Crosslinking formulations based on novel reactive disperse dyes for printing cotton fabrics

Abstract

Cotton cellulose is an excellent natural material due to its outstanding characters. Five novel crosslinking reactive disperse dyes containing bi-functional groups, two 3-chloro-2-hydroxypropyl groups, were synthesized and characterized by infrared spectroscopy, proton magnetic resonance spectroscopy and element analysis. The solvent effect on the color of the dyes was assessed by the electronic absorption spectra. The crosslinking printing properties of the five dyes (D1–5) for cotton fabrics were investigated. The electronic absorption property exhibited larger bathochromic shifts in a stronger polar solvent than in the weaker polar solvents. The crosslinking reaction between two 3-chloro-2-hydroxypropylreactive groups and the hydroxyl group of cellulose could take place. The higher color yield and excellent fixation were obtained. The building up property was good for all the dyes on cotton fabric. The printed samples had excellent washing, perspiration and rubbing fastness. The light fastness for cotton fabrics was moderate.

Keywords

cotton fabric printing reactive disperse dye crosslinking

Printed cellulose and its blend materials have wide applications in many high-tech and industrial textile fields, such as biological materials, home textiles, garments and composite materials.^1–3 Cotton cellulose is an excellent natural material for its characteristics, such as biodegradability, biocompatibility and comfortable handle.^4,5 Its blend materials, such as the polyester/cotton blend, have the advantage of polyester's tensile strength, abrasion resistance and dimensional stability as well as cotton's hydrophilicity and biocompatibility.^6–8 Usually, cotton cellulose can be printed with reactive dyes under the alkali condition. Polyester fabrics can be printed with disperse dyes under the acid condition. Polyester/cotton blend fabrics can also be printed with two kinds of dyes, reactive dyes and disperse dyes, in one paste. However, polyester/cotton blend fabrics cannot be printed with one kind of dye at the same time. Because of environmental and wastewater issue, many efforts have been made in chemical engineering and the textile industry to print different substrates in one step using the same paste.^9–13 In the meantime, for cotton printing, since the fixation of the traditional reactive dyes on cellulose materials is only about 60–80%, a large amount of effluent arises from washing-off. Unfixed reactive dyes in wastewater may further pose an environmental hazard.^14–16

Reactive disperse dyes are novel structure dyes containing a reactive group without water-soluble groups, such as $- {SO}_{3}^{-}$ , which have the two characteristics of both disperse and reactive dyes.^17,18 Reactive disperse dyes are able to print two components, cotton and polyester fibers, at the same time. So far, different reactive groups have been introduced to reactive disperse dyes, such as β-sulphatoethylsulphonyl, α, β-dibromopropionylamido, dichloro-s-triazinyl, acetoxyethylsulphone and so on.^19–21 In our previous work, the reactive disperse dyes containing one 3-chloro-2-hydroxypropyl group were synthesized.²² This kind of reactive disperse dye for printing cellulose fabric has good building up and printing properties. However, the fixing rates of the dyes are low because there is only one reactive group. If two reactive 3-chloro-2-hydroxypropyl groups are introduced to dye molecules, they can crosslink cellulose macromolecules to improve the fixation.

In this paper, five novel crosslinking reactive disperse dyes based on an azo structure, containing two functional groups, were synthesized. Their electronic absorption spectra were discussed. The crosslinking printing properties on cotton fabrics were also investigated.

Experimental methods

Materials

3-[N-bis (3-chloro-2-hydroxypropyl)] amino acetanilide, 3-[[N-bis (3-chloro-2-hydroxypropyl) amino]-4-methoxyphenyl] acetamide, 4-nitroaniline, 3-nitroaniline, 2-chlorine-4-nitroaniline and 2-bromo-4,6-dinitroaniline were obtained from Zhejiang Wanfeng Chemical Company (Shaoxing, China). Epichlorohydrin and other chemicals used were obtained from Shanghai Chemical Reagent Plant (Shanghai, China). Scoured and bleached cotton fabric was obtained from Zhejiang Jinqiu Textile Co. (Shaoxing, China). The standard detergent specially used for the ISO 105-C color fastness to washing test was obtained from Shanghai Textile Industry Institute of Technical Supervision (Shanghai, China).

