Amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres with high coloration performance for enhancing cotton dyeability

Abstract

Reactive dye is widely used for cotton dyeing, but its low utilization results in vast amounts of colored effluent with high salinity discharge. Amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (Am-RPNs) are a kind of novel colorant that exhibit excellent dyeing ability for cotton fabrics and higher dye utilization than original reactive dyes. The colored polymer nanospheres demonstrated small size, high stability and dye content in the dispersion system when cationic polymer nanospheres were dyed at an optimal dye dosage of 100%. Transmission electron microscopy images showed that the polymer nanospheres have smooth spherical shapes. Am-RPNs with an average hydration diameter of 96.5 nm and zeta potential of −33.7 mV were fabricated after being modified with ethylenediamine at pH 11. Both analytical techniques, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, indicated the presence of –NH₂ on the surface of Am-RPNs. The amino-modification mechanism of the Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres depended on the dyeing bath pH. The color depths of the cotton fabrics dyed with Am-RPNs reached up to 3.1 times higher than those with Reactive Red 195. Scanning electron microscopy images showed that Am-RPNs form stable deposits on the surface of the modified fibers. The cotton fabrics dyed with Am-RPNs possessed excellent rubbing and washing fastness, satisfactory light fastness, and desirable handle. This study provides an innovative method that employ Am-RPNs with high coloration performance to endow the cotton fabric with deep color and good colorfastness without using inorganic salt.

Keywords

reactive dye colored polymer nanospheres modification cotton fabrics dyeing

Reactive dye is one of the most widely used synthetic dyes for cotton dyeing in the textile industry.¹ It has received increasing attention from academia and industry because of its excellent dyeing properties.² However, reactive dye hydrolyzes in a dyeing bath, which results in low dye utilization and large amount of colored wastewater.^3,4

As one of the effective approaches to increase dye utilization, the synthesis of novel colorants has attracted extensively attention.^5–7 Novel hetero bi-functional reactive dyes with high reactivity^8,9 were prepared, which exhibited strong chromatic characteristics but displayed a dull shade. Cationic reactive dyes containing quaternary ammonium were synthesized to increase the electrostatic interaction between cellulosic fiber and dyes for improving the color strength.^10,11 However, these dyes have poor wash-off performance. Significant improvements in the color strength and colorfastness of dyed cotton fabrics were achieved by employing reactive disperse dyes^12–14 in a supercritical CO₂ system. However, this dyeing process is complex, and the equipment requirements are strict. Polyamine crosslinking dyes exhibit excellent dye utilization and high fiber–dye bonding stability, as well as good washing and rubbing fastness when used in cotton fabric, due to the formation of a covalent bond between the crosslinking dyes and fibers through the crosslinkers.^15,16 However, their light fastness needs to be improved¹⁷ regardless if the dyeing performance of the polyamine crosslinking dyes is closely related to the crosslinker.

Colored polymer nanospheres are used in many areas, such as biomedical engineering,^18,19 electronic inks,^20,21 sensors,²² and coatings.^23,24 These nanospheres, which have a large specific surface area, exhibit excellent chromatic properties and good processability.^25,26 The result of our previous works^27–29 showed that colored polymer nanospheres composed of an essential dye and a suitable polymeric matrix enhanced the dye utilization on textile. Disperse dye/poly(styrene-methacrylic acid) with a rough surface designed to increase the amount of dyes contained in the nanospheres showed good dyeability for cotton fabrics.³⁰ Reactive dye/poly(styrene-butyl acrylate-trimethyl(vinylbenzyl) ammonium chloride) nanospheres containing four reactive dyes exhibited much better dyeing property than the original reactive dyes. However, reactive dyes attached to nanospheres are still prone to hydrolysis in dyeing baths, which can decrease the dye utilization.³¹ Ethylenediamine is one of the important components in the preparation of aminoalkyl crosslinking dyes, which have excellent dye utilization and colorfastness for cotton fabrics. In this study, we discuss the application of amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (Am-RPNs) modified with ethylenediamine for dyeing cotton fabrics.

The objective of this study is to prepare a high-performance colorant with two important features: (1) reactive dye grafted with amino groups to obtain high utilization and (2) nanoparticle features to achieve brilliant color and the desired colorfastness. Firstly, the P(St-BA-VBT) nanosphere dispersion was prepared and directly colored using the Reactive Red 195. The morphology of the polymer nanospheres was observed through transmission electron microscopy (TEM). Then the Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (RPNs) were modified using ethylenediamine. The amino-modified colored polymer nanospheres (Am-RPNs) were characterized through X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Lastly, the cationic modified cotton fabrics were dyed using Am-RPNs, and the morphology of the fiber was evaluated through scanning electron microscopy (SEM).

