Optimization of the polyester fabric dyeing process using coumarin as a green carrier

Abstract

The present study aims to evaluate the application of coumarin as a green carrier alternative for dyeing of polyester fabrics, as well as to optimize key dyeing parameters in order to obtain greater color strength (K/S) at lower temperatures than 130°C using single azo class dispersed dye. For this purpose, a full-factorial design was used to study the influence of the single and interactive effects of four factors involved in the dyeing process, namely, pH, temperature, and coumarin and dye concentrations. The chosen technique was a 24-factorial, one-center point, and three replicates at the center point resulting on a response surface, which has shown an increase of the color strength of five times at 90°C, and of three times at 100°C when compared to dyeing at the same temperatures without the use of a carrier. In addition, excellent fastness to washing and to rubbing were obtained.

Keywords

Coumarin carrier dyeing polyester low temperature

Polyethylene terephthalate (PET) fiber has been gaining ground in the textile industry due to its unique properties such as: ease of drying, high resistance to wrinkling, having a low cost benefit and being easily mixed with other types of fibrous inputs.¹ Thus, polyester fibers have become one of the most produced fibers, with a global demand that has increased over the years.^2,3 However, as this fiber has a hydrophobic characteristic, does not have active chemical groups, and has a glass transition temperature (Tg) around 80°C,⁴ dyeing of aromatic polyester becomes difficult under normal atmospheric conditions, requiring the use of high temperatures under pressure to dye it (usually at 130°C) and this is reflected in high dyeing costs and special equipment.^5,6

For PET dyeing, disperse dyes are usually used,⁷ which are poorly soluble in water, with the aid of dispersants. Several methods of synthesis for disperse dyes are described in the literature.⁸ The different types of dyes (anthraquinone dyes, methine dyes, nitrodiphenylamine dyes, azo dyes) can be applied to textile fibers, depending on the types of fixatives chosen.^8–12 Carriers can also be used, which facilitate the adsorption and diffusion of dyes at temperatures below 130°C, usually at 100°C.⁵ Yet, most carriers currently available on the market are harmful to the environment.^7,13 Carriers have problems with poor light resistance, high toxicity, unpleasant odor, high wastewater treatment costs, are poorly biodegradable, and contribute to environmental contamination.^5,7,13–15 Among the auxiliaries which can be used as carriers are butyl benzoate, methylnaphthalene, dichlorobenzene, diphenyl, and o-phenylphenol.^16,17

Due to growing environmental concern, stricter regulations for textile dyeing and finishing processes have led to the increased search for new ways to reduce the environmental damage caused by these processes.^13,18 As a result, there has been a need for the textile industry to develop new dyeing processes for polyester that reduce environmental impacts and are more economically viable. There are already studies related to the application of alternative carriers in combination with a low proportion of conventional carriers to reduce the consumption of toxic carriers or as their substitutes in dyeing polyester fabrics at low temperatures (in the range of 75–100°C), thus being an option for a clean and sustainable environment dyeing.^7,13,19,20

Use of ortho-vanillin (o-vanillin) and para-vanillin to replace toxic carriers was reported in dyeing at low temperatures (90°C) with two disperse dyes, of low and high molecular weight, thus being an option for a less polluting dyeing process. Acceptable absorption and washing strength for the ortho-vanillin carrier was achieved, and the non-toxicity of these carriers was verified by the USEtoxTM model, which is an environmental model for characterizing human health and ecotoxic impacts in comparative assessment and for classifying chemicals according to their inherent hazard characteristics.⁷

Microemulsions containing a low proportion of a non-toxic organic solvent and alternative dyeing auxiliaries (o-vanillin and coumarin) were prepared under ultrasound and turned out to be an option for dyeing polyester at temperatures below 100°C with low molecular weight disperse dyes.¹³ This research demonstrated that both o-vanillin and coumarin positively influenced the behavior of the polyester dyeing system. As a result, it exhibited acceptable exhaustion after 120 min for dyeing at 75–95°C.

The kinetics of PET dyeing at temperatures under 100°C (83, 90, 95, and 100°C) by using low-molecular weight disperse dyes, were evaluated by a microemulsion system with a low proportion of n-butyl acetate, comparing two auxiliaries (o-vanillin and coumarin). It was found that the adsorption rate constant of both dyes increased with the temperature. In addition, o-vanillin led to a greater dye adsorption and color strength than coumarin. In terms of hot press fastness and wash fastness, acceptable results were obtained and being slightly better for o-vanillin when compared to coumarin (with gray scale ratings sometimes 4–5 for coumarin and 5 for vanillin).¹⁹

In a recent investigation, Jalali et al.²⁰ analyzed the mixture of two components of carrier agents, a chlorobenzoyl derivative (CTM), Levegal PEW (N-alkyl phthalimide structure), and vanillin in order to reduce the consumption of toxic carrier agents (1/6 of the ideal amount) mixed with vanillin. As a result, there was compatibility of the commercial carrier agents with that of vanillin, and these mixtures led to a greater adsorption of dyes compared to each individually, with excellent results of dyeing fastness.