Measurements

The Fourier transform infrared (FT-IR) spectrum was measured by an OMNI 98 Sampler of the Nexus-670 FT-IR-Raman Spectrometer (Nicolet Analytical Instruments, Madison, WI). The proton magnetic resonance (¹HNMR) spectrum was recorded on a Bruker Avance 400 (Bruker Co., Faellanden, Switzerland). Element analyses for C, H and N were performed on a Vario EL III (Elmentar Co., Germany). The visible spectra were measured using a U-3310 spectrophotometer (Hitachi Limited Co.).

Synthesis of the reactive disperse dyes

The chemical structures of the designed new dyes, D1–5, are shown in Scheme 1. The synthesized methods of the dyes, including the diazotization and coupling reaction, were similar to the previous reference.²¹ Five reactive disperse dyes were obtained. All the dyes were recrystallized from ethanol. The structures were characterized by element analysis, FT-IR and ¹H NMR. One kind of reactive disperse dye for dyeing nylon was also investigated by Scott and Vickerstaff.²³

Scheme 1.

Chemical structure of the synthesized dyes.

D1: Yield is 87%. M.P. is 164–166℃. Element analysis: Calc: C 49.58, H 4.75, N 14.46. Found: C 49.40, H 4.75, N 14.63. FT-IR (KBr, cm⁻¹): 3440, 3242, 3098, 2982, 2838, 1633, 1528, 1528, 1396 and 1106. ¹HNMR(DMSO-d6, ppm): 10.457, 10.441(d, 1H, –NHCO); 8.69–6.62(t, 7H, Ar–H); 5.89–5.17 (dd, 2H, –CHOH); 4.18–3.9 (m, 2H, –CH₂–CH–CH₂); 3.867–3.404 (m, 8H, –CH₂CHCH₂); 3.35 (t, H₂O); 2.50 (s, DMSO); 2.231 (s, 3H, –NHCOCH₃).

D2: Yield is 91%. M.P. is 142–144℃. Element analysis: Calc: C 46.29, H 4.24, N 13.50. Found: C 46.38, H 4.33, N, 13.46. FT-IR (KBr, cm⁻¹): 3430, 3206, 3107, 2999, 2830, 1626, 1567, 1518, 1393 and 1175. ¹HNMR (DMSO-d6, ppm): 11.217 (s, 1H, –NH), 8.449 (s, 1H, Ar–H); 8.271, 8.248 (d, 1H, Ar–H); 8.161–7.861 (m, 2H, Ar–H); 7.791–7.768 (d, 1H, Ar–H); 6.945–6.734 (m, 1H, Ar–H); 5.774–5.505 (dd, 2H, –OH); 4.233–3.990 (m, 2H, –CH₂–CH–CH₂); 3.874–3.496 (m, 8H, –CH₂–CH–CH₂); 3.35 (m, H₂O); 2.50 (s, DMSO); 2.201 (s, 3H, –NHCOCH₃).

D3: Yield is 94%. M.P. is 134–136℃. Element analysis: Calc: C 49.02, H 4.86, N 13.62. Found: C 48.49, H 4.86, N 13.90. FT-IR (KBr, cm⁻¹): 3443, 3232, 3107, 2979, 2831, 1633, 1555, 1508, 1396 and 1241. ¹HNMR (DMSO-d6, ppm): 10.057 (s, 1H, –NHCO): 8.481–7.215 (m, 6H, Ar–H); 5.392–5.338 (dd, 2H, OH); 4.098–3.912 (m, 2H, –CH₂CHCH₂); 3.837 (s, 3H, –OCH₃); 3.780–3.401 (m, 8H, –CH₂CHCH₂); 3.35 (s, H₂O); 2.50 (s, DMSO); 2.215 (s, 3H, –NHCOCH₃).

