New Natural Blue Dye from Water Jasmine (Wrightia Religiosa Benth.) for Silk

ABSTRACT This study investigates the color values and colorfastness of silk fabrics dyed with dye extracted from Water Jasmine (Wrightia religiosa Benth.) using three different alkaline agents: red lime, lime, and sodium carbonate. The color values (L*, a*, b*, C*, h*, and K/S) were measured before laundering to evaluate the color characteristics of the dyed silk. Notably, red lime produced the deepest shade (L* value of 50.46), closely followed by lime (77.07) and sodium carbonate (59.48). The h* values indicated that red lime (246.83) and sodium carbonate (292.17) produced blue shades, while lime (92.54) leaned toward green-yellow. Regarding color strength (K/S), red lime and sodium carbonate exhibited the highest color strength (1.74), whereas lime had the lowest (0.59). After laundering, colorfastness was evaluated using DL*, Da*, Db*, DC*, DH*, and DE* values. Red lime showed the best color durability, with a DE* value of 6.46, indicating fair color retention. Lime and sodium carbonate had poorer color durability, with DE* values of 12.05 and 16.15, respectively. Thus, the results clearly show that Water Jasmine with red lime possesses significant potential for development as a natural dye source, specifically for creating novel blue-colored natural dye material for silk dyeing.


Introduction
Natural dyes and herbal products have been used in textile dyeing since ancient times (Bahtiyari and Yılmaz 2018;Berkli, Zencirkıran, and Yılmaz 2023).Since the last decade, natural dyes have been replaced by artificial dyes because of their lower cost and durability (Kasiri and Safapour 2014).However, it was found recently that artificial dying caused severe health risks from product use and the production process (Safapour, Sadeghi-Kiakhani, and Eshaghloo-Galugahi 2018).Therefore, the natural dyes or herbal-based bio-colorants (Adeel et al. 2021) became interesting as the use of natural products have been proven to be healthier for human and have eco-friendly nature that can be considered an alternative to toxic dye in order to reduce environmental pollution (Batool et al. 2022;Kiran et al. 2020;Yılmaz et al. 2020).Although the natural dye originally comes from plants, animals, or minerals (Haji 2012), the most common source of natural dye is from plants (Adeel et al. 2019) which has a variety upon the local wisdom.These natural sources, however, give paler colors than the artificial ones.Therefore, improvement must be done on the extraction and dying technology (Haji, Nasiriboroumand, and Qavamnia 2018).
Water Jasmine (Wrightia religiosa Benth.) in the family Apocynaceae is a common plant in Thailand.It is a shrub with a height of two to 2-3 m and it is generally used as an ornamental tree in the garden.The research (Sahakitpichan et al. 2018) discovered that the leaves contain benzoxazinoids and indoxyl glycosides.Traxler et al. (2021) reported that the family Apocynaceae which are as follows: Wrightia religiosa (Teijsm.& Binn.)Benth.and Wrightia pubescens R. Br. contained an indole complex that gave indigo blue color.However, there is no report on using the Water Jasmine as the source of natural dye in Thailand.
The dye extracted from the Water Jasmine, which contains indoxyl glycosides, should be similar to indigos (Maugard et al. 2002;Wada, Rice, and Barton 2012).The fresh leaves are soaked in water.This causes the indicant, colorless, and insoluble substances, in the leaves to be hydrolyzed.The betaglucosidase enzyme contained in the chloroplasts of the mesophyll cells of the leaves of this indigo would result in colorless water-soluble indoxyl and these indoxyl compounds, when oxidized by oxygen in the air, would change to indigo blue compounds that is blue but insoluble white ready to be color for dyeing process.Ahlström, Eskilsson, and Björklund (2005) also noted that the color extraction in Thailand commonly adds various types of alkaline into fermented mixture in order to separate the color paste from the fermented leaves.The solution is left for one night for the blue color paste to be bound to lime.Li et al. (2019) described the indigo paste required red lime or lime and the indigo water was beaten with red lime or lime for 15-30 min, then was left for 1-3 days for the indigo paste to sink below.It was noted that the concentration of alkaline also effected the color of the dyed fabric.
The studies on alternative sources of natural blue color are still in small quantities.It was found that Water Jasmine (Wrightia religiosa Benth.)belonging to some species of the family Apocynaceae also gives blue color (Aggarwal 2021;Gokhale et al. 2004).This is also mentioned in pharmaceutical studies (Sahakitpichan et al. 2018) that leaves and branches of Water Jasmine contain indoxyl glycosides.It is in complex compounds which are similar to "Kram" and "Hom" and it gives blue color.However, the use of the Water Jasmine in textile dyeing is still very limited.
This article is a part of the project targeted to use Water Jasmine as an alternative source of the natural blue color for textile dyeing.In the first stage, a lab-scale extraction to obtain the natural blue color from Water Jasmine was practiced.The three types of common alkalines, which are red lime, lime, and sodium carbonate, were used in the experiment.The result has already been presented in another publication.The second stage, which is presented in this paper, focused on the dyeing silk fabric capacity of Water Jasmine from the comparison of color properties among the three types of alkaline extraction methods.The purposes of this research were: (1) To compare the color values CIELAB (L*, a*, b*, C*, h*) and dyeing performance (K/S) of the dye extracted from Water Jasmine on silk among three types of alkaline.(2) To compare the color difference (DL*, Da*, Db*, DC*, DH*), colorfastness to laundering, and total color difference (DE*) of the dye extracted from Water Jasmine on silk among three types of alkaline.

