Application of nanobubble technology to the dyeing process of polyester fabrics and the investigation of fabrics dyeing properties

Abstract

Nanobubble technology has recently emerged as a promising approach for improving mass transfer and dye–fibre interactions in textile dyeing systems. Nanobubbles are generally defined as gas bubbles with diameters typically smaller than 200 nm that remain stable in aqueous media for extended periods due to their high internal pressure and surface charge characteristics These unique physicochemical properties allow nanobubbles to influence interfacial processes in liquid systems and enhance the transport of dissolved species, including dye molecules. As a result, nanobubble-enriched dye baths can provide improved dye dispersion and more efficient transport of dye molecules towards textile fibre surfaces. In this study, polyester fabrics were dyed with nanobubble water and with soft water, and the CIELAB colour values, washing, and rubbing fastness values were examined after dyeing. It was found that the washing and rubbing fastness values after dyeing with nanobubble water were very close to those after dyeing with soft water. The effects of dye molecular size, dye concentration, yarn twist level, and yarn linear density on the K/S values were found to be statistically significant. For all parameters, higher K/S values were obtained when nanobubble-containing solutions were used.

Keywords

polyester nanobubble microbubble yarn dyeing washing fastness colour values

Introduction

Polyester fibre is the most widely used synthetic fibre in the world. It is used as a raw material in the manufacture of many products due to its properties such as high strength and water repellency. The presence of benzene rings in the structure of polyester makes its dyeing process exceedingly difficult; therefore, high temperature (HT) dyeing is a frequently preferred method for dyeing polyester. The amount of water used during dyeing and the wastewater coming from dyeing create serious threats to the environment. In general, one of the main problems of the whole textile industry is that finishing processes lead to serious environmental pollution. It is for this reason that studies are today being carried out to develop new and more environmentally friendly, effective and economical processes and methods to be employed in textile finishing processes.

The newest of these method is based on the use of oxygen and air nanobubble suspension water, which is a method that has been widely used in food, cosmetic, agriculture, and water treatment industries, and that has been newly started to be used in textile finishing processes.

Nanobubbles (NB_s) are nanoscopic gaseous (typically air) cavities in aqueous solutions that have the ability to change the normal characteristics of water.^1,2 Ordinary bubbles have a diameter which range from 1 µm and larger.^3,4 Nanobubble size classification, according to ISO 20480-1-2017, is given in Figure 1.⁵

Figure 1.

Nanobubble size classification (µm).⁵

Larger bubbles quickly rise to the surface of a liquid and collapse. Microbubbles tend to gradually decrease in water, and after they remain relatively still in the water for a long time, the gas within them dissolves into the water and bubbles disappear, while the nanobubbles can remain that way for months and do not burst out at once.⁶ Nanobubbles which are <100–200 nm⁷ in diameter will randomly drift owing to what is termed, Brownian Motion and can remain in liquids for an extended period of time. Furthermore, NB enriched water has entirely different physicochemical properties than water without NB_s.⁴ Nanobubbles present high mass transfer efficiency and oxidation ability because of the increased gas-liquid contact area and the generation of hydroxyl radicals when collapsing.^2,3,8–12

One of the primary mechanisms by which nanobubbles enhance textile dyeing is through the improvement of mass transfer within the dye bath.¹³ The extremely large surface area of nanobubbles increases the contact between gas, liquid, and solid phases, thereby intensifying diffusion processes.¹⁴ In addition, the negative surface charge commonly associated with nanobubbles can generate electrostatic interactions with charged dye molecules, promoting their mobility and transport towards fibre surfaces.⁶ Experimental studies have demonstrated that nanobubbles can accelerate the liquid-phase diffusion of various dyes under different pH conditions, indicating their strong influence on dye transport behaviour in aqueous environments.^15,16

