Coloration Technology

doi: 10.1111/j.1478-4408.2012.00356.x

Influence of grafting with acrylic acid on the dyeing properties of polyamide 6.6 fibres

Coloration Technology

2 C Makhlouf,a N Ladhari,b,* S Roudeslia and F Saklyb a

Laboratory of Polymers–Biopolymers and Organic Materials (LPBMO), Faculty of Sciences of Monastir, University of Monastir, Bd. of Environment, 5019 Monastir, Tunisia

b

Textile Research Unit, ISET of Ksar Hellal, B P 68 Ksar Hellal 5070, Tunisia Email: [email protected]

Society of Dyers and Colourists

3 4 Received: XX Xxxx XXXX; Accepted: XX Xxxxx XXXX

ª 2012 The Authors. Coloration Technology ª 2012 Society of Dyers and Colourists, Color. Technol., 128, 1–8

1

Journal: COTE CE: Rajeswari V.

No. of pages: 8 PE: Senthil Author Received:

B Manuscript No. Journal Name

6

The fibre surface has been investigated by many experimental characterisation techniques, such as Fourier transform–infrared (FITR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and contact angle measurements. The findings of these analyses showed clearly the efficiency of the grafting reaction used, leading to a significant increase of the hydrophilic character of the polyamide 6.6 surface and the tinctorial affinity to the cationic dyes. Grafting of acrylic acid, in particular, will increase the carboxylic groups onto the polyamide 6.6 fibres and improve their hydrophilic properties and their ability to be dyed (increase of anionic sites) with these dyes [1]. Polyamide 6.6 fibre can be dyed with acid as well as with metallic dyes 1.2. However, the wash fastness properties of polyamide 6.6 with acid dyes rank from average to good (the greyscale ratings are between 3 and 4). With regard to metallic dyes 1.2, the wash fastness properties are good but the obtained nuances are usually drab. This modification of polyamide 6.6 allows us to dye this fibre with cationic dyes, which results in widening the nuances with higher wash fastness. In our previous study [5], the dyeing behaviour of 7 unmodified and modified polyamide 6.6 fibres of different levels of fineness was examined. The obtained results revealed that the unmodified microfibres appeared to be more accessible to dyes than the conventional ones, especially when small dye molecules were used. The purpose of the present study is to evaluate the influence of grafting with acrylic acid on the dyeing properties of polyamide 6.6 fibres, the kinetic of dyeing and the modelling of the adsorption isotherms using Langmuir, Freundlich and Jossen relations.

5

Thanks to their particular properties, such as good mechanical resistance, flexibility, etc., an increasingly significant field of application in the textile industry is 5 being found for polyamide 6.6 fibres. Polyamide 6.6 is a fibre that is utilised in several fields, in particular clothing and furniture, as well as in textiles for technical use. However, this fibre has some defects; namely, a tendency to stain, very poor flame resistance, and a weak tinctorial affinity and low wash fastness towards cationic dyes. Indeed, the somewhat hydrophobic nature of the semi-crystalline polyamide 6.6 fibres, attributable to the low presence of carboxylic groups, lead to the fibres having a poor tinctorial affinity to the cationic dyes [1]. In order to improve some of these properties, modifications to the surface of polyamide 6.6 were carried out [2]. Chemical grafting is one of the methods used for the textile fibre modification of surfaces. The majority of the studies quoted in the literature focused on the improvement of the properties of the textiles. Hirta and Fujii [3] studied the grafting of polyamide fibres by interfacial polymerisation with methacrylic acid, methyl methacrylate and 2-(dimethylamino) ethyl methacrylate. They concluded that changes in the physicochemical properties of the modified fibre surfaces greatly affect the dyeability of the modified fibres. In another study, 6 Bendak and Aggour [4] showed that the dyeing properties of polyamide fibres are greatly affected by the grafting reaction. It was observed that the grafting of these fibres decreased its anionic dyeability and increased the cationic dyeability. In our previous report, we focused our study on the grafting of acrylic acid monomer on polyamide 6.6 [1].