Dyeing process on silk fabric
In this research, three types of alkalines: red lime (calcium hydroxide (Ca(OH) 2 )), lime (calcium oxide (CaO)), and sodium carbonate (Na 2 CO 3 ), were used to extract dyes from Water Jasmine leaves (Figure 1).It was found that after lime was added to the fermented Water Jasmine leaves and it was left for 2 h, the color paste settled down at the bottom and the upper part was clear yellow liquid.The Water Jasmine color paste was blue and mud-like while the color paste had a rough texture and lighter blue than that from red lime.When sodium carbonate was added, the amount of color paste was not found, but the fermented liquid changed to darker blue.This part focused on the dyeing process.It was found that the dye extracted from Water Jasmine could be applied on silk.It is greenish-blue, similar to the indigo extract color (Saithong 2012) as shown in Figure 2.
The three types of dye extracted from Water Jasmine were prepared using 2 Kg of fresh Water Jasmine leaves.These leaves were soaked in 10 L of water at a ratio of 1:5 (w/v) for 18 h and then filtered.Twenty grams of each type of alkalines were added to each 10 L sample.The mixture solutions were stirred continuously for 30 min and then left undisturbed for 1 day.Upon pouring off the water, a colored paste settled at the bottom of the container.In this state, the color paste resembled mud and required adjustment with tamarind water and ash water to increase its volume to 500 mL.For the dyeing process, silk samples were prepared and dyed for 45 min.

The color values
The Datacolor 550 spectrophotometer was used to measure the color values of the dye extracted from Water Jasmine on silk before laundering.Three types of alkaline agents were compared.The color values in this study were measured in terms of CIELAB (L*, a*, b*, C*, h*) and K/S, which are explained as follows: • The L* value refers to the lightness of the color, ranging from 0 to 100 (0 = black, 100 = white), where a higher value indicates a lighter color.• The C* value (chroma) refers to the color brightness, which is calculated as follows: ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi • The h* value refers to the position of the color value, represented as a hue angle, where 0° = red, 90° = yellow, 180° = green, and 270° = blue.This value is calculated as follows: Where Equation 2expresses on a 0° to 360° scale with the a* positive axis being 0° and the b* positive axis at 90°. • The K/S value refers to the strength of color, where a higher value indicates greater color strength.The Kubelka -Munk equation is commonly used for calculation of the K/S value, as shown in the equation below: Where R λ is the reflectance factor of the specimen at wavelength (λ) (the %R value is normally measured by a spectrophotometer and normalized to 1.0 [i.e., 100% = 1.0]) as per AATCC EP6-2016(AATCC 2017).

