**5. Effect of the tannic acid onto the zeta potential and surface free energy components of leacril fibers**

In this part of the work we have used tannic acid as a surface active agent in the treatment of the Leacril fibers. This compound could be interesting to improve the conditions of dyeing the above acrylic fibers with a cationic dye (Chibowski et al., 1998). Chemical structure is shown is scheme 4.

Scheme 4.

Tannic acid, C76H52O46, was A.R. grade from Merck, and it was used without further purification. It is a derivative of glucose in which five hydroxyl groups are substituted for digalic acid. The result is a large number of phenolic hydroxyl groups in the tannic acid molecule.

The adsorption measurements of tannic acid onto Leacril were conducted using 1 g of the fibers that was contacted with 100 mL of the solution in the concentration range from 10-6 to 10-2 M in conical Pyrex flasks fitted with ground glass stoppers. The flasks were kept in a water bath at a desired temperature. Both the adsorption kinetic (from 5x10-5 M solution) and adsorption isotherms were determined at 275, 283, 293, and 303°K. The maximum absorbance was at λ = 271 nm. The adsorption equilibrium has been attained within 2-3 h. However, the adsorption measurements were conducted up to 24 h. To determine kinetics of the adsorption, first it was measured every second minute, up to the 30nd minute of the process duration, then every 4-5 min, and later for longer periods of time. Zeta potentials of

0 36±2 2.5±0.4 58±6 74±5 10-5 60±3 0.01±0.1 54±1 61±4 10-3 58±1 0.5±0.1 20±1 64±2

solid phase 43.8±0.4 1.0±0.2 35.7±0.8 56±1

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

**5. Effect of the tannic acid onto the zeta potential and surface free energy** 

In this part of the work we have used tannic acid as a surface active agent in the treatment of the Leacril fibers. This compound could be interesting to improve the conditions of dyeing the above acrylic fibers with a cationic dye (Chibowski et al., 1998). Chemical structure is

Tannic acid, C76H52O46, was A.R. grade from Merck, and it was used without further purification. It is a derivative of glucose in which five hydroxyl groups are substituted for digalic acid. The result is a large number of phenolic hydroxyl groups in the tannic acid

The adsorption measurements of tannic acid onto Leacril were conducted using 1 g of the fibers that was contacted with 100 mL of the solution in the concentration range from 10-6 to 10-2 M in conical Pyrex flasks fitted with ground glass stoppers. The flasks were kept in a water bath at a desired temperature. Both the adsorption kinetic (from 5x10-5 M solution) and adsorption isotherms were determined at 275, 283, 293, and 303°K. The maximum absorbance was at λ = 271 nm. The adsorption equilibrium has been attained within 2-3 h. However, the adsorption measurements were conducted up to 24 h. To determine kinetics of the adsorption, first it was measured every second minute, up to the 30nd minute of the process duration, then every 4-5 min, and later for longer periods of time. Zeta potentials of

(mJ/m2) STOT (mJ/m2)

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

RBB-R

Pure RBB-R in

with RBB-R.

shown is scheme 4.

Scheme 4.

molecule.

**components of leacril fibers** 

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 Rame-Hart goniometer.

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 presented in Figure 9.

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

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, Lyklema 1995)

$$M\_t = M\_{eq}(1 - e^{-kt})\tag{6}$$

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

Improvement in Acrylic Fibres Dyeing 103

(Figures 9 and 10) of tannic acid with different temperatures, is similar, adsorption decreases with increasing temperature. This results, can be explained, probably, because of the hydrogen bonding generated between the reactive groups of Leacril and the phenolic hydroxyl groups in the tannic acid molecules adsorbed onto the surface of Leacril (Jacobash

Fig. 10. Adsorption isotherms of tannic acid at 275, 283, and 303°K versus its equilibrium

The surface free energy components of Leacril bare and treated with tannic acid are shown

C (M) SLW (mJ/m2) S+ (mJ/m2) S- (mJ/m2) WS (mJ/m2) 0 43.3 0.00 60.5 -5.6 10-5 51.2 0.66 62.2 9.2 10-4 51.2 0.00 48.5 -5.4 10-3 51.2 0.00 12.0 -41.4 10-2 66.9 28.5 10.8 15.9 Table 5. Surface free energy components of Leacril surface and work of spreading of water

It can be seen that the apolar Lifshitz-van der Waals interaction, γSLW, increases slightly after the surface treatment with 10-5-10-3 M solutions, from 43.4 mJ/m2 (untreated surface) to 51.2 mJ/m2, but the component does not change after treatment in this concentration range. When the surface was equilibrated with 10-2M solution, the component increases up to 66.9 mJ/m2. The analysis of the electron acceptor component, γS+ (Table 3), show how its values is practically zero for bare surface and with adsorbed tannic acid solutions from 10-5 to 10-3 M. However, it becomes significant (28.5 mJ/m2) if the surface was contacted with 10-2 M solution. The changes of the electron donor component, γS- , are more complicated. At the lowest concentration of tannic acid (10-5M) the component is practically the same as for the untreated surface, but the surface treated with higher tannic acid concentrations becomes

of untreated and treated with different concentration of tannic acid.

et al., 1985, 1988).

in Table 5.

tannic acid

concentration in the range of 10-6–10-2M.

$$\mathbf{t}\_{1/2} = \frac{\ln 2}{k} \tag{7}$$

which is independent of initial concentration of the adsorbate. These values are also placed in Table 4. Having determined the rate constant k, it is possible to calculate the activation energy of the adsorption process from an Arrhenius type equation

$$k = A \cdot e^{-(E/RT)} \tag{8}$$

whose logarithmic form should be a linear dependence against 1/T, and this appeared to be the case in the studied system. As can be seen from Table 3, the rate constant k decreases with the adsorption process temperature increase. From the slope, the activation energy can be estimated. It was found to be 13.63kJ/mol. Finally, Fick's equation may be applied to calculate the diffusion coefficient D at the cylindrical walls of the fibers, (Crank 1956)

$$\frac{M\_t}{M\_{aq}} = \frac{4}{\pi^{1/2}} \left(\frac{D \cdot t}{a^2}\right)^{1/2} \tag{9}$$

For short periods of time, t, *a*, is the fiber radius, which for this Leacril was 1.5 x 10-3 cm. This equation is only exact for a constant concentration of the surfactant on the surface, whose condition is actually never fulfilled exactly. Nevertheless, the calculated values may be informative for the total insight into the adsorption process. We observe that the apparent diffusion coefficient decreases from 5.39 x 10-10 to 1.14x10-10 cm2/s, if the temperature of adsorption increases from 275 to 303°K. This is obviously a consequence of the decreasing adsorption with the temperature increase and may be a result of higher thermal energy of tannic acid molecules in the solution. It is also possible to calculate the activation energy of diffusion, E\*, using again an equation of Arrhenius type

$$D = D\_0 \cdot e^{-(E^\*/RT)}\tag{10}$$

Here D is the diffusion coefficient and Do is a factor that may be interpreted as the diffusion coefficient for the activation energy being zero. The slope of logarithmic form of this equation (which is linear against 1/T) allows calculation of the energy. For the system studied, the calculated value is 38.13 kJ/mol. This value is about twice that estimated for the activation energy of the diffusion for NCPCl on Leacril (48) and is much higher than that given above for the activation energy of this adsorption process (13.63 mJ/mol).


Table 4. Equilibrium adsorbed Amounts of Tannic Acid, Meq, Adsorption rate constant, k, half time of adsorption,, and diffusion coefficient, D.

On the other hand, the adsorption isotherms of tannic acid at 275, 283, and 303°K versus its equilibrium concentration in the range of 10-6–10-2M are presented in Figure 10. Similarly as in the kinetic experiments, the adsorption decreases with increasing temperature. The isotherms are concave and the adsorbed amount increases with the increase of equilibrium concentration. The behavior of both the adsorption kinetics and the adsorption isotherms

���� <sup>=</sup> ���

which is independent of initial concentration of the adsorbate. These values are also placed in Table 4. Having determined the rate constant k, it is possible to calculate the activation

whose logarithmic form should be a linear dependence against 1/T, and this appeared to be the case in the studied system. As can be seen from Table 3, the rate constant k decreases with the adsorption process temperature increase. From the slope, the activation energy can be estimated. It was found to be 13.63kJ/mol. Finally, Fick's equation may be applied to

For short periods of time, t, *a*, is the fiber radius, which for this Leacril was 1.5 x 10-3 cm. This equation is only exact for a constant concentration of the surfactant on the surface, whose condition is actually never fulfilled exactly. Nevertheless, the calculated values may be informative for the total insight into the adsorption process. We observe that the apparent diffusion coefficient decreases from 5.39 x 10-10 to 1.14x10-10 cm2/s, if the temperature of adsorption increases from 275 to 303°K. This is obviously a consequence of the decreasing adsorption with the temperature increase and may be a result of higher thermal energy of tannic acid molecules in the solution. It is also possible to calculate the activation energy of

Here D is the diffusion coefficient and Do is a factor that may be interpreted as the diffusion coefficient for the activation energy being zero. The slope of logarithmic form of this equation (which is linear against 1/T) allows calculation of the energy. For the system studied, the calculated value is 38.13 kJ/mol. This value is about twice that estimated for the activation energy of the diffusion for NCPCl on Leacril (48) and is much higher than that

T (K) k (min-1) 1/2 ·10-3 (min) Meq (mmol/kg) D·10-10 (cm2/s) 275 50.39 13.75 0.54 5.39 283 44.92 15.43 0.47 4.34 293 31.73 21.84 0.30 2.64 303 30.60 22.65 0.22 1.14 Table 4. Equilibrium adsorbed Amounts of Tannic Acid, Meq, Adsorption rate constant, k,

On the other hand, the adsorption isotherms of tannic acid at 275, 283, and 303°K versus its equilibrium concentration in the range of 10-6–10-2M are presented in Figure 10. Similarly as in the kinetic experiments, the adsorption decreases with increasing temperature. The isotherms are concave and the adsorbed amount increases with the increase of equilibrium concentration. The behavior of both the adsorption kinetics and the adsorption isotherms

given above for the activation energy of this adsorption process (13.63 mJ/mol).

calculate the diffusion coefficient D at the cylindrical walls of the fibers, (Crank 1956)

�� ��� <sup>=</sup> � ���� � ��� �� � ���

energy of the adsorption process from an Arrhenius type equation

diffusion, E\*, using again an equation of Arrhenius type

half time of adsorption,, and diffusion coefficient, D.