3

Introduction

Dispatch: 18.1.12

Polyamide 6.6 fibres were modified for the improvement of dyeing affinity using a graft copolymerisation method. These fibres were grafted with acrylic acid as monomer. The influence of the chemical modification of polyamide 6.6 fibres on the dyeing properties was investigated using a cationic dye (Red Astrazon 5BL). It was shown that the dye uptake of the modified fibres was greater than that of the unmodified fibres. The kinetic study of the cationic dye used at various grafting percentages showed an improvement of the dye build-up rate, such as its exhaustion. In addition, an increase in the adsorption of the dye quantity fixed on the surface layer of the fibre made up of the grafted molecules was announced. Colour fastness to washing was improved with the grafting percentage. The modelling of the adsorption isotherms using Langmuir, Freundlich and Jossen relations allows the determination of isotherm constants. The results obtained from this modelling study show the existence of several models corresponding to various percentages of grafting.

C O T E

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

Makhlouf et al. Acrylic acid grafting in dyeing of polyamide 6.6 fibre

Experimental

120

Materials Samples of polyamide 6.6 were generously supplied by the 8 manufacturer Nylstar (XXXXX) and were used in the experiment in the form of knitted fabrics. The cationic dye, Red Astrazon 5BL (CI Basic Red 24, 1) used in this study was kindly supplied by DyStar (USA). The acrylic acid monomer supplied by Fluka (Switzerland) was purified before use by distillation under vacuum and deoxygenated with nitrogen in the presence of metallic copper [6]. All other chemicals used were laboratory grade reagents. CN NO 2

+

N N

N

CH 2 CH 2 N(CH 3 )3

–

, O3S

O

CH 3

C 2H 5

1

Grafting procedure Polyamide fibres (1 g) were introduced into 100 ml of mixture at 70 ⁄ 30 (v ⁄ v) water ⁄ hexane. A known amount of benzoyl peroxide, used as an initiator was added. The acrylic acid monomer was then added to the reaction medium. Copolymerisation reaction was carried out at 85 C. As soon as the copolymerisation time was reached, the homopolymer present in the grafting reaction mixture was removed with a solution of 6 g sodium chloride and 9 1 g sodium hydroxide. After soxhlet extraction with this solution, the grafted fibres were dried in an oven at 60 C until they reached a constant weight [5]. Determination of grafting percentage The grafting percentage (%G) was calculated from the weight uptake applying the following formula [7,8]: %G ¼

W W0 100 W0

ð1Þ

where W0 and W are the weight of the polyamide 6.6 fibres before and after graft polymerisation, respectively. Surface topography The surface topography of the unmodified and modified fibres was examined by atomic force microscopy (AFM) in order to elucidate the topological changes attributable to grafting. Topographical images of polyamide 6.6 fibres were obtained by tapping mode atomic force microscopy (TM-AFM), using a Nanoscope III instrument 10 manufactured by Digital Instrument Co. (XXXX). Dyeing All dyeings of polyamide 6.6 knitted samples were carried out in sealed stainless steel dye pots with a capacity of 120 cm3 in a laboratory-scale dyeing machine (Datacolor11 Ahiba nuance; XXXX, XXXX). Figure 1 illustrates the dyeing temperature profile for the cationic dye. The dyeing experiments were carried out at 95 C with the cationic dye until equilibrium was reached. In a first step, the fabric and dyeing auxiliaries (CH3COOH, CH3COONa and Na2SO4) were introduced into the dyeing bath at 60 C. Then, 5 min later, the X% of dye was added at the same temperature. In a last step, after 5 min, the mixture was heated to 95 C. The bath temperature was increased at a rate of 2 C ⁄ min until the equilibrium temperature was reached. To remove any dye adsorbed 2

Temperature, °C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

1

80 60

60 min

95°C

100

2°C/min

4°C/min

10 min

40°C

40 20 0 0

20

40

60 80 T, min

100

120

140

Figure 1 The dyeing temperature profile for the cationic dye

on the outer surface of the polyamide 6.6 fibres, the samples were rinsed in distilled water at 60 C for 15 min and then dried in an oven at 80 C. The dyeing of polyamide 6.6 by the cationic dye was carried out under the following conditions. Conditions of dyeing (RdB): 1:80 (1 g of matter in 80 ml of bath) Weight of sample: 1 g

