Synthesis, generic dyeing of nindigo derivatives on unmodified polypropylene; first time application in dyeing technology

Article abstract of DOI:10.1166/jnn.2019.16643

Hydrophobic nindigo dyes were designed and successfully synthesized from indigo by reacting with substituted anilines in a simple route. Four nindigo dyes were fruitfully analyzed by ¹H NMR ¹³C NMR, electronic and mass spectrometry.

Full text of DOI:10.1166/jnn.2019.16643

Article
Journal of
Nanoscience and Nanotechnology
Vol. 19, 7105–7111, 2019
Copyright © 2019 American Scientific Publishers
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Printed in the United States of America
Synthesis, Generic Dyeing of Nindigo Derivatives on
Unmodified Polypropylene; First Time
Application in Dyeing Technology
Raju Penthala, Rangaraju Satish Kumar, Hyorim Kim, Gisu Heo, and Young-A Son∗
Department of Advanced Organic Materials Engineering, Chungnam National University, 220 Gung-dong, Yuseong-gu,
Daejeon 305-764, South Korea
Hydrophobic nindigo dyes were designed and successfully synthesized from indigo by reacting
with substituted anilines in a simple route. Four nindigo dyes were fruitfully analyzed by 1H NMR
13C NMR, electronic and mass spectrometry. Here, we have firstly introduced these nindigo dyes
into dyeing area for the dyeing of unmodified polypropylene fiber in aqueous medium. Dyeing exper-
iments has been performed by using didodecyldimethylammonium bromide dispersing agent to
make dye-dispersant complex for enhancing the dispersion of dyes. All the dyes were displayed pro-
found blue color hue on polypropylene. The dyeing efficiency and dye fixation order of the nindigo
dyes are 3d > 3c ≥ 3b > 3a. Compound 3d having higher the hydrophobic character (logP = 7ꢀ04),
so greater the dye ability on the polypropylene fiber and exhibiting deep coloration.
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Keywords: Nindigo Dyes, Hydrophobicity, Dyeing, Polypropylene Fiber.
Copyright: American Scientific Publishers
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1. INTRODUCTION
additives (basic nitrogen atoms) to preferable dyeing with
acid dyes,8ꢀ9 (c) chemical modification involves chlorina-
tion/bromination of fiber with chlorine/bromine to react
with cationic dyes.10ꢀ11 While these two routes are expen-
sive and also mainly effect on the mechanical properties
of polypropylene fiber. (d) Dyeing of unmodified fiber
method is possible at the established process by selecting
super hydrophobic dyes.12–15 This process has significant
importance over other, since fiber doesn’t loss its physical
character and having more demand in rising market for its
relatively inexpensive fiber.16
Indigo is well-known blue colored natural vat dye.
It is valuable and having unique properties.17 Further-
more, it has very low chronic and acute toxicity.18
However, potential applications are limited due to its low
solubility. In its leuco form indigo has more dyeing affin-
ity with cotton silk and wool, but for synthetic fibers
like polyester and polypropylene indigo has less dye-
ing affinity.19ꢀ20 Reintroduction of natural dyes is con-
siderable interest in textile industry due to increased
attention to environmental aspects and sustainability of
raw materials and products.21ꢀ22 In order to improve the
hydrophobic character of indigo dye will challenge us to
Polypropylene fibers are widely used in industrial and tex-
tile applications due to its intrinsic, attractive properties
such as inexpensive, resilience, resistant to chemicals and
abrasion.1–4 The major application aspects are; this fiber
does not absorb moisture; it helps quick transport of mois-
ture required applications as babies ever-dry nappies. Ther-
mal conductivity of PP fiber is very low hence, it is used
in thermal wear. The density of PP is 0.90–0.92, it helps
for the usage in light weight sportswear. Polypropylene
possesses hydrophobic character due to its aliphatic and
stereo-regular isotactic polymeric structure.5 Because of
the extreme hydrophobic character of the polypropylene,
it is very difficult to dyeing of these fibers at any dyeing
systems.6 Hence, several investigations have been reported
to enhancing the dye ability on isotactic polypropylene.