Experimental details

Materials

Plain woven cotton fabrics (176 g/m²) were supplied by Sunvim Group Co., Ltd, Gaomi, China. Styrene (St) was purchased from Tianjin Ruijinte Chemical Reagent Co., Ltd, Tianjin, China. Butyl acrylate (BA) was provided by Tianjin BASF Chemical Co., Ltd, Tianjin, China. Vinylbenzyltrimethyl ammonium chloride (VBT) was purchased from Tianjin Heowns Biochemical Technology Co., Ltd, Tianjin, China. AIBA (2,2’-azo bis(2-methylpropionamidine) dihydrochloride) was provided by Qingdao Kexin New Material Technology Co., Ltd, Qingdao, China. Ethylenediamine was obtained from Tianjin Fengchuan Chemical Reagent Co., Ltd, Tianjin, China. EPTAC (2,3-epoxypropyltrimethylammonium chloride) was purchased from Shanghai Macklin Biochemical Co., Ltd, Shanghai, China. Analytical grade NaOH and HCl (36%) were obtained from Tianjin Kemiou Chemical Reagent Co., Ltd, Tianjin, China. The C.I. Reactive Red 195 was supplied by Tianjin Dekai Chemical Co., Ltd, Tianjin, China, and the dialysis bag (7000 D cutoff) was purchased from MYM Biological Technology Co., Ltd, USA. Distilled water was used in all experiments.

Preparation and coloration of the cationic polymer nanospheres

Cationic poly(St-BA-VBT) nanospheres with an average hydration diameter of 74.2 nm and zeta potential of +59.8 mV were synthesized through emulsifier-free emulsion polymerization. Distilled water (80 mL) was added to a 250 mL four-necked round-bottomed flask with a digital stirrer, reflux condenser, constant-pressure funnel, and nitrogen inlet. After allowing N gas in for 15 min, a VBT solution (5 mL, 84.6 g/L) was added into the flask and stirred for 15 min at a stirring speed of 300 r/min. Then, the mixed solution with St (9.2 g) and BA (0.8 g) was added and stirred for 120 min. Subsequently, the temperature of the system was raised from 25℃ to 80℃ and maintained for 5 min. The AIBA solution (5 mL, 20 g/L) was added dropwise for 30 min and reacted at 80℃ for 4 h. Finally, the materials were cooled and filtered using a Buchner funnel to eliminate the large particles.³¹

The C.I. Reactive Red 195 (Figure 1) solution (15 mL) in the concentration range of 10–120% (dye to nanosphere mass ratio) was added to a 50 mL three-necked flask, followed by the dropwise addition of the nanosphere dispersion (10 mL, 1 g/L) for 60 min at a stirring speed of 400 r/min. The pH of the mixture was adjusted to 5 using 0.01 mol/L HCl solution. Subsequently, the temperature of the system was raised from 25℃ to 65℃ and maintained for 120 min. Then, the colored samples were cooled to room temperature.³² The samples were dialyzed to remove the free dyes that were not firmly bonded to the cationic nanospheres, and the pure RPN dispersion was obtained. The purified colored nanosphere dispersion was transferred to evaporating dishes and then dried at 40℃ to obtain pure RPN powder.
Figure 1.
Molecular structure of C.I. Reactive Red 195, ethylenediamine, and 2,3-epoxypropyltrimethylammonium chloride.

Amino-modification of RPNs

Firstly, RPN dispersion (20 mL, 2 g/L) was added into a 100 mL three-necked flask. Secondly, 30 mL of ethylenediamine (Figure 1) was slowly added into the flask at 25℃ and stirred at a speed of 400 r/min for 120 min. The pH of the mixture was adjusted using 1 mol/L HCl and NaOH. Subsequently, the system was heated to 60℃ and maintained for 120 min. The materials were then cooled to room temperature after the reaction was completed.

Dyeing of cotton fabrics

Dyeing of cationic cotton fabrics

The cotton fabrics were modified using EPTAC (Figure 1) before use.³³ Firstly, the cotton fabrics were immersed in 20 g/L of EPTAC solution with a liquor ratio of 50:1 at 70℃ for 30 min, and 5 g/L of NaOH solution was added and reacted for 30 min. Secondly, after washing with distilled water, 2 g/L of glacial acetic acid solution was added to neutralize the NaOH in the cotton fabrics. Lastly, after washing with distilled water, the modified cotton fabrics were dried at 40℃ in a DGG-101-2BS drying oven (Tianjin Tianyu Experimentation Instrument Co., Ltd, Tianjin, China).

