Innovation and application of dyes with high fixation

Shufen Zhang,Wei Ma ,Bingtao Tang ,Bin Shan

1 State Key Laboratory of Fine Chemicals,Dalian University of Technology,Dalian 116024,China

2 School of Environmental and Municipal Engineering,Qingdao University of Technology,Qingdao 266033,China

Keywords:Reactive dyes Macromolecular crosslinking dyes Cotton fibers Fixation Dyeing properties

ABSTRACT Reactive dyes are the main species for cotton dyeing due to their wide range of hue,satisfactory color fastness and facile application method.Aiming at increasing fixation on cotton fibers,benzimidazolone yellow reactive dyes,sulfonamide red reactive dyes and anthraquinone azo blue reactive dyes are designed.The preparation,characterization and application properties of these dyes with high fixation are introduced in detail.In order to achieve dye fixation to near 100%,macromolecular crosslinking reactive dyes are designed,their dyeing and fixing mechanism are discussed.These novel reactive dyes show promising application prospect in dyeing and printing of cotton fibers.

1.Introduction

Dyes are organic chemicals with specific conjugated structures(called chromophores).They are mainly used for coloration of textile fibers,leather,paper,and can produce bright colors.China has been the world’s largest manufacturer and user of dyes for many years,accounting for more than 70%of the world’s dye output[1].

Textile fibers can be divided into synthetic and natural fibers.Among synthetic fibers,polyester is the most widely used and it is commonly dyed with disperse dyes.In the dyeing process,almost all the disperse dyes can be utilized to achieve high fixation.Moreover,because of their weak water solubility,disperse dyes show high wash fastness,and their rub fastness is also good.For natural fiber dyeing,reactive dyes with superior color fastness are usually used owing to formation of covalent bonds between dyes and fibers,and they are the most important dye species for natural fiber dyeing.

Natural fibers include amino-containing fibers,such as silk and wool;and hydroxyl-containing ones,such as cotton and hemp.Among them,cotton fibers,which account for nearly 95%of natural fibers,are the most important fiber species,and their dyeing study is a representative in natural fiber dyeing.When reactive dyes are used to dye cotton,their fixation is only 70%-80% even if bifunctional reactive dyes are employed [2,3].Monofunctional reactive dyes present even lower fixation,hence producing a large amount of dyeing wastewater which is quite difficult to deal with.

The molecular structure of reactive dye consists of chromophore and reactive group,which decides the color and the ability of the dye to react with the fibers,respectively.Usually dye reactivity is represented byR(%),which is the percentage of the dye fixed on the fibers to that adsorbed.The proportion of the dye adsorbed on the fibers to that applied,which is represented byE(exhaustion,%),is determined by the dye structure containing both chromophore and reactive group.In addition,the percentage of the dye chemically bonded to the fibers is called dye fixation,which is expressed asF(F=E×R).Reactive dyes with bifunctional reactive groups can achieveR(%) higher than 90%,however,the dye exhaustionE(%)is commonly lower than 90%,soF(%)of most dyes is lower than 80%.Therefore,increasing adsorption capacityE(%)of the reactive dyes is one of the effective way to enhance dyeF(%) on the fibers.

In this paper,by enlarging chromophore structure or decreasing water-solubility,reactive dyes with high adsorption capacity on cotton were designed and investigated.Besides that,macromolecular crosslinking reactive dyes were also designed to achieve near 100% fixation of the dyes on cotton.

2.Design of Reactive Dyes with High Fixation and Good Dyeing Properties

Yellow,red and blue are primary colors of dyes,a whole set of dyes include three primary colors to meet the basic demand and realize precise regulation of various colors.So,in our study,we designed yellow,red and blue reactive dyes with high fixation.

2.1.Design and preparation of benzimidazolone yellow azo reactive dyes

Water-soluble yellow azo dyes whose maximum absorption wavelengths are lower than 430 nm are mainly based on benzene-azo-benzene structures.The main coupling components are pyrazolone sulfonic acid,pyridinone sulfonic acid and their derivatives.Azo dyes prepared with amino C-acid as diazo component contain naphthalene-azo-benzene structure,and the absorption spectra of the dyes shift to longer wavelength,resulting in orange color.Reactive Yellow M-5G (also called Reactive Brilliant Yellow M-3G in China,Fig.1) with single chromophore and two reactive groups,and Reactive Yellow 160 (Fig.2) are yellow dyes with good application performance in dyestuff industry.Their molecular structures are shown as follows:

Fig.1.Reactive Yellow M-5G (Reactive Brilliant Yellow M-3G).

