Modification of Mg/Al-layered double hydroxide with L-aspartic acid containing dicarboxylic acid and its application in the enhancement of the thermal stability of chiral poly(amide-imide)

Article abstract of DOI:10.1039/c4ra05754f

In this study, Mg/Al-layered double hydroxide (LDH) was intercalated with diacid containing l-aspartic acid in one step using an ultrasonic method under green conditions. Organic diacid was used as a modifier to enhance their compatibility and led to bett

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Modification of Mg/Al-layered double hydroxide with L-aspartic acid
containing dicarboxylic acid and its application in enhancement of
thermal stability of chiral poly(amide-imide)
Shadpour Mallakpou,* a ,b,c Mohammad Dinari a,b and Masoud Hatami a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
In this study, Mg/Al-layered double hydroxide (LDH) was intercalated with diacid containing L-
aspartic acid in one step using ultrasonic method under green conditions. Organic diacid was used
as modifier to enhance their compatibility and led to better dispersion of LDH nanoclay in polymer
10 matrix. An effective intercalation of the examined diacid in LDH was confirmed by increasing in
2-
basal spacing of the obtained products in comparison with Mg/Al–CO3 LDH precursors using X-
ray diffraction. An optically active poly(amide-imide) (PAI) was synthesized via polycondensation
of N,N-(pyromellitoyl)-bis-phenylalanine diacid with 4,4-diaminodiphenylsulfone in molten
tetrabutylammoniom bromide. The modified LDH (M-LDH) was used as a filler into the PAI
15 matrix and PAI/M-LDH nanocomposites containing 2, 4 and 8% of M-LDH were fabricated.
Thermogravimetric analysis showed improvement in thermal stability and morphology
investigations by field emission scanning electron microscopy and transmission electron microscopy
displayed that M-LDH is dispersed in the PAI matrix.
20 1. Introduction
45 Anꢀ is the exchangeable anion (often carbonate, chloride or
Aspartic acid is an αꢀamino acid with the chemical formula of
HOOCCH(NH2)CH2COOH.1 It was classified as an acidic amino
acid and can be used in synthesis of polymers with relatively low
molecular weight as well as high molecular weight with
nitrate).8ꢀ11 Recently the synthesis, structure and properties of
LDHs have been widely studied because of their potential
applications in catalysts,12 drug delivery,13 remove harmful
oxyanions,14 adsorption of acid red from dye wastewater,15
25 polycondensation reaction.2 There are two enantiomers of 50 optics,16 biosensors,17 synthesis of highly efficient flame
aspartic acid and the name aspartic acid can refer to either
enantiomer or a mixture of two of these two forms, one Lꢀaspartic
acid, is directly incorporated into the proteins and Lꢀaspartic acid
is a chosen amino acid which has been applied to the synthesize
30 of fresh polymers due to its multifunctionality.3 Dꢀaspartic acid is
an internal amino acid, which has been found in nervous and
endocrine texture of both invertebrates and vertebrates. Dꢀ
aspartic acid has a lot of applications in the chicken and rat brain,
human and so on.4
retardant nonocomposites (NCs),18ꢀ23 and other areas. LDHs are
also naturally abundant, readily synthesized at industrial scale,
o
inexpensive and stable at high temperature (up to 500ꢀ600 C)
and pH conditions.24
55
In the last decade there has been considerable interest in
polymerꢀLDH NCs due to their remarkably enhanced mechanical,
thermal, electrical, magnetic and fire retardant properties.25 These
enhanced properties are mainly attributed to the dispersion of
layered compounds within the polymer matrix. The use of LDHs
35
Layered double hydroxides (LDHs), known as hydrotalcite 60 as nanofillers has some limitations. The high charge density of
like compounds, have attracted attention, because of their layered
structure and very high anionꢀexchange capacity.5 The structure
of these compounds consists of positively charged bruciteꢀlike
layers with interlayer space containing charge compensating
LDH layers and the high content of anionic compounds and water
molecules, result in strong interlayer interactions between the
sheets and pronounced hydrophilic properties. Thus, monomer
and or polymer cannot easily penetrate within the LDH layers and
40 anions and water molecule. The positive charges on the LDH 65 the homogeneously dispersed of LDH layers within the
surface are balanced by interlayer anions and water molecules.5ꢀ7
hydrophobic polymer matrix is difficult. To facilitate the
intercalation of LDH within the polymer matrix and to gain a
desirable degree of dispersion, the interlayer space should be
modified with suitable and capable organic anions.26ꢀ28 Among
3+
The general formula of LDHs is [M2+
M
x(OH)2] Anꢀx/n .yH2O,
1ꢀx
where M2+ is a divalent metal ions such as Mg2+, Ca2+, Fe2+, Co2+
and M3+ is a trivalent ions such as Al3+ , Fe3+ , Cr3+ , Mn3+ and
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the numerous types of polymer structure, optically active
polymers offer a number of advantages in terms of their thermal
temperature for 12 h and then the solution was refluxed at 120 oC
for 12 h. The solvent was removed under reduced pressure and to
stability, chemical resistance and efficiency of binding.29 60 the residue, 50 mL of cold mixture of water and hydrochloric acid
Poly(amideꢀimide) (PAI) are known to have the property
advantages of both polyamides and polyimides such as high
strength, good solubility in polar amideꢀtype solvent, hydrogen
bonding interaction and extensive chemical resistant, being a
promising matrix candidate for hybrid materials.30ꢀ32
(10%) was added. The solution was then stirred for 2 h. A white
precipitate was formed, filtered off, and dried to give 0.58 g
(89%) of aspartic acid containing diacid. melting point (m.p.)