� (7)

(9)

�=���������� (8)

�=�� � ����∗���� (10)

(Figures 9 and 10) of tannic acid with different temperatures, is similar, adsorption decreases with increasing temperature. This results, can be explained, probably, because of the hydrogen bonding generated between the reactive groups of Leacril and the phenolic hydroxyl groups in the tannic acid molecules adsorbed onto the surface of Leacril (Jacobash et al., 1985, 1988).

Fig. 10. Adsorption isotherms of tannic acid at 275, 283, and 303°K versus its equilibrium concentration in the range of 10-6–10-2M.

The surface free energy components of Leacril bare and treated with tannic acid are shown in Table 5.


Table 5. Surface free energy components of Leacril surface and work of spreading of water of untreated and treated with different concentration of tannic acid.

It can be seen that the apolar Lifshitz-van der Waals interaction, γSLW, increases slightly after the surface treatment with 10-5-10-3 M solutions, from 43.4 mJ/m2 (untreated surface) to 51.2 mJ/m2, but the component does not change after treatment in this concentration range. When the surface was equilibrated with 10-2M solution, the component increases up to 66.9 mJ/m2. The analysis of the electron acceptor component, γS+ (Table 3), show how its values is practically zero for bare surface and with adsorbed tannic acid solutions from 10-5 to 10-3 M. However, it becomes significant (28.5 mJ/m2) if the surface was contacted with 10-2 M solution. The changes of the electron donor component, γS- , are more complicated. At the lowest concentration of tannic acid (10-5M) the component is practically the same as for the untreated surface, but the surface treated with higher tannic acid concentrations becomes

Improvement in Acrylic Fibres Dyeing 105

which results from Table 5.Thus, it seems that the changes of surface free energy components of Leacril caused by the adsorbed tannic acid molecules can be explained with

To evaluate possible electrostatic interaction, determinations of the zeta potential were conducted by means of the streaming potential method. As was discussed in above paragraph, three models of the capillary bundles were considered, and it seems to us that the most appropriate one is that Goring and Mason. Zeta potential values as a function of tannic acid

It is seen that the zeta potentials are small negative, but the absolute values drop practically to zero when the concentration is higher than 10-4 M. In our previous paper (Chibowski et al., 1998), ) we have found that the hydrogen and hydroxyl ions are potential determining for the Leacril surface and the isoelectric point occurred at pH= 2.2. The decrease in zeta potentials in tannic acid solutions with its increasing concentration may be explained by adsorption of tannic acid molecules whose polar groups are partially dissociated, thus possessing positive charge. Anyway, from the results presented in Figure 12 it can be concluded that the electrostatic interaction plays a minor role in the adsorption process of tannic acid and total interfacial interactions, because the zeta potentials are low. It may be postulated that apolar

concentration applying three models of capillary bundles are plotted in Figure 12.

Lifshitz-van der Waals and polar Lewis acid-base interactions are the dominant ones.

Fig. 12. Zeta potential of Leacril fibers as function of tannic acid concentration.

**6. Effect of tannic acid on the sorption of a cationic dye onto leacril fibers** 

Our purpose in this study is to investigate both the electrokinetic behavior of Leacril fabrics in the process of adsorption of a cationic dye where the Leacril fibers were previously treated with tannic acid and the behavior of the surface free energy components in the above treatment of fibers and also in the adsorption process of the cationic dye on Leacril pretreated with tannic acid. These studies are very interesting with the aim of improving the dyeing properties of Leacril, as has been observed before with cellulosic fibers.(Espinosa Jimenez et al., 1986). To explain the interactions between Leacril pretreated with tannic acid

a help of c.m.c of tannic acid solutions.

less electron-donating. To learn about hydrophobicity of the surface, the work of spreading for water was calculated. Some interesting conclusions can be draw from these values. The work for the bare surface of Leacril is a small negative. This means, that a water droplet will not fully spread on its surface. Thus, the surface is slightly hydrophobic. After equilibration with 10-5M tannic acid, it becomes low hydrophilic because positive work of spreading. With increasing concentration of tannic acid (10-4 and 10-3M) it becomes increasingly hydrophobic, and finally when equilibrated with 10-2M tannic acid, the surface converts to hydrophilic. To explain such behavior, determination of c.m.c for tannic acid could be helpful. The c.m.c was determined from surface tension measurements of its solutions. The results are shown in Figure 11, from which results show that c.m.c of tannic acid lies at ca. 3x10-4M solution.

Fig. 11. c.m.c of tannic acid obtained from surface tension of tannic acid solutions against its concentration.

Taking this into account, the changes in the hydrophobicity of tannic acid treated Leacril can be explained as follows. At low concentration (10-5 M) only a few molecules of tannic acid are adsorbed on the Leacril surface (see Figure 10), probably by hydrogen bonding between phenolic hydroxyl groups of the acid and sulphonate and sulfate end groups of the Leacril., as well electrostatic interaction. The molecules may lie flat. With this, more polar hydrogen bonding interactions appear on the surface, and the surface becomes slightly hydrophilic. When the concentration of tannic acid increases, there is less and less room for the adsorbed molecules and they have to pack, probably, with polar groups directed toward the Leacril surface. This leads to increasing hydrophobization of the surface (10-4 and 10-3M). However, at concentrations above 3x10-4M micellarization takes place, and on the surface premicelles and then micelles adsorb. It is possible to imagine that in the case of, say two-molecule premicelles, they have mutually saturated polar interactions thus giving rise to hydrophobicity of the Leacril surface.However, when micelles are already formed and adsorbed on the surface, their polar –OH groups will interact with the Leacril surface, as well as directed toward liquid phase (water), thus causing hydrophilization of the surface,

less electron-donating. To learn about hydrophobicity of the surface, the work of spreading for water was calculated. Some interesting conclusions can be draw from these values. The work for the bare surface of Leacril is a small negative. This means, that a water droplet will not fully spread on its surface. Thus, the surface is slightly hydrophobic. After equilibration with 10-5M tannic acid, it becomes low hydrophilic because positive work of spreading. With increasing concentration of tannic acid (10-4 and 10-3M) it becomes increasingly hydrophobic, and finally when equilibrated with 10-2M tannic acid, the surface converts to hydrophilic. To explain such behavior, determination of c.m.c for tannic acid could be helpful. The c.m.c was determined from surface tension measurements of its solutions. The results are shown in Figure 11, from which results show that c.m.c of tannic acid lies at ca.

Fig. 11. c.m.c of tannic acid obtained from surface tension of tannic acid solutions against its

Taking this into account, the changes in the hydrophobicity of tannic acid treated Leacril can be explained as follows. At low concentration (10-5 M) only a few molecules of tannic acid are adsorbed on the Leacril surface (see Figure 10), probably by hydrogen bonding between phenolic hydroxyl groups of the acid and sulphonate and sulfate end groups of the Leacril., as well electrostatic interaction. The molecules may lie flat. With this, more polar hydrogen bonding interactions appear on the surface, and the surface becomes slightly hydrophilic. When the concentration of tannic acid increases, there is less and less room for the adsorbed molecules and they have to pack, probably, with polar groups directed toward the Leacril surface. This leads to increasing hydrophobization of the surface (10-4 and 10-3M). However, at concentrations above 3x10-4M micellarization takes place, and on the surface premicelles and then micelles adsorb. It is possible to imagine that in the case of, say two-molecule premicelles, they have mutually saturated polar interactions thus giving rise to hydrophobicity of the Leacril surface.However, when micelles are already formed and adsorbed on the surface, their polar –OH groups will interact with the Leacril surface, as well as directed toward liquid phase (water), thus causing hydrophilization of the surface,

3x10-4M solution.

concentration.

which results from Table 5.Thus, it seems that the changes of surface free energy components of Leacril caused by the adsorbed tannic acid molecules can be explained with a help of c.m.c of tannic acid solutions.

To evaluate possible electrostatic interaction, determinations of the zeta potential were conducted by means of the streaming potential method. As was discussed in above paragraph, three models of the capillary bundles were considered, and it seems to us that the most appropriate one is that Goring and Mason. Zeta potential values as a function of tannic acid concentration applying three models of capillary bundles are plotted in Figure 12.

It is seen that the zeta potentials are small negative, but the absolute values drop practically to zero when the concentration is higher than 10-4 M. In our previous paper (Chibowski et al., 1998), ) we have found that the hydrogen and hydroxyl ions are potential determining for the Leacril surface and the isoelectric point occurred at pH= 2.2. The decrease in zeta potentials in tannic acid solutions with its increasing concentration may be explained by adsorption of tannic acid molecules whose polar groups are partially dissociated, thus possessing positive charge. Anyway, from the results presented in Figure 12 it can be concluded that the electrostatic interaction plays a minor role in the adsorption process of tannic acid and total interfacial interactions, because the zeta potentials are low. It may be postulated that apolar Lifshitz-van der Waals and polar Lewis acid-base interactions are the dominant ones.

Fig. 12. Zeta potential of Leacril fibers as function of tannic acid concentration.