D4: Yield is 91%. M.P. is 146–148℃. Element analysis: Calc: C 45.94, H 4.37, N 12.76. Found: C 45.63, H 4.35, N 13.09. FT-IR (KBr, cm⁻¹): 3444, 3236, 3104, 2992, 2844, 1630, 1557, 1508, 1380 and 1175. ¹HNMR (DMSO-d6, ppm): 10.533, 10.495 (d, 1H, –NH), 8.458 (s, 1H, Ar–H), 8.282–8.260 (d, 1H, Ar–H), 8.101, 8.079 (d, 1H, Ar–H), 8.033 (s, 1H, Ar–H), 7.354 (s, 1H, Ar–H), 5.530–5.236 (dd, 2H, OH), 4.092–3.943 (m, 2H, –CH₂CHCH₂), 3.834 (s, 3H, –OCH₃); 3.8–3.432 (m, 8H, –CH₂CHCH₂), 3.35 (m, H₂O); 2.50 (s, DMSO); 2.220 (s, 3H, –NHCOCH₃).

D5: Yield is 89%. M.P. is 166–168℃. Element analysis: Calc: C 39.50, H 3.60, N 13.17. Found: C 39.53, H 3.60, N 13.78. FT-IR (KBr, cm⁻¹): 3440, 3377, 3111, 2999, 2831, 1610, 1570, 1518, 1389 and 1172. ¹HNMR (DMSO-d6, ppm): 9.366 (s, 1H, –NH); 8.902–7.087 (m, 4H, Ar–H); 5.854–5.191 (dd, 2H, –OH); 4.388–3.990 (m, 2H, –CH₂CHCH₂); 3.827 (s, 3H, –OCH₃); 3.990–3.398 (m, 8H, –CH₂CHCH₂); 3.45 (m, H₂O), 2.50 (s, DMSO); 2.170 (s, 3H, –NHCOCH₃).

Dispersion of the reactive disperse dyes and preparation of the printing paste

The dispersion of the reactive disperse dyes was carried out according to Li et al.²² The dye (75 g), the dispersing agent MF (45 g) and water (180 ml) were added to a grinding mill (8.5 cm inner diameter), and the mixture was stirred for 15 min. Then, the grinding material, silica sand (density 2.66 g/cm³; fineness 100–150 mesh; 600 g), was added and subsequently grinded for 30 min at 30℃ with 1260 r/min. Finally, the mixture was filtered and dried at 75℃.

The printing pastes of the dyes were respectively formulated according to the following procedure: dyes, 80 g (including synthesized dye and dispersing agent MF), sodium alginate paste (40 g/L) 60 g, urea 60 g and resist salt S (sodium 3-nitrobenzene sulfonate) 15 g, triethanolamine (TEA) 20 g. The balance of water was added for a total of 1000 g.

Printing for cotton fabrics

The flat screen-printing method was applied to cotton fabrics. The printed fabrics were cured at different temperatures for 12 min. They were subsequently washed with soaping agent of 5 g/L at 98℃ for 10 min. Then all the printed samples were rinsed thoroughly with cold water.

Color yield analysis and dye fixation on cotton fabric

The methods of testing the color yield (K/S) and dye absorbance were similar to Li et al.²²

The dye fixation yield (F%) was measured and calculated using equation (1)

F % = \frac{(K / S) afte r_{DMF}}{(K / S) afte r_{soaping}} \times 100 %

(1)

where (K/S)after_DMF and (K/S)after_soaping are the K/S values of the printed fabrics after and before extraction with 50% dimethylformamide (DMF) for 10 min. (K/S)after_soaping includes the color yields of the covalent and non-covalent bond combination of the dyes on the fabric. (K/S)after_DMF represents the dyes on the fabric by the covalent bond. The dyes, which combined with cellulose by the non-covalent bond, can be washed away by the 50% DMF solution.