Fig.2.Reactive Yellow 160.

The fixation of these two reactive dyes is both over 80%.However,due to complex synthesis technique and limited structure adjustability of the coupling components-pyrazolone sulfonic acid and pyridinone derivatives,dye fixation is difficult to be further improved.In this study,we designed benzimidazolone yellow dye [4,5] and chose Reactive Yellow M-5G as contrast dye for comparison.

5-Aminobenzimidazolone without water-soluble group shows larger conjugated structure compared with benzene ring.We used 5-aminobenzimidazolone as diazo component,and coupled with phenyl coupling components to produce yellow dyes with maximum absorption wavelengths of about 420 nm.The dyes show larger conjugated structures compared with Reactive Yellow M-5G and Reactive Yellow 160,resulting in higher dye exhaustion on the fibers.5-Aminobenzimidazolone can be facilely prepared by solid state reaction of benzimidazolone with urea andophenylenediamine at 150-250 °C,then through nitration and reduction,5-aminobenzimidazolone is prepared.For dye synthesis,diazo salt of 5-aminobenzimidazolone is synthesized first,then it couples with the condensates of 2,4-diaminobenzenesulfonic acid and chloro-s-trazines to yield 5-aminobenzimidazolidone monoazo reactive dyes.The structures of the yellow dyes are shown in Fig.3.

Representative structures of R1,R2,R3and R4,and the maximum absorption wavelength and molar absorption coefficient of the dyes are shown in Table 1.

IR and HRMS data of the benzimidazolone yellow dyes are shown in Table 2,and the dyeing properties are shown in Table 3.

Fig.3.General structural formula of benzimidazolone-based reactive dyes.

Table 1Substituent groups of benzimidazolone-based reactive dyes

As can be seen from Tables 1-3,presence of benzimidazolidinone group increases the adsorption capacity of the dyes on cotton,even if there are two sulfonic groups on the aromatic amines,dye exhaustion (E) can reach 82.7%.When the dye molecule contains only one reactive group,the reactivity (R) is less than 80%,and the dye fixation (F) on cotton is only 62.3%.When the dye was designed to contain an ethyl sulfone sulfate group (Y3),Ereached 96.7% andRwas 91.8%,resulting inFas high as 88.8%.In comparison with Reactive Yellow M-5G,although these two dyes have similar reactivity,the exhaustion of benzimidazolone yellow dye is increased by about 10%,and the final fixation is increased by 9.6%.

Table 2FT-IR and MS data of benzimidazolone-based reactive dyes

Table 3Dyeing properties of benzimidazolone-based reactive dyes

Table 4R1,R2 and spectral properties of the sulfonamide azo red reactive dyes

Based on the above results,we prepared a yellow bifunctional reactive dye with simple structure,single chromophore,high fixation of 88.8% and satisfactory color fastness.

2.2.Design and preparation of red reactive dyes containing sulfonamide groups

Industrial practice shows that bright red dyes with blue hue are all monoazo species with H-acid as coupling component.H-acid has two sulfonic groups,diazo components used also have sulfonic groups,and some reactive groups bear sulfate or sulfonic groups,so there are multiple sulfonic acid groups in this kind of monoazo dyes.These groups endow the dyes with good water-solubility,but low adsorption capacity on the fibers.In order to improve exhaustion of red dyes on cotton,it is necessary to reduce the water solubility,that is,to reduce the number of sulfonic acid groups or to increase the adsorption capacity of the dye on the fibers.

Through sulfonamidation of the sulfonic acid of the diazo component,we designed a kind of red reactive dyes containing sulfonamide group to increase the adsorption capacity of the dyes [6,7].In consideration of steric effects,p-aminobenzenesulfonamide was employed as diazo component and a new series of sulfonamide-bearing red reactive dyes were prepared.Their structures are presented in Fig.4.

Fig.4.General structural formula of sulfonamide-containing red reactive dyes.

R1,R2,dye parameters,characterization data and dyeing properties are shown in Tables 4-6,respectively.

