Journal of Engineered Fibers and Fabrics 113 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

Cationic Modification of Cotton Fabrics and Reactive Dyeing Characteristics

Nebojša Ristić, Ivanka Ristić

High Professional School of Textile, Leskovac, Jablanicki Okrug Serbia And Montenegro

Correspondence to:

Nebojsa Ristic email: bojana1998@ptt.rs

ABSTRACT The effect of cationic modification of cotton fabrics, using commercial agent Sintegal V7conc, on reactive dyeing characteristics was studied in this work. The changes after cationization and their effects on practical application of reactive dyes were identified by various methods. Cationically modified fabrics have more positive zeta potential, compared to untreated fabrics, which has a favorable influence on reactive dyeing in the absence or presence of salt. Color intensities of reactive dyes reached their maximum on samples treated with the highest concentration of Sintegal V7conc solution and dyed in the presence of standard salt concentration. The results obtained indicate that color intensity increase is a combined contribution of both salt and cationic agent on adsorption and fixation of reactive dyes on cotton. Keywords: Cationic modification, cotton, zeta potential, reactive dye, dyeing. INTRODUCTION For cotton dyeing, reactive dyes have been used very often and they are, by consumption, the most important textile dyes [1]. High popularity of reactive dyes is based on producing brilliant and fast colors with a wide range of shades using various environmentally friendly procedures. Reactive dyes stand out from other dyes by their ability to make covalent bonds between carbon atoms of dye reactive group and oxygen atoms of cotton hydroxyl groups under alkaline conditions [2]. Reactive dyes are divided, according to the structure of reactive group, in haloheterocycle and vinyl sulfone based dyes, which react with cellulose through nucleophilic substitution and addition mechanisms, respectively. Commercially, the widest used systems are: vinyl sulfone (VS), monochlorotriazine (MCT), bifunctional dyes, difluoro chloropyridine (DFCP), monofluorotriazine (MFT) and dichlorotriazine (DCT). In addition to reacting with fiber, reactive dyes also react with water (dye hydrolysis) in a form which cannot bond to cotton, but behaves as a

substantive dye and affects color fastness on fabric. The most important parameters affecting exhaustion and “fixation” of reactive dyes are temperature, salt concentration, alkali concentration, and liquid ratio [3]. The main drawback of reactive dyes is low equilibrium exhaustion, due to low dye affinity for cotton, requiring high amounts of salt and alkali in the dyeing bath, which, when released into the water streams, produce disturbances in delicate biochemistry of water organisms. The purpose of physical and chemical procedures for modification of cellulose fibers is to increase reactive dye exhaustion and fixation degree and saving electrolytes. The pretreatment to improve functionality and dyeing ability of cellulose fibers, using cationic agents, has attracted attention recently [4-7]. The reason for such treatment is improvement of cationic activities of cellulose fibers and reduction of electrostatic repulsion of negative ions resulting in a positive effect on absorption of anionic dyes and poly electrolytes. Recently reported were the results of chemical, structural and morphological changes of cotton after treatment with triazine derivatives containing cationic and anionic groups [8], and the effects of the treatment on dyeing with reactive dyes [9]. A number of changes are identified on modified cotton: formation of new molecular structures containing cationic and anionic groups, very low reduction of crystallinity degree, and modification of surface morphology. Modified cotton was dyed with reactive dyes and a higher exhaustion and fixation degree of reactive dyes was achieved as a result of reaction with new groups. The pretreatment of cotton fabrics with cationic polyvinyl amino-chloride increases dye reactivity and induces the Freundlich type of isotherm to be replaced by Langmuir type after modification [10]. The increased yield of reactive dye on cotton fabrics treated with commercial cationic agent is explained by positive surface charge of cationized cotton fiber [11]. Moreover, introduction of amine groups in the cotton structure increases reactive dye yields due to ionic

