**Improvement in Acrylic Fibres Dyeing**

E. Giménez-Martín, A. Ontiveros-Ortega and M. Espinosa-Jiménez *Department of Physics, EPSJ Jaén,University of Jaén, Campus "Las Lagunillas", Jaén, Spain* 

### **1. Introduction**

88 Textile Dyeing

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At the interface of an electrically charged textile fabric and an aqueous solution containing an electrolyte, a surface-active agent, or a dye, an electrical double layer is set up. An electrokinetic potential or zeta potential, ζ, is developed when one of these two charged surfaces moves with respect to the other. This potential plays an important role in the electrical characterization of textile materials and in dyeing and, more generally, in many important wet processes to which textile fibers are subjected (Dai, 1994; Jacobash, 1985; Lokhande, 1970; Teli, 1993). In our opinion, the most appropriate electrokinetic technique to study the zeta potential of fibrous systems is the streaming potential method (Espinosa &Gonzalez, 1991, Gonzalez &Espinosa, 1988).Studies of the sorption of ionic and reactive dyestuff on textile fabrics shows that the electrokinetic potential and surface charge density of fibers can be influenced to a great extent by surfactant and dyes (Anders, 1965). Analysis of the solid surface free energy, together with electrokinetic measurements of the system and an investigation of the adsorption of surfactants and dyes on textiles, provides extensive information about dyeing and finishing mechanisms of fabrics (Peters, 1975). The determination of the surface free energy of a solid surface is important in a wide range of problems in pure and applied science. The surface free energy concept can be used for investigating physicochemical surface properties of textile fabrics and the results of these investigations can be correlated with important technical properties of textile applications (Grundke et al., 1991, Chibowski & Gonzalez, 1993; Holys &Chibowski, 1992; Espinosa et al., 1997; Chibowski et al. 1998). Because of the importance of acrylic fibers in textile industry, investigations in improving their dyeing properties are very interesting. In the present study, we have used as acrylic fibres samples of 100% pure Leacril fibers, of 1.3 dtex, from Montefibre S.A., Barcelona (Spain). Leacril fibers practically do not swell in water (Shukla et al., 1991). The retention of water vapor on the fibers is of the order of ca. 0.8% (Frushour & Knorr, 1985). These fibers are hydrophobic in nature, and they are not easily penetrated by the dyes ((Lokhande, 1970). The use of the surfactants to assist wetting of textile fabrics and, more particularly, for the level of dyeing has become widespread (Cegarra et al. 1984). In the present study, we have used various cationic and reactive dyes in the dyeing process of Leacril fibers. For improvement in Leacril fibers dyeing, we have used various surfactants in the pretreatment of the fibers, in order to obtain the conditions that increase the amount of dye uptaken by the mentioned acrylic fibers. On the other hand, also our purpose is to know the different physico-chemical mechanisms that govern the adsorption of different dyes onto the textile materials when these materials have been pretreated with different ionic surfactants.

Improvement in Acrylic Fibres Dyeing 91

Fig. 1. Zeta potential of Leacril, as a function of NCPCl concentration 293°K..

as a function of the final (equilibrium) concentration of the surfactant in solution.

Fig. 2. Amount of NCPCl adsorbed, Meq , at different temperatures.

Sorption experiments at different temperatures have been done to explain the electrokinetic behavior. Figure 2 shows the amount of N-CPCl in the Leacril, Meq, at different temperatures,

It can be seen that Meq increases with both increasing concentration of N-CPCl in solution and increasing temperature of sorption. The amount of surfactant taken up by the fiber is low when the equilibrium concentration is lower than 10-4 M, and increases abruptly above this value, attaining a value of 730mmol/kg at 10-2 M of surfactant in solution and 313°K. The results shown in Figures 1 and 2, suggest a mode of binding that can be interpreted, probably, on the basis of electrostatic attraction between both the sulphonate and sulfate end-groups of the Leacril fibers and the cation of the surfactant. The increase of the amount of surfactant taken up by the fiber at increasing temperature of the sorption is due, probably, to the increasing ionization of the sulphonate and sulfate end-group of the Leacril at pH=5.8, and the electrostatic attraction between the mentioned end-groups of the fiber

#### **2. Effect of n-cetylpyridinium chloride on the zeta potential and surface free energy of the leacril fibers**

Acrylic fibers consist of ca. 90% acrylonitrile and ca. 9% vinyl acetate,(Frushour & Knorr, 1985). Sulfur dioxide and potassium persulfate were used as initiating agents for the copolymerization reaction. These compounds produce a large number of both sulphonate and sulfate end-groups on the fiber (Adamson, 1982). These end-groups are ionized in aqueous medium and hence these groups produce negative charge on the fiber surface. The fibrous samples were rinsed repeatedly with deionized water until the conductivity of the washing water remained constant. Finally, they were dried in an oven at 313 °K.

In this work we have used N-Cetylpyridinium chloride (N-CPCl) surfactant, as the agent which we have tested for the pretreatment of Leacril to improve the posterior adsorption of different dyes onto Leacril fibers. This surfactant is A.R. grade from Merck, and was used without further purification. Chemical structure is shown in scheme 1.

$$\operatorname{co}\left[\bigvee\_{\square} \mathbb{H}^{\operatorname{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\bf{\cdots}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}} $$
}}} }} }} 

Scheme 1.

Water with a conductivity of ca. 10-6 S cm-1 was used to prepare the different solutions. For the determination of the zeta potential of Leacril fibers, we have used porous plugs with constant Leacril content (1 g) and densities of packing in the plug of 75.7, 86.6, 101, 121.2, 151.5 and 202 kg m-3, in the streaming potential experiments. An Anton Paar EKA, Electrokinetic Analyzer, from Graz (Austria) was used for the determination of the zeta potential of the Leacril samples in the pretreatment of the fibers with the surfactant and also in the posterior dyeing, with different dyes, of the above pretreated samples. The samples of untreated Leacril fibers were conditioned before the electrokinetic and sorption experiments with solutions of N-Cetylpyridinium chloride at temperatures of 283°K., 293°K., 303°K. and 313°K. for 72 h, this time being sufficient to attain equilibrium.

