Application of foam dyeing technology on ultra-fine polyamide filament fabrics with acid dye

Abstract

In this approach, the foam dyeing of polyamide filament fabrics with acid dye has been studied as a clean dyeing technology. The foam dyeing process parameters, including the blow ratio (BR), steaming temperature, time and humidity, were evaluated by color strength and color fastness. The results show that dodecanol and sodium carboxymethyl cellulose (CMC) mixed stabilizer could improve the foam stability and reduce the harm to human health. The optimum batch formula of dodecanol and CMC was 4:6. The K/S value reached 3.58 at 11 BR, 100℃ steaming temperature, 20 min and 6.59% fabric moisture content. Compared with the exhaust dyeing process, foam dyeing can achieve the same level of color fastness with a higher K/S value. These results suggest that foam dyeing is a simple and effective method for polyamide filament fabrics with acid dye, which can reduce the consumption of water, chemicals and energy, and accelerate production.

Keywords

foam dyeing polyamide filament fabrics mixed stabilizer color fastness

In recent years, there has been a turn in major government, leading to actions to conserve energy and reduce pollution for environmental protection. However, the dyeing of textiles consumes large amounts of electricity and thermal energy, of which roughly 50% is consumed in wet processing.¹ Polyamide filament fabrics as important garment materials are widely used in clothing (protective clothing, down jackets and stockings) because of their uniquely promising properties, such as high toughness, good elasticity, high thermal stability, good weatherability and excellent wearability.² However, polyamide filament fabrics cannot be dyed directly by pad dyeing due to their poor hygroscopicity.³ Polyamide filament fabrics are usually dyed by the batchwise exhaust dyeing method with special dyeing equipment, which consumes a lot of water and electric energy. However, the migration of dyes is serious due to the poor hygroscopicity for polyamide filament fabrics in the pad-mangle. Polyamide filament fabrics cannot be continuously dyed by pad dyeing because of this serious migration phenomenon. Therefore, there is a need to develop an effective and facile dyeing process for the dyeing of polyamide filament fabrics.

The foam dyeing technique is a low liquid loading and high energy saving process,^4,5 which might be useful as a continuous dyeing method for polyamide filament fabrics with acid dye. The foam dyeing process has been investigated as a high-efficiency method for the dyeing of textiles. In 1970s, foam dyeing technology was successfully applied in the dyeing of pile fabric.⁶ Li et al.⁷ analyzed the feasibility of the dyeing of cotton fabrics by using foam dyeing and optimized the process. Yu et al.⁸ investigated the foamability and stability of foam and the dyeing properties of reactive dye on cotton fabric, which was evaluated by the color strength and dye fixation rate. Dawson⁹ applied the foam paste to polyamide carpets by a rotary screen, horizontal pad, doctor roller and slots, which proved the commercial and environmental benefits of foam printing. However, these studies were performed on standard fibers.^10–14 There has been little research on ultra-fine polyamide filament fabrics. Thus, it is significant to study the application of foam dyeing on ultra-fine polyamide filament fabrics.

At present, the most effective stabilizer used for foam dyeing technique is dodecanol, which has proved to be a pretty good stabilizing agent.^15–18 However, dodecanol had a strong irritating odor, which is harmful to human health. To reduce the damage, it is essential to develop a new environment-friendly and low-cost stabilizer or mixed stabilizers.

In this paper, ultra-fine polyamide filament fabrics were dyed with acid dye through foam dyeing. The foaming formula (the stabilizer species and its addition amounts, the ratios of different stabilizers) was optimized according to the foam properties, such as foamability and stability. The stabilization mechanism of the selected stabilizers was analyzed. Furthermore, the influences of the foam dyeing process parameters on the foam properties and color strength were investigated, including the acid dye concentration, blow ratio (BR), steaming temperature, steaming time and fabric moisture content.

