Extraction of natural dyes from the stem of Caulis spatholobi and their application on wool

Abstract

Researchers are continuously exploring new candidates in the field of natural dyeing to lighten the burden of synthetic dyestuff on living organisms. In this research, novel natural dye was explored using the Caulis spatholobi plant. The extraction was carried out through the conventional extraction method in the aqueous medium. Various parameters of the natural dye extraction process, such as the material-to-liquor ratio, pH, time and temperature, were optimized to 1:40, 12, 120 min and 100℃, respectively. The extract was filtered twice and used for the characterization and dyeing of wool fabric. The extract was characterized using Fourier transform infrared spectroscopy for the determination of dominant functional groups. Natural dyeing of wool was carried out with and without metal mordants, such as aluminum sulfate, ferrous sulfate, copper sulfate and zinc sulfate. Pre-mordanting, meta-mordanting and post-mordanting techniques were employed. The performances of dyed fabrics were evaluated in terms of color strength K/S values. The fastness properties of dyed fabrics were also measured. The dyed fabric showed various color shades based on the type of mordant used. Furthermore, enhancement in the colorfastness was observed with mordanting.

Keywords

dyeing color waste reduction surface modification

Synthetic dyes, especially reactive dyes, are widely used in textile industries for the coloration of cotton and other cellulosic fibers. Compared with natural dyes, synthetic dyes can produce a variety of bright shades, with fairly good color fastness, dyeing reproducibility and low cost.^1–5 However, some synthetic dyes contain heavy metals and azo groups, which are harmful to the environment and human health.^6–8 Also, the dyeing and printing wastewater usually contains high salt dosages, residual dyes and chemical auxiliaries, which may cause serious health issues and disturb the ecological balance.^3,9 Therefore, most dyestuff and auxiliaries manufacturers nowadays set up factories in the countryside and suburbs where the environmental law is weak.¹⁰ The textile dyeing and printing industries are facing threats of hazardous conditions arising from the extensive utilization of synthetic dyes. For this reason, the development of non-allergic, non-toxic and environment friendly natural dyes has gained the attention of both researchers and industries.^11–13

Dyestuff and auxiliaries manufacturers have started using less harmful and non-toxic substances in order to reduce pollution.^14–17 There has been growing interest in the exploration of natural dyes for textile industry; however, these dyes are facing limitations of higher cost and restricted applicability for large-scale production.¹⁸ Natural dyes extracted from stem, roots, leaves, flowers and fruits have been reported by many researchers, for example, Prusty et al.¹¹ and El Ksibi et al.¹⁹ extracted natural colorants from agrifood.

Caulis spatholobi is a traditional Chinese medicine that is commonly found in China and Southeast Asian countries, such as Thailand.²⁰ It helps to cure blood stasis syndrome and has strong anti-inflammatory properties. It is composed of various chemical compounds, such as flavonoids, isoflavone, chalcone, anthraquinone, catechin and sterol.^20,21 Caulis spatholobi colorant contains –OH and –C=O groups, which are present in most commonly used dyes. The chemical structures of some of polyphenolic colorants found in Caulis Spatholobi, which contain the groups responsible for the bonding and coloration of textile materials,^22,23 are shown in Figure 1.

Figure 1.

Molecular structure of some of the polyphenolic compounds found in Caulis Spatholobi extract.

So far, no work has been reported on the dyeing of textiles using Caulis spatholobi. The aim of this research is to explore the stem of this plant for the extraction of dyes and dyeing of wool fabric using the exhaust method.

Experimental details

Materials

Caulis spatholobi in chopped form, as shown in Figure 2, was purchased from a local market in Wuhan, China. Scoured wool fabric (plain weave) with a surface mass of 180 g m⁻² was purchased from Ningbo Zhongxin Wool Textile Group Co., Ltd, China. Acetic acid, sodium hydroxide, aluminum sulfate, ferrous sulfate, copper sulfate and zinc sulfate were of AR (analytical reagent) grade and supplied by Sinopharm Chemical Reagent Company, China. A commercial detergent, “Alconox,” was purchased from Sigma-Aldrich.

Figure 2.

Chopped and dried pieces of Caulis spatholobi plant stem.