5
267–269 oC, (Literature 265ꢀ267 oC),27 [α]17
(N,Nꢀ
589
65 dimethylformamide) = +76 degꢀ1gꢀ1cm3 . FTꢀIR (KBr, cmꢀ1): 3433
(br), 2939 (m), 1779, 1725 (s, br), 1425 (m), 1389 (s), 1342 (s,
m), 1292 (s), 1202 (s, w), 1119 (s), 1027 (w), 950 (s, br), 921
(br), 827 (w), 752 (s, m), 669 (s, m), 640 (s, m), 520 (s, w), 421
(s, w).
In this work, Mg/AlꢀLDH was modified with dicarboxylic acid
10 containing Lꢀaspartic acid and tetrabromophthalic anhydride
under ultrasound irradiation as green and safety technique via coꢀ
precipitation method in aqueous media. The product (MꢀLDH)
was applied as filler with different percent's (2, 4 and 8 wt %) in
the PAI matrix for the preparation of LDH/PAI NCs. Fourier
15 transform infrared (FT-IR), Xꢀray diffraction (XRD), field
emission scanning electron microscopy (FEꢀSEM) and
transmission electron microscopy (TEM) were used to study the
morphological features and the nature of LDH particle dispersion
in PAI matrix. The thermal features of the NCs were studied by
20 means of thermogravimetric analysis (TGA) to probe the effects
of LDH nanoclay on the thermal stability of the resulting NCs.
2. Experimental section
70 2.4 Synthesis of M-LDH via ultrasonic method
In this work MꢀLDH was prepared by the coꢀprecipitation
method under ultrasonic irradiation. The mixed solution of 0.50 g
(2.0 mmol) of Mg(NO3)2. 6H2O and 0.37 g (1.0 mmol) of
Al(NO3)3. 9H2O (molar ratio 2/1) was prepared in the 20 mL of
75 deionized water (solution A). On the other hand, 0.83 g (1.5
mmol) of Lꢀaspartic based diacid and 0.12 g (3.0 mmol) of NaOH
was dissolved in the 20 mL deionized water (solution B).
Solution A was added into the solution B and stirred at room
temperature for 3h. Then the pH of obtained suspension was
80 adjusted to 10 by adding 1M NaOH. Finally the resulting product
was sonicated for 1h and obtained precipitate filtered and washed
2.1 Materials
Materials used in the synthesis of LDHs are aluminum nitrate
25 nonahydrate [Al(NO3)3. 9H2O] and magnesium nitrate
hexahydrate [Mg(NO3)2. 6H2O] were purchased from Aldrich
Chemical CO. (USA). Tetrabromophthalic anhydride (TBPA),
tetrabutylammoniom bromide (TBAB), triphenyle phosphite
(TPP) and pyromellitic dianhydride (benzeneꢀ1,2,4,5ꢀ
30 tetracarboxylic dianhydride) (PMDA) were purchased from
Merck Chemical CO. (Germany). Amino acids Lꢀaspartic acid
and Lꢀphenylalanine were used without more purification. The
other solvents and materials were used as gained without further
purification.
o
by deionized water and then was dried at 60 C for 24h. The
2ꢀ
Mg/AlꢀCO3 was synthesized by similar procedure without
adding diacid molecule.