#### **6. Effect of tannic acid on the sorption of a cationic dye onto leacril fibers**

Our purpose in this study is to investigate both the electrokinetic behavior of Leacril fabrics in the process of adsorption of a cationic dye where the Leacril fibers were previously treated with tannic acid and the behavior of the surface free energy components in the above treatment of fibers and also in the adsorption process of the cationic dye on Leacril pretreated with tannic acid. These studies are very interesting with the aim of improving the dyeing properties of Leacril, as has been observed before with cellulosic fibers.(Espinosa Jimenez et al., 1986). To explain the interactions between Leacril pretreated with tannic acid

Improvement in Acrylic Fibres Dyeing 107

Fig. 13. Zeta potential of the system untreated Leacril/Rhodamine B at different

dye in solution.

concentrations of the cationic dye in solution for the different models of capillary bundles. On the other hand, we have carried out adsorption experiments of Rhodamine B on Leacril at different temperatures. Figure 14 shows the amount of Rhodamine B adsorbed on Leacril, Meq, at different temperatures as a function of the final (equilibrium) concentration of the

Fig. 14. Amount of Rhodamine B adsorbed on Leacril, Meq, at different temperatures as a

It can be seen that Meq increases in all cases with both increasing concentration of dye in solution and increasing temperature of adsorption. The amount of dye taken up by Leacril is low when the equilibrium concentration is lower than 10-4M of dye and increases abruptly above this value, attaining a value of ca. 200 mmol/kg at 10-2M of dye in solution and 313°K. The observed increase in Meq with the increase in temperature of adsorption can be

function of the equilibrium concentration of the dye in solution.

and later died with the cationic dye, the electrostatic contribution will be analyzed from data of the ζ potential of the system Leacril pretreated with tannic acid/cationic dye at different concentrations of dye in the liquid phase.

 The cationic dye used is Rhodamine B (C.I. 45170). The molecular structure of this dye is shown scheme 5.

Scheme 5.

Temperatures tested in our experiments of adsorption were 283, 293, 303, and 313°K. The adsorbed amount was determined after conditioning the fibers with the solution under study for 96 h, this time being sufficient to attain the equilibrium. We have measured the optical absorbance of the dye solutions at a wavelength of 554 nm.

Figure 13 shows the behavior of the zeta potential of the system untreated Leacril/Rhodamine B at different concentrations of the cationic dye in solution for the different models of capillary bundles above described, but, the model that presents the highest correlation coefficient to obtain the data of the zeta potential of the system is the linear model of Goring and Mason that is the model to be employed to obtain zeta potential of the different pretreatments of the Leacril with tannic acid.

We can observe that the zeta potential increases in absolute value for concentrations of dye from 10-6 to 5x10-6 M of dye solution. The negative value of the zeta potential of the fiber at the lowest concentrations of dye in solution can be attributed to the existence on the surface of Leacril of the sulphonate and sulfate end groups ionized at pH 4, which is the pH condition. On the other hand, the increase in absolute value of the zeta potential of the system shown in Figure 13 for concentrations of the cationic dye from 10-6 to 5x10-6M in solution can be explained by the increase of the ionization of the carboxyl group of the Rhodamine B in the molecule of dye at the mentioned value of pH 4. Also this behavior can be explained by the increase in the hydrophobic attractions between the hydrophobic chains of the dye and the Leacril fiber in aqueous media. This fact favors the approximation of the carboxyl groups of the cationic dye to the surface of the fiber. For concentrations above 5x10-6M Rhodamine B in solution one can observe a strong decrease in the absolute value of ζ potential of the system. For the highest range of concentration of dye in solution the zeta potential of the system changes its sign. This change of sign is shown between ca. 10-4 and 10-2 M of cationic dye in solution. The mentioned decrease of the zeta potential and the change of the sign observed in this parameter can be attributed to the electrostatic attraction between the sulphonate and sulfate end groups of the Leacril and the amine groups of the Rhodamine B. The low values observed in the zeta potential of the system for 10-4 to 10-2M of dye in solution also can be attributed to the compression of the electric double layer.

and later died with the cationic dye, the electrostatic contribution will be analyzed from data of the ζ potential of the system Leacril pretreated with tannic acid/cationic dye at different

The cationic dye used is Rhodamine B (C.I. 45170). The molecular structure of this dye is

Temperatures tested in our experiments of adsorption were 283, 293, 303, and 313°K. The adsorbed amount was determined after conditioning the fibers with the solution under study for 96 h, this time being sufficient to attain the equilibrium. We have measured the

Figure 13 shows the behavior of the zeta potential of the system untreated Leacril/Rhodamine B at different concentrations of the cationic dye in solution for the different models of capillary bundles above described, but, the model that presents the highest correlation coefficient to obtain the data of the zeta potential of the system is the linear model of Goring and Mason that is the model to be employed to obtain zeta potential

We can observe that the zeta potential increases in absolute value for concentrations of dye from 10-6 to 5x10-6 M of dye solution. The negative value of the zeta potential of the fiber at the lowest concentrations of dye in solution can be attributed to the existence on the surface of Leacril of the sulphonate and sulfate end groups ionized at pH 4, which is the pH condition. On the other hand, the increase in absolute value of the zeta potential of the system shown in Figure 13 for concentrations of the cationic dye from 10-6 to 5x10-6M in solution can be explained by the increase of the ionization of the carboxyl group of the Rhodamine B in the molecule of dye at the mentioned value of pH 4. Also this behavior can be explained by the increase in the hydrophobic attractions between the hydrophobic chains of the dye and the Leacril fiber in aqueous media. This fact favors the approximation of the carboxyl groups of the cationic dye to the surface of the fiber. For concentrations above 5x10-6M Rhodamine B in solution one can observe a strong decrease in the absolute value of ζ potential of the system. For the highest range of concentration of dye in solution the zeta potential of the system changes its sign. This change of sign is shown between ca. 10-4 and 10-2 M of cationic dye in solution. The mentioned decrease of the zeta potential and the change of the sign observed in this parameter can be attributed to the electrostatic attraction between the sulphonate and sulfate end groups of the Leacril and the amine groups of the Rhodamine B. The low values observed in the zeta potential of the system for 10-4 to 10-2M of dye in solution also can be attributed to the compression

optical absorbance of the dye solutions at a wavelength of 554 nm.

of the different pretreatments of the Leacril with tannic acid.

concentrations of dye in the liquid phase.

shown scheme 5.

Scheme 5.

of the electric double layer.

Fig. 13. Zeta potential of the system untreated Leacril/Rhodamine B at different concentrations of the cationic dye in solution for the different models of capillary bundles.

On the other hand, we have carried out adsorption experiments of Rhodamine B on Leacril at different temperatures. Figure 14 shows the amount of Rhodamine B adsorbed on Leacril, Meq, at different temperatures as a function of the final (equilibrium) concentration of the dye in solution.

Fig. 14. Amount of Rhodamine B adsorbed on Leacril, Meq, at different temperatures as a function of the equilibrium concentration of the dye in solution.

It can be seen that Meq increases in all cases with both increasing concentration of dye in solution and increasing temperature of adsorption. The amount of dye taken up by Leacril is low when the equilibrium concentration is lower than 10-4M of dye and increases abruptly above this value, attaining a value of ca. 200 mmol/kg at 10-2M of dye in solution and 313°K. The observed increase in Meq with the increase in temperature of adsorption can be

Improvement in Acrylic Fibres Dyeing 109

with 10-5M tannic acid, it can be observed an increase of the zeta potential of the system from 10-6 to 10-5M of dye, where a maximum value of the zeta potential exists. At still higher concentrations of dye in solution (from 10-5 to 10-4M), an abrupt decrease in the zeta potential of the system can be observed. The increase in the zeta potential of the system from 10-6 to 10- 5M can be explained by the formation of hydrogen bonding between the phenolic hydroxyl groups of the tannic acid and the sulphonate and sulfate end groups of Leacril. In this process the negative charge is increased and hence the zeta potential of the system is also increased. Also, this behavior can be explained by the increase in the hydrophobic attractions between the hydrophobic groups of the dye and the pretreated Leacril fiber in aqueous media. This fact favors the approximation of the carboxyl group of the cationic dye to the surface of the fiber being this group ionized at the acid medium (pH = 4). Figure 15 shows that increasing the concentration of tannic acid in the pretreatment of Leacril results in an rise up of zeta potential of the system due to increasing formation of hydrogen bonding between the phenolic hydroxyl groups of tannic acid and the sulphonate and sulfate end groups of Leacril, even, the observed maximum of zeta potential of the system is displaced to the lowest concentration of

cationic dye in solution. This fact is in according with the hypothesis proposed before.

attributed to the compression of the electric double layer.

surface free energy components of Leacril with the treatment.

The strong decrease observed in the zeta potential of the system for concentrations higher than 10-5M of dye in solution in the two pretreatments of Leacril with tannic acid can be explained by the electrostatic attractions between the amine groups of the Rhodamine B and the sulphonate and sulfate end groups of Leacril. This fact is particularly marked for increasing pretreatment of Leacril with the tannic acid. It can also be observed that in the range of concentration from ca. 4x10-5 to 10-4M of dye in solution, the zeta potential of the system changes its sign. The change of sign is displaced to the lowest range of concentration of dye in the liquid phase when the Leacril fibers are pretreated with increasing concentrations of tannic acid. This fact shows that the tannic acid increases its effect on the dyeing of Leacril with the cationic dye at increasing concentration of tannic acid in the treatment of the fibers. The low values observed in zeta potential of the system from 10-4 to 10-2M of dye in solution also can be