For the determination of the zeta potential of the system, the models of bundle of capillaries, Goring and Mason, Biefer and Mason, and Chang and Robertson (Goring & Mason, 1950; Biefer & Mason, 1050; Chang & Robertson, 1967) were applied to evaluate the zeta potentials of the Leacril plugs. However we have verified that the Goring and Mason model is, in our case, the model which presents a superior correlation coefficient both over the whole tested range of concentration of N-Cetylpyridinium chloride in solution and for all the investigated packing densities of Leacril in the plug (Espinosa &Giménez, 1996).

In the Figure 1, are shown the zeta potentials obtained for Leacril, as a function of the molar concentration of N-CPCl at 293°K. It can be observed that the values of zeta potential are not high. The zeta potential of the system is negative at low concentrations of the surfactant in solution. Zeta potential sign changes at concentrations higher than ca. 2x10-5 M of surfactant in solution, its value being zero at this concentration. It increases for values up to 10-4 M of N-CPCl, where ζ is maximum, and then decreases as the concentration of the surfactant in solution increases. Further, zeta potential is very low at concentrations between 5x10-3 M and 10-2 M of surfactant.

**2. Effect of n-cetylpyridinium chloride on the zeta potential and surface free** 

Acrylic fibers consist of ca. 90% acrylonitrile and ca. 9% vinyl acetate,(Frushour & Knorr, 1985). Sulfur dioxide and potassium persulfate were used as initiating agents for the copolymerization reaction. These compounds produce a large number of both sulphonate and sulfate end-groups on the fiber (Adamson, 1982). These end-groups are ionized in aqueous medium and hence these groups produce negative charge on the fiber surface. The fibrous samples were rinsed repeatedly with deionized water until the conductivity of the

In this work we have used N-Cetylpyridinium chloride (N-CPCl) surfactant, as the agent which we have tested for the pretreatment of Leacril to improve the posterior adsorption of different dyes onto Leacril fibers. This surfactant is A.R. grade from Merck, and was used

Water with a conductivity of ca. 10-6 S cm-1 was used to prepare the different solutions. For the determination of the zeta potential of Leacril fibers, we have used porous plugs with constant Leacril content (1 g) and densities of packing in the plug of 75.7, 86.6, 101, 121.2, 151.5 and 202 kg m-3, in the streaming potential experiments. An Anton Paar EKA, Electrokinetic Analyzer, from Graz (Austria) was used for the determination of the zeta potential of the Leacril samples in the pretreatment of the fibers with the surfactant and also in the posterior dyeing, with different dyes, of the above pretreated samples. The samples of untreated Leacril fibers were conditioned before the electrokinetic and sorption experiments with solutions of N-Cetylpyridinium chloride at temperatures of 283°K., 293°K., 303°K. and 313°K. for 72 h, this time being sufficient to attain

For the determination of the zeta potential of the system, the models of bundle of capillaries, Goring and Mason, Biefer and Mason, and Chang and Robertson (Goring & Mason, 1950; Biefer & Mason, 1050; Chang & Robertson, 1967) were applied to evaluate the zeta potentials of the Leacril plugs. However we have verified that the Goring and Mason model is, in our case, the model which presents a superior correlation coefficient both over the whole tested range of concentration of N-Cetylpyridinium chloride in solution and for all the investigated

In the Figure 1, are shown the zeta potentials obtained for Leacril, as a function of the molar concentration of N-CPCl at 293°K. It can be observed that the values of zeta potential are not high. The zeta potential of the system is negative at low concentrations of the surfactant in solution. Zeta potential sign changes at concentrations higher than ca. 2x10-5 M of surfactant in solution, its value being zero at this concentration. It increases for values up to 10-4 M of N-CPCl, where ζ is maximum, and then decreases as the concentration of the surfactant in solution increases. Further, zeta potential is very low at concentrations between

washing water remained constant. Finally, they were dried in an oven at 313 °K.

without further purification. Chemical structure is shown in scheme 1.

packing densities of Leacril in the plug (Espinosa &Giménez, 1996).

**energy of the leacril fibers** 

Scheme 1.

equilibrium.

5x10-3 M and 10-2 M of surfactant.

Fig. 1. Zeta potential of Leacril, as a function of NCPCl concentration 293°K..

Sorption experiments at different temperatures have been done to explain the electrokinetic behavior. Figure 2 shows the amount of N-CPCl in the Leacril, Meq, at different temperatures, as a function of the final (equilibrium) concentration of the surfactant in solution.

Fig. 2. Amount of NCPCl adsorbed, Meq , at different temperatures.

It can be seen that Meq increases with both increasing concentration of N-CPCl in solution and increasing temperature of sorption. The amount of surfactant taken up by the fiber is low when the equilibrium concentration is lower than 10-4 M, and increases abruptly above this value, attaining a value of 730mmol/kg at 10-2 M of surfactant in solution and 313°K. The results shown in Figures 1 and 2, suggest a mode of binding that can be interpreted, probably, on the basis of electrostatic attraction between both the sulphonate and sulfate end-groups of the Leacril fibers and the cation of the surfactant. The increase of the amount of surfactant taken up by the fiber at increasing temperature of the sorption is due, probably, to the increasing ionization of the sulphonate and sulfate end-group of the Leacril at pH=5.8, and the electrostatic attraction between the mentioned end-groups of the fiber

Improvement in Acrylic Fibres Dyeing 93

3. The solid surface is precontacted with a polar liquid vapor but the penetrating liquid (water or formamide) does not completely spread onto the solid surface. A dynamic

4. The same liquid as in case (iii) is used. The solid surface is bare and the liquid forms a dynamic contact angle, θ. In this situation free energy changes involved are:

From the combination between eq.[4] and eq. [5], and using two different polar liquids as

Our experiments were performed with water, n-decane, and formamide (Table 1). Straight lines are obtained in the plots of the penetrated distance, x, vs. the time of penetration, t. From the slope of the straight lines, ΔG is obtained, and from this data, the surface free

> γ LW (mJ/m2)

Table 1. Surface tension parameters of liquids used for thin-layer wicking and contact angle

Table 2. Lifshitz-van der Waals, and acid-base components of surface free energy of Leacril

water and formamide, we can obtained the values of the acid-base components, ��

�� � ��

�� + 2���

cohesion ��. This allows determination of SLW and eq. [2] is given by:

��� = �� � �� = 2���

contact angle, θ, appears and ��� is now:

��� = ������ + �� � �� = ������ + 2���

the solid surface (Chibowski et al., 1998).