The methods included (a) spin coloration with organic and
inorganic pigments7 however, this method has some limit
to the inventor for the developing of various satisfied fash-
ion demands of the current market. (b) Physical modi-
fication of polypropylene involves the addition of polar
∗Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2019, Vol. 19, No. 11
1533-4880/2019/19/7105/007
doi:10.1166/jnn.2019.16643
7105

Synthesis, Generic Dyeing of Nindigo Derivatives on Unmodified Polypropylene
Penthala et al.
designing of new molecules. Our main aim is to design
of novel molecules (nindigo dyes) which imparted super
hydrophobic character and have strong dyeing affinity with
the hydrophobic polypropylene fiber. Here we have suc-
cessfully synthesized four super hydrophobic nindigo dyes
and were efficiently applied on unmodified polypropylene
fibers using conventional dyeing.
and substituted anilines 2(a–d) (9.523 mmol). To this
stirred mixture, solution of TiCl4 (1 M in toluene,
5.724 mmol, 5.5 mL) was slowly added. After completion
of the TiCl4 addition, solid indigo (1 g, 3.816 mmol) was
added to the above stirred mixture. Then reaction mixture
ꢀ
was heated to 160 C for 24 h. After reaction comple-
tion [checked by TLC (thin layer chromatography), the
Rf value of nindigo is 0.6 in 10% ethyl acetate: hexane].
The hot solution of reaction was directly filtered through
celite pad, and several times washed with dichloromethane
until the filtrate was colorless. The filtrate was concen-
trated under reduced pressure. The crude reaction mixture
was absorbed with silica and performed a column purifi-
cation using 3% n-hexane and ethyl acetate as eluent to
afford dark blue powders 3(a–d).
2. EXPERIMENTAL DETAILS
2.1. Materials
All the chemicals and commercial reagents were bought
from Sigma Aldrich and Alfa Aesar. Solvents were dis-
tilled and dried under nitrogen atmosphere before going
to use. 1H NMR and 13C NMR spectra were recorded
at RT using an AVANCE III spectrometer operating on
either 600 MHz and 150 MHz respectively with CDCl3
as solvent. The chemical shifts (ꢁ) values were given
in ppm downfield from an internal standard tetramethyl
silane. UV-visible absorption and reflectance spectra were
recorded using a Shimadz UV 26000 spectrophotometer.
Mass spectra were recorded on a Q-TOF II instrument
using electrospray ionization source in the positive mode.
Dyeing experiments has been performed by using ACE-
6000 T model Infrared dyeing machine.
2.3.1. N,Nꢁ-([2,2ꢁ-Biindolinylidene]-3,3ꢁ-Diylidene)
Bis(4-Methylaniline) (3a)
Dark Blue solid; Yield: 75% (1.25 g), mp: 290–292 C;
ꢀ
1H NMR (CDCl3, 600 MHz): ꢁ 9.86 (brs, 2H), 7.20–7.14
(m, 8H), 7.05–7.01 (m, 4H), 6.94–6.90 (m, 2H), 6.70–
6.66 (m, 2H), 2.34 (s, 6H); 13C NMR (CDCl3, 150 MHz):
ꢁ 143.3, 132.8, 129.5, 128.7, 123.8, 119.6, 118.9, 117.7,
114.1, 19.9. MS m/z: 441 [M+H]+.
2.3.2. N,Nꢁ-[2,2ꢁ-Biindolinylidene]-3,3ꢁ-Diylidene)
Bis(4-Ethylaniline) (3b)
2.2. Synthesis
Our key task of the present exeIrPti:on5.1is89to.2d0e7v.e1l5op7 Oconm: -Tue, 07 May 2019 05:59:52
mercially most acceptable super hydrophobic dyes for
polypropylene fabric. For that instance, we have syn-
thesized nindigo dyes and are applied on polypropylene
fabric.