On the other hand, we have carried out adsorption experiments of Rhodamine B on pretreated Leacril (with 10-5 and 10-4M tannic acid) at different temperatures of adsorption. Figures 16 and 17 show the amounts of Rhodamine B adsorbed on Leacril, Meq, at different temperatures as a function of the final (equilibrium) concentration of the dye in solution. It can be seen that Meq increases in all cases with increasing concentration of dye in solution. Also, it can be observed that at the highest temperature the amount adsorbed decreases. This behavior can be explained by the formation of hydrogen bonding between the carboxyl group of Rhodamine B and the phenolic hydroxyl groups of the tannic acid preadsorbed onto the fiber. (Hiemenz, 1986). Also, this fact can be explained by the electrostatic attraction between the cation of the dye and the negative charge of the fiber generated by the existence of phenolic hydroxyl groups on the fiber and the existence of sulphonate and sulfate end groups of Leacril. When comparing the values of adsorption, Meq, in Figures 16 and 17 for the two treatments of Leacril with tannic acid, one can see that the adsorption of Rhodamine B on Leacril is favored by the increasing tannic acid concentration in the pretreatment. This shows the effect of tannic acid on the sorption of a cationic dye onto Leacril. On the other hand, the behavior of the zeta potential in Figure 15 at the highest range of concentration of dye in solution, where the values of the zeta potential are very low, suggests the existence of other interactions in the systems mentioned above. Hence it is necessary to carry out other studies with the aim of understanding this behavior, such as determinations of evolution of

attributed to the increasing ionization of the sulphonate and sulfate end groups of the Leacril with increasing temperature of the system. The fact that the values of zeta potential of the system are very low in the range of concentration higher than 10-4M of dye in solution and, on the other hand, the values of adsorption, Meq, obtained in the same range of concentration increase with the concentration of dye and with temperature of adsorption shows that the electrostatic interaction cannot be the only interaction responsible for the uptake of dye by Leacril: some sort of specific interactions between Leacril and the dye must exist. Given the hydrophobic character of Leacril and the amphiphilic nature of the dye molecules, hydrophobic attractions between the fiber and the hydrophobic part of the dye might account for the interaction, explaining the sorption of Rhodamine B on the Leacril even when it is hindered by electrostatic repulsion. However, the behavior of the zeta potential, practically constant, at the highest range of concentration of dye in the liquid phase also must be a consequence of electrical double layer compression.

With the aim of improving the dyeing process of Leacril with a cationic dye, we have treated the Leacril fibers with different concentrations of tannic acid and later the treated fibers have been dyed with increasing concentrations of Rhodamine B from 10-6 to 10-2M of dye in solution. Figure 15 shows the behavior of the zeta potential of untreated Leacril and Leacril pretreated with two concentrations of tannic acid versus the molar concentration of the dye in solution. The obtained values of the zeta potential of the system shown in this figure have been obtained from the linear model of Goring and Mason, which has the highest correlation coefficient.

Fig. 15. Zeta potential of Leacril untreated and pretreated with two concentrations of tannic acid versus the molar concentration of the Rhodamine B in solution.

It can be observed that the effect of the tannic acid on the zeta potential of the system pretreated Leacril/Rhodamine B is a general increase in the absolute value of the zeta potential of the system for the all the range of concentration of dye in solution tested. The effect of the tannic acid is more marked at the higher concentrations of this compound in the pretreatment of Leacril. For the concentration range lower than 10-4 M of dye in solution and pretreatment

attributed to the increasing ionization of the sulphonate and sulfate end groups of the Leacril with increasing temperature of the system. The fact that the values of zeta potential of the system are very low in the range of concentration higher than 10-4M of dye in solution and, on the other hand, the values of adsorption, Meq, obtained in the same range of concentration increase with the concentration of dye and with temperature of adsorption shows that the electrostatic interaction cannot be the only interaction responsible for the uptake of dye by Leacril: some sort of specific interactions between Leacril and the dye must exist. Given the hydrophobic character of Leacril and the amphiphilic nature of the dye molecules, hydrophobic attractions between the fiber and the hydrophobic part of the dye might account for the interaction, explaining the sorption of Rhodamine B on the Leacril even when it is hindered by electrostatic repulsion. However, the behavior of the zeta potential, practically constant, at the highest range of concentration of dye in the liquid

With the aim of improving the dyeing process of Leacril with a cationic dye, we have treated the Leacril fibers with different concentrations of tannic acid and later the treated fibers have been dyed with increasing concentrations of Rhodamine B from 10-6 to 10-2M of dye in solution. Figure 15 shows the behavior of the zeta potential of untreated Leacril and Leacril pretreated with two concentrations of tannic acid versus the molar concentration of the dye in solution. The obtained values of the zeta potential of the system shown in this figure have been obtained from the linear model of Goring and Mason, which has the highest

Fig. 15. Zeta potential of Leacril untreated and pretreated with two concentrations of tannic

It can be observed that the effect of the tannic acid on the zeta potential of the system pretreated Leacril/Rhodamine B is a general increase in the absolute value of the zeta potential of the system for the all the range of concentration of dye in solution tested. The effect of the tannic acid is more marked at the higher concentrations of this compound in the pretreatment of Leacril. For the concentration range lower than 10-4 M of dye in solution and pretreatment

acid versus the molar concentration of the Rhodamine B in solution.

phase also must be a consequence of electrical double layer compression.

correlation coefficient.

with 10-5M tannic acid, it can be observed an increase of the zeta potential of the system from 10-6 to 10-5M of dye, where a maximum value of the zeta potential exists. At still higher concentrations of dye in solution (from 10-5 to 10-4M), an abrupt decrease in the zeta potential of the system can be observed. The increase in the zeta potential of the system from 10-6 to 10- 5M can be explained by the formation of hydrogen bonding between the phenolic hydroxyl groups of the tannic acid and the sulphonate and sulfate end groups of Leacril. In this process the negative charge is increased and hence the zeta potential of the system is also increased. Also, this behavior can be explained by the increase in the hydrophobic attractions between the hydrophobic groups of the dye and the pretreated Leacril fiber in aqueous media. This fact favors the approximation of the carboxyl group of the cationic dye to the surface of the fiber being this group ionized at the acid medium (pH = 4). Figure 15 shows that increasing the concentration of tannic acid in the pretreatment of Leacril results in an rise up of zeta potential of the system due to increasing formation of hydrogen bonding between the phenolic hydroxyl groups of tannic acid and the sulphonate and sulfate end groups of Leacril, even, the observed maximum of zeta potential of the system is displaced to the lowest concentration of cationic dye in solution. This fact is in according with the hypothesis proposed before.

The strong decrease observed in the zeta potential of the system for concentrations higher than 10-5M of dye in solution in the two pretreatments of Leacril with tannic acid can be explained by the electrostatic attractions between the amine groups of the Rhodamine B and the sulphonate and sulfate end groups of Leacril. This fact is particularly marked for increasing pretreatment of Leacril with the tannic acid. It can also be observed that in the range of concentration from ca. 4x10-5 to 10-4M of dye in solution, the zeta potential of the system changes its sign. The change of sign is displaced to the lowest range of concentration of dye in the liquid phase when the Leacril fibers are pretreated with increasing concentrations of tannic acid. This fact shows that the tannic acid increases its effect on the dyeing of Leacril with the cationic dye at increasing concentration of tannic acid in the treatment of the fibers. The low values observed in zeta potential of the system from 10-4 to 10-2M of dye in solution also can be attributed to the compression of the electric double layer.

On the other hand, we have carried out adsorption experiments of Rhodamine B on pretreated Leacril (with 10-5 and 10-4M tannic acid) at different temperatures of adsorption. Figures 16 and 17 show the amounts of Rhodamine B adsorbed on Leacril, Meq, at different temperatures as a function of the final (equilibrium) concentration of the dye in solution. It can be seen that Meq increases in all cases with increasing concentration of dye in solution. Also, it can be observed that at the highest temperature the amount adsorbed decreases. This behavior can be explained by the formation of hydrogen bonding between the carboxyl group of Rhodamine B and the phenolic hydroxyl groups of the tannic acid preadsorbed onto the fiber. (Hiemenz, 1986). Also, this fact can be explained by the electrostatic attraction between the cation of the dye and the negative charge of the fiber generated by the existence of phenolic hydroxyl groups on the fiber and the existence of sulphonate and sulfate end groups of Leacril. When comparing the values of adsorption, Meq, in Figures 16 and 17 for the two treatments of Leacril with tannic acid, one can see that the adsorption of Rhodamine B on Leacril is favored by the increasing tannic acid concentration in the pretreatment. This shows the effect of tannic acid on the sorption of a cationic dye onto Leacril. On the other hand, the behavior of the zeta potential in Figure 15 at the highest range of concentration of dye in solution, where the values of the zeta potential are very low, suggests the existence of other interactions in the systems mentioned above. Hence it is necessary to carry out other studies with the aim of understanding this behavior, such as determinations of evolution of surface free energy components of Leacril with the treatment.

Improvement in Acrylic Fibres Dyeing 111

which corresponds to the value of this component obtained for Rhodamine B from contact angle measurements. The electron-donor component, γS- , decreases from 61.7 to 51.6 mJ/m2. These values correspond practically to the obtained values of this component for untreated Leacril and Rhodamine B, respectively. This observed behavior of the components, γ <sup>S</sup>LW, γS+, and γS-, for the dyeing of Leacril with the cationic dye can be explained for the total covering of the Leacril fabric with the cationic dye due to the adsorption of this chemical component onto the Leacril surface. The high values of the electron-donor component, γS- , observed in Table 6 can be attributed to the presence of both amine and carboxyl groups in the molecule of Rhodamine B, these groups being strong donors of electrons. Also, the value of 61.7 mJ/m2 for the dyeing of Leacril with 10-5M Rhodamine B can be attributed to the presence of the above groups on the surface of the Leacril and mainly the presence of sulphonate and sulfate end groups on the Leacril fabric that at lowest concentration range of dye in solution are not totally blockaded for the

On the other hand, Table 7 shows the values of the components of the surface free energy, γ <sup>S</sup>LW, γS+, and γS- , for the dyeing of Leacril with increasing concentrations of Rhodamine B, this fabric being pretreated with 10-4 M tannic acid. It can be seen in this table, that the Lifshitz-van der Waals component, γsLW , of the system notably decreases with increasing concentration of Rhodamine B used in this treatment. This fact can be due to the increasing of the adsorption of the dye onto Leacril at increasing concentration of this cationic dye, which is favored by the presence of the mordant, tannic acid, in the pretreatment. These results can be explained by the greater fixation of the dipoles of the molecules involved in these processes by the presence of the tannic acid in the surface of the fabric which produces a greater adsorption of the cationic dye according to the results shown in Figures 16 and 17 of this work. The obtained value of γSLW for pretreated Leacril and dyeing with 10-3 M Rhodamine B, 37.6 mJ/m2 is close to the value of 38.6 mJ/m2 obtained for pure Rhodamine B (Table 7) and the general behavior of this component is to decrease their value in the presence of tannic acid preadsorbed onto the fabric. These facts show that the effect of tannic

acid is to favor the adsorption of the cationic dye onto the Leacril fabric.

died with different concentration of Rhodamine B.

