Flammability and thermal properties of novel semi aromatic polyamide/organoclay nanocomposite

Article abstract of DOI:10.1016/j.tca.2014.03.045

The development of semi aromatic polyamide/organoclays nanocomposites (PANC) is reported in this communication. New polyamide (PA) was successfully synthesized through direct polycondensation reaction between bio-based diacid and aromatic diamine. PA exhibited strong UV-vis absorption band at 412 nm. Its photoluminescence spectrum showed maximum band at 511 nm in the green region. The surface modification of montmorillonite was carried out through ion-exchange reaction using 1,4-bis[4-aminophenoxy]butane (APB) as a modifier. Then PANCs containing 3 and 6 wt.% of the modified montmorillonite (MMT-APB) were prepared. Flammability and thermal properties of PA and the nanocomposites were studied by microscale combustion calorimeter (MCC), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA results in both air and nitrogen atmospheres indicated improving in thermal properties of PANCs compared to the neat PA. According to MCC analysis, a 31.6% reduction in pHRR value has been achieved by introducing 6 wt.% of the organoclay in PA matrix.

Full text of DOI:10.1016/j.tca.2014.03.045

Accepted Manuscript
Title: Flammability and Thermal Properties of Novel Semi
Aromatic Polyamide/Organoclay Nanocomposite
Author: Meisam Shabanian Zeinab Mirzakhanian Nemat
Basaki Hossein Ali Khonakdar Khalil Faghihi Faegheh
Hoshyargar Udo Wagenknecht
PII:
S0040-6031(14)00142-7
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.tca.2014.03.045
TCA 76834
To appear in:
Thermochimica Acta
Received date:
Revised date:
Accepted date:
20-11-2013
27-3-2014
28-3-2014
Please cite this article as: M. Shabanian, Z. Mirzakhanian, N. Basaki, H.A. Khonakdar,
K. Faghihi, F. Hoshyargar, U. Wagenknecht, Flammability and Thermal Properties of
Novel Semi Aromatic Polyamide/Organoclay Nanocomposite, Thermochimica Acta
(2014), http://dx.doi.org/10.1016/j.tca.2014.03.045
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Graphical Abstract
1
Page 1 of 31

Research Highlights
►
Development of new polyamide/organoclay nanocomposites was reported.
Thermal performance of the nanocomposites was improved under inert and
reactive atmospheres.
Organoclay increased flame retardancy of nanocomposites.
►
►
2
Page 2 of 31

Flammability and Thermal Properties of Novel Semi Aromatic
Polyamide/Organoclay Nanocomposite
a,
b
c
d
Meisam Shabanian *, Zeinab Mirzakhanian , Nemat Basaki , Hossein Ali Khonakdar ,
b
e
e
Khalil Faghihi , Faegheh Hoshyargar , Udo Wagenknecht
a
Faculty of Chemistry and Petrochemical Engineering, Standard Research Institute (SRI), P.O. Box
1745-139, Karaj, Iran
3
b
Department of Chemistry, Faculty of Science, Arak University, 38156-8-8349 Arak, Iran
c
Department of Chemistry, Farahan Branch, Islamic Azad University, Farahan, Iran
d
Iran Polymer and Petrochemical Institute, P.O. Box 14965/115, Tehran, Iran
e
Leibniz-Institut für Polymerforschung Dresden e.V., Hohe Strasse 6, D-01069 Dresden, Germany
-
-----------------------------------------------------------
*
Corresponding author: Meisam Shabanian, Tel: +98 26 66426557; Fax: +98 26
6
6461169; Email: m.shabanian@standard.ac.ir, shabanian.m44@gmail.com
3
Page 3 of 31

