Retarding action of poly(amidoamine) dendrimers and cationic gemini surfactants in acrylic dyeing

Article abstract of DOI:10.1016/j.dyepig.2015.10.037

Two cationic gemini surfactants and two generations of poly(amidoamine) (PAMAM) dendrimers (G = -0.5 and G = 0.5) were studied as retarders in acrylic dyeing with a cationic dye. Effects of retarder concentrations, dyeing time, and temperature were investigated by means of UV-Vis spectrophotometry. The results indicated that the dye adsorption decreased in the presence of the species and more uniform dyeing was achieved. The PAMAM dendrimers had lower retarding action than the cationic gemini surfactants which was attributed to their non-permanent and lower cationic charge density. Kinetics of the dyeing systems were also evaluated by four different empirical models. The modified Cegarra-Puente model fitted the dyeing kinetic data somewhat better than the other empirical kinetic models. Moreover, the activation energy of the dyeing systems was calculated and reported.

Full text of DOI:10.1016/j.dyepig.2015.10.037

Accepted Manuscript
Retarding action of poly(amidoamine) dendrimers and cationic gemini surfactants in
acrylic dyeing
Mousa Sadeghi-Kiakhani, Ali Reza Tehrani-Bagha
PII:
S0143-7208(15)00420-9
10.1016/j.dyepig.2015.10.037
DYPI 4984
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 10 June 2015
Revised Date: 26 September 2015
Accepted Date: 26 October 2015
Please cite this article as: Sadeghi-Kiakhani M, Tehrani-Bagha AR, Retarding action of
poly(amidoamine) dendrimers and cationic gemini surfactants in acrylic dyeing, Dyes and Pigments
(2015), doi: 10.1016/j.dyepig.2015.10.037.
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ACCEPTED MANUSCRIPT
Graphical abstract

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Retarding action of poly(amidoamine) dendrimers and cationic gemini surfactants in
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acrylic dyeing
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Mousa Sadeghi-Kiakhani1* and Ali Reza Tehrani-Bagha2
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1: Institute for Color Science and Technology, Department of Organic Colorants, Tehran-
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Iran
2: Department of Chemical and Petroleum Engineering, American University of Beirut,
Beirut-Lebanon
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Corresponding author: Tel: +98 21 22969774; fax: +98 21 22969774; E-mail: sadeghi-
mo@icrc.ac.ir
Abstract
Two cationic gemini surfactants and two generations of poly(amidoamine) (PAMAM)
dendrimers (G=-0.5 and G=0.5) were studied as retarders in acrylic dyeing with a cationic
dye. Effects of retarder concentrations, dyeing time, and temperature were investigated by
means of UV-Vis spectrophotometry. The results indicated that the dye adsorption decreased
in the presence of all species and more uniform dyeing was achieved. The PAMAM
dendrimers had lower retarding action than the cationic gemini surfactants which was
attributed to their non-permanent and lower cationic charge density. Kinetics of the dyeing
systems were also evaluated by four different empirical models. The modified Cegarra-
Puente model fitted the dyeing kinetic data somewhat better than the other empirical kinetic
models. Moreover, the activation energy of the dyeing systems was calculated and reported.
Keywords: Acrylic dyeing, Dye adsorption, Cationic dye, Poly(amidoamine) dendrimers,
Cationic Gemini surfactants.
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1. Introduction
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Dendrimers are highly branched molecules typically symmetric around a core with a three-
dimensional morphology. The presence of different functional groups at their outer shell
enables them to react with other molecules [1, 2]. The properties of dendrimers can be
modified by changing the type and the distribution of the functional groups [3-5]. As a result
of unique chemical structures, dendrimers have many interesting properties and applications
which have inspired the researchers all over the world. Their applications are in power/energy
sectors, engineering, electronics/optoelectronics, and health to name a few [6, 7].
There are two defined methods of dendrimer synthesis: (a) divergent method in which the
dendrimer is assembled from a multifunctional core and is extended outward by a series of
reactions (Scheme 1), and (b) convergent method in which small units are reacted inward and
are attached to a core. Each of these methods has its own pros and cons which can be read
elsewhere [8, 9].