In Table 8 it can be seen that the electron-donor component, γS-

C(M) <sup>γ</sup> LW(mJ/m2) <sup>γ</sup> +(mJ/m2) <sup>γ</sup> -(mJ/m2) 10-5 55.7±0.6 1.6±0.5 40.8±0.2 10-4 38.9±0.2 2.37±1 60±5 10-3 37.6±0.2 4.6±0.4 65.9±0.2

Table 8. Surface free energy components for Leacril pretreated with 10-4M of tannic acid and

increases from 40.8 to 65.9 mJ/m2 for Leacril pretreated with 10-4 M tannic acid and subsequently dyed with increasing concentrations of the cationic dye Rhodamine B. This behavior can be explained by the increasing presence on the surface of Leacril of the hydroxyl end groups of the tannic acid taken up by Leacril in its treatment and also by the presence on the surface of the fabric of both the carboxyl groups and amine groups of the chromophore of the Rhodamine B taken up by Leacril in its dyeing. These groups have a strong electron-donor character and their effects on the behavior of the surface free energy are additive. Hence the high value of γS- obtained for 10-3M Rhodamine B by the

, of the surface free energy

molecules of the cationic dye.

Rodamine B

Fig. 16. and 17. Amount of Rhodamine B adsorbed on Leacril pretreated 10-5 M and 10-4 M of tannic acid, Meq, at different temperatures as a function of the equilibrium concentration of the dye in solution, respectively.

Surface free energy components of treated Leacril dyed with Rhodamine B are shown in Table 6. To explain the behavior shown in Table 6, Table 7 shows the values of surface free energy of untreated Leacril of tannic acid and Rhodamine B in solid phase, from contact angle measurements.


Table 6. Surface free energy components of Leacril treated with different concentration of RhodamineB.


Table 7. Surface free energy components f or untreated Leacril, tannic acid and RhodamineB pure in solid phase , and Leacril treated with 10-4M of tannic acid.

In table 6 we can observe that the Lifshitz-van der Waals component, γ <sup>S</sup>LW , decreases with the increase in the amount of Rhodamine B taken up by the fabric, up to the value of 37.4 mJ/ m 2. This value is very close to the value of 38.6 mJ/m2 obtained for pure Rhodamine B with contact angle measurements. These results can be explained by the greater fixation of the dipoles of the molecules involved in these processes of adsorption. On the other hand (Table 7), the electron-acceptor component γS+, increases slightly from 0.7 to 1.4 mJ/m 2,

Fig. 16. and 17. Amount of Rhodamine B adsorbed on Leacril pretreated 10-5 M and 10-4 M of tannic acid, Meq, at different temperatures as a function of the equilibrium concentration of

Surface free energy components of treated Leacril dyed with Rhodamine B are shown in Table 6. To explain the behavior shown in Table 6, Table 7 shows the values of surface free energy of untreated Leacril of tannic acid and Rhodamine B in solid phase, from contact

C(M) <sup>γ</sup> LW(mJ/m2) <sup>γ</sup> + (mJ/m2) <sup>γ</sup> - (mJ/m2) 10-5 60.8±0.02 0.7±0.4 61.7±0.4 10-4 47.5±0.5 0.5±0.5 53.6±0.5 10-3 38.1±0.3 1.3±0.4 52.3±0.1 10-2 37.4±0.4 1.4±0.5 51.6±0.1

Untreated Leacrila 43.3±0.4 0±0.5 60.5±0.1 Tannic acid 38.2±0.3 0.4±0.4 58.7±0.1 Rhodamine Bb 38.6±0.2 1.4±0.4 51.7±0.4

acid 51.2±0.2 0±0.1 48.5±0.3

Table 7. Surface free energy components f or untreated Leacril, tannic acid and RhodamineB

In table 6 we can observe that the Lifshitz-van der Waals component, γ <sup>S</sup>LW , decreases with the increase in the amount of Rhodamine B taken up by the fabric, up to the value of 37.4 mJ/ m 2. This value is very close to the value of 38.6 mJ/m2 obtained for pure Rhodamine B with contact angle measurements. These results can be explained by the greater fixation of the dipoles of the molecules involved in these processes of adsorption. On the other hand (Table 7), the electron-acceptor component γS+, increases slightly from 0.7 to 1.4 mJ/m 2,

(mJ/m2)

pure in solid phase , and Leacril treated with 10-4M of tannic acid.

Table 6. Surface free energy components of Leacril treated with different concentration of

γ <sup>+</sup> (mJ/m2) γ - (mJ/m2)

the dye in solution, respectively.

Material <sup>γ</sup> LW

Leacril treted with 10-4 tannic

angle measurements.

Rodamine B

RhodamineB.

which corresponds to the value of this component obtained for Rhodamine B from contact angle measurements. The electron-donor component, γS- , decreases from 61.7 to 51.6 mJ/m2. These values correspond practically to the obtained values of this component for untreated Leacril and Rhodamine B, respectively. This observed behavior of the components, γ <sup>S</sup>LW, γS+, and γS-, for the dyeing of Leacril with the cationic dye can be explained for the total covering of the Leacril fabric with the cationic dye due to the adsorption of this chemical component onto the Leacril surface. The high values of the electron-donor component, γS- , observed in Table 6 can be attributed to the presence of both amine and carboxyl groups in the molecule of Rhodamine B, these groups being strong donors of electrons. Also, the value of 61.7 mJ/m2 for the dyeing of Leacril with 10-5M Rhodamine B can be attributed to the presence of the above groups on the surface of the Leacril and mainly the presence of sulphonate and sulfate end groups on the Leacril fabric that at lowest concentration range of dye in solution are not totally blockaded for the molecules of the cationic dye.

On the other hand, Table 7 shows the values of the components of the surface free energy, γ <sup>S</sup>LW, γS+, and γS- , for the dyeing of Leacril with increasing concentrations of Rhodamine B, this fabric being pretreated with 10-4 M tannic acid. It can be seen in this table, that the Lifshitz-van der Waals component, γsLW , of the system notably decreases with increasing concentration of Rhodamine B used in this treatment. This fact can be due to the increasing of the adsorption of the dye onto Leacril at increasing concentration of this cationic dye, which is favored by the presence of the mordant, tannic acid, in the pretreatment. These results can be explained by the greater fixation of the dipoles of the molecules involved in these processes by the presence of the tannic acid in the surface of the fabric which produces a greater adsorption of the cationic dye according to the results shown in Figures 16 and 17 of this work. The obtained value of γSLW for pretreated Leacril and dyeing with 10-3 M Rhodamine B, 37.6 mJ/m2 is close to the value of 38.6 mJ/m2 obtained for pure Rhodamine B (Table 7) and the general behavior of this component is to decrease their value in the presence of tannic acid preadsorbed onto the fabric. These facts show that the effect of tannic acid is to favor the adsorption of the cationic dye onto the Leacril fabric.


Table 8. Surface free energy components for Leacril pretreated with 10-4M of tannic acid and died with different concentration of Rhodamine B.

In Table 8 it can be seen that the electron-donor component, γS- , of the surface free energy increases from 40.8 to 65.9 mJ/m2 for Leacril pretreated with 10-4 M tannic acid and subsequently dyed with increasing concentrations of the cationic dye Rhodamine B. This behavior can be explained by the increasing presence on the surface of Leacril of the hydroxyl end groups of the tannic acid taken up by Leacril in its treatment and also by the presence on the surface of the fabric of both the carboxyl groups and amine groups of the chromophore of the Rhodamine B taken up by Leacril in its dyeing. These groups have a strong electron-donor character and their effects on the behavior of the surface free energy are additive. Hence the high value of γS- obtained for 10-3M Rhodamine B by the

Improvement in Acrylic Fibres Dyeing 113

 (a) (b) Fig. 18. (a) Amount of Rhodamine B adsorbed onto Leacril from its 10-3M emulsion phase containing 10-3M tannic acid at 293, 313, and 333°K, as function of time. (b) Amount of

Isothermal rates of adsorption are shown in Figures 18A and 18B. The curves in Figure 18A relate amounts of cationic dye Rhodamine B adsorbed onto Leacril from its 10-3M solution in the emulsion phase containing 10-3 M tannic acid at 293, 313, and 333°K, respectively. In Figure 18B are shown the adsorbed amounts of Rhodamine B from its 10-3M solution alone. Because the adsorption from the emulsion at 333°K is small, therefore in Figure 18B is also shown adsorption of Rhodamine B from the emulsion at this temperature. From Figures 18A and18 B it is evident that at 293 and 313°K the adsorption of dye on the Leacril is much higher in the case of the emulsion. However, at 333°K the adsorption of dye is much lower from the emulsion than from the solution of Rhodamine B. Moreover, with increasing temperature the adsorbed amount decreases from emulsion, while it increases from solution. A decreasing adsorption with increasing temperature of the process is typical for physical adsorption. The shape of the adsorption isotherms is evidence of the first-order process and therefore the adsorption rate constant can be estimated from an equation relating adsorption vs time [6]. We have determined the values of the rate constant and

> t1/2 (min)

Emulsion of the Dye 293 125.7 5.51 325.2 9.75 313 124.4 5.57 140.6 1.30 333 107.6 6.44 3.15 1.10 Solution of the Dye 293 65.5 10.3 21.85 0.44 313 77.3 8.96 32.2 1.12 333 120.8 5.73 55.51 1.52 Table 9. Equilibrium adsorbed Amounts of Rhodamine B, Meq, Adsorption rate constant, k, half time of adsorption,t, and diffusion coefficient, D for the systems 10-3M Rhodamine B in

Meq (mmol/kg) D x 1010 Cm2/s)

Rhodamine B from its 10-3M solution onto Leacril, as function of time.

half-adsorption time eq. [7] presented in Table 9.

kx103 (min-1)

emulsion/Leacril and systems 10-3M Rhodamine B in solution/Leacril.