Materials and methods

Materials

Scoured and bleached ultra-fine polyamide filament fabrics (plain-weave, warp and weft fiber fineness 20 denier, warp and weft density 564 × 264 picks/10 cm, weight 29.5 g m⁻², thickness 210 µm) were obtained from the market (China). Weak acid Brilliant Blue Rawl, sodium dodecyl sulfate (SDS), sodium carboxymethyl cellulose (CMC-Na), dodecanol, sodium alginate (SA) and guar gum were purchased from Sinopharm Chemical Reagent Co., Ltd (China). All chemicals were of analytical regent grade and used as received.

Preparation of the foam

Foam volume and half-life values are usually used to evaluate the foam properties. It has been reported that the foam stabilizer plays an important role in the foaming system.^7,8 According to the method of Yu et al.,⁸ various foaming agents and stabilizers were added to 100 mL deionized water. After stirring for 3 min at 1100 r min⁻¹, the foam volume and half-life value results were obtained. The half-life was the time that the aqueous liquid in the foam liquid below was precipitated to 50 mL. All the experiments were performed under the same processing condition (relative humidity 65%, room temperature 25℃). Each measurement was repeated at least three times, and the average value was calculated.

Foam dyeing process

Before foam dyeing, the dyeing liquors containing surfactant, stabilizer and the selected dye (ANOSET Red 2BF, Yellow R and Brilliant Blue Rawl) were stirred by mechanical agitation. The pH value was fixed at 5.5 by adjusting by acetic acid. For the foam process, a 02BEC01CFE auto-foam machine (UK) was employed (as shown in Figure 1). To obtain the dyeing foam, the dyeing liquors were firstly added to the stainless steel dye vat of 2000 cm³ capacity in a laboratory-scale auto-foam dyeing machine. Then the dyeing foam was used to dye the ultra-fine polyamide filament fabrics by the applicator (one foam head) with the feed speed of 0.30 g L⁻¹, rotor speed of 960 r min⁻¹ and fabric speed of 15.55 r min⁻¹. Finally, the foam-dyed fabrics were padded by the padder at room temperature without any drying. The pick-up was kept at around 30%. This was followed by steam fixation. The effects of steaming temperature, steaming time and fabric moisture content (computing method as shown in formula (1)) were investigated. Then, both sides of colored fabrics were treated with anti-staining agents (2 g L⁻¹, liquor ratio 40:1) at 60℃ for 20 min. At the end of treatment, the treated samples were rinsed in tap water and allowed to dry. All the experiments were repeated three times and only average values are presented. The K/S values were determined after soaping and washing

SH (%) = \frac{(W_{s} - W_{o})}{W_{o}} \times 100 %

(1)

where SH is the moisture absorption of the ultra-fine polyamide filament fabrics under a certain steaming humidity, W_S is the weight of the fabrics after steaming and W₀ is the weight of fabrics before steaming.

Figure 1.

Diagram of the foam dyeing process.

Color strength measurement

Colorimetric data (K/S values and color difference values) of dyed ultra-fine polyamide filament fabrics were determined using a Data Color SF 600 plus spectrophotometer under D65 illuminant.

Color fastness

Rubbing fastness assessments were performed on a Crockmeter (James H. Heal Co., UK) by following ISO 105-X12-2016. Soaping fastness assessments were performed in a Gyrowash (James H. Heal Co., UK) according to ISO 105-C06:2010. Light fastness measurements were carried out as per ISO 105-B02-2013.

Results and discussion

Optimization of the foam system

For satisfactory foam dyeing results, the foam system must have good foamability and stability. Toward this direction, sodium lauryl sulfate was selected as the foaming agent (see the first section). Moreover, various foam stabilizers, including dodecanol, sodium alginate, CMC-Na and guar gum, have been used to attempt to make the foam with strongly steady properties for dyeing and finishing processes. The optimal ratios of the foam formulation are determined by foam volume and half-life (t_1/2) values. Under the selected experimental conditions (3 g L⁻¹ SDS, 0.3 g L⁻¹ stabilizer, 1100 r min⁻¹ stirring rate), the effects of different stabilizers on the foam volume and half-life (t_1/2) of the foam system are as shown in Figure 2. For dodecanol, CMC-Na and sodium alginate, the t_1/2 value of the foam system was much higher than that without a stabilizer (see Figure 2(a)), but that of the guar gum foam system was decreased slightly. Because adding these stabilizers could strengthen the surface viscoelasticity and weaken the fluidity of the foam film, the time of foam rupture becomes longer.^19,20 The reasons for the t_1/2 decrease of the guar gum foam need further research. However, the foam volume was decreased when dodecanol, CMC-Na, sodium alginate and guar gum were used as stabilizers (see Figure 2(b)). The decrease of foam volume might be due to stabilizers suppressing the generation of foam to some extent.