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Dendrimers are molecules with a tendency to adopt spherical or globular shapes in a solution
[10-12]. Other small molecules, depending on their size and charge, can be adsorbed at the
outer shell or entrapped within the porous inner shell [13]. A large number of dendrimers
with various chemical structures have been synthesized and investigated for adsorption and
extraction of organic dyes from aqueous solutions and organic solvents, as illustrated here via
an incomplete and arbitrary listing: Poly(propyleneimine) dendrimers for extraction of
anionic xanthene dyes from water into organic solvents [14]; Fluorinated dendrimers to
extract methyl orange from water into super critical CO2; Dendritic peptides with carboxylic
acid functional groups at the outer surface for extraction of polybasic aromatic dyes from the
solution; dendrimers for solubilization of proflavine hydrochloride dye in CH2Cl2 [13, 15].
Dendrimers can also be used as capsules that reversibly trap and release guest molecules (e.g.
dyes, drugs) [12-16].
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Most gemini surfactants are composed of two conventional single chain surfactant molecules
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chemically bonded together by a spacer. The synthesis and examination of a large number of
gemini surfactants with various chemical structures (e.g. anionic, cationic, nonionic, …) have
drawn international attention since 1991 [17-20]. Compared to their monomeric counterparts,
gemini surfactants typically have higher surface activity and lower CMC values. Therefore,
lesser amount of gemini surfactants is needed for the same applications (e.g. detergency,
adsorption, surface modification, etc.) which is very important from economic and
environmental points of view [21-23]. Gemini surfactants have been proved to be much more
effective than their monomeric counterparts in many different applications [17, 24-26].
Cationic dyes can not migrate freely after being adsorbed on polyacrylonitrile (PAN) fibers.
This is due to strong dye-fiber bonding via electrostatic interaction over small temperature
range above the glass transition (Tg) of the fiber [27]. The quick rate of dyeing can increase
the risk of unlevel dyeing (i.e. non-uniform distribution of dye molecules during adsorption
process). This can be prevented by adding retarders (i.e. typically cationic, anionic or
polymeric surfactants) to the solution during the dyeing process. Cationic retarders are
usually colorless, water-soluble, quaternary ammonium salts containing long aliphatic chains
that compete with dye cations for limited anionic sites at the surface of the fiber [27-29].
They reduce the rate of dyeing by lowering the dye concentration gradient across the fiber
and enhance dye migration by increasing the total number of cations in the dye-fiber system.
There are a few studies on the retarding efficiencies of cationic gemini surfactants [17, 24,
30], but we could not find any similar studies for dendrimers. This research project concerns
investigations of the retarding effectiveness of two different generations of poly(amidoamine)
(PAMAM) dendrimers (Scheme 1) and two cationic gemini surfactants (Scheme 2) in acrylic
dyeing with a cationic dye. Effects of different parameters (i.e. temperature and retarder
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concentration) on the kinetic of dyeing process are studied in acrylic dyeing. Moreover, the
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activation energy of diffusion of the dye into the fiber is investigated.
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2. Experimental
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2.1. Materials and apparatus
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N,N-dimethyldodecylamine, 1,3-dibromopropane, 2-dimethylaminoethanol, decanoyl
chloride, acetone, ethanol, diethyl ether, magnesium sulfate, and sodium hydrogen carbonate
were all purchased from Aldrich for synthesis of the cationic gemini surfactants. For
preparation of PAMAM dendrimers, Ethylenediamine, methyl acrylate, and methanol were
obtained from Merck Co. All the chemicals and solvents were of analytical reagent grade and
used without further purification.
High bulk acrylic yarn 24/2 Nm type , obtained from Nakh Iran Textile Co., was used after
washing ,with a nonionic detergent at 40C for 30 min, and drying processes. A commercial
cationic dye, C.I. Basic Red 46 (BR46), was purchased from Dystar Co. and used without
further purification. The chemical structure of BR46 is shown in Figure 1. Absorbance
changes of dye solutions were measured with a Cecil 9200 double beam UV-Vis
spectrophotometer.