85 2.5 Synthesis of L-phenylalanine containing diacid
N,Nꢀ(Pyromellitoyl)ꢀbisꢀLꢀphenylalanine monomer was prepared
according to earlier study.34
2.6 Synthesis of chiral PAI
PAI was prepared according to the reported procedure in the
90 provirus work.35 An optically active Lꢀphenylalanine containing
PAI was prepared by the polycondensation reaction of an
equimolar mixture of 0.29 mmol of monomer 3 and 0.29 mmol of
4,4ꢀdiaminodiphenyle sulfone (diamine 4) in the 1.16 mmol of
molten TBAB. After the reagents dissolved completely, 0.28 mL
95 of TPP was added and the reaction mixture was stirred for 12h at
35 2.2 Apparatus
Jascoꢀ680 (Japan) spectrophotometer was used for FTꢀIR
analyses of the synthesized materials. Spectra of solid samples
were obtained with KBr disk. The vibration transition frequencies
are described in the range of 400ꢀ4000 cmꢀ1. The XRD patterns
o
the 120 C. The viscous and yellow solution was poured into 40
mL of methanol and the precipitate solid was filtered using
Whatman filter paper. The inherent viscosity of the resulting
polymer was 0.34 dL/g and the yield was 88%. The specific
100 rotation was measured [α]D25=ꢀ134o (at a concentration of 0.5
40 were accumulated by using
a Philips Xpert MPD Xꢀray
diffractometer. The diffractograms were measured for 2θ, in the
range of 5ꢀ80º, using a voltage of 40 kV and Cu Kα incident light
(λ=1.51418 A°). TGA data were obtained on a STA503 TA
o
o
g/dL in DMF at 25 C), confirming the optical activity of this
polymer.
2.7 Synthesis of PAI/M-LDH NCs
apparatus in an argon atmosphere by heating rate of 10 C/min
45 from room temperature to 800 oC. The dispersion morphology of
the mixtures was detected using TEM (a Philips CM 120
operated, Netherlands) and FEꢀSEM (Hitachi, Sꢀ4160, Japan).
The reaction was happened on a MISONIX ultrasonic liquid
processor, XLꢀ2000 series with a wave of frequency 2.25×104 Hz
50 and power 100 W.
Different NC of PAI/MꢀLDH (2, 4 and 8 wt.%) were prepared by
105 following method. 0.1g of PAI was dispersed in the 8 mL ethanol
and a uniform colloidal dispersion was obtained after sonication
for 15 min (solution 1). Different percent's of MꢀLDH were
dispersed in 8 mL of ethanol and was sonicated for 30 min
(solution 2). Two solutions were mixed together at room
110 temperature and sonicated for 3h. After irradiation, the ethanol
was removed and the obtained solid was dried in the room
temperature for 24 h.
2.3 Synthesis of biosafe diacid containing aspartic acid
Lꢀaspartic acid containing diacid was synthesized according to
the procedure reported by Tagle et al.33 The mixed solution of
55 0.50 g (1.0 mmol) of TBPA, 0.15 g (1.1 mmol) of aspartic acid
and 8 mL of acetic acid were prepared and 1 mL of pyridine was
added into this solution. The mixed solution was stirred at room
3. Result and discussions
2
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O
O
O
O
O
O
3.1 Preparation of chiral diacid and M-LDH
O
H
O
H
NH2
CH2
Acetic acid
Reflux
+
O
N
N
HO
OH
HO
LꢀAspartic acid containing diacid was synthesized from the
reaction of the TBPA and Lꢀaspartic amino acid in refluxed acetic
acid at the presence of pyridine as shown in Scheme 1.33 This
diacid was used for organoꢀmodification of Mg/AlꢀLDH by a
simple and green method under ultrasonic irradiation. The
schematic of such an adsorption process between chiral diacid
and Mg/AlꢀLDH is shown in Figure 1. The elementary reason for
selecting Mg/Al based LDH is their typical metal hydroxideꢀlike
10 chemistry and conventional clayꢀlike layered crystalline structure
which makes them appropriate for polymer NCs preparation and
can progress their dispersion in polymer matrix. Mg/AlꢀLDH
can't be easily dispersed in polymer matrix; this failure is due to
the weak interactions between the polymer and the LDH. In fact,
15 the organic component of the organoclay increases interactions
H
CH2
H2C
O
O
O
O
1
3
2
5
Scheme 2. Synthesis of N,Nꢀ(pyromellitoyl)ꢀbisꢀLꢀphenylalanine
50 monomer
O
O
O
S
O
H
O
TBAB/TPP
O
S
3
N
N
+
H2
N
NH2
H
N
N
12h , 120 oC
H
H
O
4
CH2
O
O
O
CH2
n
5
Scheme 3. Synthesis of chiral PAI
3.3 Preparation of PAI/M-LDH NCs
PAI/MꢀLDH NCs were synthesized by a solutionꢀintercalation
55 method using ultrasound radiation. The organic anions containing
the polar groups are intercalated in LDH interlayers and can
allow anchoring of the polymeric unit onto LDH. The inorganic
nanoparticles (hydroxide nanosheets) are randomly dispersed in
the PAI matrix. The adsorption of PAI onto the surfaces of Mꢀ
60 LDH was presumed to occur through hydrogen bonding (Figure
2). Although, van der Waals forces between PAI matrix and Mꢀ
LDH surface would also play an essential role in the overall
adsorption process.
between the polymer and the MꢀLDH.