12

Composition of dyebath Dye: X% with X e {0.3; 1; 2; 3; 4; 5} CH3COOH 80%: 2 (% owf) (4.5 < pH < 5) CH3COONa: 1.5 (% owf) Na2SO4: 10 (% owf) Analysis of dyeing Determination of dyebath exhaustion The extent of dyebath exhaustion was determined spectrophotometrically. The absorbance of each dyebath solution was measured using a 1-cm path length quartz cell housed in an ultraviolet (UV)-2401 PC spectrophotometer (Schimadzu, XXXX) both before and 13 after the dyeing process at the maximum wavelength (kmax = 513 nm) of cationic dye used in this study. The percentage of dyebath exhaustion (%E) was determined using Eqn 2, where C0 and Cb are the quantities of dye in the dyebath before and after dyeing, respectively. %E ¼

C0 Cb Abs0 Absb 100 ¼ 100 C0 Abs0

ð2Þ

Determination of time of half-dyeing Dyeing of the polyamide 6.6 fibres was performed using 2% dye (owf). Each set included dyeing for 2, 5, 10, 20, 40, 60, 80, 100 and 108 min. Samples from the dyebath were removed immediately after the prescribed dyeing time and the amount of dye remaining in the liquor was determined by spectrophotometric techniques at the maximum wavelength (kmax = 513 nm). For each dyeing time, the graph representing the dye uptake vs the dyeing time was drawn. The time of half-dyeing t1 ⁄ 2 (min) was determined on the basis of these curves. Determination of diffusion coefficient The diffusion coefficient D was calculated by using the relation of Eqn 3 [9]:


Makhlouf et al. Acrylic acid grafting in dyeing of polyamide 6.6 fibre 1

Ct D¼ C1

2

4pd2 ðcm2 s1 Þ t

ð3Þ

where C¥ is the dye exhaustion in the equilibrium (mg ⁄ g), Ct is the dye exhaustion at a time (t) (mg ⁄ g), d is the diameter of fibre (cm) and t is the time (in seconds). Washing fastness The washing fastness of the dyed samples was determined by following the standard ISO 105-A02 test method [10]. Staining and change in colour were assessed using the visual greyscale. The five grades in washing fastness rating are: 5, excellent; 4, good; 3, fair; 2, poor; 1, very poor.

Results and Discussion Surface topography analysis Polyamide 6.6 fibres were characterised by atomic force microscopy, which provides us with topographic images with both high lateral and high vertical resolution. The atomic force microscopy images of unmodified and modified polyamide 6.6 fibres are presented in Figure 2a– d. Figure 2a shows the atomic force microscopy image of the original polyamide 6.6 fibre and Figure 2b–d summarises the results of acrylic acid–graft–polyamide 6.6 fibre at different grafting percentages. From Figure 2a, it seems that the unmodified polyamide 6.6 fibre had a smooth surface. In contrast, the images shown in Figure 2b–d exhibited a heterogeneous grafting layer with enormous unevenesses and bumps and which is formed on the surface of the fibre, resulting in

LOW RESOLUTION COLOR FIG

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

Image Data Data scale Engage X Pos Engage Y Pos

(a)