Abstract:
The development of semi aromatic polyamide/organoclays nanocomposites (PANC) is
reported in this communication. New polyamide (PA) was successfully synthesized
through direct polycondensation reaction between bio-based diacid and aromatic diamine.
PA exhibited strong UV-Vis absorption band at 412 nm. Its photoluminescence spectrum
showed maximum band at 511 nm in the green region. The surface modification of
montmorillonite was carried out through ion-exchange reaction using 1,4-bis[4-
aminophenoxy]butane (APB) as a modifier. Then PANCs containing 3 and 6 wt. % of the
modified montmorillonite (MMT-APB) were prepared. Flammability and thermal
properties of PA and the nanocomposites were studied by microscale combustion
calorimeter (MCC), thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC). TGA results in both air and nitrogen atmospheres indicated
improving in thermal properties of PANCs compared to the neat PA. According to MCC
analysis, a 31.6 % reduction in pHRR value has been achieved by introducing 6 wt. % of
the organoclay in PA matrix.
Key words: Nanocomposite, Polyamide, Thermal Stability, Flammability, Organoclay
1
. Introduction
Over the last decade, the polymer/layered silicate nanocomposites have received rising
attention owing to their unique thermal, mechanical and gas barrier properties compared
with those of neat polymer. While 30-40 wt. % microfillers are required for conventional
composites, diverse properties of polymer can be significantly improved by incorporation
of only minute amounts of clay (2−8 wt. %) in polymer matrices [1-4].
4
Page 4 of 31

The typical selected clay for these types of nanocomposites is montmorillonite. The
high aspect ratio of the platelets serves as interfacial volumes extender in nanocomposite
and thus provides improved physico-chemical and mechanical properties [5]. However,
incorporating of hydrophilic montmorillonite platelets into the hydrophobic polymer
matrix has been a major challenge due to the incompatibility between polymer and
montmorillonite. To overwhelm this deficiency, montmorillonite is organically modified
by adequate modifiers such as quaternary ammonium or phosphonium salts [1, 6]. The
blending of unmodified montmorillonite is limited to hydrophilic polymers such as
polyethylene oxide and polyvinyl alcohol.
Polyamides are one of the most promising classes of engineering polymers. Due
to their properties, such engineering polymers are potential matrices for nanocomposites.
Semi-aromatic polyamides in particular, are of special interest because of their enhanced
transparency, thermal stability, excellent barrier properties and solvent resistance [7-12].
Still, several applications of these polymers are only achieved through their
nanocomposites. However, the limiting factors for processing and application of aromatic
polyamides (aramids) (e. g. poor solubility in common organic solvents and extremely
high transition temperatures) have been improved for semi-aromatic polyamides [13-18].
The polyamide/montmorillonite nanocomposites have recently raised so much attention
as they offer tremendous applications in coatings, flame retardant agents and barrier and
electronic materials and the advances toward their applications have been recently
studied in details [19].
Incorporating of pyridine and its derivatives has been already reported to improve
thermal stability of the polymeric matrices [20-23]. The rigid hetero-aromatic pyridine
5
Page 5 of 31

ring develops thermal and chemical stability of polymers while the polarizability of
nitrogen atom can improve the solubility in organic solvents. Pyridine containing
polymers easily undergo chemical modifications. Protonation or alkylation of the
heterocyclic nitrogen atom, for instance, improves optical properties of polymers once
used as luminescent (fluorescent) materials [24, 25].
The global reliance on petroleum-derived plastics along with growing environmental
concerns has motivated developments in production and application of bio-based
polymers [26]. Bio-based materials are fabricated using plant-derived substances as their
main ingredients. These substances, as sustainable and eco-efficient products, can
substitute the petrochemical-derived stocks. Their ingredients are normally a renewable
resource and generally do not contain environmentally hazardous substances [27-30].
The present study deals with the synthesis of new semi aromatic polyamide (PA) and
its subsequent nanocomposites with organically modified montmorillonite. Different
properties of the developed nanocomposites are presented. Interesting findings on
improvement of flame retardancy and thermal properties of the nanocomposites are
discussed here.
2
. Experimental
2
.1. Materials
Oleic acid, 4-nitroacetophenone, 4-dimethylaminobenzaldehyde, ammonium acetate,
N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylformamide
DMF), palladium charcoal, potassium permanganate (KMnO ), hydrazine hydrate,
(
4
pyridine, glacial acetic acid, ethanol, methanol and triphenyl phosphite (TPP) (all
6
Page 6 of 31