The dyeing properties of the red dyes on cotton are listed in Table 6.For comparison,a commercial red reactive dye C.I.Reactive Red 227 (see Fig.5),also known as Reactive Red M-2BE in China,is also used to dye cotton.This dye has been recognized as the best red reactive dye in industry,and its molecular structure is as follows.

It can be seen from Tables 4 and 6 that after introduction of sulfonamide or sulfonamide derivatives,Eof the corresponding dyes on cotton fibers is increased by at least 3%;In comparison of the dyeing properties of C.I.Reactive Red 227,M-SA-a showed not only enhanced exhaustion by 3.6%,but also increased reactivity by 2.2%.As a result,its final dye fixation reached 81.3%.When the sulfonic acid group was replaced by aminopyrimidine sulfonamide,the hydrophobicity of dye M-SD-a was further improved.It can be observed from the table,EandRwere increased by 5.1% and 3.3%,respectively.And dye fixation on cotton finally reached 83.7%.

Table 5MS and FT-IR data of sulfonamide azo red reactive dyes

Table 6Dyeing properties of the sulfonamide azo red reactive dyes

Fig.5.C.I.Reactive Red 227.

Fig.6.Reactive Blue KP-BR.

As discussed above,H-acid monoazo bifunctional reactive dyes with sulfonamide derivatives as diazo components can achieve fixation as high as 83.7% and good color fastness at the same time,which is superior to the H-acid monoazo bifunctional reactive red dye commonly used in industry.

2.3.Design and preparation of reactive dyes with anthraquinone azo chromophores

Bromamine acid is an important intermediate in manufacture of blue anthraquinone dyes.Bifunctional reactive dye KP-BR has bright blue color,good dyeing performance and color fastness,especially high light fastness up to 6 grade.The chemical structure of Reactive Blue KP-BR is shown below in Fig.6.

H-acid diazo dye,such as C.I.Reactive Black 5(see Fig.5),called Reactive Black 5 in China,shows color of Tibetan blue and high molar absorption coefficient.Its structure is as follows (Fig.7).

Anthraquinone dyes usually show the disadvantages of low color strength and high price,which restrict their wide application.Azo dyes have higher color intensity but lower light fastness.In order to make full use of the light stability of anthraquinone structures and high color intensity of azo dyes,we designed azoanthraquinone dyes and prepared a kind of blue dyes with double H-acid monoazo-anthraquinone structures (see Fig.8) [8-10].

The substituent group,the maximum absorption wavelength and molar absorption coefficient of the dyes are shown in Table 7.

IR and HRMS data of the dyes are shown in Table 8.

From Table 9,the fixation of this kind of dyes on cotton is all above 88%,and the highest one reached 94.2%.Light fastness of the dyes is all above grade 4,and the highest is grade 5.Dry and wet rub fastness can reach grade 4-5 and grade 4,respectively,and wash fastness is above grade 4.So these dyes exhibit very good application performance.

Table 7Structure and spectral data of bis-H-acid monoazo-anthraquinone reactive dyes

Table 8MS and FT-IR data of of H-acid monoazo-anthraquinone reactive dyes

Table 9Fixation and color fastness of H-acid monoazao-anthraquinone reactive dyes

Table 10Dyeing properties of macromolecular crosslinking dyes

The anthraquinone ring in the dye molecule forms a conjugated system with the phenylazo bond on the 1,4-position.Thus the conjugated chain of the molecule is extended through two azo groups,and the dye shows blue color (Figs.9 and 10).

Based on the above results,we developed bis-H-acid monoazoanthraquinone blue reactive dyes,which is a kind of new blue dyes with excellent comprehensive properties.Among them,dye B4 showed fixation as high as 94.2% with very good color fastness.

3.Design and Dyeing Properties of Macromolecular Crosslinking Reactive Dyes

Although bis-H-acid monoazo-anthraquinone reactive dye with large chromophore could reach fixation of 94%,there are still about 6%of the dyes being wasted.If further enlarge the molecular structure to increase adsorption,the preparation process will be complex and the cost for dye manufacture will not be acceptable in industry.Therefore,dye chemists find a new way to solve the problem.They designed two kinds of dyes:cross-linking dyes and polymer dyes.

