- Email: [email protected]
Amphiphilic acid dyes. Dyeing properties and interactions with surface-active systems
Colloids and Surfaces, 35 (1989) 251-260 Elsevier Science Publishers B.V., Amsterdam-- Printed in The Netherlands
251
Amphiphilic Acid Dyes. Dyeing Properties and Interactions with Surface-Active Systems P. SAVARINO, G. VISCARDI, R. C A R P I G N A N O and E. BARNI
Istitutodi Chimica Organica Industriale, Universit~ di Torino, Corso Massimo D'Azeglio 48, 10125 Torino (Italy)
(Received 31 December 1987; accepted 25 July 1988)
ABSTRACT
The equilibria of a series of amphiphilic azo dyes with nylon 6.6 have been investigated.Acidbase interaction and partial solubilizationof the dye in the fibre was found to control the whole dyeing process. The anionic additive SDS competed in the dye-substrate interaction, but this effect was least in the case of the dye with the longest hydrocarbonchain. The behaviour of dyes in dimethylsulpboxideand in aqueoussolutionsof surfactants at differentpH has been examined by UV-VIS and 1H- and 13C-NMRspectra.
INTRODUCTION The synthesis and the properties of a series of azo dyes derived from p-aminosalicylic acid have been reported recently [1]. In order to overcome some difficulties encountered in the interpretation of the dyeing mechanism in our systems, it was necessary to prepare a second set of dyes, not containing the carboxyl but still having a hydrophobic moiety (-SO3Na) and a modular alkyl chain ( - R ) , as indicated in general formula I. NaO3S
N
N
OH
C7H~5(dye 2) Cl11-123 ( dye 3)
I
NHCOR
EXPERIMENTAL
Products
Sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB) and Ethofor RO/40 (ethoxylated castor oil, degree of ethoxylation 40) were purchased commercially. Dyes 1, 2 and 3 have been prepared, coupling diazotized sulphanilic acid to
0166-6622/89/$03.50
© 1989 Elsevier Science Publishers B.V.
252
the suitable m-alkylamidophenol, as indicated in Ref. [2 ]. The crude dyes were crystallized from ethanol. The RE values of the dyes were 0.61, 0.75 and 0.87, respectively.
Measurements Electronic spectra were recorded on a Pye Unicam SP 8-100 spectrophotometer. ~H- and ~aC-NMR spectra were recorded in DMSO-d6 with a Jeol G X 270 spectrometer. The R F values were determined on silica gel 60 F-254 tlc plates (Merck), using as eluent BAW (butanol-acetic acid-water) 4:1:5. Surface tension measurements were performed with a Kriiss tensiometer at 25°C. The dyeing baths were prepared by dissolving the dyes in distilled water in the presence of a phosphate buffer solution (pH 4.8). The dyeings were performed at a fibre-to-liquor ratio of about 1 : 500. The dyeing rate curves were obtained by measuring the absorbance of the bath continuously by pumping a portion of the dyeing bath into a flux cell placed in a colorimeter. All the dyeings were performed at 80 ° C. RESULTS AND DISCUSSION
Characterization of dyes and their interaction with surfactants The RF values (see Experimental ) are a function of the lipophylic properties of the dyes and therefore increase with increasing alkyl chain length. The dyes exhibit surface activity, due to their amphiphilic nature, as shown in Fig. 1. Except for the case of dye 1 having a short chain, the 7 versus log C plots show the typical break points, indicating that a critical micelle concentration (c.m.c.) is attained (c.m.c. of dye 2 is 3.98×10 -4, c.m.c, for dye 3 is 3.37 × 10 -5 mol l- 1). The longer-chain member (dye 3, Cll) appears to be more efficient and more effective than the shorter-chain counterpart (dye 2, C7). The spectral patterns of the three dyes in ethanol are the same, with the main absorption at 382 nm (log e=4.32). Figure 2a shows the hypsochromic and hypochromic shifts of the above maxima ( 2 ~ = 3 6 8 nm; log e=4.28), occurring when the ethanolic solutions are compared with aqueous solutions at pH 4.8. The validity of Lambert-Beer's law has been investigated in the range of concentrations indicated in Fig. 2b for dye 3, taken as an example. At the temperature of 80 °C only one straight line is depicted (full line), whereas, at room temperature, two distinct linear plots are observed. Below 7)< 10 -5 mol l-~ the plot is practically superimposed to the previous one (first part of the full line), whereas at higher concentrations the slope is lower (dotted line).