+
purchased from Merck) and MMT-Na (Southern Clay Products, Inc.) were used without
further purification. Commercially available calcium chloride (CaCl , Merck) was dried
2
under vacuum at 150 ºC for 6 h.
2
.2. Monomer Synthesis
Synthesis of azelaic acid from oleic acid
Azelaic acid was synthesized through the oxidation of oleic acid’s double bond using
KMnO , following the procedure already reported in ref. [31] (Yield: 63 %).
4
4
-(4-dimethylamino)phenyl)-2,6-bis (4-nitrophenyl)pyridine
In a 500 mL round-bottom flask, a mixture of 6.0 g (41 mmol) 4-
dimethylaminobenzaldehyde, 13.5 g (82 mmol) 4-nitroacetophenone, ammonium acetate
excess) and 150 mL glacial acetic acid was refluxed for 24 h. Upon cooling, the
(
precipitated orange solid was collected by filtration and washed with ethanol. The yield
of the crude product was 57%. Other specifications include m.p. 268-270 °C; FTIR
(KBr): 3066 (s, br), 1591 (s), 1520 (s), 1440 (s), 1346 (s), 1208 (m), 1107 (s), 856 (s),
-
1 1
8
6
4
10 (s) and 731 (m) cm . H-NMR (DMSO-d
6
, TMS) δ: 8.6 (4H), 8.4 (6H), 8.0 (d, 2H),
.8 (d, 2H) and 2.9 (s, 6H) ppm.
-(4-dimethylamino)phenyl)-2,6-bis(4-aminophenyl)pyridine
In a 250 ml round-bottom flask equipped with a reflux condenser and a dropping
funnel, a suspension of the synthesized dinitro (5 g, 12 mmol) and palladium on carbon
0 % (0.1 g) in a mixture of ethanol (30 mL) and DMF (5 ml) was prepared. While
heated to 80 °C and being stirred magnetically, a solution of hydrazine monohydrate
0 % (10 ml) in ethanol (15 ml) was added dropwise through the dropping funnel over 1
h. After 4 h, the mixture was filtered, yet too hot to remove Pd/C, and the solvent was
1
8
7
Page 7 of 31

evaporated in vacuum to afford the orange solid product. Yield (%)=95; m.p. (°C) =118-
20; FTIR (KBr): 3056 (m, br), 1593 (s), 1542 (s), 1512 (s), 1348 (s), 1276 (m), 1109 (m),
1
-1 1
8
52 (m), 819 (s) and 690 (m) cm . H-NMR (DMSO-d , TMS) δ: 8.6 (d, 4H), 8.4 (m,
6
6
1
1
H), 7.9 (d, 2H) and 6.8 (d, 2H) ppm.
,4-bis(4-aminophenoxy)butane
,4-bis(4-aminophenoxy)butane (APB) was synthesized according to the procedure
reported in ref. [32].
2
.3. Synthesis of semi aromatic polyamide (PA)
In a 50 mL round-bottom flask fitted with a stirring bar, 4-(4-dimethylamino)phenyl-
,6-bis(4-aminophenyl)pyridine (5.32 g, 14 mmol), azelaic acid (2.7 g, 14 mmol),
2
calcium chloride (0.5 g, 4.5 mmol), triphenyl phosphite (8.7 mL, 28 mmol), pyridine (1
mL) and N-methyl-2-pyrrolidone (9 mL) were mixed and heated at 120 °C and refluxed
in an oil bath for 10 h. Subsequently, the reaction mixture was poured into 200 mL
methanol. The precipitated product was collected by filtration and rinsed thoroughly with
hot methanol. Finally, the product was dried at 70 °C for 10 h inside a vacuum oven
(
Yield (%) =97).
2
.4. Surface modification of montmorillonite
The surface modification of montmorillonite was carried out by a cation exchange
+
reaction between MMT-Na and the ammonium salt of APB to yield MMT-APB [33].
+
Briefly, 5 g MMT-Na montmorillonite was suspended in 700 mL distilled water at room
temperature and stirred overnight. In another flask, 2 g APB was dissolved in 40 mL
distilled water under magnetic stirring and the pH was adjusted to 3-4 using 1.0 M HCl
aqueous solution. After stirring for 3 h, the second solution was added to the MMT
8
Page 8 of 31