Figure 1
2.2. Synthesis of dendrimers and surfactants
Details of synthesis and purification of poly(amidoamine) dendrimers (scheme 1) and
cationic gemini surfactants (scheme 2) have been provided in our previous papers [31, 32].
Only a brief description of the synthesis methods is provided here.
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2.2.1. Preparation of PAMAM (G=-0.5) and (G=0.5)
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PAMAM dendrimers were prepared by the divergent method starting from ethylene diamine
as can be seen in Scheme 1. Briefly, a solution of etheylenamine (EA) in methanol was added
to methyl acrylate (four molar excess). The mixture was stirred for 5 days at 40 C. Then, the
mixture was evaporated to give PAMAM (G=-0.5) [31, 32].
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The solution of PAMAM (G=-0.5) in methanol was added to EA (four molar excess), and the
mixture was stirred at room temperature for 3 days. After evaporation of the solvent, the
residue was dried completely in 40 ˚C under vacuum to remove the excess amount of EA,
and PAMAM (G=0) was obtained. For synthesis of PAMAM (G=0.5), PAMAM (G=0) was
reacted with methyl acrylate as it was described elsewhere [31, 32].
Scheme 1
2.2.2. Preparation of cationic gemini surfactants
The procedure for synthesis and purification of the gemini cationic surfactants in this study
has been reported in the previous papers in details [17, 23, 24]. The gemini surfactants were
synthesized by reacting the tertiary amine with the appropriate dihalide (Scheme 2).
The
non-ester-containing
cationic
gemini
surfactant,
dodecyl-[3-
[dodecyl(dimethyl)ammonio]propyl]-dimethyl-ammonium dibromide (12Q-3-Q12), was
synthesized in one step: 1,3-Dibromopropane was added drop-wise to the stirring mixture of
N,N-dimethyldodecylamine (5% excess) in dry acetone and refluxed for 48 h. Upon cooling,
a white solid precipitated which was filtered and washed with cold acetone. The product was
recrystallized once again and its purity was secured by H NMR analysis.
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The ester-containing surfactant, N,N’-bis(2-(dodecanoyloxy)ethyl)-N,N,N’,N’-tetramethyl-
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1,3-propanediammonium dibromide (11E2Q-3-Q2E11), was synthesized in two steps: First,
N-(2-(dodecanoyloxy)ethyl)-N,N-dimethylamine was obtained from the reaction of
Dimethylethanolamine with dodecyl chloride in dichloromethane ; Second, 11E2Q-3-Q2E11
was synthesized with the reaction of N-(2-(dodecanoyloxy)ethyl)-N,N-dimethylamine with
1,3-Dibromepropane similar to what it was described for 12Q-3-Q12.
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Scheme 2
2.3. Acrylic dyeing
Common acrylic fibers dye-able by cationic dyes normally show a finite saturation value
associated with the number of available dye-sites at the fiber surface. The most convenient
practical definition of fiber saturation is the amount of a cationic dye which after dyeing
under conventional condition is found to give 90% exhaustion on to the fiber. The saturation
concentration (Cs) of BR46 - acrylic fiber system was obtained to be 5 % over weight of fiber
(o.w.f.) based on the standard test procedure [33]. One quarter of the saturation concentration
(i.e. 1.25 % o.w.f.) was then chosen to be the initial dye concentration in dye-bath for acrylic
dyeing for the rest of the experiments. Therefore, the dye concentration is always lower than
the amount needed to interact with all the available oppositely charged dye-sites on the fiber..
