# Polyamide 66/Brazilian Clay Nanocomposites

Authors: E. M. Araújo; K. D. Araujo; R. A. Paz; T. R. Gouveia; R. Barbosa; E. N. Ito
Journal: Journal of Nanomaterials
 (2009)

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## Abstract

Polyamide 66 (PA66)/Brazilian clay nanocomposites were produced via direct melt intercalation. A montmorillonite sample from the Brazilian state of Paraíba was organically modified with esthearildimethylammonium chloride (Praepagen), quaternary ammonium salt and has been tested to be used in polymer nanocomposites. The dispersion analysis and the interlayer spacing of the clay particles in matrix were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal behavior of the obtained systems was investigated by differential scanning calorimetry (DSC), thermogravimetry (TG), and heat deflection temperature (HDT) was reported too. The nanocomposites exhibited a partially exfoliated structure, very interesting HDT values which are higher than those of pure PA66, and good thermal stability.


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## Body

## 1. Introduction

Polymer/organoclay  nanocomposites present unique properties that are not
observed in conventional composites. Incorporation of small amounts of
organoclay (<10 wt.%) into polymer matrices may remarkably  improve dimension stability, mechanical,
thermal, optical, electrical, and gas barrier properties, and decrease the flammability.
This happens due to the large contact area between polymer and clay on a
nanoscale as reported on literature [1–11]. The
incorporation of organoclays into polymer matrices has been known for 50 years
and one of the pioneering works was from Toyota
as reported by Cho and Paul [2]. To be compatible with polymer matrices, sodium smectite clays need to be modified by using quaternary
ammonium salts with at least 12 carbon atoms in aqueous dispersions. In these dispersions, the clay particles
or layers must be separated one from another and not be stacked in order to
facilitate the introduction of the organic compounds. As a result, the clay
exchangeable cations are replaced by the organic cations of the quaternary
ammonium salt that are adsorbed on the negative sites of the clay surfaces. The
obtained clay is known as organoclay [7–12]. Polyamide 66
(PA66) is an important engineering plastic, but PA66 matrix nanocomposites have
been little investigated by researchers up to now [13–15].The purpose of this paper is to analyze the effect
of the Brazilian clay incorporation on the thermal behavior and morphology of Polyamide
66/clay nanocomposites.


## 2. Experimental

### 2.1. Materials

Polyamide 66 (PA66, Technyl A216,  São Paulo/SP, Brazil) was supplied by Rhodia/Brazil and used;
as a composite matrix. Na-montmorillonite  (MMT, Brasgel PA, Boa Vista/PB,
Northeast of Brazil) supplied by Bentonit União do Nordeste with a cation exchange capacity (CEC) of 90 meq/100 g, and interlayer spacingd001=12.5Å was used as nanofiller. The quaternary ammonium salt
esthearildimethylammonium chloride—Praepagen (P) with industrial grade,
supplied by Clariant/Brazil, was used (as soon as it was received) for MMT clay modification.


### 2.2. Preparation of Organoclays

The Na-MMT clay was
modified organically (named as organoclay) with quaternary ammonium salt
according to the procedure described by  Barbosa  [4] and Araújo et al.  [7–12, 16].


### 2.3. Preparation of Nanocomposites

PA66/unmodified  clay (MMT) as well as
PA66/modified clay (organoclay-OMMT) nanocomposites, containing 2 wt.% of clay, were melt compounded in a
counterrotating twin-screw extruder (attached to a Haake System 90 Torque
Rheometer) operating at 270–280°C and 40 rpm.
Samples for tensile tests (ASTM D638) were injection molded in a Fluidmec
machine at 280°C. Before each processing, the PA66 pellets were dried under
vacuum at 80°C for 24 hours. The rheological characterization of the nanocomposites containing
2 wt.% of clay was carried out in an intensive batch mixer Rheomix 600 equipped
with roller blades attached to a Haake System 90, operating at 280°C, 60 rpm,
and 10 minutes. The clays were added to PA66, after 2.5 minutes.