Figure 2.

The effects of different stabilizers on (a) t_1/2 and (b) the foam volume of the foam system. CMC-Na: sodium carboxymethyl cellulose. SA: sodium alginate.

Dodecanol showed good foam properties with t_1/2 of 155 s and foam volume of 475 ml, which makes it suitable as a stabilizer for this foam system. This result is consistent with the literature reports.²⁰ However, Dodecanol is a combustible liquid with an irritating smell. To obtain a foam system with low irritation and good foam properties, it is essential to apply mixed stabilizers. Therefore, dodecanol and CMC-Na were blended as a stabilizer in this paper. Figure 3 shows the effects of the proportion of CMC-Na on the foam properties of the system, where 3 g L⁻¹ of SDS and 0.3 g L⁻¹ of complexes were mixed. For 100% CMC-Na, the foam volume was up to the maximum (440 ml). However, the foam volume did not change significantly when the proportion of CMC-Na was less than 80% (as shown in Figure 3(a)). The half-life was improved obviously by the adding of CMC-Na, and the proportion of CMC-Na had greater influence on t_1/2 (as shown in Figure 3(b)). For pure dodecanol and pure CMC-Na, the half-lives were 130 and 60 s, respectively. The foams of the mixed stabilizers were more stable than that of the pure one, which indicates that there is a synergistic effect between dodecanol and CMC-Na. The half-life of the foam was increased with the amount of addition (CMC-Na) from 20% to 60%. However, the half-life decreased with the further increasing of CMC-Na. The maximum value of t_1/2 reached 240.6 s when the proportion of CMC-Na was 60%.

Figure 3.

The effects of the proportion of sodium carboxymethyl cellulose (CMC-Na) on the (a) foam volume and (b) half-life.

The synergistic effect of dodecanol and CMC-Na might be proposed, as both the elasticity and viscosity improved on the surface of the foam film (see Figure 4). For the foam system without stabilizers, the foam could only exist for a very short time (unstable) due to the repulsive force between SDS, which could not be applied in the foam dyeing process (see Figure 4(a)). The foam was more stable when dodecanol was added to the foam liquor. Adding dodecanol to the foam liquor could reduce the repulsive force between SDS molecules at the air–water interface via the formation of a hydrogen bond between the –OH of dodecanol and the –OSO^3– of SDS. Hence, dodecanol increased the density of SDS molecules at the air–water interface, simultaneously enhancing the strength of bubble films (see Figure 4(b)) and t_1/2 (see Figure 2(b)). Adding CMC-Na (see Figure 4(c)) could markedly increase the foam viscosity, making the foam distribution more uniform and not easy to break, resulting in the improving of t_1/2 (see Figure 3(b)). The mixed systems of dodecanol and CMC-Na (4:6) can significantly improve foam stability. Therefore, dodecanol and CMC-Na were selected as the foam stabilizers in the foam system.

Figure 4.

Schematic illustrations of the synergistic effect between dodecanol and sodium carboxymethyl cellulose (CMC-Na): (a) only sodium dodecyl sulfate (SDS) without stabilizers; (b) SDS with dodecanol and (c) SDS with dodecanol and CMC-Na.