Dye-baths’ pH was adjusted to 4.5 by using 1% (o.w.f.) acetic acid (glacial) and 1% (o.w.f.)
sodium acetate crystals. The liquor to acrylic fiber ratio was adjusted to 50:1 by adding
distilled water. Acrylic dyeing was investigated at three different temperatures (i.e. 90, 95
and 100 °C), and at various surfactant to dye molar ratios. Dyeing procedure was carried out
using a sample dyeing machine (Smart dyer rapid sd-16, India). Absorbance changes of all
samples (1 g each) were monitored and determined at certain time intervals (i.e. 5, 10, 15, 20,
30, 60, 90 and 120 min) during the adsorption process. Each dyeing capsule was removed
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from the dyeing machine and was cooled down immediately by cold tap water. This
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procedure was followed by the sample removal from each capsule to quick quenching of the
dyeing procedure; The rate of dye adsorption on acrylic fiber drops to a large extent at
temperature below the glass transition temperature (Tg) of the fiber (around 85 C). The
percentage of dye adsorption onto acrylic sample or dyebath exhaustion (E %) was calculated
using Eq. 1:
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(C0 Ct )
E % =
100
Eq. 1
C0
Where, C0 and Ct are the dye concentrations in the dye-bath solution before and after the
dyeing process, respectively.
There was no change in the visible spectra of cationic dye solution in the presence of
dendrimers / cationic surfactants. This showed that that there is not apparent interaction
between the cationic dye and the cationic dendrimers/surfactants in the solution.
The color strength expressed as K/S was measured according to a previously reported method
[29, 32] by the light reflectance technique, and the relative color strength was calculated by
applying the Kubetka-Munk equation:
(1 R)2
K / S 
Eq. 2
2R
Where, R is the reflectance value of the fabric at peak wavelength, K is the absorption
coefficient and S is the scattering coefficient.
Gretag Macbeth (USA) 7000A spectrophotometer under D65 illuminant and 10° observer
was used for measuring the colorimetric properties (λmax, L*, a*, b*, C*, h˚) and the light
reflectance of dyed samples. L* defines lightness; a* denotes the red/green value; and b* the
yellow/blue value and C* is the saturation which were calculated from the reflectance data
[34-36].The average (Eq. 3) and standard deviation (Eq. 4) of K/S values measured at 8
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different points on the surface of the dyed samples were used for leveling assessment of
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dyeing process:
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n
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K
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S
(K / S) 
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i1
Eq. 3
Eq. 4
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n
[(K / S)  (K / S) ]2
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
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S()

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Where, S(λ) is the standard deviation of the K/S values and sample mean on each sample point
of a dyed fabric; λ is the wavelength of the measurement; n is the total number of the
measurements; (K/S)i,λ is the K/S value of i measurement at λ wavelength. Smaller S(λ) can be
considered as higher dyeing uniformity [37].
2.4. Empirical kinetic models
Four empirical kinetic models (i.e. parabolic, first order, Cegarra-Puente, and modified
Cegarra-Puente) were used for calculation of the dyeing rate constant (k) from experimental
dye adsorption data at various time intervals of the dyeing process (Equations 5-8) [30, 38].
In all these equations (Eqs. 5-8), Ct is the dye concentration of the sample at time t, C∞ is the
dye concentration at the equilibrium, k is the absorption rate constant and t is the dyeing time.
dCt
dt
k

 Ct  k t
Parabolic
Eq. 5
Eq. 6
Eq. 7
Ct
dCt
dt
Ct
 k(CCt )  ln(1
)  kt
Exponential / First Order
Cegarra-Puente
C
Ct2
C2
ln(1
)  kt
Ct2
C2


ln ln(1 )  aln k  aln t
Modified Cegarra-Puente
Eq. 8




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2.5. Activation Energy
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The apparent activation energy of the diffusion (Ea), the energy that must be overcome in
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order for a dyeing process to occur, was calculated by the empirical Arrhenius equation Eq. 9
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[36]:
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Ea
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ln k  ln k0 
Eq. 9
RT
Where, R is the gas constant (8.314 J/mol K), k is the rate constant; and T is the absolute
temperature (˚K), and Ea is the apparent activation energy of adsorption (J/mol). Plotting the
rate of the adsorption against the reciprocal temperature gives a reasonably straight line, the
gradient of which is -Ea/R [30, 39].