ꢀ
Dark Blue solid; Yield: 73% (1.3 g), mp: 286–288 C;
Copyright: American Scientific Publishers
1H NMR (CDCl3, 600 MHz): ꢁ 9.87 (brs, 2H), 7.21–7.16
(m, 6H), 7.15–7.13 (m, 2H), 7.08–7.04 (m, 4H), 6.95–6.92
(m, 2H), 6.71–6.67 (m, 2H), 2.64 (q, J = 7.5 Hz, 4H),
1.23 (t, J = 7.5 Hz, 6H); 13C NMR (CDCl3, 150 MHz):
ꢁ 143.5, 139.3, 129.4, 127.6, 123.8, 119.6, 118.9, 117.7,
114.1, 27.4, 14.7. MS m/z: 469 [M+H]+.
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Nindigo derivatives synthesis is involved the
reaction of indigo
1
with excess of substituted
anilines 2(a–d), titanium tetrachloride (TiCl4) and 1,4-
diazabicyclo[2.2.2]octane (DABCO) in bromobenzene23
(Scheme 1). Here bromobenzene is required for solubilize
indigo. By using this method, we have successfully syn-
thesized four nindigo dyes and corresponding structures
were represented in Figure 1.
2.3.3. N,Nꢁ-Bis(3-Ethylphenyl)-[2,2ꢁ-Biindolinylidene]-
3,3ꢁ-Diimine (3c)
Dark Blue solid; Yield: 72% (1.28 g), mp: 280–282 C;
ꢀ
1H NMR (CDCl3, 600 MHz): ꢁ 9.88 (brs, 2H), 7.26 (t, J =
8.0 Hz, 2H), 7.21–7.15 (m, 4H), 6.99–6.89 (m, 8H), 6.69
(td, J = 8.0, 1.1 Hz, 2H), 2.62 (q, J = 7.5 Hz, 4H), 1.20
(t, J = 7.5 Hz, 6H); 13C NMR (CDCl3, 150 MHz): ꢁ 146.0,
144.6, 129.5, 128.1, 123.9, 122.6, 119.7, 118.1, 117.8,
115.9, 114.1, 27.9, 14.6. MS m/z: 469 [M+H]+.
2.3. General Experimental Procedure for the
Synthesis of Nindigo Derivatives 3(a–d)
In a two neck round bottom flask (100 mL) charged with
bromobenzene (10 mL), DABCO (2.52 g, 22.896 mmol)
2.3.4. N,Nꢁ-Bis(4-Propylphenyl)-[2,2ꢁ-Biindolinylidene]-
3,3ꢁ-Diimine (3d)
Dark Blue solid; Yield: 66% (1.24 g), mp: 262–264 C;
R
R
ꢀ
H2N
O
N
H
H
2(a-d)
1H NMR (CDCl3, 600 MHz): ꢁ 9.86 (brs, 2H), 7.20–
7.12 (m, 8H), 7.05 (d, J = 8.0 Hz, 4H), 6.91 (d, J =
7.9 Hz, 2H), 6.68 (t, J = 7.7 Hz, 2H), 2.57 (t, J =
7.5 Hz, 4H), 1.67–1.60 (m, 4H), 0.92 (t, J = 7.3 Hz,
6H); 13C NMR (CDCl3, 150 MHz): ꢁ 143.5, 137.7, 129.5,
128.2, 123.8, 119.6, 118.8, 117.7, 114.1, 36.5, 23.7, 12.7.
MS m/z: 497 [M+H]+.
N
N
TiTCl4, DABCO,
Bromobenzene, 150 ºC, 24 h
N
H
N
H
N
O
1
R
3(a-d)
Scheme 1. Synthesis of nindigo 3(a–d).
7106
J. Nanosci. Nanotechnol. 19, 7105–7111, 2019

Penthala et al.
Synthesis, Generic Dyeing of Nindigo Derivatives on Unmodified Polypropylene
N
H
N
N
H
N
N
H
H
N
N
N
N
H
N
N
N
N
H
N
H
H
N
N
3a
3b
3c
3d
Figure 1. Structures of nindigo 3(a–d).
