Study of the Disperse Dyeing Properties of Low-Temperature Dyeable Polyesteramide Fibre Raziskava lastnosti nizkotemperaturnega barvanja poliesteramidnih vlaken z disperznimi barvili

Polyethylene terephthalate (PET) is the most important synthetic fi bre, and is widely used in the textile industry. However, the disperse dyeing of PET fi bre must be carried out at a high temperature and under high pressure. This leads to high energy consumption and damage to the wool in a PET/wool blend. Some copolyesters and novel polyesters that can be dyed under normal pressure have proven to be good alternatives to PET. In this work, the low-temperature dyeable polyesteramide fi bre was used, and its disperse dyeing properties were studied in terms of adsorption isotherms, the temperature-dependence of uptake, uptake rate, migration ability, building-up property, and colour fastness of disperse dyes. The adsorption isotherms of disperse dyes on polyesteramide fi bre followed the Nernst adsorption model. Disperse dyes exhibited high exhaustion at 100 °C, indicating the good dyeability of polyesteramide fi bre under atmospheric pressure. The uptake of dyes by polyesteramide fi bre was considerably faster than that of PET fi bre, while the majority of dye uptake occurred in the temperature range of 70 to 90 °C. Azo disperse dyes exhibited higher adsorption saturation and better a building-up property than anthraquinone dyes. Disperse dyes had a good migration ability on polyesteramide fi bre, and the colour fastness of the dyed polyesteramide fabrics was also satisfactory.


Introduction
Textile processing uses an enormous amount of electricity, fuel, water and chemicals, and produces a signifi cant amount of contaminated effl uent [1][2][3][4].Reducing energy and water consumption, as well as hazardous industrial effl uents, represents the biggest sustainability challenge for the textile industry.In order to reduce energy consumption, low-temperature scouring and dyeing, and emerging techniques have become part of the industry's strategy, and attracted a great deal of attention [1,2,5].Polyethylene terephthalate (PET) is the most important synthetic fi bre, and is predominant on the manmade fi bre market [5].PET fi bre has been widely used in clothing, home textiles and other industries due to its numerous outstanding properties, such as high strength, good thermal and chemical stability, and excellent wrinkle resistance, as well as its relatively low price [6].However, it also has some shortcomings, such as low moisture regain, poor antistatic properties and poor dyeability due to its high structural regularity and crystallinity, lack of reactive dyeing sites and polar groups, and high hydrophobicity [6].Th e biggest disadvantage of the wet processing of PET fi bre is that it must be dyed under a high pressure at 125-130 °C in a weakly acidic condition, or at about 110 °C in the presence of carriers.High-temperature dyeing not only consumes a great deal of energy, but also requires expensive dyeing equipment and causes potential risks.When used, most carriers are associated with toxicological issues [7].In addition, the high-temperature dyeing of a PET/wool blend leads to the damage of the wool.Th e low-temperature dyeing of PET is a very difficult task if conventional dyes and chemicals are used.One successful approach to address this issue is to modify PET fi bre for enhanced dyeability.Th e introduction of third and fourth monomers during the stage of polyester synthesis is a basic strategy.Th e copolymerisation of PET with dimethyl 5-sulfoisophthalate sodium salt as the third monomer confers cationic dyeability to PET fi bre [8].Th e addition of the fourth monomer, such as polyethylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, or 2,2dimethyl-1,3-propanediol, further improves the dyeability of PET fi bre at the boiling point under normal pressure [8].Today, cationic dyeable polyester (CDP) is deemed an industrial success.On the other hand, the application of new polyester polymers, such as polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT) and polylactic acid (PLA), is also an eff ective method for obtaining lowtemperature dyeable polyester fi bres [1,5,9].In recent years, a new type of polyesteramide copolymer has been developed as an alternative to PET [10,11].Polyesteramide copolymer can be synthesised through the polycondensation reaction of ethylene glycol terephthalate and aliphatic amide [10,11], and has both ester and amide blocks on its backbone.Polyesteramide fi bre can be manufactured by using the melting spinning of polyesteramide chips.Previous researchers have found that while polyesteramide fi bre has a lower tensile strength and whiteness than PET fi bre [10][11][12], it possesses better dyeability, soft ness and anti-pilling properties [13,14].Very importantly, the incorporation of amide groups into an ester main chain results in a decrease in structural regularity and an increase in the amorphous region of the fi bre.Th e glass transition and melting temperatures of polyesteramide fi bre are 68-72 °C and 235 °C, respectively, which are lower than those of PET fi bre [13].Th ese factors make polyesteramide fi bre dyeable using disperse dyes at the boiling point under normal pressure.Th e development of polyesteramide fi bre provides the possibility of manufacturing pure polyester textiles as well as natural fi bre (e.g.wool, silk and cotton) blends using a low-temperature dyeing technique, with the added advantage of energy savings.Although preliminary studies demonstrated the disperse dyeability of polyesteramide fi bre [13,14], more detailed dyeing properties need to be studied with the aim of better understanding the mechanism of disperse dyeing, and providing assistance in the selection of dyes and the determination of dyeing conditions.In this work, the adsorption isotherms of disperse dyes on polyesteramide fi bre were studied in order to understand the mechanisms of dyeing, and the temperature-dependence of uptake, uptake rate, migration ability, build-up property and colour fastness of disperse dyes on polyesteramide fi bre were assessed.