Liquid <sup>γ</sup> TOT

The results are shown in Table 2.

measurements.

N-CPCl

energy components of the fabric are estimated.

(mJ/m2)

n-Decane 23.9 23.9 0 0 Diiodomethane 50.8 50.8 0.0 0.0 Water 72.8 21.8 25.5 25.5 Formamide 58 39.0 2.28 39.6

C(M) SLW (mJ/m2) S+ (mJ/m2) S- (mJ/m2)

0 43.35 0 60.50 10-4 44.4 0.14 57.81 5·10-4 45.7 0.16 55.71 10-3 46.96 0.19 53.59 10-2 47.9 1.40 35.80

as function of the concentration N-CPCl of the treatment.

duplex film is formed onto the solid surface (precontacted plate), then ��� in the wicking process is: ��� = ��, (the surface tension of the liquid) and then R can be estimated. 2. The same liquid (n-decane) is used as above, but the strip has not been exposed to the saturated vapor (bare strip) the specific free energy changes, ���, in the penetration process, is determined from the difference between work of adhesion, �� and work of

�� � ��

�� � 2�� (3)

��� = ������ (4)

� � ��

γ <sup>+</sup> (mJ/m2)

� + 2���

� � ��

γ - (mJ/m2)

� � 2�� (5)

�� �� � of

and the cation of the surfactant is favored by the increasing temperature of sorption of the system under these conditions. The fact that the positive value of the zeta potential decreases in the concentration range where the highest amount of the surfactant in the fiber, Meq, appears (Figures 1 and 2), shows that the electrostatic interactions cannot be the only interaction responsible for the uptake of the surfactant by the fibers, some sort of specific interactions between Leacril and N-CPCl must exist. Given the hydrophobic character of the Leacril and the amphiphilic nature of the surfactant molecules, hydrophobic attractions between the fiber and the hydrophobic part of the surfactant might account for the interaction, explaining the sorption of N-CPCl on the Leacril even when it is hindered by electrostatic repulsion. The low zeta potential values for 5x10-3M and 10-2M surfactant concentration must be consequence of double layer compression.

On the other hand, analysis of the solid surface free energy together with investigation of both, the adsorption and electrokinetic behavior of the system, in the process of adsorption of surfactants and dyes onto textile fabrics, provide extensive information concerning the dyeing, wetting, and finishing mechanisms of the textile materials (Mittal, 1993). Such an investigation has not been reported previously for Leacril fabric, and studies of the surface free energy of Leacril in the processes of dyeing are very scarce.

According to the van Oss et al. approach (Van Oss, 1987,1988a, 1988b, 1989, 1992a,1992b1994), the interaction between a liquid and a solid surface can be determined from the relationship between the work of adhesion of the liquid to the solid surface, ��,and the work of cohesion between the liquid molecules,���, which is called work of spreading �� and it is defined by the equation:

$$W\_a - W\_c = W\_s = 2\sqrt{\chi\_S^{LW} \cdot \chi\_L^{LW}} + 2\sqrt{\chi\_S^+ \cdot \chi\_L^-} + 2\sqrt{\chi\_S^- \cdot \chi\_L^+} - 2\chi\_L \tag{1}$$

Where �� ��, �� �, �� �and �� ��, �� �, �� � were the components, Lifshitz-van der Waals, and acidbase, electron-acceptor and electron-donor, of solid surface and liquid, respectively. The thermodynamic characterization of the fabric surface was determined, using the thin-layer wicking method (Chibowski, 1992; Chibowski &Gonzalez, 1993; Chibowski & Holysz, 1992; Duran et al., 1994). According to the Washburn equation, eq.[2], a linear relationship must be obtained between the time (t) that a liquid takes to penetrate a distance (x) through a thin porous layer of a solid, in our experiments, through a piece of Leacril fabric of 25x4 cm2 :

$$
\omega^2 = \frac{Rt}{2\eta} \,\Delta \,\mathcal{G} \tag{2}
$$

where Δ� is the surface free energy change that takes place when the initial solid-air interface is substituted by the solid-liquid interface in the wicking process. R is the average pore radius of the solid, and η the viscosity of the liquid. In order to determine four unknown parameters of the solid surface, R effective radius porous, and the surface free energy components, γSLW, Lifshitz-van der Waals component, γS- , electron-donor and γS+, electron-acceptor components, four wicking systems can be considered in which different values of ΔG in eq. [2] appear. This systems result from the combination of two kind of liquid, non-polar and polar liquid, and two different situations of the solid sample, precontacted strip, if the sample has been previously exposed to saturated vapor of the liquid, and bare strip, when the sample is clean and dry. The situations studied were:

1. When the liquid used wets the solid completely, we used a non-polar liquid such us ndecane, and the solid has been previously saturated with its vapor in such a way that a

and the cation of the surfactant is favored by the increasing temperature of sorption of the system under these conditions. The fact that the positive value of the zeta potential decreases in the concentration range where the highest amount of the surfactant in the fiber, Meq, appears (Figures 1 and 2), shows that the electrostatic interactions cannot be the only interaction responsible for the uptake of the surfactant by the fibers, some sort of specific interactions between Leacril and N-CPCl must exist. Given the hydrophobic character of the Leacril and the amphiphilic nature of the surfactant molecules, hydrophobic attractions between the fiber and the hydrophobic part of the surfactant might account for the interaction, explaining the sorption of N-CPCl on the Leacril even when it is hindered by electrostatic repulsion. The low zeta potential values for 5x10-3M and 10-2M surfactant