### 2.4. Characterization of Dispersibility of The Clay in Polymer Matrix

The
structure of PA66/MMT and PA66/OMMT composites was characterized by X-ray diffraction (XRD) and transmission electron
microscopy (TEM). XRD measurement was performed using an XRD-6000
Shimadzu diffractometer (40 kV, 30 mA) with 2θ scan range of 2–30° at room
temperature, at a scanning speed of 2°/min with Cu (λ=0.154 nm). TEM analysis was carried out in a
Philips CM120 Equipment with 120 kV. Samples were cryogenically microtomed into
ultrathin sections (25–50 nm thick) with
a diamond knife using an RMC MT-7000 under cryogenic conditions (−80°C) inside
the microtoming chamber.


### 2.5. Differential Scanning Calorimetry (dsc)

DSC analyses were carried out using
a Shimadzu DSC-50 differential scanning calorimeter thermal analyzer. About 10 mg of the polymer sample was weighed very accurately in the aluminum DSC pan and placed in the DSC cell. It was heated
from 30 to 300°C at a rate of 20°C/min under nitrogen atmosphere. The sample
was kept for 5 minutes at this temperature to eliminate the heat history. The
ΔHmo
values for PA66
matrix were taken as 195.9 J/g [14].


### 2.6. Thermogravimetry (tg)

The thermal stability was measured
by thermogravimetry using a Shimadzu TGA-51equipment, with a heating ramp of 20°C/min in
nitrogen and air atmospheres from 20 to 900°C.


### 2.7. Heat Deflection Temperature (hdt)

Heat deflection temperature (HDT)
was obtained in a Davenport
equipment, 09z64, with 1800 kPa, according to ASTM D648. The samples were
immersed in a silicon oil bath at a rate of 120°C/h.


## 2.1. Materials

Polyamide 66 (PA66, Technyl A216,  São Paulo/SP, Brazil) was supplied by Rhodia/Brazil and used;
as a composite matrix. Na-montmorillonite  (MMT, Brasgel PA, Boa Vista/PB,
Northeast of Brazil) supplied by Bentonit União do Nordeste with a cation exchange capacity (CEC) of 90 meq/100 g, and interlayer spacingd001=12.5Å was used as nanofiller. The quaternary ammonium salt
esthearildimethylammonium chloride—Praepagen (P) with industrial grade,
supplied by Clariant/Brazil, was used (as soon as it was received) for MMT clay modification.


## 2.2. Preparation of Organoclays

The Na-MMT clay was
modified organically (named as organoclay) with quaternary ammonium salt
according to the procedure described by  Barbosa  [4] and Araújo et al.  [7–12, 16].


## 2.3. Preparation of Nanocomposites

PA66/unmodified  clay (MMT) as well as
PA66/modified clay (organoclay-OMMT) nanocomposites, containing 2 wt.% of clay, were melt compounded in a
counterrotating twin-screw extruder (attached to a Haake System 90 Torque
Rheometer) operating at 270–280°C and 40 rpm.
Samples for tensile tests (ASTM D638) were injection molded in a Fluidmec
machine at 280°C. Before each processing, the PA66 pellets were dried under
vacuum at 80°C for 24 hours. The rheological characterization of the nanocomposites containing
2 wt.% of clay was carried out in an intensive batch mixer Rheomix 600 equipped
with roller blades attached to a Haake System 90, operating at 280°C, 60 rpm,
and 10 minutes. The clays were added to PA66, after 2.5 minutes.


## 2.4. Characterization of Dispersibility of The Clay in Polymer Matrix

The
structure of PA66/MMT and PA66/OMMT composites was characterized by X-ray diffraction (XRD) and transmission electron
microscopy (TEM). XRD measurement was performed using an XRD-6000
Shimadzu diffractometer (40 kV, 30 mA) with 2θ scan range of 2–30° at room
temperature, at a scanning speed of 2°/min with Cu (λ=0.154 nm). TEM analysis was carried out in a
Philips CM120 Equipment with 120 kV. Samples were cryogenically microtomed into
ultrathin sections (25–50 nm thick) with
a diamond knife using an RMC MT-7000 under cryogenic conditions (−80°C) inside
the microtoming chamber.