the roughness of the original polyamide 6.6 fibre. This clearly highlights that the anionic carboxylic groups have been grafted onto the surface of polyamide 6.6 fibres. Dyeing Dyeing investigations were carried out on unmodified and modified polyamide 6.6 fibres with various percentages of grafting (3%, 6%, 8% and 12%) using the cationic dye (Red Astrazon 5BL). During the dyeing, the comparison tests were carried out by taking account of the time of the build-up in temperature. The follow-up of the dyeing kinetics corresponds to the determination of the fibre dye concentration through time. A plot of the amount of cationic dye adsorbed per gram polyamide 6.6 Ye (mg ⁄ g) vs contact time (t) for various percentages of grafting is shown in Figure 3. It was found that the unmodified polyamide 6.6 fibres have a very weak affinity in respect of the cationic dye, as only 20% of the total dye quantity introduced into the initial bath was absorbed on fibre, whereas, in the case of modified polyamide 6.6 fibres, an increase in the percentage of grafting led to an increase in the amount of cationic dye absorbed onto these fibres. This indicated that the grafting had a greater influence on the dyeing properties of polyamide 6.6 fibres. This also suggested that the higher the percentage of grafting, the more quickly the dyeing equilibrium is reached, and the more significant the rate of dyebath exhaustion becomes. It was shown that, by varying the percentage of grafting, the shape of the kinetic curve changes. Indeed, for the percentages of grafting of 3%, 6% and 8%, a Data scale Engage X Pos Engage Y Pos

(b)

µm 2.5

4

2.0

3

1.5 2

1.0 1

0.5 (c)

Engage X Pos Engage Y Pos

Data scale Engage X Pos Engage Y Pos

(d)

µm

µm 4

4 3

3 2

2 1

1

Figure 2 Characterisation of the polyamide 6.6 surface by atomic force microscopy: (a) unmodified polyamide 6.6 fibre; (b) polyamide 25 6.6 g–acrylic acid, 3% grafting; (c) polyamide 6.6 g–acrylic acid, 8% grafting; and (d) polyamide 6.6 g–acrylic acid, 12% grafting ª 2012 The Authors. Coloration Technology ª 2012 Society of Dyers and Colourists, Color. Technol., 128, 1–8

3

1

Time of half-dyeing, s

20 Ye, mg/g

15

%G = 12 %G = 8 %G = 6 %G = 3 %G = 0

10 5

600

20

40

80 60 T, min

100

120

T = 95 °C

500 400 300 200 100 0

0

LOW RESOLUTION FIG

700

25

0

140

0

2

4

6

%G

8

10

12

14

Figure 5 Evolution of the time of half-dyeing vs the percentage 28 Figure 3 Dyeing kinetics of the dye Red Astrazon 5BL on 26 of grafting modified polyamide 6.6 fibres

parabolic branch is obtained, which tends towards a value limit that corresponds to the totality of the dissolved quantity of dye in the bath. In other words, the exhaustion of the bath reaches 100% quickly. For %G = 12, a much faster dye build-up was noticed. Therefore, this finding shows that the higher the number of the active sites, the more quickly the equilibrium state is reached. The evolution of the rate of exhaustion at equilibrium vs the percentage of grafting is represented in Figure 4. From Figure 4, it was observed that the tendency curve follows a logarithmic law and tends towards a value limit corresponding to a maximum rate of dyebath exhaustion for %G = 8. Time of half-dyeing The time of half-dyeing is one of the most significant elements in the evaluation of the dyeing kinetics as it gives an approximate idea on the dye build-up rate on fibre [11]. The evolution of the time of half-dyeing vs the percentage of grafting is shown in Figure 5. The tendency curve is a hyperbolic branch, which is inclined towards a value limit approximate to zero. As observed, the time of half-dyeing depends on the percentage of grafting. Indeed, by increasing this parameter, the time of half-dyeing becomes shorter. Dye diffusion It is generally agreed that the dyeing process involves three continuous steps. The first step is the diffusion of

80 60

Table 1 The diffusion coefficients (D) of the unmodified and 24 modified polyamide 6.6 fibres at T = 80 C and t = 20 min