It is noteworthy that, among the alternative carriers, coumarin has been gaining special attention. Coumarin (2H, 1-benzopyran-2-one) is a white crystalline compound with a very characteristic, sweet, and pleasant odor. It has a low molecular weight (146.143 g.mol⁻¹), with a melting point between 68–70°C, and a boiling point of 298–302°C. When dissolved in chloroform, it absorbs at a maximum wavelength of 272 nm in ultraviolet light.²¹ In the free state it is soluble in organic solvents such as ethanol, chloroform, diethyl ether, and partially soluble in hot water, being slightly soluble in water at room temperature, with solubility of 1.7 g.l⁻¹ at 20°C.²² Coumarins (1,2-benzopyran) and their derivatives are widely distributed in the plant kingdom. They consist of a large class of phenolic substances found in plants and are made from the fusion of benzene and 1,2-pyrone ring.^23–25 Such compounds are applied as anticoagulants,^26,27 flavoring additives in foods and cosmetics,²⁸ in the preparation of insecticides,²⁹ optical brighteners, disperse fluorescent dyes, and laser dyes.³⁰ Coumarins are divided into four main subtypes: simple coumarins (derived from coumarin per se), furanocoumarins, pyranocoumarins, and coumarins substituted in the lactone ring.³¹

The present study aims to carry out the dyeing process on 100% polyester fabrics by using coumarin as a carrier, at temperatures below 130°C. The novelty is the advantage of using coumarin directly in the dyeing bath without previous preparation of microemulsion. The influence of process variables, such as dye/coumarin concentrations, pH, and temperature, are evaluated by a full factorial design of experiments. The main objective is to improve the polyester dyeing process, resulting in intense colors, generating effluent with lower pollution load, and lower energy consumption.

Materials and methods

Materials

For this study, a twill fabric was used, with 1 × 2 ligament, 100% PET composition and average weight of 109.0 g.m⁻². The Disperse Red SE-3B (CI Disperse Red 343) was supplied by Golden Technology São Paulo/Brazil. The analytical grade coumarin came from Labsynth, São Paulo, Brazil. Distilled water was used as transport medium/solvent, Goldlevel E-PES (Golden Technology) as dispersing/leveling agent, sodium hydroxide 10.0 g.l⁻¹, and acetic acid 1.0 g.l⁻¹ for pH adjustment to 5.00, 7.00, and 9.00. The non-ionic surfactant Renex 100 from Oxiteno SA was used for pre-dyeing wash. The post-dyeing reduction clearing was done with use of industrial grade sodium dithionite 87%, Renex 100, and sodium hydroxide (36°Be - Baumé degrees density).

The chemical structures of the coumarin and disperse dye are shown in Table 1.

Table 1

. Chemical structures of the alternative carrier and dye

Reagent	Chemical structure
Coumarin
Disperse red SE-3BCI Disperse red 343³²

Experimental

Preliminary study of optimal concentration of coumarin

Initially, the PET fabric was pre-washed with Renex 100 2.0 g.l⁻¹ at 80°C for 30 min. The fabric was dried in a stenter at 120°C for 2 min. Then the samples were cut into small pieces of 2.0 g each.

The samples were dyed, with different concentrations of coumarin on weight of fabric (% owf). The dyeing was carried out by exhaustion in the ALT-B TOUCH 35 equipment from Mathis, São Paulo, Brazil. Table 2 shows the process parameters.

Table 2.

Formulation of the polyester fabric dyeing process

Reagent	Concentration (% owf)
Coumarin	0.0; 1.0; 2.5; 5.0; 7.5; 10.0;12.5; 15.0; 17.5; 20.0
Disperse red SE-3B	1.0
Dispersing/leveling agent	3.0

For the dyeing process, a bath ratio of 1:25 (g.ml⁻¹) was used. The pH was adjusted to 5.0. Dyeing started at room temperature (approximately 30°C), and the bath was heated to 100°C with a temperature gradient of 2°C/min. The bath was kept for 30 min at 100°C, then was cooled to 40°C with a gradient of 4°C/min as shown in Figure 1.

Figure 1.

Dyeing chart for preliminary study of the optimal concentration of coumarin.

After dyeing, the samples were washed in a reductive medium with a bath ratio of 1:50 (g.ml⁻¹) for removal of the unfixed dye. The reductive clearing was performed according to Figure 2. Table 3 shows the reduction clearing bath composition.

Figure 2.

Chart of post-dyeing reduction clearing.

Table 3.