Fastness properties of the printed cotton fabrics

Fastness properties to washing, dry and wet rubbing, perspiration and light were evaluated according to the respective international standards: ISO 105-C04 (2010), ISO 105-X12 (2001), ISO 105/E04 (2013) and ISO 105-B02 (2013).

Results and discussion

Electronic absorption spectra and solvent effect of the synthesized dyes

The electronic absorption spectra of the synthesized dyes in different solvents were measured. The maximum absorption wavelength (λ_max) and the calculated molar extinction coefficient (ε) of D1–5 in DMF, acetone (AT) and acetonitrile (ACN) are summarized in Table 1. The maximum absorptions of D1–5 were from 474 to 601 nm, which were orange to blue shades. The electronic absorptions of all five dyes had a larger bathochromic shift in DMF. D4 showed a bathochromic shift of 28 nm in comparison with D3 in DMF, due to a chlorine group in the o-position. By introducing two strong electron-withdrawing nitro groups and bromine groups, D5 exhibited a larger bathochromic shift than that of D1–4. For steric hindrance, compared with mono-substituted in the aromatic cycle, D5 showed general strength. The electronic absorption properties of D1–5 were found to be solvent dependent, which showed larger bathochromic shifts in a stronger polar solvent than that in the weaker polar solvents, and the order is DMF > ACN > AT.

Table 1.

λ_max and the molar extinction coefficient of the synthesized dyes

Dye	λ_max (nm)			ɛ (L mol⁻¹cm⁻¹)
Dye	DMF	AT	ACN	DMF	AT	ACN
D1	474	466	462	32,728	31,460	31,114
D2	532	520	518	38,177	42,930	41,202
D3	530	524	518	22,809	24,843	23,665
D4	558	552	542	27,204	32,387	29,906
D5	601	588	584	28,533	39,816	37,571

DMF: dimethylformamide; AT: acetone; ACN: acetonitrile

Printing property of the synthesized dyes for cotton fabrics

Five synthesized dyes, D1–5, were applied to cotton fabrics with the flat screen-printing method. TEA as a catalyst was added to the crosslinking reactive system. TEA is a tertiary amine and the outermost electron of the N atom has a pair of unshared electrons. It has a nucleophilic nature and is a proton accepter. The alkyl group in TEA has strong electro negativity, and it is easy for it to attack the Cδ⁺ in the epoxy group. TEA can promote the reaction between the hydroxyl group of cotton cellulose and the epoxy group of the dyes. Urea was used as an additive in the printing paste. It plays an important role in the cotton printing process, which is usually added in the reactive dye printing paste as a dye solubilization and disaggregating agent in the paste and a swelling agent for cellulose during steaming.

Because the synthesized reactive disperse dyes could dye two kinds of fibers, cotton and polyester, at the same time during the printing procedure, the curing fixing method of cotton fabric printing was applied in this study.

Effect of curing temperature on the fixation of the printed cotton fabrics

The synthesized reactive disperse dyes have two functional groups, 3-chloro-2-hydroxypropyl. The 3-chloro-2-hydroxypropyl functional group of the dyes could form a covalent bond with the hydroxyl group on cellulose by a crosslinking reaction. The mechanism of the crosslinking reaction at the alkaline condition is shown in Scheme 2.

Scheme 2.

Reaction mechanism of the cotton fiber and epoxy group on the dyes.

The temperature is a crucial factor for the crosslinking reaction between the epoxy group and the hydroxyl group on cotton cellulose. The fixation of D1–5 on cotton fabrics at different temperatures was measured at TEA 20 g, sodium bicarbonate 20 g. The results are shown in Figure 1. It can be found that the F(%) of the printed cotton fabrics rapidly increased with temperature increasing. The good color yields of D1–5 on cotton fabrics were obtained at 165–180℃. The fixation yield of the five dyes on cotton fabrics was more than 90%. The fixation yield of D1 reached 95%. This is because the two reactive groups of the dyes possess an excellent reaction property with cellulose. The fixation yield in addition to related to the reactive group is also associated with the chromophore. The molecular structures of D1 and D2 are small and therefore easy to spread into the fiber, whereas the molecular structure of D5 is the largest, which is not easy to spread into the fiber, affecting the reaction and further affecting the fixation yield.