40 20 0

dye through the aqueous dyebath on to the fibre. The second step is the adsorption of dye into the outer layer of the fibre. And the third step is the diffusion of dye to the interior of the fibre from the adsorbed surface. The second step, the actual adsorption process, is generally assumed to be much more rapid than either of the other diffusion steps. Of the two diffusion steps, the diffusion into the inner layer is much slower than the movement of dye through the aqueous solution because of the physical obstruction of dye diffusion [12]. In addition, fast dye diffusion can be achieved from a softer and more flexible polymer substrate [9]. As the polymer chains of the modified polyamide 6.6 are more flexible than those of the unmodified fibres [1], the diffusion of dye molecules into these polymers could be faster than into unmodified polyamide 6.6 fibres. For a short period of dyeing (t = 20 min), the diffusion coefficients (D) of the unmodified and modified polyamide 6.6 fibres are presented in Table 1. From Table 1, it can be seen that, by increasing the percentage of grafting, the dye diffusion inside the fibre becomes faster. This result could be explained by the existence of a polar force between the dye and the modified polymer [9]. Indeed, the force of attraction greatly increased with the increasing number of the active sites distributed on the fibre surface. Therefore, this force facilitated, on the one hand, the migration of the dye towards the fibre and, on the other hand, the diffusion of the dye inside the fibre. In order to evaluate fixation of the dye, an analysis of wash fastness was carried out. 14 Washing fastness The washing fastness properties of both unmodified and modified polyamide 6.6 fibre dyeings with the cationic

100 Rate of exhaustion, %

LOW RESOLUTION FIG

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

LOW RESOLUTION FIG


(%) G

0 3 6 Figure 4 Evolution of the rate of exhaustion at equilibrium 27 8 according to the percentage of grafting for 80 min (equilibrium 12 time)

0

2

4

8

6

%G

4

10

12

14

C¥ (mg ⁄ g)

Ct (mg ⁄ g) (t = 1200 s)

D (cm2 s)1) 10)7

5.30 16.10 17.00 19.36 19.20

3.73 13.08 14.43 17.18 18.90

4.14 5.46 7.35 8.03 9.88



Dye adsorption of cationic dye onto polyamide 6.6 fibres In this part, the adsorption isotherms of unmodified and modified polyamide 6.6 fibres that have different percentages of grafting at 95 C were studied. Plotting of the amount of dye adsorbed per gram of polyamide 6.6 (Ye) (mg ⁄ g polyamide 6.6) vs the concentration of the dye remaining in solution Ce is shown in Figure 6. It was found that the unmodified polyamide 6.6 fibres present a low affinity for the cationic dye. This behaviour confirms the results already obtained in the kinetic study. It could also be seen from Figure 6 that the amount of the dye adsorbed per gram of modified polyamide 6.6 fibres depended on the percentage of grafting. This amount rose with the increasing percentage of grafting, which indicated that the modified polyamide 6.6 fibres have a higher adsorption capacity of cationic dye compared with that of the unmodified fibres. This is attributable to the presence of the anionic groups, which are able to interact by an ionic mechanism with the (N+) groups present in the structure of the cationic dye molecule (Red Astrazon 5BL). Adsorption isotherms The equilibrium adsorption isotherm is fundamental in describing the interaction behaviour between solutes and adsorbents, and is important in the design of an adsorption system. The polyamide 6.6 adsorption data for the cationic dye (Red Astrazon 5BL) were treated with the Langmuir, Freundlich and Jossen relations. The Langmuir isotherm The Langmuir adsorption isotherm has been successfully applied to many other real sorption processes [14,15]. A

40

LOW RESOLUTION FIG

dye were measured. The change in shade and the degree of cross-staining were assessed using the visual greyscale. The values found during the wash fastness tests carried out on samples at various percentages of grafting are shown in Table 2. The results show that the unmodified fibres had an average washing fastness. This may be attributable to the low number of the negatively charged sites on unmodified fibres, whereas, for modified fibres, the 15 washing fastness was improved (from 3 to 4–5) by the increase of the percentage of grafting. Indeed, this improvement is attributable to the presence of a great number of the anionic sites that are able to ensure electrostatic interactions, to which Van-Der-Waals and hydrogen interactions are added [13].