3. Results and discussion
3.1. Retarding action of dendrimers and surfactants
3.2.1. Effect of temperature
The effect of temperature on the dye absorption (%) at the same molar concentration of
retarder to dye was studied. Figure 2 shows that the adsorption of BR46 on acrylic fiber in the
absence of retarder is quite fast even at temperature as low as 90 C. The complete cationic
dye adsorption onto the acrylic fiber (i.e. exhaustion in textile terminology) occurs in about
10-20 min. Such a high adsorption rate in dyeing process can result in unlevel dyeing. The
presence of dendrimers and cationic surfactants as retarders reduces the dyeing rate and the
time needed for the complete dye exhaustion.
Figure 2
As can be seen from Figure 2, the stable gemini cationic surfactant (i.e. 12Q-3-Q12) is the
strongest retarder tested and it causes blocking effect (i.e. complete dye exhaustion is not
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achievable). Compared with 12Q-3-Q12, the ester-containing cationic gemini surfactant
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shows somewhat weaker retarding effect as can be seen in Figure 2. This has been discussed
in details in our recent publication on retarding efficiencies of ester-containing cationic
gemini surfactants [30] and we are not going to repeat the discussion here.
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The retarding action of PAMAM dendrimers is weaker than the cationic gemini surfactants.
PAMAM (G=-0.5) and PAMAM (G=0.5) have 2 and 6 tertiary amines in their chemical
structures, respectively. These groups are quaternized in acidic media by adsorbing protons
from the solution (i.e. dyeing pH 4.5). The charge of PAMAM is pH-dependent, and the
interactions between PAMAM and the acrylic fiber anionic sites are stronger in acidic pH as
the number of cationic groups at PAMAM surface increases. The ester bonds in the chemical
structures should be stable in mild acidic condition and the chance of chemical hydrolysis of
these groups at mild acidic pH is very low [40]. It should be noted that methyl-ester
terminated dendrimers can be hydrolyzed with stoichiometric amounts of NaOH in water to
obtain external carboxylate groups with sodium which is not the case here [41].
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Lower retarding action of these cationic PAMAM dendrimers (at pH 4.5) compared with
those of cationic gemini surfactants suggests that the charge density of the dendrimers is
lower than that of the geminis. So, the cationic dendrimers with larger molecular size and
lower charge density are weaker retarders.
The retarding action of PAMAM (G=-0.5) is weaker than that of PAMAM (G=+0.5).
PAMAM (G=0.5), with larger molecular size and having 6 cationic groups in its structure,
adsorb on the anionic sites of acrylic fiber somewhat better than PAMAM (G=-0.5) with
smaller molecular size and having 2 cationic groups.
The segmental motion of polymer molecules increases with temperature increase above the
Tg of acrylic fiber. Therefore, additional cationic dye molecules can diffuse and find new
anionic dye-sites at and within the fiber (i.e. the dye adsorption rate increases). Fast dyeing
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process is the main reason behind the dyeing unlevelness and non-uniform adsorption of
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cationic dye molecules at the surface of the acrylic fiber. Considering the thermoplasticity of
acrylic fibers, it would not be advisable to prolong the dyeing process at high temperatures in
order to improve the dyeing levelness. The dye adsorption rate should be controlled from the
beginning of the dyeing process [42-44].
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3.1.2. Effect of retarder concentration
The effect of retarder concentration on the cationic dye adsorption onto acrylic sample at
initial dye concentration of 1.25 % (o.w.f) was investigated at 100 °C for the dendrimers and
the cationic gemini surfactants (Figure 3). The results clearly showed that: (a) in the absence
of any retarder, the dye adsorption onto acrylic fiber is very fast (i.e. 100% dye adsorption in
less than 15 min), (b) the rate of dye adsorption decreases in the presence of the dendrimers
and the surfactants, (c) the rate of dye adsorption decreases by increasing the retarders’
concentration.
The retarding effect of the investigated retarders is as follows: 12Q-3-Q12 > 11E2Q-3-Q2E11
>= PAMAM (G=0.5) > PAMAM (G=-0.5). It seems the charge density of the retarders plays
an important role on their retarding action. Both of the dendrimers have cationaizable groups
(i.e. tertiary amine) in their structures. These groups can be quaternized in acidic media by
adsorbing proton from aqueous solution. Therefore, they have weaker charge density than the
cationic gemini surfactants with permanent cationic head groups.