Br
Br
O
O
O
O
Br
Br
Br
Br
Acetic acid
Pyridine
OH
N
OH
OH
+
O
HO
H
NH2
O
H2C
O
O
Br
Br
O
Scheme 1. Preparation of diacid from reaction between TBPA and
aspartic acid
20
Figure 1. Intercalation of diacid in the interlayer of LDH
65 Figure 2. Synthesis of NCs of PAI and MꢀLDH
3.4.1 FT-IR
3.2 Synthesis of PAI
FTꢀIR spectroscopy has been mostly employed to study the
structural accommodation of interlayer species and hydrogen
bond network in LDH. FTꢀIR spectra of the LDHꢀCO32ꢀ, Lꢀ
70 aspartic containing diacid and MꢀLDH are represented in Figure
3. For LDHꢀCO32ꢀ, the broad peak in the 3150ꢀ3500 cmꢀ1 is
ascribed to the water molecules where the hydrogen bonding in
the interlayer region between water molecules and the hydroxide
sheet is obvious from shoulder at 3050–3100 cmꢀ1. The
75 asymmetric stretching of carbonate in the interlayer space of
LDH was shown in the range 1350ꢀ1380 cmꢀ1. The strong band at
455 cmꢀ1 and the broad one at 651 cmꢀ1 are ascribed to the
vibrations of metal oxides (MgꢀO and AlꢀO), respectively. The
FTꢀIR spectrum of diacid showed a broad and strong peak at
80 2350ꢀ3650 cm−1, which was assigned to the COOH groups and
two absorption bands at 1779 and 1725 cm−1, which are
corresponding to the unsymmetrical and symmetrical stretching
vibrations of imide C=O group. The adsorption peaks showed at
1389 and 752 cmꢀ1 region is related to the presence of the imide
85 heterocycle ring and showed peak in the 1119 cmꢀ1 due to the Cꢀ
Br. FTꢀIR spectra for MꢀLDH shows the adsorption peaks at
1775 and 1720 cmꢀ1 related to the stretching vibration of C=O, at
From a technological point of view, the use of an organic solvent
25 in big scale preparation is not very friendly and highly polar
conventional solvents such as N,Nꢀ dimethylformamide, N,Nꢀ
dimethylacetamide,
pyridine,
Nꢀmethylpyrrolidone
and
chlorinated solvents which are used in polycondensation
polymerizations are volatile and most of them are flammable,
30 toxic, quite hazardous and harmful compared to ionic liquids.36,37
in this study, molten TBAB ionic liquid was selected because it
proved to be the most valuable among those employed. Due to
their nonvolatility, ionic liquid have a little effect on the
environment and human health and so, they are known as green
35 solvents due to their properties such as chemical stability, low to
high viscosity, and high ionic conductivity properties.38,39 For the
preparation of the polymer, first an optically active and bioactive
dicarboxylic acid 3 was synthesized via the reaction of Lꢀ
phenylalanine and PMDA in refluxing acetic acid solution
40 (Scheme 2). Then PAI 5 was successfully synthesized by the
polycondensation reactions of an equimolar mixture of 3 with
aromatic diamines 4 in molten TBAB as an ionic liquid media
and TPP which acted as activating agent in good yield and
moderated inherent viscosity (Scheme 3). The obtained PAI
45 displayed optical rotation, which showed that the polymer is
optically active and chirality was introduced into the backbone of
the polymer.
1124 cmꢀ1 related to the CꢀBr and 1388 and 752 cmꢀ1 can be
2ꢀ
related to the imide C=O group in comparison with LDHꢀCO3
,
90 which may confirm the presence of diacid in the interlayer of
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LDH. Peak due to the carbonate anion (1378 cm−1) is also
observed, because the process was applied without N2
atmosphere and CO2 can be absorbed from the atmosphere during
the process.