Journal of Engineered Fibers and Fabrics 114 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

attraction between cationic groups and reactive dye anions [12]. Precationization of cotton using commercial agents containing epoxide group gave better color yield during printing of cotton fabrics with pigments and anionic dyes and lower loss of color after several washing cycles [13]. It was found that during cationization of cotton, etherification of primary hydroxyl groups on cellulose takes place [14]. The reaction is superficial since X-ray diffraction showed that cationization has no effect on cotton crystalline structure [15]. Dyeing of cationized cotton without salt indicated that reactive group type did not affect the dye yield on cationized cotton and color fastness was not changed [16]. Commercial cationic agents can also be successfully used to enhance cotton dyeing with natural dyes in acidic medium with ultrasound [17, 18]. In this study, cotton fabric was treated with commercial cationic agent in order to enhance dyeing ability of cotton with reactive dyes of various functional groups. The dyeing was performed both with and without salt. Identification of cationic agent on cotton fabric samples was done by measuring fabric zeta potential, retained water quantity, and the use of scanning electron microscopy. The aim of this work was to determine the changes on the surface of cationized cotton fabrics and to correlate them with reactive dyeing characteristics to improve reactive dye utilization. EXPERIMENTAL Materials Bleached cotton fabric with surface mass of 204.5 g/m2 was used in the experiment. Pretreatment was made using commercial cationic agent Sintegal V7conc (Chemapol, Czech Republic). Sintegal V7conc is quaternized polyglykol ether of fatty amine with cationic character. For dyeing the samples the following dyes were used: monochloro triazine reactive dyes Ostazin Red H-3B (C.I. Reactive Red 45:1) and Ostazin Blue H-BR (C.I. Reactive Blue 5) (Chemapol, Czech Republic) and vinyl sulfone reactive dyes Remazol Red B (C.I. Reactive Red 22) and Remazol Brilliant Blue R (C.I. Reactive Blue 19) (Dy Star, Germany). The dyes used were of commercial grade. Cationization of Cotton Fabric The cotton fabric was treated with cationic agent Sintegal V7conc solutions with three concentrations (0, 5 g/L, 1 g/L and 2 g/L) by exhaustion method at 50oC without salt. After 30 minutes, 10 g/L Na2CO3 was added and the treatment prolonged for an additional 30 minutes. The cationized samples were neutralized with diluted acetic acid solution, rinsed

with water and dried at room temperature. Table I shows sample labels and treatment parameters.

TABLE I. Sample labels and treatment parameters.

MEASUREMENTS AND ANALYSIS Zeta Potential Measurement The Zeta potential of cotton fibers was measured by the streaming method using an electrokinetic analyzer (EKA, A. Paar) in a cylinder cell adjusted for textile fiber measurement. Measurement was performed in relation to pH values of electrolyte solution (10-3 mol/dm3 KCl). The fiber sample, 1 g mass, is placed in the instrument measuring cell between two electrodes (Ag/AgCl). Under the influence of the given pressure, electrolyte solution flows through the measuring cell with the stationary sample. As a result of hydrodynamic streaming of liquid through the sample, a streaming potential (Up) or streaming current (Ip) arises which is then measured on an electrokinetic analyzer. From the given values, zeta potential is calculated according to the Helmholtz-Smoluchowsky equation [19]:

pRQ

LU p

0

(1)

or

pRQ

LI p

0

(2)

where, ζ – zeta potential (mV), Up – streaming potential (mV), Ip – streaming current (mA), ε – permittivity electrolyte solution (Fm-1)(kgm-3s4A2), ε0 – vacuum permittivity (Fm-1)(kgm-3s4A2), η – dynamic viscosity of solution (Pas)(kgm-1s-1), Δp – pressure difference between capillary ends (Pa) (Nm-2), L – capillary length (m), R – electrical resistance (Ω), Q – capillary cross-section (m2). To measure zeta potential, the samples of cotton fabric were washed in deionized water to conductivity of 1-4 μS/cm. SEM Analysis For the characterization of surface morphological changes, the scanning electron microscope JEOL JCM 5300 (Jeol-Japan) was used. The samples were prepared for scanning using the standard preparation

Journal of Engineered Fibers and Fabrics 115 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

procedure applying gold vapor to fiber surface for five minutes to make it conductive for cathode deposition of gold vapor. Water Retention Value To determine the water retention, the samples of cotton fabrics were immersed in distilled water for 24 hours and then centrifuged at 7800 min-1 for 2 minutes. After weighing (Ww) and drying at 105oC, the mass of dry samples (Wd) was measured and water retention values calculated from:

ddw WWWWRV / (3)