On the other hand, analysis of the solid surface free energy together with investigation of both, the adsorption and electrokinetic behavior of the system, in the process of adsorption of surfactants and dyes onto textile fabrics, provide extensive information concerning the dyeing, wetting, and finishing mechanisms of the textile materials (Mittal, 1993). Such an investigation has not been reported previously for Leacril fabric, and studies of the surface

According to the van Oss et al. approach (Van Oss, 1987,1988a, 1988b, 1989, 1992a,1992b1994), the interaction between a liquid and a solid surface can be determined from the relationship between the work of adhesion of the liquid to the solid surface, ��,and the work of cohesion between the liquid molecules,���, which is called work of spreading �� and it is defined by

�� + 2���

base, electron-acceptor and electron-donor, of solid surface and liquid, respectively. The thermodynamic characterization of the fabric surface was determined, using the thin-layer wicking method (Chibowski, 1992; Chibowski &Gonzalez, 1993; Chibowski & Holysz, 1992; Duran et al., 1994). According to the Washburn equation, eq.[2], a linear relationship must be obtained between the time (t) that a liquid takes to penetrate a distance (x) through a thin porous layer of a solid, in our experiments, through a piece of Leacril fabric of 25x4 cm2 :

�� <sup>=</sup> ��

where Δ� is the surface free energy change that takes place when the initial solid-air interface is substituted by the solid-liquid interface in the wicking process. R is the average pore radius of the solid, and η the viscosity of the liquid. In order to determine four unknown parameters of the solid surface, R effective radius porous, and the surface free

electron-acceptor components, four wicking systems can be considered in which different values of ΔG in eq. [2] appear. This systems result from the combination of two kind of liquid, non-polar and polar liquid, and two different situations of the solid sample, precontacted strip, if the sample has been previously exposed to saturated vapor of the liquid, and bare strip, when the sample is clean and dry. The situations studied were: 1. When the liquid used wets the solid completely, we used a non-polar liquid such us ndecane, and the solid has been previously saturated with its vapor in such a way that a

� � ��

� + 2���

� were the components, Lifshitz-van der Waals, and acid-

� � ��

�� <sup>Δ</sup>� (2)

� � 2�� (1)

, electron-donor and γS+,

�� � ��

concentration must be consequence of double layer compression.

free energy of Leacril in the processes of dyeing are very scarce.

�� � �� = �� = 2���

��, �� �, ��

energy components, γSLW, Lifshitz-van der Waals component, γS-

�and ��

the equation:

Where ��

��, �� �, �� duplex film is formed onto the solid surface (precontacted plate), then ��� in the wicking process is: ��� = ��, (the surface tension of the liquid) and then R can be estimated.

2. The same liquid (n-decane) is used as above, but the strip has not been exposed to the saturated vapor (bare strip) the specific free energy changes, ���, in the penetration process, is determined from the difference between work of adhesion, �� and work of cohesion ��. This allows determination of SLW and eq. [2] is given by:

$$
\Delta G\_b = W\_a - W\_c = 2\sqrt{\chi\_S^{LW} \cdot \chi\_L^{LW}} - 2\chi\_L \tag{3}
$$

3. The solid surface is precontacted with a polar liquid vapor but the penetrating liquid (water or formamide) does not completely spread onto the solid surface. A dynamic contact angle, θ, appears and ��� is now:

$$
\Delta G\_P = \chi\_L \cos \theta \tag{4}
$$

4. The same liquid as in case (iii) is used. The solid surface is bare and the liquid forms a dynamic contact angle, θ. In this situation free energy changes involved are:

$$
\Delta G\_{\rm b} = \chi\_L \cos \theta + W\_a - W\_c = \chi\_L \cos \theta + 2\sqrt{\chi\_S^{LW} \cdot \chi\_L^{LW} + 2\sqrt{\chi\_S^+ \cdot \chi\_L^-} + 2\sqrt{\chi\_S^- \cdot \chi\_L^+} - 2\chi\_L} \tag{5}
$$

From the combination between eq.[4] and eq. [5], and using two different polar liquids as water and formamide, we can obtained the values of the acid-base components, �� �� �� � of the solid surface (Chibowski et al., 1998).

Our experiments were performed with water, n-decane, and formamide (Table 1). Straight lines are obtained in the plots of the penetrated distance, x, vs. the time of penetration, t. From the slope of the straight lines, ΔG is obtained, and from this data, the surface free energy components of the fabric are estimated.


Table 1. Surface tension parameters of liquids used for thin-layer wicking and contact angle measurements.

The results are shown in Table 2.


Table 2. Lifshitz-van der Waals, and acid-base components of surface free energy of Leacril as function of the concentration N-CPCl of the treatment.

Improvement in Acrylic Fibres Dyeing 95

Experiments were done as we have described in part 1. In Figure 3 are shown the zeta potential of the system untreated Leacril/RBB-R, as a function of the concentration of RBB-R in the liquid phase. We have used the Goring and Mason model for the determination of the zeta potential of the above system. All the values of the zeta potential of the system (Fig. 3) are negative. The increase in the zeta potential for concentrations of dye between 10-6 M up to 10-5 M of dye in solution can be attributed at the hydrophobic interactions between the fiber and the hydrophobic part of the dye molecule. In this process, the electric charge of the interface increase due to the presence of sulphonate groups in the dye onto the surface of fibers, in the adsorption process of the dye onto the Leacril in these conditions. On the other hand, by concentrations of dye higher than 10-5 M the chemical reactions between the –NH2 and –NH groups of the reactive dye and the sulphonate and sulfate end-groups of Leacril could be the responsible of the decrease in the zeta potential of the system shown in Figure 3 in this range of dye concentration. In this process the negative charge of the fiber and hence the zeta potential of the system, decrease in this range of concentration of reactive dye.

Fig. 3. Zeta potential of the system untreated Leacril/RBB-R, as a function of RBB-R

confirms the behavior of the zeta potential of the system shown in Figure 3.