−
1
suspension at a rate of approximately 15 mL min while vigorously stirring. The mixture
was stirred overnight at room temperature. The dark violet precipitates were filtered
using a Buchner funnel and washed at least four times to remove any excess ammonium
ions. The product was dried in a vacuum oven at 60 °C for 24 h.
2
.5. Synthesis of PA/organoclay nanocomposite
The nanocomposite was prepared by mixing the appropriate amounts of PA and
MMT-APB. To achieve a uniform dispersion of montmorillonite platelets in the PA
matrix, the mixture was vigorously agitated at 25 °C for 24 h. The nanocomposite was
prepared in different concentrations of MMT-APB. The nanocomposites containing 3
and 6 wt. % MMT-APB (PANC 3 and PANC 6) were prepared by adding 0.97 g and 0.94
g PA into 50 mL flask containing 5 mL DMAc followed by the addition of 0.03 and 0.06
g MMT-APB, respectively. The reaction mixture was agitated overnight at 25 °C. The
nanocomposites were obtained by pouring the hybrid solutions into petri dishes, followed
by solvent evaporation under reduced pressure.
2
.6. Characterization
Fourier transform infrared (FT-IR) data were recorded on Galaxy series FT-IR 5000
spectrophotometer (England). Vibration transition frequencies were reported in terms of
-1
wave number (cm ). Band intensities were assigned as weak (w), medium (m), shoulder
(
sh), strong (s) and broad (br). For sample preparation, the powdered species were mixed
with KBr and pressed in form of pellets and used for further characterization.
1
H NMR measurements were performed using a Bruker Avance III 500 spectrometer
1
(
Rheinstetten, Germany) operating at 500 MHz ( H). DMSO-d6 was used as the solvent
1
and the solvent signal was used for internal calibration (DMSOd6: δ( H)=2.5 ppm).
9
Page 9 of 31

Molar mass (weight-average (M ) and number-average (M ) molecular weights)
w
n
determination
was
performed
by
size
exclusion
chromatography (SEC)
using Agilent Series 1100 (Agilent) system equipped with a pump, degasser and
differential refractive index (RI) detector. Two Zorbax PSM Trimodal-S 250 mm x 6.2
mm columns (Rockland Tech, USA) were used. The measurements were performed
using a mixed eluent N, N-dimethylacetamide (DMAc) with 2 vol% water and 3 g/L LiCl
-1
at a flow rate of 0.5 mLmin . The molar mass was calculated after calibration with
poly(2-vinylpyridine).
Solid state UV-Visible spectrum was recorded at room temperature in 190-790 nm
spectral regions using a Cary 6000i UV-Visible/Near-infrared spectrophotometer
(
Varian).
Photoluminescence (PL) spectra were investigated using a Fluorolog 3 (Horiba
JobinYvon, USA) fluorescence spectrophotometer.
The morphological analysis was carried out using transmission electron microscopy
(
TEM) on a LEO 912 microscope operated with an acceleration voltage of 120 kVat
room temperature in bright field illumination mode.
Wide angle X-ray scattering (WAXS) was performed using 2-circle diffractometer
XRD 3003 θ/θ (GE Inspection Technologies /Seifert-FPM, Freiberg, Germany) using Cu-
o
K
α
radiation ( = 0.154 nm) generated at 30 mA and 40 kV in the range of 2θ = 2°- 12
o
with 0.05 as the step length.
The thermal stability of the samples was measured by thermogravimetric analysis
(TGA, TA instruments Q 5000) in the range between room temperature and 700 °C at a
heating rate of 10 °C/min in nitrogen atmosphere. The thermal properties of samples were
1
0
Page 10 of 31

measured by differential scanning calorimetry (DSC, TA instrument Q1000) in the range
between -80 °C and 230 °C at a heating rate of 10 °C/min in nitrogen atmosphere.
Microscale combustion calorimeter (MCC-1, FTT) was used for the investigation of
flammability of the samples [34, 35].
Quantum Chemical Calculation
The density functional theory (DFT) with a three-parameter Becke-style hybrid
functional (B LYP) was adopted for the calculations of the electronic structures of the PA
3
[
36]. The structure was optimized using the PA segment unit with terminal hydrogen.
++
The 6-311 G(d,p) basis set was utilized for the geometry optimizations [37, 38]. All
calculations were performed using the Gaussian-03 D.02 [39] program package.
3
. Results and discussions
3
.1. Synthesis of the monomers
Oleic acid, being the precursor for the synthesis of azelaic acid, is a monounsaturated
8-carbon fatty acid mostly found in animal fats and vegetable oils. The oxidation of
1
unsaturated oleic acid in presence of potassium permanganate yields azaleic acid.
Chichibabin method was used for preparation of dinitro compound containing pyridine
group (Scheme 1) [40, 41]. In particular, the condensation of 4-
dimethylaminobenzaldehyde along with 4-nitroacetophenone in presence of ammonium
acetate afforded the dinitro compound in one step. This product was subsequently
reduced using hydrazine monohydrate and as a catalyst palladium on charcoal (10%) was
used.
1
1
Page 11 of 31