The EPTAC modified cotton fabrics were then immersed in the Am-RPN dispersion with a concentration range of 0.46–1.37% (dye to fabric mass ratio) and the liquor ratio of 50:1 at 25℃ for 30 min. The samples were dried at 40℃ after washing with distilled water.

Conventional dyeing of cotton fabrics

The cotton fabrics were immersed in the dye solution with a concentration range of 0.46–1.37% (dye to fabric mass ratio) at 60℃ for 15 min. Then, Na₂SO₄ (40 g/L) was added and reacted for 15 min. Subsequently, the temperature of the system was raised from 60℃ to 90℃, and Na₂CO₃ (10 g/L) was added and reacted at 90℃ for 30 min. After the reaction was completed, the colored samples were washed with distilled water, standard soap solution, and running tap water, and then dried at 40℃.

Analytical investigation

TEM

The polymer nanosphere dispersion was ultrasonically diluted 50-fold with deionized water and dropped onto Cu meshes. The morphology of the polymer nanospheres was observed using an H-7650 transmission electron microscope (Hitachi, Tokyo, Japan).³⁴

Size and zeta potential of the nanospheres

The colored polymer nanosphere dispersion was diluted 50-fold with deionized water before testing, and the size and zeta potential of the nanospheres were determined using a Nano ZS90 instrument (Malvern Panalytical Ltd, Malvern, UK) at 25℃.³⁵

Dye content

The pH of the Na₂HPO₄-NaH₂PO₄ buffer solution was adjusted to 5 using 50 mmol/L of Na₂HPO₄ and NaH₂PO4. A dialysis bag containing 20 mL of colored polymer nanosphere dispersion and 2 mL of buffer solution was immersed in 60 mL of buffer solution at 25℃. The visible absorption spectrum (400–800 nm) of the dye solution outside the dialysis bag was measured using a double-beam ultraviolet-visible spectrophotometer (UV-3200, Mapada Instruments Co., Ltd, Shanghai, China) after 90 h. Subsequently, the absorbance of the dye solution was measured at 541 nm (the maximum absorption wavelength of the C.I. Reactive Red 195), and the dye content of the colored polymer nanospheres was calculated on the basis of the Lambert–Beer law.

The dye exhaustion can be calculated as³¹
$Q = (1 - \frac{C \times V}{C_{0} \times V_{0}}) \times 100 %$
(1)
where Q is the dye exhaustion (%), C is the concentration of the dye (g/L) outside the dialysis bag, V is the sum of the volumes of the liquids inside and outside the dialysis bag (L), and $C_{0}$ and $V_{0}$ are the original concentration (g/L) and volume (L) of the dye solution, respectively.

The dye content in the polymer nanospheres is determined as
$Q_{t} = Q \times \frac{M_{0}}{M} \times 1000$
(2)
where Q_t is the dye content in the polymer nanospheres (mg/g), $M_{0}$ is the mass of the original reactive dyes (g), and M is the mass of the raw polymer nanospheres in the colored polymer nanosphere dispersion (g).

FTIR

The FTIR spectra of the RPN and Am-RPN powders were obtained on a TENSPR37 spectrometer (Bruker Co., Ltd, Hamburg, Germany) using the KBr disc technique. The spectra were recorded over the range of 4000–400 cm^–1 with a resolution of 1 cm^–1.^36,37

XPS

The chemical compositions of the RPNs and Am-RPNs were determined by XPS using a K-Alpha X-ray photoelectron spectrometer (Thermo Fisher Scientific Co., Ltd, Waltham, MA, USA) with an Al K-Alpha source type at an incident energy of 1486.6 eV. For analyzing the spectra, the spot size, pass energy, and energy step size were set as 400 µm, 200.0 eV, and 1.0 eV, respectively. All measurements were conducted at an ultra-high vacuum chamber pressure between 5 × 10^–9 and 2 × 10^–8Torr.³⁸

Field emission SEM

The raw, cationized, and Am-RPN-dyed cotton fabrics were dried at 80℃ for 5 min. Small pieces of the samples were cut down and mounted on a field emission scanning electron microscopy (FE-SEM) sample mount using conductive tape. The samples were then sputter-coated with gold. The surface morphology of the sample was observed using a Sigma 500VP field emission scanning electron microscope (Carl Zeiss, Oberkochen, Germany) operating at 5.00 kV.

Color investigation

The colorimetric data of the dyed fabrics were obtained using a Datacolor SF-600 Plus (Datacolor Co., Lawrenceville, NJ, USA) system with a D₆₅ illumination and 10° standard observer.³⁹ The absorption and scattering coefficient (K/S) values were assessed at 541 nm. Each fabric sample was folded into four layers and measured at 10 random chosen locations. The average K/S value was calculated using the Kubelka–Munk equation
$K / S = (1 - R)^{2} / 2 R$
(3)
where R is the reflectance of the dyed fabric at the maximum absorption wavelength, and K and S are the spectral absorption and scattering coefficients of the dyed fabric, respectively.