Temp. (°K)

pretreatment of the fabric with the tannic acid, this value being 65.9 mJ/m, is higher than the value obtained for this component by Rhodamine B (Table7). This fact shows the additive effects of the groups mentioned above on the behavior of γS in these processes of dyeing Leacril with the assistance of the mordant, tannic acid. The behavior of the electronacceptor component, γS+, observed in Table 5, where an increase of this component is observed, having the value of 4.6 mJ/m2 for 10-3M Rhodamine B can be due to the formation of micelles of the cationic dye since the c.m.c of Rhodamine B is close to 10-3 M (this data was obtained from conductivity measurements). In these conditions the micelles are adsorbed, but now with polar heads directed also towards the solution phase. Hence this fact leads to an increase in the electron-acceptor component, γS+, for the higher concentration range of Rhodamine B in solution.

#### **7. Study of the leacril dyeing process by a cationic dye from an emulsion system**

In this part of the work a dye-in-emulsion dyeing process onto Leacril was investigated using a cationic dye, Rhodamine B. The process was analyzed through the changes in surface free energy of the Leacril. To our knowledge, no work has been reported in the literature dealing with the application of the dye-in-emulsion system to improve the adsorption onto Leacril. The Leacril used is the same of the above studies. The emulsion of Rhodamine B was prepared in the following way: 0.15 ml of n-hexadecane was dissolved in 7.7 ml of 2-propanol (p.a.) placed in a 100-ml flask, and then 10 ml of 0.01 M tannic acid was added (as a surfactant) in which 48 mg of Rhodamine B ( as a cationic dye) was dissolved. The content was mixed and doubly distilled water (Milli-Q System) was added up to a volume of ca. 50 ml. Next, the flask was placed in an ultrasonic bath for 15 min and again water was added to reach the final volume of 100 ml. Finally, the obtained emulsion was shaken vigorously by hand.

Studies of the kinetics of Rhodamine B adsorption onto Leacril fibers were carried out, both from its solution alone or from the emulsion (Chibowski et al., 2001). In both systems the dye concentration was 10-5M, and in the case of the emulsion tannic acid was present as a mordant agent and/ or stabilized the emulsion. For the experiments of adsorption kinetics, in Pyrex conical flasks fitted with ground glass stoppers, 1 g Leacril fiber samples were conditioned with 250 cm3 of a 10-3 M aqueous solution of Rhodamine B or the emulsion. The flasks were immersed in a water bath and the temperature was kept constant within ± 0.1°K. The adsorption was carried out at 293, 313 and 333 K. The amount of adsorbed dye on the Leacril fibers was determined from absorbency as measured with a Hitachi U-2000 spectrophotometer at a 554-nm wavelength, at which the maximum absorbency occurred. Moreover, desorption experiments were also carried out for Rhodamine B from the Leacril surface. These experiments were conducted by washing with deionized water 1g samples of Leacril fibers dyed under the described above conditions. Desorption experiments were carried out in a thermostated bath at constant agitation and a temperature of 293°K. The zeta potentials of the Leacril suspensions in water (Milli-Q system) and in tannic acid solutions were determined electrophoretically. The water pH was regulated with the help of HCl or NaOH concentrated solutions. Zetameter ZetaPlus/Pals (Brookhaven Co) was applied for this purpose. To obtain Leacril powder the fibers were ground in a coffee mill after being cooled in liquid nitrogen. To determine the Leacril surface free energy components the thinlayer wicking technique was applied.

pretreatment of the fabric with the tannic acid, this value being 65.9 mJ/m, is higher than the value obtained for this component by Rhodamine B (Table7). This fact shows the

dyeing Leacril with the assistance of the mordant, tannic acid. The behavior of the electronacceptor component, γS+, observed in Table 5, where an increase of this component is observed, having the value of 4.6 mJ/m2 for 10-3M Rhodamine B can be due to the formation of micelles of the cationic dye since the c.m.c of Rhodamine B is close to 10-3 M (this data was obtained from conductivity measurements). In these conditions the micelles are adsorbed, but now with polar heads directed also towards the solution phase. Hence this fact leads to an increase in the electron-acceptor component, γS+, for the higher concentration

**7. Study of the leacril dyeing process by a cationic dye from an emulsion** 

In this part of the work a dye-in-emulsion dyeing process onto Leacril was investigated using a cationic dye, Rhodamine B. The process was analyzed through the changes in surface free energy of the Leacril. To our knowledge, no work has been reported in the literature dealing with the application of the dye-in-emulsion system to improve the adsorption onto Leacril. The Leacril used is the same of the above studies. The emulsion of Rhodamine B was prepared in the following way: 0.15 ml of n-hexadecane was dissolved in 7.7 ml of 2-propanol (p.a.) placed in a 100-ml flask, and then 10 ml of 0.01 M tannic acid was added (as a surfactant) in which 48 mg of Rhodamine B ( as a cationic dye) was dissolved. The content was mixed and doubly distilled water (Milli-Q System) was added up to a volume of ca. 50 ml. Next, the flask was placed in an ultrasonic bath for 15 min and again water was added to reach the final volume of 100 ml. Finally, the obtained emulsion was

Studies of the kinetics of Rhodamine B adsorption onto Leacril fibers were carried out, both from its solution alone or from the emulsion (Chibowski et al., 2001). In both systems the dye concentration was 10-5M, and in the case of the emulsion tannic acid was present as a mordant agent and/ or stabilized the emulsion. For the experiments of adsorption kinetics, in Pyrex conical flasks fitted with ground glass stoppers, 1 g Leacril fiber samples were conditioned with 250 cm3 of a 10-3 M aqueous solution of Rhodamine B or the emulsion. The flasks were immersed in a water bath and the temperature was kept constant within ± 0.1°K. The adsorption was carried out at 293, 313 and 333 K. The amount of adsorbed dye on the Leacril fibers was determined from absorbency as measured with a Hitachi U-2000 spectrophotometer at a 554-nm wavelength, at which the maximum absorbency occurred. Moreover, desorption experiments were also carried out for Rhodamine B from the Leacril surface. These experiments were conducted by washing with deionized water 1g samples of Leacril fibers dyed under the described above conditions. Desorption experiments were carried out in a thermostated bath at constant agitation and a temperature of 293°K. The zeta potentials of the Leacril suspensions in water (Milli-Q system) and in tannic acid solutions were determined electrophoretically. The water pH was regulated with the help of HCl or NaOH concentrated solutions. Zetameter ZetaPlus/Pals (Brookhaven Co) was applied for this purpose. To obtain Leacril powder the fibers were ground in a coffee mill after being cooled in liquid nitrogen. To determine the Leacril surface free energy components the thin-

in these processes of

additive effects of the groups mentioned above on the behavior of γS-

range of Rhodamine B in solution.

shaken vigorously by hand.

layer wicking technique was applied.

**system** 

Fig. 18. (a) Amount of Rhodamine B adsorbed onto Leacril from its 10-3M emulsion phase containing 10-3M tannic acid at 293, 313, and 333°K, as function of time. (b) Amount of Rhodamine B from its 10-3M solution onto Leacril, as function of time.

Isothermal rates of adsorption are shown in Figures 18A and 18B. The curves in Figure 18A relate amounts of cationic dye Rhodamine B adsorbed onto Leacril from its 10-3M solution in the emulsion phase containing 10-3 M tannic acid at 293, 313, and 333°K, respectively. In Figure 18B are shown the adsorbed amounts of Rhodamine B from its 10-3M solution alone. Because the adsorption from the emulsion at 333°K is small, therefore in Figure 18B is also shown adsorption of Rhodamine B from the emulsion at this temperature. From Figures 18A and18 B it is evident that at 293 and 313°K the adsorption of dye on the Leacril is much higher in the case of the emulsion. However, at 333°K the adsorption of dye is much lower from the emulsion than from the solution of Rhodamine B. Moreover, with increasing temperature the adsorbed amount decreases from emulsion, while it increases from solution. A decreasing adsorption with increasing temperature of the process is typical for physical adsorption. The shape of the adsorption isotherms is evidence of the first-order process and therefore the adsorption rate constant can be estimated from an equation relating adsorption vs time [6]. We have determined the values of the rate constant and half-adsorption time eq. [7] presented in Table 9.


Table 9. Equilibrium adsorbed Amounts of Rhodamine B, Meq, Adsorption rate constant, k, half time of adsorption,t, and diffusion coefficient, D for the systems 10-3M Rhodamine B in emulsion/Leacril and systems 10-3M Rhodamine B in solution/Leacril.

Improvement in Acrylic Fibres Dyeing 115

Fig. 19. Kinetic of Rhodamine B desorption from Leacril surface at 293°K adsorbed from

γ<sup>s</sup> LW (mJ/m2)

Temp (K)

To obtain more information about the dyeing processes of Leacril from both the emulsion and solution of the cationic dye used, the surface free energy components of the Leacril samples dyed at various temperatures and different conditions were determined. The components are collected in Tables 10 and 11, together with calculated values of the work of

γ<sup>s</sup> <sup>+</sup>

293 53.7 0.0 58.4 0.01 313 52.5 0.2 54.6 1.1 333 53.8 0.1 24.5 -23.9

Table 10. Surface free energy components and work of spreading of Leacril dyed with 10-3M Rhodamine B from emulsion containing 10-3M of tannic acid at different temperatures.