In Fig. 4 are shown the amount of RBB-R uptaken by untreated Leacril at equilibrium, Meq as function of the equilibrium concentration of dye in solution, at different temperatures of adsorption. This adsorption is scarce at concentrations of dye lower than 10-4 M and increases abruptly for the highest concentrations of dye in the liquid phase. Also it can be observed that this adsorption is favored by an increase in the temperature of adsorption process of the RBB-R onto the fiber. This behavior can be explained for the above chemical reactions between the above mentioned groups of the fiber and the reactive dye. This fact

With the aim of to improve the dyeing conditions of the Leacril fibers with RBB-R, we have used 10-3M of N-CPCl in the pretreatment of the Leacril. Subsequently, the treated Leacril with 10-3M of the surfactant, have been dyed with different concentrations of RBB-R at the same temperatures used in the Figure 4. Also we have determined the zeta potential of the system in these conditions. In Figure 5 can be observed the behavior of the zeta potential of the system as a function of the equilibrium concentration of the reactive dye in the liquid

concentration.

In Table 2, we observe that there are no appreciable differences between the obtained values of �� �� in the different processes investigated. The high value for �� � 60.5 mJ/m2, obtained in the case of untreated Leacril, is probably due to the presence of sulphonate and sulfate end-groups in the Leacril fabrics (Espinosa et al. 1997a, 1997b; 1998). These groups are donors of electrons and produce a high value in the component �� � for untreated Leacril. This above value is similar to that obtained by van Oss et al. with water-soluble polyethyleneoxide (PEO) (van Oss, 1994). A value of �� � = 60.5 mJ/m2 consistent with these authors, findings suggests that the Leacril surface is a stronger electron donor and hence hydrophilic in nature. Also consistent with van Oss et al., values of �� � higher than28.3 mJ/m2 indicate that the solid surfaces that present this behavior have a hydrophilic character. In our case, for Leacril fabrics, the hydrophilicity of the surface could be attributed to the presence of the sulphonate and sulfate end-groups on the surface of the fabric due to their strong electron-donor character (Espinosa et al., 1998).

In previous studies (Espinosa & Giménez, 1996; Espinosa et al.,1997), it was discussed that the adsorption of N-CPCl on Leacril fabrics probably occurs by electrostatic attraction between the cation of the surfactant and the sulphonate and sulfate end-groups of the Leacril. These processes produce a decrease in the negative charge of the Leacril, and, the �� � decreases with the increasing treatment of Leacril. This may be observed in Table 2. In contrast, �� � is almost constant for both untreated Leacril and treated Leacril with increasing concentrations of NCPCl in solution. The small variation of the values of �� � shown in Table 2 is not sufficiently significant to allow conclusions to be reached about this question.

The value of �� � 35.8 mJ/m2, at 10-2 M of N-CPCl in the treatment of the fabric (Table 2 ) is probably due to the presence of N+ - pyridinium groups in the N-CPCl adsorbed on the fabrics, which is very evident at the highest concentrations of the surfactant on the fabric (see Fig. 1 and Table 1). In this process, there is probably a notable acid-base neutralization due to the interaction between the cation of the surfactant and the sulphonate and sulfate end-groups on the surface of the Leacril.

#### **3. Effect of n-cetylpyridinium chloride on the adsorption of a reactive dye onto leacril fabrics**

In this study, we have used the samples of Leacril fibers above mentioned in the paragraph no. 1 of this work. Also we have used the above surfactant N-Cetylpyridinium chloride in the pretreatment of Leacril, before of posterior dyeing of Leacril with the reactive dye. The reactive dye used has been Remazol Brilliant Blue R (RBB-R), C.I. 61200, reactive blue 19, and this dye is an amineantraquinone vinilsulphonated. This dye is referred by Hagen et al. (Hagen et al.,1966). On the other hand, this dye is of AR grade from Sigma Chemical Co. (USA) and was used without further purification. The chemical structure of the RBB-R dye is shown in scheme 2:

Scheme 2.

In Table 2, we observe that there are no appreciable differences between the obtained values

in the case of untreated Leacril, is probably due to the presence of sulphonate and sulfate end-groups in the Leacril fabrics (Espinosa et al. 1997a, 1997b; 1998). These groups are

This above value is similar to that obtained by van Oss et al. with water-soluble

mJ/m2 indicate that the solid surfaces that present this behavior have a hydrophilic character. In our case, for Leacril fabrics, the hydrophilicity of the surface could be attributed to the presence of the sulphonate and sulfate end-groups on the surface of the

In previous studies (Espinosa & Giménez, 1996; Espinosa et al.,1997), it was discussed that the adsorption of N-CPCl on Leacril fabrics probably occurs by electrostatic attraction between the cation of the surfactant and the sulphonate and sulfate end-groups of the Leacril. These processes produce a decrease in the negative charge of the Leacril, and, the ��

decreases with the increasing treatment of Leacril. This may be observed in Table 2. In

probably due to the presence of N+ - pyridinium groups in the N-CPCl adsorbed on the fabrics, which is very evident at the highest concentrations of the surfactant on the fabric (see Fig. 1 and Table 1). In this process, there is probably a notable acid-base neutralization due to the interaction between the cation of the surfactant and the sulphonate and sulfate

2 is not sufficiently significant to allow conclusions to be reached about this question.

**3. Effect of n-cetylpyridinium chloride on the adsorption of a reactive dye** 

In this study, we have used the samples of Leacril fibers above mentioned in the paragraph no. 1 of this work. Also we have used the above surfactant N-Cetylpyridinium chloride in the pretreatment of Leacril, before of posterior dyeing of Leacril with the reactive dye. The reactive dye used has been Remazol Brilliant Blue R (RBB-R), C.I. 61200, reactive blue 19, and this dye is an amineantraquinone vinilsulphonated. This dye is referred by Hagen et al. (Hagen et al.,1966). On the other hand, this dye is of AR grade from Sigma Chemical Co. (USA) and was used without further purification. The chemical structure of the RBB-R dye is shown in scheme 2:

� is almost constant for both untreated Leacril and treated Leacril with increasing

� 35.8 mJ/m2, at 10-2 M of N-CPCl in the treatment of the fabric (Table 2 ) is

findings suggests that the Leacril surface is a stronger electron donor and hence

� 60.5 mJ/m2, obtained

� for untreated Leacril.