To evaluate the feasibility of the acid dye foam for dyeing, the dyeing liquors containing a surfactant, stabilizer and selected dye (from 30 to 60 g L⁻¹) were stirred by mechanical agitation, and the dyeing foam was obtained. Before foam dyeing, the properties of the dyeing foam were also investigated, the results of which are shown in Figure 5 (the size and distribution of the foam are shown in the second section). The dyeing foam exhibited good foam properties, and the acid dye dosage had a certain effect on the foam volume and t_1/2. With the increasing of the acid dye amount, the foam volume decreased continuously and t_1/2 was enhanced constantly. When the acid dye dosage was over 50 g L⁻¹, t_1/2 increased to 378 s, which was stable enough for the foam dyeing process. The foam volume reached the minimum at the dye dosage of 60 g L⁻¹. We can conclude that the dyeing foam is suitable for foam dyeing, and light and dark fabric could be obtained by changing the acid dye dosage.

Figure 5.

The effect of acid dye dosage on the (a) foam volume (b) and half-life.

Optimization of the foam dyeing process

Besides the foam volume and t_1/2 of the foam system, the foam dyeing process also has a large influence on the results of ultra-fine polyamide filament fabric dyeing, including the BR, steaming temperature, steaming time and fabric moisture content. Herein, the effects of the foam dyeing process on the color strength were also investigated.

The effect of the BR (ranging from 6:1 to 11:1, other parameters were invariant) was investigated, and the results of dyeing are shown in Figure 6 (K/S value) and Figure 7 (reflectance curve). It can be seen from Figure 6 that the K/S value increased with the increasing of the BR from 6:1 to 11:1. In contrast, the reflectance decreased with the increase in the BR, as is seen in Figure 7. The improvement of the K/S value or the decrease of reflectance might be caused by the reduction of the water in foam, which had an impact on the concentration of acid dye in foam under the same foam output. With the increasing of the BR, the concentration of the dye in the dyeing foam was enhanced, further leading to an increase in the amount of dye fixation in polyamide filament fabrics, so that the color of the fabric was much deeper.²¹ So BR 11 was much more suitable for the foam dyeing of ultra-fine polyamide filament fabrics. The foam dyeing mechanism of acid dye will be discussed later.

Figure 6.

K/S value curves of the fabrics with different blow ratios (BRs).

Figure 7.

Reflectance curves of the fabrics with different blow ratios (BRs).

To evaluate the effects of steaming on the color yield, the steaming temperature, steaming duration and fabric moisture content were investigated, respectively. The K/S value results of the fabrics treated with various steaming temperatures are shown in Figure 8 (BR 11, dye dosage 4 g L⁻¹, steaming for 15 min, maximum absorbance wavelength 650 nm). The steaming temperature had a large effect on the K/S value of the fabrics. The K/S value increased from 5.51 to 6.41 as the steaming temperature increasing from 90℃ to 100℃, and the K/S value reached the maximum when the steaming temperature was 100℃. This could be explained as follows: an increase in temperature could lead to the increase of the diffusion rate of the acid dyes, and therefore cause more dye molecule adsorption and diffusion into the fiber, which improved the K/S value. When the steaming temperature was kept at 120℃, the K/S value gradually decreased to 4.75. This might be due to the decrease in the equilibrium adsorption capacity of acid dyes and hence the decrease in K/S value. Thus, the best steaming temperature was 100℃.

Figure 8.

The effect of steaming temperature on the K/S value.

As presented in Figure 9, the K/S value at the maximum absorbance wavelength of 650 nm was varied with the steaming duration when the other conditions were fixed (steaming temperature of 100℃ and fabric moisture content of 6.59%). As shown in Figure 9, the K/S value of the fabrics increased during the first 20 min and then approached a constant value as the time further increased. The K/S value reached its saturation of 6.43 when the steaming duration was 20 min. The K/S value increase might be due to the improvement of the dye-uptake during the steaming. When the steaming time was increased to 20 min, the dye-uptake achieved balance, and the final K/S value remained constant.

Figure 9.

The effect of the steaming duration on the K/S value.