Dyeing and Colo r Measurements The dyeing of 4 g samples was carried out in an Ahiba type G7B laboratory apparatus with vertical movement of material at a bath ratio of 1:45. All dyeing was carried out using the All-in method. Dye concentration was 1% based on material mass, Na2CO3 20 g/L and NaCl concentrations were 0, 10 and 50 g/L. Dyeing was carried out at 80oC (Ostazin dyes) and 60oC (Remazol dyes) for two hours, reaching temperatures in 20 min. Dyeing start was at room temperature. After dyeing, the samples were washed and divided in two parts. One sample part was treated in anionic washing agent solution Jugopon 50 (sodium salt of alkyl benzene sulfonate, Chromos, Croatia) with 2 g/L concentration at 95oC for 10 min. After rinsing and drying at room temperature, coloristic measurements were made on both sample parts on reflexion spectrophotometer Spectraflash SF 600X (Datacolor, USA) to determine color intensity (K/S), fixation degree F, percentage increase in color intensity (I), and color uniformity σ(λ). Color intensities (K/S) were determined at maximum dye absorption wave length (Ostazin Red H-3B, λ = 550 nm; Ostazin Blue H-BR, λ = 630 nm; Remazol Red B, λ = 520 nm and Remazol Brilliant Blue R, λ = 610 nm) using Kubelka-Munk equation:

R

R

S

K

2

1 2 (4)

where: K – light absorption coefficient, S – light scattering coefficient, R – D65/10 light reflection. K/S values were calculated based on reflection values of untreated and soap solution treated sample, and fixation degree was calculated from Eq. (5):

%100

0

S

KS

K

F T (5)

Where subscript T refers to fabric treated in soap solution and subscript 0 to untreated fabric. Percentage of dye intensity increase (I) on cationized samples compared to untreated sample is given by the following equation:

I =

%100/

//

o

ok

SK

SKSK (6)

Where subscript k refers to cationized fabric samples and subscript 0 to untreated fabric. Color uniformity was calculated by measuring K/S values on 20 random sample spots at maximum absorption wave lengths λ using Eq. (7) and Eq. (8):

2

1,

1

)/()/()(

n

SKSKn

ii

(7)

n

iin SKSK

1,

1 // (8)

Where σ(λ) is the standard deviation of each random spot K/S value with (K/S)λ, λ is the maximum absorption wave length, n is the number of measured spots, and (K/S)i,λ is the K/S value of each random spot. Color uniformity expressed by σ(λ) is improved when σ(λ) value decreases [20]. Wash fastness was determined according to ISO 105-CO6 (1994). RESULTS AND DISCUSSION Zeta Potential The surface of textile fibers in neutral water solutions is negatively charged due to dissociation of functional groups and adsorption of ions from the solution, inducing formation of electrical double layer in water solutions of electrolytes. Dissociated carboxyl groups formed by oxidation of aldehyde groups on terminal glucoside units also contribute to

Journal of Engineered Fibers and Fabrics 116 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

the negative charge of the cotton surface apart from dissociation of functional hydroxyl group. The negative surface charge of textile fibers, known as zeta potential (ζ), hampers anionic dye adsorption on the fiber surface [21] and has a greater significance for dye utilization if dye affinity is lower. The Zeta potential of cotton fabric was measured by streaming current method depending on pH values of 0,001 M KCl solution in a pH range of 2, 5 to 10. Measured zeta potential values, shown in Figure 1, indicate dissociation of functional groups (-OH and –COOH) of cotton cellulose inducing negative fabric charge. At all solution pH values, untreated cotton fabric had the lowest zeta potential value and the lowest pH value when ζ = 0. Negative charge of cationized cotton fabrics is significantly lower irrespective of treatment agent concentration. It is obvious, from measured zeta potential values at pH 10, that all cationized fabrics are much more positively charged and, therefore, show better adsorption of anionic dyes [22, 23]. In this work, a long chain cationic compound, commercial product Sintegal V7conc was used at three different concentrations. Binding of cationic surfactant during the treatment leads to the change of fabric surface charge. The change appears first inside the so called Stern's layer. Due to long hydrophobic chain, the next step of adsorption is tail-to-tail binding resulting in orientation of positive molecule part toward solution, so the positive charge appears to be more positive zeta potential. It was shown that this molecular orientation increases zeta potential of cotton fabrics cationized with Sintegal V7conc from ζ = -19 mV for P0 to ζ = -15,3 mV for P0,5, to ζ = -14,9 for P1 and to ζ = -13,7 mV for P2 at pH 10, which are reactive dyeing conditions.