2.4. Dye Dispersions Preparation
for 3c, 11.28, 12.56, 13.83 for 3d and 3.01, 3.69, 4.93 for
compound 1 respectively (Fig. 2). Based on the results,
higher temperature could increase the color strength val-
ues, because the dye particles were moved very fast,
which enhances the rate of interaction with solvent parti-
cles. Therefore, the dyes solubility is increases and more
absorption of dye particles on the surface of polypropylene
fibers. Meanwhile, it also could enhance freedom oꢀf the
polypropylene macromolecular chains.3 Finally, 130 C is
the considerable optimized dyeing temperature.
First to prepare uniform dyes and dispersing agent mix-
tures, 5% owf amount of synthesized nindigo dyes were
separately dissolved in 50 ml of tetrahydrofuran and mixed
thoroughly with the solution of DDAB [2 molar ratio
compared to the dye amount] in 50 ml tetrahydrofuran
(THF).25 The solution mixture was concentrated with the
help of rotatory evaporator and dried for 12 h for complete
removing of tetrahydrofuran. The mixture was dissolved
in water and sonicate for 1 h. Finally, this solution can be
used for dyeing.
3.2. Dye and Dispersing Agent Concentration
Effect on Color Strength (K/S)
2.5. Dyeing
The unmodified polypropylene fiber samples (500 mg)
To study, dye concentration effect on color strength values,
were used for dyeing with appropriate 1%, 3% and 5% owf
we have performed the experiments using three variable
concentrations (1%, 3% and 5%) at constant temperature
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dye dispersion solution at the liquor ratio of 1:50. DDAB
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used for dye dispersion solution [1, 2 and 3 molar ratio]
(130 C) and constant molar ratio of dispersing agent
(1 molar ratio). Based on the results, we observed that the
dye concentration is increased, the color strength values
are also increases (Fig. 3). This is due to that on increasing
concentration of the dye, more and more dye molecules
are available to interact with fiber in the dye bath. There-
fore, the rate of absorption is increased as well as color
strength values are also increased.
compared to the dye amount. The dyꢀe bath tempeꢀ ratures
ꢀ
were used in this study is 70 C, 100 C and 130 C. The
ꢀ
dye bath temperatures were used in this study is 70 C,
ꢀ
ꢀ
100 C and 130 C. These temperatures were maintained
for 1 h at a rate of 2 ꢀC/min. After dyeing the dyeing bath
was cooled and then polypropylene fabrics were removed.
The dyed fabrics were treated with sodium hydroxide and
ꢀ
sodium hydrosulfite (1;1, 2 g/l) at 70 C for 15 min to
completing reducing step.
3. RESULTS AND DISCUSSION
In our experiments we have studied the effect of dyeing
temperature, dye concentration and dispersing agent quan-
tity on color strength values.
3.1. Dyeing Temperature Effect on
Color Strength (K/S)
Dyeing temperature plays an essential role on color
strength values. We have perfoꢀrmed the dyeing experi-
ꢀ
ꢀ
ments using three variable (70 C, 100 C and 130 C)
temperatures. Here we didn’t try the higher temperatures
after 130 ꢀC because of the poor thermal property of
poly propylene.14 At 70 ꢀC, 100 ꢀC and 130 ꢀC the
color strength values of dyed fabrics 7.46, 8.13, 9.38 for
compound 3a, 7.53, 8.84, 9.96 for 3b, 7.79, 8.93, 10.19
Figure 2. Effect of dye temperature on color strength (K/S) values.
J. Nanosci. Nanotechnol. 19, 7105–7111, 2019
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Synthesis, Generic Dyeing of Nindigo Derivatives on Unmodified Polypropylene
3.3. Dye Ability
Penthala et al.