Colorfastness investigation

The dry and wet rubbing fastness properties of dyed cotton fabrics were tested according to ISO 105-X12 using a Y571 crock colorfastness tester (Nantong Hongda Experiment Instruments Co., Ltd, Nantong, China), and the amount of color transferred from the samples to the white square was examined by means of the gray scale. The washing fastness was evaluated according to the methods established in ISO 105-C10 using a SW-24 washing colorfastness tester (Laizhou Yuanmao Instruments, Co., Ltd, Laizhou, China). The washing fastness was tested using 5 g/L soap liquid at 40℃ for 30 min. The light fastness was determined using a YG (B) 611-II-type sun weather test machine (Wenzhou Darong Textile Standard Instruments, Co., Ltd, Wenzhou, China)⁴⁰ with a Xe arc lamp according to ISO 105-B02 for colorfastness to artificial light. The light-fastness rating was determined on the basis of the change in the color of the tested fabrics and blue wool reference materials.

Handle investigation

The softness and smoothness of the dyed cotton fabrics were evaluated according to AATCC 202-2014: Apparatus evaluation method of relative handle value of textiles, using a F1S3-10 PhabrOmeter fabric handle feeling evaluation tester (Nucybertek Technology Co., Ltd, USA).^41,42

Results and discussion

Influence of dye dosage on RPN properties

The changes in the size, zeta potential, and dye content of the RPNs with different dye dosages are listed in Table 1.
Table 1.
Effect of dye dosage on the size, zeta potential, and dye content of Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres^a

Dye dosage (%)^b Powder Size (nm) PDI Zeta potential (mV) Q (mg/g)

10 99.7 0.114 –27.0 100.0

30 102.1 0.136 –37.4 115.2

50 108.0 0.148 –40.2 124.6

70 101.2 0.121 –43.3 147.6

90 96.8 0.095 –43.9 175.7

100 95.3 0.092 –45.4 164.9

120 93.6 0.092 –45.4 163.7

a
The cationic poly(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres with an average size of 74.2 nm, polydispersity index (PDI) of 0.072, and a zeta potential of +59.8 mV were dyed at 60℃ and pH 5 for 120 min.

b
The mass ratio of dye to nanosphere.

The size of the RPNs related to the specific area is an important parameter for determining the properties of absorbing, reflecting, and scattering light. As shown in Table 1, the size of the RPNs increases first and then decreases when the dye dosage increases. The maximum size (108.0 nm) is obtained when the dye dosage reaches 50%. This might be because the cationic polymer nanospheres with quaternary ammonium groups attract the anionic reactive dye molecules through electrostatic attraction and van der Waals forces,⁴³ which leads to the increasing anionic reactive dye on the polymer nanosphere surfaces. However, a further dosage increment results in a slow downtrend of the size. This phenomenon occurs because the electric double layer around the RPNs are compressed by the increasing Na⁺, which causes the decrease in size. It is found that when the dye dosage reaches 100%, the size and polydispersity index (PDI) are 95.3 nm and 0.092, respectively, which indicate that the size is small and the size distribution is relatively centralized.

Table 1 also presents the effect of dye dosage on the zeta potential and dye content of RPNs. The absolute values of zeta potential and dye content initially increase with the increase of dye dosage. When the dye dosage is increased to 90% and 100%, the dye content and the absolute value of zeta potential reach the maximum values of 175.7 and 45.4, respectively. A high dye dosage signifies the absolute values of zeta potential and dye content, which can be ascribed to the continuous absorption of the dye due to the van der Waals forces among the dye molecules. When the dye dosage is further increased to 120%, the zeta potential displays no change, and the dye content slightly decreases. This suggests that the adsorption of reactive dyes on the polymer nanospheres reaches an equilibrium. The decrease in the dye content can be attributed to redissolution of the dyes in the outer surface of the polymer nanospheres because of the weak bonding among the outer dye molecules during the test. It is found that when the dye dosage reaches 100%, the zeta potential and dye content of the RPNs are −45.4 mV and 164.9 mg/g, respectively, indicating that a dispersion system with good stability and dark color strength may be obtained.

On the basis of the above analysis, the optimal dye dosage is 100%, which is then adopted in the subsequent investigations.