� higher than28.3

� shown in Table

�

� = 60.5 mJ/m2 consistent with these

�� in the different processes investigated. The high value for ��

hydrophilic in nature. Also consistent with van Oss et al., values of ��

fabric due to their strong electron-donor character (Espinosa et al., 1998).

concentrations of NCPCl in solution. The small variation of the values of ��

donors of electrons and produce a high value in the component ��

polyethyleneoxide (PEO) (van Oss, 1994). A value of ��

of ��

authors,

contrast, ��

The value of ��

**onto leacril fabrics** 

Scheme 2.

end-groups on the surface of the Leacril.

Experiments were done as we have described in part 1. In Figure 3 are shown the zeta potential of the system untreated Leacril/RBB-R, as a function of the concentration of RBB-R in the liquid phase. We have used the Goring and Mason model for the determination of the zeta potential of the above system. All the values of the zeta potential of the system (Fig. 3) are negative. The increase in the zeta potential for concentrations of dye between 10-6 M up to 10-5 M of dye in solution can be attributed at the hydrophobic interactions between the fiber and the hydrophobic part of the dye molecule. In this process, the electric charge of the interface increase due to the presence of sulphonate groups in the dye onto the surface of fibers, in the adsorption process of the dye onto the Leacril in these conditions. On the other hand, by concentrations of dye higher than 10-5 M the chemical reactions between the –NH2 and –NH groups of the reactive dye and the sulphonate and sulfate end-groups of Leacril could be the responsible of the decrease in the zeta potential of the system shown in Figure 3 in this range of dye concentration. In this process the negative charge of the fiber and hence the zeta potential of the system, decrease in this range of concentration of reactive dye.

Fig. 3. Zeta potential of the system untreated Leacril/RBB-R, as a function of RBB-R concentration.

In Fig. 4 are shown the amount of RBB-R uptaken by untreated Leacril at equilibrium, Meq as function of the equilibrium concentration of dye in solution, at different temperatures of adsorption. This adsorption is scarce at concentrations of dye lower than 10-4 M and increases abruptly for the highest concentrations of dye in the liquid phase. Also it can be observed that this adsorption is favored by an increase in the temperature of adsorption process of the RBB-R onto the fiber. This behavior can be explained for the above chemical reactions between the above mentioned groups of the fiber and the reactive dye. This fact confirms the behavior of the zeta potential of the system shown in Figure 3.

With the aim of to improve the dyeing conditions of the Leacril fibers with RBB-R, we have used 10-3M of N-CPCl in the pretreatment of the Leacril. Subsequently, the treated Leacril with 10-3M of the surfactant, have been dyed with different concentrations of RBB-R at the same temperatures used in the Figure 4. Also we have determined the zeta potential of the system in these conditions. In Figure 5 can be observed the behavior of the zeta potential of the system as a function of the equilibrium concentration of the reactive dye in the liquid

Improvement in Acrylic Fibres Dyeing 97

In these processes the negative charge of the Leacril increases due to the presence of sulphonate groups in the molecules of the reactive dye adsorbed onto the pretreated fiber. When the concentration of the reactive dye in solution is between 10-5M up to 10-2M, the electrostatic interactions between both the cationic group of the pyridinium ring of the surfactant previously adsorbed and the sulphonate groups of the RBB-R could be responsible of the strong decreased in the negative value of zeta potential of the system in the concentration range mentioned. On the other hand, the chemical reactions between the groups –NH2 and –NH of the RBB-R and the sulphonate and sulfate end-groups of the Leacril also contributes in a great measure at the strong decrease in the zeta potential of the system treated Leacril/RBB-R at the highest concentrations range of the reactive dye in the liquid phase. Hence, due to the above adsorption mechanisms the negative zeta potentials of the system treated Leacril/RBB-R attain higher values in the case of pretreated Leacril with 10-3M of N-CPCl that in the case of untreated Leacril, in all concentration range of RBB-R in the liquid phase. It is evident in Figure 5 that the reactive dye is adsorbed in a superior amount for treated Leacril with the surfactant than in the

Fig. 6. Amount of RBB-R uptaken by Leacril pretreated with 10-3 M N-CPCl at equilibrium,

In Figure 6 are shown the amount of the RBB-R adsorbed at equilibrium, Meq, onto pretreated Leacril with 10-3 M of the surfactant as a function of the equilibrium concentration of the reactive dye in solution. These experiments have been done at the same temperatures shown in the above Figure 4. It can be seen in Figure 6, that all the values of Meq, of pretreated Leacril with the surfactant are higher than they are in the case of untreated Leacril shown in Figure 4. Also it can be seen, that an increase in the temperature of adsorption favors the adsorption of RBB-R onto pretreated Leacril. These facts show that, probably, the above mentioned chemical reactions between the treated fibers and the RBB-R dye are responsible for the strong adsorption of the reactive dye onto the treated Leacril (Gonzalez et al., 1987; Espinosa et al., 1997c). It is evident that the pretreatment of the Leacril

Meq, as function of the equilibrium concentration of dye in solution, at different

with the surfactant improve the adsorption of the RBB-R onto Leacril.

case of untreated Leacril.

temperatures.

phase for untreated Leacril and for Leacril treated previously with 10-3M of the above surfactant. Also we have used the Goring and Mason model for the determination of the zeta potential in these conditions.

Fig. 4. RBB-R uptaken by untreated Leacril at equilibrium, Meq, at different temperatures, as function of the equilibrium concentration of dye in solution.

In Figure 5, it can be observed a similar behavior of the zeta potential of the system in both cases. However, in this Figure can be observed that the zeta potential values of the system are higher for Leacril treated with 10-3 M of N-CPCl that in the case of untreated Leacril, in all range of concentration of RBB-R in the liquid phase. In Figure 5 the increase in the zeta potential for treated fiber in the range of 10-6M up to 10-5M of RBB-R in solution could be explained by the increase of the hydrophobic interactions between the hydrophobic part of the reactive dye and the hydrophobic parts of the Leacril/N-CPCl in the pretreatment of the Leacril.