Another important mechanism is related to the hydrodynamic effects generated by nanobubbles. During their formation, movement, or collapse, nanobubbles can produce localised microstreaming and turbulence in the surrounding liquid.^17,18 These micro-scale fluid motions enhance the mixing behaviour within the dye bath and reduce boundary layer resistance around textile fibres. Consequently, dye molecules can penetrate more easily into the fibre structure, which leads to improved dye uptake and more uniform colour distribution. In textile dyeing systems where diffusion limitations often reduce dye fixation efficiency, this micro-mixing effect plays a critical role in improving overall dyeing performance.¹³

Nanobubbles can also influence the dyeing process through physicochemical and chemical effects at the fibre–liquid interface. Depending on the type of gas used, nanobubbles may generate reactive species such as hydroxyl radicals or reactive oxygen species when they collapse or dissolve in water.^19,20 These reactive species can enhance surface activation of textile fibres and increase the affinity between dye molecules and fibre surfaces.¹⁶ This phenomenon has been widely investigated in water treatment and pollutant degradation processes, where nanobubble collapse has been shown to produce localised high-energy conditions capable of initiating chemical reactions.²¹

Furthermore, nanobubbles can improve the dispersion stability of dye particles within the dye bath. Due to their surface charge and interfacial properties, nanobubbles may prevent aggregation of dye molecules and maintain a more homogeneous dye distribution in the liquid phase.²² This effect ensures that dye molecules remain evenly distributed throughout the dye bath, reducing uneven dyeing or shade variation during the process.²³

From a process perspective, the integration of nanobubble technology into textile dyeing systems may lead to several operational advantages. Enhanced mass transfer and improved dye dispersion can reduce the amount of auxiliary chemicals required for dyeing, such as salts or dispersing agents.¹³ In addition, the improved interaction between dye molecules and fibres may increase dye fixation efficiency, thereby reducing dye loss in wastewater streams. These improvements contribute to lower chemical consumption, reduced wastewater pollution, and improved sustainability of textile dyeing processes.²⁴ Recent studies have also demonstrated that nanobubble technology can play a role in the decolorisation of textile dye wastewater and reduction of chemical oxygen demand, highlighting its potential environmental benefits for textile processing industries.¹⁶

There are different approaches for the nanobubbles production in the cases of surface and bulk nanobubbles. Electrolysis method, membrane method, cavitation method are the most efficient methods for bulk nanobubbles. In this study, nanobubble-containing water obtained by membrane method was used. The compression of gas through immersion into a liquid membrane is described as the “membrane method” for nanobubble production.²

In the membrane method, bubbles are produced by gas injection through holes of different diameters. The effect of hole size on the size and shape of the produced bubble is very important. In general, it was observed that the bubbles tend to be smaller, depart sooner, and remain more spherical for the smallest orifice.²⁵ For the larger orifices the bubbles tend to elongate vertically due the buoyancy action and depart in longer times with larger volumes. The idea here is to use compression of the wanted gas stream to dissolve it into liquid, which is subsequently released through a specially designed nozzle system, and finally to nucleate small bubbles as potential nanobubbles. A porous material, a membrane, could play the role of the array of orifices with different diameters in order to create a “cloud” of countless bubbles/nanobubbles of different sizes and shapes into a flowing aqueous/liquid is an efficient method for producing bulk nanobubbles. A membrane nanobubble generator is usually consists of the following components: a pressurised gas tank, a gas pressure regulator, a gas flow metre, and the porous membrane, usually a ceramic tube.² The designs of bubble generators are generally kept confidential and protected through patents (Figure 2).

Figure 2.

Decompression and gas–water circulation methods for the generation of MBs/NBs.²⁶

A literature survey on nanobubble technology showed that most of the scientific studies are focused on the study of the principles of nanobubble technology and the formation and detection of nanoparticles.^{18,20,27–34} However, it was also found that there is an increasing number of studies investigating the use of nanobubble technology in many sectors such as agriculture, medical, environmental, and engineering.^35–48

A review of the literature shows that there are few studies which have been performed with air and oxygen suspension water in textile wet processing^24,49; therefore, the present study is expected to provide useful information for both the textile plants and the companies that produce this technology.