Figure 4. FTꢀIR spectra of PAI and NCs of PAI with different amount of
35 the MꢀLDHs
5
3.4.2 X-ray diffraction
Figure 3. FTꢀIR spectra of (a) LDHꢀCO32ꢀ, (b) diacid and (c) MꢀLDH
The XRD patterns are very valuable and main analytical
technique for the characterization of LDHs and crystalline
phases.40 It is also used to determine the interlayer spacing and
40 for the determination of the structure of layered samples. The
XRD patterns of LDHꢀCO32ꢀ, MꢀLDH, NC4 and 8 wt% were
shown in Figure 5. Before organic treatment, the basal spacing of
the pure LDH, that is, LDHꢀCO32ꢀ is 0.75 nm, which corresponds
to the (003) diffraction peak with 2θ=11.84º.28 After modified
45 LDH with the diacid molecule, the Xꢀray reflections have been
shifted to a lower angle position. The MꢀLDH displays a (003)
diffraction peak at 2θ=7.87º corresponding to an interlayer
distance of 1.12 nm. In conclusion, these increases in the
interlayer distances show the intercalation of bigger anionic
50 diacid functionalized between the LDH layers. The size of the
guest diacid was estimated and compared to the obtained basal
spacing via XRD patterns. Based on previous work, the thickness
Figure 4 shows the FTꢀIR spectra of the pure PAI and NCs of
PAI with different amount of the MꢀLDHs. The FTꢀIR spectrum
of PAI showed absorption peaks around 3360 cmꢀ1 (N–H), and
10 two overlapped carbonyl (amide and imide’s C=O) absorptions at
1779, 1725, and 1663 cmꢀ1, respectively. Absorption at 1380 and
727 cmꢀ1 indicate the presence of the imide heterocycle in this
polymer structure. Absorptions at 1251 and 1150 cmꢀ1 are due to
the sulfone moiety (SO2 stretching).35 The spectra of the prepared
15 NCs clearly exhibit the characteristic absorption peaks
corresponding to the polymeric groups, although some peak
intensity may be changed. The new peaks showed in the range
400ꢀ600 cmꢀ1 are correspond to metal oxide (MgꢀO and AlꢀO) in
the NCs spectra. This result in sum confirmed the presence of Mꢀ
20 LDH nanoclay in the PAI matrix.
2ꢀ
of LDHꢀCO3 hydroxide sheets is 0.48 nm.10 The increase of
interlayer distance in the MꢀLDH, calculated from the d003
55 spacing and thickness of the inorganic layer, is approximately
0.64 nm. This means that the anionic diacid are horizontally
oriented in the interlayer space (Figure 1), which are confirmed
by the approximate molecule length diacid which were calculated
by gauss view (Scheme 4).
25
60
For PAI/LDH NCs (4% and 8%), the XRD patterns don’t
showed any peak for MꢀLDH in the samples. The only new broad
and vast diffraction peak that appeared at 2θ=17.70° related to the
PAI polymer matrix. In PAI/clay NCs, complete exfoliation of
LDH results in disappearance of the diffraction maxima in their
Scheme
4.
Molecule
30 structure and size of the
diacid
65 XRD patterns. Moreover, this can also happen due to other
reasons, such as extremely low concentration of clay materials in
the polymer matrix, crystal defects, etc. The high degree of
exfoliation of the LDH clay layers in polymer NCs has also been
reported using several studies.41,42 However, XRD analysis alone
70 is not adequate for proven of the dispersion in the polymer
matrix.
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25
Figure 7 shows the thermal decomposition of neat PAI and
PAI/MꢀLDH NCs with different contents of MꢀLDH and
resulting TGA data are summarized in Table 1. The thermal
stability of the PAI and PAI/MꢀLDH NCs was studied on the
basis of 5 and 10% weight losses (T5 and T10, respectively) of the
30 samples and the char yield (residue weight at 800 oC). The initial
decomposition temperatures of the NCs with different MꢀLDH
percent (2, 4 and 8 %) were over 315°C, which can be related to
the decomposition of pristine polymer matrix.35 According to the
Table 1, T5, T10 and char yield for NCs with different MꢀLDH
35 content are higher than of pure PAI. It is clear that the PAI/Mꢀ
LDH materials improved thermal properties due to the
incorporation of MꢀLDH. The improvement of thermal property
of PAI/MꢀLDH NCs can be attributed to the homogeneous
dispersion of MꢀLDH nanoclay in polymer matrix and the strong
40 hydrogen bonding between OꢀH groups on the surface of MꢀLDH
and nitrogen atoms or carbonyl group of PAI matrix. Char yield
can be applied as a crucial factor for estimating limiting oxygen
index (LOI) of the polymers based on Van Krevelen and Hoftyzer
equation.43
45 LOI = 17.5+ 0.4 CR
Where CR = char yield. According to this equation, LOI
values calculated based on their CR at 800 C were higher than
Figure 5. XRD patterns of LDH, MꢀLDH and NCs of PAI 4 and 8% of
the MꢀLDHs
o
30, showing that such macromolecules can be classified as selfꢀ
extinguishing polymers.
3.4.3 Thermal analysis
5
TGA is used to measure variations in the mass of LDH and
evaluation of the content of water and anion molecules.30 The
TGA curves for LDH and MꢀLDH are shown in the Figure 6.