The reduction clearing bath composition

Reagent	Concentration (g.l⁻¹)
Sodium dithionite	2.0
Renex 100	1.0
Sodium hydroxide 36°Bé	4.0

The samples were dried and analyzed by reflectance spectrophotometry using the Konica Minolta CM-2600d spectrophotometer to identify the optimal coumarin concentration.

Color strength

The colorimetric coordinates and the color strength (K/S) were obtained using the Konica Minolta CM-2600d spectrophotometer, with D65 illuminant, 9.0 mm beam aperture, and 10° standard observer. The dyed substrate was analyzed as the average of five measurements at different points. The K/S values were obtained according to the American Association of Textile Chemists and Colorists (AATCC) evaluation procedure 6-2008 based on the Kubelka-Munk Equation 1.³³

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

(1)

where R is the decimal fraction of reflectance of the dyed substrate, K is the absorption coefficient, and S is the light scattering coefficient.

The instrument was calibrated with a white and black balance standard according to the Konica Minolta calibration procedure.

Color difference

The color difference was defined by the numerical comparison of the color of a sample with the standard (sample used as a color reference), indicating the differences in absolute color coordinates (L*, a*, b*) between the sample and the standard, known as delta (Δ). From Equation 2, the difference between two colors, according to the Commission Internationale de l'Eclairage (CIE), in the color space L*a*b* is calculated to identify inconsistencies or deviation from a standard color and to be able to control the color of the dyed samples more effectively, obtaining the total difference (ΔE).³⁴

Δ E=[(Δ L^{*})^{2} + Δ a^{*})^{2} + {(Δ b^{*})}^{2}]^{1 / 2}

(2)

where ΔL* = L*_sample–L*_standard; Δa* = a*_sample–a*_standard; Δb* = b*_sample–b*_standard.

Statistical analysis

The experimental design and data analysis were performed by Design‐Expert V8.0 StatEase Inc., USA. Dye and coumarin concentrations, temperature, and pH were chosen as independent variables assigned in a statistical design of experiments (DOE) in which the response variable was the color strength (K/S). Thus, the combined effects of these variables on the response variable were studied using a 2⁴ full factorial with four central points. Table 4 shows the structure of the full factorial design used in this study, considering all combinations of two levels for each factor (minimum (–1), maximum (+1)), and the central point (0), which represents the midpoint of each factor range.

Table 4.

Variables and control levels for the design of experiments

Symbol	Variables	Coded levels
Symbol	Variables	–1	0	+1
A	pH	5.00	7.00	9.00
B	Coumarin concentration (%owf)	0.00	5.00	10.00
C	Dye concentration (%owf)	0.50	0.75	1.00
D	Temperature (°C)	90	110	130

In addition to the variables defined by the statistical program Design-Expert for the 20 experiments (pH, coumarin concentration, dye concentration, temperature), fixed dyeing parameters were used: the bath ratio of 1:25 (g.ml⁻¹), the dyeing time of 30 min, and the dispersant concentration (3.0% owf).

Color fastness to washing

The wash fastness test was performed in the Wash Tester machine, model WT-B by Mathis according to ISO 105-C06 standard.³⁵ The color change and the degree of color transfer to the core were evaluated using the gray scale.

Color fastness to rubbing

The dry and wet rubbing fastness tests were performed using the Mesdan 198b electronic Crockmeter. The test was performed according to ISO 105-X12: 2001. The staining of the rubbing cloth specimen was then assessed using the Grey Scale for Staining.³⁶

Breaking strength and elongation of textile fabrics (Grab test)

The colored fabric samples were analyzed regarding their tensile strength in the Mesdan Tensolab 3000 Plus equipment, according to the technical standard ASTM D 5034-09. The distance between the jaws was 75 mm and a speed of 250 m.min⁻¹ were used.³⁷

Scanning electron microscopy (SEM)

Surface characterization of samples before and after the dyeing process at 100°C and 130°C was performed using a scanning electron microscope Hitachi TM-3000.

Results and discussion

Preliminary study of the optimal concentration of coumarin

As can be seen in Figure 3, the dye uptake increases as the concentration of coumarin rises. However, from 10% owf of coumarin on, the K/S value does not change significantly, indicating that the carrier concentration has reached a limiting value.

Figure 3.

Color strength (K/S) values as a function of different concentrations of coumarin in dyeing polyethylene terephthalate (PET) fabric.

In addition, thus, confirming that the increase in the concentration of this alternative carrier in the dyeing bath significantly influences the adsorption of the dye by the fiber. When comparing the concentration of the residual dyebaths in the absence and presence of different concentrations of coumarin (Figure 4), the concentration of the residual liquor decreases with increase in concentration of coumarin. This confirms the effect of concentration of coumarin on the dye pick up by the fiber.

Figure 4.

Comparison of the color intensity of residual liquor of dye baths in the absence and presence of different concentrations of coumarin (1% to 10% owf).