Experimental

Materials and methods

In this study, 100, 150, and 270 denier polyester yarns with three different twist levels (400, 600, and 800 tpm) were used (Table 1). All polyester yarns were produced from the same raw materials and their production parameters were kept constant. Faycon CKM-01-S knitting machine with a gauge of 18 was utilised to produce the knitted fabrics. Dyeing and washing processes were carried out using soft water (S.W) and nanobubble water (NBW; Tables 2 and 3).

Table 1.

The properties of 100, 150, and 270 denier yarns.⁵⁰

Twist amount (turns/metre)	Dyeing method	Dyestuff concentration (%)	Dyestuff molecule size
400	Conventional	1	Small
		1	Large
		4	Small
		4	Large
	Nanobubble	1	Small
		1	Large
		4	Small
		4	Large
600	Conventional	1	Small
		1	Large
		4	Small
		4	Large
	Nanobubble	1	Small
		1	Large
		4	Small
		4	Large
800	Conventional	1	Small
		1	Large
		4	Small
		4	Large
	Nanobubble	1	Small
		1	Large
		4	Small
		4	Large

Conventional: Method using soft water, Nanobubble: Method using water containing nanobubbles.

Table 2.

The properties of soft water and nanobubble water.

Water properties	Soft water	Nanobubble water
Dissolved oxygen value (mg/l)	9.20 mg/l	10.35
pH value	8.37	8.35
Conductivity value (µs/cm)	319 µs/cm	36.13

Table 3.

Time-dependent changes in the average particle size, polydispersity index (PDI), and zeta potential of soft water, nanobubble-containing water (NBW), and dyeing solutions.

Solution type	Average particle size (nm)			Polydispersity index (PDI)			Zeta potential(mV)
Solution type	4 h	6 h	24 h	4 h	6 h	24 h	4 h	6 h	24 h
1	729.8	729.8	729.8	0.657	0.657	0.657	−13.4	−13.4	−13.4
2	415.3	545.9	601.8	0.436	0.384	0.685	−8.94	−6.83	−10.7
3	171.4	209.3	228.8	0.322	0.452	0.304	−12.1	−11	−13.3
4	91.53	97.61	117.4	0.208	0.184	0.204	−4.48	−3.66	−4.02

Solution 1: Soft water; Solution 2: Nanobubble-containing water; Solution 3: Acidic medium with nanobubble-containing water; Solution 4: Non-ionic surfactant with nanobubble-containing water.

The PET fabrics produced for the study were washed in warm water for 20 min using a Dyetech sample dyeing machine at a liquor ratio of 1:10, with a solution containing 2 g/l Na₂CO₃ and 2 g/l soap. Subsequently, the fabrics were dyed using C.I. Disperse Blue 56 (small molecules) and C.I. Disperse Blue 148 (large molecules) disperse dyes at concentrations of 1% and 4% (on weight of fabric). The dyeing procedure was carried out as follows: first, the chemicals listed in Table 4 were added sequentially. The dyeing process was initiated at room temperature (20°C), and the temperature was increased to 130°C at a heating rate of 1.5°C/min. The dyeing was maintained at this temperature for 45 min, after which the dye bath was cooled to 70°C at a cooling rate of 2°C/min. Following the dyeing process, a reduction clearing treatment was performed at a liquor ratio of 1:10 using the recipe provided in Table 5. This treatment was initiated at 20°C, and the temperature was raised to 75°C at a heating rate of 1.5°C/min. The reduction clearing was continued for 30 min, followed by the rinsing steps. The fabrics were first rinsed with warm water (50°C) and subsequently with cold water to complete the rinsing process. Finally, the fabrics were left to dry at room temperature. The same procedure was repeated using nanobubble-containing water. All dyeings were performed in triplicate.

Table 4.