Three massꢀloss steps are noticed for LDH. The weight loss
before 200 oC is recognized to the releasing of the physically
10 adsorbed water and water molecules around Mg and Al cations
and the about 400 oC removal of water molecules by deꢀ
hydroxylation process was showed. Third weight loss is related to
the removal of the interlayer carbonate anions.10 For MꢀLDH the
numbers of decomposition stages have enhanced. Diacid
15 modified LDH have similar massꢀloss behavior before 400 oC. In
comparison to LDHꢀCO32ꢀ, residual weight percent of the diacid
intercalated LDH was decreased. Also the presence of a larger
weight loss step within 410ꢀ540 °C for LDHꢀdicarboxylate anion
compared to the LDH, confirmed the presence of interlayer
20 surfactant anions in LDH, because the presence of organic groups
in the interlayer of MꢀLDH reduced the thermal stability of the
hybrid compounds.10
50
Figure 7. TGA curve of PAI and NCs of PAI with different amount of the
MꢀLDHs
Table 1. The data obtained from TGA thermogram of PAI and PAI/Mꢀ
LDH NCs
Sample
T5
(
T10 ( oC)a
Char yield ( % )b
LOI
oC)a
PAI
289
316
349
379
39.00
41.23
33.10
33.99
PAI/MꢀLDH 2%
PAI/MꢀLDH 4%
PAI/MꢀLDH 8%
342
342
382
400
42.42
46.46
34.46
36.08
a
55 Temperature at which 5 and 10% weight loss was recorded by TGA at
heating rate of 10 oC/min under a nitrogen atmosphere
b Weight percentage of material left undecomposed after TGA analysis at
a temperature of 800 oC under a nitrogen atmosphere
Figure 6. TGA curves for LDH and MꢀLDH
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3.4.4 Morphological analysis by electron microscopy
FEꢀSEM and TEM provide beneficial and crucial images of
textural and crystal morphologies of LDH intercalated materials.
LDH generally shows a hexagonal platelet morphology.27 The
2ꢀ
5
FEꢀSEM images of LDHꢀCO3 and MꢀLDH with different
magnification are showed in the Figure 8. The LDH displayed the
nature of LDH particles, which roughly contained of plateꢀlike
shapes with lateral dimensions and thickness ranging over few
nanometer (Figures 8a and 8b).The FEꢀSEM images for MꢀLDH
10 showed formation of plateꢀlike nanoparticles with regular shape,
as commonly observed for the typical organic anionic intercalated
LDH compounds. The layer nanoparticles have a diameter over a
few hundred nanometers and a thickness over several tens of
nanometers (Figures 8c and 8d).
40
Figure 9. FEꢀSEM images of (a, b) PAI (c, d) PAI/MꢀLDH NC 2% (e, f)
PAI/MꢀLDH NC 4% and (g, h) PAI/MꢀLDH NC 8%
15
Figure 8. FEꢀSEM images of (a, b) LDHꢀCO32ꢀ and (c, d) MꢀLDH
The FEꢀSEM micrograph for neat PAI and NCs with different
percent represent in the Figure 9. The morphology of neat PAI
seems to be smooth relatively (Figures 9a and 9b). After
20 modification of PAI with MꢀLDH the surface morphology of the
NCs is changed and the micrograph showed uniform distribution
and excellent dispersion of MꢀLDH into the PAI matrix (Figures
9cꢀ9f). These observations are perhaps a result of modification of
LDH with diacid. TEM shows a real image of nanoclay platelets
25 to allow identification of internal morphology and hybrid
structure of NCs. In Figures 10a and 10b, TEM images of LDHꢀ
CO32− showed and the synthesized LDHꢀCO32− are smooth, wellꢀ
shaped in a hexagonal form, crystalline and don’t showed any
aggregated platelets. After modification of LDH with Lꢀaspartic
30 containing diacid, the expected plateꢀlike nature of the crystallites
and hexagonal structure is clearly apparent and there are no signs
of aggregation visible in the micrographs (Figures 10c and 10d).
Figures 10e and 10f shows the TEM images of PAI/MꢀLDH NCs
with 8 wt% of MꢀLDH. The TEM image showed that the LDHs
35 are dispersed throughout the polymer matrix. The layers are well
shown in this image and the thickness and lateral sizes of the
LDH layers can be calculated as being about nanometric size.
2ꢀ
Fig. 10. TEM images of LDHꢀCO3 (a, b), MꢀLDH (c, d) and PAI/Mꢀ
45 LDH NC 8% (e, f)
4. Conclusions
LDH was modified with diacid containing TBPA and aspartic
acid by coꢀprecipitation method through applying the ultrasonic
irradiation as green, easy and safety tool. The increase in basal
50 spacing of MꢀLDH in comparison to the LDH, showed by XRD
analyses, indicated an intercalation of bigger organic anions into
the LDH interlayer space. Polycondensation reaction of chiral
diacid with solfonated diamin furnished a chiral PAI, due to Lꢀ
phenylalanine amino acid in the polymer structure. LDH
55 nanoclay modified with organic diacid as a bifunctional coupling
agent was used to enhance the compatibility between PAI matrix
and LDHs. The morphology and textural of NCs was study by
FEꢀSEM and TEM techniques and the results showed well
dispersed and formation of intercalated and or exfoliated
60 modified LDH platelets in the PAI matrix. Thermal properties
increase for NCs in the presence of MꢀLDH due to the hydrogen
bonding between the MꢀLDH nanoclay and the PAI matrix.