On the other hand, dyeing baths with coumarin concentrations of 12.5% owf and above show with coumarin concentrations from 12.5% owf a gradual increase in the color intensity of the residual liquor, which is still hot. However, as they are left to cool, a precipitate of crystallized coumarin appears, which shows that there is an excess carrier of the mentioned concentrations, as shown in Figure 5.

Figure 5.

Hot dyebaths (a), and at ambient temperature (b).

The color intensity difference between the dyed samples without coumarin and with different concentrations of coumarin is shown in Table 5. An increase in the color intensity difference of the dyed samples is observed, as coumarin concentration increases, due to the increase in color strength. However, for samples dyed with a concentration above 10.0% coumarin owf there was no significant color difference (ΔE). This indicates that above 10.0% coumarin concentration, no significant increase in dye uptake occurs and coumarin may be wasted.

Table 5.

Colorimetric coordinates, color strngth (K/S) and color difference between samples dyed in different concentrations of coumarin and the sample dyed without coumarin

Coumarin concentration in dyeing (% owf)	L*	a*	b*	K/S	ΔE
0.0	52.82	55.00	−1.68	54.47	1.80
1.0	51.53	56.07	−1.01	61.78	1.80
0.0	52.82	55.00	−1.68	54.47	3.35
2.5	50.13	56.63	−0.52	70.01	3.35
0.0	52.82	55.00	−1.68	54.47	8.01
5.0	46.69	59.15	1.61	100.52	8.01
0.0	52.82	55.00	−1.68	54.47	11.41
7.5	44.21	60.18	3.73	131.18	11.41
0.0	52.82	55.00	−1.68	54.47	14.48
10.0	41.78	60.59	5.83	170.06	14.48
0.0	52.82	55.00	−1.68	54.47	15.27
12.5	41.07	60.60	6.30	182.40	15.27
0.0	52.82	55.00	−1.68	54.47	15.00
15.0	41.13	60.52	5.93	180.13	15.00
0.0	52.82	55.00	−1.68	54.47	15.84
17.5	40.57	60.79	6.52	193.45	15.84
0.0	52.82	55.00	−1.68	54.47	15.02
20.0	41.32	61.08	5.83	181.30	15.02

From these results, the coumarin concentration was set to 10.0% owf for the following experiments to be optimized by statistical analysis, as well as wash fastness, rubbing fastness, and tensile strength measurements.

Experimental design

Considering the previous preliminary results, the color strength (K/S) was then measured in 20 replicated runs with different combinations of the four factors.³⁸

The mathematical model in coded terms obtained from a multiple regression of experimental data (Table 6) is described in Equation 3.

\begin{array}{l} \frac{K}{S} = 106.43 + 9.25 \times 10^{- 4} A + 12.98 B + 25.54 C \\ + 66.21 D - 0.69 A B + 0.13 A C + 0.42 A D \\ + 1.16 B C - 13.12 B D + 23.79 C D + 0.065 A B C \\ + 0.94 A B D + 1.23 A C D - 0.23 B C D - 0.28 A BCD \end{array}

(3)

Table 6.

Factors, levels and central points studied in the factorial design

						K/S
	Run	A	B	C	D	Experimental	Predicted
17	1	0	0	0	0	155.0895	106.4300
5	2	−1	−1	1	−1	14.7072	14.7141
6	3	1	−1	1	−1	14.2422	14.2459
19	4	0	0	0	0	157.9585	106.4300
20	5	0	0	0	0	163.1189	106.4300
4	6	1	1	−1	−1	61.8987	61.8859
11	7	−1	1	−1	1	122.7141	122.7141
18	8	0	0	0	0	155.5927	106.4300
12	9	1	1	−1	1	121.7690	117.9733
15	10	−1	1	1	1	220.9391	231.8396
7	11	−1	1	1	−1	72.2648	72.2641
16	12	1	1	1	1	224.5786	224.5759
13	13	−1	−1	1	1	219.4407	219.4341
10	14	1	−1	−1	1	122.9611	122.9759
8	15	1	1	1	−1	66.6582	66.6559
3	16	−1	1	−1	−1	64.4680	64.4741
14	17	1	−1	1	1	222.9088	222.9259
2	18	1	−1	−1	−1	16.4267	16.4159
9	19	−1	−1	−1	1	125.7727	125.7841
1	20	−1	−1	−1	−1	11.1219	11.1041

The model predictions are in good agreement with the experimental values, as shown in the right column of Table 6.

From an analysis of Equation 3, it can be seen that the parameters that showed statistical significance for the process with a 95% confidence interval were B (coumarin concentration), C (dye concentration), D (temperature), and interactions CD (dye concentration/temperature) and BD (coumarin concentration/temperature. The pH factor (A), as well as the other combinations of variables that fell below the t-value line, have no significant effect on the process. Figure 6 highlights the absolute values of the effects of main factors and the effects of interaction of factors.

Figure 6.

Pareto chart.