Scheme 1. Synthesis route of the diamine
3
.2. Synthesis of PA
The PA was synthesized via direct polycondensation reaction of an equimolar mixture
of azelaic acid with the aromatic diamine (Scheme 2).
1
2
Page 12 of 31

Scheme 2. Schematic representation of the synthesis of PA
In order to investigate the electronic structure of PA and the repeated position of groups,
3
computational calculations at B LYP/6-311++G(d,p) level were used. Fig. 1
demonstrates the optimized molecular structure of PA.
1
3
Page 13 of 31

Figure 1. Theoretical optimized spatial structure for ground state of PA
1
The H-NMR spectrum of PA is displayed in Fig. 2. The appearance of N-H protons at
1
0.1 ppm is indicative of the amide groups in the main chain. The CH proton is evident
3
at 3.0 ppm while the resonance of aromatic protons occurs in the range of 6.9-8.3 ppm
and CH protons of the CH group appear in the range of 1.8-2.3 ppm.
2
2
1
4
Page 14 of 31

1
Figure 2. H NMR spectrum of PA in DMSO-d
The SEC measurement of the synthesized PA exhibited number-average molecular
weight (M ) and weight-average molecular weight (M ) of ca. 22800 and 48100 g/mol,
6
n
w
respectively, according to poly(vinyl pyridine) (PVP) standard. The polydispersity index
is 2.1.
Optical properties of PA
The optical properties of PA were investigated by UV-Vis and photoluminescence
techniques. As shown in Fig. 3, PA exhibits strong UV-Vis absorption bands at 350–440
nm with a maximum absorption (λmax) at 412 nm, assignable to π-π* transition resulting
from the conjugation between the aromatic rings and nitrogen atoms. Photoluminescence
spectrum of PA film shows a strong fluorescence at around 511 nm in green region.
1
5
Page 15 of 31

Figure 3. UV-Vis and PL spectra of PA in the solid film
3
.3. Preparation of PANC
Novel bio-based PANCs containing 3 and 6 wt. % MMT-APB (PANC 3 and PANC 6,
respectively) were successfully prepared in dry DMAc media through a solution
intercalation technique. The interaction of MMT-APB in polymer matrices can improve
physical properties and morphology of the resulting nanocomposite.
3
.4. Characterization of nanocomposite
FTIR study
1
6
Page 16 of 31

Fig. 4 shows FTIR spectra of the neat PA and its nanocomposites. The FTIR spectrum of
-1
PA shows a peak at 3410 cm which has been assigned to the NH groups. In the
-1
spectrum of the nanocomposites, the presence of a peak at 1040 cm
-1
corresponding to the Si–O bonding and peaks at 400–600 cm corresponding
to Al–O and Mg–O bondings indicated the incorporation of organoclay in the PA
matrix. It can be concluded that the PANCs have characteristic pick not only for neat PA
bands, but also for organoclay.
Figure 4. FTIR spectra of PA and PANCs
Nanocomposite structure
1
7
Page 17 of 31