253 Y
mN m 7O
60 Ull
llm
50 w
40 - 5
- 4
-3
-1
-
,og I t ]
Fig. 1. Surface tension data for dye I (4), dye 2 (II) and dye 3 (@). logE
o
b fh
4-
//#
U ./
I! 3,5
•
.
//
2.
logE:
c
... •" '...
;
.
;
t
3.53 ~ ~ / v
2.5
J
,
500
,
,
400 300 ;k nm
,
200
, 1
,
L
2 3 C ( - 1 0 4) mol*1-1
i
4
Fig. 2. (a) Spectra of dyes 1, 2 and 3 in ethanol (---) and in water ( ). (b) Lambert-Beer's plotsofdye 3at 80°C (e-o-e),25°CbelowTX10-Smoll -I (o-o-o) and at 25 °C above 7X10 -s tool l- I (o-. - o ) (points overlapped in the lower region). (c) Spectra of dye 2 at p H 1 (---), p H 4.8 ( ),p H 7 (--.--) and p H 12 ( ....).
254 This behaviour is consistent with the formation of a micellar system at 7 × 10 -5 mol l - 1. Due to their phenolic nature, the spectra of dyes are sensitive to variation in pH. Figure 2c shows t h a t in the pH range 1-4.8 the main m a x i m u m is displayed at 368 nm; at pH 7 a shoulder appears, which turns into a welldefined m a x i m u m at 457 nm when pH is increased to 12. Such a batho-hyperchromic effect can be correlated with the enhanced electron-releasing effect of the phenoxide ion. The electronic spectra have also been recorded at pH 4.8 (1 X 10 -5 mol l - 1 ) in the presence of the non-ionic surfactant Ethofor RO/40, of the anionic SDS and of the cationic CTAB, below, at and above their c.m.c. Table I summarizes the data. Only the positions and the intensities of the maxima are affected by the additives and this occurs only above their c.m.c. (dyes 2 and 3 with CTAB below its c.m.c, give precipitates probably due to ion-pair formation). Dye 3 is the most sensitive to the addition of surfactants, and the cationic surfactant promotes the most marked bathochromic shift in the spectrum of the dye. It is worth mentioning what happens in dimethylsulphoxide (DMSO) at a concentration of 7 X 10 -s mol 1-1. The three dyes display the main absorption at 389 nm (Fig. 3) and the same happens for dyes I and 2 at higher concentration (7 × 10-4 mol l-1). At this latter concentration, however, the long-chain dye shows a further m a x i m u m at 503 nm. A similar behaviour is also evidenced by N M R spectra. The 1H signals are easily assigned and the chemical shift values are reported in Table 2. Again, only dye 3 in concentrated solution shows TABLE 1 Absorption maximaand intensity of dyes in aqueoussolution of surfactants Surfactant (moll -1)
Dye 1 )~max
Dye 2 log ~
(rim)
Dye 3
)~x
log e
~x
(nm)
log
(rim)
EthoforRO/40 7× 10-7 7X 10-6 7X 10-5
368 368 368
4.24 4.26 4.22
368 368 374
4.31 4.29 4.29
370 374 389
4.19 4.19 4.23
SDS 8X10 -4 8X10 -3 8×10 -2
368 368 372
4.20 4.27 4.23
368 370 382
4.26 4.25 4.26
369 383 386
4.18 4.23 4.21
CTAB 7 X 10-~ 7 X 10- 4 7X10 -3
368 386 386
4.22 4.20 4.20
. 390 390
. 4.26 4.26
.
.
390 390
4.20 4.21
255
IogE
3.5
3
2.5 I
I
t
I
500
400 300 200 7,,nm Fig. 3. Spectra of dyes in D M S O : ( ) dyes I, 2 and 3 at 7 X I0 -s mol I-I and dyes i and 2 at 7 X 1 0 - 4 m o l l - ~ ; ( . . . . . ) dye 3 at 7 X 1 0 - 4 m o l l - L
TABLE 2 Chemical shiftvalues (J) for I H - N M R spectraof dyes in D M S O - d 6
9
10
HO" ~ ~ 7
3
N~- N~ S 0 3 N Q
6\ NH--CO
Dye number
1 2 3 3
2
--R
Concentration (tool 1-1 )
9.3 × 10 -2 9.3 × 10 -2 9.3 X 10 - 2 1.5 X 10-4
Proton number 2
3
7
9
10
7.79 7.78 7.52 7.76
7.92 7.89 7.63 7.87
7.92 7.92 7.29 7.92
6.64 6.62 6.02 6.61
7.71 7.71 7.39 7.71
a general upfield shift, more marked for Hv and H 9. The 13C signals (Table 3) of dyes 1 and 2 are consistent with those calculated on the basis of the additivity of the effects of substituents for an 'azo' structure, whereas for dye 3 important deviations from the above trend are noted. In conclusion, this set of spectroscopic results suggests a strong tendency of the long-chain dye to give aggregates in DMSO at sufficiently high concentrations (however, the contribution of an azo-hydrazone tautomerism to the explanation of the observed phenomena cannot reasonably be excluded).