Morphology of the RPNs

The TEM images and size distribution of the cationic P(St-BA-VBT) nanospheres before and after coloration are presented in Figure 2. The cationic polymer nanospheres synthesized through the soap-free emulsion polymerization method display a smooth homogeneous spherical shape with an average hydration diameter of 74.2 nm and zeta potential of +59.8 mV (Figures 2(a) and (c)). As shown in Figures 2(b) and (c), the change in the morphology of the RPNs is minimal. However, after the coloration, the average hydration diameter increases 21.1 nm to 95.3 nm, and the zeta potential decreases to −45.5 mV. This phenomenon may be caused by a large number of dye molecules adsorbed on the polymer nanosphere surface, which increases the size of the polymer nanospheres and makes the zeta potential become negative.^27,44
Figure 2.
Transmission electron microscopy photograph and size distribution of the polymer nanospheres: (a) the cationic polymer nanospheres; (b) the polymer nanospheres colored with 100 wt.% Reactive Red 195 (the ratio to dry nanospheres); the preparation was carried out at 60℃ and pH 5 for 120 min; (c) size distributions of polymer nanospheres and colored polymer nanospheres dyed with 100 wt.% Reactive Red 195.

The size, zeta potential, FTIR, and XPS analysis of the Am-RPNs

The size and zeta potential of the Am-RPNs were studied to describe the dispersion system. The influence of pH on the size of Am-RPNs is illustrated in Figure 3(a). The size decreases first and then slightly changes when the pH of the bath increased from 8 to 12. The size increases with the decrease of bath pH in the range of 10–8, which implies that the lower the bath pH in an alkaline environment, the larger the size of Am-RPNs. In the dispersion system, two forms of ethylenediamine are present, namely, free amino and NH₃⁺ groups. With the decrease of the bath pH from 10 to 8, the number of the free amino and NH₃⁺ groups gradually decreases and slowly increases, respectively. This phenomenon can be ascribed to NH₃⁺ as counter ions, which can promote the agglomeration of the Am-RPNs with negative charges, resulting in an increase of the particle size. With the increase of the bath pH from 10 to 12, the size of the Am-RPNs slightly changes. The reason for this phenomenon might be the gradual increase in the number of free amino groups in the dispersion. These groups have high activity and can undergo nucleophilic substitution and nucleophilic addition reactions with the triazine and vinyl sulfone groups of Reactive Red 195 attached to the nanosphere, respectively. Moreover, because the ethylenediamine segment is small, the size of the Am-RPNs does not exhibit a remarkable change. At pH 11, the minimum value of the average diameter of Am-RPNs and the PDI are 96.5 and 0.075, respectively, which indicates that the size is small and the size distribution is relatively centralized. The small diameter and centralized distribution of the Am-RPNs ensure the uniformity of the dispersion system, which can bring a powerful coloration ability when used for dyeing fabric.³⁹
Figure 3.
Effect of pH on size (a) and zeta potential (b) of the amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres. Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres were modified with 40 wt.% ethylenediamine (the ratio to dry nanospheres). The preparation was carried out at 60℃ for 120 min.

Zeta potential is an important parameter to determine the stability of the colloidal dispersion. Figure 3(b) presents the effect of pH on the zeta potential of the Am-RPNs. The absolute value of the zeta potential increases from 21.1 to 37.0 when the bath pH increases from 8 to 12, thereby suggesting that the zeta potential of the Am-RPN dispersion is pH dependent, because the protonation of the sulfonate groups of the dye is strongly related to the pH.^45,46 When the bath pH exceeds 10, the absolute values are higher than 30, which represents a sufficient mutual electric repulsion that can disperse Am-RPNs homogeneously and prevent them from aggregation. At pH 11, the absolute value of the zeta potential is 33.7, which indicates that the dispersion system is sufficiently stable.

Based on the analysis of the size and zeta potential of Am-RPNs, the optimal pH is 11, which is then selected in the preparation of Am-RPN dispersion to dye cotton fabrics.

The FTIR spectra of the RPNs and Am-RPNs are shown in Figure 4(a). The respective characteristic peaks of both samples at 2922 and 2850 cm^–1 can be ascribed to the stretching vibration of C-H. The characteristic peak at approximately 1728 cm^–1 is assigned to the stretching vibration of C=O in BA. In the spectrum of the Am-RPNs, a new absorption peak occurs at 1562 cm^–1, which can be attributed to the bending vibration of N-H in the primary amine group (-NH₂-) of ethylenediamine. This result indicates that the colored nanospheres are effectively grafted with the amino groups of ethylenediamine.
Figure 4.
Fourier transform infrared spectroscopy (a) and X-ray photoelectron spectroscopy (b) spectra of Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (RPNs) and amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (Am-RPNs).