Analysis of variance (ANOVA)

The significance of the model terms has been evaluated by ANOVA and significance was found with p-values <0.05 (Table 7).

Table 7.

Analysis of variance table - response K/S

Partial sum of squares - Type III
Source	Sum of squares	Degrees of freedom	Mean square	F Value	p-Value Prob>F
Model	95146.823	15	6343.122	470.300	0.0001
A-pH	1.37E-05	1	1.37E-05	1.02E-06	0.9993
B-coumarin	2696.444	1	2696.444	199.923	0.0008
C-dye	10435	1	10435	773.685	0.0001
D-temperature	70131.8	1	70131.8	5199.799	<0.0001
AB	7.532	1	7.532	0.558	0.5091
AC	0.265	1	0.265	0.020	0.8975
AD	2.795	1	2.795	0.207	0.6799
BC	21.563	1	21.563	1.599	0.2954
BD	2752.949	1	2752.949	204.113	0.0007
CD	9057.957	1	9057.957	671.586	0.0001
ABC	0.067	1	0.067	0.005	0.9481
ABD	14.163	1	14.163	1.050	0.3809
ACD	24.185	1	24.185	1.793	0.2730
BCD	0.873	1	0.873	0.065	0.8157
ABCD	1.225	1	1.225	0.091	0.7828
Std dev.		3.67	R²		0.9996

Standard deviation = 3.67; R² = 0.9999; adjusted R² = 0.9974; predictable R² = 0.95; CV% = 3.15; adequate precision = 63,043.

The coefficient of determination (R²) was found to be 0.9996, denoting that the model replicates well the observed outcomes for a 95% confidence limit, giving good estimates of the response in the studied range.

It can be seen in Table 7 that the determination of coefficients R², adjusted R², and predictable R² are close to one, thus indicating that the values obtained experimentally are in agreement and adjusted with the proposed statistical model. Adequate accuracy measures of the signal-to-noise ratio, where a ratio greater than four is considered acceptable. Adequate precision ratio of 63.043 was obtained, which indicates that the quadratic model is suitable. The F-value model of 470.30 implies that the model is significant. And “Prob>F” values less than 0.0500 indicate that the terms of the model are significant. In this case, B, C, D, BD, CD are significant model terms. While values greater than 0.1000 point out that the terms of the model are not significant.

The normal plot of the residuals shows clearly the significant factor effects, which deviate from the straight line, as presented in Figure 7.

Figure 7.

Normal probability plot of the residuals.

Response surface methodology

As the model proved to be statistically significant, it was possible to create response surfaces in order to verify the ranges of the input variables under study that contribute to the increase in the K/S property.

As can be seen, Figure 8 shows a marked increase in the strength of the color with the increase in the concentration of dye, which is expected. On the other hand, the coumarin concentration has a significant effect from 90°C, with an increase in the K/S value as the temperature increases.

Figure 8.

Response surfaces as a function of the dyeing temperature of the polyester fabric.

According to Figure 9, it should be pointed out that there is a decrease in the influence of coumarin in the process as the temperature increases. This is explained by the fact that, at high temperatures, such as 130°C, there is a great increase in the movement of the amorphous regions, causing a greater opening of the polymer. Furthermore, there is a considerable increase in the kinetic energy of the dye molecules in solution.^5,39 These two factors, synergistically, may improve the diffusion of the dye into the same fiber without the aid of a carrier.

Figure 9.

Effect of coumarin concentration on dyeing of polyester fabrics at low temperatures.

It is noteworthy to mention the influence of coumarin on dyeing at 90°C, with an increase in K/S as coumarin concentration increases. Although K/S values at 90°C are low, they went up from 14.24 (without coumarin) to 66.65 (with 10% coumarin), that is more than four times, indicating coumarin concentration has effects that are more significant at low temperatures. Azo dispersed dyes can suffer degradation if the pH is in strongly acidic or alkaline conditions (with pH>9 and lower pH<4).³⁹ According to the experimental plan, the pH variation in the range of 5–9 had no significant influence on the K/S value.

Color fastness to washing

All the dyed samples have shown excellent fastness, both for color fading and staining. Table 8 shows the values assessed according to the gray scale.

Table 8.

Results of color fastness to washing

Sample	Temperature (°C)	Color staining	Color fading
No carrier	100	4	4
Coumarin 10% owf	100	4/5	4/5
No carrier	130	4	4/5
Coumarin 10% owf	130	4	4/5

A slightly better color transfer result was achieved for the sample dyed at 100°C with coumarin when compared to the other dyeings. This is explained by the increase in the adsorption of the dye, which was more effective at temperatures below 130°C.

For color change, samples dyed at 100°C/130°C with coumarin and 130°C in absence of coumarin obtained a grade 4/5 with a slightly higher fastness than samples dyed at 100°C without coumarin with grade 4.