6
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DOI: 10.1039/C4RA05754F
17 F. T. Zhang, X. Long, D. W. Zhang, Y. L. Sun, Y. L. Zhou, Y. R.
Ma, L. M. Qi and X. X. Zhong, Sens. Actuators, B, 2014, 192, 150ꢀ156
Acknowledgments
18 C. Nyambo, P. Songtipya, E. Manias, M. M. JimenezꢀGascoc and C.
A. Wilkie, J. Mater. Chem., 2008, 18, 4827ꢀ4838
We wish to sincerely thank the Research Affairs Division Isfahan
University of Technology (IUT), Isfahan, for the financial
support of this work. Further financial support from National
Elite Foundation (NEF), and Iran Nanotechnology Initiative
Council (INIC) is gratefully acknowledged.
5
60 19 Y. Gao, Q. Wang, J. Wang, L. Huang, X. Yan, X. Zhang, Q. He, Z.
Xing and Z. Guo, ACS Appl. Mater. Interface., 2014, 6, 5094ꢀ5104
20 Q. wang, J. Wu, Y. Gao, Z. Zhang, J. Wang, X. Zhang, A. Umar, Z.
Guo and D. O'Hare, RSC Adv., 2013, 3, 26017ꢀ26024
Notes and references
aOrganic Polymer Chemistry Research Laboratory, Department of
10 Chemistry, Isfahan University of Technology, Isfahan, 84156ꢀ83111, I. R.
Iran. FAX: +98ꢀ311ꢀ391ꢀ2350, Tel; +98ꢀ311ꢀ391ꢀ3267; Eꢀmail:
mallak@cc.iut.ac.ir,mallak777@yahoo.com,
21 Y. Gao, J. Wu, Z. Zhang, R. Jin, X. Zhang, X. Yan, A. Umar, Z. Guo
65 and Q. Wang, J. Mater. Chem. A, 2013, 1, 9928ꢀ9934
22 Q. Wang, X. Zhang, J. Zhu, Z. Guo and D. O'Hare, Chem. Comm.,
2012, 48, 7450ꢀ7452
mallakpour84@alumni.ufl.edu (Shadpour Mallakpour).
bNanotechnology and Advanced Materials Institute, Isfahan University of
15 Technology, Isfahan, 84156ꢀ83111, I. R. Iran. FAX: +98ꢀ311ꢀ391ꢀ2350,
23 Q. Wang, X. Zhang, C. J. Wang, J. Zhu, Z. Guo, and D. O'Hare, j.
Mater. Chem., 2012, 22, 19113ꢀ19ꢀ121
Tel;
+98ꢀ311ꢀ391ꢀ3267;
Eꢀmail:
mallak@cc.iut.ac.ir,
mallak777@yahoo.com,
Mallakpour).
mallakpour84@alumni.ufl.edu
(Shadpour 70 24 F. L. Theiss, S. J. Couperthwaite, G. A. Ayoko and R. L. Frost, J.
Colloid Interface Sci., 2013, 402, 114ꢀ121
cCenter of excellent in sensor and green chemistry, Department of
25 N. Muksing, R. Magaraphan, S. Coiai and E. Passaglia, Express
Polym. Lett., 2011, 5 428ꢀ448
20 chemistry, Isfahan University of Technology, Isfahan 84156ꢀ83111,
Islamic
Republic
of
Iran,
eꢀmail:
mallak@cc.iut.ac.ir;