Study of the Disperse Dyeing Properties of Low-Temperature Dyeable Polyesteramide Fibre
China.Fine denier PET knitted fabric (182 g/m 2 ) was obtained from Suzhou TA&A Ultra Clean Technology Co. Ltd., China.In order to remove the fi nish oils added to the fi bres during the spinning process, the fabrics were treated in a scouring bath containing 4 g/L sodium carbonate and 2g/L Leveler O at 50 °C for 60 minutes.Aft er scouring, the fabrics were thoroughly rinsed in distilled water and allowed to dry in the open air.Disperse dyes were selected based on their chemical structures, energy levels, colours and applicability.Th e characteristics of the dyes are summarised in Table 1.Longsperse and Terasil dyes were provided by Zhejiang Longsheng Group Co. Ltd., China, and Huntsman International LLC (Shanghai Division), respectively, while other dyes were obtained from Zhejiang Runtu Co. Ltd., China.Sodium carbonate, citric acid, disodium hydrogen phosphate, sodium hydrosulfi te and acetone were of analytical grade.Dispersant NNO was an industrial product from Anyang Double Circle Auxiliary Co. Ltd., China.Leveler O (polyoxyethylene alkyl ether) was provided by Jiangsu Hai'an Petrochemical Plant, China.

Dyeing methods
All dyeing processes were carried out in a laboratory using an infrared dyeing machine (FAD-7-18P; Yabo Textile Machinery Co. Ltd., Wuxi, China).Th e weight of the fabrics used for dyeing was 1 g, and the liquor ratio was 50:1.Th e dye solutions consisted of dyes, buff er and Dispersant NNO (1 g/L).Th e pH of the dyeing bath was adjusted to 5 by adding a McIlvaine buff er (citric acid and disodium hydrogen phosphate).At the end of dyeing process, polyesteramide fabrics were rinsed with distilled water and then dried in the open air.
Adsorption isotherm.Polyesteramide fabrics were dyed in solutions containing 0.5-12% owf (on the weight of fabric) dyes.Th e temperature was raised at the rate of 1.5 °C/minute from 30 to 80 °C prior to the addition of fabric samples, and then raised to 100 °C at the rate of 3 °C/minute.Th e dyeing process was continued at 100 °C for 150 minutes until the dye adsorption reached the equilibrium state.Dyeing temperature.In order to study the temperature eff ect of dye uptake, the dyeing process was carried out according to the procedure illustrated in Figure 1.Th e dyeing solutions contained 2% owf dyes, 1 g/L Dispersant NNO and a buff er.Th e time for the dipping of each fabric in the dye solution was 120 minutes.