The colorfastness to laundering
The dyes extracted from Water Jasmine on silk were tested according to AATCC TM61-2013 Test No. 1A (AATCC 2015) with laundering temperature 40 ± 2°C, detergent solution 200 mL by using 0.37% 1993 AATCC standard reference detergent WOB, and 10 stainless steel balls were put for laundering time of 45 min.The samples were rinsed with water three times and left to dry.The spectrophotometer was used to measure the color values: L*, a*, b*, C*, h*, and K/S after laundering.

Evaluation of color differences
The CIELAB color difference values were calculated and evaluated between the standard (before laundering) and specimen (after laundering) in pairs.According to ASTM D2244-22 standard (ASTM International 2022), the direction of the color difference is described by the magnitude and algebraic signs of the components DL*, Da*, and Db*, calculated as follows: Chroma difference (DC* ab ) and hue difference (DH* ab ) between the standard and specimen are calculated as follows: ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi The total color difference (DE* ab ) is calculated between pairs represented in terms of L*, a*, b* as shown in equation below: ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi ffi

To compare the color values of the dye extracted from Water Jasmine on silk among three types of alkalines
From the comparisons of three different types of Water Jasmine adding alkaline agents dyed silk fabric with cold dyeing process, the color values were tested by spectrophotometer to evaluate L*, a*, b*, C*, h*, and K/S.The color values from the samples are shown in Table 1 and Figure 3.The results revealed that the color obtained from lime had the highest L* value, while red lime had the lowest L* value.It indicated that red lime had a better color deep shade than lime and sodium carbonate.In accordance with Mongkholrattanasit et al. (2017), the process of converting indoxyl to oxidize in order to convert to indigo is recommended to add appropriate alkalinity such as ammonia, sodium carbonate, and calcium hydroxide because these substances stimulate the oxidation reaction of indoxyl to indigo to be faster.The added red lime had calcium hydroxide (Ca(OH) 2 ), which increased the alkalinity, which was a good condition for indoxyl to be oxidized and changed to indigo.Therefore, the color position value (h*) on natural dyed silk extracted from Water Jasmine leaves showed that red lime positioned at 246.83, within the range of 180-270 degrees.According to the color measurement method in the CIELAB system, the color of the fabric was in blue range.Lime positioned at 92.54, within the range of 90-180 degrees and the color of the fabric was in green-yellow range but very light blue by naked eyes.The sodium carbonate positioned at 292.17, within the range of 270-360 degrees and the results indicated that the color of the fabric was in the blue-red range.
The color strength values (K/S) of the red lime sample showed the best color strength setting at 1.74, equal to that of sodium carbonate with the K/S setting at 1.74 and lime had the lowest color strength at 0.59.
The results in this part indicated that the dye extracted from Water Jasmine could be dyed on silk.The dye extracted from Water Jasmine using cold extraction methods was greenish-blue and similar to indigo.The study (Phumchai and Watcharaporn 2017) showed that a higher pH value of dye solution gave a darker color value of indigo dyeing effect.It was consistent with this research which found that the natural color obtained from Water Jasmine leaves gave the dark blue color by adding red lime to the extraction process.In this regard, the alkalinity in the addition of red lime had the highest value compared to the addition of lime and sodium carbonate.