As can be seen from the Figure 3, the stable gemini surfactant (i.e. 12Q-3-Q12) has shown a
blocking effect (i.e. 100% dye absorption has not been reached even after 120 min). 11E2Q-
3-Q2E11 and the dendrimers have not shown such a problem (i.e. permanent blocking effect)
which is beneficial from dyeing point of view. This suggests that inserting an electron
withdrawing group (e.g. ester bond or amide) in the chemical structure of a cationic retarder
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in a close distance from the cationic group can reduce the charge density of the retarder and
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decrease the oppositely charged interactions between the cationic retarders and the anionic
sites of acrylic fiber which solves the blocking effect of the cationic retarders.
Figure 3
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3.2. Leveling Properties Analysis
The colorimetric properties of dyed acrylic fibers and K/S values were measured by
reflection spectrophotometer (Table 1). The colorimetric data confirmed that the dyed
samples in the presence of retarders had a difference as compared with the sample of no
retarder. In general, dyed fibers in the presence of retarders were light and bright. The results
from Table 1 clearly indicate that the lightness (L*) of dyed fibers in the presence of retarders
follow the order: 12Q-3-Q12 > 11E2Q-3-Q2E11 > PAMAM G=0.5 >= PAMAM G=-0.5. In
addition, K/S values of the dyed samples were noticeably lower for the cationic gemini
surfactants in comparison to those of the dendrimers showing that surfactants are much
stronger retarders than the dendrimers.
The leveling properties in acrylic dyeing (i.e. uniform dye adsorption) in the presence of the
retarders are given in Table 1. The results indicated that the difference of the S(λ) is distinct,
and the retarding agents are basically able to meet the actual production applications for its
uniform dyeing performance [37].
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Table 1. Results of various leveling properties of BR46 on acrylic fibers in λmax=530 at dye:
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3
retarding agent molar ratio: 0.5, time 30 min, and temperature 100 ˚C
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5
6
Retarding agent
L*
a*
b*
c*
h
S(λ)
K / S
7
8
38.53 59.37 11.05
60.38 10.54 33.84 1.09
No retarder
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41.46 62.99 12.29 64.17 11.04 27.28 0.97
43.47 62.49 11.77 63.59 10.67 25.68 0.95
PAMAM, G=-0.5
PAMAM, G=0.5
11E2Q-3-Q2E11
12Q-3-12Q
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46.81 57.91
51.7 56.55
3.70
2.06
58.03
56.59
3.65
2.09
14.02 0.93
7.94 0.87
3.2. Kinetic study
The empirical kinetic models (Equations 5-8) were employed to obtain the dyeing rate
constant (k). The k values along with the correlation coefficients (R2) for various dyeing
systems in the absence and presence of various concentrations of retarders are reported in
Table 2. Twenty three different dyeing systems were studied by these models, and based on
the obtained regression coefficients, the modified Cegarra-Puente empirical model (Eq. 8)
showed somewhat better fit with the dyeing kinetics (i.e. the average and minimum of R2
values were 0.99 and 0.975. respectively). The values obtained from the Cegarra-Puente
empirical model (Eq.7) have not been reported in this table as the correlation was even poorer
than that of the exponential model (Eq. 6).