In order to understand the effects of the steaming process parameters on the dyeing performance, the K/S values of the fabrics colored by foam dyeing with various moisture content were measured under the same conditions (steaming temperature of 100℃ and steaming time of 20 min), and the results are shown in Figure 10. Obviously, the K/S value was significantly increased when the moisture content was increased from 0% to 6.95%. When the moisture content of the fabrics was 0% (that is, drying without any water), the fabrics could be colored, which was far beyond expectation. The possible reason was that the ultra-fine polyamide filament fabrics still had an equilibrium moisture content of about 4.5%, which mainly existed in the form of bound water. These water molecules as carriers played an important role in the diffusion of the dyes. The dyes could enter into the instantaneous holes of the fiber through these carriers. However, this water content was very low, and the final K/S value was not high. The K/S value was remarkably enhanced with the increasing of the moisture content of the fabric. The reason for this improvement might be as follows: with the increase of moisture content, the free water content within the fiber increased, which caused the enhancing of the degree of the swelling, then the diffusion rate of the dye increased, and finally the K/S value increased.¹⁶ The further increase of the moisture content had little effect on the dyeing performance. This was because steaming required a large amount of moisture to promote the dissolution and diffusion of dye molecules inside the fiber. Therefore, the dyeing performance could be adjusted by changing the moisture content of the fabric.

Figure 10.

The effect of the fabric moisture content on the K/S value.

The mechanism of foam dyeing is illustrated in Figure 11. Most of the dyes were distributed on the surface of filaments, and few were in the interspace between the polyamide filaments after the padder, which relied mainly on physical adsorption. Because there were very few holes at room temperature, the degree of swelling was limited. Steaming at high temperature with moisture content could introduce instantaneous holes in the fibers, which was beneficial to the diffusion and fixation of acid dyes in the fiber (as shown in Figure 11).

Figure 11.

Schematic diagram of the foam dyeing mechanism.

Comparison of foam dyeing and exhaust dyeing

To evaluate the practicality of the foam dyeing, a contrast test using exhaust dyeing with the same fabrics and dyes was carried out (dyed at 90℃ for 45 min, rinsed by warm and cold water), and the results are shown in Figure 12 and Table 1. We can see that the K/S value at the maximum absorbance wavelength of 650 nm (Figure 12) and the color strength (Table 1) were better than that of exhaust dyeing. The soaping fastness and dry and wet rubbing fastness of the foam dyeing were level 4–5, level 5 and level 3–4, respectively. The soaping fastness was equivalent to that of exhaust dyeing, as well as rubbing fastness, which can meet the requirements of the garment industry. In comparison with exhaust dyeing, the foam dyeing was a simple and efficient method (see the third section). The most important advantage of foam dyeing is water and energy saving. Therefore, foam dyeing technology can be utilized in polyamide filament fabrics with acid dyes.

Figure 12.

K/S value comparison between foam dyeing and exhaust dyeing.

Table 1.

Comparison of dyeing effects between foam dyeing and exhaust dyeing

Methods	Weak acid Brilliant Blue Rawl, % o.w.f.	Color strength	Soaping fastness	Rub fastness
Methods	Weak acid Brilliant Blue Rawl, % o.w.f.	Color strength	Soaping fastness	Dry RF Wet RF
Foam dyeing	0.9	3.5895	4–5	5 3–4
Exhaust dyeing	0.9	3.2892	4–5	5 3

RF: rubbing fastness.

Conclusion

In summary, the foam dyeing of polyamide filament fabrics with acid dye is feasible and effective. A dodecanol and CMC-Na mixed stabilizer can improve the foam stability and reduce the harm to human health. The optimum batch formula of dodecanol and CMC were 4:6. The K/S value reached 3.58 at 11 BR, 100℃ steaming temperature, 20 min steaming time and 6.59% fabric moisture content. Compared with the exhaust dyeing process, foam dyeing can achieve the same level of color fastness with a higher K/S value. These results suggest that foam dyeing is a simple and effective method for polyamide filament fabrics with acid dyes, which can reduce the consumption of water, chemicals and energy, and accelerate production.

Footnotes

Acknowledgement

The Henan Joint International Research Laboratory of Novel Textile Materials is gratefully acknowledged.

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 Zhengzhou Programs for Science and Technology Development (Grant No. 153PKJGG129) and the Scientific Research Foundation of the Higher Education Institutions of Henan Province (Grant No. 16A540005).

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