## 2.5. Differential Scanning Calorimetry (dsc)

DSC analyses were carried out using
a Shimadzu DSC-50 differential scanning calorimeter thermal analyzer. About 10 mg of the polymer sample was weighed very accurately in the aluminum DSC pan and placed in the DSC cell. It was heated
from 30 to 300°C at a rate of 20°C/min under nitrogen atmosphere. The sample
was kept for 5 minutes at this temperature to eliminate the heat history. The
ΔHmo
values for PA66
matrix were taken as 195.9 J/g [14].


## 2.6. Thermogravimetry (tg)

The thermal stability was measured
by thermogravimetry using a Shimadzu TGA-51equipment, with a heating ramp of 20°C/min in
nitrogen and air atmospheres from 20 to 900°C.


## 2.7. Heat Deflection Temperature (hdt)

Heat deflection temperature (HDT)
was obtained in a Davenport
equipment, 09z64, with 1800 kPa, according to ASTM D648. The samples were
immersed in a silicon oil bath at a rate of 120°C/h.


## 3. Results and Discussion

### 3.1. Structure of Pa66/clay Nanocomposites

Figure1 presents the X-ray diffraction patterns for the PA66 systems with 2 wt.% of unmodified
(MMT) and modified clay (OMMT). The interlayer distancewas determined by the diffraction
peak in the X-ray method, using the Bragg equation. It can be observed for the
modified clay (OMMT) three peaks corresponding to an interlayer spacing d001 of 29.2, 19.2, and 12.5Å. The two first peaks indicate that the
intercalation of the salt between the layers of clay has occurred. Another peak
corresponding to interlayer spacings of 12.5Å (d001 for unmodified
clay-MMT) is probably due to an incomplete ion exchange, with some residual
Na-MMT remaining in the material, according to the literature [7, 8]. The
results indicated that the quaternary ammonium salt was intercalated between
two basal planes of MMT, leading to an expansion of the interlayer spacing. It
can be observed too for PA6/MMT system a diffraction peak around 14.71Å, which
is close to the distance of 12.5Å of the unmodified clay, indicating that the
increase of the basal spacing practically did not occur. On the other hand, the
sample of the nanocomposite of PA66 with the modified clay (OMMT) presented the
displacement of the XRD peak toward a lower angle values, what represents an
increase to 19.20Å in the basal spacing. It can be thus noticed that with the organoclay
presence, the peak related to the PA66/unmodified clay interlayer spacing
disappeared, and a new broad diffraction peak appeared. This peak can be due to
the intercalation/partially exfoliation of the polymer chains between the
layers of organoclay. These results will be confirmed by TEM.XRD patterns of montmorillonite clay modified with
Praepagen salt (OMMT), PA66/MMT, and PA66/OMMT nanocomposites.
(a)(b)(c)Figure2 shows the TEM images of the
PA66 systems. In Figure 2(a), it can be seen clearly agglomerates of clay and
in Figure 2(b) exists intercalated clay layers but it can be seen
too several exfoliated clay layers present in the PA66 matrix. Therefore, the
obtained PA66/OMMT systems are partially exfoliated nanocomposites according to
the XRD pattern (Figure 1) and the literature [2, 3, 5, 13–15].TEM photomicrographs of (a) PA66/MMT and (b)
PA66/OMMT nanocomposites.
(a)(b)