Methods

Extraction of dyes

The aqueous extraction method was employed for extracting coloring components from Caulis spatholobi. The raw material was collected, dried and then ground into a fine powder with a pestle and mortar and then finally with an electric grinder. The powder was soaked in distilled water at a material-to-liquor ratio (MLR) of 1:10–1:60, heated to a temperature of 50–100 ºC at pH 2–14 and the extraction time of 30–180 min was used. Finally, the extract was filtered twice using nylon cloth and was used for dyeing. The pH, temperature, MLR and time combination that yielded maximum absorption was taken as the optimum condition for the extraction of dye. The effect of the variation of extraction parameters on the dyeing properties of wool was studied.

Dyeing and mordanting

The mordanting and dyeing of wool fabric was carried out in a Rota dyer machine (Xiamen Rabbit Precision Instrument Co., Ltd, China). Three different mordanting methods, namely pre-mordanting, meta-mordanting and post-mordanting, were used. Pre-mordanting of wool fabric was carried out by 1 g L⁻¹ mordant (aluminum sulfate, ferrous sulfate, copper sulfate and zinc sulfate) at 70ºC keeping the MLR of 1:15 for 60 min. The dyeing process was done by the exhaustion method with three different mordanting methods (Figures 3(a)–(c)). The dyed fabric was washed off using the commercial non-ionic detergent Alconox (g L⁻¹).

Figure 3.

Dyeing profiles using Caulis Spatholobi extract employing three mordanting techniques: ① pre-mordanting; ② meta-mordanting; ③ post-mordanting.

Testing and analysis

Color strength measurements

The dyed samples were evaluated for color strength using the reflectance method using an SPF600 color measurement instrument. The CIELab color coordinates L*, a* and b* represent lightness, redness–greenness of the color and yellowness–blueness of color, respectively. The color strength (K/S) values were calculated by the Kubelka–Munk equation (Equation 1)

K / S = (1 - R)^{2} / 2 R

(1)

where R is the reflectance of the dyed fabric, K is the absorption coefficient and S is the scattering coefficient.

Fastness test

The color fastness to washing, rubbing, perspiration and light was tested according to the standard methods, namely ISO 105 C06 (A2S)-2010,^6,24 AATCC Test Method 8-2007,^6,25 AATCC Test Method 15-2002²⁶ and ISO 105 B02-1994,²⁷ respectively.

Fourier transform infrared spectroscopy

Natural dye was extracted at optimized conditions from Caulis spatholobi and transformed into powder by spray drying. Fourier transform infrared (FTIR) spectra of Caulis spatholobi powder were recorded from 4000 to 500 cm⁻¹ using a Perkin-Elmer System 2000 FTIR Spectrometer.

Results and discussion

Optimization of process parameters for Caulis Spatholobi colorant extraction

Effect of pH

In order to optimize the pH of extraction, the pH was varied from 2 to 14 by keeping the extraction time (60 min), temperature (90℃) and MLR (1:40) constant.

Figure 4 shows the K/S values of the fabric dyed with Caulis spatholobi colorant extracted at various pH values. The obtained extracts at all designated pH values were used for the exhaust dyeing of wool fabric using the optimum dyeing conditions, that is, MLR 1:25, 90℃ for 60 min at pH 4. It was observed that an increase in extraction pH value up to 12 results in higher K/S values on wool fabric, while a further increase in extraction pH had a negative effect on K/S values. This might be due to the polyphenolic nature of colorant molecules, as shown in Figure 1, which are ionized to phenoxide ions in basic pH. This ionization is increased with the increase in extraction pH up to 12, resulting in higher solubility of colorant molecules in the extract. However, it was found that a further increase in alkalinity could destroy the structure of the colorant and results in lower K/S values on wool. So, the pH range of 10–12 can be used during extraction to achieve higher color strength on wool.

Figure 4.

Effect of extraction pH on the K/S (λ = 490 nm) values of dyed wool samples.

Effect of extraction time

In order to optimize the time of extraction, the time was varied from 30 to 180 min by keeping the pH (12), temperature (90℃) and MLR (1:40) constant.

The extracts obtained after various time intervals were used for exhaust dyeing of wool fabric using the optimum dyeing conditions, that is,. MLR 1:25, 90℃ for 60 min at pH 4. The effect of extraction time on the K/S of dyed fabric can be seen in Figure 5. It is obvious that the K/S of dyed wool increased initially with the increase in extraction time up to 120 min. When the extraction was carried out for 120 min, the K/S of dyed fabrics reached its maximum. Beyond 120 min, there was a slight decrease in the K/S of dyed fabric. Hence, 120 min was taken as the optimum extraction time.

Figure 5.

Effect of extraction time on the K/S (λ = 490 nm) values of dyed fabric.