Coumarin influences swelling of the polymer chains at 100°C. When the temperature reaches 130°C, the polymer chains are already open, which increases diffusion of the dye into the fiber. Thus, the amount of dye on the fiber surface is decreased, improving the color fastness to wash.

Color fastness to rubbing

The results of the color fastness tests wet and dry rubbing are shown in Table 9.

Table 9.

Color fastness to dry and wet rubbing

Sample	Temperature (°C)	Dry	Wet
No carrier	100	4/5	4/5
Coumarin 10% owf	100	5	5
No carrier	130	5	5
Coumarin 10% owf	130	5	5

Samples dyed with coumarin and those dyed at 130°C without coumarin were classified as grade 5 regarding the results of color fastness to dry and wet rubbing, without color fading. For samples dyed without coumarin at 100°C, results of light staining (4/5) were obtained, yet a very satisfactory result.

As mentioned before, the swelling phenomenon at 100°C facilitates adsorption/diffusion effects into the fiber. Coumarin acts as a carrier by lowering the temperature at which such effects occur, usually 130°C. Then, at 100°C, the dye is carried to the bulk of the fiber, giving rise to better fastness results, both to washing and rubbing.

The carrier action of coumarin in the dyeing of PET fabric is mainly due to the ability of carriers with a smaller molecular size (146.15 g.mol⁻¹ coumarin) compared to the molecular size of the dye (410.49 g.mol⁻¹ CI Disperse Red 343 dye) to penetrate into the amorphous regions of polyester, and open the macromolecular structure of the polymer at temperatures above the Tg. Such carriers can also partially plasticize the polyester fibers, decreasing the Tg of the polymer. Thus, coumarin molecules diffuse more quickly into the amorphous regions of PET, causing the polymer to swell and creating spaces between its macromolecular chains, facilitating the access of the dye molecules within the fiber.^15,19 In this way, coumarin contributes to increase the adsorption/diffusion of the dye and to the better color fastness.

Breaking strength and elongation of polyester fabric (Grab test)

Figures 10 and 11 show the results for tensile strength and elongation in the weft direction, respectively, for dyeings at 100°C and 130°C with and without coumarin.

Figure 10.

Average tensile strength in the weft direction for dyeing at 100°C and 130°C with and without coumarin.

Figure 11.

Tensile elongation in the weft direction for dyeing at 100°C and 130°C with and without coumarin.

Regarding the average maximum tensile strength (N), and the average elongation (%) results did not change for all samples, indicating that the presence of coumarin in the dyebath does not affect mechanical properties of the fabrics.

SEM

In order to verify changes on fiber surface, dyed samples were compared to undyed ones by SEM. Although there was presence of powdery oligomer deposits on the fiber surface, no pits or voids in the dyed samples were noticed. Images presented in Figure 12 (with 1000× magnification), show the presence of powdery oligomer deposits on the surface, which are produced as a side-reaction during manufacture of polyethylene terephthalate.⁴⁰

Figure 12.

Scanning electron micrographs of undyed (a); dyed samples at 100°C: without coumarin (b); with coumarin (c); and at 130°C: without coumarin (d), and with coumarin (e).

Satisfactory results of color fastness to washing and rubbing were obtained and there was no change in the mechanical properties for polyester fabrics dyed with coumarin at 100°C. Thus, using coumarin as an alternative carrier has the advantage of avoiding the use of toxic chemicals, without risk of deformation of the fabric, using low temperature dyeing, with the possibility of reusing wastewater as natural herbicides.⁴¹ Moreover, it can be recommended to the industry, due to the properties of the coumarin being used as an agent with antimicrobial activity,^42,43 antioxidant,⁴³ insecticides,⁴⁴ antimutagenic, non-genotoxic, and biodegradable.^17,19,41

Based on the results, a dyeing procedure was developed, as shown in Table 10.

Table 10.

Best dyeing procedure

Component	Percentage owf
CI Disperse red 343	1.0
Goldlevel E-PES (anionic dispersing agent)	3.0
Coumarin	10.0
Bath ratio=1:25 g.ml⁻¹
Temperature=100°C

High K/S values can be obtained by dyeing at 100°C, avoiding energy expenditure of conventional dyeing (at 130°C). In addition, the method allows using a neutral pH without the need for chemicals to adjust it.

Conclusion

Processes that are less aggressive to the environment are the focus of a growing area of research. Highly toxic carriers are replaced by more economical and environmentally friendly alternatives.

The effect of coumarin on the dyeing of polyester fabric as a green carrier, based on the results obtained, shows that coumarin is considered an efficient alternative carrier for dyeing PET at temperatures below 130°C. The response surface graph showed that coumarin applied in dyeing from 90°C reaches values up to five times higher in the color strength property when compared to dyeing in the same conditions without a carrier.

In addition, the increase in temperature generates a greater opening of the amorphous zones of the polymer, causing a reduction in the effect of coumarin on the K/S values.