256 TABLE 3 Chemical shift values (6) for 13C-NMRspectra of dyes in DMSO-de (9.3 X 10-2 tool l- 1)
HOrN~ N ~ SO3Na NH --CO--R
Dye number
Carbonnumber 1
2
3
4
5
6
7
8
9
10
149.8 149.6 149.7 145.7
126.7 126.6 126.7 126.5
121.5 122.1 122.0 119.4
152.0 152.1 152.0 153.2
135.6 135.9 133.9 128.0
136.2 138.9 138.7 138.6
106.2 107.2 107.3 108.7
161.2 162.1 162.1 177.5
110.5 111.6 111.6 117.0
125.2 120.1 120.8 128.7
Calculated
for 'azo' structure 1 2 3
Effect of surfactants on dyeing isotherms The dyes have been tested in the dyeing of nylon 6.6 fibres. The dyeing curves, i.e. the variation of the concentration of the dyes in the fibre with time of dyeing, are reported in Fig. 4 (dye 2 as an example). From these data the equilibrium concentrations in the fibre ( C , ~ ) are obtained by extrapolation; hence, the corresponding concentrations in the baths (C8~o) can be calculated. The dyeing isotherms, reported in Fig. 5, are the C¢~oversus Csooplots for each dyeing experiment. Each isotherm tends asymptotically to a plateau, the position of which is a function of chain length. The saturation values, i.e. the maximum dye uptake in the fibre, increase as the length of the chain increases. Dye 1 in Fig. 5 does not attain the saturation determined by the apparent surface density, being the number of positively charged terminal amino groups strongly influenced by pH. At p H 4.8 only a fraction of the amino groups is reasonably charged. In two cases the saturation exceeds the number of active sites in the fibre, i.e. terminal charged amino groups, determined by titration (40 mmol kg-1, dotted line in Fig. 5). The isotherm form is coherent with the acid-base interactions between the sulphonic groups of the dyes and the terminal charged amino groups of the polyamide fibre. The trend of saturation values suggests the existence of a further dyeing mechanism due to the solubilization of the dye in the fibre, strongly dependent on the hydrophobicity of the dye. The saturation values of the dyeings in the presence of surfactants are reported in Table 4.
257 40
3o
E~20 -m-
0 r
,
,
20
,
60
,
100
140
f/-~
t [~in] Fig. 4. Dyeing rate curves of dye 2 at initialconcentrations of 1.3 X 10 -5 mol I- i (O), 2.7 X 10 -s tool l-I (O) and 12.5 × 10 -5 tool l-I (B).
60
45
~0 30 8
S
O
S I 5
I 10
I 15
J 20
,
25
If
Csco (.105) m / I
Fig. 5. Dyeing isotherms for dye I (A ), dye 2 (O) and dye 3 (• ).
The cationic surfactant, below its c.m.c., gives rise to cloudy solutions, thus preventing any kind of measurements; on the other hand, above its c.m.c., it inhibits the dyeings. It is, therefore, necessary to use simultaneously the nonionic additive, capable of solubilizing the dye 2-CTAB ion pairs. Figure 6 shows a comparison between the dyeing isotherms in the presence of Ethofor RO/40 alone and with the addition of CTAB. The latter situation shows a strong reduction of the saturation, which could be due to the formation of ion pairs and to their subsequent solubilization in the micellar phase. It is, therefore, interesting to investigate the effect of non-ionic surfactants on the three dyes, using the parameter S. Figure 7 is a plot of S versus Ethofor concentration. Dyes 2
258 TABLE 4 Saturationvalues (S X 103) in the presenceof surfactants(toolI-t) Dye number
No surfactant
S
Ethofor RO/40
S
1
-
204-1
1.8X10 -5 4.4X 10 -4
154-1 244-1
3 . 5 X 1 0 -5 1.7X 10 -4
194-1 154-4
2
-
404-1
3.5 X 1 0 - s 1.8X10 -5 1.8X10 -4" 4.4 X 10-4 9.3 X 10-4
35 4-1 344-1 304-2
3.5 X
10 - 4
6.9 X
10 - 4
38+1 33+2 7+1 1+0.5
1.8 X 10-3
30 4-1
2 . 1 X 1 0 -3
294-1
4.4 X 10-4 2.1XlO -3
40 4-1 31+1
3
-
584-1
30 4-1
SDS
S
3.5 X 10 - 3 22.5 X 10 -3
28 4-1
3.5X I0-4 6.9XI0 -4 3.5XI0 -3 9.7XI0 -3
67+3 75+4
94+6 40+4
aAlso in the presenceof CTAB, 2.7X I0-4.
