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shown at 3650–3250 cmꢁ1 in Fig. 1(a) and (d) and at 3685–3370
cmꢁ1 in Fig. 1(b) and (e) indicated the completely depolymer-
ization of PET. The absorption peaks around 1600, 1515 and
1428 cmꢁ1 for all compounds in Fig. 1 were due to the benzene
ring groups. The absorption bands at 1350–1250 cmꢁ1 in
Fig. 1(c)–(e) were due to the stretching vibration of C–N.
1H NMR spectroscopy
Fig. 2 shows the structures and 1H NMR spectra of BHET (a) and
dye A (b). In addition, the structures and 1H NMR spectra of TPA
(a) and dye B (b) are shown in Fig. 3. 1H NMR of BHET (DMSO-
d6) d: 8.12 (t, 4H, ArH), 4.92 (t, 2H, OH), 4.33 (t, 4H, CH2), 3.74 (q,
4H, CH2); 1H NMR of dye A (DMSO-d6) d: 8.10 (m, 3H, ArH), 7.21,
7.02, 6.81, 6.70 (4H, ArH), 4.33 (t, 4H, CH2), 3.83 (m, 4H, CH2),
3.10, 2.88 (6H, CH3); 1H NMR of TPA (DMSO-d6) d: 13.26 (s, 2H,
OH), 8.06 (s, 4H, ArH); 1H NMR of dye B (DMSO-d6) d: 8.14, 7.99,
7.78 (3H, ArH), 7.38, 7.23, 7.00, 6.88 (4H, ArH), 4.33 (s, 6H, CH3).
Fig. 5 Photographs of dye baths prepared from dye B, dyed nylon
filaments and dyed polyester filaments from top to bottom, respec-
tively. The pH of the dye bath was: (a) 3.6, (b) 4.0, (c) 4.5, (d) 5.0, (e) 5.5,
and (f) 5.8, respectively.
Variation of dyeing performances with pH
CIE 1976 L*a*b* (CIELAB) is the most commonly used color
space to characterize colors. The three coordinates of CIELAB
represent the lightness of the color (L* ¼ 0 yields black and L* ¼
100 indicates diffuse white), its position between red and green
(a*, negative values indicate green while positive values indicate
red) and its position between yellow and blue (b*, negative
values indicate blue and positive values indicate yellow).24
According to the Kubelka–Munk equation, the data of color
values (K/S) are representative of the color depth of the dyed
fabrics.25
The relative color values of samples dyed with dye A and dye
B are given in Tables 1 and 2, respectively. For both the
synthesized azo dyestuffs, the K/S values of dyed nylon samples
were higher than that of the dyed polyester at the same pH. This
indicated the higher dyeing capacity of the dye molecules for
nylon compared to polyester. For all the samples, the K/S value
increased when the pH of dye bath decreased. It was considered
that the hydrion facilitated the adsorption and xation of
dyestuff on nylon or polyester bers through hydrogen bonding.
The positive a* and b* values indicated the red and yellow tones
of the dyestuffs, whereas the higher L* values conrm the color
brilliancy at lower pH. The maximum absorption wavelength
(lmax) of dyed samples prepared by dye A was 443–521 nm when
the pH varied from 5.8–3.6, which corresponded to a color
change from a yellow tone to a red tone (Fig. 4). In addition, a
similar variation of the lmax of samples prepared with dye B also
occurred with the change in pH, and the color of the samples
changed from an orange tone to a red tone (Fig. 5). In brief, the
bathochromic shis occurred in both dye A solution and dye B
solution when the solution pH decreased.
as a reference material. The scanning range was 650–4000 cmꢁ1
and the resolution was 1 cmꢁ1
.
Proton nuclear magnetic resonance (1H NMR) spectra of
BHET, TPA and synthesized dyestuffs were recorded on a Bruker
DRX-400 spectrometer (Germany) at 400 MHz in deuterated
dimethylsulphoxide (DMSO-d6), and the chemical shis d were
measured using tetramethyl silane as an internal reference.
The performances of synthesized azo dyestuffs were evalu-
ated by the maximum absorption wavelength and the relative
color values (K/S, L*, a*, b*) of the dyed polyester and nylon
laments, respectively.
Both the dyestuffs were prepared as a dye bath by dispersion
in distilled water at 3% (o. w. f.) with a dispersing agent. The pH
of the dye baths were varied from 3.6 to 5.8 by utilizing phos-
phate buffer solution. Dyeing of polyester laments was carried
out in closed stainless steel beakers in a high-temperature
dyeing machine at 120 ꢀC for 60 min at a liquor ratio of 80. The
dyed polyester laments were washed with distilled water and
dried in an oven at 70 ꢀC. Nylon laments were immersed in the
dye bath at the liquor ratio of 80 at 95 ꢀC for 40 min, washed by
ꢀ
distilled water and dried in an oven at 70 C, successively.
Relative color values (K/S, L*, a*, b*) and the maximum
absorption wavelength (lmax
) of each dyed sample was
measured by a COLOR-Eye-7000A spectrophotometer (Gre-
tagMacbeth, USA).
Results and discussion
FTIR spectroscopy
Conclusions
Fig. 1 showed the Fourier-transform infrared (FTIR) spectra of
BHET, TPA, N,N-dimethylaniline, dye A and dye B. The peaks at In this work, waste PET bers were chemically degraded into
1417, 1426, 1426, and 1417 cmꢁ1 in Fig. 1(a), (b), (d) and (e) were BHET and TPA. The resulting monomers were converted into
due to the stretching vibration of –COO– of BHET, TPA, dye A azo disperse dyestuffs. The synthesized dyestuff could be
and dye B, respectively. The absorption bands due to –OH group applied for dyeing nylon and polyester laments. Both of the
This journal is © The Royal Society of Chemistry 2014
RSC Adv., 2014, 4, 46476–46480 | 46479