> γ LW (mJ/m2)

10-3 M Tannic acid treated 293 59.3 0 56.6 2.3 10-3 M Tannic acid treated 333 54.0 0.41 52.1 2.4 10-2 M Tannic acid treated 293 63.6 0 66.9 11.5 10-3 M Rodamine dyed 293 31.8 1.3 52.3 -3.4 10-3 M Rodamine dyed 333 53.7 0.4 55.1 4.2 Table 11. Surface free energy components and work of spreading of Leacril dyed with 10-3M Rhodamine B from solution and treated with different concentration of tannic acid at

0 293 51.9 0.02 53.9 -2.8

(mJ/m2) γ<sup>s</sup> -

γ <sup>+</sup>

(mJ/m2) Ws

(mJ/m2) <sup>γ</sup> -(mJ/m2) Ws

(mJ/m2)

(mJ/m2)

10-3M solution or emulsion.

spreading for water, WS.

Temp of dyeing (K)

Sample of Leacril

different temperatures

As it can be seen from this table, when Rhodamine B was adsorbed from the emulsion system the rate constant k decreased a little with increasing temperature, and for adsorption from the solution k increased markedly. The adsorption rate constants from emulsion are practically the same at 293°K and 313°K, and they are much higher than those determined for adsorption from the solution at the same temperatures.

Looking for an explanation for such relationships the activation energies and diffusion coefficients for the adsorption process were determined next. Applying the equation [8] of this work, the activation energies E of the adsorption process of the dye in the case of both emulsion and solution were then estimated. The results obtained are E= 3.2 kJ/mol, for the emulsion system, and E=11.7 kJ/mol, for the adsorption from solution. These values show that the activation energies are low and hence it can be concluded that both processes are governed by interactions of a physical nature. On the other hand, applying equations [9], we have obtained the values of the apparent diffusion coefficient, D, for the adsorption process from both the emulsion and solution, respectively. These values are also presented in Table 9. Moreover, it is also possible to determine the activation energy of diffusion process, E\*, applying the equation [10] of this work. The calculated results for E\* in the diffusion process of the dye from emulsion and solution are following E\* = 45.0 kJ/mol for the emulsion and E\*= 25.4 kJ/mol for the solution. It appears that the activation energy for the diffusion process is much higher in the emulsion system than in the solution. From the data given in Table 9 and the determined activation energies of adsorption and diffusion one may conclude that the adsorption process in both systems is diffusion controlled. It is much faster in the case of the emulsion than the solution system although it needs higher activation energy. If one assumes that the hydrocarbon forms a film on the Leacril surface, then the diffusion activation energies would indicate that a higher energy is needed to diffuse through the film into the surface. Another reason might be that the Rhodamine B molecules interact (hydrogen bonding) with tannic acid which stabilizes the emulsion droplets. Therefore, a higher energy is needed to adsorb such "complexes" on the Leacril surface, possibly together with the hexadecane droplets. At higher temperatures (313 and 333°K) the diffusion coefficients are practically the same for both systems (Table 9), and both processes occur at similar rates. It is worth mentioning that no visible extraction take place from the aquous solution of Rhodamine B to the hexadecane phase after vigorous shaking of the system. The same was true if the dye was dissolved in 1 M isopropyl alcohol. This concentration corresponds to that used in the emulsion. We have also found that tannic acid caused formation of a very stable emulsion of water droplets in hexadecane. This means that tannic acid because of its molecule structure is a very good stabilizing agent for both oil-inwater and water-in-oil emulsions. These observations support the above discussion.

The adsorption strengths were also tested by desorption experiments. It was realized by means of a washing process with deionized water. The dyed fibers were placed in a bath with a mechanical stirrer at the temperature of 293°K. These results are presented in Figure 19. The desorbed amounts of the dye are much higher for the sample dyed from 10-3M solution of Rhodamine B (ca. 4 mmol/kg) than for the sample dyed from the emulsion phase and the same concentration of tannic acid (ca. 2.5 mmol/kg). Moreover, the desorption of the dye decreases essentially when the dyeing process have been conducted from the emulsion system and at an increased amount of tannic acid present (10-2M). The results in Figure 19 clearly show that at room temperature the dyeing process of Leacril with Rhodamine B from the emulsion is of a superior efficiency, especially when 10-2 M tannic acid is present as a stabilizing agent, whose role seems to be crucial.

As it can be seen from this table, when Rhodamine B was adsorbed from the emulsion system the rate constant k decreased a little with increasing temperature, and for adsorption from the solution k increased markedly. The adsorption rate constants from emulsion are practically the same at 293°K and 313°K, and they are much higher than those determined

Looking for an explanation for such relationships the activation energies and diffusion coefficients for the adsorption process were determined next. Applying the equation [8] of this work, the activation energies E of the adsorption process of the dye in the case of both emulsion and solution were then estimated. The results obtained are E= 3.2 kJ/mol, for the emulsion system, and E=11.7 kJ/mol, for the adsorption from solution. These values show that the activation energies are low and hence it can be concluded that both processes are governed by interactions of a physical nature. On the other hand, applying equations [9], we have obtained the values of the apparent diffusion coefficient, D, for the adsorption process from both the emulsion and solution, respectively. These values are also presented in Table 9. Moreover, it is also possible to determine the activation energy of diffusion process, E\*, applying the equation [10] of this work. The calculated results for E\* in the diffusion process of the dye from emulsion and solution are following E\* = 45.0 kJ/mol for the emulsion and E\*= 25.4 kJ/mol for the solution. It appears that the activation energy for the diffusion process is much higher in the emulsion system than in the solution. From the data given in Table 9 and the determined activation energies of adsorption and diffusion one may conclude that the adsorption process in both systems is diffusion controlled. It is much faster in the case of the emulsion than the solution system although it needs higher activation energy. If one assumes that the hydrocarbon forms a film on the Leacril surface, then the diffusion activation energies would indicate that a higher energy is needed to diffuse through the film into the surface. Another reason might be that the Rhodamine B molecules interact (hydrogen bonding) with tannic acid which stabilizes the emulsion droplets. Therefore, a higher energy is needed to adsorb such "complexes" on the Leacril surface, possibly together with the hexadecane droplets. At higher temperatures (313 and 333°K) the diffusion coefficients are practically the same for both systems (Table 9), and both processes occur at similar rates. It is worth mentioning that no visible extraction take place from the aquous solution of Rhodamine B to the hexadecane phase after vigorous shaking of the system. The same was true if the dye was dissolved in 1 M isopropyl alcohol. This concentration corresponds to that used in the emulsion. We have also found that tannic acid caused formation of a very stable emulsion of water droplets in hexadecane. This means that tannic acid because of its molecule structure is a very good stabilizing agent for both oil-in-

water and water-in-oil emulsions. These observations support the above discussion.

acid is present as a stabilizing agent, whose role seems to be crucial.

The adsorption strengths were also tested by desorption experiments. It was realized by means of a washing process with deionized water. The dyed fibers were placed in a bath with a mechanical stirrer at the temperature of 293°K. These results are presented in Figure 19. The desorbed amounts of the dye are much higher for the sample dyed from 10-3M solution of Rhodamine B (ca. 4 mmol/kg) than for the sample dyed from the emulsion phase and the same concentration of tannic acid (ca. 2.5 mmol/kg). Moreover, the desorption of the dye decreases essentially when the dyeing process have been conducted from the emulsion system and at an increased amount of tannic acid present (10-2M). The results in Figure 19 clearly show that at room temperature the dyeing process of Leacril with Rhodamine B from the emulsion is of a superior efficiency, especially when 10-2 M tannic

for adsorption from the solution at the same temperatures.

Fig. 19. Kinetic of Rhodamine B desorption from Leacril surface at 293°K adsorbed from 10-3M solution or emulsion.

To obtain more information about the dyeing processes of Leacril from both the emulsion and solution of the cationic dye used, the surface free energy components of the Leacril samples dyed at various temperatures and different conditions were determined. The components are collected in Tables 10 and 11, together with calculated values of the work of spreading for water, WS.


Table 10. Surface free energy components and work of spreading of Leacril dyed with 10-3M Rhodamine B from emulsion containing 10-3M of tannic acid at different temperatures.


Table 11. Surface free energy components and work of spreading of Leacril dyed with 10-3M Rhodamine B from solution and treated with different concentration of tannic acid at different temperatures

systems.

electrophoresis.

**8. References** 

York.

*Langmuir*, 14, 5237.

*Appl.Surf. Sci*.,81,1.

67(9), 677.

*J. Colloid Interface Sci.*164, 223.

*J.Chem.Soc.,* Faraday Trans.,1, 82, 329

Improvement in Acrylic Fibres Dyeing 117

need further studies for us to better understand the processes that take place in these

Fig. 20. Zeta potential of Leacril suspension in tannic acid solution determined by

[1] Adamson, A.W., 1982, *Physical Chemistry of Surfaces*,4th ed. ed. Wiley and Sons. New

[4] Cegarra, J.,Puente, P., Veleva, S., and Valdeperas J., 1984, *Tintura de Fibras* 

[7] Chibowski, E., Espinosa-Jiménez, M., Ontiveros-Ortega,. A., Giménez-Martín, E, 1998,

[10] Crank, J.,1956, *The mathematics of Diffusion*, Ed. Clarendon Press. Oxford. Dai.M., 1994,

[11] Duran, J.D., Zurita, L., Guindo, M.C., Delgado, A.V., and González-Caballero, F., 1994,

[12] Espinosa-Jiménez M., González-Caballero F., González-Fernández C.F., 1986,

[14] Espinosa-Jimenez, M., Giménez-Martín E., Ontiveros- Ortega, A.,1997c, *Textile Res. J*.

[13] Espinosa-Jiménez, M., Giménez-Martín E., 1996 *Acta Polym. Sci*, 47, 181.

[2] Anders P., and Sonessa, A.P., 1965, *Principles of Chemistry*, ed. Mc. Millan, New York.