-20

-15

-10

-5

0

5

10

2 3 4 5 6 7 8 9 10

pH

[m

V]

P0

P0,5

P1

P2

FIGURE 1. Zeta potential (ζ) of cotton fabric cationized with different concentrations of Sintegal V7conc in relation to pH of electrolyte 0,001M KCl.

Surface Morphology Cotton fiber surface structure was examined by scanning electron microscopy in order to estimate the cationization effect on surface morphology. Figure 2(a) shows a micrograph of untreated cotton fiber surface where a system of shallow parallel grooves can be seen. Figure 2(b) and Figure 2(c) depict micrographs of cationized fiber surface. It can be noticed, based on these micrographs, that there are no big changes in surface morphology, though the cationized fiber surfaces are slightly rougher than that of untreated cotton fiber, due to cationization agent deposits. Apart from increased roughness of modified cotton fibers, it can be concluded that the extent of cationization did not affect the fiber physical structure, so the hand of treated samples remained unchanged. This is an advantage of the treatment compared to polymer material treatment which produces certain stiffness of fabrics. Water Retention Value Wetting and soaking of liquids is especially important in industrial processes such as dyeing and finishing. Wetting, transport and retention of liquids in porous textile materials are complex phenomena depending on fiber surface morphology and geometry of fabric pores. Changes of chemical composition, fiber surface morphology, and structure of fiber pores can modify fabric hydrophilic characteristics. Figure 3 shows retained water values for untreated and cationically modified fabrics. On cationically modified cotton fabrics, water retention value is minimally reduced because cationization occurs mainly on primary hydroxyl groups of C-6 atom of cotton cellulose [24], so certain number of functional groups is blocked for water molecules. Probably, the fabric pore structure is slightly changed, resulting also in slightly reduced water retention values. Very small change of hydrophilicity of cationized samples cannot negatively affect cotton fiber swelling during dyeing and hygienic properties during product exploitation.

Journal of Engineered Fibers and Fabrics 117 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

(a)

(b)

(c)

FIGURE 2. SEM micrographs of untreated cotton (a) and cotton treated with 1 g/l (b) and 2 g/l Sintegal V7conc solution (c).

0

0,1

0,2

0,3

0,4

0,5

P0 P0,5 P1 P2

WR

V (

g/g

)

FIGURE 3. Retained water value of cationized cotton fabrics.

Dyeing Characteristics As already mentioned in the introduction, reactive dyes have a low affinity for cotton and, therefore, high salt (NaCl or Na2SO4) concentrations are added to the dyeing bath, which with deep shades amount up to 100 g/L. Although high quantities of salts are added, utilization of these dyes, in practical systems, amounts up to 50-60%. From this reason, increasing reactive dye utilization would have great environmental and economic importance, which is why cationic modification of cotton is suggested. In this work, standard commercial dyes with different functional groups and a commercial cationic agent were used in order to evaluate precationization efficiency and effect on reactive dye absorption and fixation, and to estimate application possibilities in actual industrial systems. Figures 4-7 clearly indicate the color intensities of Ostazin and Remazol reactive dyes on cationized fabrics are much higher than untreated cotton fabrics in the presence or absence of salt. With untreated samples the lowest intensity is obtained without salt. Salt addition progressively increases reactive dye color intensity, indicating the importance of using salt in conventional dyeing of cotton with reactive dyes. High quantities of salt are necessary to reduce negative surface potential of cotton and to overcome potential barrier which exists in absorption of dyes from solution to the fiber surface. With cationized samples, the lowest dye intensities were obtained in the absence of salt and the highest ones with the highest concentrations of cationized agent and salt.