Figure 1: Dyeing profi le for polyesteramide fabric at various temperatures
Dyeing rate.Th e dyeing rates of polyesteramide fi bre were characterised by the uptake rates of Disperse Orange 30 for polyesteramide fi bre in the conditions of 2% owf dyes, 1 g/L Dispersant NNO and pH 5. Two heating rates (2 °C/minute and 1 °C/minute) and two fi nal holding temperatures (120 °C and 100 °C) were used.For the purpose of comparison, the uptake rate of Disperse Orange 30 for PET fi bre was also determined.
Building-up properties.Th e building-up properties of various dyes on polyesteramide fabrics were measured in a dye concentration range from 0.5% to 8% owf.Th e dyeing process was carried out at 100 °C for 80 minutes according to the profi le illustrated in Figure 1.

Measurements
Exhaustion and adsorption of disperse dyes.Th e absorbance of dye solutions was measured using a Shimadzu UV-1800 UV-Vis spectrophotometer (Shimadzu Co. Ltd., Japan).Th e exhaustion of disperse dyes was assessed using the colourimetric method.Due to the poor water solubility of disperse dyes, a mixture of aqueous dye solution and acetone at a ratio of 30:70 (v/v) was prepared before the colourimetric analysis.Th e exhaustion percentage (E) of disperse dyes was calculated using equation 1: where A 0 and A 1 are the absorbance at the maximum absorption wavelength of the dye solution before and aft er exhaustion, respectively.Th e quantity of disperse dyes (C f ) on polyesteramide fi bre was calculated using the exhaustion percentage of dyes, the initial dye concentration and the weight of the fabric using equation 2: where W d is the initial dye weight (g) determined by fabric weight (1 g) and dye dosage (% owf) and W f is the fabric weight (1 g).Th e quantity of disperse dyes (C s ) in the solution after dyeing was calculated using equation 3: where V is the volume of the dye bath (L).Migration properties.Two undyed fabrics (A and B) with the same weight were prepared.Sample B was dyed with 2% owf dyes at 100 and 120 °C.Afterwards, dyed sample B and undyed sample A, at a liquor ratio of 50:1, were immersed in a blank dyeing bath that consisted of 1 g/L Dispersant NNO and a buff er, without the addition of dyes.In order to carry out the dye migration test, the temperature was raised at a rate of 2 °C /minute from 30 to 100 and 120 °C.At this temperature, the dye migration was continued for 60 minutes, aft er which the temperature was lowered to 80 °C.Th e migration rate was calculated using equation 4:

Adsorption isotherm of disperse dyes on polyesteramide fi bre
Th e adsorption isotherms of disperse dyes can be described by the relationship between the adsorption quantity of dyes on polyesteramide fi bre (C f ) and the concentration of dyes in a solution (C s ) at equilibrium.Figure 2 shows the adsorption isotherms of two azo dyes and two anthraquinone dyes.Th ere was a clear linear relationship between C f and C s , suggesting that the adsorption of disperse