~ l # 4°
,~,
o 30
•
8
----*- ~ 4 - - .
---,
/
& 2O
10
0
,/
!
f t
!
!
5
10
15
; 0
Csoo
(.i05) moL I
I
I
25
30
Fig. 6. Dyeing isotherms of dye 2 in t h e presence of E t h o f o r R O / 4 0 alone ( ~ ) a n d with addition of CTAB ( • ) .
and 3 display a neat diminution of S, whereas dye 1, after an initialdiminution, shows an enhancement (at high dispersant concentration, S values coalesce). Bearing in mind that for dyes 2 and 3 the dissolution appears to play an important role, it can be hypothesized that the non-ionic surfactant, whilst enhancing the solution of long-chain dyes in the micelles, hinders their dissolu-
259
45 ~30 ~5 =If
I -5
i
I
l
-4 -3 Log [Disp] mfl
-2
-1
Fig. 7. Plot of saturation versus concentration of Ethofor RO/40 for dye 1 ( • ) , dye 2 ( • ) and
dye3 (A).
401
~. ~--
{~30 E"
/
~ 2o 10
o/
w
5
10
15
20
-"
2
30
Csco(,10 5) moII Fig.8.Dyeing isothermsof dye 2 in the presenceofvariableamounts of SDS (moll- *X 103):0.00 ( O O O ) , 0.35 ( O - O - O ) , 0.69 ( O . O), 3.50 ( - O - O - • ) and 22.50 ( A - A - A ) .
tion in the fibre. The short-chain m e m b e r appears to be less soluble in the micelles and more soluble in the fibre. The inhibiting effect of non-ionic surfactants towards the dyeing of polyamide fibres with acid dyes is well k n o w n [4,5 ]. Here, the magnitude of this effect is a function of chain length. Dye i is completely inhibited in the presence of S D S above a concentration of 1.7X 10 -4 tool l-I, whereas dyes 2 and 3 have a lower susceptibility. Figure 8 shows the behaviour of dye 2. As the S D S concentration increases, S values decrease and the curves are flattened; in particular, for a S D S concentration of 2.25 X 10 -2 tool I- I,the isotherm is linear and its slope is virtually zero.
260
Important dye-substrate interactions of a hydrophobic nature have been suggested by the dependence of saturation values on the length of hydrocarbon tails and by the different susceptibilities to the addition of surfactants. These hydrophobic interactions take shape either by a simple adsorption, or by a dissolution if the analogy with disperse dyeings is considered. CONCLUSIONS
The amphiphilic azo dyes derived from sulphanilic acid and m-alkylamidophenols interact with polyamide 6.6 fibres in two ways. Besides the classical acid-base reaction between sulphonic and charged terminal amino groups, t h e y also dissolve in the substrate. From a practical point of view, the long-chain term, due to its hydrophobicity, shows a more favourable dyeing isotherm, leading to a better exhaustion of liquors. The surfactants, in general, hinder the dyeing process. The anionic additive (SDS), which inhibits the acid-base interactions, exerts a less-marked effect on the most hydrophobic dye. ACKNOWLEDGEMENT
W e thank the Ministero della Pubblica Istruzione (Italy) for providing a research grant.
REFERENCES I P. Savarino, G. Viscardi, E. Barni, E. Pelizzetti,E. Pramauro and C. Minero, Ann. Chim. (Rome), 77 (1987) 285. 2 H.E. Fierz-David and H. Meister, Helv. Chim. Acta, 22 (1939) 579. 3 C.L. Bird and W.S. Boston, The Theory of Coloration of Textiles,The Dyers Company PublicationsTrust, Bradford, 1975. 4 M. Mitsuishi,D. Yoshida, H. Maruyama and T. Ishiwatari,Sen'i Gakkaishi, 39 (1983) 40. 5 M. Mitsuishi, T. Ishiwatari,D. Yoshida and S. Takano, Sen'i Gakkaishi, 37 (1981) 108.