35 30 Ye, mg/g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

25 20 %G = 12 %G = 6 %G = 3 %G = 0

15 10 5 0

0

2

4

6

8

10 12 14 Ce, 103 mg/l

16

18

20

22

24

Figure 6 Adsorption isotherms of Red Astrazon 5BL on 29 unmodified and modified polyamide 6.6 fibres with various percentages of grafting

basic assumption of the Langmuir theory is that sorption takes place at specific homogeneous sites within the adsorbent. It is then assumed that, once a dye molecule occupies a site, no further adsorption can take place at that site. Theoretically therefore a saturation value is reached beyond which no further sorption can take place. The saturated monolayer curve can be represented by the expression: Ye ¼

Q b Ce 1 þ b Ce

ð4Þ

A linear form of this expression is: Ce 1 Ce þ ¼ Ye Q b Q

ð5Þ

In the above equation, Q (mg ⁄ g) is the maximum amount of the dye per unit weight of polyamide 6.6 to form a complete monolayer coverage on the surface bound at high equilibrium dye concentration Ce. Ye is the amount of dye adsorbed per gram of polyamide 6.6 (mg ⁄ g) at equilibrium and b is the Langmuir constant related to the affinity of the binding sites (l ⁄ mg). The value of Q represents a practical limiting adsorption capacity when the surface is fully covered with dye molecules and assists in the comparison of adsorption performance [14]. The linear plot of Ce ⁄ Ye vs Ce is obtained from this model, as shown in Figure 7. The values of Q and b are calculated from the intercepts and slopes of different straight lines representing the different percentages of grafting. The

Table 2 Evaluation of wash fastness at different percentages of grafting Change in colour

Staining cotton

Staining polyamide 6.6

Dye concentration (%)



(%) G

0.3

1

3

4

5

0.3

1

3

4

5

0.3

1

3

4

5

0 3 6 12

3 4 4 4–5

3–4 3–4 4–5 4–5

3–4 3–4 4–5 4–5

3 4 4–5 4–5

3 4–5 4–5 4–5

3–4 4–5 4–5 4–5

3–4 4–5 4–5 4–5

3–4 4 4 4

3–4 4 4 4

4 3–4 4 4

3–4 4–5 4–5 4–5

3–4 4–5 4–5 4–5

3–4 2–3 4 4

2–2 2–3 3–4 4

2 2 3–4 4


5

1

1 0.8 Ce / Ye, l/g

0.6 %G = 12

0.4

%G = 6 0.2 0

%G = 3 0

2

4

6

8

10 12

14

16

18

20

22

24

3

Ce, 10 mg/l

(Red Astrazon 5BL) used in this study. The values are presented in Table 4 and the Freundlich equation isotherms are shown in Figure 8. The magnitude of the exponent 1 ⁄ n gives an indication of the favourableness of adsorption. For all experiments, 16 the values of n > 1 obtained represent favourable adsorption conditions [14]. The P values increased with the increasing percentages of grafting. From Table 4, the Freundlich equation can be applied to fit the experiment data as well as the Langmuir equation because it gives a high correlation coefficient (0.98) for each percentage of grafting.

Figure 7 Langmuir isotherms for the cationic dye (Red Astrazon 30 The Jossen isotherm 5BL) on modified polyamide 6.6 fibres (temperature 95 C)

Red 3 Astrazon 6 5BL 12

15.142 31.218 76.652

28.57 32.25 37.03

0.53 0.97 2.07

27.2 31.9 37.5

0.984 0.978 0.967

Langmuir equilibrium constant KL = Qb (l ⁄ g) is measured at different percentages of grafting; Table 3 lists the calculated results. In the present study, there is a good agreement between the experimental value Yref (limit value of Ye) and the calculated value Q. As expected, the Q values increased with the increasing percentage of grafting, indicating that an important amount of cationic dye has been adsorbed by the modified fibre surface. According to the literature, the higher the values of b that are close to zero the more heterogeneous the fibre surface [16]. In this work, the b values indicate that the modified polyamide 6.6 has a maximum affinity for the cationic dye at a higher percentage of grafting (%G = 12). This result highlights that the modified fibre surface becomes more homogeneous. The Freundlich isotherm The Freundlich isotherm [14,15] is a special case for heterogeneous surface energy in which the energy in the Langmuir equation varies as a function of surface coverage strictly attributable to the variation of the sorption. The Freundlich equation is given as: Ye ¼ P C1=n e