Dyeing receipt.⁴²

1 g/l RUCOGAL STAR (dispersing agent/levelling agent)

1 g/l RUCO-ACID ATC (acidic buffers)

C.I. Disperse Blue 56 (small molecules)

C.I. Disperse Blue 148 (large molecules)

pH 4–4.5

Liquor ratio: 1:10

Table 5.

Washing receipt.

2 g/l RUCORIT RGI (reducing agent)

2 g/l NaOH

Liquor ratio: 1:10

The chemicals used in the dyeing processes and in the washing processes were given in Tables 4 and 5, respectively.

The molecular weights of the dyestuffs used in this study were 349 g/mol for C.I. Disperse Blue 56 (small molecule) and 413 g/mol for C.I. Disperse Blue 148 (large molecule). C.I. Disperse Blue 56 has an anthraquinone-based, compact structure with a relatively lower molecular volume, whereas C.I. Disperse Blue 148 possesses a heterocyclic structure containing azo and benzothiazole groups.

The nanobubble water used in this study was generated using a membrane method nanobubble generator supplied by BST Water Treatment Company. The water pressure was set to 20 psi (138 kPa; Pounds per square inch), the air pressure to a value between 100 (689 kPa) and 120 psi (827 kPa), and the air flow rate to 3 lpm (Litre per minute) to obtain nanobubble water. The pH, conductivity, and dissolved oxygen values of the nanobubble-containing water and soft water water were measured using a Hach Lange HQ instrument, following the procedures specified in the device standard. For each sample, three measurements were performed, and the average values were used.

Colour fastness tests of the fabrics to rubbing were performed according to EN ISO 105-12 using James H. Heal Crockmeter and results were measured on the grey-scale using Colour Mission Program. Colour fastness tests to domestic and commercial laundering of the fabrics were carried out according to EN ISO 105 C06. Colour measurements of the samples were conducted using a Konica Minolta CM-3600D spectrophotometer equipped with Colour Mission software (v.3.4.1, Argetek). The measurements were recorded within the wavelength range of 360–740 nm. To ensure representativeness, four readings were taken from different areas of each sample, rotating the specimen 90° between each measurement to minimise the effects of surface orientation. Colour measurements were performed on the technical face of the single jersey fabric. All measurements were performed under a D65 illuminant and a 10 standard observer. The results obtained from these tests were evaluated by SPSS statistical programme.⁴² All the fabrics were conditioned according to ISO 139 standard at relative humidity of 65 ± 4% and temperature of 20°C ±2 for 24 h prior to testing.

Result and discussion

The effects of the dyeing methods on the colour values of polyester fabric

Analysis of variance indicated that the dyeing method had a significant effect on the colour values K/S, L*, and a* of the fabrics (p < 0.05). According to the SNK test results and Figure 3, the K/S (colour strength) value was found to be higher for dyeing with nanobubble-containing water (23.54) than for dyeing with soft water (21.80). The L* (lightness) value was determined to be lower for dyeing with nanobubble-containing water (26.10) compared with dyeing with soft water (26.87), supporting the observed increase in colour strength. Consequently, darker colours were obtained when nanobubble-containing water was used. Although a statistically significant difference between the two methods was detected for a* values, the magnitude of this difference was relatively small (a* ≈ 0.5). The difference in b* values between the two dyeing methods was 0.09 and was not statistically significant.

Figure 3.

Colour values according to dyeing method.

The higher K/S values and lower L* values obtained with nanobubble-containing water can be attributed to enhanced mass transfer, improved dye dispersion stability, and increased dye–fibre interactions. Nanobubbles, due to their high surface area and negative surface charge, promote the transport and uniform distribution of dye molecules while reducing aggregation. Additionally, their affinity for hydrophobic surfaces enhances dye uptake in polyester fibres. As a result, deeper shades are achieved without significantly altering the chromatic coordinates (a* and b*), indicating that nanobubbles primarily influence colour depth rather than hue.^4,6,18,22,51

The effects of the dyestuff concentrations on the colour values of polyester fabrics

Within the scope of the study, the effects of the dyeing method with nanobubble-containing water at different concentrations were examined. All dyeing processes were performed at two different concentrations. According to the analysis of variance, the effects of dyestuff concentration on K/S, L*, a*, and b* colour values were found to be statistically significant (p < 0.05).