251
Amphiphilic Acid Dyes. Dyeing Properties and Interactions with Surface-Active Systems P. SAVARINO, G. VISCARDI, R. C A R P I G N A N O and E. BARNI
Istitutodi Chimica Organica Industriale, Universit~ di Torino, Corso Massimo D'Azeglio 48, 10125 Torino (Italy)
(Received 31 December 1987; accepted 25 July 1988)
ABSTRACT
The equilibria of a series of amphiphilic azo dyes with nylon 6.6 have been investigated.Acidbase interaction and partial solubilizationof the dye in the fibre was found to control the whole dyeing process. The anionic additive SDS competed in the dye-substrate interaction, but this effect was least in the case of the dye with the longest hydrocarbonchain. The behaviour of dyes in dimethylsulpboxideand in aqueoussolutionsof surfactants at differentpH has been examined by UV-VIS and 1H- and 13C-NMRspectra.
INTRODUCTION The synthesis and the properties of a series of azo dyes derived from p-aminosalicylic acid have been reported recently [1]. In order to overcome some difficulties encountered in the interpretation of the dyeing mechanism in our systems, it was necessary to prepare a second set of dyes, not containing the carboxyl but still having a hydrophobic moiety (-SO3Na) and a modular alkyl chain ( - R ) , as indicated in general formula I. NaO3S
N
N
OH
C7H~5(dye 2) Cl11-123 ( dye 3)
I
NHCOR
EXPERIMENTAL
Products
Sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB) and Ethofor RO/40 (ethoxylated castor oil, degree of ethoxylation 40) were purchased commercially. Dyes 1, 2 and 3 have been prepared, coupling diazotized sulphanilic acid to
0166-6622/89/$03.50
© 1989 Elsevier Science Publishers B.V.
252
the suitable m-alkylamidophenol, as indicated in Ref. [2 ]. The crude dyes were crystallized from ethanol. The RE values of the dyes were 0.61, 0.75 and 0.87, respectively.
Measurements Electronic spectra were recorded on a Pye Unicam SP 8-100 spectrophotometer. ~H- and ~aC-NMR spectra were recorded in DMSO-d6 with a Jeol G X 270 spectrometer. The R F values were determined on silica gel 60 F-254 tlc plates (Merck), using as eluent BAW (butanol-acetic acid-water) 4:1:5. Surface tension measurements were performed with a Kriiss tensiometer at 25°C. The dyeing baths were prepared by dissolving the dyes in distilled water in the presence of a phosphate buffer solution (pH 4.8). The dyeings were performed at a fibre-to-liquor ratio of about 1 : 500. The dyeing rate curves were obtained by measuring the absorbance of the bath continuously by pumping a portion of the dyeing bath into a flux cell placed in a colorimeter. All the dyeings were performed at 80 ° C. RESULTS AND DISCUSSION
Characterization of dyes and their interaction with surfactants The RF values (see Experimental ) are a function of the lipophylic properties of the dyes and therefore increase with increasing alkyl chain length. The dyes exhibit surface activity, due to their amphiphilic nature, as shown in Fig. 1. Except for the case of dye 1 having a short chain, the 7 versus log C plots show the typical break points, indicating that a critical micelle concentration (c.m.c.) is attained (c.m.c. of dye 2 is 3.98×10 -4, c.m.c, for dye 3 is 3.37 × 10 -5 mol l- 1). The longer-chain member (dye 3, Cll) appears to be more efficient and more effective than the shorter-chain counterpart (dye 2, C7). The spectral patterns of the three dyes in ethanol are the same, with the main absorption at 382 nm (log e=4.32). Figure 2a shows the hypsochromic and hypochromic shifts of the above maxima ( 2 ~ = 3 6 8 nm; log e=4.28), occurring when the ethanolic solutions are compared with aqueous solutions at pH 4.8. The validity of Lambert-Beer's law has been investigated in the range of concentrations indicated in Fig. 2b for dye 3, taken as an example. At the temperature of 80 °C only one straight line is depicted (full line), whereas, at room temperature, two distinct linear plots are observed. Below 7)< 10 -5 mol l-~ the plot is practically superimposed to the previous one (first part of the full line), whereas at higher concentrations the slope is lower (dotted line).
253 Y
mN m 7O
60 Ull
llm
50 w
40 - 5
- 4
-3
-1
-
,og I t ]
Fig. 1. Surface tension data for dye I (4), dye 2 (II) and dye 3 (@). logE
o
b fh
4-
//#
U ./
I! 3,5
•
.