The factorial design parameters with statistical significance for dyeing the PET fabric with CI Disperse Red 343 dye using coumarin were: coumarin concentration, dye concentration, temperature, interactions dye concentration/temperature, and coumarin concentration/temperature. The pH variation in the range of 5.0–9.0 had no significant influence on the K/S value, making it possible to use neutral pH in dyeing with coumarin and, thus, avoid use of chemicals to adjust the pH.

The dyeing at 100°C with coumarin gave better results of tensile strength and fastness to washing and rubbing of the samples. Tensile strength and elongation of the PET fabric were not affected by the presence of coumarin in the dyeing bath. Coumarin as an alternative carrier has the advantage of avoiding the use of toxic chemicals, without risk of fabric deformation. Low temperature dyeing brings the possibility of reusing effluents as natural herbicides. Therefore, this process can be suggested as a very attractive green method for dyeing polyester fabric.

Footnotes

Declaration of conflicting interests

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

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: Financial support from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) is gratefully acknowledged.

ORCID iDs

CN Lima

MA Granato

FR Oliveira

References

Romão

Spinacé

MAS

, and De Paoli

Poli(tereftalato de etileno), PET: Uma revisão sobre os processos de síntese, mecanismos de degradação e sua reciclagem. Polímeros 2009; 19: 121–132.

Mishra

Charan Rath

Das

AP.

Marine microfiber pollution: A review on present status and future challenges. Mar Pollut Bull 2019; 140: 188–197.

Henry B, Laitala K and Klepp IG. Microplastic pollution from textiles: A literature review. Project report no. 1. Consumption Research Norway SIFO, Oslo and Akershus University College of Applied Sciences, Oslo, 2018.

Fité

FJC.

Dyeing polyester at low temperatures: Kinetics of dyeing with disperse dyes. Text Res J 1995; 65: 362–368.

Wang

, et al. Carrier-free and low-temperature ultradeep dyeing of poly(ethylene terephthalate) copolyester modified with sodium-5-sulfo-bis(hydroxyethyl)-isophthalate and 2-methyl-1,3-propanediol. ACS Sustain Chem Eng 2016; 4: 3285–3291.

Georgiadou

Tsatsaroni

Eleftheriadis

, et al. Disperse dyeing of polyester fibers: Kinetic and equilibrium study. J Appl Polym Sci 2002; 83: 2785–2790.

Pasquet

Perwuelz

Behary

, et al. Vanillin, a potential carrier for low temperature dyeing of polyester fabrics. J Clean Prod 2013; 43: 20–26.

Shuttleworth L and Weaver MA. Dyes for polyester fibers. In: Waring DR and Hallas G (eds) The Chemistry and Application of Dyes. Boston, MA: Springer, 1990, pp. 107–163.

Patel

H M

Dixit

B C.

Synthesis, characterization and dyeing assessment of novel acid azo dyes and mordent acid azo dyes based on 2-hydroxy-4-methoxybenzophenone-5- sulfonic acid on wool and silk fabrics. J Saudi Chem Soc 2014; 18: 507–512.

10.

Patel

H M.

Synthesis, characterization and dyeing behaviour of heterocyclic aCId dyes and mordant acid dyes on wool and silk fabrics. J Serb Chem Soc 2012; 77: 1551–1560.

11.

Patel H M. Synthesis, characterization and application of some novel mordent and heterocyclic disperse dyes based on 2-Butyl-3-(4-hydroxybenzoyl)benzofuran. Der Chemica Sinica 2011; 2: 89–96.

12.

Patel

HM.

Material applications of novel heterocyclic disperse and mordent dyes based on 2-butyl-3- (4-hydroxybenzoyl) benzofuran

Advances in Applied Science Research 2012; 3: 235–241.

13.

Carrion-Fite

Radei

Development auxiliaries for dyeing polyester with disperse dyes at low temperatures. IOP Conf Ser-Mat Sci 2017; 254: 082006.

14.

Mashaly

Abdelghaffar

Kamel

, et al. Dyeing of polyester fabric using nano disperse dyes and improving their light fastness using ZnO nano powder. Indian J Sci Technol 2014; 7: 960–967.

15.

Harifi

Montazer

Free carrier dyeing of polyester fabric using nano TiO₂.

Dyes Pigments 2013; 97: 440–445.

16.

Broadbent

AD.

Basic principles of textile coloration. West Yorkshire: Society of Dyers and Colourists, 2001.

17.

Salem

Tingimento têxtil: Fibras, conceitos e tecnologias. São Paulo: Blucher, 2010.

18.

Moore

Ausley

LW.

Systems thinking and green chemistry in the textile industry: Concepts, technologies and benefits. J Clean Prod 2004; 12: 585–601.

19.