As shown in Figure 4, higher K/S and a* values were obtained at 4% dye concentration compared to 1% for both methods; this indicates that colour strength increases with the amount of dye absorbed by the fibre, which is a well-known phenomenon. Conversely, L* and b* values were lower, further supporting the higher K/S values. With increasing dyestuff concentration, the K/S value increased by 82% in soft water dyeing, whereas an increase of 88.5% was observed after dyeing with nanobubble-containing water.

Figure 4.

Colour values according to dyestuff concentration.

For dyeing with a 1% dye concentration, the K/S value obtained using the soft water method was 15.46, whereas a K/S value of 16.32 was obtained when nanobubble-containing water was used. In other words, an increase of 5.6% in the K/S value was observed with nanobubble-containing water. This improvement can be explained by the role of nanobubbles in enhancing mass transfer and stabilising dye dispersions.^6,22 This increase rose to 9.36% at a dye concentration of 4%. Nanobubbles may improve local concentration gradients and facilitate deeper dye penetration into the fibre structure.^15,18 As a result, the use of nanobubble-containing water may enable more efficient utilisation of dye, particularly at higher concentrations, leading to higher K/S values and lower L* values without substantial changes in chromatic coordinates (a* and b*). This may suggest that nanobubbles primarily enhance colour depth rather than altering the intrinsic hue of the dye, which is generally consistent with fundamental dyeing theory.⁵²

The effects of the dyestuff molecule sizes on the colour values of polyester fabrics

In this study, the effect of nanobubble water on the dyeing properties of polyester fabrics was investigated and dyestuff molecule size was also taken into consideration. All dyeing processes were carried out separately with large molecule and small molecule dyestuffs. According to the analysis of variance, the effects of dyestuff molecule size on the colour values K/S, L*, a*, and b* were found to be statistically significant (p < 0.05).

As shown in Figure 5, higher K/S and a* values were obtained after dyeing with large-molecule dyestuffs (K/S = 23.92; a* = 11.07) than after dyeing with small-molecule dyestuffs (K/S = 21.40; a* = 4.30) for two dyeing methods. Lower L* and b* values were also obtained, which is consistent with the K/S results.

Figure 5.

Colour values according to dyestuff molecule size.

Significant differences in the dyeing behaviour of C.I. Disperse Blue 56 (small molecular structure) and C.I. Disperse Blue 148 (large molecular structure) were observed in terms of diffusion kinetics and colour yield (K/S values), which can be attributed to their molecular characteristics and interactions with polyester fibres. It is well established that the diffusion coefficient of disperse dyes is inversely related to molecular size, leading to faster diffusion for smaller molecules.^52,53

For C.I. Disperse Blue 56, which possesses a lower molecular weight and smaller molecular size, a higher diffusion rate into the polyester fibre was observed. This behaviour may facilitate rapid dye uptake, particularly during the initial stages of dyeing. However, due to its relatively high mobility, dye molecules may exhibit less controlled distribution within the fibre at higher concentrations, which could limit build-up performance and reduce colour depth in darker shades.⁵³

In contrast, C.I. Disperse Blue 148, characterised by a larger molecular structure and higher molecular weight, was found to exhibit slower but more controlled diffusion behaviour. The lower diffusion coefficient may allow a more gradual penetration into the fibre, leading to a more uniform distribution within the amorphous regions of polyester. As a result, improved build-up properties and higher colour yield, particularly in medium to dark shades, may be achieved.⁵²

When nanobubble-containing water was used in the dyeing process, an increase in K/S values was observed for both dyes; however, the effect was more pronounced for C.I. Disperse Blue 148. This enhancement may be associated with the improved mass transfer characteristics provided by nanobubbles. Due to their high specific surface area, long-term stability, and surface charge, nanobubbles are known to enhance the transport and dispersion of dissolved species in aqueous systems.^13,51

For small molecular dyes such as C.I. Disperse Blue 56, where diffusion is already relatively rapid, the contribution of nanobubbles may remain limited. In contrast, for larger molecular dyes such as C.I. Disperse Blue 148, where diffusion can act as the rate-limiting step, the presence of nanobubbles may significantly enhance dye uptake efficiency by facilitating improved dye transport and fibre penetration.