//
2.
logE:
c
... •" '...
;
.
;
t
3.53 ~ ~ / v
2.5
J
,
500
,
,
400 300 ;k nm
,
200
, 1
,
L
2 3 C ( - 1 0 4) mol*1-1
i
4
Fig. 2. (a) Spectra of dyes 1, 2 and 3 in ethanol (---) and in water ( ). (b) Lambert-Beer's plotsofdye 3at 80°C (e-o-e),25°CbelowTX10-Smoll -I (o-o-o) and at 25 °C above 7X10 -s tool l- I (o-. - o ) (points overlapped in the lower region). (c) Spectra of dye 2 at p H 1 (---), p H 4.8 ( ),p H 7 (--.--) and p H 12 ( ....).
254 This behaviour is consistent with the formation of a micellar system at 7 × 10 -5 mol l - 1. Due to their phenolic nature, the spectra of dyes are sensitive to variation in pH. Figure 2c shows t h a t in the pH range 1-4.8 the main m a x i m u m is displayed at 368 nm; at pH 7 a shoulder appears, which turns into a welldefined m a x i m u m at 457 nm when pH is increased to 12. Such a batho-hyperchromic effect can be correlated with the enhanced electron-releasing effect of the phenoxide ion. The electronic spectra have also been recorded at pH 4.8 (1 X 10 -5 mol l - 1 ) in the presence of the non-ionic surfactant Ethofor RO/40, of the anionic SDS and of the cationic CTAB, below, at and above their c.m.c. Table I summarizes the data. Only the positions and the intensities of the maxima are affected by the additives and this occurs only above their c.m.c. (dyes 2 and 3 with CTAB below its c.m.c, give precipitates probably due to ion-pair formation). Dye 3 is the most sensitive to the addition of surfactants, and the cationic surfactant promotes the most marked bathochromic shift in the spectrum of the dye. It is worth mentioning what happens in dimethylsulphoxide (DMSO) at a concentration of 7 X 10 -s mol 1-1. The three dyes display the main absorption at 389 nm (Fig. 3) and the same happens for dyes I and 2 at higher concentration (7 × 10-4 mol l-1). At this latter concentration, however, the long-chain dye shows a further m a x i m u m at 503 nm. A similar behaviour is also evidenced by N M R spectra. The 1H signals are easily assigned and the chemical shift values are reported in Table 2. Again, only dye 3 in concentrated solution shows TABLE 1 Absorption maximaand intensity of dyes in aqueoussolution of surfactants Surfactant (moll -1)
Dye 1 )~max
Dye 2 log ~
(rim)
Dye 3
)~x
log e
~x
(nm)
log
(rim)
EthoforRO/40 7× 10-7 7X 10-6 7X 10-5
368 368 368
4.24 4.26 4.22
368 368 374
4.31 4.29 4.29
370 374 389
4.19 4.19 4.23
SDS 8X10 -4 8X10 -3 8×10 -2
368 368 372
4.20 4.27 4.23
368 370 382
4.26 4.25 4.26
369 383 386
4.18 4.23 4.21
CTAB 7 X 10-~ 7 X 10- 4 7X10 -3
368 386 386
4.22 4.20 4.20
. 390 390
. 4.26 4.26
.
.
390 390
4.20 4.21
255
IogE
3.5
3
2.5 I
I
t
I
500
400 300 200 7,,nm Fig. 3. Spectra of dyes in D M S O : ( ) dyes I, 2 and 3 at 7 X I0 -s mol I-I and dyes i and 2 at 7 X 1 0 - 4 m o l l - ~ ; ( . . . . . ) dye 3 at 7 X 1 0 - 4 m o l l - L
TABLE 2 Chemical shiftvalues (J) for I H - N M R spectraof dyes in D M S O - d 6
9
10
HO" ~ ~ 7
3
N~- N~ S 0 3 N Q
6\ NH--CO
Dye number
1 2 3 3
2
--R
Concentration (tool 1-1 )
9.3 × 10 -2 9.3 × 10 -2 9.3 X 10 - 2 1.5 X 10-4
Proton number 2
3
7
9
10
7.79 7.78 7.52 7.76
7.92 7.89 7.63 7.87
7.92 7.92 7.29 7.92
6.64 6.62 6.02 6.61
7.71 7.71 7.39 7.71
a general upfield shift, more marked for Hv and H 9. The 13C signals (Table 3) of dyes 1 and 2 are consistent with those calculated on the basis of the additivity of the effects of substituents for an 'azo' structure, whereas for dye 3 important deviations from the above trend are noted. In conclusion, this set of spectroscopic results suggests a strong tendency of the long-chain dye to give aggregates in DMSO at sufficiently high concentrations (however, the contribution of an azo-hydrazone tautomerism to the explanation of the observed phenomena cannot reasonably be excluded).