Radei

Carrión-Fité

Ardanuy

, et al. Kinetics of low temperature polyester dyeing with high molecular weight disperse dyes by solvent microemulsion and agrosourced auxiliaries. Polymers 2018; 10: 200.

20.

Jalali

Rezaei

Afjeh

, et al. Effect of vanilla as a natural alternative to traditional carriers in polyester dyeing with disperse dyes. Fibers Polym 2019; 20: 86–92.

21.

Egan

O’Kennedy

Moran

, et al. The pharmacology, metabolism, analysis, and applications of coumarin and coumarin-related compounds. Drug Metab Rev 1990; 22: 503–529.

22.

Lake

BG.

Coumarin metabolism, toxicity and carcinogenicity: Relevance for human risk assessment. Food Chem Toxicol 1999; 37: 423–453.

23.

Petrul’ová-Poracká

Repčák

Vilková

, et al. Coumarins of Matricaria chamomilla L.: Aglycones and glycosides. Food Chem 2013; 141: 54–59.

24.

Maistro

Marques

Fedato

, et al. In vitro assessment of mutagenic and genotoxic effects of coumarin derivatives 6,7-dihydroxycoumarin and 4-methylesculetin. J Toxicol Environ Health A 2015; 78: 109–118.

25.

Venugopala

Rashmi

Odhav

Review on natural coumarin lead compounds for their pharmacological activity. Biomed Res Int 2013; 1–14.

26.

Dias ARSVG. Cumarinas: Origem, distribuição e efeitos tóxicos. MSc Diss, Instituto superior de Ciências da saude Egas Moniz, Brasil, 2015.

27.

Borges

Roleira

Milhazes

, et al. Simple coumarins and analogues in medicinal chemistry: Occurrence, synthesis and biological activity. Curr Med Chem 2005; 12: 887–916.

28.

Sproll

Ruge

Andlauer

, et al. HPLC analysis and safety assessment of coumarin in foods. Food Chem 2008; 109: 462–469.

29.

Araujo

Della Lucia

Moreira

, et al. Toxicidade de extratos hexânicos de plantas às operárias de ‘Atta laevigata’ e ‘Acromyrmex subterraneus’ (Formicidae: ‘Attini’). Rev Bras Agroecol 2008; 14: 106–114.

30.

Kalita

Kumar

Solvent-free coumarin synthesis via Pechmann reaction using solid catalysts. Microporous Mesoporous Mat 2012; 149: 1–9.

31.

Jain

P K

Joshi

Coumarin: Chemical and pharmacological profile. J Appl Pharm Sci 2012; 2: 236–240.

32.

World Dye Varity. Disperse red 343, http://www.worlddyevariety.com/disperse-dyes/disperse-red-343.html (2013, accessed 2 January 2020).

33.

American Association of Textile Chemists and Colorists (AATCC). AATCC Technical Manual. NC USA: Research Triangle Park, 2015; 90: 512.

34.

Konica Minolta. Identifying color differences using L*a*b* or L*C*H* coordinates, https://sensing.konicaminolta.us/us/blog/identifying-color-differences-using-l-a-b-or-l-c-h-coordinates/ (2020, accessed 15 February 2021).

35.

ISO 105-A01: 2010 and ISO 105-C06: 2010. Textiles – tests for colour fastness – part A01. General principles of testing. The International Organization for Standardization. www.iso.org.

36.

ISO 105-X12: 2016. Textiles – tests for colour fastness – part X12: Colour fastness to rubbing. ISO Standard, The International Organization for Standardization. www.iso.org.

37.

American Society for Testing and Materials. ASTM D5034-09: 2013. Standard test method for breaking strength and elongation of textile fabrics (Grab test). ASTM International. www.astm.org.

38.

Montgomery

DC.

Estatistica aplicada e probabilidade para engenheiros. 5th ed. Rio de Janeiro: LTC, 2012.

39.

Koh J. Dyeing with disperse dyes. In: Hauser, P. J. (ed.). Textile dyeing. Rijeka: InTech, 2011, pp. 195–220.

40.

Gacén

Salem

Oligômeros de poliéster PET Parte 1. Descrição, problemas e remédios. Química Têxtil 2007; 86: 34–47.

41.

Niro

Marzaioli

De Crescenzo

, et al. Effects of the allelochemical coumarin on plants and soil microbial community. Soil Biol Biochem 2016; 95: 30–39.

42.

Souza

Monache

Smânia

Antibacterial activity of coumarins antibacterial activity of coumarins.

Z Naturforsch C J Biosci 2015; 60: 693–700.

43.

Kubrak T, Podgorski R and Stompor M. Natural and synthetic coumarins and their pharmacological activity natural and synthetic coumarins and their pharmacological activity. Int J Clin Exp Med 2017; 15: 169–175.

44.

Hussain

Qamar Abbas

Reigosa

MJ.

Activities and novel applications of secondary metabolite coumarins. Planta Daninha 2018; 36.