When dyeing processes performed with nanobubble-containing water were evaluated in terms of dye molecular size and dyestuff concentration, increases in K/S values ranging from approximately 5.3%–17% were observed. As discussed in the Introduction, this enhancement may be attributed to the combined effects of enhanced mass transfer, micro-mixing phenomena, electrostatic interactions, and potential chemical activation processes associated with nanobubble systems.^13,51 These mechanisms may collectively contribute to improved dye diffusion and increased dye uptake efficiency.¹³

The effects of the yarn linear densities and yarn twist value on the colour values of polyester fabric

According to the analysis of variance, the effects of yarn linear density and yarn twist coefficient on the colour values (K/S, L*, a*, and b*) were found to be statistically significant (p < 0.05). According to the SNK test results, Figures 6 and 7, for both dyeing methods, as the yarn linear density and yarn twist coefficient increased, the K/S and a* values obtained after dyeing increased, whereas the L* and b* values decreased. These trends may be attributed to structural changes in the yarn, where increased fibre mass and higher twist levels lead to a more compact structure with reduced inter-fibre spacing. Such structural modifications are likely to enhance light absorption and reduce light scattering, resulting in higher apparent colour depth (K/S) and lower lightness (L*).^52,53

Figure 6.

Colour values according to yarn linear density.

Figure 7.

Colour values according to yarn twist value.

For all yarn linear densities and twist levels, higher K/S values were obtained with nanobubble-containing water compared to the soft water method. This enhancement may be associated with improved mass transfer and dye–fibre interactions provided by nanobubbles. Due to their high surface area and negative surface charge, nanobubbles are known to promote more uniform dye dispersion and potentially deeper penetration of dye molecules into the fibre structure.^13,51

The effects of the dyeing methods, the dyestuff concentration, the dyestuff molecule size, the yarn linear density, and the yarn twist amount on the colour washing fastness properties of polyester fabrics

Based on the analysis of variance, the dyeing method was found to have a statistically significant effect on the washing fastness values of CA, PES, and PAN multifibre fabrics (p < 0.05), whereas no significant effect was observed for CO, PA, and WO fibres. According to the SNK test results, the washing fastness values obtained using nanobubble-containing water were generally comparable to those achieved with soft water, with all values remaining above 4.5, indicating good overall washing fastness performance (Table 6). Slight decreases observed for CA, PES, and PAN fibres in the nanobubble system may be attributed to increased dye uptake and deeper penetration into the fibre structure, which could lead to a higher proportion of loosely bound dye molecules being present during washing.^52,53

Table 6.

SNK test results on the colour washing fastness values according to dyeing method.