256 TABLE 3 Chemical shift values (6) for 13C-NMRspectra of dyes in DMSO-de (9.3 X 10-2 tool l- 1)
HOrN~ N ~ SO3Na NH --CO--R
Dye number
Carbonnumber 1
2
3
4
5
6
7
8
9
10
149.8 149.6 149.7 145.7
126.7 126.6 126.7 126.5
121.5 122.1 122.0 119.4
152.0 152.1 152.0 153.2
135.6 135.9 133.9 128.0
136.2 138.9 138.7 138.6
106.2 107.2 107.3 108.7
161.2 162.1 162.1 177.5
110.5 111.6 111.6 117.0
125.2 120.1 120.8 128.7
Calculated
for 'azo' structure 1 2 3
Effect of surfactants on dyeing isotherms The dyes have been tested in the dyeing of nylon 6.6 fibres. The dyeing curves, i.e. the variation of the concentration of the dyes in the fibre with time of dyeing, are reported in Fig. 4 (dye 2 as an example). From these data the equilibrium concentrations in the fibre ( C , ~ ) are obtained by extrapolation; hence, the corresponding concentrations in the baths (C8~o) can be calculated. The dyeing isotherms, reported in Fig. 5, are the C¢~oversus Csooplots for each dyeing experiment. Each isotherm tends asymptotically to a plateau, the position of which is a function of chain length. The saturation values, i.e. the maximum dye uptake in the fibre, increase as the length of the chain increases. Dye 1 in Fig. 5 does not attain the saturation determined by the apparent surface density, being the number of positively charged terminal amino groups strongly influenced by pH. At p H 4.8 only a fraction of the amino groups is reasonably charged. In two cases the saturation exceeds the number of active sites in the fibre, i.e. terminal charged amino groups, determined by titration (40 mmol kg-1, dotted line in Fig. 5). The isotherm form is coherent with the acid-base interactions between the sulphonic groups of the dyes and the terminal charged amino groups of the polyamide fibre. The trend of saturation values suggests the existence of a further dyeing mechanism due to the solubilization of the dye in the fibre, strongly dependent on the hydrophobicity of the dye. The saturation values of the dyeings in the presence of surfactants are reported in Table 4.
257 40
3o
E~20 -m-
0 r
,
,
20
,
60
,
100
140
f/-~
t [~in] Fig. 4. Dyeing rate curves of dye 2 at initialconcentrations of 1.3 X 10 -5 mol I- i (O), 2.7 X 10 -s tool l-I (O) and 12.5 × 10 -5 tool l-I (B).
60
45
~0 30 8
S
O
S I 5
I 10
I 15
J 20
,
25
If
Csco (.105) m / I
Fig. 5. Dyeing isotherms for dye I (A ), dye 2 (O) and dye 3 (• ).
The cationic surfactant, below its c.m.c., gives rise to cloudy solutions, thus preventing any kind of measurements; on the other hand, above its c.m.c., it inhibits the dyeings. It is, therefore, necessary to use simultaneously the nonionic additive, capable of solubilizing the dye 2-CTAB ion pairs. Figure 6 shows a comparison between the dyeing isotherms in the presence of Ethofor RO/40 alone and with the addition of CTAB. The latter situation shows a strong reduction of the saturation, which could be due to the formation of ion pairs and to their subsequent solubilization in the micellar phase. It is, therefore, interesting to investigate the effect of non-ionic surfactants on the three dyes, using the parameter S. Figure 7 is a plot of S versus Ethofor concentration. Dyes 2
258 TABLE 4 Saturationvalues (S X 103) in the presenceof surfactants(toolI-t) Dye number
No surfactant
S
Ethofor RO/40
S
1
-
204-1
1.8X10 -5 4.4X 10 -4
154-1 244-1
3 . 5 X 1 0 -5 1.7X 10 -4
194-1 154-4
2
-
404-1
3.5 X 1 0 - s 1.8X10 -5 1.8X10 -4" 4.4 X 10-4 9.3 X 10-4
35 4-1 344-1 304-2
3.5 X
10 - 4
6.9 X
10 - 4
38+1 33+2 7+1 1+0.5
1.8 X 10-3
30 4-1
2 . 1 X 1 0 -3
294-1
4.4 X 10-4 2.1XlO -3
40 4-1 31+1
3
-
584-1
30 4-1
SDS
S
3.5 X 10 - 3 22.5 X 10 -3
28 4-1
3.5X I0-4 6.9XI0 -4 3.5XI0 -3 9.7XI0 -3
67+3 75+4
94+6 40+4
aAlso in the presenceof CTAB, 2.7X I0-4.