To compare the color fastness of the dye extracted from Water Jasmine on silk among three types of alkalines
The results of colorfastness test on dyed silk samples were exhibited in terms of DL*, Da*, Db*, DC*, DH*, and DE* referring to the differences in the color values before and after laundering test.The results were shown in Tables 2, 3, and Figure 4. From Table 2, the differences of the chroma or brightness (DC*) refer to the fastness of dye to laundering.When DC* values are positive, this means that the sample becomes brighter after the laundering.On the other hand, if the values are negative values, it means that the sample becomes duller.Red lime (−1.04), lime (−6.13), and sodium carbonate (−1.54) showed negative values which indicated that the samples were duller.
The differences in the lightness values (DL*) showed that if the color value increased after laundering, it means that the lightness is greater than before the laundering; therefore, the color is lighter.If the color value decreased, it means that the lightness is reduced after laundering; therefore, the color is duller.However, lime gave the positive and also highest DL* values at 8.14, which means the color of the sample was getting lighter after laundering, while the other agents such as sodium carbonate (−4.67) and red lime (−13.84)gave negative values, which means the color of the samples were getting duller after laundering.
The differences in the hue angle values (DH*) showed if the h* color value increased after laundering, it means that the hue was changed to the color of the right-hand side (Clockwise) quadrant before the laundering.If the h* color value decreased after laundering, it means that the hue was changed to the color of the left-hand side (Counterclockwise) quadrant before the laundering.The differences of color position values of red lime still gave the blue color and it was negative at −2.26, which means it was getting greener after laundering.However, lime gave the green-yellow color and the difference of color position was negative at −1.36, which means it was getting redder after laundering.Sodium carbonate gave the blue-red color and the difference in color position was positive at 13.16, which means it was getting redder after laundering as well.
The total color differences (DE*) refer to the total color durability to laundering.If the difference of total color is more than 2, it means that the change of color is detected by human naked eyes.This indicator showed up to two levels, which was in the acceptable level (1-2) for fabric industry.According to Table 3, sodium carbonate had the highest difference value at 16.15, followed by lime at 12.05, while red lime had the best result with the lowest difference value at 6.46.This means that all of the samples were poor to fair durability when compared with grayscale.

Conclusions
This study explored the potential of Water Jasmine (Wrightia religiosa Benth.) as a source of natural blue dye for silk fabric.The dye extracted from Water Jasmine leaves using three different alkaline agents in a cold process resulted in a greenish-blue color paste similar to indigo.These three types of alkaline agents, namely red lime, lime, and sodium carbonate, were used in the dye extraction process.The extracted dyes, in both paste and solution forms, were then used to dye silk fabric, and their effects on the color properties and colorfastness of the resulting dye were investigated.
Our findings indicate that red lime extraction produces the deepest and richest blue color on silk fabric, with the highest color strength (K/S) and the most desirable hue angle (h*) within the blue color range.On the other hand, lime extraction resulted in a lighter greenish-blue shade, while sodium carbonate extraction yielded a dark blue-red hue.
In terms of colorfastness to laundering, red lime extraction demonstrated the best performance, showing minimal changes in color values after washing.Lime and sodium carbonate extractions, on the other hand, exhibited more significant alterations in color, including lightening and shifting toward different color quadrants.However, further studies are required to improve other types of color durability or color fastness.
Overall, the study revealed that Water Jasmine can be a viable source of natural blue dye for silk fabric, with red lime extraction showing the most promising results in terms of color depth and durability.These findings contribute to the exploration of sustainable and ecofriendly alternatives to synthetic dyes, which can have adverse health and environmental effects.Further research and development in this area may lead to the broader utilization of natural dyes, reducing the environmental impact of the textile industry and promoting healthier, eco-friendly practices.

Highlights
• A new natural blue dye was successfully extracted from Water Jasmine leaves using red lime.It resulted in a greenish-blue color paste that was similar to indigo.
• The new natural blue dye extracted from Water Jasmine leaves could be applied to dye silk fabric, resulting in a blue color.• Silk dyed with Water Jasmine leaves extracted using red lime had a deeper shade of blue compared to lime and sodium carbonate.Additionally, red lime was the most effective agent in terms of both color strength and colorfastness to laundering.

•
The a* value refers to the red and green; a positive a* value indicates red, while a negative a* value indicates green.•The b* value refers to the yellow and blue; a positive b* value indicates yellow, while a negative b* value indicates blue.

Table 1 .
The color values of K/S and CIELAB (L*, a*, b*, C*, h*) of the dyed silk with Water Jasmine using different alkaline before laundering.

Table 2 .
Color differences after laundering test of the dyed silk with Water Jasmine using different alkalines.

Table 3 .
The total color differences of the dyed silk with Water Jasmine using different alkalines after laundering test compared with grayscale.