Journal of Engineered Fibers and Fabrics 118 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

Color intensities on cationized samples dyed in the absence of salt are higher than to color intensities of untreated samples dyed with the addition of 10 g/L NaCl. Untreated samples dyed in the presence of standard salt quantity (50 g/L) have higher color intensities compared to cationized samples dyed in the absence of salt and, therefore, increased intensities of cationized samples dyed in the presence of salt can be explained as a mutual contribution of salt and cationic agent to reactive dye adsorption. On cationized samples, apart from reaction of dye reactive group and cotton functional hydroxyl group, increased reactive dye adsorption takes place due to ionic attraction of surfactant cationic groups and reactive dye molecule anionic groups [20]. The increased dye utilization with precationized samples could be explained by detected zeta potential reduction due to the presence of cationic surfactant (Figure 1).

0

0,5

1

1,5

2

2,5

3

3,5

K/S

P0 P0,5 P1 P2

0 g/L NaCl

10 g/L NaCl

50 g/L NaCl

FIGURE 4. C.I. Reactive Red 45:1 intensity on cationized cotton fabrics in relation to salt concentration.

0

0,2

0,4

0,6

0,8

1

1,2

1,4

K/S

P0 P0,5 P1 P2

0 g/L NaCl

10 g/L NaCl

50 g/L NaCl

FIGURE 5. C. I. Reactive Blue 5 intensity on cationized cotton fabrics in relation to salt concentration.

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

K/S

P0 P0,5 P1 P2

0 g/L NaCl

10 g/L NaCl

50 g/L NaCl

FIGURE 6. C.I. Reactive Red 22 intensity on cationized cotton fabrics in relation to salt concentration.

0

0,5

1

1,5

2

2,5

3

K/S

P0 P0,5 P1 P2

0 g/L NaCl

10 g/L NaCl

50 g/L NaCl

FIGURE 7. C.I. Reactive Blue 19 intensity on cationized cotton fabrics in relation to salt concentration

In Tables II and III given are values of the increase in color intensity, I, fixation degree, F, color uniformity, σ(λ), and wash fastness. From the results presented, a rapid increase of color intensities on cationized fabric is obvious compared to untreated fabric. On the fabrics dyed with Ostazin dyes, the highest intensity increase was detected with dyeing without salt, while in case of Remazol dyes; the highest color intensity increase percentage was on the samples dyed in the presence of minimum salt quantity. Cationized fabrics contain positive groups which increase reactive dye exhaustion due to ionic attraction and this is most distinctive when the dye is in dissociated form in the solution, i.e. with minimum salt content. At higher salt concentrations the dye dissociation is progressively suppressed and, therefore, the ionic attraction is lower and the color intensity increase is also reduced. Irrespective of described effect, cationization efficiency for reactive dye adsorption is complemented with salt action in the way that dye chemical potential in the solution is increased, i.e. the dye affinity for fiber is increased

Journal of Engineered Fibers and Fabrics 119 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

shifting dye distribution equilibrium to the fiber side. Moreover, dyeing characteristics of cationized fabrics using reactive dyes in the presence of salt are the result of both salt and cationic agent action, simultaneously reducing cotton zeta potential and increasing dye affinity for fiber. Fixation degree, F, of reactive dyes applied on cationic modified fabrics is 5-12% lower compared to untreated samples. Lower percentage of fixed dye on modified fabrics is the consequence of reactive dye–cationic agent complex formation [25] which, due to steric hindrance, can block dye diffusion in the fiber and prevent access of dye molecules to cotton cellulose functional hydroxyl groups. It is possible to remove (by washing in soap solution) the dye remaining in the complex form on cotton surfaces, giving lower fixation degree. Despite lower values of fixation degree, F, the amount of fixed reactive dye

on cationized cotton fabrics is significantly higher than on untreated fabrics because dye exhaustion is higher on cationized fabrics. Standard deviation values σ(λ) in Tables II and III clearly indicate that higher color uniformity is obtained on cationized samples. The high level of color uniformity can be attributed to new embedded cationic groups in cotton outer layer, because non polymer cationic agent can penetrate the cotton fiber increasing the number of substantive groups toward reactive dye ions and molecules, positively influencing the color uniformity. The level of dye fastness on samples, after one or more washing cycles, has identical values which is evidence of stable covalent bonds formed on modified samples as well as in conventional dyeing.