### 3.2. Thermal Behavior

Table1 shows the melting and
crystallization parameters of the pure PA66 and its mixtures obtained by DSC,
respectively. It can be seen that there was no significant change in the
melting and crystallization temperatures of the mixtures. On the other hand, it
seems that the presence of the clay improved the heat of fusion, which leaded
to higher crystallinity degree. Probably, the clay acts as nucleation agent in
the matrix.Table 1
Melting and
crystallization parameters for PA66 and its nanocomposites.Tm:
melting temperature taken at the melt peak;  Tc:
crystallization temperature taken at the crystallization peak;  ΔHm: heat of fusion due to PA66
melting, measured through the melting peak;  Xc:
degree of crystallinity, taken fromΔHm/ΔHmo; ΔHmo: heat of fusion for PA66, 100%
crystalline, 195.9 J/g [14].
HeatingCoolingMaterialsTm (°C)ΔHm (J/g)Tc (°C)Xc (%)PA66266.9850.07223.4525.55PA66/MMT263.8260.43224.7430.23PA66/OMMT263.6760.80223.1130.41In
order to investigate the effect of the organoclay on the thermal stability of
PA66/clay nanocomposite, the TG analysis of the systems is presented. The
thermal stability of PA66/clay nanocomposites is a little improved with the
presence of the organoclay in nitrogen atmosphere, as pointed out in Figure3. Pure PA66 degrades a little faster than PA66/clay nanocomposites, that
is, the nanocomposites are stable up to ~400°C. Figure 4 shows
TG curves using air atmosphere. In these conditions, it can be seen that the
nanocomposite containing organoclay presents thermal stability a little superior
than PA66/MMT. This suggests that at the range of the used processing
temperatures, the degradation of the system did not occur. Apparently, the
organoclay has two opposing functions in the thermal stability of the
nanocomposites, one is due to barrier property to the oxygen and the other is
due to the catalysis effect toward the degradation of the polymer, but the
barrier effect is predominant with the addition of low fraction of clay to the polymer
matrix, as observed in this work. Only with increasing loading, the catalyzing effect
rapidly rises and becomes dominant and the thermal stability of the nanocomposites
decreases, according to Araújo et al.  [8] and Zhao et al.  [17].Figure 3
TG curves of PA66 and its nanocomposites in
nitrogen atmosphere.Figure 4
TG curves of PA66 and its nanocomposites in
air atmosphere.


### 3.3. Heat Deflection Temperature (hdt)

The heat deflection temperature
(HDT) can be   used to simulate the polymer application in temperatures above the environment temperature and to
evaluate the compatibility of the polymer systems. Figure5 shows the obtained
data for HDT of the nanocomposites and pure PA66. The HDT of the  pure PA66 stayed in the range of 50°C and
for nanocomposites in the range of 56°C. Of the point of view technologic, these
values are very interesting since the literature in general mentions that the
formation of nanoparticles increases the HDT, the rigidity of the system, and
the barrier properties. The presence of organoclay in the PA66 matrix increased
the HDT compared to pure PA66.Figure 5
Heat deflection temperature of PA66 and its nanocomposites.


## 3.1. Structure of Pa66/clay Nanocomposites

Figure1 presents the X-ray diffraction patterns for the PA66 systems with 2 wt.% of unmodified
(MMT) and modified clay (OMMT). The interlayer distancewas determined by the diffraction
peak in the X-ray method, using the Bragg equation. It can be observed for the
modified clay (OMMT) three peaks corresponding to an interlayer spacing d001 of 29.2, 19.2, and 12.5Å. The two first peaks indicate that the
intercalation of the salt between the layers of clay has occurred. Another peak
corresponding to interlayer spacings of 12.5Å (d001 for unmodified
clay-MMT) is probably due to an incomplete ion exchange, with some residual
Na-MMT remaining in the material, according to the literature [7, 8]. The
results indicated that the quaternary ammonium salt was intercalated between
two basal planes of MMT, leading to an expansion of the interlayer spacing. It
can be observed too for PA6/MMT system a diffraction peak around 14.71Å, which
is close to the distance of 12.5Å of the unmodified clay, indicating that the
increase of the basal spacing practically did not occur. On the other hand, the
sample of the nanocomposite of PA66 with the modified clay (OMMT) presented the
displacement of the XRD peak toward a lower angle values, what represents an
increase to 19.20Å in the basal spacing. It can be thus noticed that with the organoclay
presence, the peak related to the PA66/unmodified clay interlayer spacing
disappeared, and a new broad diffraction peak appeared. This peak can be due to
the intercalation/partially exfoliation of the polymer chains between the
layers of organoclay. These results will be confirmed by TEM.XRD patterns of montmorillonite clay modified with
Praepagen salt (OMMT), PA66/MMT, and PA66/OMMT nanocomposites.
(a)(b)(c)Figure2 shows the TEM images of the
PA66 systems. In Figure 2(a), it can be seen clearly agglomerates of clay and
in Figure 2(b) exists intercalated clay layers but it can be seen
too several exfoliated clay layers present in the PA66 matrix. Therefore, the
obtained PA66/OMMT systems are partially exfoliated nanocomposites according to
the XRD pattern (Figure 1) and the literature [2, 3, 5, 13–15].TEM photomicrographs of (a) PA66/MMT and (b)
PA66/OMMT nanocomposites.
(a)(b)