The dye ability of nindigo dyes on unmodified polypropy-
lene fiber mainly depending upon the partition coefficient
(logP). It represents the hydrophobic character of organic
compound. By using Chem3D we have obtained logP
values.24 In the dyeing experiments, it is very essential to
form stable dispersion of dyes, for that didodecyldimethy-
lammonium bromide surfactant was used. In common
organic solvents, this surfactant having similar solubility
to the nindigo dyes. Therefore, dye-dispersion complex
has been formed from dye and dispersing agent uniform
mixture solution. By adding the water and performed
ultra-sonication generated vesicle by dispersing of nindigo
dyes. Then, the nindigo dye molecules were transferred
from surfactant micelle to the surface of the fiber.25 The
adsorbed nindigo dyes diffused in to the fiber (Fig. 5). The
dye ability is very high for compound 3d when compare
to the others 3c, 3b, 3a and compound 1. The logP values
for the dyes are 5.37 for 3a, 6.21 for 3b and 3c, 7.04 for
3d and 0.16 for compound 1. Due to highest logP of com-
pound 3d, the distribution rate is high between polypropy-
lene fiber and solution. Therefore, the dye ability is also
very high.
Figure 3. Effect of dye concentration (% owf) on color strength (K/S)
values.
On the other hand, we have also studied that the effect of
the various amounts of didodecyldimethylammonium bro-
mide (DDAB) dispersing agent (1, 2 and 3 molar ratios)
on the color strength values and the corresponding results
were showed in Figure 4. At 1 molar ratio of dispers-
ing agent the color strength values are minimum. This is
due that in presence of small quantity of dispersing agent,
the probability of aggregation of dye particle is very less
3.4. Color Strength (K/S) and Dye Fixation (%)
The color strength (K/S) values of dyed polypropylene
fabrics were calculated from the Kubelka-Munk equation
by substituting of the reflectance (R%), which is recorded
by using Shimadz UV 26000 spectrophotometer.
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and also very difficult to formation of stable dispersion.
At 2 molar ratio of dispersing agent we have observed
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maximum color strength values. In contrast, at 3 molar
ratio of dispersing agent the color strength values are also
slightly decreased, because at this concentration dispers-
ing agent forms highly stable dye dispersion in dyeing
liquor to be adsorbed and penetrated into polypropylene
fiber from the liquor.13
ꢂ1 −Rꢃ2
K/S =
2R
Where K is absorbance and S is the scattering.
To calculate the dye fixation ꢂF ꢃ percentage values,
we have substituted the values of (K/Sꢃextracted (after
extraction) and (K/Sꢃdyed (after dyeing) in below equation.
To measure the (K/Sꢃextracted, first the dyed polypropy-
lene fibers were soaked in acetone (250 cm3) in a beaker
ꢀ
and soaked materials were heated at 60 C for 10 min
and ꢀtemperature gradually raised to boiling temperature
(80 C) and maintained at the boiling temperature for 1 h
to yield a dye extracts. The dye extract was left to stand
for 30 min at ambient temperature and filtered. The fab-
rics were removed and dried to measure the color strength
values.
ꢂK/Sꢃextracted
F =
×100%
ꢂK/Sꢃdyed
Dye 3d had comparative [ꢂK/Sꢃdyed 13.82] and
[ꢂK/Sꢃextracted 10.93] values are significantly higher than
the 3c, 3b, 3a and indigo. There is no much differentia-
tion in ꢂK/Sꢃdyed and ꢂK/Sꢃextracted values of 3b [ꢂK/Sꢃdyed
10.19 and ꢂK/Sꢃextracted 7.33] and 3c [ꢂK/Sꢃdyed 9.96
and [ꢂK/Sꢃextracted 7.07]. The justification for this result,
these two dyes are possessing equal hydrophobic charac-
ter. The percentage of dye fixation for the dyes ranked in
Figure 4. Effect of dispersing agent concentration on color strength
(K/S) values.
7108
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Penthala et al.