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Table 2. Dyeing rate constants and regression coefficients based on three different empirical
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4
5
kinetic models for dyeing the acrylic fiber with BR46 in the absence and presence of the
retarders
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7
8
9
Parabolic
(Eq. 5)
First Order
(Eq. 6)
Modified Cegarra-
Puente (Eq. 8)
C (molar
ratio)
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Retarding agent
No-retarder
k
R2
k
R2
k
R2
0.280
0.137
0.926
0.915
0.272
0.135
0.951
0.984
0.244
0.116
0.991
0.988
-
0.25
0.094
0.087
0.859
0.889
0.088
0.076
0.967
0.955
0.090
0.081
0.985
0.979
PAMAM, G=-0.5
0.5
0.75
0.085
0.081
0.076
0.956
0.961
0.958
0.027
0.022
0.018
0.970
0.803
0.878
0.094
0.079
0.070
0.990
0.975
0.986
0.25
0.5
PAMAM, G=0.5
12Q-3-12Q
0.75
0.031
0.055
0.044
0.073
0.026
0.055
0.919
0.962
0.988
0.945
0.983
0.974
0.859
0.941
0.011
0.012
0.008
0.064
0.013
0.027
0.886
0.910
0.964
0.903
0.958
0.962
0.803
0.930
0.011
0.009
0.003
0.015
0.010
0.007
0.995
0.988
0.992
0.993
0.981
0.978
0.975
0.986
0.25
0.5
0.75
0.25
0.5
11E2Q-3-Q2E11
0.75
R2 min
R2 average
The k values in the presence of various retarders are as follows: 12Q-3-Q12 < 11E2Q-3-
Q2E11 < PAMAM G=0.5 < PAMAM G=-0.5 < no retarder. In addition, the k values were
noticeably lower for the cationic gemini surfactants in comparison to those of the dendrimers
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showing that surfactants are much stronger retarders than the dendrimers. The results
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2
illustrate that in lower concentrations of retarders, k values are more than when the retarders
exist at higher concentrations. Moreover, the k values in the presence of various retarders
follow the order: 12Q-3-Q12 < 11E2Q-3-Q2E11 < PAMAM G=0.5 < PAMAM G=-0.5 < no
retarder. In addition, k values were noticeably lower for the cationic gemini surfactants in
comparison to those of the dendrimers showing that surfactants are much stronger retarders
than the dendrimers.
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Absorption rate constants at different temperatures are also given in Table 3. As it can be
seen in Table 3, the dyeing kinetic can be described by the modified Cegarra-Puente
empirical model somewhat better than the other kinetic models that were used. In the systems
studied, the correlation coefficients of the model were higher than those of other models. The
results indicated that when the temperature is increased, the k values are enhanced. As we can
see from Table 3, the k values of dendrimers are lower than that of surfactants.
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Table 3. The constant rate and correlation coefficients in the acrylic dyeing with cationic
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dyes in the presence of dendrimers and surfactants at different temperatures
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5
6
7
8
9
T
Parabolic
(Eq. 5)
First Order
(Eq. 6)
Modified Cegarra-
Puente (Eq. 8)
°(C)
Retarding agent
No-retarder
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k
R2
k
R2
k
R2
0.146
0.218
0.280
0.104
0.112
0.094
0.128
0.123
0.121
0.035
0.055
0.031
0.026
0.067
0.073
0.937
0.949
0.926
0.969
0.829
0.919
0.935
0.896
0.961
0.969
0.962
0.919
0.984
0.979
0.945
0.829
0.938
0.133
0.204
0.272
0.033
0.042
0.088
0.046
0.059
0.037
0.004
0.012
0.011
0.003
0.023
0.264
0.955
0.968
0.951
0.924
0.890
0.905
0.896
0.847
0.803
0.924
0.910
0.886
0.954
0.936
0.903
0.803
0.898
0.118
0.155
0.244
0.027
0.048
0.090
0.020
0.032
0.079
0.001
0.006
0.011
0.005
0.011
0.015
0.989
0.975
0.991
0.996
0.993
0.996
0.990
0.981
0.975
0.996
0.988
0.995
0.993
0.998
0.993
0.975
0.991
90
95
100
90
PAMAM, G=-0.5
PAMAM, G=0.5
12Q-3-12Q
95
100
90
95
100
90
95
100
90
11E2Q-3-Q2E11
95
100
R2 min
R2 average
The rate constants obtained from the modified Cegarra-Puente model are depicted vs.
temperature for the dendrimers and cationic gemini surfactants (Figure 4). In the absence of
any retarder, there is a big difference between the apparent rate constants of acrylic dyeing as
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it can be seen from the Figure 4. The values of dyeing rate constants are in the order of: 12Q-
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3-Q12<11E2Q-3-Q2E11<PAMAM G=0.5<PAMAM G=-0.5. As we have already discussed,
12Q-3-Q12 is the strongest retarder among all other investigated retarders.