Effect of extraction temperature

In order to optimize the temperature of extraction, it was varied from 50 ºC to 100ºC by keeping the pH (12), time (120 min) and MLR (1:40) constant. The extracts obtained at various extraction temperatures were used for the exhaust dyeing of wool fabric using the optimum dyeing conditions, that is, MLR 1:25, 90℃ for 60 min at pH 4. Figure 6 shows the effect of extraction temperature on the K/S of dyed wool. It is obvious from the results that the K/S value of dyed fabric was increased with the increase in the extraction temperature. Therefore, 100℃ was taken as the optimum temperature for extraction. Temperatures above 100℃ were not used because they can cause damage to protein-based fiber (wool). Hence, the extraction temperature of 100℃ can be used as the optimum in order to obtain appreciable color strength.

Figure 6.

Effect of extraction temperature on the K/S (λ = 490 nm) values of dyed fabric.

Morphology of dyed samples

The effect of dyeing temperature on the fiber morphology was also checked by scanning electron microscopy (SEM). SEM images of undyed and dyed wool at 90℃ are given in Figures 7(a) and (b), respectively, showing the structure of fibers after dyeing. This figure clearly shows that the fibers have retained their structure without any damage after all the processes of dyeing.

Figure 7.

Scanning electron microscopy images of wool samples: (a) undyed; (b) dyed at 90℃.

Effect of material-to-liquor ratio

In order to optimize the MLR during extraction, the MLR was varied from 1:10 to 1:60 by keeping the pH (12), temperature (100 ºC) and time (120 min) constant. The extract obtained after various extraction MLRs was used for the exhaust dyeing of wool fabric using the optimum dyeing conditions, that is, MLR 1:25, 90℃ for 60 min at pH 4. Figure 8 reveals that with the increase in MLR from 1:10 to 1:40, there was an increase in the K/S of dyed fabric. When the MLR exceeded 1:40, the color strength K/S value of dyed fabric gradually decreased. This might be due to the maximum extraction of colorants at the 1:40 ratio and a further increase in the liquid ratio, which resulted only in the dilution of the colorant molecules and hence resulted in lower K/S values of the dyed fabric. Hence, the MLR was optimized at 1:40.

Figure 8.

Effect of material ratio on the K/S (λ = 490 nm) values of dyed fabric.

FTIR analysis of extracted natural dye

The FTIR spectrum of Caulis spatholobi extract is shown in Figure 9. This spectrum clearly shows two prominent peaks at 3436 and 1626 cm⁻¹, which can be assigned to hydroxyl (phenolic) and carbonyl groups, respectively. This is in agreement with the already published results²³ that Caulis spatholobi stem extract consists of a large number of polyphenolic flavonoids containing –OH and C=O groups, as shown in Figure 1. Another report²⁸ also shows that the FTIR spectra of different plant extracts contain strong absorption bands at ∼3433 and ∼1640 cm⁻¹, which are related to the stretching vibrations of the –OH (phenolic) and C=O groups, respectively, of lipids and flavonoids. Therefore, this FTIR spectrum (Figure 9) helps one to conclude that the chemical nature of the natural dyes of the stem extract is polyphenolic. These –OH and C=O groups contribute toward the fixation of natural dye molecules with the fabric substrate through mordanting.

Figure 9.

Fourier transform infrared spectra of Caulis spatholobi natural dye.

Effect of mordanting methods

Dyeing and mordanting of wool fabrics was carried out using various mordants and different mordanting techniques, as mentioned in Figure 3; the color characteristics of the dyed fabrics are reported in Table 1. These results indicate that mordant-dyed fabrics in most cases show higher K/S values than the fabric dyed without mordant. On comparing various mordanting methods, in all cases, post-mordanted samples exhibited higher K/S values than pre-mordanted and meta-mordanted samples. In both the cases of pre-mordanting and meta-mordanting techniques, the same sequence of K/S values is observed, that is, copper sulfate > ferrous sulfate > zinc sulfate > un-mordanted > aluminum sulfate; however, in the case of the post-mordanting technique, the sequence was found to be copper sulfate > ferrous sulfate > zinc sulfate > un-mordanted > aluminum sulfate. Here it clear that in all the three techniques, copper sulfate mordanted fabric showed higher K/S values than the other mordants. It can also be observed from the results in Table 1 that all four mordants changed the tone of dyed fabrics as compared to samples dyed without mordant. When ferrous sulfate, zinc sulfate, copper sulfate and aluminum sulfate were used as mordants, fabrics showed black, dark red, reddish brown and yellow shades, respectively, while fabric dyed without mordant exhibited a light reddish shade. The metal ions in the mordanting substances (e.g. Fe²⁺ ion in ferrous sulfate, Cu²⁺ ion in copper sulphate, etc.) have the ability to make coordination complexes²⁹ and coordination bonds simultaneously³⁰ with the dye molecules and the fabrics. In this way, the dye molecules are firmly fixed with the substrate. Since wool is polyamide in nature, the metal ions form some bonds³¹ with the nitrogen and oxygen atoms of the wool polymeric structure and the remaining bonds are formed with hydroxyl and ketonic groups of dye molecules, as represented in Figure 10.