Water
Factor	CA	CO	PA	PES	PAN	WO
Yarn linear density (denier)
100	4.94 (1)	4.99 (1)	4.92 (1)	4.99 (1)	5.00 (1)	4.89 (3)
150	4.96 (1)	4.97 (1)	4.86 (1)	4.96 (1)	5.00 (1)	4.72 (2)
270	4.93 (1)	5.00 (1)	4.88 (1)	5.00 (1)	4.99 (1)	4.60 (1)
Yarn twist value (turns per metre)
400	4.93 (1)	4.97 (1)	4.89(1)	4.96 (1)	5.00 (1)	4.71 (1)
600	4.96 (1)	5.00 (1)	4.89 (1)	4.97 (1)	4.99 (1)	4.74 (1)
800	4.94 (1)	4.99 (1)	4.88 (1)	4.99 (1)	5.00 (1)	4.76 (1)
Nanobubble water
Yarn linear density (denier)
100	4.56 (1)	4.99 (1)	4.92 (1)	4.82 (1)	4.83 (1)	4.68 (1)
150	4.53 (1)	4.99 (1)	4.93 (1)	4.83 (1)	4.88 (1)	4.63 (1)
270	4.42 (1)	4.93 (1)	4.94 (1)	4.76 (1)	4.93 (1)	4.57 (1)
Yarn twist value (turns per metre)
400	4.57 (1)	4.94 (1)	4.93 (1)	4.8194 (1)	4.86 (1)	4.68 (1)
600	4.47 (1)	4.99 (1)	4.90 (1)	4.8056 (1)	4.88 (1)	4.54 (1)
800	4.46 (1)	4.97 (1)	4.96 (1)	4.7917 (1)	4.90 (1)	4.65 (1)

CA: Acetate; CO: Cotton; PA: Polyamide; PES: Polyester; PAN: Polyacrylonitrile; WO: Wool.

(1) indicates the lowest value, while (2) and (3) indicate higher values. The same numbers in parantheses indicate that there is no statistical difference.

The effects of dyestuff concentration and molecular size were found to be statistically significant only for PA multifibre fabrics (Table 7), suggesting that polyamide fibres are more sensitive to variations in dye diffusion and fixation behaviour. In the soft water dyeing method, the decrease in washing fastness with increasing dye concentration for PA may be explained by the accumulation of unfixed dye molecules at higher concentrations, which are more easily removed during washing.⁵³ Similarly, the improvement in washing fastness with increasing molecular size in the soft water system may be associated with the lower diffusion rate and stronger fixation tendency of larger dye molecules.

Table 7.

SNK test results on the colour washing fastness values according to dyestuff concentration and dyestuff molecule size.

Water
Factor	PA		PA
Factor	1%	4%	Small Molec.	Large Molec.
Yarn linear density (denier)
100	5 (1)	4.83 (1)	4.83 (1)	5 (1)
150	4.97 (1)	4.83 (1)	4.72 (1)	5 (1)
270	4.97 (1)	4.78 (1)	4.75 (1)	5 (1)
Yarn twist value (turns per metre)
400	4.97 (1)	4.81 (1)	4.78 (1)	5 (1)
600	5 (1)	4.78 (1)	4.78 (1)	5 (1)
800	4.97 (1)	4.78 (1)	4.75 (1)	5 (1)
Nanobubble water
Yarn linear density (denier)
100	4.92 (1)	4.92 (1)	4.86 (1)	4.97 (1)
150	4.92 (1)	4.94 (1)	4.89 (1)	4.97 (1)
270	4.97 (1)	4.92 (1)	4.97 (1)	4.92 (1)
Yarn twist value (turns per metre)
400	4.94 (1)	4.92 (1)	4.92 (1)	4.94 (1)
600	4.92 (1)	4.89 (1)	4.86 (1)	4.94 (1)
800	4.94 (1)	4.97 (1)	4.94 (1)	4.97 (1)

(1) indicates the lowest value. The same numbers in parentheses indicate that there is no statistical difference.

In contrast, when nanobubble-containing water was used, no significant changes in washing fastness were observed with increasing dye concentration or molecular size for most multifibre fabrics. This behaviour may be attributed to the enhanced mass transfer, improved dye dispersion, and more uniform dye distribution provided by nanobubbles, which can promote more effective dye–fibre interactions and reduce the presence of unfixed dye.^13,51 As a result, a more stable dyeing system may be achieved, minimising the influence of process variables such as concentration and molecular size on washing fastness.

Overall, it can be concluded that nanobubble-assisted dyeing provides comparable washing fastness performance to conventional methods while offering a more stable dyeing behaviour against changes in dye concentration and molecular size, particularly for fibres sensitive to diffusion-related effects.