[3] Biefer, G. J., and Mason S. G., 1950, *Trans. Faraday*. *Soc.* 55, 1239.

*textiles*,Universidad Politécnica de Cataluña., Barcelona. [5] Chang, M.Y. and Robertson, A.A. 1967 *Can.J.Chem.* Eng.,42, 66. [6] Chibowski, E., and Holysz, L., 1992, *Prog. Colloid Polym. Sci*., 89, 173.

[8] Chibowski, E., 1992b, *J. Adhesion Sci. Technol*.,6 (9),1069. [9] Chibowsky, E., González-Caballero F., 1993, *Langmuir,* 9, 330.

In Table 10 are shown the components of Leacril samples dyed (10-3M Rhodamine B) at various temperatures from the emulsion system and with 10-3 M tannic acid. The Lifshitzvan der Waals component, γ <sup>S</sup>LW, is practically the same, but the electron-donor component, γS- , decreases markedly with increasing temperature. It may be due to a partial change in the surface structure, from a crystalline at 293 K to an amorphous one above 353°K. However, the results presented in Table 11 deals with the Leacril dyed surface in the system where hexadecane was present. The low value of the electron-donor component (24.5 mJ/m2) for the surface dyed from the emulsion at 333°K indicates that the surface became less polar after the adsorption process had taken place. Indeed, the work of spreading is highly negative, being their value of WS = - 23.9 mJ/m2, so the surface is hydrophobic and although the adsorbed amount of the Rhodamine was low (Table 8 and Figures 18A and 18B) the surface hydrophobicity protects against its dewashing from the surface (Figure 19). Because for the same system at lower temperatures (293 and 313 °K ) the polar component is much higher, one would conclude that the decrease in polarity is mainly due to the surface structure transition. However, it seems this is not the only reason, if one compares the results presented in Table 10. It should be mentioned that the apolar and electron acceptor components for untreated Leacril surface shown in this table are somewhat different than those obtained previously ( 38.1 and 1.3 mJ/m2, respectively ), while the electron donor component is practically the same (previously 52.3 mJ/m2 ). This is probably due to a different lot of the Leacril sample used in these experiments.

From Table 10 it can be seen that treatment of the surface with tannic acid (10-3 M or 10-2M) at 293°K causes an increase in nonpolar, γSLW , and electron-donor , γS- , components, while at 333 °K the changes are minor relative to the untreated sample of Leacril. But, the treatment of the surface with Rhodamine Bsolution (10-3M) alone at both temperatures does not change much the polar component. It shows that the role of hexadecane in lowering the electron-donor interaction of the Leacril surface at 333°K is probably also important. Obviously, the studied systems are very complicated and an unambiguous mechanism of the observed changes cannot be given yet. The changes in polar components are surely due to changes in kind and density of the polar groups present on the Leacril surface originating from tannic acid, Rhodamine B molecules, and the Leacril surface itself. Thus the decrease in γS must be due to a decrease in the surface density of the electron-donor groups and/or shielding of these groups by the hexadecane film. In Fig.18 B it was observed an increase in adsorption from its solution with the temperature, in this situation electrostatic mechanism of the adsorption can be considered.

In Figure 20 are shown zeta potentials of Leacril surface as a function of pH. As can be seen from this figure the Leacril surface is negatively charged above pH 3, because of the presence of some amounts of sulfate and sulfonate end-groups. On the other hand, Rhodamine B molecules possess positively charged amine groups. With increasing temperature the number of the dissociated groups may increase, which is reflected in the increased adsorption (Figures 18A and B). On the other hand in tannic acid solutions (10-5- 10-2 M) the zeta potential of Leacril is practically constant and amounts to -12.5 ± 1 mV, as determined by electrophoresis and using the Smoluchowski equation. This means that tannic acid is not potential determining for the Leacril surface and the zeta potentials are about the same as those in water in this pH range.

To summarize briefly, dyeing of the Leacril surface with a cationic dye, Rhodamine B, from the emulsion phase at 313°K and in the presence of tannic acid as a stabilizing agent is more efficient that the dye solution alone. The dyeing systems tested are very complicated and

In Table 10 are shown the components of Leacril samples dyed (10-3M Rhodamine B) at various temperatures from the emulsion system and with 10-3 M tannic acid. The Lifshitzvan der Waals component, γ <sup>S</sup>LW, is practically the same, but the electron-donor component, γS- , decreases markedly with increasing temperature. It may be due to a partial change in the surface structure, from a crystalline at 293 K to an amorphous one above 353°K. However, the results presented in Table 11 deals with the Leacril dyed surface in the system where hexadecane was present. The low value of the electron-donor component (24.5 mJ/m2) for the surface dyed from the emulsion at 333°K indicates that the surface became less polar after the adsorption process had taken place. Indeed, the work of spreading is highly negative, being their value of WS = - 23.9 mJ/m2, so the surface is hydrophobic and although the adsorbed amount of the Rhodamine was low (Table 8 and Figures 18A and 18B) the surface hydrophobicity protects against its dewashing from the surface (Figure 19). Because for the same system at lower temperatures (293 and 313 °K ) the polar component is much higher, one would conclude that the decrease in polarity is mainly due to the surface structure transition. However, it seems this is not the only reason, if one compares the results presented in Table 10. It should be mentioned that the apolar and electron acceptor components for untreated Leacril surface shown in this table are somewhat different than those obtained previously ( 38.1 and 1.3 mJ/m2, respectively ), while the electron donor component is practically the same (previously 52.3 mJ/m2 ). This is probably due to a

From Table 10 it can be seen that treatment of the surface with tannic acid (10-3 M or 10-2M)

333 °K the changes are minor relative to the untreated sample of Leacril. But, the treatment of the surface with Rhodamine Bsolution (10-3M) alone at both temperatures does not change much the polar component. It shows that the role of hexadecane in lowering the electron-donor interaction of the Leacril surface at 333°K is probably also important. Obviously, the studied systems are very complicated and an unambiguous mechanism of the observed changes cannot be given yet. The changes in polar components are surely due to changes in kind and density of the polar groups present on the Leacril surface originating from tannic acid, Rhodamine B molecules, and the Leacril surface itself. Thus the decrease in

 must be due to a decrease in the surface density of the electron-donor groups and/or shielding of these groups by the hexadecane film. In Fig.18 B it was observed an increase in adsorption from its solution with the temperature, in this situation electrostatic mechanism

In Figure 20 are shown zeta potentials of Leacril surface as a function of pH. As can be seen from this figure the Leacril surface is negatively charged above pH 3, because of the presence of some amounts of sulfate and sulfonate end-groups. On the other hand, Rhodamine B molecules possess positively charged amine groups. With increasing temperature the number of the dissociated groups may increase, which is reflected in the increased adsorption (Figures 18A and B). On the other hand in tannic acid solutions (10-5- 10-2 M) the zeta potential of Leacril is practically constant and amounts to -12.5 ± 1 mV, as determined by electrophoresis and using the Smoluchowski equation. This means that tannic acid is not potential determining for the Leacril surface and the zeta potentials are

To summarize briefly, dyeing of the Leacril surface with a cationic dye, Rhodamine B, from the emulsion phase at 313°K and in the presence of tannic acid as a stabilizing agent is more efficient that the dye solution alone. The dyeing systems tested are very complicated and

, components, while at

different lot of the Leacril sample used in these experiments.

γS-

of the adsorption can be considered.

about the same as those in water in this pH range.

at 293°K causes an increase in nonpolar, γSLW , and electron-donor , γS-

need further studies for us to better understand the processes that take place in these systems.

Fig. 20. Zeta potential of Leacril suspension in tannic acid solution determined by electrophoresis.

#### **8. References**


**0**

**7**

Melih Günay *HueMetrix Inc.*

*USA*

**The Future of Dye House Quality Control with the**

The manufacturing of a textile begins with the fiber input, whereby each processing step results in an added cost to the final product. As dyeing of a textile is often the last step in the manufacturing of a fabric, it requires extra caution to get it right by avoiding waste and maintaining cost control. Only under favourable conditions is it possible to get it right the first time. In the past, it was not unusual for a dyer to re-dye until the target shade was reached. A typical strategy was to start with a base recipe that undershot the target shade. After each dyeing the missing dye component was added to the bath until the shade was matched. The

The Right-First-Time (RFT) dyeing concept was introduced in 1970 and became a desired feature of textile dyeing. This concept meant that at each dyeing the target shade was achieved the first time, hence not requiring re-dyeing. However, the successful evolution of the concept depended on work carried out over many years by a relatively small number of organizations. Many application research and development projects were carried out mainly by the laboratory, pilot-plant and bulk-scale equipment of the major users and manufacturers

Since the end of 20th century, with the increased competition, dye houses are asked to meet more exact requirements while they are under pressure to reduce the cost of manufacturing. In order to stay competitive and be in business, they were required to exercise tighter quality control and seek ways to optimize dyeings. This necessitated the understanding of a) dyes, chemicals and substrates and their compatibilities; and b) the parameters that influence the

The variables that are objectively measured and monitored during a dyeing for quality control purposes have traditionally been limited to time, temperature, pH, and conductivity. Measurement of the fabric shade reflectance is only utilized in the development of new recipes/procedures and the verification of the dyed fabric shade. The development of recipes/procedures and the debugging of dyeing problems continue to rely on indirect information obtained by ad-hoc trail and errors, subjective observations, and visual

The first prototype system (Beck et al., 1990; Keaton & Glover, 1985) to measure the dye build up directly in real-time during a dyeing was developed in 1990's. However, due to technological limitations such as; a) the high cost of spectrophotometers, b) the low computation speed that is not sufficient to process the data generated by the

smaller the number of reformulation, the more skilful the dyer was considered.

of dyes and equipment, as well as by universities.

rate and extent of dye uptake by the substrate (Park & Shore, 2007).

**1. Introduction**

assessments of dyers.

**Introduction of Right-First Dyeing Technologies**