TABLE II. Color characteristics of cationized cotton fabrics dyed with Ostazin reactive dyes.

Journal of Engineered Fibers and Fabrics 120 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

TABLE III. Color characteristics of cationized cotton fabrics dyed with Remazol reactive dyes.

CONCLUSION The main purpose of this work focuses on increasing reactive dye utilization by cationizing cotton fabrics using a commercial agent. By cationizing with different concentrations of commercial agent Sintegal V7conc, the extent of negative surface charge is significantly reduced, which is explained as a more positive zeta potential of fabrics. Nevertheless, all cotton fabrics have negative charge in alkaline conditions (pH 10) in reactive dye application. Retained water quantity of precationized fabrics is minimally reduced due to partially blocked hydroxyl groups of fiber surface layer. Dyeing of cationized fabrics using reactive dyes, in the absence of salts, increases color intensities progressively with the increase of cationic agent concentration. Dye exhaustion is increased due to ionic attraction of Sintegal V7conc cationic groups and reactive dye anionic groups. Presence of salt in the dye bath positively affects the exhaustion and fixation of reactive dyes on all fabrics. With salt addition, reactive dye affinity is increased and the most intense dyeing is achieved. The achieved color intensities on cationized samples, in the presence of salt, are the result of mutual contribution of salt and cationic agent activities on reactive dye absorption and fixation. Fixation degree on modified fabrics is

slightly reduced due to formation of dye-surfactant complex on fiber surface which, because of steric hindrance, blocks dye diffusion into fiber. Compared with original fabric, cationized samples have higher color uniformity and standard fastness level, indicating that surfactant cationic groups have an importance for reactive dye absorption and that dye fixation is realized by covalent bonding with cotton hydroxyl groups, similar to standard dyeing. REFERENCES [1] Petrinić, I., Čurlin, M., Racyte, J., and Simonič,

M. Obrada otpadnih voda tekstilne industrije membranskim bioreaktorom i ponovna uporaba prečišćene vode, Tekstil 2009, 58, 20-30.

[2] Tam, K. Y., Smith, E. R., Booth, J., Compton, R. G., Brennan, C. M., and Atherton J. H. Kinetics and mechanism of dyeing processes:the dyeing of cotton fabrics with a procion blue dichlorotriazinyl reactive dye, J. Colloid Interface Sci. 1997, 186, 387-398.

[3] Lewis, D. M., and Vo, L. T. T. Dyeing cotton with reactive dyes under neutral conditions, Color. Technol. 2007, 123, 306-311.

Journal of Engineered Fibers and Fabrics 121 http://www.jeffjournal.org Volume 7, Issue 4 – 2012

[4] Baoub, M. H. V., Gauthier, R., Gauthier, H., and Rammah, M. E. B. Cationized sawdust as ion exchanger for anionic residual dyes, J. Appl. Polym. Sci. 2001, 82, 31-37.

[5] Hasani, M., Westman, G., Potthast, A., and Rosenau, T. Cationization of cellulose by using n – oxiranylmethyl – n – methylmorpholinium hloride and 2 -oxiranylpyridine as etherification agents, J. Appl. Polym. Sci., 2009, 114, 1449-1456.

[6] Liu, Z. T., Yang, Y., Zhang, L., Liu Z. W., and Xiong, H. Study on the cationic modification and dyeing of ramie fiber, Cellulose 2007, 14, 337-345.

[7] Hyde, K., Dong H., and Hinestroza, J. P. Effect of surface cationization on the conformal deposition of polyelectrolytes over cotton fibers, Cellulose 2007, 14, 615-623.