Synthesis, Generic Dyeing of Nindigo Derivatives on Unmodified Polypropylene
Figure 5. Dyeing mechanism with nindigo dyes on polypropylene.
the following order 3d > 3c ≥ 3b > 3a > 1 (Fig. 6). This
could be attribute to the molecular structure and hydropho-
bic character of the dyes. If the dye molecules are having
more hydrophobic character, the substantivity is increased
with the polypropylene fiber, thus the adsorption of dye
molecules on fiber is also increased. Therefore, the dye
fixation F values are also increased. Figure 7 indicated
that the before and after dyeing of polypropylene fabrics
with our synthesized dyes (3a, 3b, 3c, 3d) and indigo.
of ꢄH∗ indicates reddish. ꢄE∗ is the total color differ-
ence. Color-opponent dimensions a∗ and b∗. Positive val-
ues (+ve) of the a∗ indicates the degree of redness and
negative values (+ve) of the a∗ indicates degree of green-
ness, similarly positive values (+ve) of the b∗ indicates
the degree of yellowness and negative values (−ve) of the
b∗ indicates degree of blueness. The color strength values
were represented with K/S.
The color coordinates were listed in Table I. Based on
the results our synthesized nindigo dyes are having good
dyeing affinity with unmodified polypropylene fabric with
3.5. Color Assessment
The color assessments of the dyed polypropylene fab-
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the following statements.
Copyright: American Scientific Publishers
rics were studied using data color 110 spectrometer.
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The CIELAB coordinates were measured and were rep-
In our study the color lightness L∗ values of nindigo
dyes varied from 61.38 to 69.52. The compound 3a exhib-
ited lighter and duller than the other compounds. Accord-
ing to the negative values of a∗, the color hues of all
the synthesized dyes 3(a–d) along with compound 1 were
shifted to greenish direction on the red–green axis. Due to
exhibiting the positive values of b∗ dye 3d color hue
shifted to yellowish direction on the yellow–blue axis and
remaining all the dyes 3a, 3b, 3c and indigo are having
negative values of b∗, therefore the color hues were shifted
to bluish direction on the yellow–blue axis. According to
C∗ dye 3b is brighter than the other compounds. The color
strength K/S values of 3d is higher than the 3c, 3b, 3a
and 1, because the hydrophobic character of 3d is high.
Whenever increasing the length of the alkyl chain logP
value (hydrophobic character) is increased, the dye affinity
is also increased with polypropylene. Therefore, the K/S
value is increased. For the dyes 3c and 3d the ꢄH value
is negative that indicates reddish shift whereas the dyes 3a
and 3b the ꢄH value is positive that indicates yellowish
shift compared to the standard values. Furthermore, ꢄL
value is negative only for dye 3b which indicates a darker
color than standard.
resented as L∗ (lightness), ꢄL∗ (difference in lightness
and darkness), positive values (+ve) of ꢄL∗ indicates
lighter and negative values (−ve) of ꢄL∗ indicates darker.
C∗ (chroma), ꢄC∗ (difference in chroma) positive val-
ues (+ve) of ꢄC∗ indicates brighter and negative values
(−ve) of ꢄC∗ indicates darker. h (hue angle from 0ꢀ to
360ꢀ), ꢄH∗ (difference in hue) where positive value (+ve)
of ꢄH∗ indicates yellowish and negative values (−ve)
3.6. Color Characteristics
Indigo having poor solubility in most of the organic sol-
vents, but our synthesized nindigo derivatives 3a, 3b, 3c
Figure 6. (K/Sꢃdyed
polypropylene fabrics.
, (K/Sꢃextracted, and % of F values of dyed
J. Nanosci. Nanotechnol. 19, 7105–7111, 2019
7109

Synthesis, Generic Dyeing of Nindigo Derivatives on Unmodified Polypropylene
Penthala et al.
Figure 7. Photographs of before and after dyeing of polypropylene fabrics.
70
and 3d were exhibiting excellent solubility in common
Indigo
3a
3b
3c
3d
organic solvents like benzene, toluene, dichloromethane,
chloroform, tetrahydrofuran and acetone. All the nindigo
derivatives were exhibited bluish green colored solutions
with these solvents. Similar to indigo, nindigo derivatives
60
50
were also comes under donor–acceptor chromogen cate-
40
gory, where the amino groups and imine groups were act
as the electron donors and electron acceptors respectively.