Figure 4
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3.3. Activation energy
The apparent activation energy of dyeing is defined as the amount of energy required for dye
molecules to overcome the resistance of the adsorbate matrix to diffuse. A lower value of Ea
means faster diffusion of dye molecules into the cross-sectional matrix and a lower
dependence on the temperature. The apparent activation energies were determined from the
absorption rate constants at different temperatures using the Arrhenius equation (Eq. 8). One
may obtain the activation energy from the slope of ln k curve versus 1/T, and the correlation
coefficients of the fit are also obtained (Table 4). A significant increase in the activation
energy can be observed when the retarders are used. Therefore, the dye molecules require
more energy to overcome the energy barrier caused by the presence of the cationic gemini
surfactants. The Ea values are as follows: no retarder<PAMAM G=-0.5< PAMAM G=0.5<
11E2Q-3-Q2E11<12Q-3-Q12 and this could be attributed to the charge density of cationic
retarder as we discussed earlier.
Table 4. The activation energy in acrylic dyeing process with cationic dyes in the presence of
dendrimers and surfactants
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Retarding agent
Ea(kJ/mol)
R2
1
2
3
4
5
6
7
8
9
122.86
135.49
144.97
175.50
223.33
0.998
0.998
0.964
0.935
0.966
No retarder
PAMAM, G=-0.5
PAMAM, G=0.5
11E2Q-3-Q2E11
12Q-3-12Q
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4. Conclusion
The conclusion remarks of this research work are as follows:
-
-
-
The order of retarding and blocking strength of the retarders in the dyeing process was
as follows: 12Q-3-Q12 > 11E2Q-3-Q2E11 > PAMAM G=0.5> PAMAM G=-0.5.
The dendrimers are protonated at acidic pH 4.5 and act as cationic retarders in the
same way as cationic surfactants do
Two cationic gemini surfactants were much stronger retarders possibly because of
their higher charge density per each molecule.
-
-
-
The rate of dyeing process increased with temperature increase.
The rate of dyeing process decreased by increasing the retarders’ concentration.
The modified Cegarra-Puente model fitted the dyeing kinetic data somewhat better
than the other empirical kinetic models
-
The presence of an electron withdrawing group (e.g. ester bond or amide) in the
chemical structure of a cationic retarder in the close distance from the cationic group
can reduce the charge density of the retarder and decrease the oppositely charged
interactions between the cationic head groups of the retarders and the anionic dye-
sites of the acrylic fiber.
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Professional, Chapman & Hall, 1995.
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Figure captions:
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Figure 1. Chemical structure and Physical-Chemical Properties of Basic Red 46 (BR46)
Scheme 1. Preparation of PAMAM dendrimers
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Scheme 2. Syntheses of two cationic gemini surfactants: (a) 12Q-3-Q12, and (b) 11E2Q-3-
Q2E11.
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Figure 2. Dye absorption (%) of dyes onto acrylic fiber in the presence of retarders (molar
ratio to dye= 0.5) at different temperatures.
Figure 3. Dye absorption (%) of BR46 onto acrylic fiber in the absence and presence of the
dendrimer (G=-0.5) and GS (molar ratios to dye= a) 0.25 and b) 0.75 at 100 °C.
Figure 4. Variation of the dyeing rate constants by temperature in the absence and presence of
the retarders
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Molecular Weight: 401g/mol ;
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Molecular Formula:C18H21BrN6;
Solubility in water (30 ˚C): 80 g/L;
λmax=530 nm
CH3
CH3
N
N
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CH2C6H5
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+
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Br
CH3
Figure 1
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MeOH
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PAMAM, G=-0.5
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EA
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Room
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Scheme 1
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(a)
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Scheme 2
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T= 90 ˚C
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No retarder
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Time (min)
Figure 2
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