Dyeing temperature of polyesteramide fi bre
It is a well-known fact that dyeing temperature plays a key role in the disperse dyeing of PET fi bre because it aff ects the exhaustion, uptake rate, migration and diff usion of dyes, the colour depth and colour fastness of dyeing, and the effi ciency of the dyeing process.High-temperature dyeing is typically used to achieve the high uptake of disperse dyes and the high colour depth of PET fi bre because of the higher kinetic energy of dye molecules and the greater segmental mobility of the less-ordered regions within the fi bre [16].
Polyesteramide fi bre has lower glass transition and melting temperatures than PET fi bre [13], and thus a lower dyeing temperature is to be expected.Figure 3 shows the eff ect of dyeing temperature on the uptake of disperse dyes by polyesteramide fi bre.Th e exhaustion of the fi ve disperse dyes increased with the raising of the temperature, and almost reached the maximum rate at 100 °C, irrespective of their energy level or structure class.A further increase in dyeing temperature did not improve the exhaustion of dyes, with the exception of Disperse Red 74.Th is fi nding shows that the dyeing of polyesteramide fi bre can be carried out under normal pressure.Th e good dyeing property of polyesteramide fi bre is attributable to the fact that the incorporation of amide backbones into the polyester chain decreases the structural regularity of the fi bre, as well as the glass transition temperature of the fibre [13].Th is study implies that the low-temperature dyeability of polyesteramide fi bre, as a novel synthetic fi bre, has tremendous advantages in terms of energy consumption and dyeing effi ciency.on the fi bre surface, the diff usion of dyes through the diff usional boundary layer, the adsorption of dyes onto the fi bre surface and the diff usion of dyes into the fi bre interior [17].Of the four steps listed above, the diff usion of dyes in the fi bre interior is the step that has the greatest impact on the dyeing rate of fi bres.Based on this, it is interesting to study the dyeing rate of polyesteramide fi bre.
Figure 4a shows the uptake rates of Disperse Orange 30 for polyesteramide and PET fi bres at a holding temperature of 120 °C and a heat rate of 2 °C/ minute.Th e rapid uptake of Orange 30 by polyesteramide fi bre clearly occurred in the range of 70 to 90 °C, while the rapid dyeing temperature range for PET fi bre was between 80 and 120 °C.Moreover, the uptake rates of Orange 30 for polyesteramide and PET fi bres were 5.9 and 3.1%/minute, respectively in the temperature range for the rapid uptake of Orange 30.Th e dyeing rate of polyesteramide fibre was almost twice as high as that of PET fi bre.
Figure 4b shows the uptake rate of Disperse Orange 30 for polyesteramide fi bre at a holding temperature of 100 °C and a heat rate of 2 °C/minute.It is evident from Figure 4b that polyesteramide fi bre displayed a rapid dyeing temperature range, dyeing rate and fi nal uptake rate of dyes similar to those in Figure 4a.Figures 4a and 4b show that polyesteramide fi bre exhibits a faster dyeing rate than PET fibre, which can be explained by the lower glass transition temperature of polyesteramide fi bre.
Although polyesteramide fi bre exhibits good lowtemperature dyeability, its high dyeing rate would lead to poor dyeing levelness.Certain special measures should therefore be taken to improve the dyeing levelness of polyesteramide fi bre.To that end, the most eff ective method is to decrease the uptake rate of disperse dyes in the faster dye-uptake temperature range or the critical temperature range (where 80% of adsorption takes place) by reducing the rate at which the temperature is raised [18].Figure 4c shows the uptake rate of Disperse Orange 30 for polyesteramide fi bre at a holding temperature of 100 °C and a heat rate of 1 °C/minute.When comparing Figures 4b and 4c, it is evident that using a heat rate of 1 °C/minute resulted in a decrease in the uptake rate of Disperse Orange 30 to 3.1%/ minute from 6.0%/minute at a heat rate of 2 °C/ minute.It can be suggested from this study that the dyeing of polyesteramide fi bre should be carried out at a low heating rate to provide a dyeing levelness eff ect.

Migration ability of disperse dyes on polyesteramide fi bre
Th e dyeing levelness of textile materials is dependent on the migration ability of dyes [18], which in turn are aff ected by many factors, such as fi bre and dye structures, dyeing temperature and time, and the dyeing auxiliaries used in the dye solution.Th e good migration ability of dyes is benefi cial for dyeing levelness.Figure 5 shows the migration ability of three diff erent disperse dyes on polyesteramide fi bre at 100 and 120 °C.All three of the disperse dyes exhibited a high migration rate at 120 °C.Disperse Orange 30 and Red 74 also exhibited a high migration rate at 100 °C.However, Red 60 displayed a much lower migration rate at 100 °C than at 120 °C.Nevertheless, the migration rate of Red 60 reached 66%.Overall, the good migration ability of disperse dyes on polyesteramide fi bre can be exploited to improve the dyeing levelness of polyesteramide textiles and to correct uneven dyeing.

Building-up property of disperse dyes on polyesteramide fi bre
Th e building-up property of dyes is of great importance for practical application.Disperse dyes with a good building-up property can impart dark shades to polyesteramide fi bre.Th e building-up property of disperse dyes primarily depends on the dye and fi bre structures, the affi nity of dyes to fi bres and dyeing temperature.Th e building-up properties of azo and anthraquinone dyes on polyesteramide fibre are illustrated in Figure 6.In the case of azo dyes, the colour depth of the polyesteramide fabrics dyed with Disperse Red 74 and Blue 183 continually increased as the dye concentration in all of the dye concentration ranges was increased, while the same trend was identifi ed for the fabrics dyed with Disperse Orange 30 and Brown 1, where dye concentrations in the range of 1% to 6% owf were used.In the case of anthraquinone dyes, the dyed fabrics dis-played continually increasing colour depth when the concentrations of Disperse Red 11 and Violet 31 were less than 4% and 6% owf, respectively.Furthermore, the fabrics dyed with azo dyes exhibited higher colour depth than anthraquinone dyes.On the whole, azo dyes demonstrated a better buildingup property than anthraquinone dyes.Th is fi nding is supported by the fact that azo dyes have a much higher adsorption saturation than anthraquinone dyes, as mentioned in subchapter 3.1.