## 3.2. Thermal Behavior

Table1 shows the melting and
crystallization parameters of the pure PA66 and its mixtures obtained by DSC,
respectively. It can be seen that there was no significant change in the
melting and crystallization temperatures of the mixtures. On the other hand, it
seems that the presence of the clay improved the heat of fusion, which leaded
to higher crystallinity degree. Probably, the clay acts as nucleation agent in
the matrix.Table 1
Melting and
crystallization parameters for PA66 and its nanocomposites.Tm:
melting temperature taken at the melt peak;  Tc:
crystallization temperature taken at the crystallization peak;  ΔHm: heat of fusion due to PA66
melting, measured through the melting peak;  Xc:
degree of crystallinity, taken fromΔHm/ΔHmo; ΔHmo: heat of fusion for PA66, 100%
crystalline, 195.9 J/g [14].
HeatingCoolingMaterialsTm (°C)ΔHm (J/g)Tc (°C)Xc (%)PA66266.9850.07223.4525.55PA66/MMT263.8260.43224.7430.23PA66/OMMT263.6760.80223.1130.41In
order to investigate the effect of the organoclay on the thermal stability of
PA66/clay nanocomposite, the TG analysis of the systems is presented. The
thermal stability of PA66/clay nanocomposites is a little improved with the
presence of the organoclay in nitrogen atmosphere, as pointed out in Figure3. Pure PA66 degrades a little faster than PA66/clay nanocomposites, that
is, the nanocomposites are stable up to ~400°C. Figure 4 shows
TG curves using air atmosphere. In these conditions, it can be seen that the
nanocomposite containing organoclay presents thermal stability a little superior
than PA66/MMT. This suggests that at the range of the used processing
temperatures, the degradation of the system did not occur. Apparently, the
organoclay has two opposing functions in the thermal stability of the
nanocomposites, one is due to barrier property to the oxygen and the other is
due to the catalysis effect toward the degradation of the polymer, but the
barrier effect is predominant with the addition of low fraction of clay to the polymer
matrix, as observed in this work. Only with increasing loading, the catalyzing effect
rapidly rises and becomes dominant and the thermal stability of the nanocomposites
decreases, according to Araújo et al.  [8] and Zhao et al.  [17].Figure 3
TG curves of PA66 and its nanocomposites in
nitrogen atmosphere.Figure 4
TG curves of PA66 and its nanocomposites in
air atmosphere.


## 3.3. Heat Deflection Temperature (hdt)

The heat deflection temperature
(HDT) can be   used to simulate the polymer application in temperatures above the environment temperature and to
evaluate the compatibility of the polymer systems. Figure5 shows the obtained
data for HDT of the nanocomposites and pure PA66. The HDT of the  pure PA66 stayed in the range of 50°C and
for nanocomposites in the range of 56°C. Of the point of view technologic, these
values are very interesting since the literature in general mentions that the
formation of nanoparticles increases the HDT, the rigidity of the system, and
the barrier properties. The presence of organoclay in the PA66 matrix increased
the HDT compared to pure PA66.Figure 5
Heat deflection temperature of PA66 and its nanocomposites.


## 4. Conclusions

Polyamide 66/Brazilian clay nanocomposites
were producedvia
direct melt intercalation. The obtained PA66/organoclay nanocomposites presented
partially exfoliated structure. XRD analysis showed that the salt was
intercalated between two basal planes of montmorillonite clay. Incorporation of
the organoclay improved the thermal stability of PA66. As expected, HDT's
properties presented very interesting values for the nanocomposites and larger ones for matrix. This also indicates that the Brazilian clay
can be used as a nanoparticle in PA66 nanocomposites.



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*Source: 136856-2008-12-10.xml*