Figure 1.

Effect of the curing temperature on the fixation yield.

Effect of alkaline on the fixation of the printed cotton fabrics

It can be shown from Scheme 2 that the reaction between cotton cellulose and the reactive disperse dyes could take place under the alkaline condition. Sodium bicarbonate could promote the ring opening reaction of the epoxy group, and it can accelerate the ionization of cotton cellulose to give oxygen anions (-O⁻). The fixation of D1–5 on cotton fabrics with different alkaline dosages was measured and is shown in Figure 2. The fixation yields of D1–5 increased obviously with the increase of the concentration of sodium bicarbonate. The concentration of sodium bicarbonate was more than 25 g/L, the fixation yields of the five dyes did not further increase. So, we selected sodium bicarbonate, 25 g/L, as a suitable concentration for the further investigation.

Figure 2.

Effect of sodium bicarbonate on the fixation.

Effect of urea as an additive on the fixation of the printed cotton fabrics

Urea is an important compound in reactive dye printing paste. It can improve the solubility of dyes in the reaction medium, dye disaggregation, retardation of water evaporation during drying and swelling of cotton fiber in the printing process. The effect of urea dosage on the fixation of the printed cotton fabric is shown in Figure 3. The results indicate that the fixation of the printed samples slightly increased with increasing the urea concentration in the printing paste.

Figure 3.

Effect of urea on the fixation.

Effect of dye concentration on the color yield of the printed cotton fabrics

The K/S values of D1–5 on the printed cotton fabrics at different concentrations, 20–120 g/L, were investigated. The results are shown in Figure 4. The dyes with two functional groups increased the reaction chance between the hydroxyl group of cotton and the epoxy group of dyes. With increasing the dye concentration, the K/S values of the printed fabrics increased rapidly until 100 g/L. The slope of the color strength slowed down over 100 g/L, suggesting that the saturation point had been reached. All dyes exhibited an excellent building up property. In particular, the K/S value of D1 reached 23.5. The results demonstrate that dyes with bi-functional, two 3-chloro-2-hydroxypropyl groups had good reactive ability.

Figure 4.

Building up property of D1–5 on cotton fabrics.

Fastness property of the printed cotton fabrics

The fastness properties of the printed cotton fabrics with five synthesized reactive disperse dyes are summarized in Table 2. The washing, perspiration and rubbing fastness of the printed samples were good. The light fastness for the printed cotton fabrics was moderate.

Table 2.

Fastness properties of the printed cotton fabrics (grade)

Samples	Light fastness	Rubbing fastness		Washing fastness		Fastness to perspiration
Samples	Light fastness	Dry	Wet	SC	SW	SC	SW
D1	2–3	3–4	3	4	4	4	4
D2	3	3	3–4	4	4	4	4
D3	3	3	3	4	4–5	5	5
D4	3	4	3	4–5	4	5	5
D5	3	3–4	3	4–5	4	5	5

SC: staining on cotton; SW: staining on wool.

Conclusion

Five crosslinking reactive disperse dyes containing two 3-chloro-2-hydroxypropyl groups were synthesized. These dyes exhibited solvent dependency, which showed larger bathochromic shifts of the dyes in a stronger polar solvent than in the weaker polar solvents. Under the alkaline condition, the functional groups of the dyes could crosslink with the hydroxyl group of cellulose. The fixation yield of the five dyes on cotton fabrics was more than 90%. The fixation yield of the reactive disperse dye, D1, reached 95%. The building up property was good for all the dyes, especially for D1. Excellent washing, perspiration and rubbing fastness of the printed fabrics were obtained. The light fastness for cotton fabrics was moderate.

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 Shanghai Natural Science Foundation (grant number 13ZR1400300) and the Chinese Universities Scientific Fund (grant number CUSF–DH–D– 2014033).

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