The XPS spectra and elemental content of the RPNs and Am-RPNs are presented in Figure 4(b) and Table 2, respectively. The characteristic peaks of C, O, and N atoms are clearly depicted in the former. In both samples, C1s, O1s, and N1s peaks are observed at 284.8, 531.2, and 400.1 eV. Table 2 summarizes the atomic composition of the RPNs and Am-RPNs. Compared with the RPNs, the C and N contents of the Am-RPNs increase by 6.86% and 53.31%, respectively, and the O content decreases by 26.79%. In addition, the O/C atomic ratio of the Am-RPNs (0.18) is lower than that of the RPNs (0.26). The greatly increased intensity of the N1s peak in the XPS spectrum of the Am-RPNs further demonstrates that the colored nanospheres are effectively grafted with the amino groups of ethylenediamine.^47,48 The amination of the RPNs with ethylenediamine presents a potential method for avoiding the hydrolysis of reactive dyes to enhance dye utilization.
Table 2.
Chemical composition of Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (RPNs) and amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (Am-RPNs)

Colored nanosphere Binding energy (eV)
Atomic concentration (%)
Atomic ratio O/C

C1s O1s N1s C1s O1s N1s

RPN 284.8 531.2 400.1 73.14 18.81 2.72 0.26

Am-RPN 78.16 13.77 4.17 0.18

Preparation mechanism of Am-RPNs

The mechanism of the polymerization and coloration of cationic polymer nanospheres is illustrated in Figure 5(a). The dye anions are adsorbed on the cationic polymer nanosphere surface through the electrostatic attraction forces between the quaternary ammonium salt groups of poly(St-BA-VBT) and the sulfonate groups of the Reactive Red 195. The colored polymer nanospheres with negative charges are obtained by absorbing the ionized reactive dye.
Figure 5.
Mechanism of synthesis (a) and modification (b) of the colored nanospheres.

During the modification of the dye attached to the nanospheres using ethylenediamine, the –NH₂ groups of the ethylenediamine can be protonated to –NH₃⁺ when the bath pH is below 7. Precipitation occurs in the dispersion system because the ethylenediamine is spontaneously adsorbed on the reactive dye attached to the nanospheres through the electrostatic attraction between the amino cation (NH₃⁺) of ethylenediamine and the sulfonate anions of dye. The decrease in the anion numbers of the Am-RPNs might weaken the electric repulsion among them, which can result in the instability of the dispersion system (Figure 5(b)).

When the pH of the bath rises from 8 to 12, gradually increasing free amino groups and gradually decreasing –NH₃⁺ groups are present in the dispersion. A free amino group of ethylenediamine is generated, and the sulfatoethylsulfone of the Reactive Red 195 is activated into its vinylsulfone form with high reactivity, which can form a covalent bond with a free amino based on the nucleophilic addition mechanism. In addition, the triazine of the Reactive Red 195 can also form a covalent bond with a free amino based on the nucleophilic substitution mechanism (Figure 5(b)). The reactive group of the Reactive Red 195 is blocked by the amino group, which decreases its hydrolysis and therefore improves its utilization. As the pH increases, the absolute value of the zeta potential increases, that is, the anion numbers of the Am-RPNs increase, which may strengthen the electric repulsion among Am-RPNs, and the dispersion system of the Am-RPNs becomes more stable.

In summary, the synthesized Am-RPNs precipitate in the acidic condition, which is not adopted in the subsequent investigations. Only the Am-RPNs prepared in an alkaline environment can be used to dye cotton fabrics. These results are consistent with the studies presented in the The size, zeta potential, FTIR, and XPS analysis of the Am-RPNs section.

Color performance of the cotton fabrics dyed with Am-RPNs

To improve the affinity between the cotton fabrics and the Am-RPNs, the fabrics were modified with 20 g/L of EPTAC at 70℃ to produce positive charges on the fiber surfaces. The Am-RPNs were attracted onto the fiber surfaces by the electrostatic forces,⁴⁹ hydrogen bonds,^50,51 and van der Waals forces⁴⁹ when the colored nanosphere dispersion contacted with the cationic cotton fabrics. The results show that the morphology of the fibers does not display obvious change after the cationic modification (Figure 6(b)), and the Am-RPNs are adsorbed on the surface of the modified fibers (Figures 6(c) and (d)).
Figure 6.
Scanning electron microscopy images of cotton fibers and amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanospheres (Am-RPNs): (a) raw cotton fibers; (b) cationized cotton fibers; (c) and (d) cationized cotton fibers after dyeing with different magnification; (e) Am-RPN powder.