~ l # 4°
,~,
o 30
•
8
----*- ~ 4 - - .
---,
/
& 2O
10
0
,/
!
f t
!
!
5
10
15
; 0
Csoo
(.i05) moL I
I
I
25
30
Fig. 6. Dyeing isotherms of dye 2 in t h e presence of E t h o f o r R O / 4 0 alone ( ~ ) a n d with addition of CTAB ( • ) .
and 3 display a neat diminution of S, whereas dye 1, after an initialdiminution, shows an enhancement (at high dispersant concentration, S values coalesce). Bearing in mind that for dyes 2 and 3 the dissolution appears to play an important role, it can be hypothesized that the non-ionic surfactant, whilst enhancing the solution of long-chain dyes in the micelles, hinders their dissolu-
259
45 ~30 ~5 =If
I -5
i
I
l
-4 -3 Log [Disp] mfl
-2
-1
Fig. 7. Plot of saturation versus concentration of Ethofor RO/40 for dye 1 ( • ) , dye 2 ( • ) and
dye3 (A).
401
~. ~--
{~30 E"
/
~ 2o 10
o/
w
5
10
15
20
-"
2
30
Csco(,10 5) moII Fig.8.Dyeing isothermsof dye 2 in the presenceofvariableamounts of SDS (moll- *X 103):0.00 ( O O O ) , 0.35 ( O - O - O ) , 0.69 ( O . O), 3.50 ( - O - O - • ) and 22.50 ( A - A - A ) .
tion in the fibre. The short-chain m e m b e r appears to be less soluble in the micelles and more soluble in the fibre. The inhibiting effect of non-ionic surfactants towards the dyeing of polyamide fibres with acid dyes is well k n o w n [4,5 ]. Here, the magnitude of this effect is a function of chain length. Dye i is completely inhibited in the presence of S D S above a concentration of 1.7X 10 -4 tool l-I, whereas dyes 2 and 3 have a lower susceptibility. Figure 8 shows the behaviour of dye 2. As the S D S concentration increases, S values decrease and the curves are flattened; in particular, for a S D S concentration of 2.25 X 10 -2 tool I- I,the isotherm is linear and its slope is virtually zero.
260
Important dye-substrate interactions of a hydrophobic nature have been suggested by the dependence of saturation values on the length of hydrocarbon tails and by the different susceptibilities to the addition of surfactants. These hydrophobic interactions take shape either by a simple adsorption, or by a dissolution if the analogy with disperse dyeings is considered. CONCLUSIONS
The amphiphilic azo dyes derived from sulphanilic acid and m-alkylamidophenols interact with polyamide 6.6 fibres in two ways. Besides the classical acid-base reaction between sulphonic and charged terminal amino groups, t h e y also dissolve in the substrate. From a practical point of view, the long-chain term, due to its hydrophobicity, shows a more favourable dyeing isotherm, leading to a better exhaustion of liquors. The surfactants, in general, hinder the dyeing process. The anionic additive (SDS), which inhibits the acid-base interactions, exerts a less-marked effect on the most hydrophobic dye. ACKNOWLEDGEMENT
W e thank the Ministero della Pubblica Istruzione (Italy) for providing a research grant.
REFERENCES I P. Savarino, G. Viscardi, E. Barni, E. Pelizzetti,E. Pramauro and C. Minero, Ann. Chim. (Rome), 77 (1987) 285. 2 H.E. Fierz-David and H. Meister, Helv. Chim. Acta, 22 (1939) 579. 3 C.L. Bird and W.S. Boston, The Theory of Coloration of Textiles,The Dyers Company PublicationsTrust, Bradford, 1975. 4 M. Mitsuishi,D. Yoshida, H. Maruyama and T. Ishiwatari,Sen'i Gakkaishi, 39 (1983) 40. 5 M. Mitsuishi, T. Ishiwatari,D. Yoshida and S. Takano, Sen'i Gakkaishi, 37 (1981) 108.