Fig. 5. Zeta potential of untreated Leacril and for Leacril treated previously with 10-3 M of N-CPCl as a function of RBB-R concentration.

phase for untreated Leacril and for Leacril treated previously with 10-3M of the above surfactant. Also we have used the Goring and Mason model for the determination of the

Fig. 4. RBB-R uptaken by untreated Leacril at equilibrium, Meq, at different temperatures,

In Figure 5, it can be observed a similar behavior of the zeta potential of the system in both cases. However, in this Figure can be observed that the zeta potential values of the system are higher for Leacril treated with 10-3 M of N-CPCl that in the case of untreated Leacril, in all range of concentration of RBB-R in the liquid phase. In Figure 5 the increase in the zeta potential for treated fiber in the range of 10-6M up to 10-5M of RBB-R in solution could be explained by the increase of the hydrophobic interactions between the hydrophobic part of the reactive dye and the hydrophobic parts of the Leacril/N-CPCl in the pretreatment of the

Fig. 5. Zeta potential of untreated Leacril and for Leacril treated previously with 10-3 M of

N-CPCl as a function of RBB-R concentration.

as function of the equilibrium concentration of dye in solution.

zeta potential in these conditions.

Leacril.

In these processes the negative charge of the Leacril increases due to the presence of sulphonate groups in the molecules of the reactive dye adsorbed onto the pretreated fiber. When the concentration of the reactive dye in solution is between 10-5M up to 10-2M, the electrostatic interactions between both the cationic group of the pyridinium ring of the surfactant previously adsorbed and the sulphonate groups of the RBB-R could be responsible of the strong decreased in the negative value of zeta potential of the system in the concentration range mentioned. On the other hand, the chemical reactions between the groups –NH2 and –NH of the RBB-R and the sulphonate and sulfate end-groups of the Leacril also contributes in a great measure at the strong decrease in the zeta potential of the system treated Leacril/RBB-R at the highest concentrations range of the reactive dye in the liquid phase. Hence, due to the above adsorption mechanisms the negative zeta potentials of the system treated Leacril/RBB-R attain higher values in the case of pretreated Leacril with 10-3M of N-CPCl that in the case of untreated Leacril, in all concentration range of RBB-R in the liquid phase. It is evident in Figure 5 that the reactive dye is adsorbed in a superior amount for treated Leacril with the surfactant than in the case of untreated Leacril.

Fig. 6. Amount of RBB-R uptaken by Leacril pretreated with 10-3 M N-CPCl at equilibrium, Meq, as function of the equilibrium concentration of dye in solution, at different temperatures.

In Figure 6 are shown the amount of the RBB-R adsorbed at equilibrium, Meq, onto pretreated Leacril with 10-3 M of the surfactant as a function of the equilibrium concentration of the reactive dye in solution. These experiments have been done at the same temperatures shown in the above Figure 4. It can be seen in Figure 6, that all the values of Meq, of pretreated Leacril with the surfactant are higher than they are in the case of untreated Leacril shown in Figure 4. Also it can be seen, that an increase in the temperature of adsorption favors the adsorption of RBB-R onto pretreated Leacril. These facts show that, probably, the above mentioned chemical reactions between the treated fibers and the RBB-R dye are responsible for the strong adsorption of the reactive dye onto the treated Leacril (Gonzalez et al., 1987; Espinosa et al., 1997c). It is evident that the pretreatment of the Leacril with the surfactant improve the adsorption of the RBB-R onto Leacril.

Improvement in Acrylic Fibres Dyeing 99

The evolution of zeta potential of the Leacril pretreated with different concentration of PEI as function of dye aqueous solution of RBB-R concentration is represented in Fig. 8. It can be observed that the zeta potential of the system increases to reach positive values when Leacril has been pretreated with PEI, in the range of low concentrations of dye in solution. This fact could be due to the presence of amine groups from the PEI molecules adsorbed onto Leacril, possibly ionized, providing the cationic charge density to the fiber as we have observed in previous works (Ramos et al. 2006). This effect becomes more significant as the PEI concentration of the pretreatment gets higher. On the other hand, we have found that at the highest RBB-R concentrations in the liquid phase, zeta potential decreases. In our opinion, probably this is caused by the presence of the RBB-R molecules in the fiber surface, which could be taken up by chemical reaction between the amine groups of PEI previously adsorbed and the reactive β-sulfato-ethylsulfanyl group of dye molecule. Finally, the negative charge of sulfonate groups of dye molecules adsorbed onto Leacril surface would

justify the decrease in zeta potential values at the highest concentration tested.

Fig. 8. Zeta potential of Leacril pretreated with different concentration of PEI as function of

In table 3 are shown the evolution of the Surface free Energy components of Leacril pretreated with 5g/l PEI as function of two concentrations of RBB-R, and also it is presented the components of dye molecule, determined with contact angle measurements and using van Oss method. The most significant result exposed in this table could be the decreases of

our opinion, the chemical interactions between the reactive acid groups of RBB-R molecule in water solution and the basic amino groups of PEI molecules previously adsorbed over Leacril surface could explain why electron-donor character of the surface falls from an initial

value of 58 mJ/m2 to 20 mJ/m2 for the higher concentration of dye tested.

ି, of the fiber-PEI with the concentration of RBB-R. In

RBB-R concentration at 293°K .

the electron-donor component value, ߛௌ

#### **4. Influence of polyethyleneimine ion on the adsorption of rbb-r onto leacril fibers**

In other works, we have also observed the positive effect of the pretreatment of Leacril with a polycationic surfactant, polyethyleneimine ion PEI, in the posterior adsorption of this reactive dye (Giménez et al., 2007; Ramos et al., 2006). Chemical structure of this compound is shown in scheme 3.

$$\left(-\mathsf{N}\mathsf{H}\,\mathsf{CH}\_{2}\,\mathsf{CH}\_{2}\,\middle\rangle\_{\times}\left(\begin{array}{c} \mathsf{N}-\mathsf{CH}\_{2}\,\mathsf{CH}\_{2}\\ \big|\,\, \begin{array}{c} \mathsf{CH}\_{2}\mathsf{CH}\_{2}\,\mathsf{NH}\_{2}\end{array} \end{array}\right)\_{\mathbb{N}}$$

Scheme 3.