ð6Þ

where P is roughly an indicator of the adsorption capacity and 1 ⁄ n of the adsorption intensity. A linear form (Eqn 7) of the Freundlich expression will yield the constants P and 1 ⁄ n: 1 logYe ¼ logP þ logCe n

ð7Þ

Therefore, P and 1 ⁄ n can be determined from the typical linear plots of log Ye vs log Ce for the cationic dye 6

Table 4 Freundlich isotherm constants of adsorption of dye onto modified polyamide 6.6 at different percentages of grafting Dye

%G

P

n

R2

Red Astrazon 5BL

3 6 12

10.79 13.58 19.32

3.43 3.26 3.83

0.985 0.988 0.979

2

LOW RESOLUTION FIG

%G KL (l ⁄ g) Q (mg ⁄ g) B (l ⁄ mg) Yref (mg ⁄ g) R2

1.6 1.2 0.8

%G = 12 %G = 6

0.4

%G = 3 –4

–3

–2

0

–1 log Ce

1

0

2

Figure 8 Freundlich adsorption isotherm of cationic dye onto 31 modified polyamide 6.6 fibres at 95 C

30 25 20 15 Experimental 10

Langmuir Freundlich

5

Jossens 0

0

5

10

15

20

25

LOW RESOLUTION FIG

Dye

log Ye

Table 3 Langmuir isotherm constants for the adsorption of cationic dye onto modified polyamide 6.6 at different percentages of grafting

The adsorption data correctly fit the Langmuir equation, as shown in Figure 8, whereas they are not in accordance with the Freundlich equation (Figure 9). A general isotherm taking into account both the Langmuir and

Ye , mg/g

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

LOW RESOLUTION FIG


3

Ce, 10 mg/l Figure 9 Comparison of theoretical isotherms with experimental 32 data for the adsorption of Red Astrazon 5BL on modified polyamide 6.6% G = 3 (temperature 95 C)



Freundlich expressions has been postulated by Weber 17 and Mathews [17] and is represented by the following equation:

As the expression contains three unknowns, namely i, j and m, these constants may be obtained from the adsorption data via an iterative procedure using a computer program. The values obtained are listed in Table 5. According to the values of the correlation coefficients that are not approximate to the unit, it was revealed that the Jossen isotherm does not appear to be able to characterise the adsorbent ⁄ adsorbate system in the entire range of concentrations. To assess the different isotherms and their ability to correlate with the experimental results, the theoretical plots arising from the application of each of the above isotherms to the adsorption data for Red Astrazon 5BL onto the modified polyamide 6.6 fibres at 95 C are compared in Figures 9–11. It appears from the three figures that several models exist and correspond to various percentages of grafting. Figure 9 shows that, for the %G = 3, the Freundlich model gave the best fit to the experimental data, in particular for the low-concentration range. The Langmuir 18 model is more suitable for the high-concentration range. The results in Figure 10 indicate that, for the %G = 6, theoretical Langmuir and Jossen isotherms were unable to characterise the adsorbent ⁄ adsorbate system. However, it can be concluded that the adsorption isotherm fits into the Freundlich model over the whole concentration range studied.

LOW RESOLUTION FIG

ð8Þ

40 35 30 Ye, mg/g

i Ce Ye ¼ 1 þ j ðCe Þm

25 20 15

Experimental

10

Langmuir

5

Freundich Jossens

0

0

5

Ce, 103 mg/l

10

15

of theoretical isotherms with 34 Figure 11 Comparison experimental data for the adsorption of Red Astrazon 5BL on modified polyamide 6.6% G = 12 (temperature 95 C)

From Figure 11, it can be seen that, for %G = 12, the Freundlich isotherm model fits the experimental data reasonably well, especially for the high concentrations. However, the theoretical Langmuir and Jossen isotherms were compared with the experimental data and poor agreement was obtained. The isotherms of the latter do not appear to be able to characterise the adsorbent ⁄ adsorbate system in the entire concentration range.