Colour fastness of dyed polyesteramide fabrics
In order to assess the colour fastness of dyed polyesteramide fabrics, the dyeing process was carried out with widely used trichromatic disperse dyes at a concentration of 3% owf.Reduction cleaning was then carried out to remove loose colours.Th e wash, sublimation, and light fastness ratings of the dyed polyesteramide fabrics are presented in Table 2. Th e Study of the Disperse Dyeing Properties of Low-Temperature Dyeable Polyesteramide Fibre fabrics dyed with Disperse Orange 30 and Blue 79 exhibited high wash, sublimation and light fastness levels.Good wash fastness was also identifi ed for the fabric dyed with Disperse Red 74, while its sublimation and light fastness ratings were fair, at 3-4 and 3, respectively.According to GB 18401-2010: National General Safety Technical Code for Textile Products (Chinese National Standards for Textiles) [19], wash colour fastness ratings greater than or equal to 3-4 for baby/children products, and 3 for products that come into direct and indirect contact with skin are defi ned as "acceptable".Th us, the fabrics dyed with three disperse dyes were found to meet GB 18401-2010 in terms of acceptable colour fastness to washing.On the whole, the dyed polyesteramide fabrics exhibited good fastness properties that meet the requirements of consumers.

Conclusion
Th is study presented the dyeing properties of lowtemperature dyeable polyesteramide fi bre.Th e high exhaustion of disperse dyes at 100 °C revealed the good dyeability of polyesteramide fi bre under atmospheric pressure.Th e Nernst adsorption isotherms of disperse dyes indicated a dyeing mechanism of polyesteramide fi bre similar to that of PET fi bre.Th e higher adsorption saturation and better building-up property of azo disperse dyes compared with anthraquinone dyes made the former a good selection for dark shades.Th e rapid uptake of dyes by fi bres in the temperature range of 70 to 90 °C suggested that raising the temperature slowly was important for the improved dyeing levelness of polyesteramide textiles.Th e good migration of dyes on polyesteramide fabric can also be used to improve dyeing levelness.Th e good colour fastness properties of the dyed polyesteramide fabrics met the requirements of consumers.In summary, polyesteramide fi bre can be used as an alternative to PET fi bre to develop textile products, with regard to dyeing properties.
Study of the Disperse Dyeing Properties of Low-Temperature Dyeable Polyesteramide Fibre dyes on polyesteramide fi bre follows the Nernst model, and hydrogen bonding and the van der Waals forces between dyes and fi bres contribute to Nernst adsorption.Th is observation is inconsistent with the mechanism of the distribution of disperse dyes on PET and the aqueous phase[15].Moreover, it is evident from Figures2a and 2bthat azo dyes (Disperse Orange 30 and Red 74) did not exhibit a saturation adsorption in the range of the used dye concentration, while the adsorption saturation of the two anthraquinone dyes (Disperse Red 11 and Violet 31) approached the range of 50-60 mg/g.It is apparent that azo dyes had much higher adsorption saturation than anthraquinone dyes.

Figure 3 :
Figure 3: Uptake of disperse dyes by polyesteramide fi bre at various temperatures3.3Dyeing rate of polyesteramide fi breIt is also a well-known fact that there are four fundamental steps involved in the uptake of dyes by textile fi bres: the diff usion of dyes in the external water phase toward the diff usional boundary layer

Figure 5 :
Figure 5: Migration ability of disperse dyes on polyesteramide fi bre

Figure 6 :
Figure 6: Building-up properties of (a) azo and (b) anthraquinone disperse dyes on polyesteramide fi bre at 100 °C

Table 1 :
Characteristics of disperse dyes