mallak777@yahoo.com; mallakpour84@alumni.ufl.edu
26 Z. Matusinovic, H. Lu and C. A. Wilkie, Polym. Degrad. Stab., 2012,
75 97, 1563ꢀ1568
1
C. Liebecq, K. L. Loening, G. P. Moss, J. Reedijk, S. L. Velick and J.
27 F. Leroux, L. Meddar, B. Mailhot, S. MorlatꢀTheriasb and J. L.
Gardette, Polymer, 2005, 46, 3571–3578
25 F. G. Vliegenthart, Pure Appi. Chem., 1984, 56, 595ꢀ624
2
M. Tomida, T. Nakato, S. Matsunami and T. Kakuchi, Polymer,
28 N. H. Huang and J. Q. Wang, Express Polym. Lett., 2009, 3, 595–604
1997, 38, 4733ꢀ4736
29 S. Mallakpour and M. Hatami, Polym. Plast. Technol. Eng., 2012, 51,
80 1106ꢀ1112
3
1630
M. R. Vakili and N. Rahneshin, Carbohydr. Polym., 2013, 98, 1624ꢀ
30 S. Mallakpour and M. Zarei, J. Reinf. Plast. Compos., 2012, 32, 574ꢀ
582
30
4
G. Macchia, E. Topo, N. Manganoc, E. D. Aniello and R. Boni,
Animal. Reproduction. Sci., 2010, 118, 337ꢀ343
31 Z. Hu, S. Li and C. Zhang, J. Appl. Polym. Sci., 2007; 106: 2494–501
5
L. Tammaro, V. Vittoria and V. Bugatti, Eur. Polym. J., 2014, 52,
32 S. Mallakpour, M. Iderli, M. R. Sabzalian, Designed Monomers
85 Polym., 2013, 16, 509ꢀ514
172ꢀ180
6
7
S. Mallakpour and M. Dinari, Prog. Org. Coat., 2014, 77, 583ꢀ589.
J. P. Cheng, J.H. Fang, M. Li, W. F. Zhang, F. Liu and X. B. Zhang,
33 L. H. Tagle, C. A. Terraza, A. TundidorꢀCamba and J. Sotoꢀ
Salamanca, Polym. Bull., 2014, 71, 287ꢀ300
35
Electrochim. Acta, 2013, 114, 68ꢀ75
34 S. Mallakpour and M. Dinari, J. Macromol. Sci. Part A: Pure Appl.
Chem., 2011, 48, 644ꢀ679
8
P. GuerreroꢀUrbaneja, C. GarciaꢀSancho, R. MorenoꢀTost, J. Meridaꢀ
Robles, J. SantamariaꢀGonzalez, A. JimenezꢀLopez and P. Mairelesꢀ
90 35 S. Mallakpour and M. Dinari, Polymer, 2011, 52, 2514ꢀ2523
36 S. Mallakpour, M. Zarei, J. Reinf. Plast. Compos., 2012, 32, 574ꢀ582
37 S. Mallakpour and M. Dinari, Iran. Polym. J., 2010, 19, 983ꢀ1004
38 S. Mallakpour, M. Dinari, Amino Acids, 2013, 44, 1021ꢀ1029
39 S. Mallakpour and M. Dinari, Iran. Polym. J., 2011, 20, 259ꢀ279
Torres, Appl. Catal., A, 2014, 470, 199ꢀ201
40
9
Z. Huang, P. Wu, B. Gong, Y. Lu, N. Zhu and Z. Hu, Appl. Surf. Sci.,
2013, 286, 371ꢀ378
10 S. Mallakpour, M. Dinari and V. Behranvand, RSC Adv., 2013, 3,
23303ꢀ23308
11 K. Klemkaite, I. Prosycevas, R. Taraskevicius, A. Khinsky and A.
45 Kareiva. Cent. Eur. J. Chem., 2011, 9, 275ꢀ282
95 40 M. Silion, M. I. Popa, G. Lisa and D. Hritcu, Rev. Roum. Chim.,
2008, 53, 827–831.
12 J. M. Hidalgo, J. S. Cesar and R. R. Jose, Appl. Catal., A, 2014; 470:
311ꢀ317
41 W. Cui, Q. Jiao, Y. Zhao, H. Li, H. Liu and M. Zhou, Express Polym
Lett, 2010, 6, 485–493
13 L. Alberto de Sousa Rodriguesa, A. Figueiras, F. Veiga, R. Mendes
de Freitas, L. C. C. Nunesa, E. Cavalcanti da Silva Filho and C. M. da
50 Silva Leite, Colloids Surf., B, 2013, 103, 642ꢀ651
42 I. Brnardic, Z. Matusinovic, J. Sipusic and J. Macan, Polymeri, 2012,
100 33, 52ꢀ57
14 K. H. Goh, T. T. Lim and Z. Dong, Water Res., 2008, 42, 1343ꢀ1368
43 D. W. Van Krevelen and P. J. Hoftyzer, Elsevier Scientific
Publishing, New York, 3rd ed., 1976
15 T. Xue, Y. Gao, Z. Zhong, A. Umar, X. Yan, X. Zhang, Z. Guo and
Q. Wang, J. Alloys. Compd., 2014, 587, 99ꢀ104
16 S. Y. Ryu, M. Yoon, J. H. Choy, S. H. Hwang, A. Frube, T. Asahi
55 and et al, Bull. Korean Chem. Soc., 2003, 24, 446ꢀ452
This journal is © The Royal Society of Chemistry [year]
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