[8] Xie, K., Hou, A., and Sun, Y. Chemical and morphological structures of modified novel cellulose with triazine derivatives containing cationic and anionic groups, Carbohyd. Polym. 2007, 70, 285-290.

[9] Xie, K., Hou A., and Wang, X. Dyeing and diffusion properties of modified novel cellulose with triazine derivatives containing cationic and anionic groups, Carbohyd. Polym. 2008, 72, 646-651.

[10] Ma, W., Zhang, S., Tang B., and Yang, J. Pretreatment of cotton with poly(vinylamine chloride) for salt-free dyeing with reactive dyes, Color. Technol. 2005, 121, 193-197.

[11] Tutak M., and Özdemir, A. O. Reactive dyeing of cationized cotton: effects on the dyeing yeld and the fastness properties, J. Appl. Polym. Sci. 2011, 119, 500-504.

[12] Michel, M. N., Tera, F. M., and Ibrahim, S. F. Effect of chemical modification of cotton fabrics on dyeing properties, J. Appl, Polym. Sci., 2002, 85, 1897-1903.

[13] El-Shishtawy, R. M., and Nassar, S.H. Cationic pretreatment of cotton fabric for anionic dye and pigment printing with better fastness properties, Color. Technol. 2002, 118, 115-120.

[14] Wang, H., and Lewis, D. M. Chemical modification of cotton to improve fibre dyeability, Color. Technol. 2001, 118, 159-168.

[15] Wang, L., Ma, W., Zhang, S., Teng, X., and Yang, J. Preparation of cationic cotton with two-bath pad-bake process and its application in salt-free dyeing, Carbohyd. Polym. 2009, 78, 602-608.

[16] Montazer, M., Malek, R. M. A., and Rahimi, A. Salt free reactive dyeing of cationized cotton, Fib. Polym. 2007, 8, 608-612.

[17] Kamel, M, M., El-Shishtawy, R. M., Youssef B. M., and Mashaly, H. Ultrasonic assisted dyeing. IV.Dyeing of cationised cotton with lac natural dye, Dyes. Pigm. 2007, 73, 279-284.

[18] Kamel, M. M., El Zawahry, M.M., Ahmed N. S. E., and Abdelghaffar, F. Ultrasonic dyeing of cationozed cotton fabric with natural dye. Part 1: Cationization of cotton using Solfix E, Ultrason. Sonochem. 2009, 16, 243-249.

[19] Grancaric, A. M., Tarbuk, A., and Pusic, T. Electrokinetic properties of textile fabrics, Color. Technol. 2005, 121, 221-227.

[20] Zhang, F., Chen, Y., Lin, H., and Lu, Y. Synthesis of amino-terminated hyperbranched polymer and its application in reactive dyenig on cotton as a salt-free dyeing auxiliary, Color. Technol. 2007, 123, 351-357

[21] Kumar A. R., and Teli, M. D. Electrokinetic studies of modified cellulosic fibres, Colloids Surf. A: Physicochem. Eng. Aspects 2007, 301, 462-468.

[22] Rong, L., and Feng, G. Dyeing properties of PECH-amine cationized cotton with acid dyes, J. Appl. Polym. Sci. 2006, 100, 3302-3306.

[23] Zhang, F., Chen, Y., Lin, H., Wang, H., and Zhao, B. HBP-NH2 grafted cotton fiber: Preparation and salt-free dyeing properties, Carbohyd. Polym.2008, 74, 250-256.

[24] Mughal, M. J., Naeem, M., Aleem, A., Saeed, R., and Ahmed, K. Effect of a cationising agent on the conventional reactive dyeing of cotton, Color. Technol. 2008, 124, 62-65.

[25] Mouxiou, E., Eleftheriadis, I., Nikolaidis, N., and Tsatsaroni, E. Reactive dyeing of cellulosic fibers: Use of cationic surfactants and their interaction with reactive dyes, J. Appl. Polym. Sci. 2008, 108, 1209-1215.

AUTHORS' ADDRESSES Nebojša Ristić Ivanka Ristić High Professional School of Textile Vilema Pusmana 17 Leskovac, Jablanicki Okrug 16000 SERBIA AND MONTENEGRO