The color strength and characteristic values of the cotton fabrics dyed with Reactive Red 195 and Am-RPNs in different concentrations are listed in Table 3. The cotton fabrics modified with EPTAC were immersed in the Am-RPN dispersion at room temperature for 30 min. The colorimetric data are given in terms of the CIELAB coordinate system, where K/S, L, a, b, C, and h° represent the color strength, lightness, redness-greenness (+value=red, –value=green), yellowness-blueness (+value=yellow, –value=blue), saturation, and hue angle, respectively.⁵²
Table 3.
The color strength and colorimetric parameters of dyed cotton fabrics

Colorant Concentration^c (%) Dyed fabrics K/S Color characteristic values

L* a* b* C* h°

Reactive Red 195^a 0.46 1.3 67.1 40.0 –10.0 41.2 346.0

0.91 2.2 61.7 46.2 –10.3 47.3 347.4

1.37 3.0 58.4 49.5 –9.8 50.5 348.8

Am-RPN^b 0.46 1.9 62.7 42.5 –9.2 43.5 347.8

0.91 5.3 51.9 53.5 –7.0 54.0 352.6

1.37 9.3 46.9 57.9 –4.6 58.1 355.5

a
Conventional dyeing conditions: Na₂SO₄ 40 g/L, Na₂CO₃ 10 g/L, liquor ratio 50:1, dyeing was carried out at 60℃ for 30 min, and then fixed at 90℃ for 30 min.

b
Dyeing of cationized cotton fabrics: liquor ratio 50:1, dyeing at 25℃ for 30 min.

c
The mass ratio of dye to fabric.

Am-RPN: amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanosphere.

The K/S and L* values of the cotton fabrics dyed with Am-RPNs are higher and lower than those dyed with Reactive Red 195, respectively, signifying that a darker color was obtained for cotton fabrics dyed with Am-RPNs. The color depths of the cotton fabrics dyed with Am-RPNs are 1.4, 2.4, and 3.1 times higher than those dyed using Reactive Red 195. The a* values of the cotton fabrics dyed with Am-RPNs are positive and higher than those dyed with Reactive Red 195, which indicates that the former appears redder than the latter. By contrast, the b* values of the cotton fabrics dyed with Am-RPNs are negative, and their absolute values are lower than those dyed with Reactive Red 195, which indicates that the color of the former is less blue than that of the latter. The C* values of the cotton fabrics dyed with Am-RPNs are higher than those dyed with Reactive Red 195, which indicates that the former is more saturated than the latter.³¹ The h° values of the cotton fabrics dyed with Am-RPNs are higher than those dyed with Reactive Red 195. The result indicates that a redder shade was obtained for cotton fabrics dyed with Am-RPNs because h°=360° corresponds to a pure red. As previously established, the cotton fabrics dyed with Am-RPNs display excellent color strength and saturation. The Am-RPNs exhibit high dyeability for cationic cotton fabrics. The major reasons may be ascribed to three aspects: (1) reactive dyes are grafted with amino groups, which decrease their hydrolysis and therefore improves their utilization; (2) the Am-RPNs are adsorbed on the surface, not in the inner of the cationic cotton fabrics, which may give a darker apparent color; (3) the Am-RPNs enhance the absorbing ability of dye molecules to light by means of the high specific surface area and uniform particle sizes of nanospheres. In addition, the exhaustion dyeing technology without addition of inorganic salt at room temperature is environmentally friendly.

Colorfastness and handle of the cotton fabrics dyed with Am-RPNs

Color durability is one of the most crucial factors for dyed textiles. The rubbing and washing colorfastness of the dyed cotton fabrics are presented in Table 4, where levels 1 and 5 represent the worst and best states, respectively. The rubbing and washing fastness of the fabrics dyed with Am-RPNs and Reactive Red 195 are almost unchanged, which means that the modification process does not affect the colorfastness of cotton fabrics. Cotton fabrics have desirable rubbing and washing fastness. For light fastness, levels 1 and 8 indicate the worst and best states, respectively. The cotton fabrics dyed using different colorants exhibit good light stability. The light fastness of the cotton fabrics dyed with Am-RPNs are a half grade higher than those dyed using the Reactive Red 195. The light fastness of samples satisfactorily meets the application requirement.
Table 4.
The colorfastness and handle of dyed fabrics

Colorant Concentration (%) Rubbing fastness
Washing fastness
Light fastness Handle

Dry Wet SC SW CC Softness Smoothness

Reactive Red 195 0.46 5 4–5 5 5 4–5 4 65.44 52.05

0.91 4–5 4 5 5 4–5 3–4 67.13 52.97

1.37 4–5 4 5 5 4–5 3 68.41 54.42

Am-RPN 0.46 4–5 4 5 5 4–5 4–5 67.44 52.42

0.91 4–5 4 5 5 4–5 4 67.59 56.07

1.37 4–5 4 5 5 4 3–4 68.66 56.76

SC: staining on cotton fabric; SW: staining on wool fabrics; CC: color change; Am-RPN: amino-modified Reactive Red 195/P(styrene-co-butyl acrylate-co-trimethyl(vinylbenzyl) ammonium chloride) nanosphere.