Conclusions

This study highlighted the influence of the chemical grafting on the tinctorial behaviour of polyamide 6.6 fibres modified by the acrylic acid. It revealed a clear improvement of the tinctorial affinity of modified fibres compared with those unmodified using a cationic dye. This is because of the increase in the number of carboxylic groups on fibre that are responsible for the absorption of the cationic dye (Red Astrazon 5BL). Table 5 Jossen isotherm constants of adsorption of dye onto The kinetics study showed an improvement in the dye modified polyamide 6.6 at different percentages of grafting build-up rate. In addition, an increase in the percentage of grafting improves the dye quantity fixed on the Dye %G i j m R2 modified fibres. According to the results of the wash fastness tests, an Red Astrazon 5BL 3 5.573 0.064 1.315 0.903 improvement in the cationic dyeings at different 6 17.971 0.555 0.990 0.873 percentages of grafting was observed (from 3 to 4–5). This 12 78.206 1.196 1.463 0.870 improvement is attributed to the presence of a great number of the anionic carboxylic groups that are able to interact by an ionic mechanism with the (N+) groups 35 present in the structure of the cationic dye molecule. 30 Adsorption data were modelled by using the Langmuir, Freundlich and Jossen adsorption isotherms. The results 25 from this study will help towards gaining a better 20 understanding of the adsorption mechanism of the dyeing process and the influence of grafting in the dyeing Experimental 15 properties of polyamide 6.6 fibres. It appears that the Langmuir 10 adsorption capacity was dependent on the percentage of Freundlich grafting and the models used in this study vary with this Jossens 5 percentage. 0 In fact, for the %G = 3, the Freundlich model is 15 20 0 5 10 suitable for the low-concentration range in particular, Ce, 103 mg/l whereas the Langmuir model is more appropriate for the 19 high-concentration range. For %G =6, the Freundlich of theoretical isotherms with 33 Figure 10 Comparison model gave the best fit to the experimental data over the experimental data for the adsorption of Red Astrazon 5BL on whole concentration range studied, whereas, for modified polyamide 6.6% G = 6 (temperature 95 C) Ye , mg/g

LOW RESOLUTION FIG

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62

%G = 12, the Freundlich model was appropriate for the high-concentration range.

References 1. C Makhlouf, S Marais and S Roudesli, Appl. Sur. Sci., 253 (2007) 5521. 2. A Bhattacharya and B N Misra, Prog. Polym. Sci., 29 (2004) 767. 3. ? Hirta and R Fujii, J. Chem. Soc (japan),Chem. Ind. Chem., 20 3 (1984) 479 . 4. A Bendak and S H Aggour, J. Soc. Fibre Sci. Tech., 43 (1987) 393. 5. C Makhlouf, C Kacem, S Roudesli and F Sakli, J. Appl. Sci., 8 (2008) 77. 6. J Buchenska, J. Appl. Polym. Sci., 80 (2001) 1914. 7. N Somanathan, B Balasubramaniam and V Subramaniam, J. Macromol. Sci. Pure Appl. Chem., 32 (1995) 1025.

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8. A Hebeish, S E Shalaby and A M Bayazeed, J. Appl. Polym. Sci., 26 (1981) 3245. 9. T-K Kim, Y-A Son and Y-J Lim, Dyes Pigm., 67 (2005) 229. 21 10. ISO 105-A02, Methods of Test for Colour Fastness of Textiles and Leather, 5th Edn (Bradford: Society of Dyers and 22 Colourists, 1990). 11. J Militky and J Rais, J.S.D.C., 93 (1977) 346. 12. T Vickerstaff, The Physical Chemistry of Dyeing, 2nd Edn (London: Oliver and Boyd, 1954) 123. 13. G Zhao, L R Wu, J Curiskis and A Deboos, Text. Res. J., 74 (2004) 27. 14. M S Chiou and H Y Li, J. Hazard. Mater., 93 (2002) 233. 15. K H Choy Keith, G McKay and J F Porter, Resour. 23 Conservat. Recycl., 27 (1999) 57. 16. C Makhlouf, M H V Baouab and S Roudesli, Ads. Sci. Tech., 26 (2008) 433. 17. W J Weber and A P Mathews, AIChE Symp. Ser., 73 (1976) 91.


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