XRD technique is widely used to investigate the dispersion degree of montmorillonite
in matrices. Intercalated and/or exfoliated polymer/montmorillonite nanocomposites can
be classified based on displacing of the peak in terms of the gallery height of the
montmorillonite.
A diffraction peak around 2θ = 8.9° corresponds to d-spacing of 9.9 A° for the layered
+
silicates in MMT-Na (Fig. 5). For MMT-APB, a strong peak at 2θ = 6.6° resulted from
diffraction of the crystal planes of layered silicates indicates that layered silicates have
been intercalated by APB molecules to a d-spacing of 13.4 A°. This is consistent with the
idea that d-spacing of the layered silicates in MMT-APB increase due to the size of
swelling agent. According to Bragg's law, a shift in 2θ value from higher to lower level is
indicative of an increase in d spacing [29]. The XRD patterns of PANC 3 and PANC 6
display peaks at 2θ = 4.2° and 4.1°, respectively. This might result from partial
exfoliation or intercalation with d-spacing of 21.03 and 21.5 A°. The intensity of peaks
increased in PANC 6 due to the extensive agglomeration of MMT-APB [42].
1
8
Page 18 of 31

+
Figure 5. XRD pattern of MMT-Na , MMT-APB, PA, PANC 3 and PANC 6
TEM investigation was carried out in order to observe the morphological structure
of the PANCs (Fig. 6). The TEM micrograph of PANC 3 (Fig. 6a) enlightens both areas
with intercalation and areas with exfoliation morphologies. PANC 6 also showed a non
homogeneous distribution in orientation and size (Fig. 6b). Moreover, a higher level of
aggregation was observed with increasing the quantity of MMT-APB. The observed
aggregation of the nanolayers could be attributed to strong van der Waals interactions of
nanolayers especially at higher concentrations. The formation of hydrogen bonds
between the nanolayers and the PA matrix does not suffice to counterbalance the strong
van der Waals interactions between nano-layers at higher concentrations.
1
9
Page 19 of 31

Figure 6. TEM images of PANC 3 (a) and PANC 6 (b)
Thermal properties of nanocomposites
The thermal degradation of PA and the corresponding nanocomposites with different
MMT-APB loadings were studied under different environments by TGA. The consequent
weight loss versus operating temperature under nitrogen and air environments are plotted
as shown in Fig. 7 and 8, respectively.
According to the TGA investigations, the effect of the selected atmosphere on
degradation of the PA and PANCs is significant. As observed from Fig. 7 and 8, the
nanocomposite undergoes single-stage decomposition in the nitrogen atmosphere and
double-stage decomposition in the air atmosphere. Under air, the first stage of
degradation reaction is observed between 325 ºC and 400 ºC for PA and between 300 ºC
and 500 ºC for PANCs. This initial reaction step was close to the one observed under
nitrogen (between 350 ºC and 500 ºC). The second stage of the decomposition under air
appeared between 400 ºC and 600 ºC for PA and between 500 ºC and 700 ºC for PANCs.
2
0
Page 20 of 31

Since it is not observed under nitrogen, this step might be oxidative in nature. It is also
notable that PA and PANCs treated in air exhibited faster degradation compared to the
corresponding samples treated in nitrogen.
Detailed TGA data, i. e. 5% (Tinitial) and 10% (T ) weight loss temperatures and char
10
yield for PA and PANCs, in nitrogen and air environments are summarized in Table 1.
The observed decomposition temperatures Tinitial and T10 in air atmosphere are almost the
same as compared with the data in nitrogen atmosphere; this suggests that the presence of
oxygen does not influence the thermal stability of the nanocomposites. Also, PA and
nanocomposites retain lower residue in air compared to the nitrogen atmosphere. This
could stem from the thermal oxidative degradation of the polymer chain in the presence
of oxygen; i. e. the presence of oxygen had caused a higher degree of cleavage of amide
groups at high temperature.
PA and the nanocomposites showed slight weight loss below 200 °C in both
environments which could be due to removal of moisture or monomer remains. After
adding MMT-APB, both the nanocomposites were more thermally stable than neat PA,
showing significant increase in Tinitial and T10. This enhancement in the thermal stability
could be associated to the presence of montmorillonite nanolayers with high thermal
stability and the great barrier properties that maximize the heat insulation. However, as
can be seen in Table 1, Tinitial and T decreased for PANC 3 with addition of MMT-APB
10
in air atmosphere. It might be due to the presence of oxygen and oxidation effect of
MMT-APB.
The glass transition temperature of PA and the nanocomposites were investigated by
DSC technique and the resulting data are summarized in Table 1. The incorporation of
2
1
Page 21 of 31

aliphatic and side chain units into the polymer back-bone results in the formation of PA
with low glass transition temperature (T ) (143 ºC). The TGA analysis in Table 1
g
g
illustrates a systematic increase in T value of nanocomposite showing interaction
between two phases. In fact, the incorporation of silicate layers reduced the segmental
motion of polymer chains and shifted the baseline of DSC curve towards higher
temperature.
2
Figure 7. TGA analysis for PA and PANCs in N atmosphere
2
2
Page 22 of 31