Softness and smoothness are used to evaluate the handle of the treated fabrics, where the smaller the values of the two measures are, the softer the handle is. Table 4 shows that the testing values of the cotton fabrics dyed with Am-RPNs are extremely close to those dyed with Reactive Red 195. This result indicates that the two kind of fabrics have similar handle feeling. The change in the softness data among the cotton fabrics with different colorants is small, thereby indicating that the softness of the cotton fabrics dyed with Am-RPNs and Reactive Red 195 are extremely close to each other. The slightly decrease in the smoothness can be ascribed to the increased surface roughness of the cotton fibers after dyeing with Am-RPNs. This dyeing process does not cause a significant effect on the fabric handle, and the cotton fabrics achieved the required handle. In summary, the cotton fabrics dyed with Am-RPNs demonstrate excellent rubbing, washing, and light fastness, as well as a satisfactory handle feeling.

Conclusions

Cationic P(St-BA-VBT) nanospheres with an average hydration diameter of 74.2 nm and zeta potential of +59.8 mV were synthesized through soap-free emulsion polymerization and dyed using Reactive Red 195. The RPNs demonstrated small size and high stability and dye content in the dispersion system when the cationic polymer nanospheres were dyed at an optimal dye dosage of 100%. Am-RPNs with an average hydration diameter of 96.5 nm and zeta potential of −33.7 mV were also fabricated through ethylenediamine modification at an optimal pH value of 11. It is found that the mechanism of the amination reaction changes with the dyeing bath pH. Am-RPNs were then utilized to dye the cationic modified cotton fabrics. The color depths of the cotton fabrics dyed with Am-RPNs were 1.4, 2.4, and 3.1 times higher than those with Reactive Red 195. In addition, the cotton fabrics dyed with Am-RPNs exhibited good rubbing, washing, and light fastness, as well as satisfactory handle.

In conclusion, the Am-RPNs modified by ethylenediamine can impart the cotton fabric with deep color and good colorfastness simultaneously due to improving the dye utilization. Moreover, this exhaustion dyeing process presents a feasible and environmentally friendly approach for dyeing cotton fabrics at room temperature without using inorganic salt.

Dye dosage (%)^b	Size (nm)	PDI	Zeta potential (mV)	Q (mg/g)
10	99.7	0.114	–27.0	100.0
30	102.1	0.136	–37.4	115.2
50	108.0	0.148	–40.2	124.6
70	101.2	0.121	–43.3	147.6
90	96.8	0.095	–43.9	175.7
100	95.3	0.092	–45.4	164.9
120	93.6	0.092	–45.4	163.7

Colored nanosphere	Binding energy (eV)	Atomic concentration (%)	Atomic ratio O/C
RPN	284.8	531.2	400.1	73.14	18.81	2.72	0.26
Am-RPN	78.16	13.77	4.17	0.18

Colorant	Concentration^c (%)	Dyed fabrics	K/S	Color characteristic values
Reactive Red 195^a	0.46		1.3	67.1	40.0	–10.0	41.2	346.0
0.91		2.2	61.7	46.2	–10.3	47.3	347.4
1.37		3.0	58.4	49.5	–9.8	50.5	348.8
Am-RPN^b	0.46		1.9	62.7	42.5	–9.2	43.5	347.8
0.91		5.3	51.9	53.5	–7.0	54.0	352.6
1.37		9.3	46.9	57.9	–4.6	58.1	355.5

Colorant	Concentration (%)	Rubbing fastness	Washing fastness	Light fastness	Handle
Reactive Red 195	0.46	5	4–5	5	5	4–5	4	65.44	52.05
0.91	4–5	4	5	5	4–5	3–4	67.13	52.97
1.37	4–5	4	5	5	4–5	3	68.41	54.42
Am-RPN	0.46	4–5	4	5	5	4–5	4–5	67.44	52.42
0.91	4–5	4	5	5	4–5	4	67.59	56.07
1.37	4–5	4	5	5	4	3–4	68.66	56.76

Footnotes

Declaration of conflicting interests

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

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Key Research and Development Program of China (Grant No. 2017YFB0309800) and the Shangdong Province Key Technology Research and Development Program (Grant No. 2019TSLH0108).

ORCID iD

Dongwei Wang

Xinqing Zhang

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