Figure 10.

Wool mordant dye complex.

Table 1.

Color strength measurements of dyed wool samples

		Test results				Images of dyed samples
Mordant and mordant dyeing process		L*	a*	b*	K/S	Images of dyed samples
Blank (no mordants)		52.27	15.2	9.24	2.29
Ferrous sulfate	①	49.72	2.38	5.51	2.94
	②	49.32	2.62	4.93	2.91
	③	41.04	3.54	3.09	3.93
Zinc sulfate	①	55.06	13.56	14.34	2.35
	②	53.27	8.99	10.02	2.50
	③	50.77	14.11	14.23	3.19
Copper sulfate	①	53.91	9.93	16.14	3.98
	②	46.03	12.19	13.13	5.80
	③	38.47	13.78	10.64	7.58
Aluminum sulfate	①	62.29	10.8	16.12	1.94
	②	62.14	12.49	13.54	1.82
	③	52.17	14.03	12.3	2.80

Note: ① pre-mordanting; ② meta-mordanting; ③ post-mordanting.

Fastness properties

Table 2 shows the colorfastness measurements of wool samples dyed by various mordanting methods. All the colorfastness tests were performed following the standard testing protocols.⁶ Significant improvement in washing and light fastness was observed in the case of all mordants and mordanting techniques. However, rubbing and perspiration fastness remained almost the same, but were improved in the case of the meta-mordanting technique. Among the four selected mordants, ferrous sulfate, zinc sulfate and aluminum sulfate rendered higher light fastness values than copper sulfate in the case of pre-mordanting and post-mordanting; however, in the case of meta-mordanting it was same for all mordants. So, it is clear from Table 2 that the usage of mordants and mordanting techniques could improve the fastness properties as well as provide a variety of shades on wool fabric.

Table 2.

Colorfastness measurements of dyed wool samples

Dyeing process		Washing fastness	Dry rubbing fastness	Wet rubbing fastness	Perspiration fastness		Light fastness
Dyeing process		Washing fastness	Dry rubbing fastness	Wet rubbing fastness	Acid	Alkaline	Light fastness
No mordanting		2	4	3	3	3	3
Pre-mordanting	④	3	4	3	3–4	3–4	5
	⑤	3–4	4	3–4	3–4	3–4	5
	⑥	3–4	4	3–4	3–4	3–4	5
	⑦	3–4	4	3–4	3–4	3–4	4
Meta-mordanting	④	3	4–5	3	3–4	3–4	5
	⑤	3–4	4–5	4	3–4	3–4	5
	⑥	3–4	4–5	4	3–4	3–4	5
	⑦	3–4	4–5	4	3–4	3–4	5
Post-mordanting	④	3	4	3–4	3	3–4	5
	⑤	3–4	4	3–4	3–4	3–4	5
	⑥	3–4	4	3–4	3–4	3–4	5
	⑦	3–4	4	3–4	3–4	3–4	4

Note: ④ ferrous sulfate; ⑤ aluminum sulfate; ⑥ zinc sulfate; ⑦ copper sulfate.

Conclusion

This research focused on exploring Caulis spatholobi for the extraction of natural dye. The extraction conditions, namely pH, time, temperature and MLR, were optimized as 12, 100℃, 120 min and 1:40, respectively. Wool fabric was dyed at optimum wool dyeing conditions using the exhaust method. In addition, the effects of various mordants and mordanting techniques were studied and found to be helpful in improving the colorfastness and achieving a variety of color shades. The future study of Caulis spatholobi natural dye should be focused on the improvement of color fastness and exploring the functional properties (antimicrobial, ultraviolet (UV) protection, anti-fungal, mosquito repellent) of dyed wool fabric.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Key Research and Development Program (Project Number 2017FB039201).

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