30
We have recorded the electronic spectra in tetrahydrofuran
solution in the range of 400–800 nm using 1ꢅ0 × 10−4
M
20
concentration (Fig. 8). At this concentration the elec-
10
0
tronic spectra contain maximum absorption band (ꢆmax
)
at 597 nm, which is results from ꢇ–ꢇ∗ transitions sim-
ilar to indigo. In addition, we have observed absorption
bands at 667 nm and 732 nm for nindigo dyes 3(a–d),
these are mainly results from solution aggregation effects.
300
400
500
600
700
800
Wavelength (nm)
Figure 9. Reflectance spectra of dyed polypropylene fabrics with
nindigo 3(a–d) and indigo.
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Here we did not observe any effect on molar extinction
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Table I. Color of dyed polypropylene fabrics.
coefficient and maximum absorption wavelength by chang-
ing the position and length (methyl, ethyl, and propyl) of
the alkyl groups on the dyes. This is concluded that the
optical properties of the dyes are almost similar.
We have also recorded the reflectance spectra of dyed
polypropylene fabrics by adopting white standard BaSO4.
The reflectance curve minimum value centered around
601 nm for 3a, 608 for 3b, 615 nm for 3c, 603 nm for 3d,
and 658 nm for compound 1 (indigo) (Fig. 9).
Color coordinates
CIELAB difference
Dye L∗
a∗
b∗
C∗
h
K/S
ꢄL ꢄC ꢄH ꢄE
3a
3b
3c
3d
1
61.38 −3ꢅ68 −4ꢅ81 6.06 232.58 9ꢅ38 0ꢅ00 0.01 0ꢅ02 0.02
61.68 −7ꢅ88 −1ꢅ99 8.13 194.17 9ꢅ96 −0ꢅ01 0.01 0ꢅ01 0.01
63.20 −4ꢅ62 −4ꢅ17 6.23 222.07 10ꢅ19 0ꢅ00 0.00 −0ꢅ03 0.03
69.52 −5ꢅ06 0ꢅ55 5.09 173.78 13ꢅ83 0ꢅ00 0.02 −0ꢅ02 0.03
63.23 −1ꢅ69 −6ꢅ67 6.88 255.75 4ꢅ93 0ꢅ02 0.02 0ꢅ00 0.03
2.0
Indigo
3a
3b
3c
3d
4. CONCLUSION
In summary we have successfully designed and synthe-
sized four super hydrophobic nindigo derivatives. These
nindigo derivatives were applied dyeing on unmodified
polypropylene fiber. Here, we have studied the effect of
main operating conditions like temperature, dye concentra-
tion and dispersing agent concentrations on color sꢀtrength
values. The optimized dyeing temperature is 130 C and
dispersing agent concentration is 2 molar ratio. In these
experiments compound 3d exhibits excellent color strength
and good dye fixation. Because this compound having
higher logP (hydrophobicity) value. As increasing the
hydrophobic character ability to interact with polypropy-
lene fiber is very high. As far as we know, this is the first
report on dyeing of unmodified polypropylene fiber with
1.5
1.0
0.5
400
500
600
700
800
Wavelength (nm)
Figure 8. Electronic spectra of nindigo 3(a–d) and indigo.
7110
J. Nanosci. Nanotechnol. 19, 7105–7111, 2019

Penthala et al.
Synthesis, Generic Dyeing of Nindigo Derivatives on Unmodified Polypropylene
hydrophobic nindigo dyes. These results will be prompted
us to further design of new hydrophobic dyes suitable for
unmodified polypropylene.
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Acknowledgments: This work was supported by the
nurture project of waterless color industry (10078334)
funded by the Ministry of Trade, Industry and Energy
(MOTIE) of Korea.
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Received: 30 August 2018. Accepted: 5 October 2018.
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