordant were also measured to assess values of L * , a * , and b * . Te lightness value of a leather sample dyed without mordant, and alum mordant dyed leather sample with the premordanting technique were relatively higher than the oxalic acid mordant dyed leather sample as illustrated in Table 5 characterizing a lighter shade. Te value of a * for a sample dyed with oxalic acid and alum mordant in the postmordanting and premordanting techniques, respectively, were found to give 20.6 and 17.5, signifying more pinker in color than the leather sample dyed without mordant.
Similarly, 16.2 and 18.5 were b * results for oxalic acid mordant dyed leather samples in premordanting and postmordanting methods respectively indicating that the samples were more yellow in color than other experimental samples. To sum up, controlled and aluminum mordant dyed leather samples were found to give a lighter hue, and an oxalic acid mordant dyed leather sample was found to give redder and yellower color.

Color Fastness Properties
Te FTIR analysis of the F. sycomorus colorant in Figure 1 revealed that the spectrum of the dye extract showed a peak at 1706.9902 cm −1 indicates the presence of a carbonyl group, and peaks at 1203.7739 and 1219.4626 cm −1 denote the presence of a C-O stretch which signify the formation of covalent bond between polyphenols of the dye extract and the leather matrix. Te development of covalent bond between the colorant and that of the leather substrate indicates strong fxation of dye with fber which leads to better fastness properties. Moreover, due to the presence of a O-H functional group in the FTIR spectrum of the dye extract at around 3383.6370 cm −1 , hydrogen bonds would be formed between the colorant and the collagen matrix.

Fastness to Dry and Wet Rubbing.
Te fastness values of a leather sample dyed with optimized dyeing conditions were assessed for dry and wet rubbing. Te results for dry and wet rub fastness values are presented in Table 6 underneath. As it can be inferred from the table, the dry rub fastness value of the postoxalic acid mordant dyed leather sample was found to be grade 5 being a good indicator of its resistance to dry rubbing.
On the other hand, a color grade of 4/5 was found for the wet rub fastness value of the postoxalic acid mordant dyed leather sample. Tis implied that oxalic acid mordant dyed leather samples have resulted in a good resistance to rubbing, as indicated in Table 6 above. As far as staining values  Journal of Engineering 5 are concerned, oxalic acid mordant dyed leather samples mordanted with the postmordanting method were comparatively better than that of controlled and alum mordant dyed leather samples.

Color Fastness to Washing
Te colorfastness to washing of a leather sample dyed with Ficus sycomorus extract was assessed by following the EN ISO 15702 standard procedure. Te change in color of a dyed leather sample and the staining onto wool and cotton textile materials were compared with the initial sample of these textile materials with the help of grey scale reading, and the value of the output is depicted in Table 7. Te staining of the controlled dyed sample has resulted in satisfactory values of 3/4 and 3, respectively. On the other hand, oxalic acid mordant dyed leather sample in postmordanting technique were found to have 4/5 and 5 staining values by cotton and wool, respectively. Tis value proved that a sample dyed with postmordanting technique of oxalic acid has very good to excellent resistance to washing.   Journal of Engineering

Color Fastness to Light and Perspiration.
A dyed leather sample was exposed to a light source for about 24 and 48 hours to assess its light fastness properties and the result is recorded in Table 8 underneath. As it can be inferred from Table 8, a sample mordanted with oxalic acid and alum in a postmordanting technique have resulted a higher color fastness to light of 7/5 and 7 when exposed to a light source for 24 and 48 hours, respectively. Tis indicates that a dyed sample mordanted with oxalic acid and alum has higher resistance to color fading. Similarly, a dyed sample mordanted with oxalic acid with premordanting technique has showed satisfactory results of 6 when exposed to 24 and 48 hours light source exposure. On the other hand, inferior resistance to color fading by light source were recorded from a controlled and prealum mordant dyed leather samples with 48 hours light source exposure. Te perspiration fastness of a dyed leather sample was assessed by following the IUF 426 method in such a way that the staining on cotton and wool were compared with the original dyed samples using grey scale measurement. Te value obtained from the staining of cotton and wool for color fastness to perspiration was presented in Table 8 below. Te staining of a postoxalic acid mordanted leather sample has revealed very good to excellent rating of 4/5 and 5 on wool and cotton, respectively.
Tis implied that the resistance to staining of a dyed leather sample mordanted with oxalic acid using the postmordanting method was higher than the controlled and other mordant dyed leather samples. Preoxalic acid and postalum mordant dyed leather samples have revealed a staining value of 3-4 and 4 with wool and cotton, respectively. On the contrary, prealum mordant dyed leather samples showed inferior color fastness properties to perspiration.

Conclusion
Natural dyestufs can be extracted from diferent parts of plants among other sources revealing eco-friendly colorants. Tis study revealed that a dyeing material obtained from Ficus sycomorus bark extract with a 120 g/l concentration at a temperature of 100°C for 60 minutes can be used as a dye for dyeing a leather matrix. Oxalic acid mordant dyed leather sample in the postmordanting method has resulted in better color strength indicating its increased dyeability. Best ratings were also recorded for the fastness properties of a dyed leather sample mordanted with oxalic acid making it suited for a feasible commercial application. Te accessibility of the plant is abundant in the Horn of Africa, making the extraction process to be economical.

Data Availability
Te data collected and analyzed during this study are included in the paper and more can be accessed from the corresponding author upon reasonable request.

Conflicts of Interest
Te authors declare that there are no conficts of interest.