Figure 8. TGA analysis for PA and PANCs in air atmosphere
Table 1. Summarized TGA analysis data for PA and PANCs
Thermal properties in air
Thermal properties in N
2
a
b
c
d
Samples
T
initial(˚C)
T
10(˚C)
Char yield
T
initial(˚C)
T
10(˚C)
Char yield
T
g
PA
PANC 3
PANC 6
287
241
283
365
348
397
29.7
30.8
31.7
243
275
264
323
374
381
61.7
64.0
67.1
143
145
152
a
b
c
g
Temperature at which 5% weight loss
Temperature at which 10% weight loss
Weight percentage of material left after TGA analysis at a maximum temperature of 800˚C
glass transition temperature was recorded by DSC at a heating rate of 10 ºCmin in N
-1
2
Flame retardant properties
In order to study the flammability of PA and nanocomposites, microscale combustion
calorimeter (MCC) was used and the heat release rate (HRR) versus temperature were
2
3
Page 23 of 31

plotted (Fig. 9). The measured parameters for all samples including heat release rate
(
HRR) (calculated from the oxygen depletion measurement) and total heat release (THR)
obtained by integrating the HRR curve) are shown in Table 2. It was observed that PA
(
-1
has a peak HRR (pHRR) value of 111 W/g and THR value of 13.7 KJ.g . PA showed
low pHRR value and high char yield amount due to high aromatic content and presence
of pyridine groups (see Table 1). The char residue formation in PA and its
nanocomposites brings in good flame retardancy properties. However, as observed in Fig.
8
, the HRR curve pattern for PA is significantly different from that of PANCs. In
particular, once compared to PA, pHRR and THR values decrease by introducing 3 wt. %
MMT-APB. Further increase in loading MMT-APB up to 6 wt. % will cause decrease of
-1
pHRR and THR to lower values (76 W/g and 10.9 KJ.g , respectively).
The relative decrease of pHRR and THR values of PANC 3 and PANC 6 compared to
PA, suggests that MMT-APB has a high efficiency on improving the flame retardancy.
Also, the shape of HRR/temperature curves seem slightly more smooth in case of PANCs
compared to PA, which means the decomposition of PA have been affected by
introducing MMT-APB into the polymer backbone.
2
4
Page 24 of 31

Figure 9. Temperature-dependent HRR analysis for PA and PANCs obtained by
microscale combustion calorimetry (MCC)
Table 2. MCC analysis data
Samples
pHRR (W/g)
THR (KJ.g )
pHRR=peak heat release rate; THR=total heat release
PA
111
13.7
PANC 3
86
PANC 6
76
10.9
-1
13.6
4
. Conclusions
New PA nanocomposite was fabricated by solution intercalation method. The
polyamide was synthesized with desired molecular weight by polycondensation reaction
between heterocyclic diamine and bio-based azelaic acid. The introduction of bulky,
electron-donating trialkylamine, pyridine and aliphatic groups disrupted the copolanarity
2
5
Page 25 of 31

of aromatic units in polymer chain and hence increased the flexibility. As this could also
cause an increase in inter-chain spacing (free volume), enhanced solubility and improved
glass transition temperature of PA are expected as well. TGA analysis in air and nitrogen
atmosphere showed that the PA leaves a high amount of char residue. In comparison to
PA, organoclay incorporated PA exhibited enhanced thermal stability and char yields.
The improved thermal properties of PA nanocomposites were mainly attributed to the
physical and heat barrier effect of MMT-APB. The MCC analysis suggests that the
presence of organoclays imposes a good effect on the flame retardancy of PA by
decreasing pHRR and THR values of nanocomposites. The concentration of MMT-APB
plays a significant role on the flame retardancy of PA nanocomposites. An enhanced fire
resistance was observed once the concentration of organoclay was reduplicated.
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