Most crosslinking dyes do not contain reactive groups,they contain -NH2,-SO2NH2and other crosslinkable groups similar to the reactive groups on the fibers.During dyeing,crosslinking agents are used as a bridge to connect the dyes with the fibers through covalent bonds,as shown in Fig.11 [11].

Fig.7.C.I.Reactive Black 5.

Fig.8.General structural formula of bis-H-acid monoazo-anthraquinone.

Traditional crosslinking dyes only contain 1 or 2 crosslinking groups,which limits their reactivity with the crosslinkers,so it is difficult to achieve 100% fixation,and the color of dyed fabric is not bright and sometimes color change occurs due to that the crosslinking group is on the chromophore and the structure of the chromophore is changed after the cross-linking reaction.In addition,the crosslinkers used in fixing are not stable or show problem of formaldehyde release.Although the crosslinking dyes do not present industrial application value,they provide a good idea to design new dyes with high fixation.

Polymer dyes are a kind of dyes with molecular weight more than tens of thousands,which are prepared by introducing small molecule chromophores into the main chain or side chain ofpolymers.They not only have bright color of small molecule dye,but also exhibit high reactivity,solvent resistance and heat resistance.As a kind of dyes applied by blending color masterbatches with substrates,polymer dyes have good coloring performance,but when they are used in aqueous solution for fiber dyeing,it is difficult to penetrate into the fiber due to large molecular weight.

On the basis of long-term research on reactive dyes and polymer dyes,our team combined the advantages of crosslinking dyes and polymer dyes to design macromolecular crosslinkingdyes [12-17].The molecular weight of the macromolecules with repeated structural units is controlled at the order of magnitude of 103,and the number of the reactive groups on the macromolecules is regulated.30% of the reactive groups on the macromolecules are used to react with the selected chromophores,and at the same time,multiple crosslinking groups which can react with cotton fibers are introduced to finally form the macromolecular crosslinking reactive dyes.During dyeing,the macromolecules and chromophores form supramolecular affinity on the fibers;in the crosslinking fixation process,multiple crosslinking groups react with the fibers,making the fixation of the dyes on cotton close to 100%[18-22].The general formula of the macromolecular crosslinking reactive dyes is shown as follows (Fig.12).

Fig.9.Isomerization structures of bis-H-acid monoazo-anthraquinone reactive dye.

Fig.10.Isosurface of HOMO of dye B4.

Fig.11.Sketch map of crosslinking dyeing.

Fig.12.Structural formula of macromolecular crosslinking reactive dye.

Fig.13.Schematic diagram of covalent crosslinking among dyes,crosslinkers and fibers.

The dyeing properties of the macromolecular crosslinking dyes are shown in Table 10.

It can be seen from Table 10 that the yellow,blue and black dyes all reached 100%exhaustion,the red one is 99%,and these dyes all have very high reactivity of 99%,resulting in fixation higher than 98%.The results also show satisfactory light,rub and wash fastness of these macromolecular crosslinking dyes.Light fastness is 4-5 or 5 grade,dry rub fastness reaches 4-5 or 5 grade,wet rub fastness is 3-4 or 4 grade,and all wash fastness achieves 4-5 or 5 grade.

The dyeing principle of macromolecular crosslinking reactive dyes is as follows (Fig.13):

The three-dimensional size of the macromolecular crosslinking reactive dyes is close to that of reactive dyes with large molecular structure,and their molecular flexibility is good.It is proved that the dyes can penetrate into the fibers completely.Meanwhile,macromolecular crosslinking dyes twine on the fibers and selfcrosslinking reaction happens among the dyes,so they display high fixation and excellent dyeing performance.

4.Conclusions

This paper introduces innovation of reactive dyes and macromolecular crosslinking reactive dyes with higher dye exhaustion and fixation compared with the best species commonly used in dye industry.By enlarging chromophore structure or decreasing water-solubility,exhaustion of the reactive dyes on cotton fibers is enhanced.The fixation of the designed yellow,red and blue reactive dyes reaches 88.8%,83.7%and 94.2%,respectively;and that of the macromolecular cross-linking dyes is all close to 100% on cotton fibers.These dyes can be used as high-fixation reactive dyes to meet the needs of dyeing and digital printing of natural fibers.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work is supported by the National Key Research &Development Plan (2017YFB0307401),the Liaoning Revitalization Talent Program (CLXC1801006),and the Fundamental Research Funds for the Central Universities (DUT19TD28).