In Fig. 7 it is shown the amount of RBB-R adsorbed onto Leacril fiber previously treated with different concentrations of PEI as function of the equilibrium concentration of dye in solution, in the range between 10-6M to 10-3M, and at 293°K. As mentioned before, the amount of reactive dye adsorbed onto Leacril untreated at room temperature is scarce; we think that the attractive interactions are very weak and do not overcome the mutual electrostatic repulsion anionic functional groups. However, when the fibers are pretreated with increasing concentrations of the polyelectrolyte in solution, the amount of reactive dye adsorbed increases, reaching values of 90 mmol/kg of dried fiber, at 10-3M RBB-R in liquid phase, for a concentration of 5 g/l of PEI in the pretreatment, and at room temperature. These data could be very interesting for textile industry because the process takes place at low temperature.

Fig. 7. Amount of RBB-R uptaken by Leacril pretreated with different concentration of PEI in solution as function of RBBR concentration at 293°K .

**4. Influence of polyethyleneimine ion on the adsorption of rbb-r onto leacril** 

In other works, we have also observed the positive effect of the pretreatment of Leacril with a polycationic surfactant, polyethyleneimine ion PEI, in the posterior adsorption of this reactive dye (Giménez et al., 2007; Ramos et al., 2006). Chemical structure of this compound

In Fig. 7 it is shown the amount of RBB-R adsorbed onto Leacril fiber previously treated with different concentrations of PEI as function of the equilibrium concentration of dye in solution, in the range between 10-6M to 10-3M, and at 293°K. As mentioned before, the amount of reactive dye adsorbed onto Leacril untreated at room temperature is scarce; we think that the attractive interactions are very weak and do not overcome the mutual electrostatic repulsion anionic functional groups. However, when the fibers are pretreated with increasing concentrations of the polyelectrolyte in solution, the amount of reactive dye adsorbed increases, reaching values of 90 mmol/kg of dried fiber, at 10-3M RBB-R in liquid phase, for a concentration of 5 g/l of PEI in the pretreatment, and at room temperature. These data could be very interesting for textile industry because the process takes place at

Fig. 7. Amount of RBB-R uptaken by Leacril pretreated with different concentration of PEI

in solution as function of RBBR concentration at 293°K .

**fibers** 

Scheme 3.

low temperature.

is shown in scheme 3.

The evolution of zeta potential of the Leacril pretreated with different concentration of PEI as function of dye aqueous solution of RBB-R concentration is represented in Fig. 8. It can be observed that the zeta potential of the system increases to reach positive values when Leacril has been pretreated with PEI, in the range of low concentrations of dye in solution. This fact could be due to the presence of amine groups from the PEI molecules adsorbed onto Leacril, possibly ionized, providing the cationic charge density to the fiber as we have observed in previous works (Ramos et al. 2006). This effect becomes more significant as the PEI concentration of the pretreatment gets higher. On the other hand, we have found that at the highest RBB-R concentrations in the liquid phase, zeta potential decreases. In our opinion, probably this is caused by the presence of the RBB-R molecules in the fiber surface, which could be taken up by chemical reaction between the amine groups of PEI previously adsorbed and the reactive β-sulfato-ethylsulfanyl group of dye molecule. Finally, the negative charge of sulfonate groups of dye molecules adsorbed onto Leacril surface would justify the decrease in zeta potential values at the highest concentration tested.

Fig. 8. Zeta potential of Leacril pretreated with different concentration of PEI as function of RBB-R concentration at 293°K .

In table 3 are shown the evolution of the Surface free Energy components of Leacril pretreated with 5g/l PEI as function of two concentrations of RBB-R, and also it is presented the components of dye molecule, determined with contact angle measurements and using van Oss method. The most significant result exposed in this table could be the decreases of the electron-donor component value, ߛௌ ି, of the fiber-PEI with the concentration of RBB-R. In our opinion, the chemical interactions between the reactive acid groups of RBB-R molecule in water solution and the basic amino groups of PEI molecules previously adsorbed over Leacril surface could explain why electron-donor character of the surface falls from an initial value of 58 mJ/m2 to 20 mJ/m2 for the higher concentration of dye tested.

Improvement in Acrylic Fibres Dyeing 101

Leacril fibers versus tannic acid concentration were determined by the streaming potential method, and we have used the three different models of the capillary, although the significant levels were always higher than 95%, the best fit was obtained with the linear model of Goring and Mason. For determination of the surface free energy components by the thin-layer wicking method (42-4 strips of the fabric, 25 cm long and 2.5 cm wide, where first equilibrated in tannic acid solutions (10-5 – 10-2 M ) for 24 h at 293°K, then dried in an oven at 313°K, and kept in a desiccators. Finally, to determine critical micelle concentration (c.m.c) in tannic acid solutions, the surface tension of the solutions was measured with a

First the adsorption kinetic of tannic acid on Leacril surface from 5x10-5 M solution was studied at four temperatures, 275, 283, 293, and 303°K. The results of the measurements are

Fig. 9. Adsorption kinetic of tannic acid on Leacril surface at different temperature.

particular temperatures, which for first-order processes are expressed as follows

It is seen that even at the highest temperature,303°K, the adsorption process lasts no more than 100 min and is very fast. The adsorbed amounts of tannic acid decrease with increasing temperature, which points out that the adsorption is physical in nature. To better visualize the adsorption kinetics, the parameters describing the process are listed in Table 4. Because the shape of the curves of adsorption kinetic suggests a first-order process, the rate constant can be determined from the following equation (Anders&Sonesa, 1965; Peters, 1975,

 ܯ௧ ൌ ܯሺͳെ݁ି௧ሻ (6) Where Mt is the adsorbed amount of tannic acid on the Leacril surface at time t, Meq is equilibrium adsorbed amount, and k is the empirical rate constant. This equation has been solved numerically and thus obtained values of the rate constant are listed in Table 4 together with equilibrium amounts adsorbed, Meq. Then, the half-adsorption times were calculated for

Rame-Hart goniometer.

presented in Figure 9.

Lyklema 1995)


Table 3. Surface free energy components of Leacril pretreated with 5 g/l PEI and later dyed with RBB-R.