The effects of yarn linear density and twist level on colour fastness to washing were found to be statistically insignificant for both dyeing methods (p < 0.05)

The effects of the dyeing methods, the dyestuff concentration, the dyestuff molecule size, the yarn linear density, and the twist amount on the colour rubbing fastness properties of polyester fabric

Based on the results obtained, the rubbing fastness values achieved with nanobubble-containing water were found to be comparable to those obtained with soft water, with all values remaining at a high level, indicating good overall rubbing fastness performance. In both dyeing methods, dry rubbing fastness values were observed to be higher than wet rubbing fastness values, which may be attributed to the increased susceptibility of loosely bound dye molecules to removal in the presence of moisture during wet rubbing (Figure 8).

Figure 8.

Colour rubbing fastness values according to dyeing method.

The increase in dye concentration from 1% to 4% resulted in slight variations in rubbing fastness values; however, these changes were not found to be statistically significant (p > 0.05), suggesting that rubbing fastness is relatively insensitive to dye concentration within the studied range. Similarly, the effect of dyestuff molecular size was not statistically significant, although a slight increase in dry rubbing fastness and a minor decrease in wet rubbing fastness were observed for larger molecular dyes. This behaviour may be associated with differences in diffusion and fixation characteristics of disperse dyes, where larger molecules tend to exhibit more controlled diffusion but may still contribute to surface-associated dye under certain conditions.

Furthermore, the effects of yarn linear density and yarn twist on rubbing fastness were also found to be statistically insignificant (p > 0.05), indicating that rubbing fastness is primarily governed by surface dye fixation rather than bulk structural properties of the yarn. Overall, it can be concluded that nanobubble-assisted dyeing does not adversely affect rubbing fastness and provides performance comparable to conventional dyeing methods, while maintaining stable behaviour against variations in dye concentration, molecular size, and yarn structural parameters.

Conclusions

In this study, the applicability of nanobubble technology in polyester dyeing was evaluated under controlled experimental conditions. Knitted fabrics produced from polyester yarns with varying yarn counts and twist levels were dyed using different dye molecular sizes and concentrations, and the results were compared with those obtained using conventional soft water.

The results indicated that the washing and rubbing fastness values obtained with nanobubble-assisted dyeing were comparable to those achieved with soft water, with all values remaining within the good fastness range. In contrast, higher K/S values and lower L* values were obtained in nanobubble-assisted dyeing, indicating that colour strength was enhanced without adversely affecting fastness properties. These findings suggest that nanobubbles may improve dye diffusion and promote a more uniform distribution of dye molecules within the fibre structure.

The improved colour yield observed in nanobubble-assisted dyeing is considered to be associated with enhanced mass transfer, micro-mixing effects, electrostatic interactions, and possible chemical activation mechanisms. These factors are thought to facilitate more efficient dye transport and dye–fibre interactions, thereby increasing dye uptake compared to conventional soft water dyeing systems. Despite this improvement, the rubbing and washing fastness values of PES fabrics were found to remain predominantly at or above 4.5 for both dyeing methods, indicating that the increase in colour strength was achieved without compromising fastness performance.

Overall, the results indicate that nanobubble-assisted dyeing may provide a promising alternative to conventional dyeing methods by enhancing colour yield while maintaining comparable fastness properties. Furthermore, the relatively stable fastness behaviour observed under different process parameters suggests that nanobubble systems may offer improved process robustness.

Further studies are required to evaluate the applicability of nanobubble technology to different fibre types and dye classes, such as reactive, acid, and basic dyes. In addition, comparative investigations under industrial-scale conditions are recommended to more comprehensively assess the effects of nanobubble-assisted dyeing on dye uptake, colour strength, and fastness properties. Moreover, the potential of nanobubble technology to reduce the consumption of auxiliary chemicals, particularly salts and dispersing agents, should be explored in order to support the development of more sustainable textile dyeing processes.

Footnotes

ORCID iDs

Pervin Anis

Sibel Şardag

Nil Okyay

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

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

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